SPINEL-MULLITE COMPOSITES WITH OPTICAL-PROPERTIES

The aim of this paper was to study the synthesis and characterization of spinel-containing mullite based materials, using sol-gel techniques . Several gels were prepared, with nominal compositions 3(A1(2-2x)M(x) TixO3). 2SiO(2) and 3(Al(2-x)M(x)O(3)). 2SiO(2), with M = Ni+2 or Co2 and 0.0 less than or equal to x less than or equal to 0.2, by hydrol ysis and condensation of mixtures of aluminum, silicon and titanium al koxides and nickel chloride. Dried gels were homogeneous and displayed a glass transition at around 750 degrees C, which indicated that the system could be described as an amorphous silicoaluminate network. Cry stallization pathway of gels were followed using differential thermal analysis and X-ray diffraction patterns of samples thermal treated at temperatures in the range between 800 and 1400 degrees C. A two-phase aluminate spinel-mullite arrangement was detected at temperatures arou nd 1200 degrees C. The microstructure of the final product was interes ting, because the minor secondary phase was homogeneously dispersed in the mullite matrix. Chemical and thermal resistance of diphasic mater ials were tested and the results indicate that these materials can be used as high temperature ceramic pigments.