bejohnson
08-23-2004, 04:54 PM
I just read an interesting tidbit from a friend of mine that works for 3M. Here is a copy of the pertinent part of his e-mail.
Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides
A. ROSENFLANZ, M. FREY, B. ENDRES, T. ANDERSON, E. RICHARDS & C. SCHARDT
3M Central Research Laboratory, Corporate Research & Development, 3M Company, St Paul, Minnesota 55144-1000, USA
Correspondence and requests for materials should be addressed to A.R. (arosenflanz@mmm.com).
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 [AlOx] polyhedra have been prepared in only a few systems under very fast cooling conditions, which limits their dimensions to a few millimetres. Yet it is desirable to prepare bulk, or monolithic, alumina-rich glasses, with the prospect of superior mechanical, chemical and optical properties. 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. The reported techniques can be extended to form glasses and nanoceramics in other oxide systems that do not include a conventional glass-forming component.
Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides
A. ROSENFLANZ, M. FREY, B. ENDRES, T. ANDERSON, E. RICHARDS & C. SCHARDT
3M Central Research Laboratory, Corporate Research & Development, 3M Company, St Paul, Minnesota 55144-1000, USA
Correspondence and requests for materials should be addressed to A.R. (arosenflanz@mmm.com).
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 [AlOx] polyhedra have been prepared in only a few systems under very fast cooling conditions, which limits their dimensions to a few millimetres. Yet it is desirable to prepare bulk, or monolithic, alumina-rich glasses, with the prospect of superior mechanical, chemical and optical properties. 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. The reported techniques can be extended to form glasses and nanoceramics in other oxide systems that do not include a conventional glass-forming component.