Аннотация
This is the first-ever report on successfully igniting a mixing-induced self-propagating reaction (MXSR) for an inorganic system just by simple intensive mixing. Namely, mixtures of nanocrystalline copper sulfides covellite (CuS) and digenite (Cu1.8S) were prepared within two minutes of intensive mixing of copper and sulfur powders utilizing a ball-free planetary ball mill jar as a reaction vessel. The content of digenite and covellite can be controlled by experimental conditions, e.g., providing sulfur over-stoichiometry leads to covellite with higher phase purity. The MXSR ignition was precisely determined utilizing a self-made in situ temperature monitoring device. For the MXSR to occur under the ball-free conditions, the following conditions are needed: jar filling ratio at least 40%, rotation speed at least 700 rpm and Cu:S molar ratio in the range between 0.625 and 1.00. When MXSR is not ignited, the powder after intensive mixing contains a mixture of digenite and non-reacted sulfur, which is transformed into covellite with time. In specific cases, the MXSR is ignited within a few minutes after the termination of mixing. The scalability of the proposed methodology is verified on the 40 and 62.5 g scale utilizing a planetary and mixer mill, respectively. The present approach is in great alignment with green chemistry principles, since it utilizes only atoms composing the product, does not create any waste and can be ignited in the absence of external heating or mechanical input which distinguishes it from self-propagating high-temperature synthesis and from mechanically induced self-propagating reaction. Moreover, the absence of milling media eliminates contamination from jar and ball abrasion. Finally, thermoelectric measurements show that the as-prepared copper sulfides can be directly processed into functional materials for waste-heat-to-electricity conversion, offering a promising basis for further optimization.