Evaluation of Al2O3 content and B2O3/SiO2 ratio in SiO2-Al2O3-B2O3-TiO2-La2O3 glasses on the infiltration behavior and optical and mechanical properties of alumina composites

Reference	Presenter	Authors (Institution)	Abstract
09-047	Henrique Takaaki Tamoto	Tamoto, H.T.(Universidade Federal do ABC); Chimanski, A.(Universidade Federal do ABC); Montedo, O.K.(Universidade do Extremo Sul Catarinense); Yoshimura, H.N.(Universidade Federal do ABC);	Glass infiltrated ceramic composites have been a good choice for dental prosthesis. Since the glass systems have structure complexity, its behavior has to be further studied. Thus, changing the composition of glasses in the SiO2-Al2O3-B2O3-TiO2-La2O3 system, evaluating its effects on glass viscosity, wettability, optical and mechanical properties, was the purpose of this study. The infiltrated ceramic was a porous alumina (porosity of 23.4%) made by slip casting and partially sintered at 1200 °C. Then the porous preform was densified by infiltration of the glass at 1200 °C. The glasses were made by quenching the raw materials melted at 1500 °C. Two groups of glasses were evaluated: changing equally the content of B2O3 and SiO2 in a system of (25+x/2)SiO2-(25-x)Al2O3-(20+x/2)B2O3-15TiO2-15La2O3 (mol%) by alumina content of 25, 20 and 15%; and changing B2O3/SiO2 ratio (1.00, 0.80, 0.67) in a composition with fixed 20% Al2O3. Glass behavior, Tsintering, Tmelting and system’s wettability was determined by hot-stage microscope; glass transition temperature was measured by differential scanning calorimetry and viscosity as a function of temperature were determined using the Vogel-Fulcher-Tammann equation (VFT). The composites were polished to be subjected to a spectrophotometry where transmittance and reflectance to calculate the contrast ratio were measured. Vickers hardness and fracture toughness were determined by indentation technique. Except for the glass containing 25% Al2O3, that had higher viscosity and contact angle on alumina substrate at 1200 °C, all of the other glasses had these properties drop down before this temperature, which was an influence of decreasing its alumina content, also, these glasses spread at the preform surface during infiltration. X-ray diffraction patterns did not show any sign of crystallization at the glasses powders. The composite optical properties were not compromised by the formula changes in the glass.
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