Аннотация
This is the first-ever report on successfully igniting a mechanically induced self-propagating reaction (MSR) 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 ball-free planetary ball mill jar as a reaction vessel. The content of each copper sulfide can be controlled by experimental conditions, e.g. providing sulfur over-stoichiometry leads to covellite with higher phase purity. The MSR ignition was precisely determined utilizing a self-made in situ temperature monitoring device. For the MSR to occur under the ball-free conditions, the following conditions have to be respected: 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 MSR is not ignited, the as-received powder contains a mixture of digenite and non-reacted sulfur, which is transformed into covellite with time. In specific cases, the MSR is ignited within a few minutes of storage. 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 eliminates the most common problem in mechanochemistry- contamination of the product by abrasion of the milling balls and jars.