Study On The Synthesis Of Cordierite And Whiskers In-Situ Reinforced Cordierite Thermal Insulation Materials

Cordierite with low thermal expansion coefficient,excellent high temperature thermal shock is a significant ternary compound of MgO-Al₂O₃-SiO₂ system.Cordierite ceramics can be used as automobile exhaust purification plant and the catalyst carrier etc,which makes the cordierite materials received unprecedented attention.Because the sintering temperature range of cordierite is relatively narrow and raw materials which synthesized cordierite have different chemical composition,which leads to difficult to use natural raw materials to prepare cordierite materials with low thermal expansion coefficient and good mechanical properties.What's more,cordierite lightweight materials not only have excellent properties of cordierite,but also have good corrosion resistance,high temperature resistance and heat insulation performance of lightweight materials.Thus,it is worth to study on the preparation of cordierite composites with optimized microstructure and excellent performance,while synthesize high-quality cordierite.This paper study on using different raw materials and methods to prepare cordierite materials firstly,which optimizes raw material ratio and process flow,explores the phase evolution process of cordierite synthesis as well.That provides theoretical guidance for obtaining high-quality cordierite materials.Then,the additive ZrO₂,WO₃ and ceramic fibers are added in cordierite materials.The influence of addition methods and the type of ceramic fibers on the thermal expansion coefficient and microstructure of cordierite materials have been studied.Last but not least,cordierite insulation materials and cordierite-mullite lightweight insulation materials are prepared with adding ceramic fibers and AlF₃ by using starch consolidation molding process.The ceramic fiber/mullite whiskers hierarchical structure in-situ generates.The formation mechanism of the structure and its effects on the properties of materials is investigated.The main work and results are as follows:?1?Cordierite materials are synthesized by using kyanite,andalusite,clay,talc as raw materials.The materials and processes used to synthesize cordierite have great influence on its properties.Cordierite materials synthesized by using talc and kyanite as raw materials have better densification degree.On the basis of one-step calcination,synthesized cordierite with pre-synthesized cordierite clinker by using two-step calcination,that the peak strength of cordierite phase enhanced obviously.When the ratio of pre-synthesized cordierite clinker and raw material is 2:1,specimens have the maximum bulk density 2.18 g/cm³,while the apparent porosity is 13.9%.The well developed cordierite grains have larger size.?2?Cordierite materials are synthesized by using pre-synthesized spinel,pre-synthesized mullite and pure oxide as raw materials,exploring the phase evolution process of cordierite synthesis.Results show that no matter what phase is contained in the starting materials,cordierite begin forming at 1250?,and there is spinel phase in the evolutionary process.The densification of cordierite materials synthesized by using pre-synthesized spinel or mullite as the starting materials is significantly better than specimens synthesized by using pure oxide as the starting materials,and its crystal grown more completely.?3?The influence of introducing ZrO₂,WO₃ and ceramic fiber on the thermal expansion coefficient of cordierite materials have been studied.ZrO₂ can promote cordierite phase generated and reduce the thermal expansion coefficient.The cordierite materials synthesized by using natural containing zirconium kyanite as raw material have the lowest thermal expansion coefficient.WO₃ can reduce the synthesis temperature of cordierite and eliminate the mesophase spinel at the same time.Cordierite materials with natural containing zirconium kyanite as raw materials introduced 15 wt.%WO₃ have higher densification degree and smaller thermal expansion coefficient.Cordierite materials added aluminosilicate ceramic fibers have improved thermal expansion coefficient and strength.?4?Cordierite-mullite lightweight insulation materials with high performance are prepared by using starch consolidation molding process.These materials by using wheat starch as pore former and curing agent have uniform-distributed pores and the highest strength,and cordierite crystals are well developed in the hole left by burning out starch.The well developed whiskers generated on the surface of ceramic fibers can be observed in specimens introduced ceramic fibers under the action of AlF₃.Cordierite-mullite lightweight insulation materials have obviously improved mechanical properties and low thermal conductivity.?5?Cordierite insulation materials with aluminosilicate ceramic fiber/mullite whiskers hierarchical structure are synthesized by using starch consolidation molding process.When aluminum silicate ceramic fiber?glass?crystal,then form small size mullite crystal nucleus,and rich silica fiber with silicon source to promote the formation of mullite whiskers..While there will generate low melting point of the liquid phase which can block the escape passage of gaseous AlOF and SiF₄ in the sintering process.The mullite whiskers grow well on the aluminosilicate ceramic fibers'surface,and the whiskers are partially interspersed among the well-developed hexagonal prism-shaped cordierite crystalline.The prepared cordierite materials had obviously improved mechanical properties and reduced thermal conductivity due to the aluminosilicate ceramic fiber/mullite whiskers hierarchical structure.The in-situ formed mullite whiskers constructed an interlocking structure,which improves the mechanical properties.In addition,the mullite whiskers formed in the pores can disperse heat during the conduction process,and the longer conduction path lead to reducing thermal conductivity.