Joint Reduction of NiO/WO3 Pair and NiWO4 by Mg + C Combined Reducer at High Heating Rates

Abstract

Functional features of Ni-W composite materials combined with successful performance enabled a breakthrough in their broad application. To disclose the formation pathway of Ni-W composite materials at extreme conditions of combustion synthesis in the NiO-WO3-Mg-C and NiWO4-Mg-C systems for the optimization of the synthesis procedure, the process was modeled under programmed linear heating conditions by thermal analysis methods. The reduction kinetics of tungsten and nickel oxides mixture and nickel tungstate by Mg + C combined reducer at non-isothermal conditions was studied at high heating rates (100–1200 °C min−1) by high-speed temperature scanner techniques. It was shown that when moving from low heating to high heating rates, the mechanism of both the magnesiothermic and magnesio-carbothermic reductions of the initial mixtures changes; that is, the transition from a solid-solid scheme to a solid-liquid scheme is observed. The strong influence of the heating rate on the reduction degree and kinetic parameters of the systems under study was affirmed. The simultaneous utilization of magnesium and carbon as reducers allowed the lowering of the starting and maximum temperatures of reduction processes, as evidenced by the synergetic effect at the utilization of a combined reducer. The effective values of activation energy (Ea) for the reactions proceeding in the mixtures NiO + WO3 + 4Mg, NiO + WO3 + 2.5Mg + 1.5C, NiWO4 + 4Mg and NiWO4 + 2Mg + 2C were estimated by Kissinger isoconversional method and were 146 ± 10, 141 ± 10, 216 ± 15 and 148 ± 15 kJ mol−1, respectively.

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.…”

“…Extreme conditions in the SHS wave (elevated temperatures and fast self-heating of substances in the combustion wave) impede the disclosure of interaction pathways in the SHS process and optimization of synthesis conditions. To tackle the challenge, the process in the Ni-Al system was modelled at guided conditions, in particular, at a programmed heating routine via tuning the interaction over the time and approximation of conditions to the combustion process, by the thermal analysis method, namely using a high-speed temperature scanner (HSTS) [23][24][25]. The influences of MUA (t UA = 0-55 min, t MA = 1-5 min) and heating rates on the kinetics, phase, and microstructure evolution pathway of Ni-Al and carbon-nanotubes augmented Ni-Al systems were examined.…”

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 ).…”

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

“…The latter was studied so far by means of X-ray diffraction, electron microscopy and thermal analysis techniques without consideration the influence of high heating rates on the interaction dynamics. Motivated by the open questions and technical difficulties of combustion kinetics exploration, our current study is aimed to disclose the interaction pathway at high heating rates in the MoO 3 -CuO-Mg-C system by a novel thermal analysis technique, called high-speed temperature scanner (HSTS) [15][16][17][18].…”