Probing the high-pressure densification of amorphous silica nanomaterials using SBA-15: An investigation into the paradoxical nature of the first sharp diffraction peak
Abstract
The densification and X-ray scattering of mesoporous silica (SBA-15) were measured simultaneously under gigapascal (GPa) pressures. The results are compared to previous work on amorphous silica (aSiO2) and demonstrate the feasibility of measuring the densification of aSiO2 nanomaterials with small angle X-ray scattering (SAXS) in-situ in a diamond anvil cell. Compared to fused silica, the position of the SBA-15 first sharp diffraction peak (FSDP) is 7 times more sensitive to pressure and has a transition in its pressure dependance at a lower pressure (∼2 GPa vs. ∼13 GPa). SBA-15 has two densification regimes, low-density amorphous and high-density amorphous, which have equations of state comparable to low-density amorphous and high-density amorphous fused silica. The transition between these two regimes occurs at a lower pressure than for fused silica (∼1.5 GPa vs. ∼13 GPa). The results suggest that there is no direct relationship between the FSDP position and the aSiO2 density during compression.
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