Structural Relaxation of High-Pressure Silicate Melts During Quenching And Decompression

Quenched silicate glasses recovered from high pressure have been used to apply structural study of densified silicate melts. Densification mechanism of silicate melts has been discussed on the basis of study on the quenched glass. It is, however, known that the structure of recovered glass is affected not only by fictive temperature during quenching but also by decompression process from high-pressure to ambient condition. It is important to understand how structure of silicate glass relaxes during quenching and decompression, in order to evaluate the structure of silicate melts under pressure. We studied the structure of some aluminosilicate melts and glasses under pressure by in situ x-ray diffraction experiments using synchrotron radiation. Structural change during quenching and decompression was evaluated from both structure factor and radial distribution function with the aid of molecular dynamics simulation. Quenching from melt to glass under pressure does not affect much the nearest neighbor environment but change significantly the intermediate range structure, such as network of TO4 tetrahedra, During quenching, the FSDP of structure is sharpened and the corresponding RDF peaks, such as O-O and T-T peaks, become clear independent peaks, which indicate strong ordering in the network of TO4 tetrahedra. On the other hand, decompression has a little effect on the glass structure, which is mainly caused by elongation of atomic distances. This decompression effects must, however, affects the number of oxygen coordinated aluminum and the distribution of bridging and non bridging oxygen.