Effects of Self-Propagating Synthesis Reactant Compact Character on Ignition, Propagation, and Microstructure

Studies of reactions involving Ti to produce TiC, TiB{sub 2}, TiC + TiB{sub 2}, or 3TiB{sub 2} + 5Al{sub 2}O{sub 3} ignited at one end of test plates showed that reactant powder compact densities were a major factor in the reaction propagation rate along the plate, i.e., a maximum in propagation rate was observed at {approx}60 {plus minus} 10% of theoretical density. At higher densities, propagation rates not only decreased but terminated due to self extinction in some cases or failed to ignite and propagate, typically at {ge}90% of theoretical density. Both reactant particle size and shape can also affect results, i.e., compacts of large (200 {mu}m in diameter) Ti particles, Ti flakes or foil, or wires failed to ignite or had slower propagation rates. Also, the ignition and propagation rates of carbon fiber tows infiltrated with titanium metal powders depended significantly on the local thermal conductivity. However, overall propagation rates for a given range of reactant compact microstructures increased with the heat of the reaction involved.