Self-propagating high-temperature synthesis in a thin-layer CuO–B–glass system

Abstract

The paper provides experimental research and mathematical models of wave synthesis and thermal explosion in a thin-layer CuO–B–glass system. It is found that burning front propagation has a multi-source behavior and its rate depends on reacting layer thickness by the parabolic law with a maximum at d = 4·10–4m. Increased reacting layer thickness improves thermal explosion properties in this system, and dilution with an inert component makes it possible to obtain copper coatings featuring good electrical conductivity. X-ray phase analysis and optical microscopy demonstrated that the coating consists of metallic copper drops fused together and surrounded by boron-lead silicate glass melt. Coatings have high electrical conductivity comparable with that of metals. It is found that layer thickness increased over 4·10–4m results in a significantly reduced layer propagation rate due to initial mixture loosening under the evaporation effect of water vapors and gases adsorbed on powders, and, as a consequence, it results in reduced heat transfer in the burning front. These coatings are not electrically conductive. Mathematical models of wave synthesis and thermal explosion in a thin-layer CuO–B–glass system using macroscopic approximation. Process dynamics are numerically calculated. Theoretical estimates correspond satisfactorily to experimental values. Thermophysical and thermokinetic process constants are determined by the inverse problem method. Experimental data obtained and mathematical models developed made it possible to obtain prototypes of electric film heaters with high electrical conductivity and operating temperature.