Research On Mullite Ceramic Materials Prepared By Reaction Sintering

Mullite is traditionally used as lining refractories on furnaces that has high melting point, low expansion, excellent creep resistance and chemical stability. Mullite is gradually used as a high temperature engineering ceramics with the technology development of high purity and ultrafine mullite. Mullite ceramics are produced as high temperature sagger, thermocouple tubes, crucibles and heat pads and nozzles that have excellent high-temperature thermal and mechanical properties It is poor sintering property for mullite ceramics prepared from fused and sintering method because of small interdiffusion rate of Si4+ and Al3+. Reaction sintering mullite ceramic was prepared from andalusite and activated alumina, by processes of ultra-fine grinding, dry and isostatic pressing. The effect of divalent(Mg2+ and Zn2+), trivalent(La3+ and Y3+) and tetravalent(Ti4+ and Ce4+) metal oxides on composition, structure, sintering and thermal shock resistance was studied. The results show that mullite ceramic can be prepared by solid reaction of andalusite and activated alumina as raw material that solid-state reaction as main crystalline phase.The sintering property can be promoted to some extent by different valence metal oxides through calculation of bulk density and apparent porosity. The bulk density can reach 3.107 g/cm3 for Y4 sample with 8% Y2O3 added, which is equivalent 98.3% of theoretical density. Compositon of reaction sintering mullite ceramics was qualitative analyzed. Lattice parameters of main phase mullite solid solution were quantitative calculated. Main phase mullite solid solution type and main phase lattice parameters and cell volume were influenced by different types and quantities of dopant ions. Spinel can be produced easily in mullite ceramic due to Mg2+ and Zn2+ doped. Mullite solid solution can be tranformed from Al4.52Si1.48O9.74 into Al4.59Si1.41O9.70 and Al4.64Si1.36O9.68 gradually owing to different numbers of La3+ doped. Lattice parameters and cell volume of mullite solid solution phase increase with the amount of Ti4+ and Ce4+ doped. Lattice parameters a, b, c and cell volume v of main phase in C4 specimen with 8% CeO2 doped reached 0.7557 nm, 0.7693 nm, 0.2886 nm and 0.1678nm3. The sintering and thermal shock resistance of reaction sintering mullite ceramic can be reflected by compressive strength before and after thermal shock and retention rate indirectly. The results showed that the sintering property of reaction mullite ceramic can be promoted significantly by MgO, Y2O3 and CeO2. Thermal shock resistance of reaction sintered mullite ceramic can be improved by significant amount of TiO2 and CeO2 introduced.