Effect of Electric Current on SHS-Processes with Complete Transformation in Wave Front

High-Temperature Combustion Synthesis: Generation of Electromagnetic Radiation and the Effect of External Electromagnetic Fields (Review)

“…The above-indicated drawbacks of FACS experiments, apparently, did not allow any meaningful conclusions from the numerical results [60][61][62][63][64]. The main conclusion about current localization in the vicinity of the high-temperature synthesis wave front is fairly obvious and was predicted many years ago [33,55]. The conclusion made in [64] about the influence of the sample size and about the transition from the volume to the wave regime of synthesis in the case of large-size samples is also obvious.…”

“…The fact that the currents and powers of electric heating are extremely high and almost cancel the main advantage of self-propagating high-temperature synthesis (low energy costs) is absolutely ignored. As the estimates of [33] show, for an electric current density of ≈10 3 -10 4 A/cm 2 , the Joule heat-release rate becomes commensurable with the heat-release rate in the reaction in the wave front and has a significant effect on temperature and synthesis-wave velocity. Under these conditions, the synthesis becomes much more energyconsuming, which restricts the practical application of the above-mentioned technologies.…”

“…Stability of the quasisteady regimes was studied. In the case of low intensity of the Joule dissipation of energy in the front, as compared to chemical heat release, it turned out [33] that the temperature of the synthesis wave remains almost unchanged and is a weakly growing quadratic function of the current density or voltage, respectively. Yet, even a weak Joule action can significantly affect the coefficient of temperature sensitivity of the front-propagation velocity and, thus, stability of the combustion mode.…”

“…A similar specific feature at the macroscopic scale (at the scale of the heating zone in the SHS wave) is typical of the Field Activated Combustion Synthesis (FACS) method [52][53][54] developed as a method for supporting high-temperature combustion synthesis in weakly exothermal compositions. The authors of the method put into practice the idea of [33,55] about macroscopic localization of transmitted current in the vicinity of the hot front in the case of transverse superposition of the electric field with respect to the combustion-wave propagation direction and the energy benefits associated with this localization. The possibility of providing such localization is ensured by a drastic (by several orders) increase in conductivity of the reacting mixture with increasing temperature of the mixture.…”

“…Generally, the theory of propagation of a hightemperature synthesis wave under conditions of an additional Joule heating by an external electric field originated in works on the influence of currents with a constant density and intensity [33,55,65,66]. Two methods of application of the external field were considered: along the wave direction (with a constant current density) and across the wave direction (with a constant voltage); quasi-steady regimes of synthesis propagation, where the wave front has enough time to fit the time-dependent temperatures of the products and initial mixture, were examined.…”