Chrome-free qandilite (Mg2TiO4) refractory aggregates: Role of titania source and evaluation of thermal expansion coefficient

As used chrome-based refractories may contain toxic Cr 6+ , the chrome-free Mg 2 TiO 4 phase is being considered which is known to improve hot strength and resistance to thermal shock and slag corrosion. As in situ Mg 2 TiO 4 formation generates porosity, preformed aggregates are desirable. Dilatometric studies revealed that when dead burned magnesia is combined with industrial anatase instead of rutile, it expanded less (1% versus 7.2%) and the reaction occurred earlier (965℃ compared to 1120℃). After sintering at 1600℃, rutile produced an aggregate with 3.8% open porosity, whereas anatase led to 0% porosity and a bulk density of 3.24 g/cm 3 with a thermal expansion coefficient (70-1600℃) of 13.5×10 -6 K -1 . Moreover, replacing rutile by anatase eliminates the undesirable MgTiO 3 phase. The anatase-based aggregate consisted of a Mg 2 TiO 4 matrix with residual unreacted MgO and an intergranular, refractory CaTiO 3 phase. The rutile-based aggregate was deemed unsuitable due to a low-melting microstructure of forsterite contiguous with CaTiO 3 .