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1 MANUFACTURING EVALUATION OF A GAS DISTRIBUTION LAYER FOR A DIRECT METHANOL FUEL CELL By MARK ALLEN POPE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011
2 2011 Mark Allen Pope
3 To my wife and children
4 ACKNOWLEDGMENTS I thank my wife, Darcy, and my children for their support and love throughout my time at the University of Florida I cannot express in words how much you all have added to my life. I also thank my advisor, Dr. Tony L. Schmitz, for his support, encouragement, and flood of helpful ideas throughout my research. Also, I thank the members of my committee, Dr. John Schuell er and Dr. William Lear, for their interest and involvement with my project. Last ly I thank the members of the Machine Tool Research Center for their advice and ideas. I especially thank Mr. Daniel Blood and Mr. Christopher Tyler for their assistance
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREV IATIONS ................................ ................................ ........................... 10 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 13 2 LITERATURE REVIEW ................................ ................................ .......................... 21 3 EXPERIMENTAL DESIGN ................................ ................................ ..................... 23 Non Contact Measurement ................................ ................................ ..................... 23 Capacitance Probe ................................ ................................ ................................ 24 Capacitance ................................ ................................ ................................ ..... 24 Calibration ................................ ................................ ................................ ........ 25 Measurement Errors ................................ ................................ ......................... 25 Parallelism ................................ ................................ ................................ 25 Flatness ................................ ................................ ................................ ..... 26 Environment ................................ ................................ ............................... 26 Vacuum Chuck ................................ ................................ ................................ ....... 27 Pre Machining Preparation ................................ ................................ ............... 27 Machining Parameters ................................ ................................ ..................... 27 Vacuum Bowing Effect ................................ ................................ ..................... 28 Scanning White Light Inter ferometer ................................ ................................ ...... 29 Programmable Furnace ................................ ................................ .......................... 30 4 EXPERIMENTAL PROCEDURE ................................ ................................ ............ 36 Thickness Measurement ................................ ................................ ......................... 36 SWLI Data Validation ................................ ................................ .............................. 36 Sintering Procedure ................................ ................................ ................................ 37 GDL Ink Production and Painting ................................ ................................ ............ 37 Membrane Hole Diameter Measurement ................................ ................................ 37 5 DATA ANALYSIS AND VALIDATION ................................ ................................ ..... 40 Thickness Calculation Algorithm ................................ ................................ ............. 40
6 Sintering Loss ................................ ................................ ................................ ......... 41 SWLI Validation Data Filtering ................................ ................................ ................ 42 Comparison Tests ................................ ................................ ................................ ... 43 6 RESULTS ................................ ................................ ................................ ............... 49 Capacitance Probe GDL Data ................................ ................................ ................ 49 Sintering Results ................................ ................................ ................................ ..... 50 Membrane Hole SWLI Measurements ................................ ................................ .... 51 7 CONCLUSIONS AND FUTURE WORK ................................ ................................ 57 APPENDIX A LABVIEW PROGRAMS ................................ ................................ .......................... 59 B MATLAB PROGRAM ................................ ................................ .............................. 61 LIST OF REFE RENCES ................................ ................................ ............................... 63 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 64
7 LIST OF TABLES Table page 5 1 The components of the PTFE based ink. ................................ ........................... 44 5 2 Micrometer, SWLI, and capacitance probe thickness of 1.27 mm thick gage block. ................................ ................................ ................................ .................. 44 6 1 GDL thickness data. ................................ ................................ ........................... 52 6 2 Results of sintering using UNF's original pr ocedure. ................................ .......... 52 6 3 Sintering results using the "literature" process. ................................ .................. 52 6 4 Air convection sintering data. ................................ ................................ .............. 53 6 5 Sintering results from GDLs sintered layer by layer ................................ ........... 53 6 6 Membrane hole diameters from the top view. ................................ ..................... 53 6 7 Membrane hole diameters from the bottom view. ................................ ............... 53
8 LIST OF FIGURES Figure page 1 1 Gas distribution layer (120 mm x 220 mm). ................................ ........................ 17 1 2 Schematic of traditional and simplified UNF DMFC. Courtesy of University of North Florida. ................................ ................................ ................................ ...... 18 1 3 Liquid barrier layer (LBL) applied to GDL (120 mm x 220 mm). ......................... 19 1 4 The GDL curls during sintering. ................................ ................................ .......... 19 1 5 20 m thick polymer membrane (120 mm x 220 mm). ................................ ....... 20 3 1 Capacitance probe measurements. A) Displays the error that occurs with a non flat target, B) a measurement of a fla t targe t ................................ ............... 30 3 2 Lion Precision CPL290 capacitance probe amplifier. ................................ ......... 30 3 3 Capacitance probe holder fabricated of aluminum and nylon. ............................ 31 3 4 JB Industries DV 285N 10 CFM Vacuum pump ................................ ................. 31 3 5 150 x 300 mm NewWay air bearing. ................................ ................................ ... 32 3 6 Custom aluminum vacuum chuck. ................................ ................................ ...... 32 3 7 Mikron U CP600 Vario 5 Axis CNC mill. ................................ .............................. 33 3 8 Isometric view of the 1.6 mm diameter hole vacuum chuck data. ....................... 33 3 9 TiAlN coated drill (0.8 mm diameter). ................................ ................................ 34 3 10 Ribbed aluminum support for vacuum chuck (104 x 186 mm). ........................... 34 3 11 Schematic of SWLI system ................................ ................................ ................ 35 3 12 Lindberg/Blue M programmable oven interior. ................................ .................... 35 4 1 Thorlabs long travel programmable stages (LTS). ................................ .............. 38 4 2 0.01 mg resolution scale with GDL placed upright i n enclosed measurement area. ................................ ................................ ................................ ................... 39 5 1 Velocity profile of the stage. The commanded velocity was 10 mm/s. ................ 45 5 2 3 Dimensional plot of the unfiltered SWLI GDL surface data. ............................ 45
9 5 3 Plot of the filtered SWLI GDL surface data. ................................ ........................ 46 5 4 SWLI height map of GDL. The scanned area is 2.83 mm long by 2.12 mm wide. ................................ ................................ ................................ ................... 46 5 5 3 D plot from the capaci tance probe data. Colorbar units are in m. This image is a small fraction of the size of Figure 6 1. ................................ .............. 47 5 6 Height map of the 1.27 mm thick gage block and surrounding area from the capacitance probe setup. Note the averaging effect near the gage block edges. ................................ ................................ ................................ ................. 47 5 7 The 1.27 mm gage block thickness profile from the SWLI. ................................ 48 6 1 GDL surface map sample of GDL 11. Mean thickness of 282. 7 m and standard deviation of 13.2 m. ................................ ................................ ........... 54 6 2 GDL surface map sample of GDL 13. Mean thickness of 311.5 m and standard deviatio n of 14.9 m. ................................ ................................ ........... 54 6 3 GDL thickness versus number of ink layers. ................................ ....................... 55 6 4 Top view oblique plot of a membrane hole. Window size is 175 by 130 m. ...... 55 6 5 Bottom view of a laser cut membrane hole. Window size is 175 by 130 m. ..... 56 A 1 LabVIEW block diagram of motor controller. ................................ ...................... 59 A 2 Schematic of a LabView VI that gathers stage position data. ............................. 60
10 LIST OF ABBREVIATION S DMFC Direct Methanol Fuel Cell GDL Gas Distribution Layer LBL Liquid Barrier Layer MTRC Machine Tool Research Center PTFE Polytetrafluoroethylene SWLI Scanning White Light Interferometer
11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science MANUFACTURING EVALUATION OF A GAS DISTRIBUTION LAYER FOR A DIRECT METHANOL FUEL CELL By Mark Allen Pope December 2011 Chair: Tony L. Schmitz Major: Mechanical Engineering A gas distribution layer (GDL) and membrane for a direct methanol fuel cell (DMFC) which is being developed under a collaboration between the University of North Florida (UNF) and the University of Florida (UF) were investigated from a viewpoint of manufacturing quality. The thickness of the GDL, which is currently produced by hand painting ink layers on a carbon fiber substrate was measu red using a novel measurement apparatus that was designed and constructed as part of this work It was found that the ink was applied to a thickness with a n average standard deviation of 13.2 m which was approximately equal to the thickness variation of the GDL carbon fiber substrate A current challenge for the DMFC implementation is potential degradation of the fuel cell by surfactants in the ink These surfactants are inherently present in the ink formulation and must be removed by sintering. In this study, the sintering process was modified to increase the percent surfactant removal Modifications included changing the heating cycle and altering the sintering environment. Surfactant removal was quantified by weighing samples before and after t he sintering process.
12 The DMFC polymer membrane which control s the methanol diffusivity water permeability and allows H + conduction, was also studied Holes were laser drilled by UNF into the membrane to allow the appropriate amount of water to travel across the membrane from the cathode to anode. The hole size and shape was examined using a scanning white light interferometer (SWLI). It was found that the hole diameters differed from one side of the membrane to the other and redeposited material (from the laser ablation process) was present. However, the hole diameter s on the backside were within the prescribed range of 5 8 m and the shape w as acceptably circular.
13 CHAPTER 1 INTRODUCTION The rising cost of fuel serves as a constant motivation for the development of alternative forms of energy in the current world climate. Crude oil, from which gasol ine is refined, has a variable cost and availability due to many factors not related to oil production To reduce energy conversion concepts have been proposed both in the United States and abroad. One option is t he fuel cell which operates by converting the chemical energy of a fuel into electrical energy. The electricity is produced by the reaction between the fuel and an oxidizing agent. Hydrogen fuel cells, which use hydrogen as the fuel and air as the oxidant, have been in development for several years and provide a potential alternative to the internal combustion engine as well as o ther applications Th e focus of th is thesis is the completion of measurements for critical components in a new direct methanol fuel cell (DMFC) under development at the University of North Florida (UNF) and the University of Florida (UF) This fuel cell wi ll be used for small portable electronic devices, such as laptops. A traditional DMFC contains several components that are necessary for the active water partition of the cell. This partition is needed, because the cathode reaction creates three water mo lecules for every methanol molecule consumed, while the anode reaction only req uires one molecule of water as shown in Eqs. 1 1 and 1 2 (1 1) (1 2) Therefore, two water molecules must be removed and exhausted. In the UNF design, a gas distribution layer (GDL) Figure 1 1 is used to allow the prescribed
14 amount of air vapor to cross the cathode, while the liquid barrier layer (LBL) restricts the flow to one water molecule per methanol molecule consumed. The combination of the GDL and LBL which will be called the GDL assembly, allow passive water partition of the fuel cell, removing several power hungry components such as the heat exchanger, water pump, and air pump that are typically included i n a DMFC ( Figure 1 2 ) The removal of these components reduce the complexity of the fuel cell and increase the energy and power densities to the performance level of lithium ion (Li ion) batteries. The performanc e increase has improved the viability of DFMCs as a commercial alternative to Li i on batteries according t o studies completed at UNF [1] The GDL is made of a carbon fiber substrate that is formed into a porous paper. A LBL consisting of a polytetrafluoroe thylene ( PTFE ) based ink is painted onto the GDL. T he water transport capability of the fuel cell is directly proportional to t he combined thickness of these two components. The GDL has a uniform weight of 1.5 mg with a standard deviation of 0.02 mg The h and painted LBL weight, and consequently thickness, is not as consistent and serves as the main contributor to variations in water transport performance. The ink is painted on in several steps First the GDL is painted with the PTFE ink Next, t he GDL is dried at 70 C to remove any excess water. This process is then repeated for a total of eight layers ( Figure 1 3 ) A primary goal of this work was the development of a platform for non contact GDL assembly thickness measurement. Due to the 120 mm x 220 mm size of the GDL assembly non contact devices with a small measurement area, such as a scanning white light interferometer (SWLI) were not practical for characteriz ation of the large
15 surface area of the GDL assembly due to the significant measurement time The refore, a capacitance probe setup with fast scanning capabilities was selected After the eight layer LBL buildup, the PTFE is sintered to remove unwanted com ponents; this causes the GDL assembly to curl at the edges as seen in Figure 1 4 The curling presented a unique challenge that required a custom measurement setup to acquire accurate data. T wo possible methods for obtaining a flat surface were identified: 1) p ulling the sample down ; or 2) pressing it down. selected and implemented using a custom made vacuum chuck, which was designed to suction down the entire GDL assembly The thickness measurement procedure is described in detail in Chapter 3. The PTFE based ink contains surfactants, which are chemicals that permit the PTFE to be made into an ink suitable for painting. Surfactants in the PTFE emulsion are added in the form of a nonionic thickener which provides the appropriate viscosity for pain ting These surfactants are a potential danger to the cell and may contribute to off state cell degradation as evidenced by recent UNF studies Since the surfactants can not be omitted from the ink formulation, they must be removed during the sintering proc ess. The original sintering profile consisted of a quick ramp to an intermediate temperature which was then increased slowly up to the PTFE curing temperature. Several solutions were considered including sintering under an inert atmosphere, convection sintering using air, and layer by layer sintering To sinter layer by layer, a new batch of ink needed to be mixed for each layer due to the short (~12 hr ) sh elf life of the ink. The GDL will be pa inted with one coat of ink sintered, and this process will be repeated eight times for the total layer build up.
16 Another component which is vital to DMFC performance is the polymer membrane ( Figure 1 5 ) Th is membrane controls the water permeability and methanol diffusivity for the cell Many comm ercially available membranes require water pumps to provide the needed amount of water transport from the cathode to anod e side of the fuel cell. The membrane used in this work was engineered to passively provide the necessary amount of water permeability, which remov ed the water pump requirement and, in turn increases the fuel cell energy density. This new membrane achieves the required amount of water permeability at a hydraulic pressure of only 34.5 kPa ( 5 psi ), compared to the 345 kPa (50 psi) to 690 kPa (100 psi ) required for commercially available membranes. Correct operation of the UNF DMFC requires specific characteristics different from those in traditional DMFCs. The refore, a post processing step was added to the membrane production where holes are laser drilled into the me m brane These holes create additional challenges to t he performance management of the cell. The laser drilled h ole size and shape were investigated using a SWLI in this work H ole size affects water flux and may also affect GDL assembly hydrostatic pressure requirements ; additionally hole defects may lead t o the formation of electrical shorts through the membrane when the electrodes are bonded together. This thesis is organized as follows. Chapter 2 provides background information on DMFCs, with an emphasis on passive water partition and sintering. Chapter 3 contains descriptions of the experimental apparatus developed /used for this project. In Chapter 4, the experimental procedures are defined for the GDL assembly thickness measurements, PTFE ink mixing and sintering, and membrane ho le surface maps. Data
17 analysis and validation are described in Chapter 5. Results of the thickness measurements, sintering, and membrane hole characteristics are presented in Chapter 6. Chapter 7 provides conclusions and future work Figure 1 1 Gas distribution layer ( 120 mm x 220 mm ) Photo courtesy of Mark Pope.
18 Figure 1 2 Schematic of tradi ti onal and simplified UNF DMFC Courtesy of University of Nort h Florida.
19 Figure 1 3 Liquid barrier layer (LBL) applied to GDL (120 mm x 220 mm) Photo courtesy of Mark Pope. Figure 1 4 The GDL assembly curls during sintering. Photo courtesy of Mark Pope.
20 Figure 1 5 20 m thick p olymer membrane ( 120 mm x 220 mm ) Photo courtesy of Mark Pope.
21 CHAPTER 2 LITERATURE REVIEW The direct methanol fuel cell (DMFC) is a developing area in the field of alternative energy and is a possible alternative to the lithium based rechargeable battery for the portable electronics market [2 ] There are two basic types of DMFC s : active and passive. Active DMFCs generally have a higher reliability and performance than the passive system s Many active systems incorporate a water pump into the design to provide circulation of the water to dilute the methanol reactant, which results in a more efficient system. Meanwhile, passive DMFC s, like the UNF design investigated here operate without the use of external devices such as a methanol / water pump [2 ]. Oxygen diffuses into the open cathode from the ambient air and methanol diffuses into the anode from a feed reservoir that is driven by a concentration gradient prescribed by the system. In addition to the simplicity and lower cost, passive DMFCs offer the possibility for lower parasitic power loss and system volume [2 ]. There are several barriers to overcome before passive DMFCs can be a commercially viable product. Methanol crossover: While high methanol concentration provides higher achievable energy density [3], it also causes severe methanol crossover to the electrolyte membrane and results in mix potential at the cathode and there fore, causes low cell performance [4]. Water management: Passive system control of water adds complexity to small DMFC design s [4]. It is des irable to recycle the water produced at the cathode to anode for dilution of fuel. Usually gas diffusion layers (GD L) for the cathode are wet proofed with a PTFE coating to ensure the pores of the layer do not fill up with water [4]. Once through the GDL, a portion of the water must pass through the membrane, which has led to the introduction of holes to be laser drill ed through the membrane and provides water transport [4]. Catalyst thickness: For a given catalyst loading, the power density increases as the catalyst thickness decreases [5].
22 Cell durability: Degradation rates of DMFCs are presumably high due to the poisoning of the cell by intermediates created by the cell processes [2]. In [2] it was found that a performance drop occurred after 200 hours of operation and became worse after 1 002 hours of operation. The cell investigated in this thesis had similar challenges to overcome. The GDL for this project had a liquid barrier layer (LBL) painted onto it to increase the hydrophobicity of the cathode. Sintering of the LBL was completed aft er eight layers were added to the GDL. A thickening agent, Natrosol was present in the formulation to increase the viscosity of the ink to an acceptable level for painting. Natrosol is a hydroxyl ethyl cellulose (HEC) a chemical which may have had an eff ect on the degradation rate of the cell. According to a thermogravimet ric analysis (TGA) described by Mutalik [6 ], HEC does not begin to burn out until 280C and cannot be fully removed until the sintering temperature reaches 800C. It is impossible to sin ter at a temperature this high due to the presence of PTFE in the ink. An alternative thickener would nee d to be procured to avoid this issue The PTFE emulsion also contains surfactants that could cause degradation to the cell. According to an indus try partner, Johnson Matthey Fuel Cells (JMFC), the majority of GDLs are sintered only once after the full number of ink coats has been applied. However, DuPont who manufactures the PTFE indicates that each coating layer should be sintered in the layer b uild up process [7 ]
23 CHAPTER 3 EXPERIMENTAL DESIGN Non Contact Measurement A non contact measurement system was chosen as the method to determine the thickness of the GDL assembly A non contact rather than tactile, measurement was required so that the built up ink layer painted onto the surface of the GDL assembly was not damaged during the measurement process Due to the large GDL assembly surface area of 120 mm x 220 mm, ability was require d. This precludes the use of high resolution, small field of view metrology, such as SWLI. H owever, SWLI was useful for data validation of selected small area s The SWLI in the Machine Tool Research Center (MTRC) at the University of Florida (UF) can captu re a maximum scanning area of 2.82 mm by 2.12 mm with a single measurement Multiple measurements one topographical image over a larger area For the GDL assembly in this research 4300 measurement results would need to be stitched together to capture the entire surface of the GDL assembly As an alternative a capacitance probe was selected for the measurement setup ( Figure 3 1 ) The measurement was conducted as follows. First, a scan of the reference surface was completed using the capacitance probe. Second, the GDL assembly was placed on the reference surface and a second (target) scan was performed Third, the difference between the target and reference surface s cans was calculated The difference is the GDL assembly thickness This approach was followed to remove any non flatness of the reference surface that supported the GDL assembly
24 Capacitance Probe Capacitance Capacitance describes how the space between two conductors affects an electric field between them. For example, if two steel plates are placed with a gap between them and a voltage is applied to one of the plates, an electric field will exis t between the p lates. This electric field is the result of the difference between electric charges that are stored on the surfaces of the plates. Capacitance refers to the capacity to hold this electrical charge. The amount of existing charge on a target determines how m uch current must be used to change the voltage of the target. When using a capacitance sensor, or probe, the sensor surface is the electrified plate and the target surface is the other plate. The sensor electronics continually change the voltage on the se nsor surface. This is called the excitation voltage. T he amount of current required to make the capacitance change is measured by the circuit and indicates the amount of capacitance between the probe and the target. The capacitive response is a functi on of the probe diameter, target gap, and dielectric constant of the electric field as shown in Equati on 3 1. (3 1) This equation identifies three characteristics of capacitance measurements. The c apacitance increases as the probe area increases. As the gap increases the capacitance decreases. The capacitance increases as the dielectric constant increase s In this project, as with most capacitance probe sensing applications the size of the sensor, the size of the target, and the dielectric material (air) are fixed The only variable is the target gap length, which reduces Equation 3 1 to a simple inverse relationship.
25 (3 2) Based on E quation 3 2 probe electronics assume that all changes in capacitance are a result of the change in gap size. Calibration The probe must be calibrated to a reference surface that mimics the target surface shape to minimize measurement e rror Because a capacitance probe outputs a very low voltage, an appropriate voltage to thickness conversion factor must be known and an amplifier is placed in line to amplify the response as shown in Figure 3 2 T ests are completed on each capacitance probe to determine the value of the conversion factor. A calibrated stage is used to determine the factor. The sta ge is moved in increments and the cap acitance probe voltage is recorded. The slope of the plot of one versus the o ther is the calibration factor. The calibration factor for the probe used in this research was provided by the manufacturer. Measurement Error s Capacitance probes have many potential areas for error when taking thickness measurements. Several of them have been investigated and their influence has been minimized as much as possible. Parallelism During calibration the surface of the sensor is made parallel to the target surface. If the probe or target is far from parallel the target shape elongates and changes the field interaction between the probe and target. If the interaction changes the behavior of the electric field, measurement errors will be introduced. The aluminum probe holder in
26 Figure 3 3 was made parallel to the surface of the target by use of a level. This was done to decrease the slope change as the sensor move d along the GDL assembly Flatness One of the requirements for accurate measurements usin g this setu p was a flat reference and target. As mentioned previously, the sintering process cause s the GDL assembly to curl, ruling out the possibilit y of simply setting the GDL assembly on a flat reference and acquiring the data. The easiest way to make something flat is to either push or pull it down; whether by air, magnetism, or some other means. It was decided that the simplest way to incorporate t he capacitance probe and a flattening apparatus would be to pull it down using a vacuum pump such as the JB Industries DV 285N pump shown in Figure 3 4 The pump is connected to an airflow device to provide the required vacuum. O ne solution that was considere d was a NewWay porous carbon air bearing ( Figure 3 5 ) The vacuum pump was fitted to th e bearing and a small GDL assembly sample was pulled down to a 0.0127 mm average surface roughness. However, several air bearings that were tested did not po ssess the flow rate required to hold the entire GDL assembly against the bearing surface. Therefore a custom aluminum vacuum chuck was machined at the MTRC ( Figure 3 6 ) The chuck that was machined could not provide the same level of flatness as the ground air bearing However, this was addressed using the reference surface measurement Environment The Lion Precision C 23B capacitance probe used for this project is compensated to minimize drift due to temperature s from 22 C to 35 C. In this temperature range errors are less than 0.5% of full scale [ 8 ] Calibration of the probe was conducted at 20
27 C by the manufacturer and no compensation is needed when data is collected at this temperature. The dielectric constant of air is affected by humidity. As humidity increases the dielectric increases. The p robe is calibrated at 50% relative humidity (RH) and no compensation is needed if the data is taken at this value F or this project data was collected in a climate controlled metrology lab held at 20 C and 50% RH. Vacuum Chuck Pre M achining Preparation The chuck was machined on a Mikron Vario UCP600 5 Axis CNC mill ( Figure 3 7 ). It was constructed from a 15.9 mm thick precision ground alloy 2024 aluminum substrate The flatness tolerance for the aluminum was 25 m ( 0.001 in) A 12.7 mm thick cavity 124 mm wide x 224 mm long was milled out of the back of the piece to provide the vacuum chamber. The piece was then attached by hex screws to a 6.35 mm thick backing plate, made of the same material. This assembly was then clamped to t he machine table. Machining Parameters The air bearing in Figure 3 4 has a porou s carbon surface which allows air to flow through the unit Conversely, a vacuum chuck contains multiple holes that allow the flow of air through the device. Tests were conducted to determine the appropriate hole size for the vacuum chuck. Vacuum chucks fabricated at the MTRC were avai lable with hole diameters of and 1.6 mm Significant localized errors were discovered at the hole locations for hole diameters of 3.2 mm ( 0.125 like features were also present, but of a lower magnitude in the 1.6 mm chuck ( Figure 3 8 ) They are a result of the flexible barrier being suctioned down into the hole
28 when the vacuum is applied. The other consideration in regards to the hole size was the need to scan the referen ce surface. The larger the hole, the greater the odds of the capacitance probe averaging the hole gap into the scan, thereby decreasing the reference height, which would increase the calculated GDL assembly thickness. Therefore, a diameter drill ( Figure 3 9 ) was chosen to provide a reasonable compromise between error reduction and machining time. Eight titanium aluminum nitride (TiAlN) coated carbide dri ll s were used to reduce the effects of tool wear on the final part Hole spacing was another important machining parameter. The challenge was to determine an interval that would provide enough suction strength and not cause localized deformations in the s ample while maintaining a reasonable machining time. Various hole spacing value s were test ed for a 5 mm x 5 mm area. A hole spacing of 0.8 mm provided a good compromise between error reduction and machining time. An additional outcome of the hole spacing tests was determining the pecking speed of the drilling operation. The plunge rate was chosen to be 20 mm/min which resulted in a drilling time of 16 seconds per hole. D ue to the drill size and hole spacing, a total of 10,850 holes needed to be drilled into the chuck, for a minimum of 48.6 hours of machining time. A new drill was inserted into the holder every 1400 holes. Taking into account the machine idle time in betwe en tool changes, the total machining time was 54 hours. Vacuum Bowing Effect Tests were conducted to verify the measurement accuracy of the vacuum chuck. It was discovered that the chuck bowed slightly, between 20 m and 60 m, after application of v acuum pressure. The bowing was due to the thin 3.2 mm ( ) chuck
29 surface which was chosen to dec rease the already significant 54 hours of drilling time. Several fixes were attempted, including placing springs at strategic intervals in the vacuum cavity which was ultimately unsuccessful at produ cing accurate thickness data. The ribbed aluminum block in Figure 3 10 was therefore machined and inserted into the vacuum cavity, providing the necessary support to prevent bowing of the chuck surface. Note that each rib was machined down to a 0.8 mm to p with a bull nose end mill A 0.8 mm top was chosen so as to not cover any of the vacuum airflow holes Scanning White Light Interferometer As noted previously the SWLI was not practical for full surface area measurements of the GDL assembly thickness However, t he SWLI proved useful in validation of the vacuum chuck /capacitance probe data A SWLI is an optical three dime nsional, or 3D, surface profiler which uses the short coherence length of white light in order to limit interference to a short depth in the focal region of the objective. Light reflected from the sample within the focal region interfere s with light reflec ted from a reference surface based on its distanc e from the objective as in Figure 3 11 When the objective is translated vertically away from the sample the region of interference also translate s and a 3D reconstruction can be generated to provide a surface map of the sample within the field of view of the objective. The interference fringes are detected by a 640x480 pixel camera which maps the intensity into vertical position data on a per pixel basis. Each pixel of the camera is then a lateral position of the sample, which is dependent on the zoom level and the objective being used.
30 Programmable Furnace A Lindberg/Blue Moldatherm BF 5184C furnace ( Figure 3 12 ) was used to sinter the GDLs. The atmospheric input was fitted with a quick connect line to enable prompt switching between inert and air oven atmospheres. A B Figure 3 1 Capacitance probe measurements. A) Displays the error that occurs with a non flat target, B) a measurement of a flat target Courtesy of Lion Precision Figure 3 2 Lion Precision CPL290 capacitance probe amplifier. Photo courtesy of Mark Pope.
31 Figure 3 3 Capacitance probe holder fabricated of aluminum and nylon. Photo courtesy of Mark Pope. Figure 3 4 JB Industries DV 285N 10 CFM Vacuum pump Photo courtesy of Mark Pope.
32 Figure 3 5 150 x 300 mm NewWay air bearing Photo courtesy of Mark Pope. Figure 3 6 Custom aluminum vacuum chuck Photo courtesy of Mark Pope. 120 mm 220 mm 150 mm 300 mm
33 Figure 3 7 Mikron UCP600 Vario 5 Axis CNC mill. Photo courtesy of Mark Pope. Figure 3 8 Isometric view of the 1.6 mm diameter hole vacuum chuck data. Chart courtesy of Mark Pope
34 Figure 3 9 TiAlN coated drill (0.8 mm diameter) Photo courtesy of Mark Pope. Figure 3 10 Ribbed aluminum support for vacuum chuck (104 x 186 mm) Rendering courtesy of Mark Pope. 4.8 mm 3.2 mm
35 Figure 3 11 Schematic of SWLI system. Drawing c ourtesy of Lee Kumanchik Figure 3 12 Lindberg/Blue M programmable oven interior Photo courtesy of Mark Pope. Michelson In terferometer Atmospheric inlet (allows input of air or nitrogen) Thermocouple Steel bed promotes airflow beneath sample
36 CHAPTER 4 EXPERIMENTAL PROCEDU RE Thickness Measurement The thickness of the GDL assembly was recorded with the use of the two programmable stages shown in Figure 4 1 and a capacitance probe. The stage motions were controlled by the Labview Virtual Instrum ent (VI) included in Appendix A, which provided time syncronization between motion initiation and data collection. The capacitance probe sensor used for this project had a 3.2 mm sensing diameter; the sample capacitance was averaged over this sensing area. Therefore, the stage was stepped along the Y axis in 1.5 mm increments and scanning was initiated in the X axis at a rate of 37,000 samples per line. The vacuum chuck surface was scanned as the reference for the thickness measurement. Then, the GDL assem bly was inserted into the apparatus and scanned. The thickness of the GDL assembly was found by differencing the target and reference surface scans. By incorporating the capacitance probe and vacuum chuck, the reference surface non flatness is removed. SWL I Data Validation A 20 mm by 10 mm height map of a representative GDL assembly was measured using the SWLI and compared to the capacitance probe height data. A total of 54 SWLI topographs (height maps) were collected using a 5x Michelson type objective wit h a 0.5x magnifier and then stitched together. This objective/magnifier combination produced a 2.83 mm x 2.12 mm field of view.
37 Sintering Procedure Unsintered GDL assembly samples were provided by UNF with an eight layer ink build up. The sample was dried at 120 C for two hours to remove any water in the barrier. The GDL assembly weight was recorded at this point to obtain an accurate pre sintering weight using a 0.01 mg resolution scale ( Figure 4 2 ). The sample was then returned to the furnace and sintered using the selected heating profile. After cool down, the sample was weighed again to record the post sintering weight. GDL Ink P rod uction and Painting The GDL assembly ink contains several materials including: Tergitol, which is a detergent; deionized (DI) water; graphite; PTFE emulsion; and Natrosol, which is a nonionic pharmaceutical grade thickener. To produce the ink, the Tergitol and graphite are added to a beaker where they are sonicated in an ice bath to reach the required level of dispersion. After transferring the beaker to a stir plate the PTFE is added via glass rod decanting. The Natrosol powder is next added, while ensuri ng that the stirring vortex (from the stir plate) is never lost. The entire ink mixture is then stirred at a high velocity for an hour and then slowed to a point where the vortex is just slightly apparent. The ink is finally painted on the carbon fiber she et using a synthetic bristle brush It must be painted with low force to avoid transfer through the carbon fiber paper, which yields an inadequate layer build up. Membrane Hole Diameter Measurement The laser drilled membrane hole diameter was determined u sing SWLI measurements. A drilled sample was placed on an aluminum plate and held flat using gauge blocks located adjacent to, but outside, the measurement area. The Michelson interferometer was focused on the top side of the membrane. A diamond shaped hol e
38 pattern was previously drilled into the 20 m thick membrane and enabled identification of individual holes. A scan length less than 20 m was chosen so that only the top surface of the membran e was imaged. Figure 4 1 Thorlabs long travel programmable stages (LTS). Photo courtesy of Mark Pope.
39 Figure 4 2 0.01 mg resolution scale with GDL assembly placed upright in enclosed measurement area. Photo courtesy of Mark Pope.
40 CHAPTER 5 DATA ANALYSIS AND VALIDATION In this chapter the conversion from capacitance probe voltage to thickness is discussed in detail. The procedure for determining the amount of sintering loss is also presented. Finally, cap acitance probe, SWLI, and manual micrometer measurements are compared to confirm the validity of the custom GDL assembly thickness measurement apparatus. Thickness Calculation Algorithm The LabView program in Appendix A provided the data collection engine for the GDL assembly thickness measurement. The voltage response for each pass along the GDL assembly was amplified and sampled by NI DAQ and exported from LabView in a single column text file. A MATLAB m file (provided in Appendix B) imported the 84 text files for the target surface response and 84 files for the reference response. Each set of 84 files was compiled into a voltage matrix. The thickness was found by multiplying each voltage matrix by the capacitance probe voltage to thickness calibration fa ctor of 62.5 m/V (manufacturer provided) and differencing the target and reference thickness matrices. This matrix is the Z axis (height) matrix over the X and Y measurement coordinates. The Z axis data was not filtered because the objective of the measur ement wa s to find the peak s and valleys in the ink loading The stages were controlled in LabView using an Active X controller provided by the manufacturer. A position method (Appendix A) was added to the VI which recorded the stage axis position throughou t the data acquisition period. There are two sections of the position, or X axis vector. The first is the constant a cceleration (0.5 mm/ s 2 ) section up to the commanded 10 mm/s maximum velocity. The second is the constant velocity
41 section that continues until data collection is ceased Deceleration is not considered as the data collection is stopped before the stage begins to slow down. The velocity profile througho ut the data collection period was calculated by a first order finite difference from the position data retrieved from the LabView VI ( Figure 5 1 ) From this graph it is seen that the commanded vel ocity is never actually reached; inste ad the stage settles at a maximum velocity of approximately 8 .2 mm/s. The acceleration, can also be found from Figure 5 1 by calculating the derivative of the pr ofile ( Eq. 5 1 ) : (5 1) where is the velocity of the stage and is the time. The acceleration was slightly less than the commanded acceleration of 0.5 mm/ s 2 Three velocity profiles were collected whic h had a standard deviation of 0.4 mm/s Small errors are expected to be introduced into the thickness differencing measurement due to the variation of the velocity profiles between two measurements. The Y axis was defin ed by creating a vector the width of the GDL assembly used to create a surface matrix of X and Y locations. The 3 D topography matrix was then complete and the GDL assembly thickness profile could be plotted. Sintering Loss The calculation of surfactant removal from the GDL assembly is provided here First, the initial amount of surfactants present in the GDL assembly was found ( Table 5 1 ) From the table, it is seen that the surfactant amount is a function of the ink loading and is 9.7% of the mixed ink. It was necessary to find the total dry weight of the GDL ass embly before sintering because the percentage of surfactants is assumed to be the dry weight amounts (i.e., no water remaining). Therefore, the GDL
42 assembly was placed in a furnace for two hours at 120 C to evaporate any remaining water from the sample. I t was immediately transferred to a 0.01 mg resolution scale and the pre sintering weight of the GDL assembly was recorded. The sample was then sintered and the post sintering weight was logged. The sintering loss is a function of the ink loading, pre sint ering weight, and post sintering weight. Consider an ink loading, of 5000 mg, pre sintering weight of 6500 mg, and post sintering weight of 6100 mg. The reduction, in ink mass is 400 mg. These parameters yield a sintering loss of 8%. The formulatio n for this result is shown in Equation 5 2 (5 2) SWLI Validation Data Filtering The GDL assembly has a dull, grey, low contrast surface. All of these attributes make it ch allenging to obtain accurate topography data using interferometry. The Zygo NewView 7200 has two light filter options between the magnifier and interferometer/objective. One of these filters attenuates the intensity and disperses the light. Several tests u sing this filter produced an acceptable image with minimal pixel dropout. The scan length was chosen to be 150 m. This large range ensured that any peaks or valleys on the actual surface would not be omitted from the image. In the analysis controls, an av erage low pass filter with low and high wavelength of 0.82 m and 20 m, respectively, was applied to the data. An average filter type indicated that the software uses all valid data points in each filter window ( in this case 7 data points ) and averages them. The averaged value is then used to replace the data point at the center of the window. These averaged values are used to generate a new data array.
43 Figure 5 2 feature in the MetroPro SWL I pr ogram as shown in Figure 5 3 This figure displays data dropout, which is a result of a slope change in the sample that is greater than is measureable by the SWLI. Comparison Tests It was desired to provide a comparison of the capacitance probe measurement data with an independent technique. Although the SWLI technique is too time consuming to measure the entire GDL assembly it could theoretically provide a comparis on over a smaller field of view. However, because the lateral resolution of the SWLI is so much higher than the capacitance based measurement (due to th e averaging effect over the prob e area), a direct comparison of the two measurements was challenging. Th e capacitance probe data in Figure 5 4 through Figure 5 5 displays a smoothin g effect due to the averaging over the capacitance probe sensing area. Validation was therefore conducted by measuring a sample of known thickness and comparing the methods A 1.27 mm thick gage block was measured by three devices, including the cap acitan ce probe setup ( Figure 5 6 ), the SWLI ( Figure 5 7 ), and a micrometer ( Table 5 2 ). The mean thickness and standard deviation for each measurement type is included in Table 5 2. The micrometer result, which was averaged from three measurements at various locations on the block, was closest to the specified thickness of 1270 m. The SWLI data was several micrometers thicker and was found by placing the 1.27 mm gage block on top of a second gage bl ock and completing a 1500 m
44 upward scan. The capacitance probe results were 20 m thicker than the exp ected value. All measurements were performed in a temperature controlled environment. One potential explanation for the SWLI measurement difference is that the gage blocks were not wrung together and debris was likely present between the two surfaces. This would lead to an increased thickness. For the capacitance probe data, it is believed that the calibration factor applied to convert the voltage into displacement was too large. This offset could be corrected in subsequent measurements. Also, the thickness was determined by differencing the voltage response of the gage block and the vacuum chuck surface. Small burrs or dust on the chuck surface would cause a larger gap between the sample and reference planes and lead to a thicker measurement. Polishing the chuck surface would likely result in a more accurate measurement for the rigid sample. Note that this measurement was different than the GDL assembly measurements because the GDL assembly conformed to the chuck surface when the vacuum was applied so this represents a worst case scenario Table 5 1 The components of the PTFE based ink. Ink Component Dry Weight (g) Weight % Weight / sheet (g) Teflon (solid resin) 38.79 47.92 2.64 Carbon 34.3 0 42.37 2.33 Tergitol TMN 100 3.3 0 4.08 0.22 Surfactants (from Teflon) 3.87 4.78 0.26 Natrosol 0.69 0.85 0.05 TOTAL 80.95 100 5.50 Extractable Portion 7.86 9.71 0.53 Table 5 2 Micrometer, SWLI, and capacitance probe thickness of 1.27 mm thick gage block. Measure Type Mean Thickness (m) Standard Dev. (m) Percent Diff. (%) Micrometer 1270 0.5 0 SWLI 1278 0.24 0.63 Cap. Probe 1290.2 22.5 1.59
45 Figure 5 1 Velocity profile of the stage The commanded velocity was 10 mm/s. Chart courtesy of Mark Pope. Figure 5 2 3 Dimensional plot of the unfiltered SWLI GDL assembly surface data. Chart courtesy of Mark Pope. 150 m 20 m m 10 m m
46 Figure 5 3 P lot of the filtered SWLI GDL assembly surface data. Chart courtesy of Mark Pope. Figure 5 4 SWLI height map of GDL assembly The scanned area is 2.83 mm long by 2.12 mm wide. Chart courtesy of Mark Pope. 150 m 20 m m 10 m m
47 Figure 5 5 3 D plot from the capacitance probe data. Colorbar units are in m. This image is a smal l fraction of the size of Figure 6 1 Chart courtesy of Mark Pope. Figure 5 6 Height map of the 1.27 mm thick gage block and surrounding area from the capacitance probe setup. Note the averaging effect near the gage block edges. Chart courtesy of Mark Pope.
48 Figure 5 7 The 1.27 mm gage block thickness profile from the SWLI. Chart courtesy of Mark Pope.
49 CHAPTER 6 RESULTS Capacitance Probe GDL Data Samples of the GDL assembly capacitance probe data were plotted in th ree dimensions using MATLAB In Figure 6 1 the GDL assembly had six co ats of ink painted onto it which resulted in an average thickness of 282.7 m and a standard deviation of 13.2 m, while Figure 6 2 describes a GDL assembly surface with eight coats of ink with an average thickness of 311.5 m and a standard deviation of 14.9 m A GDL assembly feature of interest was the thickness change with progressive ink loading. Eight individual ink coats were applied to a carbon fiber paper ( CFP ) sample and the thickness between each subseq uent coat was measured ( Figure 6 3 ) In the ink coating process, the carbon fiber paper is cut from a large roll down the middle to create both a left and a right piece. A systematic difference in barrier thickness between the left and right piece s was observed. Th is bias was investigated by conducting performance tests on GDLs from each side of the roll. These tests we re comprised of a diffusion test, which measures the methanol diffusivity of the cell, and a capillary pressure test that quantifies the water transport capacity The capillary benchmark is the easier of the two to satisfy and each side of the roll passed every time. The methanol diffusion is the more difficult target to achieve and could fail despite having conducted the painting process in the correct manner. It was found that simply adding a thicker coat or painting nine coats of ink on the left side pieces would enable the required level to be reached A total of 22 GDLs were measured and the mean thickness and standard deviation values for each are presented i n Table 6 1 GDLs 1 16 were measured as part of the progressive ink
50 loading experiment and were not sintered, w hile GDLs 17 22 had the full eight ink layers and were sintered The sintering process removes material from the GDL assembly a fact that is reinforced by the lower mean thickness of the sintered eight coat GDLs. Sintering Results Initial trials were completed using the original sintering procedure developed by UNF ( Table 6 2 ) This procedure was able to achieve an 8% sintering loss (standard deviation of 0.2%). A new procedure defined as part of this work was able to increase the sintering loss to 8.2%, but this was still 1. 5 % lower than the desired burnout of to 280 C for 10 minutes; 2) increase to 370 C over 47 minutes; and 3) hold at 370 C for one hour. Consultation with an industry partner and confidential documents provided some guidance for defining a revised procedure. Holding for some period of time at the intermediate step, in this case 280 C, was found to provide grea ter burnout of surfactants in PTFE based inks It was postulated that the hold time could be lengthy (~8 hours) and not cause chemical harm to the GDL assembly because the PTFE should not degrade at temperatures below 390 C. erature Table 6 3 used, whether air or hi gh purity nitrogen, for each trial. An inert atmosphere such as nitrogen is useful for decreasing the amount of oxidation that could take place on the surface of the GDL assembly Oxidation encloses the surfactants and restricts their release to the atmosp here. As the data indicates, the inert atmosphere increased the sintering loss slightly; however, it did not provide the required burnout level.
51 An industry partner, Johnson Matthey Fuel Cells (JMFC), had produced GDLs by sintering using a convection furna ce at a flow rate of 5 L/min The air convection promotes surfactant removal by sweeping the air across the surface of the GDL assembly removing additional surfactants, and exhausting t hem through the outlet. The furnace in Figure 3 12 was setup for air convection sintering. An air compressor was fed through a flow regulator and fitted with a quick conne ct port to link to the furnace The regulator allowed trials to b e run from 0 to 50 L/min. Results of these experim ents are provided in Table 6 4 The last extraction method investigated was sintering layer by layer. This means tha t the GDL is painted with a single coat of ink and sintered ; the process is repeated for all eight coats. GDL samples with one and two ink coats were available to test whether this method could provide increased surfactant extraction. These two samples wer e sintered using the liter ature procedure and weighed ( Table 6 5 ) It was found that this method does produce increased burn out. A full eight coat trial will be cond ucted in future work Membrane Hole SWLI Measurements A top view oblique plot of the membran e hole is provided in Figure 6 4 A total of four hole s were i dentified ( Table 6 6 ) The average diameter was 26.6 m This diameter w as well out of the prescribed range of 5 8 m. A nanosecond laser was used to drill the holes into the membrane which had a conical pattern to its light. Therefore, the reverse side of the membrane was also measured. As seen in Figure 6 5 it was found that the back side hole diameter was smaller, as expected, and was within the required range. The red areas that encircle the hole are laser ablation residue on the memb rane surface. Four more holes were a lso characterized ( Table 6 7 )
52 Table 6 1 GDL assembly thickness data. GDL Ink Coats Ink Mass Load (g) Mean Thickness (m) Std. Deviation (m) 1 1 0.6 0 228.6 12.9 2 1 0.63 225.1 12 .0 3 2 1.31 218 .0 12.1 4 2 1.22 224.5 11.4 5 3 2 .00 223.3 13.2 6 3 1.87 225.1 12.2 7 4 2.39 256.2 13.8 8 4 2.45 258.9 14.3 9 5 3.23 261.5 13.5 10 5 3.14 279.2 13.5 11 6 3.91 282.7 13.2 12 6 3.81 297.7 13.1 13 8 5.26 311.5 14.9 14 8 5.14 325.6 14.3 15 7 4.68 301 .0 13.7 16 7 4.72 319.9 13.6 17 8 4.78 286.5 14.8 18 8 4.34 276.9 13.8 19 8 5.38 301.7 14.1 20 8 2.89 245.4 12.7 21 8 4.36 279.7 12 .0 22 8 4.37 277.9 12.1 Av g 13.2 Table 6 2 Results of sintering using UNF's original procedure Sample Procedure Atmosphere Sintering Loss (%) 1 Original Air Only 7.84 2 Nitrogen Only 8.78 3 Air Only 8.44 Table 6 3 Sintering results using the "literature" process. Sample Procedure Atmosphere Sintering Loss (%) 1 Literature Air Only 8.58 2 Air Only 8.78 3 Nitrogen Only 8.89 4 Nitrogen Only 8.70
53 Table 6 4 Air convection sintering data. Sample Procedure Atmosphere Sintering Loss (%) 1 Literature Air at 20 LPM 8.17 2 Air at 15 LPM 8.69 3 Air at 15 LPM 8.59 Table 6 5 Sintering results from GDLs sintered layer by layer Sample Procedure Atmosphere Sintering Loss (%) 1 Literature Nitrogen 10.57 2 10.97 Table 6 6 Membrane hole diameters from the top view. Hole Orientation Hole Diameter (m) 1 Top View 27.3 2 26.2 3 24 4 29 Table 6 7 Membrane hole diameters from the bottom view. Hole Orientation Hole Diameter (m) 1 Bottom View 5.5 2 5 3 7.2 4 4.8
54 Figure 6 1 GDL assembly surface map sample of GDL 11 Mean thickness of 282.7 m and standard deviation of 13.2 m. Chart courtesy of Mark Pope. Figure 6 2 GDL assembly surface map sample of GDL 13. Mean thickness of 311.5 m and standard deviation of 14.9 m. Chart courtesy of Mark Pope.
55 Figure 6 3 GDL assembly thick ness versus number of ink layers Chart courtesy of Mark Pope. Figure 6 4 Top view o blique plot of a membrane hole. The measurement area is 175 m x 130 m. Chart courtesy of Mark Pope. 200 220 240 260 280 300 320 340 0 2 4 6 8 Barrier Thickness, m # of ink coats Left Side Pieces Right Side Pieces 24 m Laser redeposit
56 Figure 6 5 Bottom view of a laser cut membrane hole. The measurement area is 175 m x 130 m. Chart courtesy of Mark Pope. 5 m Laser redeposit
57 CHAPTER 7 CONCLUSION S AND FUTURE WORK M easurements were performed on two components of a new direct methanol fuel cell (DMFC). The first component was the gas distribution layer (GDL). A measurement apparatus was constructed to determine GDL assembly thickness and v ariation and, therefore, enable the quality and repeatability of the ink application to the surface of the GDL to be assessed It was found that the ink application is evenly applied to a standard deviation of 13.2 m over the surface of the GDLs. The vari ation between two halves of the carbon fiber substrate roll was concluded to be a lack of quality control in the vendor and could be overcome by simply adding more ink to the thinner side. Alternate deposition methods, which include spraying and rod coatin g, should be investigated for two reasons. The first is to decrease the standard deviation of the thickness, thereby increasing the likelihood that the GDL assembly will pass the diffusion and capillary performance tests. The second is a cost benefit issue The labor cost of the ink painting process is extremely high. GDL assembly batches are currently manufactured in lots of eleven pieces. From these eleven pieces, four laptop sized batteries can be constructed if each piece passes the performance tests. T he formulation of the ink and deposition onto the carbon fiber paper takes, at minimum, 7 hours for one worker to complete. Design scale up is therefore a concern because the painting procedure is ineffective for high volume production. Initial investigati ons into rod coating have been conducted by the industry partner, Johnson Matthey. However, the thickness variation has not yet been tested Degradation of the fuel cell due to poisoning by surfactants is another concern. It is believed that optimizing the GDL assembly sintering profile and atmosphere could be
58 used to increase the cell life. I n this study, i t was found that using a sintering pro file which incorporated an intermediate burnout step produced a 0.8% greater average surfactant removal. The addition of a nitrogen inert atmosphere produced only marginally higher sintering losses. This likely occurred due to the tradeoff between oxidation reduction by the inert atmosphere and reduced surfactant burnout due to reduced oxygen content S everal sources indicated that sintering layer by layer could increase the sintering loss. A one, two, and four coat GDL assembly was sintered to determine the validity of this information. The one and two layer trials were promising where 1.8% more surfactant w as removed than the previous best results. An eight coat GDL assembly will be produced in the future, sintered layer by layer and inserted into a test bed for cell degradation tests. The se cond component of the DMFC that was investigated was the cathode membrane. Specifically the characteristics of laser drilled holes were evaluated The average hole diameter on one side of the membrane was 5.6 m. This was within the prescribed range of 5 7 m ; however, redeposited material (from the laser ablation process) was present on the surface which could break away under the capillary test pressure of 620.5 kPa ( 90 psi ).
59 APPENDIX A LABVIEW PROGRAM S Figure A 1 LabVIEW block diagram of motor controller Graphic courtesy of Mark Pope.
60 Figure A 2. Schematic of a LabView VI that gathers stage position data. Graphic courtesy of Mark Pope.
61 APPENDIX B MATLAB PROGRAM % plot surface profile for carbon fiber paper (CFP) and its measure thickness % Mark Pope % 09/24/2010 % Unsintered Barrier_7 clc; clear all; close all; %% Import Labview Data % %CFP thickness for cnt = 1:84 filename = sprintf('CFP_%d.txt',cnt); V_CFP = textread(filename,'%f'); T_CFP = V_CFP*62.5; % Thickness (um) (62.5 um/V: calibration factor) N = 1; % Divider T1_CFP = T_CFP(1:N:length(T_CFP)); T_CFP_mat(cnt,:) = T1_CFP; % Change CFP thickness vectors into a matrix end %Total Bearing Surface before machining for cnt = 1:84 filename = sprintf('R EF_%d.txt',cnt); V_REF = textread(filename,'%f'); T_REF = V_REF*62.5; % Thickness (um) (62.5 um/V: calibration factor) T1_REF = T_REF(1:N:length(T_REF)); T_REF_mat(cnt,:) = T1_REF; % Change Ref. surface vectors into a matrix end %% Generate plot vectors and graphs a1 = 0.5; % Acceleration of stage t1 = (linspac e(0,20,20000))'; % Time to accelerate to full speed x1 = 1/2*a1*t1.^2; % Position of stage up to full spee d x_data = [x1; (linspace(100,224,17000))']; % Generate x direction vector y_data = (0:1.5:124.5)'; % Generate y direction vector [X,Y] = meshgrid(x_data,y_data); % Form a mesh of the x and y vectors Z_CFP_1 = T_CFP_mat(1:41,:); Z_CFP_2 = T_CFP_mat(42:84,:) 10; Z_CFP = [Z_CFP_1;Z_CFP_2]; Z_REF = T_REF_mat + 8.5; Z = Z_CFP Z_REF; % Pure CFP surface map by subtracting REF surface Z1 = [Z(7,500:3500) Z(8,500:3500) Z(9,500:3500) Z(10,500:3500 ) Z(11,500:3500) Z(12,500:3500) ... Z(13,500:3500) Z(14,500:3500) Z(15,500:3500) Z(16,500:3500) Z(17,500:3500) Z(18,500:3500) ... Z(19,500:3500) Z(20,500:3500) Z(21,500:3500) Z(22,500:3500) Z(23,500:3500) Z(24,500:3500) ... Z(25,500:3500) Z(26 ,500:3500) Z(27,500:3500) Z(28,500:3500) Z(29,500:3500) Z(30,500:3500) ... Z(31,500:3500) Z(32,500:3500) Z(33,500:3500) Z(34,500:3500) Z(35,500:3500) Z(36,500:3500) ... Z(37,500:3500) Z(38,500:3500) Z(39,500:3500) Z(40,500:3500) Z(41,500:3500) Z(42 ,500:3500) ... Z(43,500:3500) Z(44,500:3500) Z(45,500:3500) Z(46,500:3500) Z(47,500:3500) Z(48,500:3500) ... Z(49,500:3500) Z(50,500:3500) Z(51,500:3500) Z(52,500:3500) Z(53,500:3500) Z(54,500:3500) ...
62 Z(55,500:3500) Z(56,500:3500) Z(57,500:35 00) Z(58,500:3500) Z(59,500:3500) Z(60,500:3500) ... Z(61,500:3500) Z(62,500:3500) Z(63,500:3500) Z(64,500:3500) Z(65,500:3500) Z(66,500:3500) ... Z(67,500:3500) Z(68,500:3500) Z(69,500:3500) Z(70,500:3500) Z(71,500:3500) Z(72,500:3500) ... Z(7 3,500:3500)]'; m = mean(Z1) s = std(Z1) minimum = min(Z1) maximum = max(Z1) index_min = find(Z1 == min(Z1)) Z1(index_min,1) index_max = find(Z1 == max(Z1)) Z1(index_max,1) figure(1) mesh(X,Y,Z) colorbar set(gca,'Fontsize', 14) xlabel('x (mm)') ylabel('y (mm)') zlabel('Thickness ( \ mum)') grid on
63 LIST OF REFERENCES [1] I. Horuz J. Fletcher, C.C. Kuo, S. Credle, W. Lear, Comparison of Direct Methanol Fuel Cells Against Conventional Batteries, International Energy Conversi on Engineering Conference 2008, Cleveland, Ohio AIAA 2008 [ 2 ] S.K. Kamarudin, F. Achmad W.R.W. Daud, Overview on the Application of Direct Methanol Fuel Cell (DMFC) for Portable Electronic Devices International Journal of Hydrogen Energy 34 (2009) 6902 6916 [ 3 ] Y.H. Chan T.S. Zhao R. Chen, C. Xu, A Small Mono Polar Direct Methanol Fuel Cell Stack With Passive Ooperation Journal of Power Sources 178 (2008) 118 124 [ 4 ] S.K. Kamarudin W.R.W. Daud, S.L. Ho, U.A. Hasran Overview on the Challenges and Developments of Micro Direct Methanol Fuel Cells (DMFC), Journal of Power Sources 163 (2007) 743 754 [ 5 ] C.Y. Chen P. Yang, Performance of an Air Breathing Direct Methanol Fuel Cell, Journal of Power Sources 123 (2003) 37 42. [ 6 ] V. Mutalik, et.al., Thermodynamics/Hydrodynamics of Aqueous Polymer Solutions and Dynamic Mechanical Characterization of Solid Films of Chitosan, Sodium Alginate, Guar Gum, Hydroxy Ethyl Cellulose and Hydroxypropyl Methycellulose at Different Temperatures, Carbohydrate Polym ers 65 (2006) 9 21. [ 7 ] DuPont Teflon PTFE TE 3893 http://www2.dupont.com/Teflon_Industrial/en_US/products/product_by_name/tefl on_ptfe/aqu eous.html acces sed at University of Florida, 21 Apr 2010. [ 8 ] http://www.lionpreci sion.com/tech library/technotes/cap 0020 sensor theory.html#env accessed at University of Florida, 10 July 2011.
64 BIOGRAPHICAL SKETCH Mark Pope was born in Port Charlotte, FL to Larry and Sarah Pope He was raised in Port Charlotte and was awarded his Associate of Arts degree from Edison College. He is married to his wife, Darcy with whom he has two children; their son, David and daughter, Chloe. He earned his Bachelor of Science degree s in m echanical and aerospace e ngineering at the University of Florida in May 2010 In June 2010 he joined the Machine Tool Research Center (MTRC) under the guidance of Dr. Tony Schmitz and receive d his Master of Science degree in December 2011


text:
Can Sarcoidosis Cause Neurological Problems?
As a person with Sarcoidosis for many years it is so frustrating dealing with Physicians who are lacking in their knowledge of the condition. I had a spinal fluid test and no Sarcoidosis was found. However, I am suffering from Seizures that are difficult to diagnosis and locate a cause. At the present time, my symptoms would identify that I have Partial Complex Seizures although the EEG is normal and I am being told it could be due to stress. Well, dealing with the Medical community is stressful in itself. My question is although the spinal fluid is negative for Sarcoidosis, is it still possible that the Sarcoidosis is causing Neurologic problems? I have had the condition for 31 years and seizure symptoms since 2004, but no one paid any attention until I experienced a blackout while driving in 2009. Since 2009 I have the additional symptom of blackouts that last 5-10 minutes.
Dear Sir/Madam- Sarcoidosis can involve the central nervous system (a.k.a., neurosarcoidosis), and is a known cause of seizures.
Most cases of neurosarcoidosis associated with seizures are associated with abnormalities discovered while imaging the brain.
MRI scanning is very sensitive for the detection of neurosarcoidosis. Lumbar puncture (spinal tap) is abnormal in about 2/3 of cases. However, lumbar puncture findings cannot confirm or exclude the diagnosis.
The only way to confirm the diagnosis is to perform a biopsy of the affected tissue (brain, spinal cord, or the lining of the brain). Because most patients and doctors are reluctant to biopsy the brain, the diagnosis of neurosarcoidosis is often presumptive (based upon circumstantial evidence).
For instance, a person presenting with unexplained neurological findings (abnormal MRI findings, unexplained seizures, etc.) in the setting of confirmed sarcoidosis outside of the brain would increase the doctor's suspicion of neurosarcoidosis.
For more information:
Go to the Sarcoidosis health topic.

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Below Mt. Sugarloaf, a farmer tends his crops. South Deerfield, Massachusetts' position along the Connecticut River meant that the periodic floods deposited some of the richest soil in the northeast onto lands adjacent to its banks. Behind the farmer, tall poles stand for the summer's snap bean crop as he tends to his strawberry beds. By the turn of the 20th century, reliable rail transportation meant that farmers were able to send crops to far-away markets that in previous years would have been entirely dependent on local produce. Behind him, the S&G Mill with its distinctive cupola stood ready to grind the fall's harvest.
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Mornings have been hard for me lately. I'm not exactly sure why. My life hasn't really changed much. The same things are difficult. The same things are good. If anything, some of the good things have gotten a bit more good. So why have I been waking up in a state of despondent gloom? And, more to the point, what can I do to make things a little bit lighter?
Mulling over these questions the last few days, it hit me that I'd failed to note perhaps the most salient clue: The fact that, however I feel, I am indeed getting up!
What is it, I wondered, that gets me moving on days I could easily burrow in? Could the answer be to figure that out—and then do more of it?
In that spirit, I asked myself: "Self? What gets you out of bed on those mornings when nothing seems worth the effort?"
The answer came immediately. "I get up for the coffee."
A year or so back, I received a fancy coffee maker as a gift, and it's this primo coffee—not just any coffee—that's been making all the difference. Sometimes I contemplate returning to my previous caffeine habits. The capsules for the new machine are pricey, and I'm trying to conserve. But for now, the expense is worth it. The coffee is something I look forward to, and that means a lot.
And right then, it hit me. I was onto something. This idea of "looking forward to"—what role did it have in my life? It occurred to me that perhaps I've grown looking-forward-to deprived.
The more I thought about it, the more sense it made. Life in Plan B Nation tends to be focused on getting things done, on keeping the nose to the proverbial grindstone, on being responsible, plugging ahead, and keeping emotions in check. It's easy to feel that we don't deserve special rewards and treats—not when we're so far behind where think we ought to be.
The problem with this approach: We. Get. Tired. The fact that success is in short supply doesn't mean we haven't been working, often way harder than we did when our careers were thriving.
Which got me to thinking about Buddhist teacher Cheri Huber's spot-on description of how exacting we tend to be with ourselves—and because it's so great and because I have the book right here, I might as well share it with you:
You go along in life and you do what you're supposed to do. And every time you do something you're supposed to do, you put a dollar in the bank. Okay. Every time you're kind, patient, or you do the thing you're supposed to do—whatever it is (you know what those things are for your)—every time you put a dollar in the bank, a dollar in the bank, a dollar in the bank . . . .
Finally, you feel like you're just kind of worn out. You feel like you need a little pleasure in your life, a little time on the beach or something. And so you think "I'm going to go to the bank, and I'm going to take out some money, and I'm going to do something nice for myself."
So you go to the bank and you say, "Here I am. I want to take out some of the money I've saved so that I can do something nice for myself."
And the response is, "Oh no. You haven't earned nearly enough to get anything for yourself. Oh, you have to work much harder—you have to put much, much more money in before you can get anything for yourself."
And, of course, if this were First National you were dealing with, you would say, "No, this is not the way this is going to work. This is my money. You can't tell me when and where and how I can spend it." And yet, with this system of self-hate that's exactly what's going on!
She concludes: "THERE'S NO MYSTERY IN THIS FOLKS! . . . [T]he person at the bank DOES NOT LIKE YOU! *It's important to get that*. . . . THIS PERSON IS NEVER GOING TO GIVE YOU A DIME! YOU WILL WORK YOURSELF TO DEATH, AND YOU'LL NEVER GET A THING FOR IT. IT IS REALLY IMPORTANT TO UNDERSTAND THAT!"
Here is what I am going to do: First, I am going to incline my mind (as the Buddhists say) towards things on the horizon to which I'm looking forward. The workshop for foster kids that I'm co-facilitating. Watching a TV show I refuse to name with my friend Wendy. Hotdogs and a movie at Popcorn Noir in Easthampton (not to be confused with East Hampton).
Next: I am going to give some thought to other things I might look forward to and how I can make them happen. Tango lessons? A day trip? The specifics are up for grabs. And while I don't know what I'll come up with, I look forward to finding out.
Note: The quoted passage is taken from Cheri Huber's There Is Nothing Wrong with You (Keep It Simple Books, 1993). It also has pictures that will make you smile.


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Wetpixel D800 review
Posted 14 July 2012 - 10:14 PM
The image quality of that crop is god awful, but I know that wasn't a high priority with these particular shots. I'd blame your lens combo more than the camera for such poor detail - the camera is better than that at ISO 1600.
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 15 July 2012 - 01:01 AM
Tim's crab image won the British Underwater Photography Championship at Plymouth, UK yesterday.
He had gone to bed (or was posting on this forum) when the results were announced
Congratulations Tim!
A full report on the event will follow later today.
Posted 15 July 2012 - 03:32 AM
However. I discovered that it doesn't matter which camera you have. What matters is the photo opportunities presented. A young man with a Canon 5D got two better pictures than me because he got the close encounters I would have loved to have been given. Meanwhile...with my 15mm Sigma:
I used the Sea & Sea (Athena) optical dome port. It vignettes slightly but I usually find it can be cloned in or cropped out.
Edited by John Bantin, 15 July 2012 - 10:18 PM.
I buy my own photographic kit. Diving equipment manufacturers and diving services suppliers get even-handed treatment from me whether they choose to advertise in the publications I write for or not. All the equipment I get on loan is returned as soon as it is finished with. Did you know you can now get Diver Mag as an iPad/Android app?
Posted 15 July 2012 - 10:44 AM
The image quality of that crop is god awful...
Oh. I shouldn't be such a fool, then.
Flickr galleries
Photobox; images on sale!
The Fin Foundation
Nikon D800 in Nauticam housing...
Posted 20 July 2012 - 07:58 AM
Hi Erol,
I think that those of us using the D800 are still adjusting to just how good it (potentially) is
I have used Alex's 16-35mm and it is very clean I does need a big (9"+) dome and a long extension though.
Hey Adam - this string is exceptional and I love your reviews. One thing I haven't been able to find much info on is the comparison between the D700 and the D800 for UW photography. Do you have any thoughts or experience with this? Clearly you get the video bonus with the D800 but I'm wondering what impact the 3x MPs have underwater...is that a good thing, or do you get fewer quality images because of motion blur? Most photogs I know using the D800 on land use tripods almost all of the time to minimize the blur.
Thanks much,
Posted 20 July 2012 - 07:10 PM
Edited by loftus, 20 July 2012 - 07:26 PM.
Posted 20 July 2012 - 11:20 PM
The D800 will always take great pictures. It is a lovely camera to use - a very good camera for getting the shot - with great ergonomics and excellent AF.
But you need to get everything right to make the most of the full 36MP. And I found, underwater, in the clear Red Sea, shooting with flash, it was actually easy to get everything right. Good technique and be mindful of the rules of shooting Nikon FX.
Importantly, there is no real need to worry if you don't, you still get a great picture, but maybe you end up with a useable resolution of <20MP. We'll that's hardly the end of the world (it is probably still more than your old camera!). It is still a completely useable file for just about any need.
I think Tim's crop of the crab is a perfect example of this phenomenon, which he posted above and with a crop. Shot without strobes it is pretty lousy at a pixel level.
But seen as a whole image it is great. The D800 has so many pixels, that even if circumstances that prohibit you getting a technically perfect shot at 36MP, it should still look great when downsized.
So all you really loose is some of the crop-ability of those very big files.
p.s. I note that it has been over a month now since I came back from the Red Sea - where Adam kindly lent me his D800 and Nauticam housing. I must share some results and further thoughts.
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 12:47 AM
(I want to thank Pascal of Hugyfot for getting a housing for the D800 to me in time for the trip.)
Edited by John Bantin, 21 July 2012 - 12:51 AM.
I buy my own photographic kit. Diving equipment manufacturers and diving services suppliers get even-handed treatment from me whether they choose to advertise in the publications I write for or not. All the equipment I get on loan is returned as soon as it is finished with. Did you know you can now get Diver Mag as an iPad/Android app?
Posted 21 July 2012 - 02:40 AM
It was a workshop trip, so my own photography was pretty low on the agenda, so I wasn't able to do more than shoot it out there. Then, I went directly from the Red Sea to Scotland (via Adam's to return the camera) on another shoot and so I've not really had a moment to look through the D800 shots (in fact there are so dives I've not looked at all) and certainly no time to write a formal review. Feeling guilty, I've quickly batch processed some shots, that I hope make some important points about this amazing camera (don't judge the camera's ultimate quality from the images I have chosen, they are here mainly to make specific points).
Yes, the D800 is AMAZING. It forces you to recalibrate possibilities and probably the best way to shoot. If you can get the best out of the D800, I am in no doubt that it moves the game on considerably. That said, it comes with the problems/challenges/compromises of shooting FX underwater.
I only had a week shooting it underwater, but we had such great diving, that I was able to shoot so many subjects - I feel I've given it a good workout. So I'll share some thoughts below, which I am sure will form the core of my contribution to the Wetpixel review, when I have time to write it up (I guess this will be a very rough, first draft)! But with the Wetpixel Whaleshark trip looming at the end of the week, I am not sure when that will be.
King Of The Dive Deck?
Central to the D800 experience is that amazing 36MP sensor, which as is well documented isn't just thrashing other SLRs in tests, but also some medium format systems. There is no better question to be asked as a D800 owner than "How many megapixels has that got then, mister?" As John Bantin has already jokingly remarked he only got one for dive deck credibility!
And my experiences are that it is well deserved credibility. The camera delivers stunning resolution, excellent dynamic range and resolution on a whole new level. It has 100% viewfinder, 1/320th flash synch and a pop-up flash, ideal for running TTL strobes via fibres. It is also small(er than D-series Nikons and 1D series Canons) and competitively priced.
It also delivers where it matters from macro:
To wide angle:
And here is a fun video of me shooting the camera in the Red Sea:
More to follow...
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 03:04 AM
As many have discussed in this thread, 36MP brings many advantages and a few disadvantages. I think that they also bring more stress than they need to. Read the posts of Jeff (Loftus), Me and John before these ones - and you will see that all our experiences is that while it requires precise technique to realise the full potential of the 36MP, if you don't, the files doesn't go in the bin, it is still useable when down sampled a bit to a mere 18MP, say!
That said, I would like to suggest that the D800 is easier to shoot underwater (in terms of realising that full 36MP resolution) than it is on land. But underwater I mean in clear water and with subject matter that can be easily and fully illuminated by strobes. And the reason is those strobes. Underwater we mainly shoot with strobes and this near instant artificial light - gives us sharp, still detail for the D800 to record.
Perhaps what surprised me most about the D800 in the Red Sea is that almost every shot I took had incredibly sharp detail when zoomed in to 100%.
I don't believe there are many outputs that really require 36MP, so the main advantage of getting great detail at 36MP is the ability to crop. Which means even poorly composed or posed shots can be highly useful.
This was originally a poorly framed image of a grouper. So I cropped it. It is now only 25MP!
File Sizes
That said 36MP don't come cheap for hard drive space. I shot 3346 photos in a week in the Red Sea. OK we had a particularly amazing week in terms of plentiful subject matter and I was taking extra pictures for test shots (see below). And the files are big.
Earlier in the thread I posted that
my largest file is 48.7MB. Most of the wide angles are 44MB - as I am shooting schools of fish with sunbursts etc - so lots of detail throughout the picture. The smallest file is 39MB. Macro with black background.
Assuming an average file size of 44MB, I shot close to 150 GB in a week (I can't give the exact figure because I was deleting as I shot)!
The D800 creates a lot of data and a needs a fairly neatly laptop to throw the files around in the field. The payback is the detail. This yawning snapper is cropped out of a wide angle shot.
He's so small in the original you have to look twice to spot him:
Frame Rate
Another consequence of so much resolution is that the D800 has a slow-ish frame rate. A lot of mileage has been made of this. Probably because it is one of the few areas that the D4 and 5DMk3 can better the D800 on paper. I really did not find the frame rate a limitation for mainstream photography. This is a sequence of the Goose taking to the air (which I took with his D800). How many more frames per second do you really need?
More to follow...
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 03:23 AM
These are outstanding. Shows two things, a great photographer can probably take great photographs with any camera, and a great photographer can really show how awesome this camera really is.
What lens / dome setup did you shoot the over under with; can you tell us a bit about exposure etc?
Edited by loftus, 21 July 2012 - 03:23 AM.
Posted 21 July 2012 - 03:35 AM
This is a fire coral detail, no strobe, backlit by the sun:
And here is a 100% crop, which shows good pixel level detail:
To achieve its resolution the D800 has smaller pixels than other full frame cameras, yet tests on land show excellent noise performance. However one of the first things everyone said about the D800 files when they saw them on board is - "they are a bit noisy".
This is because we're used to judging noise in files by looking at them at 100% and quantifying the amount of speckles! But the 36MP has so much more resolution than other cameras that it does not make sense to look for noise at the pixel level - because most printing won't be using this pixel detail and the noise will disappear when the image is downsized (either by you or by the printer when it tries to put it on the paper).
I felt that the D800 showed a similar level of pixel noise underwater to the D7000 and therefore looks much worse than a D3 or D700. But this is not the fair test - because when down sampled to the resolution of the D3 or D700 it is actually better. I hope that makes sense.
One consequence of this as a D800 shooter is that by downsizing to hide noise you loose the crop-ability of the 36MP. But the plus is that you have the choice in post, which to sacrifice. And of course, you can do a bit of both. But you can't have low noise at high ISO and a full 36MP of goodness for crop-ability.
Detail and Noise
Here is an available light/Magic filter shot of the Giannis D wreck (Note that this is one of the few pictures here that I have done a bit of post on - although I have not applied noise reduction):
Here are some crops - I am very impressed with the detail for an available light shot - where there is no strobe to help ensure the pixel level sharpness:
But there is also plenty of noise in shadow areas:
These are at ISO 320.
More to follow...
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 03:46 AM
Here is what I mean: First a D800 100% crop in Aperture - look at the little window to the right that shows the proportion of the crop to the whole image, then the D700, see how much bigger the 100% crop is.
Edited by loftus, 21 July 2012 - 03:59 AM.
Posted 21 July 2012 - 03:57 AM
A feature of the new Nikon files (both D800 and D4) than has attracted a lot of excitement is the amount of detail that can be lifted from shadows in post production. This is indeed very impressive, however I think enthusiasm needs to be constrained slightly for underwater pictures.
I know Adam and Keri have both posted very impressive examples of shadow lifting in underwater images - but both of their examples are available light shots. I am sure most people get this point - but someone asked me about this by email - so I think it is worth clarifying. I know Adam agrees on this.
Yes, you can open up shadows extensively on the D800. But in an underwater photo, if you didn't light the shadows with your strobe (hence why it is a shadow) then when you open it up you will get detail, but not much colour. In other words, this feature is great for available light shots, but doesn't mean you should go around under exposing everything with the D800!
The second problem I have found with the technique is that with an underwater picture if you colour correct and open up shadows on the same file it gets very noisy, very quickly.
This is an unprocessed shot of a dark, high dynamic range scene, inside the same wreck as above:
This is the same scene, different file, with the shadows opened up extensively and some colour correction:
Viewed at 100% it is pretty ugly (ISO 320):
For this reason I still think there is a need for shooting HDR for these scenes. This is a post processed HDR (just a quick one with JPGs), but produces a much cleaner result (I don't have a 100% crop of this):
OK, final bit on pixel peeping. Resolution and Diffraction.
I have never felt that diffraction has been significant in underwater pictures before, but I do with the D800. AFAI understand, the D7000 and 7D should show more as they have more densely packed pixels, but I see it in the D800 files, but not in the other cameras. I am not sure why.
Here is an example shooting a macro coral detail. This type of shot needs the lens stopped down so that everything is sharp. Even at this low resolution, f/13 is too open and you can see the top of the frame is out of focus - f/25 looks great - plenty of depth of field:
However, stopping the lens down does loose us detail due to diffraction (note this is a real world test, not controlled conditions) - at 100% I definitely see a fall off of detail above f/16-f/20, f/29 and f/45 definitely soft:
These were shot with 105mm. No dioptres.
So for macro you do have to be very careful on stopping down if you want to achieve ultimate resolution. Going above f/22 is clearly softening the detail at 36MP.
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 04:01 AM
When shooting the backlit fire coral (backlit by the sun) I decided I wanted a black background. But there wasn't one I could frame against. So I took off my fin and held that behind the coral! However my arms weren't long enough to back away and get the composition I used before - so in the end it didn't work. It must have looked funny, though.
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 04:09 AM
It will be interesting to compare diffraction quality drop off looking at equivalent magnification as I just mentioned above. 100% with 12 or 16MP is not enlarged as much as 100% with 36MP
Edited by loftus, 21 July 2012 - 04:10 AM.
Posted 21 July 2012 - 04:22 AM
Or the white ball of death, as they are know to some photographers. The D800 is the best digital camera I have used for shooting sunbursts. But in all honesty I found it only a small improvement over the D7000. In fact on some of the dives, photographers on the workshop shooting with D7000s, as it happens, were definitely getting equal or better sunbursts than I was with the D800.
I think in controlled conditions the D800 would always win. But the sea isn't controlled conditions and my point is that I don't think the D800 is revolution in this regard. I think conditions (and more importantly photographers making the most of them) still play the dominant role in capturing a great digital sunburst and this is a much bigger differentiator than the difference between the modern Nikons.
Here is a lovely sun taken with the D800:
And with a green turtle:
And here are some when you (me) don't get it right. Not particularly ugly, just detracting from the picture, rather than enhancing (and if it not enhancing, then why is it in the frame?):
And other poorly put together shot results in an ugly sun - showing you (I) still need discipline to get a good sunburst with the D800:
More to follow - I want to talk about the NA-D800 and domes and wide angle with D800/FX
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 05:02 AM
Ok back to it.
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).
Posted 21 July 2012 - 06:48 AM
Posted 21 July 2012 - 07:08 AM
I've not seen any other brand of housings yet for the D800 in the flesh. But I see from Wetpixel and other places that Ikelite, Nexus, Seacam, Aquatica, Isotta, Sea & Sea and Hugyfot housings are out there now, and I hear the Subal is due this coming week or the one after. But a month ago the Nauticam was the only option open to me.
And I have to say I was very, very impressed. Ergonomically this is one the best housings I have ever used for any camera - we'll have to wait to try more of its direct competitors to see how it stacks up against the latest offerings from the manufacturer's listed above.
Nauticam have put so much effort into the design and it really shows underwater. The primary controls of shutter, shutter speed and aperture (these front and rear command dials are also used for scrolling through). The aperture (above) and shutter speed controls (below) fall right under your fingers/thumb and the design of the dials mean that they can be easily adjusted with a single finger and without taking your eye from the viewfinder. Few housings get them as right as this.
The ease of access to these controls makes all the difference when shooting, allowing fast changes to be made to the settings so that no opportunities are missed. I inadvertently took a perfect example to show this, which I only discovered when talking about the settings I was using during the workshop.
Below are three consecutive photos of schooling snappers that I took as I drifted under the school in the current. As an almost automatic/instinctive reaction I shut down my aperture as I drifted closer and closer to the school to compensate for the shorter strobe to subject distance and also the more upward camera angle that I was now using, thus getting in more of the bright surface. I certainly didn't think about this before hand, it was just a trained response, I suppose. Just 5 seconds elapsed between the first shot and the third.
But the important point is that the design of the Nauticam housing allowed me to do this without having to stop or take my eye from the viewfinder. To achieve this, a housing needs shutter speed and aperture dials that can be rotated easily with a single finger (not ones that need a thumb and finger - which mean taking your hand off the shutter release). For me this is the mark of a very well designed housing.
The feature that impressed me most on the NA-D800, though, is the new multi-selector - used for positioning the focus point in the frame and for navigating menus etc. This feature is incredibly intuitive and easy to use, indeed it is just a scaled up version of the one on the back of the camera and can be easily reached from the handle.
This is rte ally great for macro and the ease of use of this feature on the NA-D800 meant I found myself encouraged to move the focus point around the frame, much more than I would always be bothered to before. Giving me exactly the composition I wanted, with the focus precisely where it needed to be. Here I moved the focus point to be exactly on the left-side (as we look) rhinophore.
As with the NA-D4 I reviewed, I also really like the ears - the pair of paddles on the top corners of the back of the housing, where important controls are placed and are easily reached with your thumbs.
Perhaps the one change I would make is not to have the ISO here on the D800, as I certainly didn't feel as inclined to want to change ISO as freely on the D800 as I do on the D4. Although that may just be me needing to get used to the fact that although the D800 clearly shows noise as ISO is increased, it is not significant when you think of print sizes rather than viewing the file at 100%. Anyway I would prefer to see the INFO on one of these levers. The INFO button is hard to locate on the back of the DN-D800 without looking, and it is easy to press the live view button instead. The INFO button is important on Nauticams because they typically do not have a screen for the top LCD panel, and you cannot over turn the on/off switch to bring up INFO that way.
However, when discussing this with Adam, he pointed out that as a video shooting you are much more likely to change ISO all the time (often as your main exposure control, to avoid changing depth of field or loosing that all important rolling shutter look) and therefore Nauticam choosing to prioritise the ISO control does make a lot of sense.
I am wracking my brains for some negatives on this really well designed housing. Drew's post earlier in this thread pointed out some minor rusting issues, although Adam's housing, although scuffed, showed no signs of this. And I guess, much as a praise the ergonomic quality of the Nauticam, they do have a complex engineering style (compare the insides with the Seacam D800, Steve Frink has posted pictures of), and this does make me a little nervous for reliability. That said Nauticam dealers have a very strong reputation for immediately fixing any problems that come up. And not that I had any problems at all on my trip.
Complex doesn't equal less reliable and running workshops I have seen every single housing brand there is go wrong or break in one way or another.
The housing performed faultless for me. For a week! Of course most users plan a rather longer ownership. And it was in fact that D800 that was a little buggy. I did have a recurring problem with the camera. From time to time, after taking a picture, it would take 20-30 seconds for the D800 to show the picture on the LCD screen. It would occur when taking the first picture after the camera had been in active for a while. It could be a bit annoying when you wanted to check exposures/lighting on the first shot in a sequence. But was not of serious consequence. One other D800 owner on board said his camera did this too. Maybe the latest firmware fixes this problem.
OK, I'll do the dome bit now...
Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D5 (Subal housing). Nikon D850 (Subal housing). Olympus EM10-Mk3 (Nauticam housing).