アルミニウム液相と結晶石英粒子の反応に及ぼすマグネシウムとカルシウムの影響

抄録

  A thermite reaction begins when quartz particles are incorporated into molten aluminum (Al) : the quartz is reduced and the Al is oxidized simultaneously. Consequently, alumina particles are dispersed into the Al-Si alloy matrix to produce a composite slurry. This study investigates the influence of additional elements on the reaction based on the microstructural observation of reacted particles. Magnesium (Mg) and calcium (Ca) were prepared as additional elements ; they served as a wettability modifier to the Al melt. Addition of Mg and Ca promoted dispersion of quartz particles into the molten alloy. Furthermore, Mg addition up to 10 mass% activated reaction. The outer layers of the particles formed a spinel up to 10 mass% Mg addition. However, reaction was significantly suppressed at 20 mass% Mg addition. Such marked retardation of reaction was also observed upon addition of 1 mass% Ca. Addition of Ca or 20 mass% Mg formed dense layers at the surface of quartz particles. The layer formed in the Ca added alloy was identified as CaAl₂O₄ in X ray diffraction (XRD) analysis. Without addition of these elements, the Al as a reducing agent was supplied to the front of the reaction inside the particles through microchannels as a result of the volume shrinkage from quartz to alumina. Reaction retardation by addition of Mg or Ca occurs due to the change in the supply route of the reducing agent from the microchannels to solid diffusion in the dense reactant solid formed at the outer layer of particles.