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A Microcomputer-Controlled Apparatus for Measuring Thermal Absorption or Desorption of Hydrogen from Milligram Samples*

An apparatus for monitoring the thermal desorption of gas from small samples is described. The material is heated by a nichrome resistance furnace controlled by a BBC microcomputer. Heating rates of 1 to 60 K/min can be achieved between 20°C and 1000°C, with an accuracy of 0.5 K. Hydrogen release is detected as a pressure change in a 3 cm sample space. A piezoresistive pressure transducer linked to the internal ADC allows fully automatic data acquisition by the computer. Resolution of 0.5 mbar over the range from vacuum to 2 bar is obtained, giving a detection limit of 10~7 mol of H2. Sample masses of 1 to 100 mg can be used. The working space may be evacuated to avoid oxidation problems at high temperatures, or filled with other gasses, such as hydrogen, to allow absorption to be investigated. Use of the system to monitor hydrogen desorption from electrolytically loaded amorphous ribbons and to determine their hydrogen content are described. The conditions required for H2 absorption by some crystalline alloys, including Nd2Fe14B, are also presented.