Self-Propagating High-Temperature Synthesis of a Thin-Layer CuO–B–Glass System

Аннотация

Experimental studies are performed and mathematical models of the wave synthesis and thermal explosion in a thin-layer CuO–B–glass system are constructed. It is established that the propagation of the combustion front occurs in a multisource mode and its rate depends on the reaction layer thickness (d) according to the parabolic law with a maximum at d = 4 × 10^–4 m. An increase in the reaction layer thickness promotes the improvement of thermal explosion characteristics in this system, while its dilution with an inert component makes it possible to form copper coatings with high electrical conductivity. An X-ray phase analysis and optical microscopy showed that the coating consists of metallic copper drops fused together and surrounded by a boron–lead silicate glass melt. Coatings have high electrical conductivity comparable with that of metals. It is found that an increase in the layer thickness above 4 × 10^–4 m leads to a considerable decrease in the propagation rate of the combustion wave front due to loosening the initial mixture under the effect of evaporation of water vapor and gases adsorbed on powders and, consequently, to a decrease in heat transfer in the combustion front. Such coatings are nonconductive. Mathematical models of the wave synthesis and thermal explosion in a thin-layer Cu–B–glass system are developed in a macroscopic approximation. Numerical calculations of the process dynamics are performed. Theoretical evaluations satisfactorily correspond to the experimental data. Thermal and thermokinetic process constants are determined by the inverse problem method. Experimental samples of film electric heaters with high electrical conductivity and operational temperature are fabricated based on the experimental data and mathematical models.