Reaction kinetic studies of metal-doped magnesium silicides

摘要

Metal-doped magnesium silicides are promising thermoelectric materials for waste heat recovery application at 500-800 K because of their low density, large natural availability, non-toxicity, good thermal stability, and transport properties. Reaction kinetics of metal-doped magnesium silicides, Mg2SiXm (X = Ti, Nb, Mn, and Co; m = 0.02, 0.04, and 0.08 mol) were investigated in this study. A simple and rapid synthesis of Mg2SiX (m) samples was carried out using pelletizing, and sintering method at 773-823 K for 300 s. The effect of metal doping on the lattice constants of Mg2SiXm samples was examined using X-ray diffraction technique. Differential thermal analysis heat flow experiments were conducted on (2Mg + Si + mX) sample mixtures to study the solid-state reaction kinetics of Mg2SiX (m) alloys formation at different scan rates of 0.08, 0.16, 0.25, 0.33 Ks(-1). Activation energies for the formation reaction of Mg2Si were determined using Ozawa, and Kissinger-Akahira-Sunrose equations. A 3-D diffusion-controlled reaction mechanism was proposed based on Coats-Redfern (CR) model. The effect of concentration of the metal-dopants on the formation activation energies of Mg2SiXm was investigated using the CR equation plots.