Basic Research On Controllable Lightweight Technology And Application Of Magnesia Refractory

With the rapid development of high temperature industry of iron and steel metallurgy,it is particularly important to improve the thermal insulation performance of the refractory insulation layer for basic lining.In order to effectively reduce the heat loss of lining materials and maintain the stability of the molten steel temperature,it is an important measure to develop a lightweight magnesia refractory material with high porosity,low thermal conductivity and high strength as thermal insulation lining.From the current research on the lightweight process of magnesia refractories,the main obstacles affecting its industrial application are the poor thermal shock stability,large thermal conductivity and single pore-forming mechanism of Mg O.In view of the above problems,the caustic calcined magnesia is used as raw material,the magnesite with abundant reserves in China is selected as homologous pore-forming agent,and the sol impregnation technology is combined to carry out the controllable lightweight design of magnesia refractories in this paper.Finally,the thermal insulation effect of the lightweight magnesia refractory insulation layer on the molten steel is tested by simulating the temperature field of the eight-flow tundish.The non-isothermal kinetic model of the thermal decomposition of magnesite is regulated,the heating system during the calcination process of magnesite is set,the non-isothermal kinetic parameters of MTD by the two approximation functions at different heating rates is calculated,and the regulation of heating rate on the evolution of the microscopic morphology of the sintered magnesite particles is explored.The study find that the increase of the heating rate promotes the decomposition rate curve and reaction rate curve of magnesite to move to high temperature;According to the linear relationship between the activation energy and the pre-exponential factor in the magnesite thermal decomposition process,the Doyle approximation function is an effective method to obtain the kinetic parameters of the non-isothermal magnesite thermal decomposition reaction;Magnesia formed from magnesite at a heating rate of 10℃/min is a network-like particle with uniform distribution.The controllable lightweight mechanism of magnesia refractories is explored.The different mass ratios of magnesite fine powder and caustic calcined magnesia powder are used to synthesize lightweight aggregates of different particle sizes,and lightweight magnesia refractories are prepared by particle composition.A magnesite sintering kinetic model is established,and the microscopic pore-forming mechanism of magnesite is explored on the basis of process pore-forming.The study find that the residual vacancies formed by CO₂discharged from magnesite（the first-step pore-making）,the porous periclase microcrystalline aggregates formed by the original salt pseudomorph,and the particle gradation（the second-step pore-making）together promoted the lightweight of the materials;When the optimum pore-forming agent content is20 wt%,the pore size of the lightweight magnesia refractory sintered at 1600°C is controlled within the range of 2.6～3.2μm.The hierarchical porous-lightweight technology of magnesia refractories is further studied.The Mg（OH）₂ sol synthesized by chemical method is impregnated into the magnesite fine powder to form a composite pore-forming agent.The isothermal kinetics in the dehydration process of the Mg（OH）₂ sol and the sintering phase transition mechanism of the composite pore former are studied,and then the control mechanism of the micro-nano composite pore size is explored.The prepared lightweight magnesia refractory material is applied to the thermal insulation layer of the tundish lining.The eight-flow tundish of a steel plant as the research object,the temperature field of molten steel in the tundish is numerically simulated,and the influence of different types of thermal insulation layers on the temperature change of the tundish is investigated.The study found that there is the best thermal insulation effect to the magnesia refractory aggregates of micro-sized and nano-sized double pores structure with the low thermal conductivity and the cold crushing strength controlled in the range of 0.364～0.549 W·m^-1·K^-1 and 4.9～21.4 MPa,respectively.It provides a theoretical basis for the industrial application and research methods of lightweight magnesia refractories in metallurgical thermal insulation lining materials.