Preparation And Properties Of Mullite Whisker Thermal Insulation Materials

Energy consumption of metallurgical,building materials,chemical and other high temperature industrial energy consumption,accounting for more than 25%of the total national energy consumption,accounting for about 60%of the total industrial energy consumption.In the process of high-temperature industrial production,in addition to the composition of hate source,sintering process,combustion process,and kiln structure,the performance of refractory materials,especially thermal insulation materials,has an important impact on the energy conservation and consumption reduction of high-temperature industrial equipment and processes.Mullite thermal insulation materials has the advantages of high temperature resistance,low bulk density and remakable energy saving effects,which is widely used for thermal insulation linings of various high temperature thermal equipment.However,there are still some problems in mullite thermal insulation materials,such as the mismatch between bulk density and strength,the large thermal conductivity of mullite and the instability in reducing atmosphere,which seriously restrict its application and development.In order to solve the above problems,this paper hopes to prepare mullite whisker insulation materials with mullite whiskers as the main body,inherit the advantages of high strength and high toughness of the whiskers,improve the microstructure and improve the thermal insulation ability.Based on the characteristics of the formation process of mullite whisker,the relationship between the growth state of whisker and the microstructure and thermodynamic properties of thermal insulation material was studied in this paper.The results are as follows:（1）The effects of AlF₃?5H₂O and V₂O₅ on the growth process of mullite whiskers were compared.Al F₃ can promote the formation of gas phase reactants.Mullite whisker growth follows the V-S mechanism.The reactants are transported through the gas phase.AlF₃ can increase the gas-solid reaction rate and promote the formation of mullite.V₂O₅ can form a low-temperature liquid phase due to its low melting point,which increases the material transfer rate,promotes the solid phase reaction of SiO₂and Al₂O₃,and promotes the increase in the size of mullite whiskers.After the addition of ceramic fibers,with the assistance of the V₂O₅ liquid phase,vertically grown mullite whiskers were dissolved on the surface to form a fiber/whisker hierarchical structure.The formation of the graded structure and the effects of fiber bridging,pinning and pulling have significantly improved the strength of the sample.（2）The mullite hollow whiskers were synthesized in situ by solid-phase reaction method using industrial alumina and analytical pure Si O₂ as raw materials and AMT as catalyst.The formation mechanism is:Al₂O₃ reacts with WO₃ to form Al₂（WO₄）₃columnar particles about 900°C,which was coated with Al-Si-O aggregates.At about1000°C,Al-Si-O aggregates on the surface of Al₂（WO₄）₃ columnar particles were formed Mullite and developed constantly.The core of Al₂（WO₄）₃ columnar particles decomposes to form a mullite hollow structure at 1200°C.Increasing the amount of AMT and increasing the heat treatment temperature can lead to an increase in t he size of the hollow whiskers.The average diameter of the hollow whiskers was 1.26～7.53μm,and the wall thickness was 0.28～1.80μm.The in-situ formation of hollow whiskers can effectively improve the thermal insulation performance,and can improve the thermal insulation performance of the material by 1.46～1.66 times under the same conditions.（3）The mullite heat insulation material with graded pore structure was prepared by foaming method.Impurity oxides can reduce the formation temperature and viscosity of the liquid phase,increase the amount of liquid phase formation,promote material transport,and promote the formation and development of mullite whiskers.After adding Al（OH）₃,the diameter of mullite whiskers in the sample decreases,the length increases,and the bulk density decreases.At the same time,the pores formed by the decomposition of Al（OH）₃ form"window holes"in the macropores.（4）After being treated with carbon,the mullite in the sample decomposed,resulting in the relative content of mullite decreasing with the time of burying the carbon.The reaction product mullite will slow down the decomposition of mullite.The initial treatment of carbon burial promotes the development of mullite whiskers,resulting in an increase in the aspect ratio,and therefore an increase in strength.Fe₂O₃ can reduce the erosion resistance of mullite thermal insulation materials.When Fe₂O₃ was reduced in a CO atmosphere,it would promote the decomposition of mullite.Its decomposition products can act as a catalyst for CO disproportionation reaction,leading to the decomposition of material components and the formation of cracks.Increasing the temperature of buried carbon will aggravate the decomposition of mullite and reduce the strength and fracture toughness of the sample.