LUO Haoming ^1,2, HAN Dan ¹, ZHANG Jian ^{1, 2}, WANG Shiwei ^{1, 2}

(1. The State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, ChineseAcademy of Sciences, Shanghai 200050, China；2. Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Sciences, Beijing 100049, China)

Abstract: Magnesium aluminate spinel transparent ceramics have excellent optical and mechanical properties, making them an ideal candidate for infrared windows. Commercial magnesium aluminate spinel powder was used as raw material, which was washed with  acid to reduce the  content  of impurities. ICP, XRF and  SEM were  employed to  check the  efficiency  of the acid-washing process  in reducing the  content  of impurity  and  improvement  in microstructure  of the powder.  Magnesium aluminate  spinel transparent  ceramics were  obtained through pressureless presintering,  followed by hot isostatic pressing, without  using  any  sintering  aids.  The  effects  of acid-washing  on  densification  process  and  properties  of the  transparent magnesium  aluminate  spinel  ceramics were  systematically  studied.  HNO₃ acid-washing  is  an  effective way to purify  the powder, reducing the content of K, Ca and Na to be less than 1 ppm, while the particle size and surface morphology were not affected and no agglomeration was brought out. Moreover, HNO₃  acid-washing resulted in an increase in sintering activity of the spinel powder. Comparatively, pre-sintering temperature of the HNO₃  acid-washed powder was reduced by 30 ℃, thus leading to relatively lower sintering temperature to fabricate the transparent ceramics. The sample derived from the HNO3 acid-washed  powder  exhibited  transmittance  of 87%  at  1100  nm  to  be  closer  to  the  theoretical  level  and  had  stronger mechanical properties.
Key words: MgAl₂O₄ ; powder; transparent ceramic; acid-washing; sintering activity; densification