Fig. 1.  Al single pulse MAS-NMR spectra of the metakaolins A (a) and B (b) with spectra simulations.
Fig. 1. Al single pulse MAS-NMR spectra of the metakaolins A (a) and B (b) with spectra simulations.

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Refractory paints based on silicon carbide (SiC) were developed using inorganic alkali aluminosilicates binders. In order to optimize the binders, different raw materials have been tested for their preparations (calcined kaolin, commercial metakaolin, α-alumina and fumed silica synthetic powders). The alkali activator was an aqueous solution of KOH/K2SiO3. The SiO2:Al2O3 molar ratio was equal to 4 and the SiO2:K2O molar ratio was 2. Calcined kaolin and metakaolin in alkaline conditions dissolved and re-precipitated to form geopolymer resins acting as a glue for the un-reacted Al–Si materials and SiC (90 wt.%). Binders based on α-alumina and fumed silica behaved as water glass. Binders and SiC paints were tested and characterized in inert and oxidative atmospheres up to 1300 °C. The oxidation of the SiC paints was 50% lower than that of pure SiC, evidencing a key role of the alkali aluminosilicate binders during the thermal treatments.

This article originally appeared in Journal of the European Ceramic Society 31(12)2011, Pages 2155-2165

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