Exothermic reaction waves in ZrSiO4/Mg/diluent systems

An experimental study of thermal behavior in exothermic wave propagation in ZrSiO4 + 4Mg + kSH systems (where SH is a sodium halide) was conducted using a thermocouple technique. Temperature–time profile investigations provide deeper insight into the combustion wave propagation mechanism and reveal the values of combustion parameters: ignition and combustion temperatures, wave propagation velocity, and the actual size of pre-flame and reaction zones. It was shown that the measured maximum temperature was reduced from 1900 °C for the undiluted sample to 1490 °C for samples containing 1.5 mol of sodium halide. As a consequence, pure-phase zirconium monosilicide (ZrSi) was obtained under theses temperature conditions. Scanning electron microscope (SEM) examination revealed that ZrSi particles were spherical in shape and uniform in size when NaCl was used as an inert diluent. The obtained ZrSi particles had mean diameters ranging from 0.4 to 2.5 μm based on NaCl concentration. The chemical mechanism of ZrSi formation is discussed, and a simple model for nucleation and grain growth processes is proposed.