Preparation And Properties Of SiC All-Particle Porous Ceramics

Silicon carbide porous ceramics not only have the common characteristics of porous ceramics such as large specific surface area and high temperature resistance,but also have the characteristics of oxidation resistance,low specific gravity,thermal shock resistance and good corrosion resistance.They are widely used in sound absorption,heat insulation,filtration,and composite skeletons.However,the existing preparation process is complicated,with high preparation temperature and special requirements for equipment,and the resulting porous silicon carbide ceramics have low porosity and low strength,which are difficult to meet the needs of modern production.The coefficient of thermal expansion of SiC(4.4×10^-6℃^-1)is similar to that of Al₂TiO₅(9.5×10^-6℃^-1)is similar,so the use of aluminum titanate as a sintering aid can improve the thermal shock performance of SiC porous ceramics and make them more stable when applied at high temperatures.However,aluminum titanate has disadvantages such as easy cracking during high-temperature calcination,poor mechanical strength,and easy decomposition at medium temperature.By introducing MgO as well as CeO₂ as sintering additives,the generation of microcracks can be reduced and the densification process of aluminotitanate can be improved.It can effectively improve the disadvantages of poor mechanical strength of aluminosilicate titanate.The addition of CeO₂,on the other hand,mainly reduces the co-fusion temperature of the material,and the liquid phase is formed at the reduced temperature to promote the sintering of the material.Compared with other methods,this method uses millimeter-sized large particles of silicon carbide as the main raw material for the first time,while not using organic porous substances and dispersants,etc.It has the advantages of simple process,less organic additives,environmental friendly and low price,etc.The prepared porous ceramics have higher service temperature,adjustable pore size,and significantly improved corrosion resistance and lifetime.In this paper,Al₂TiO₅ was firstly prepared by solid phase sintering at 1400℃,1450℃,1500℃,1550℃ and 1600℃.Then,Al₂TiO₅ was used as binder,MgO and CeO₂ as sintering aids and PVB as molding binder to prepare the slurry for injection molding,and finally mixed with SiC particles and sintered to prepare SiC full particle porous ceramics.The effect of PVB content,solid content,SiC to slurry ratio on the rheological properties of the slurry and the sample forming was investigated.2 wt.%PVB content gave the best flow properties,easy demoulding and a more complete blank.At 70%solids,the surface of the dried blanks was homogeneous with no obvious exposure of SiC particles.The surface of the blanks with SiC to slurry ratios of 1:0.08 and 1:0.1 did not differ much and the blanks were intact,while the slurry was poorly wrapped around the silicon carbide particles and the grains fell out.Based on the above study,the effects of sintering temperature（1350℃to 1450℃）and holding time on the mechanical properties,thermal shock resistance and porosity and density of SiC porous ceramics were investigated.It was finally determined that the SiC porous ceramic blanks prepared by injection molding method with SiC particles and Al₂TiO₅ slurry（MgO content of 6 wt.%and CeO₂ of 3 wt.%）had the best performance at a sintering temperature of 1400℃and a holding time of 20 min.The density of 1.8713 g/cm3,porosity of 43.64%,flexural strength of 6.67 MPa,compressive strength of 14.24 MPa,and the maximum allowable temperature difference of 328.57℃showed the best thermal shock resistance with this ratio.The samples were not destroyed and the composition was stable after soaking in aluminum for 48 hours,and the binder aluminum titanate did not show decomposition.The selection of different sizes of silicon carbide particles can change the internal pore size of SiC full-particle porous ceramics,and also change the bulk density of the samples.The particle size of silicon carbide particles has a great influence on the mechanical properties of the samples.As the particle size of SiC increases,the pore size of the sample increases,but the porosity of the sample decreases,the bulk density increases,and the flexural and compressive strengths both decrease to some extent.