Preparation Of Mullite Whiskers From Fly Ash And Study On The Modification Of Ceramics

Mullite is a stable phase of Al₂O₃-Si O₂binary system,which has low thermal expansion coefficient,eminent corrosion resistance,good mechanical properties and high temperature stability.Mullite whisker is a single crystal structure with mullite as crystalline phase.The introduction of mullite whisker into ceramic materials will significantly improve the strength and toughness of ceramic matrix,thereby improving the overall performance of the material.In this paper,mullite whiskers reinforced ceramic materials were prepared with industrial solid waste fly ash as main raw material,industrial alumina powder as external aluminium source and aluminium fluoride as whisker promoter by solid-state sintering method.Specific work include:1)Using fly ash as raw material and adding alumina as aluminium source,the influence of Al/Si ratio in raw material composition on mullite of ceramic material was studied;2)The preparation process parameters were optimized by orthogonal test method,including adding aluminium source,whisker promoter,binder and sintering temperature,and the effects of various factors on mullite and mechanical properties of ceramic material were studied;3)Mullite whiskers were produced by acid pickling pretreatment of fly ash raw materials,the mullite whisker-rich ceramic materials were prepared by referring to the optimized parameters obtained by orthogonal design in the previous work.The effects of acid pickling process and the amount of whisker promoter on the mechanical properties of ceramic materials were studied;4)The growth mechanism of mullite whisker and the modification mechanism of ceramic materials were analyzed.Mullite whisker-rich ceramic materials were prepared with fly ash as the main raw material.The effects of aluminium addition,whisker promoter addition,binder addition and sintering temperature on the flexural strength of ceramic materials were studied by orthogonal test method.The results showed that the order of influence degree of each parameter on the flexural strength of ceramic materials was sintering temperature>alumina addition>aluminium fluoride addition>binder addition.Mullite ceramics were prepared with fly ash pretreated by acid pickling.The results show that the process of pickling is an effective way to obtain mullite whiskers and improve the flexural strength of mullite ceramics.The process of pickling is helpful to the formation of mullite whiskers.Aluminum fluoride content and sintering temperature also have significant effects on the growth of mullite whiskers.With the increase of aluminium fluoride content,the process of mullite whisker formation is accelerated and the aspect ratio of the whiskers is improved.Mullite whiskers interweave with each other to form a dense network framework,which can improve the flexural strength of ceramics.In this study,fly ash as the main raw material to prepare light-weight,high-strength and economic ceramic materials is an ideal candidate material for ceramisite proppant for unconventional oil and gas resources development.