Thermal Conductivity Effects on SHS (Self-Propagating High-Temperature Synthesis) Reactions

摘要

The effects of green compact thermal conductivity on SHS reaction initiation and propagation velocity have been modeled for the titanium and carbon system. This modeling predicts that, for a given filament power input, the time required to ignite an SHS reaction is a strong function of the green compact thermal conductivity. It also predicts that, for systems where the mass diffusion rate is high, the green compact thermal conductivity controls the reaction front velocity. Thermal conductivities of mixed titanium and graphite powder compacts have been measured for compact densities ranging from 58% to 81% of maximum theoretical density and have been found to increase by a factor of four in this density range. Modeling results suggest this change in thermal conductivity with density is sufficient to have marked affect on SHS initiation and reaction velocity. An anisotropy of the mixed titanium and graphite powder compact thermal conductivities, which increase with increasing compaction density, was also observed. This anisotropy is thought to be the result of graphite powder particle orientation and pore deformation resulting from the uniaxial compacting force. The importance of controlling green compact thermal conductivities, methods of accomplishing this by varying the ratio of crystalline to amorphous carbon in the powder mixture and the application of this control to processing and final product material characteristics are discussed.