XRD patterns of shock-recovered samples and starting mullite. Previous results for 29, 40, and samples (from Ref. 4) are also shown for comparison. Diffraction intensities of shocked samples are magnified for viewability. The XRD patterns of shock-recovered samples show an amorphous halo. Reflections from , which are observed in 65 and samples, are indexed with cubic indices.
MAS NMR spectra of shock-recovered samples and starting mullite. NMR peaks become increasingly broader with pressure, indicating that the structural disorder of mullite increases with pressure. The NMR spectrum of sample shows the presence of a densified amorphous phase (additional peak around ).
The fitting of the NMR spectrum of sample by two Gaussian line shapes clearly shows the presence of an additional peak centered at . This peak represents the dense four-coordinated amorphous with a mean Si–O–Si bond angle roughly 7° narrower than that of the fused glass.
Typical TEM micrograph of the sample. Nanocrystals with grain sizes of about are dispersed in the amorphous phase. Electron diffraction shows that these nanocrystals correspond to the phase. Diffracton rings are indexed with .
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