Preparation And Performance Of In-Situ Cordierite Bonded SiC Composite Materials

Due to silicon carbide has high thermal conductivity,low thermal expansion coefficient,silicon carbide refractory materials with good thermal shock resistanc are greatly developed and widely used as kiln furniture in ceramics calcining kiln.However,silicon carbide has strong covalent bond and low diffusivity and it is very difficult to sinter SiC materials.Generally SiC are sintered under high temperature and high pressure even with sintering additives.Therefore,adoption of new technological process or addition of second-phase substance promotes SiC materials sintering.Currently,cordierite bonded silicon carbide composite materials attract wide attention because of the combination of the characteristics of cordierite and silicon carbide.In view of the facts that the poor combinability beteen oxide and non-oxide,the cordierite bonded silicon carbide composite materials usually have low strength,poor high-temperature performance and thermal shock resistance etc.In this work,using SiC as the aggregate and talc,clay,kyanite and quartz power as the matrix,cordierite bonded SiC composite materials were prepared by in-situ synthesis method.The effects of the kinds of matrix,the pre-oxidation of silicon carbide aggregate and introduction of Al₂O₃-SiO₂ ceramic fibers on the properties of cordierite bonded SiC composite materials were investigated.The main research achievements are as follows:?1?Different raw mineral materials are used as matrix materials to prepare cordierite bonded SiC composite materials.Even though the sources of magnesium oxide or aluminium oxide and silicon oxide in matrix are different,the phase of cordierite is formed when calcination temperature is 1250?,and the main crystal phases of the composite are silicon carbide,cordierite phase,and a small amount of cristobalite phase when calcination temperature is 1350?.The crystal of the composite materials with kyanite/andalusite/sillimanite as matrix grew better.Using talc/clay or magnesia/clay as matrix materials,the volume shrinkage was detected in the composite materials preparation process.However,using talc/kyanite,talc/andalusite or talc/sillimanite as matrix to prepare the composite,it has the volume expansion.Moreover,when talc/sillimanite was used as raw materials to form cordierite matrix,the volume effect was less obvious,the interface between the aggregate and matrix bonded more tightly.The rupture strength at room temperature and hot rupture strength at high temperature was 16.77MPa and 10.08MPa,respectively.?2?After pre-oxidation treatment,the forming amount of SiO₂ on the surface of silicon carbide particle is related to prtreatment temperature and holding time.The influences of pre-oxidation temperature on degree of SiC oxidation are greater than the oxidation time.The production of SiO₂ liquid-phase during the pre-oxidation of SiC particles promoted sintering densification of cordierite bonded SiC composite materials,and reduced porosity of the materials.The pre-treatment at 1400?and soaking time 4h is favorable to sintering of the composites,and the high rupture strength of samples can be obtained.It can be up to 15.23MPa.At the same time,the SiO₂ film produced by pre-oxidation treatment makes the interface in the sample particles have close combination and thus improves the thermal shock resistance.With the increase of pre-oxidation treatment temperature,the thermal shock resistance of cordierite bonded SiC composite materials is better.?3?Al₂O₃-SiO₂ ceramic fibers?2 to 10 wt%?were introduced to prepare cordierite bonded SiC composite materials.With the increase of Al₂O₃-SiO₂ fibers content,the apparent porosity of composite materials prepared under different calcination temperature showed a rising tendency and its bulk density showed a decrease tendency.The thermal shock resistance of the materials with the addition of Al₂O₃-SiO₂ fiber were remarkably improved and the mechanical properties of the materials showed a tendency of rising first and then declined.The strength reached maximum when the content of Al₂O₃-SiO₂ fiber is 8%.The compressive strength and rupture strength of the sample sintered at 1350?are 80.74MPa and 33.14MPa respectively,which respectively increases by 97.33%and 84.59%compared with the composite materials without ceramic fibers.