Structural response of a highly viscous aluminoborosilicate meltto isotropic and anisotropic compressions

摘要

Aluminoborosilicate melts of E-glass composition have been compressed at pressures up to 500MPa and subsequently cooled (4-5 K min~(-1)) under pressure from well above the glass transitionto room temperature. It is found that increasing uniaxial pressure lead to anisotropic glasses withincreasing permanent birefringence, while increasing isostatic pressure resulted in isotropic glasseswith increasing density (compaction of 2.1 at 500 MPa). Static and magic-angle spinning nuclear tr~(11)B ~(23)Na, ~(27)Al,magnetic resonance spectroscopy ofAI and ~(29)Siwere performed to explore pressure-induced changes in the short-range structure of these glasses. NMR experiments readilydetected increasing ~(IV)B, ~VAl, and ~(VI)Alconcentrations with pressure as well a decrease in themean distance of sodium to oxygen atoms (0.7 at 500 MPa), but no detectible evidence ofshort-range structural orientation around these atoms in the birefringent glasses were found.Quantifying the changes in the local boron, aluminum, silicon, and sodium environments revealedthat the measured increase of recovered density with pressure in E-glass can only be partlyexplained by increase in B and Al coordination, and that overall compression of the network and ofthe network modifier cation volumes must also be important. Structural changes in the intermediaterange, which were not detected by NMR, are discussed as a source of birefringence in anisotropicE-glass.