Kinetics of magnesium preparation by vacuum-assisted carbothermic reduction method

Metallic magnesium was prepared by vacuum-assisted carbothermic reduction method, and its morphologies were observed and analyzed. The reduction ratios of reactions were carried out under various vacuums, reaction temperatures, and time. Reaction kinetics of carbothermic reduction process was investigated. The results reveal that the morphologies of metallic magnesium sample that crystallized in the bottom and top sections of the condensation cap appear as the shape of feather with close-packing needle structure and the shape of schistose with metal luster, compactly clumpy structure, respectively. The reduction ratio of reaction process can be facilitated through reducing vacuum, increasing temperature, lengthening time, or their combinations and can reach up to 83.7 % under the condition of 10 Pa and 1573 K with 60 min reaction time. At 1423–1573 K, the reaction rate constant k of carbothermic reduction of magnesia in vacuum gets greater with the increase of temperature. The reaction activity energy is 190.28, 219.71 and 451.12–528.54 kJ·mol^?1 when the procedure of carbon gasification reaction, interfacial reaction, or gaseous diffusion is the reaction rate-determining step at 1423–1573 K, respectively. The gaseous diffusion procedure has the largest activity energy value and is, therefore, the main reaction rate-determining step.