Study On Preparation At Low Temperature And Properties Of Silicon Carbide Foam Ceramics

Silicon carbide foam ceramics,which have excellent properties,such as high passability,specific surface area,good heat insulation,excellent thermal shock resistance and high temperature performance have wide application prospects in automobile tail gas treatment,industrial wastewater treatment,catalyst carrier,molten metal filter and insulation materials and so on.Silicon carbide foam ceramics were prepared at 800?and 950?by polymer sponge replicas method with polyurethane sponge as template,aluminum dihydrogen phosphate as binder,silicon carbide powder as aggregate,and then the ceramics by different binders were treated at high temperature.The effect of aluminum dihydrogen phosphate content,solid content and treatment temperature on linear shrinkage,volume density,flexural strength,porosity and microstructure of the silicon carbide foam ceramics were studied,and the pyrolysis characteristics of aluminum dihydrogen phosphate and the sintered mechanism of silicon carbide ceramic were revealed by TG-DSC,XRD,SEM,universal testing machine and hydraulic balance analysis methods.The results showed that the linear shrinkage of the SiC foam ceramics prepared at 800?was less than 1%,the volume density was less than 0.6g/cm³,the flexural strength was?1.24±0.01?MPa when the aluminum dihydrogen phosphate and SiC contents were 40%and 60%,respectively.The linear shrinkage of the SiC foam ceramics prepared at 950?was more than 1%,the volume density was less than0.5g/cm³,the open porosity was from 75%to 91%.With the increase of the aluminum dihydrogen phosphate content,the SiC foam ceramic microstructure has microcracks and they gradually increases.the through-hole structure of the SiC foam ceramics was good,when the aluminum dihydrogen phosphate and SiC contents were 30%and60%,respectively.the flexural strength of the SiC foam ceramics was?2.22±0.26?MPa when the aluminum dihydrogen phosphate and SiC contents were40%and 60%,respectively,the silicon carbide powder was coated and bonded with metaphosphate.After high temperature treatment,the open porosity of preparation of SiC foam ceramics by phosphate binder at low temperature increased firstly and then decreased with increasing temperature.At the treatment temperature of 1000?,the flexural strength reached maximum.At the treatment temperature of 1400?,the flexural strength was minimal.The silicon carbide powder was coated and bonded with Al?PO₃?₃ and Al PO₄ phase.After high temperature treatment,the open porosity of preparation of SiC foam ceramics by double binders at low temperature increased with increasing temperature,while flexural strength increased firstly and then decreased.At the treatment temperature of 1400?.The flexural strength reached?1.43±0.12?MPa,the silicon carbide powder was coated and bonded with Al PO₄ and mullite phase.Dihydrogen phosphate converted to six-membered cyclic aluminophosphate Al₂P₆O₁₈ at 561?,then the six-membered cyclic metaphosphate began to transform to a quaternary cyclic aluminum metaphosphate Al₄(P₄O₁₂)₃ at 680?,furthermore most of the B-Al?PO₃?₃ transformed to A-Al?PO₃?₃ At 950?and A-Al?PO₃?₃ was decomposed into Al PO₄ and P₂O₅ gas at the same time,and finally Al?PO₃?₃ was accelerate decomposed into Al PO ₄ and P₂O₅ gas after 1100?.