Characteristics of Reaction Propagation in TiN Combustion Synthesis Using Concentric Bilayered Cylindrical Compact

Based on combustion synthesis of titanium nitride with liquid nitrogen, the geometrical effects of the Ti compact has been investigated for the improvement of low conversion from Ti to TiN. Concentric bilayered cylindrical compacts with two kinds of packing densities, which consist of an inner column and an outer cylinder; normal cylindrical compacts were applied. It was clear that the propagation rate in the outer cylinder of the bilayered compact is almost the same as that of the normal compact under the same packing density condition, and that the propagation rate in the inner column of the bilayered compact is smaller than that in the outer cylinder. These facts imply that the propagation rate in the inner column could be drastically changed by outer packing density. By using the compact with smaller inner packing density than the outer one, advantageous conditions of using the inner column for nitridation could be realized: a greater quantity of liquid nitrogen is inside a sample (due to lower packing density) and smaller propagation rate (due to the above-mentioned geometrical effect). In spite of the condition that liquid nitrogen was used under 1 atm, products with higher conversion ratio could be obtained. In these experiments, the possibility of high nitridation using a concentric bilayered compact is indicated.