Glass–ceramics and composites containing aluminum borate whiskers

Glass–ceramics and composites containing aluminum borate whisker crystals were developed using two different approaches: crystallization of an aluminum borosilicate glass or addition of an aluminum borate precursor powder to a glass frit. Two different glass frits were used, a commercially available borosilicate glass or the same aluminum borosilicate glass used in the crystallization experiments. X-ray diffraction analysis showed that Al4B2O9 or Al18B4O33 whiskers formed in all samples, indicating that the glass crystallized significantly with increasing heating temperature, and that the precursor can be effectively be used to generate in situ aluminum borate crystals within glass matrices. However, the samples produced by mixing the aluminum precursor with glass frits contained porosity after processing, indicating that pressureless viscous sintering was not efficient. The hardness of the glass–ceramic did not vary significantly with processing temperature, but the (indentation) fracture toughness measured showed a >100% increase (after heating at 1200 °C), demonstrating that whisker-shaped crystals are effective in increasing the mechanical toughness of the glass matrix. The hardness of the composites showed a dependence on the amount of aluminum borate crystals present.