Abstract
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 TiO2 to the raw material mixture. Bricks with 0, 1, 3, 5, and 7 mass% TiO2 were produced and compared in terms of spinel formation; the role of the tetravalent cation Ti4+ 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% TiO2 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.
Highlights
Magnesia-chromite and chromite-magnesia bricks are mainly used in the non-ferrous industry (in smelters and converters used in platinum group metal (PGM), copper, nickel, and lead extraction), and in vacuum degassers in the steel industry and CLU (Creusot-Loire-Uddeholm) converters in the ferroalloy industry [1,2,3,4]
The energy dispersive analyses clearly show that the Ti is exclusively incorporated in the secondary spinel B that is primarily associated with the periclase
The impact of adding micro-size TiO2 to a chromite-magnesia brick formulation was examined in terms of phase formation and how it impacts on the physical and thermal properties of the brick
Summary
Magnesia-chromite and chromite-magnesia bricks are mainly used in the non-ferrous industry (in smelters and converters used in platinum group metal (PGM), copper, nickel, and lead extraction), and in vacuum degassers in the steel industry and CLU (Creusot-Loire-Uddeholm) converters in the ferroalloy industry [1,2,3,4] These bricks have the benefit of enhanced thermal shock resistance as compared to magnesia-based materials, as well as high corrosion resistance with respect to slightly acidic to basic slags, to fayalitic slags that are rich in both silica and iron oxide [1,2,3]. Previous work has shown that direct bonding and the use of fused magnesia-chromite grains are essential in improving the properties of the bricks
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