High-density ceramic materials from nanosize ceramic powders were prod
uced by high pressure under nearly hydrostatic environment up to 5.6 G
Pa, on a special configuration in a toroidal-type apparatus, at room t
emperature. Attempts to use a common solid pressure transmitting mediu
m, as NaCl, resulted in cracked samples. Lead and indium, which have a
n extremely low shear strength, proved to be the suitable choices as a
pressure-transmitting medium to compact these ceramic materials, in o
rder to obtain high-density samples. Transparent amorphous SiO2-gel an
d translucent gamma-Al2O3 samples, in bulk, with volumes about 40 mm(3
), hard and crack-free were obtained. Densities over 90% of full densi
ty for the gamma-Al2O3 samples and over 80% for the compacted SiO2-gel
samples were obtained. In addition, from the density-pressure curve,
the yield strength (sigma) for gamma-Al2O3 was estimated, for the firs
t time, as 2.6 GPa. Vickers microhardness values were in the range of
5.7 GPa for the gamma-Al2O3 samples, and 4.0 GPa for the SiO2-gel samp
les, under loads of 50 g. An important and practical application of th
ese results is the possibility of producing bulk gamma-Al2O3, a new al
umina material, which was not possible to prepare before due to the co
nversion to ct phase during the normal sintering process. Additionally
, specially for SiO2-gel, a very important application of this study i
s the possibility of incorporation of organic substances in an inorgan
ic matrix, using high pressure at room temperature.