Mechanism Of Dopant On The Reaction Synthesis Of Ternary Carbide

Al4SiC4 and Al8B4C7 are two potential materials for refratory and high temperature structural material, and they have received considerable attention for its high melting point, low density and excellent oxidation resistance. There is main synthesis way have been generally used some artificial materials, and heated at high temperature. Obviously, the synthesis of Al4SiC4 and Al8B4C7 from the raw mineral materials could reduce remarkably the costs of their industrial application. However, raw mineral materials contain some impurities will inevitably have an impact on the synthesis of these carbides, and affect performance and application of these carbides. So, it is necessary to investigate the mechanism of impurities on the reaction synthsis of ternary carbide.In our present work, Al4SiC4 and Al8B4C7 have been synthesized by using flint clay or borax as the staring materials, respectively. The effect of K2O,Na2O,Fe2O3 and TiO2 on the phase composition and microstructure of Al4SiC4 or Al8B4C7 have been investigated by TG analysis, chemical analysis, XRD and SEM methods.In the synthesis process of ternary carbides, the content of K2O and Na2O decreased because of evaporation, Fe2O3 and TiO2 only had a small amount of loss.In the synthesis process of Al4SiC4, K2O was advantaged for the generation of Al4SiC4, and could promote Al4SiC4 grains growth and better crystallinity. Na2O led to defects in the surface of Al4SiC4 grains. Fe2O3 had transformed into Fe3Si which has a low melting point and would generate liquid to promote nucleation and grain refinement of Al4SiC4, and Fe3Si also could coat Al4SiC4 grains. TiO2 has transformed into TiC which enhance the formation temperature of Al4SiC4 from 1500℃to 1600℃, and caused the decomposition of Al4SiC4 at 1700℃.In the synthesis process of Al8B4C7, K2O and TiO2 enhance the formation temperature of Al8B4C7 from 1300℃to 1400℃, and generated new unkonwn phase at 1700℃. K2O reduce the generation of Al8B4C7, and it was some irregular particles. Fe2O3 has not transformed into a independent phse contaning Fe, but Fe3+ reacted with Al8B4C7 to form the continuous substitution solid solution, and Al8B4C7 was also irregular particle. TiO2 has transformed into TiB2, and with the increasing additive amount of TiO2, the generation of Al8B4C7 decreased,irregular particle change to unconsolidated plate-like particle gradually.