Research On Preparation Of Nanocrystalline Magnesium Aluminium Spinel Transparent Ceramic

Nanocrystalline magnesium aluminium spinel transparent ceramic, which has goodtransmittance, high strength and good fracture toughness, has been widely used in bothmilitary and civil use. In this work, nano spinel powder was obtained through thermaldecomposition method with high pure MgSO4·7H2O and AlNH4(SO4)2·12H2O as rawmaterial. The influence of different sintering temperature and doping concentration onthe properties and microstructure of ceramic when sintered in vacuum was studied. Newmethod for sintering nano transparent ceramic under vacuum was explored.The synthesis method of magnesium aluminium spinel powder was studied at600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃and 1200℃. The X-RayDiffraction(XRD) results of powder shows there were no magnesium aluminium spinelphase when calcination temperature was below 800℃; phase pure magnesiumaluminium spinel was obtained when calcination temperature was above 900℃. Thecalculated results of Scherrer Formula shows the particle size was between 10 and 20nmwhen calcination temperature was 900℃; the particle size was below 100nm when thecalcination temperature was between 1000 and 1200℃. The powder was analysed byHigh Resolution Transmission Electron Microscopy(TEM), the particle size wasaccordant with calculated results, the powder has strong dispersity.The obtained was used as raw material, doped with yttrium oxide by 0.2%, 0.3%and 0.4% to prepare magnesium aluminium spinel ceramic at 1350℃, 1400℃, 1450℃and 1700℃. The SEM results shows with the same doping concentration, the grain sizegrows with the calcination temperature, the ceramic crystallized better when the sinteredat higher temperature, The doping concentration of 0.4wt% Yttrium oxide was optimalin inhibition of grain growth. Sintered at 1700℃, the sample has good micro-structureas transparent ceramic, its grain size was over 50μm and grain boundary was indistinct.