Synthesis And Properties Of Al₄ SiC₄

Al₄SiC₄ has some excellent properties, such as high melting point (2037℃), high strength, stability of chemistry, low density and thermal expansion coefficient, excellent hydration resistance and oxidation resistance, etc. Al₄SiC₄ is a potential material for refratory and high temperature structural material, and it have received considerable attention this years. So far, the main synthesis way have been generally used some artificial materials, the cost is very high. Obviously, the synthesis of Al₄SiC₄ from the raw mineral materials could reduce the costs of its industrial application.In our present work, Al₄SiC₄ have been synthesized at high temperatures using flint clay, aluminum and active carbon powders. We studied the mechanism and process of the reaction, analyzed the best ratio of the raw materials, synthesis temperature and holding time so as to improve the yield of Al₄SiC₄.The phase compositions of the samples were determined by X-ray diffractometry (XRD). The microstructures of the samples were examined by scanning electron microscope (SEM), and the elemental and quantitative compositions of the samples were determined by the energy dispersive X-ray spectroscopy (EDX). The oxidation process of the samples was researched by the differential thermal analysis (DTA) and the thermal gravity analysis (TG). In addition, we have researched the sintering property, oxidation resistance, hydration resistance and slag resistance of the synthetic materials.By analyzing the experimental results, we got some conclusions as follows:(1) At 1700℃and 1800℃, use flint clay, aluminum and active carbon powders as raw materials can synthesis Al₄SiC₄. With the temperature increased, more Al₄SiC₄ was generated, and the phase compositions tend to be more single. Eventually can be obtained the sample contains only Al₄SiC₄ and Al₄O₄C.(2) After sintering, the porosity of sintered samples significantly reduced, bulk density increased, compressive strength has greatly improved. Al₄SiC₄ grains stacked more closely, and their thickness have increased to some extent.(3) Al₄SiC₄ powders start oxidated at about 800℃. Oxidation the Al₄SiC₄ bulk and the oxide layer have three components: the reaction layer, internal oxidation layer and the outer oxide layer. Erosion the Al₄SiC₄ bulk and the slag line was very clear and separated from the internal. Al₄SiC₄ material showed good oxidation-resisting property and erosion-resisting property.(4) In the anti-hydration experiments, the excess of Al powder have a negative impact on the hydration resistance of composite materials. The minimum rate of weight growth is the sample 1800A4, its phase composition does not changed, it have the best hydration resistance in all the samples.The shape of the synthesized Al₄SiC₄ in the synthesized multi-phase materials was flake or block. The grain size was about more than 10 microns to tens of microns. As the temperature increase, crystal grain gradually grew up, Al₄SiC₄ changed from irregular particles into the six-sheet, and then have the shape of more regularly. The grains of Al₄O₄C were smaller, and existed in the surrounding and gap of Al₄SiC₄ grains.