Platinum Metals Rev., 1965, 9, (1), 11
Crystallisation of Glasses Containing Platinum
A Study of The Mechanism of Nucleation
Glass of high strength can be produced by suitably controlling the process of crystallisation (1), Its formation can be better understood by studying the mechanism of the nucleation and crystallisation of glass.
Work has been carried out recently on this problem by R. L. Thakur of the Central Glass and Ceramics Research Institute of India with K. Tazikawa, T. Sakaino and T. Moriya, of the Tokyo Institute of Technology (2). They chose for their studies a eutectic composition glass of lithia-alumina-silica melting at 975 °C, which is reasonably homogeneous after melting at 1400°C. Platinum was introduced as dilute platinum chloride solution. Tests were made on glasses with and without platinum as nucleating agent.
Differential thermal analysis was used to determine the transformation temperature, the nucleation and crystallisation temperatures, and the heat treatment necessary for the samples. The crystals were studied by electron microscopy and X-ray diffraction.
Glasses containing no platinum always commenced to crystallise from the surface inwards and there was no phase separation except at the interface with the part already crystallised. The crystals were much larger than when platinum was present.
The appearance of crystals in the platinum-containing glass was always preceded by phase separation, and crystallisation then took place throughout the whole mass. Heat treatment at 550°C produced complete nucleation within eight hours but nucleation remained incomplete at this temperature when no platinum was present even after eleven days.
A series of electron micrographs was produced that clearly indicated the phenomena described. The ability of platinum to act as a nucleating agent for the controlled crystallisation was fully confirmed and the paper is a valuable contribution to studies of the platinum metals for this purpose.
- 1 Platinum Metals Rev., 1961, 5, 140
- 2 Central Glass & Ceramics Res. Inst. Bull., 1964, 11, 1 – 22