Gelcasting And Properties Of The Transparent MgAl₂O₄ Spinel Ceramics

Transparent magnesium aluminum spinel?MgAl₂O₄?has been known as a polycrystalline optical material,being applied to transparent armour,infrared window and dome,with its excellent optical and mechanical property.The MgAl₂O₄ transparent ceramics forming process is vital in the kinds of fabrication technology.Transparent MgAl₂O₄ spinel ceramics were fabricated by traditional drying combined with clod isostatic pressing technology.However,there have been very few reports on fabrication of MgAl₂O₄ transparent ceramic by gelcasting.In recent years,a new gelling system of PIBM with small dosage of spinel powder,nontoxic and no oxygen polymerization,was developed.In this paper,the slurries of transparent MgAl₂O₄ ceramics have been prepared through aqueous gelcasting forming technique starting from commercial MgAl₂O₄ powders?T-20;S-30?.The stable slurries were puted through degassing,casting and drying processes,and sintered by vacuum pressure-less sintering combined with post-HIP,and finally the transparent MgAl₂O₄ ceramics with high optical quality were obtained.Main contents of the work were summarized as follows:1.The stable slurries containing 54 vol%solid loading?T-20?was prepared by dissolving 0.7 wt%of organic additive in deionized water,and then sintered the green bodies at 1650^oC with 1650^oC post-HIP.Finally the high transparent MgAl₂O₄ ceramics with an average grain size of 22?m and the in-line transmittance of 85.3%at wavelength 1100 nm had been obtained.2.The bending strength of the green bodies prepared from slurry with 50 vol%solids loading and 0.7 wt%Ib600 and 0.1 wt%Ib104 was found to reach 2.62 MPa.As the solids loading increased,the optical quality of the ceramics increased as well.3.The MgAl₂O₄ powder?S-30?should be pre-sintering to 1550 ^oC and then dispersed in an aqueous-organic solution,which can prepare stable slurries containing47 vol%solids loading.The in-line transmittance of sintered sample was 87%at 1100nm.The advantages of gelcasting spinel transparent ceramics with the PIBM gelling system,has been explored.By further optimizing the fabrication process,the future application of the spinel transparent ceramic can be expected.