1. 3M Central Research Laboratory, Corporate Research & Development, 3M Company, St Paul, Minnesota 55144-1000, USA

Correspondence to: A. Rosenflanz Email: arosenflanz@mmm.com

Abstract

Although often regarded as a network-former in conventional silicate glasses, Al₂O₃ alone cannot be obtained as a bulk glass. Until now, glasses comprising continuously linked [AlO_x] polyhedra have been prepared in only a few systems under very fast cooling conditions, which limits their dimensions to a few millimetres^{1, 2, 3}. Yet it is desirable to prepare bulk, or monolithic, alumina-rich glasses, with the prospect of superior mechanical, chemical and optical properties⁴. Here we report a novel process for preparing very-high-alumina glasses and nanoscale glass-ceramics. Fully dense bulk articles in net shape are obtained through viscous sintering of glass microbeads. Additional heat treatment of the consolidated glasses leads to fully crystallized transparent glass-converted nanoceramics with a hardness similar to that of alumina. This method avoids the impracticably high applied pressures (more than 1 GPa) that have been required in most cases to prepare nanocrystalline ceramics by sintering, owing to the concurrent nature of densification and grain growth under pressureless conditions^{5, 6}. The reported techniques can be extended to form glasses and nanoceramics in other oxide systems that do not include a conventional glass-forming component.

1. 3M Central Research Laboratory, Corporate Research & Development, 3M Company, St Paul, Minnesota 55144-1000, USA

Correspondence to: A. Rosenflanz Email: arosenflanz@mmm.com

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