Mechanochemical Reactions in the Sn-Zn-S System: Further Studies

Although ball milling initiates self-sustaining thermal reaction (combustion) in both Sn–S and Zn–S powder blends, the reaction may be gradual when Sn-Zn-S mixtures are processed under the same conditions. Milling experiments were carried out at several Sn-Zn-S compositions, using different milling balls and ball-to-powder ratios. The ignition time was measured and the phase composition was determined at different stages of the process. The activation time before ignition scales with the ball-topowder ratio in most cases, showing that the "mechanical dose" is suitable to describe the degree of activation. More energetic milling results in earlier ignition, but it also intensifies the formation of reaction products before ignition, thereby promoting gradual kinetics. The initiation and propagation of a combustion front is similar to self-propagating high-temperature synthesis in a powder compact, but heat transfer to the milling tools is a more important factor.