Study On Properties Of Silicon Carbide Ceramic Slurry With High Solid Content And Preparation Of Ceramic Foams

Silicon carbide ceramic foams has a promising prospect in the filed of molten metal filtration, because it has unique combination of properties such as high temperature resistance, corrosion resistance, high porosity, large specific area, and so on. In this thesis, using Si C powder as the main raw material, alumina and clay as sintering aids, the dispersants and their content, p H value and solid content on the rheological properties and stability of Si C ceramic slurry were studied. O n this basis, silicon carbide ceramic foams was prepared by the replication process with polyurethane sponges as the templates. The results obtained in this thesis are as follows:（1） The effect of p H value and the dispersants on the properties of silicon carbide ceramic slurry were studied. The result shows that the isoelectric point（IEP） of the original Si C powder is between 4 and 6 in p H, and the absolute value of Zeta potential is 44.8 m V. And when 0.6 wt% PEG, 0.4 wt% Na₂SiO₃ and 0.2 wt% CMC were added, isoelectric point migrates to the acidic region, and when the p H is about to 10, zeta potential absolute value to 70.3 m V, 61.1 m V and 75.1 m V, respectively. The conclusion is that the fluidity and stability of Si C slurry are best when p H is about 10.（2） The effect of dispersants and their content on the properties of silicon carbide ceramic slurry were studied. The result shows that when PEG and Na₂SiO₃ are increasingly added, the viscosity and sedimentation of Si C slurry first decreased and then increased. when the content of PEG and Na₂SiO₃ are 0.6 wt% and 0.4 wt%, the viscosity of Si C slurry is on its lowest level（6.8 Pa·s and 2.3 Pa·s）, and its rheological property and stability are the best. With the content of CMC increased, the Si C slurry viscosity gradually increased, at the mean time, the sedimentation decreased. When the content of CMC is 0.2 wt%, the viscosity is on the lowest level（0.95 Pa·s）, and the dispersion effect is best. Using PAM as dispersing agent, its content should be less than 0.1 wt%, if we add more than 0.1 wt%, the result appears flocculation phenomenon, which is bad to slurry’s dispersion.（3） The effect of solid content on the properties of silicon carbide ceramic slurry was studied, when the p H is 10, CMC as dispersing agent with 0.2 wt%, along with the increase of the solid content, Si C slurry viscosity gradually increased, the best solid content was 65wt%. With the increase of shear rate, the viscosity of ceramic slurry showed a decreasing trend, and the flow curve showed obvious "shear thinning" phenomenon, which was a typical pseudo plastic fluid.（4） The effect of CMC, PVA, silica sol and dextrin on the properties of silicon carbide ceramic slurry were studied. The result indicates that the CMC has the most coating amount, and the slurry has best performance when the content of CMC is 1.5wt%. When using 1.5 wt% CMC and 5 wt% silica sol, we are abled to get 75wt% solid content. However, when the solid content is higher than 65 wt%, the viscosity increases too fast and the fluidity is poor, which are not beneficial to the impregnation.（5） On the basis of optimizing the technological condition, the thesis prepares Si C ceramic foams by using polymer replica technique. The results show that when CMC and silica sol mixes, the silicon carbide ceramic foams have fewer holes and uniform structure, at this time the compressive strength is 2.08 MPa.