Variations of nano-structure and physical properties of silicate glasses by static and shock compressions

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In order to obtain information for magma at lower crust and upper mantle regions and structural changes of glass materials by meteorite impacts, the following studies for the nano-structure change of silicate glass under high pressure condition were carried out.1. SiO_2 glass was compressed under static high pressure up 15 GPa, about 28% of density increase was observed. It was concluded that formations of 3,4 membered rings of SiO_4 tetrahedrons with non bridging oxygen are responsible for the density increase. SiO_2-GeO_2 glasses were also compressed by shock experiments. Increase of GeO_2 component accelerates their structure change.2. The structures changes of CaSiO_3-MgSiO_3 glasses compressed by static and shock compression were investigated by X-ray diffraction measurements, Raman spectroscopy and Molecular dynamics calculations. About 5% of density increase by static compression of 7.5 GPa was observed. Ii is suggested that this density increase caused by the formations of 3,4 membered rings of SiO_4 tetrahedrons. On the other hand, Almost no density increases were observed for shock compressed CaSiO_3-MgSiO_3 glasses. This fact may indicate that 3,4 membered rings of SiO_4 tetrahedrons may not be formed by shock compression and compressed structure was relaxed by pressure release and subsequent temperature increase.3. Structural change of opal nano-structure by shock compression was investigated. About 10% of density increase of opal at 20-30 GPa and density decrease at higher pressure. By X-ray diffraction measurements, the crystalline part of opal was change to amorphous state by shock. By IR spectroscopy, OH of opal decrease and frequency of OH band changed toward higher wavenumver were investigated.4. The results of these studies were presented at National and International Meetings such as IMA and also published as scientific papers.