The Mechanism of Joint Reduction of MoO3 and CuO by Combined Mg/C Reducer at High Heating Rates

Abstract

Understanding of the decisive role of non-isothermal treatment on the interaction mechanism and kinetics of the MoO3-CuO-Mg-C system is highly relevant for the elaboration of optimal conditions at obtaining Mo-Cu composite powder in the combustion processes. The reduction pathway of copper and molybdenum oxides with combined Mg + C reducing agents at high heating rates from 100 to 5200 K min−1 was delivered. In particular the sequence of the reactions in all the studied binary, ternary and quaternary systems contemporaneously demonstrating the effect of the heating rate on products’ phase composition and microstructure was elucidated. The combination of two highly exothermic and speedy reactions (MoO3 + 3Mg and CuO + Mg vs. MoO3 + CuO + 4Mg) led to a slow interaction with weak self-heating (dysynergistic effect) due to a change in the reaction mechanism. Furthermore, it has been shown that upon the simultaneous utilization of the Mg and C reducing agents, the process initiates exclusively with carbothermic reduction, and at relatively high temperatures it continues with magnesiothermic reaction. The effective activation energy values of the magnesiothermic stages of the studied reactions were determined by Kissinger isoconversional method.

The Interaction Pathway in the Mechano-Ultrasonically Assisted and Carbon-Nanotubes Augmented Nickel–Aluminum System

“…The principle operation of the HSTS [23][24][25][26] device was based on the direct electrical heating of a cell made of a thin metal sheet containing a reactive mixture (Figure 1). The latter (50 mg) was poured into a thin envelope made from nickel (100 µm in thickness), installed in the reactor, and attached to electrical contacts.…”

“…The experimental steps for the kinetic studies using a high-speed temperature scanner. (a) envelope-heater with reactive mixture under study; (b) reaction chamber and controller: 1-reactive mixture, 2-boat made from nickel foil, 3-powder mixture in Ni boat, 4-envelope with mixture and thermocouple wire, 5-heated sample, 6-reaction chamber, 7-electronic unit and PC for control and registration[26]…”

Kinetic Highlights of the Reduction of Silver Tungstate by Mg + C Combined Reducer

“…The HSTS-1 setup (Figure 1) [28][29][30][31][32][33] was utilized for the kinetic investigations of the Ag 2 WO 4 -Mg-C system under the programmed linear heating rates up to 1200 • C min −1 , which are closer to the heating rates of reagents in the combustion wave at the synthesis of tungsten-based composite materials. The principle of operation of the device is based on the direct electric heating of a cell made of thin metal foil containing reactive powder.…”

“…On the other hand, the extreme conditions of the synthesis of metal-based composites in the combustion wave (high temperatures, high heating rates of initial material) and the limited toolkit for the study of the associated interaction mechanism hinder the comprehensive management of the process. To meet the challenge, the processes in the combustion wave are modeled by a high-speed temperature scanner (HSTS) [28][29][30][31][32][33]. This technique allows one to perform detailed examinations in the reactive powder mixtures or compacts from RT up to 1700 • C and fast heating (up to 10,000 • C min −1 ).…”