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Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides


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 millimetres1,2,3. 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 conditions5,6. The reported techniques can be extended to form glasses and nanoceramics in other oxide systems that do not include a conventional glass-forming component.

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Figure 1: Effect of rare-earth ion size on ΔTx.
Figure 2: Bulk rare-earth aluminate glasses.
Figure 3: Consolidation of glass microbeads by hot-pressing.
Figure 4: Scanning electron micrographs of fracture surfaces.
Figure 5: Map of hardness against Al2O3 content in different material classes.


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We thank C. Goodbrake (3M Company) for help with microscopy, and I.-W. Chen (University of Pennsylvania) for helpful comments during the preparation of the manuscript.

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Correspondence to A. Rosenflanz.

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The authors are all employees of 3M Corporation.

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Rosenflanz, A., Frey, M., Endres, B. et al. Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides. Nature 430, 761–764 (2004).

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