Study Of SiC Porous Ceramics With Directional Lamellar Structure Prepared By Freeze-casting Process

Aluminum composite material exhibit excellent propertie s of high strength,high toughne ss and other excellent features benefit from lamellar structures similar to the shell.As a kind of the t ypical reinforcement for aluminum composite material similar to the shell,the research for layered and pol yporous ceramic is the base for the preparation of high performance aluminum composite material similar to the shell.Directionall y frozen casting method has become preferred technology layered and pol yporous ceramic because of the advantages of simple operation,low cost,environmental protection.Although Si C/Al composite have been widel y used,while the high performance Si C/Al composite material similar to the shell still needs further study.Therefore,this work focuses on the study of layered Si C porous ceramics,which makes preparation for the next for the manufacture of Si C/Al composites similar to the shell used layered Si C porous ceramics as reinforcement.In this paper,la yered ceramic porous SiC ceramics were prepared by using directionall y frozen casting method by using Si C as raw material,water as the solvent and carrageenan,dispersant,PEG and gl ycerol as additives.The micro porous morphology of layered Si C porous ceramics was characterized and the mechanism of the formation of pores was summarized.The effects of various factors on the micro pore morphology of layered Si C porous ceramics were anal yzed.The main results are displayed as follows:With the increase of the distance between sample and cold source,the zone of densit y,transition and layer appear in succession,and the three zones show honeycomb,columnar and lamellar pore morphology,and the pore size range from 10 ~80 ?m.The pore forming mechanism is mainl y related to the cr ystal structu re and cr ystallization kinetics.The conditions of forming the layered pores are affected by factors such as solid content,freezing temperature,particle size and gl ycerol content.When the solid concentration increased from 20 vol.% to 35 vol.%,the porosit y decreased from 68.8 vol.% to 52.3 vol.%,pore diameter decreased from 84 ?m to 14 ?m and the wall thickness of ceramic increased from 37 ?m to 72 ?m;When the freezing temperature is-5 ?C,porosity presents disordered structure,w hen the freezing temperature is below-10 ?C,the porosit y presents layered structure,the lower the freezing tem perature is,the smaller the pore size of the ceramic wall is and the average pore diameter is 63 ?m when the freezing temperature is-30 ?C.The diameter of particle has an effect on the outline of pores and surface roughness for ceramic,the results indicate porous ceram ics composed of small particles has a clear outline,smooth surface and complete copy for the morphology of ice crystals.When the gl ycerinum increased from 3 vol.% to 6 vol.%,the diameter of pore decreased from 109 ?m to 46 ?m,the ceramic wall decreased from 49 ?m to 22 ?m,however,appl ying more gl ycerinum has little impact on the pore diameter and ceramic wall and pore has a transformation from layer to alveolate.Further,when the gl yceri num was 12 vol.%,the pore has become alveolate structure completel y.In this paper,the directional Si C porous ceramics were prepared through directional freezing method by adj usting the solid content,freezing temperature,gl ycerol content and particle size to control the pore morphology of layerd Si C porous ceramics.