Composition and pressure effects on the structure, elastic properties and hardness of aluminoborosilicate glass

A series of calcium-aluminoborosilicate glasses with different ratios of B2O3/SiO2 have been isostatically compressed at 1 and 2 GPa at temperatures above their glass transition temperatures. Boron and aluminum coordination numbers were quantified for recovered samples by 11B magic angle spinning (MAS) nuclear magnetic resonance (NMR) and 27Al MAS NMR spectroscopy at ambient pressure and temperature. The average coordination numbers increase as the glass was compressed to higher pressure and the glass with higher concentration of boron shows higher recoverable densification. The atomic structure changes can be represented by oxygen packing density, Young's modulus and Vickers hardness number show good correlations with oxygen packing density as well. In general Poisson's ratio decreases as the average coordination number of network formers increases, however the interpretation of the changes in Poisson's ratio with pressure for each glass composition presents a more complicated case and no straightforward trend with compaction was found.