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High pressure compaction of nanosize ceramic powders

Published online by Cambridge University Press:  31 January 2011

M. R. Gallas
Affiliation:
Instituto de Física, Universidade Federal do Rio Grande do Sul, P.O. Box 15051, Porto Alegre 91501-970, RS, Brazil
A. R. Rosa
Affiliation:
Instituto de Física, Universidade Federal do Rio Grande do Sul, P.O. Box 15051, Porto Alegre 91501-970, RS, Brazil
T. H. Costa
Affiliation:
Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
J. A. H. da Jornada
Affiliation:
Instituto de Física, Universidade Federal do Rio Grande do Sul, P.O. Box 15051, Porto Alegre 91501–970, RS, Brazil
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Abstract

High-density ceramic materials from nanosize ceramic powders were produced by high pressure under nearly hydrostatic environment up to 5.6 GPa, on a special configuration in a toroidal-type apparatus, at room temperature. Attempts to use a common solid pressure transmitting medium, as NaCl, resulted in cracked samples. Lead and indium, which have an extremely low shear strength, proved to be the suitable choices as a pressure-transmitting medium to compact these ceramic materials, in order to obtain high-density samples. Transparent amorphous SiO2-gel and translucent γ−Al2O3 samples, in bulk, with volumes about 40 mm3, hard and crack-free were obtained. Densities over 90% of full density for the γ−Al2O3 samples and over 80% for the compacted SiO2-gel samples were obtained. In addition, from the density-pressure curve, the yield strength (σ) for γ−Al2O3 was estimated, for the first time, as 2.6 GPa. Vickers microhardness values were in the range of 5.7 GPa for the γ−Al2O3 samples, and 4.0 GPa for the SiO2-gel samples, under loads of 50 g. An important and practical application of these results is the possibility of producing bulk γ−Al2O3, a new alumina material, which was not possible to prepare before due to the conversion to a phase during the normal sintering process. Additionally, specially for SiO2-gel, a very important application of this study is the possibility of incorporation of organic substances in an inorganic matrix, using high pressure at room temperature.

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Articles
Copyright
Copyright © Materials Research Society 1997

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