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

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 Fe 2 O 3 addition. The results showed that adding Fe 2 O 3 caused MgO lattice distortion and formation of MgFe 2 O 4 phase, leading to obvious MgO grain growth and reduction of apparent porosity. Due to lattice distortion and formation of low thermal conductivity intergranular MgFe 2 O 4 networks, thermal insulation was enhanced apparently. The MgFe 2 O 4 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 Fe 2 O 3 to 12 wt% because of the reduced apparent porosity and enlarged MgO grain size, but then lowered with further increasing Fe 2 O 3 amount due to presence of more unstable intergranular MgFe 2 O 4 . The specimen with 12 wt% Fe 2 O 3 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. • Adding Fe 2 O 3 caused formation of cationic vacancies and MgFe 2 O 4 , promoting grain growth and elimination of open pores. • The networks of intergranular MgFe 2 O 4 phase significantly enhanced thermal insulation, strength and thermal shock resistance. • Corrosion resistance improved with increasing grain size, but reduced as more unstable MgFe 2 O 4 phase formed.