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COMPOSITE MATERIALS WITH CERAMIC AND METALLIC PARTICLES REINFORCED CLAY MATRIX

The paper includes a research on the obtaining characteristics and mechanical properties of the composites with Al2O3, SiC, Cu, Al and Fe particles reinforced clay and bentonite ceramic matrix. Were obtained four types of composite materials namely: Al2O3 and SiC particles reinforced clay matrix, Al2O3 and SiC particles reinforced bentonite matrix, Al2O3, SiC, Cu, Al and Fe particles reinforced clay matrix and Al2O3, SiC, Cu, Al and Fe particles reinforced bentonite matrix. The composites prepared were subjected to a study to analyze the mechanical properties (compressive resistance).


Introduction
The composite material is composed of a basic material, the matrix, in which the additional material is dispersed in the form of particles or fibers [11,8,2,7].
Particulate ceramic matrix composites have been developed to achieve damage tolerant fracture behaviour while maintaining other advantages of monolithic ceramics. It is established that particulate ceramic matrix composites are among those promising materials for high performance applications under severe environment such as high temperature. Particles reinforced ceramic composites are used as functional components in brake assembly, furnace materials, energy conversion systems, gas turbines, heat engines etc. [13].
Clay is a natural inorganic binder consisting of oxides, hydroxides, carbonates, feldspars, mica etc. impure kaolin. Depending on the amount of water absorbed, the clay swells, acquires bonding properties. Bentonites are a variety of clays with a high montmorillonite content (over 70%). Due to the high water adsorption and ion exchange capacities, bentonite can be used in many different technological applications, e.g. catalysts in chemical and oil processing industries, admixtures for plastification and manipulation of viscosity of ceramic pastes or sealing materials for civil and environmental engineering [6].
Delage et al. [5] studied the obtaining of bentonite matrix composites by conventional methods, and drying techniques induce significant capillary forces which may lead to drying shrinkage artifacts. Chenu and Tessier [4] and Smart et al. [12], studied the obtaining these types of composites by cryo-preparation techniques freezing under liquid nitrogen or propane atmosphere for samples with a maximum thickness of 5 µm.
The paper focuses on the synthesis and characterisation of a promising ceramic and metallic particles reinforced ceramic matrix composite.
Firstly, were made composites with ceramic matrix and reinforcement components (Table 1). Then, to the same amounts were added Cu (Table 2), Al (Table 3) and Fe (Table 4) metallic particle to obtain the other types of composite.
For achieving the composites, the quantitative dosed materials were introduced in a container according to Tables 1-4, where for homogenization they were mixed in a dry state. After 5 minutes of mixing, the material thus prepared was introduced into a metallic mold where it was pressed to the test machine. The mold was sprayed with a mold release agent to prevent adhesion of composites and also to ensure smooth sample surface. The samples thus obtained were sintered in a Nabertherm furnace according to the temperatures in the Tables 1, 2, 3 and 4 . After sintering, the obtained samples were subjected to a study to specify the compressive strength. Compressive strength was performed on the universal testing machine. The test are cylindrical (diameters: 15-16 mm and heights 11-15 mm). From the machine test chart, were extracted the specific values which were used to interpret the results. A minimum of 3 tests were performed for each type of composite sample. Then, the mean for the values obtained from the determinations are calculated (Tables 5-8, the diagrams of Figures 1-4).

Results and Discussion
The values arithmetic mean for the measurements extracted from the compressive test charts are shown in Tables 5-8. For a better interpretation of experimental results, for each type of composites made, compressive strength dependence graphs were constructed depending on the proportions modification of the used components (Figures 1-4). In the following figures are represented the compressive strength variation depending on the granular material content.  (Figures 1 and 2). This type of variation can be explained in correlation with the obtaining composites of mixed, pressed and dry particles. Also taking into account the fact that both the SiC and the Al 2 O 3 are introduced as impurities in the matrix, without to achieve to sintering the monolithic structure of the composite.

Compressive test results for SiC, Al 2 O 3 and Cu particles reinforced powders matrix
The behavior changes radically by adding the metallic particles to the composite. In this time, compressive strengths increase with the increasing of SiC and Al 2 O 3 particles (Figures 1, 2, 3 and 4). Influences are specific to each type of composite.
For SiC particles reinforced clay matrix composites the Cu, Fe and Al admixture cause, in this order, increases of compressive strengths. In the case of Al 2 O 3 particles reinforced clay matrix is found the same type of arrangement. At the same time, the admixture of metallic particles has different effects for the same type of composite materials. In the Cu admixture case is obtained a compressive strengths higher for SiC particle reinforced matrix composite than Al 2 O 3 particle reinforced matrix composite. In the case of Al and Fe is obtained a compressive strengths higher for Al 2 O 3 particle reinforced matrix composite.
The SiC, Al 2 O 3 and Cu particles reinforced bentonite matrix composite have not been tested to resistance because the Cu has created slagging reactions to sintering. For these composites with Al and Fe admixture the compressive strength increases in this order also. In each case, the compressive strengths were higher for Al 2 O 3 particles composites than for SiC particles composites.
The positive effects of the metallic particles admixture on compressive strength can be attributed to different behavior of the materials in terms of taking over the test loads. The metallic particles give a high elastic component.
The highest values of compressive strength were obtained for Al 2 O 3 and Fe particles reinforced bentonite matrix composites.

Conclusion
The SiC and Al 2 O 3 ceramic powders addition to clay and bentonite matrix composites lead to compressive strength lower.
The addition of metallic particles into composites changes completely this type of behavior. The compressive strength increases with the SiC and Al 2 O 3 quantities of composite. The effect is stronger for SiC when adding Cu and Al 2 O 3 to Al and Fe.
In the case of composites with SiC particles better results are obtained to Cu adding and in the case of composites with Al 2 O 3 particles better results are obtained to Al and Fe adding.
For clay matrix composites, the effect of metallic particles is in increasing order Cu↗, Fe↗, Al↗. In the case of bentonite matrix composites the order is Al, Fe. The highest compressive strength was obtained for bentonite matrix composites with 15% Al 2 O 3 and 10% Fe (141 MP). In all cases, bentonite matrix composites have higher compressive strength than clay matrix composites.