Preparation And Properties Of Unfired Magnesia Refractory

The ladle is an important equipment for secondary refining.Mg O-C refractories are usually used in the slag line of refining furnace,but it can not meet the clean steel smelting.Magnesia refractories possess some advantages,such as no polluted molten steel and excellent corrosion resistance,but it has poor thermal shock resistance and penetration resistance.In order to cope the above problems,the unfired magnesia refractory was prepared and the effect of additives on the microstructure and properties of magnesia refractories were explored.Through systematic research,the following conclusions were drawn:（1）The raw material form the magnesium citrate,magnesium gluconate during the mixing and curing and glucose and its compounds are dehydrated and condensed,improving the green mechanical strength of the sample.Compared with in air,when the temperature is higher than 1100°C,not only AlN and MgAl₂O₄ whiskers but also Al₄C₃ are detected in coke bed.But the sintering process is insufficient and addition of metallic aluminum causes volume expansion,which reduces the cold strength of the sample.（2）In air,the sample with Al-Si alloy is more conducive to the formation of AlN whiskers,plate-like MgAl₂O₄ and Mg₂SiO₄ crystal grains at high temperatures.Therefore,it has higher cold mechanical strength than the sample contanining Si in the same heat treatment temperature.Introducing Si C and Si₃N₄ contanining metallic aluminum respectively into the sample,compared with metallic additives,Si C and Si₃N₄ have a stronger covalent bond and a lower self-diffusion coefficient,which inhibits the sintering process of the samples,so the cold mechanical strength is lower.（3）In coke bed,introducing the Si,Al-Si alloy,Si C and Si₃N₄ can in situ form AlN whiskers,columnar/granular Mg₂SiO₄ grains,and rod-shaped MgAl₂O₄ grains during the heat treatment process,which is conductive to improve the cold mechanical strength.Compared with sample heat treated in air,the sintering process of the sample is poor in coke bed,which is harmful to its densification.Therefore,the cold strength of the sample after heat treatment at the same temperature is lower.（4）Research on the slag resistance shows that CaMgSiO₄ and Fe_0.18Mg_1.82SiO₄are formed in the corrosion area of the sample in air;Fe₃O₄ is also formed in the corrosion area in coke bed,which is beneficial to increase the viscosity of the slag.The rod-shaped MgAl₂O₄ and long columnar Mg₂SiO₄crystal grains formed in grain gaps of the original layer,which improved the corrosion resistance.Compared with Si,Al-Si alloy preferentially react with Mg O in situ form rod-shaped MgAl₂O₄ and long columnar Mg₂SiO₄ grains at high temperature,which improves the thermal shock resistance and fracture toughness of the sample;but in coke bed the sintering process of sample inhibited and resulting in loose structure,so the thermal shock resistance and fracture toughness of the sample are low.