REACTION SYNTHESIS OF HIGH-TEMPERATURE SILICIDES

An attempt has been made to understand the reaction mechanisms involved in the synthesis of high-temperature silicides by combustion synthesis of MoSi2, reactive sintering and simultaneous hot pressing of MoSi2, shock-assisted reaction synthesis of NiSi and Ni2Si, and shock-induced reaction synthesis of Ti5Si3. The experimental results on combustion synthesis, and on the reactive sintering and simultaneous hot pressing of Mo + 2Si, indicate a heterogeneous reaction between liquid Si and Mo powder. In contrast to the above techniques, Mo5Si3 is observed as a secondary phase along with MoSi2 when the mixture is heated at low heating rates. Densities of reactive-sintered and simultaneously hot-pressed MoSi2 are close to 85% of MoSi2 density. The results indicate that densification and synthesis can effectively be combined, eliminating the need to hot-press a pre-alloyed powder. Shock-processed mixtures of Ni + Si and 2Ni + Si result in single-phase NiSi and Ni2Si, respectively, in the solid state upon subsequent reaction sintering. Mixtures of 5Ti + 3Si also result in single-phase ti(5)Si(3) compound by solid-state shock-induced reaction mechanism.