Effect of TiO₂ addition on microstructures and properties of MgO–CaO refractory aggregates

MgO–CaO (40 wt.% CaO) refractory aggregates were prepared using the calcined dolomite and light-burned magnesia fine powder as raw materials and TiO₂ as additive. The effect of TiO₂ on their phase composition, microstructures and properties was investigated by X-ray diffraction and scanning electron microscopy. The properties such as bulk density, apparent porosity, relative aggregate tube strength and hydration resistance were also investigated. The results showed that the CaTiO₃ generated by the reaction between CaO and TiO₂ was distributed around the CaO grain boundaries and intermittently distributed with MgO, which formed an isolation layer around CaO and greatly improved the hydration resistance. Meanwhile, the introduction of TiO₂ promoted sintering and increased the grain size, further improving the strengths and hydration resistance of the materials. In addition, the most significant enhancement in the hydration resistance and strengths of the samples was achieved when 1.0–2.0 wt.% TiO₂ was added. In this case, the relative strength of aggregate increased from 33.3% to 37.3%–43.1%, and the mass gain after the hydration test decreased from 3.13% to 1.26%–1.45%.