| Summary: | The microstructure of a direct-bonded chromite-magnesia refractory brick, typically used in copper and platinum converters, was modified by adding different amounts of nano-size TiO<sub>2</sub> to the raw material mixture. Bricks with 0, 1, 3, 5, and 7 mass% TiO<sub>2</sub> were produced and compared in terms of spinel formation; the role of the tetravalent cation Ti<sup>4+</sup> in the bonding phase; as well as changes in density, porosity, thermal expansion, and internal stress. This was done through a comprehensive XRD and SEM-EDS study. It was found that Ti is accommodated in the secondary spinel that has formed, where Mg in excess of unity in the tetrahedral site combines with an equal amount of Ti in the octahedral sites to maintain charge balance. The 1 mass% TiO<sub>2</sub> brick had the lowest bulk density (but not significantly different from the original chromite-magnesia brick), the smallest difference in unit cell volumes between the primary and secondary spinels, and the lowest stress arising from the smallest difference in linear thermal expansion coefficients of the phases present. The calculated porosities correspond well with experimentally determined apparent porosity values, whereas the linear thermal expansion coefficients calculated at 1392K are similar to the values measured from 293 to 1273 K.
|
|---|
