Preparation And Properties Of Porous Magnesium Aluminate Spinel Composite Ceramics

Porous spinel-forsterite and spinel-mullite composite ceramics were fabricated via an in-situ reaction sintering method using fused magnesia,alumina and quartz powders as starting raw materials,zirconia as admixture and sulphite liquor as binder.The phase compositions and pore characteristics were characterized by means of X-ray diffraction（XRD）and scanning electronic microscopy（SEM）.Apparent porosity and bulk density of sintered samples were measured by Archimedes principle,the flexural strength and compressive strength of the samples were measured in a electronic universal testing machine,and the residual flexural strength of samples were also characterized after three thermal shocks at 1000℃.The results show that:（1）30 wt%Al₂O₃was introduced into the MgO-SiO₂system,the magnesium aluminum spinel-forsterite composite ceramic was fabricated via an in-situ reaction sintering method sintering at 1450℃for 3 h.The porous ceramic possess apparent porosity of over 40%,high flexural strength of 22.95 MPa,and high compressive strength of 68.17 MPa.The phase composition of the sample are magnesium aluminum spinel,forsterite and some periclase.Microstructure indicates that magnesium aluminum spinel has a a typical octahedral shape,and forms a embedded structure with forsterite each other,2～5μm isolated pores are distributed uniformly,which is conducive to reducing the thermal conductivity and improving the mechanical properties of porous ceramics.（2）10 wt%ZrO₂was added into the Mg Al₂O₄-Mg₂SiO₄system,the magnesium aluminum spinel-forsterite-zirconia composite ceramic was fabricated via an in-situ reaction sintering method sintering at 1400℃for 3 h.MgO in raw material can be used as a stabilizer to stabilize part of t-ZrO₂at room temperature,ZrO₂grain with a size larger than the critical grain size may produce micro-cracks in the process of transforming into monoclinal phase,which plays a toughening and reinforcing effect.Flexural strength and compressive strength of porous magnesium aluminate spinel-forsterite-zirconia composite ceramics increase to 46.88 MPa and 176.59 MPa,respectively.Compare to the sample without ZrO₂,flexural strength and compressive strength are increased by 42.93%and 36.41%,respectively.（3）The mass ratio of alumina（Al₂O₃）and quartz（SiO₂）is 2.57,5 wt%MgO was introduced into the Al₂O₃-SiO₂system,the corundum-spinel-mullite composite ceramic was fabricated via an in-situ reaction sintering method sintering at 1450℃for 3 h.The porous ceramic possess apparent porosity of 26.46%,high flexural strength of 45.86 MPa,and high compressive strength of 270.25 MPa,and the retention percent of residual flexural strength is 27.06%after three thermal shocks.The formation of columnar ceramic grains is conducive to improving the mechanical properties of porous ceramic,when apparent porosity of samples increase from19.82%to 26.46%,flexural strength also increase from 21.63 MPa to 45.86 MPa.