Preparation And Mechanical Properties Of Zirconia Reinforced Mullite Porous Ceramics Via Foam-gelcasting Method

Mullite porous ceramics are widely used as thermal insulation materials,catalyst carriers,gas-liquid filtration and separation materials due to their excellent properties.Meanwhile,zirconia was widely used as ceramics reinforcement phase,because of it not only has the advantages of high melting point,good chemical stability and high strength,but also can significantly improve the strength of ceramics by phase transformation and particle dispersion in the matrix.In this thesis,zirconia reinforced mullite porous ceramics were fabricated via foam-gelcasting using mullite powder as raw material,Al₂O₃ and SiO₂/ZrSiO₄ as starting materials of mullite self-bonded phase,AlF₃·3H₂O,ZrO₂ and Y₂O₃ as additives.The influences of the content of foaming agent,mullite self-bonded phase powder content,and the type and content of the additive on the bulk density,line shrinkage rate,microstructure,mechanical properties at room temperature and thermal conductivity of zirconia reinforced mullite porous ceramics were studied.The research results showed that:?1?Zirconiareinforced mullite porous ceramics were prepared using mullite powder and 6 wt%AlF₃·3H₂O as raw materials,ZrO₂ and Y₂O₃ as additives.The mechanical properties of porous ceramics were significantly improved by added proper content of ZrO₂ and Y₂O₃.When ZrO₂ was 6 wt%and Y₂O₃ was 8 wt%,the compressive strength and flexural strength of as-prepared porous ceramics with 66.4%-porosity and the large pore diameter of 168?m respectively reached 14.3 MPa and 36.3 MPa,which were much better than that of mullite porous samples without Y₂O₃?flexural strength of 11.3 MPa and compressive strength of 29.4 MPa?.?2?Zirconia reinforced self-bonded mullite porous ceramics were prepared by foam-gelcasing method using mullite,6 wt%AlF₃·3H₂O and 6 wt%ZrO₂ powders as raw materials,Al₂O₃ and SiO₂ as self-bonded phase powders.The strength of mullite porous ceramics was significantly improved with addition of Y₂O₃.When the content of Y₂O₃ was6 wt%,the compressive strength of as-prepared porous ceramics with 66.8%porosity was25.1 MPa,which was about 1.3 times higher than that of mullite porous ceramic without additive.?3?The zirconia enhanced self-bonded mullite porous ceramics were prepared with porosity of 69.3%using mullite as raw material,ZrSiO₄ and Al₂O₃ as self-bonding phase powder and 0.6 vol%triethanolamine lauryl sulfate as foaming agent via foam-gelcasting method combined in-situ reaction sintering at 1600°C/2 h.The compressive strength of them reached 28.6 MPa,which was obviously superior to the strength of porous ceramics with the same porosity prepared by the conventional foaming method.The addition of Y₂O₃ further improved the mechanical properties of porous ceramics.When 6 wt%Y₂O₃content was added,the compressive strength of zirconia reinforced self-bonded mullite porous ceramic with a porosity of 67.1%had the highest value of 34.6 MPa,which was increased about 21.0%more than that of the sample prepared without Y₂O₃??4?Zirconia reinforced self-binded mullite porous ceramics were prepared via foam-gelcasting method,using ZrSiO₄ and Al₂O₃ powders as starting materials of self-binded mullite,AlF₃·3H₂O and Y₂O₃ as additives,respectively.the flexural strength ofas-prepared mullite porous ceramic with a porosity of 75.6%and the average pore size of 159?m reached7.7 MPa,which was about 42.9%higher than that of the porous sample prepared without additive.When the content of Y₂O₃ was 6 wt%,the flexural strength of zirconia reinforced mullite porous ceramics was 13.0 MPa,which was about 2 times higher than that of the porous ceramics with the same porosity prepared without Y₂O₃ additive.