Vitrocerâmicas do sistema Li2O - Al2O3 - SiO2 (LAS) via sinterização com cristalização concorrente
Resumo
LAS (Li2O-Al2O3-SiO2) glasses have been often used to produce glass-
ceramics with near zero thermal expansion coefficient. These glass-ceramics
are very important for applications that require high thermal shock resistance.
However, they are still produced by traditional techniques, such as melting and
forming followed by internal nucleation (induced by the addition of catalysts)
and crystal growth in the volume of monolithic glass pieces. An alternative route
for the production of glass-ceramics is via sintering of catalyst-free glass
particles with controlled surface crystallization. The purpose of the present work
was to determine the appropriate compositions and sintering conditions to
produce dense LAS glass-ceramics having almost null porosity. Three
compositions were analyzed to achieve near zero thermal expansion coefficient.
The precursor glasses were analyzed by thermal analysis, and the glassceramics
were analyzed by X-ray diffraction, optical microscopy and electron
microscopy. Dense glass-ceramics were obtained with porosity below 1.5%.
The results show that reduction of crystallization by an ion exchange promotes
sintering. However, the high amount of vitreous phase present in these samples
increases the thermal expansion coefficient. At least for one composition we
obtained a glass-ceramic having a porosity of 1.4% and a thermal expansion
coefficient of 0.5 x 10 -6 °C-1, a value similar to that of vitreous silica.