Preparation Of Sintered Corundum And SiC-Mullite-Zirconia Composite Materials By Nano-η-Al₂O₃ Powder

In this paper,dense sintered corundum was prepared by solid-state sintering at atmospheric pressure using nano-η-Al₂O₃ powder with high activity as raw material.The properties of sintered corundum under different sintering processes and the influence of sintering assistant titanium dioxide on its properties were studied.The sintering behavior of η-Al₂O₃ powder was analyzed by calculating sintering activation energy.The transformation mechanism of η-Al₂O₃ was analyzed by constructing a transformation model.In order to determine the optimum sintering process of mullite-bound phase in Si C-Mullite-Zirconia composite material,mullite was synthesized by in-situ solid state reaction sintering.The effects of different silicon sources and temperatures on the synthesis of mullite and the effects of sintering additive titanium dioxide on the properties of mullite were studied,and the formation mechanism of mullite was analyzed.On this basis,the properties of Si C-Mullite-Zirconia composite materials under different sintering processes were studied by buried carbon sintering after pre-oxidation treatment.Through the above research,the following conclusions are drawn:（1）At 1650 ℃ for 6 h,the bulk density of sintered corundum is 3.74 g·cm-3,and the apparent porosity is 1.7%;the intergranular bonding is tight,and the transgranular fracture is dominant,and the grain size is 3.5～7.5 μm;at this time,the low sintering activation energy of nano-η-Al₂O₃ is conducive to the low temperature preparation of dense corundum.（2）When the amount of TiO₂ is 2wt%,the bulk density of sintered corundum is more than 3.70 g/cm³ at 1600 ℃,the apparent porosity is the smallest,which is 1.2%;the crystal is well developed,and the grain size is 10-30 μm;the transformation from η-Al₂O₃ to α-Al₂O₃ takes place on the surface of alumina particles first.（3）Compared with quartz powder,silica fume and composite powder（white mud: quartz powder = 25:75）,the mullite synthesized at 1550 ℃ with white mud as silicon source has the best performance,with volume density of 2.86 g/cm³,apparent porosity of 3.5%,and flexural strength of 135.6 MPa;mullite crystal prepared with quartz powder and silica fume as silicon source is short column,mullite crystal prepared with white mud and composite powder as silicon source is long columnar.（4）Nano-η-Al₂O₃ first reacts with amorphous SiO₂ decomposed from white mudto form mullite.When reacting with SiO₂ in quartz powder and silica fume,η-Al₂O₃ first transforms into α-Al₂O₃ and then reacts with SiO₂ to form mullite.（5）When the amount of TiO₂ is 4wt%,the volume density of mullite synthesized from silica fume is 2.98 g·cm-3 at 1500 ℃,the apparent porosity is 2.3%,and the flexural strength is 285.1 MPa.（6）The bulk density of the composite material is 2.81 g/cm³,the apparent porosity is 3.1%,the flexural strength is 142.6 MPa,and the oxidation weight increase rate is 0.67% at 1600 ℃,and the instability of the composite material changes from c-ZrO₂ to m-ZrO₂ after calcination,which is evenly distributed in the sample.Mullite crystal is well developed and closely combined with silicon carbide.