1966 Volume 30 Issue 9 Pages 840-846
The thermal behavoirs of the Japanese colloidal earth available as the source material in the direct reduction of aluminium were investigated by means of thermo-balance, differential thermal analysis, X-ray analysis, infrared spectrum and neuclear magnetic resonance.
The colloidal earth was amorphous by X-ray analysis and contained 15∼30 percent moisture.
The greater part of the moisture was removed at 100°∼250°C and the moisture was found to be physically combined water located in cavities of particles or lattice layers. The residual moisture was clearly detected by infrared spectum even at 900°C and was inferred to be the water combined on the surface of lattice layers and crystal water.
With the advance of heating and dehydration, the infrared absorption spectrum of O-Al-OH binding was weakened, and the strengthening of Si-O and the formation of Si-O-Al binding were observed at temperatures over 500°C.
This result shows the preparatory process involving separating of SiO2 and formation of mullite from the pseudo-metakaoline structure, and this was detected by differential thermal analysis by a exthothermal peak at about 950°C.
Moreovers, this exthothermal peak was derived from the nucleation of mullite, and clear needle-like crystals of mullite were observed over 1200°C.
