May 13, 2008, Chantilly, Virginia:

Structural studies of Mg₂SiO₄ glass have proved to be difficult in the past due to the experimental challenges involved in the synthesis of such glasses, arising primarily from their extremely poor glass-forming tendency. Sen and Tangeman have carried out an ab initio molecular dynamics (AIMD) simulation of Mg₂SiO₄ melt structure. The ²⁹Si NMR chemical shift parameters of the Si sites in this structure are calculated from first principles and have been compared with the experimental ²⁹Si NMR spectra of near-stoichiometric Mg₂SiO₄ glass synthesized via container-less levitation technique. Here they present the results of this study that, when taken together, provide a consistent picture of the structure of Mg₂SiO₄ glass and melt.

The conventional method to determine fracture toughness (K_IC) from indentation is based on radial crack lengths measurements, which is difficult to estimate owing to the ease with which kyanite cleaves. An alternative method is proposed by Mikowski et al. to determine the K_IC for the perfect cleavage plane (100) of kyanite based on the estimation of the crack nucleation threshold load from a discontinuity or "pop-in" in the DSI load-unload curve. A closed expression is proposed to obtain the fracture toughness value. In addition, scratch hardness, indentation hardness, and elastic modulus are determined by depth-sensing indentation (DSI) in the perfect cleavage plane (100) and in the plane (010) for comparison.

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