Preparation of novel magnesia aggregates with large grain size and high thermal insulation using brine Mg(OH)2

Abstract

Magnesia, as major components of MgO-based refractories, has high refractoriness and excellent resistance to cement clinker and basic slag. To address the environmental and quality issues of traditional sintered magnesia fabricated by magnesite, novel sintered magnesia with low thermal conductivity, large grain size and enhanced properties was produced at 1400 °C in air from brine Mg(OH)₂ with incorporating Fe₂O₃ addition. The results showed that adding Fe₂O₃ caused MgO lattice distortion and formation of MgFe₂O₄ phase, leading to obvious MgO grain growth and reduction of apparent porosity. Due to lattice distortion and formation of low thermal conductivity intergranular MgFe₂O₄ networks, thermal insulation was enhanced apparently. The MgFe₂O₄ formation lowered thermal expansion coefficient and caused transgranular fracture and crack deflection, effectively improving the thermal shock resistance. Besides, slag corrosion resistance improved with increasing Fe₂O₃ to 12 wt% because of the reduced apparent porosity and enlarged MgO grain size, but then lowered with further increasing Fe₂O₃ amount due to presence of more unstable intergranular MgFe₂O₄. The specimen with 12 wt% Fe₂O₃ showed optimum comprehensive performance with an apparent porosity of 0.5 %, average MgO grain size of 17.5 μm, flexural strength of 127.9 MPa, and thermal conductivity of 10.8 W/(m·K) at 500 °C.