Research On Lightweight Of Mullite-Cordierite Castables

With the proposal of sustainable development concept,energy conservation and emission reduction have gradually become a hot topic of concern.In order to achieve the goal of "carbon peaking and carbon neutrality",the low-carbon development of high-temperature industries such as steel,non-ferrous metals,building materials and petrochemicals is imperative.As the lining material of high-temperature industrial kilns,refractory materials are an important support for energy-saving,emission-reduction,and low-carbon development of high-temperature industries.On the other hand,refractory manufacturing also requires green and low-carbon sustainable development.Refractory castables are an important part of refractory materials,and have the characteristics of no need for firing,simple production process,easy construction and good overall air tightness.However,the existing refractory castables for the working layer of the existing high-temperature furnace adopt dense matrix and aggregates,and the thermal conductivity is high,resulting in high heat loss and energy consumption.Therefore,light weight,low cost,low thermal conductivity and high strength castables has become one of the development directions of refractory materials.In view of the above problems,the paper took mullite-cordierite castable as the research object,and the influence of various factors such as the type and amount of lightweight aggregates were studied,the amount of calcium aluminate cement,the type and amount of pore-forming agent on the microstructure,the phase composition and the physical properties of castables.An experimental scheme was proposed for realizing the lightweight of castables while little decreasing of the mechanical properties,which could provide guidance and reference for the lightweight of furnace lining materials and the energy saving of high temperature industrial kilns.In the research on the types and additions of lightweight aggregates,it is found that the addition of lightweight aggregates has a great influence on the properties of castables:the bulk density is significantly reduced,and the mechanical strength is reduced.The test results show that: compared with the castables with the microporous mullite aggregate,the castable with the lightweight mullite spheres has higher mechanical strength,lower thermal conductivity,and better energy saving and environmental protection effect;when the light mullite completely replaces the sintered mullite,the bulk density of the castable decreases significantly,the thermal conductivity decreases significantly,and the thermal shock resistance first increases and then decreases.In the study of adjusting the cement addition,it is found that with the increase of the cement addition,the hydration products increase in the dried sample,and the strength of the sample after drying is significantly improved.However,after high temperature heat treatment,the water evaporates,and the number of microcracks in the sample increases.The volume density of the sample decreases slightly,and the mechanical strength decreases,and the thermal shock resistance is improved.However,with the cement addition further increasing,a large number of cracks form,which destroy the structure,and the mechanical strength of the sample decreases,and the thermal shock resistance decreases.In the research of adding pore-forming agent,it is found that compared with the sample with other pore-forming agents,the sample with nano-carbon black has smaller the pore diameter of the pores formed,lower thermal conductivity;higher mechanical strength,and better thermal shock resistance.Nano-carbon black is a suitable pore-forming agent.With the addition of nano-carbon black increasing,a large number of micro pores are formed in the sample.The micro pores can alleviate the damage of thermal stress inside the material,and the thermal shock resistance of the sample is enhanced;the uniformly dispersed micro pores are not conducive to the heat transfer;so the thermal conductivity of the sample decreases.When the addition of nano-carbon black exceeds 0.5%,the pores merge and grow into large pores,destroying the internal structure,so the strength of the sample decreases,and the thermal shock resistance decreases,and the thermal conductivity increases.In general,the use of lightweight aggregate instead of dense aggregate and the further introduction of pores in the matrix by pore-forming agents are effective ways to reduce the weight of refractory castables.However,the composition of lightweight aggregate,the proportion of substitution,the selection and addition of pore-forming agents will affect the strength,the thermal shock resistance and the thermal conductivity of lightweight castables,which need to be comprehensively considered and utilized.