Effect of doping elements on the thermal stability of transition alumina

The thermal stability of porous transition alumina at high temperature is a crucial challenge for several applications. To delay the a to alpha -alumi na transition temperature (1180 degreesC), the synthesis by sol-gel method and the introduction of doping element as nitrate salt M(NO3)(x) (M=Ba, Mg, Pr, La and Ce) have been investigated. Over three preparation procedures, the introduction of the doping element through the sol-gel process gave the higher BET surface area. Additional thermal analysis and powder X-ray diff raction studies have shown that only a few amount (1 mol percent) of doping element is sufficient to increase the theta->alpha -Al2O3 phase transition temperature up to 1315 degreesC. The most promising samples are (Al2O3)(0. 98)Ba-0.02 and (Al2O3)(0.99)Pr-0.01. Even after 5 h at 1200 degreesC, they maintain a rather good specific area (32 m(2)/g) in relation with the incom plete and very slow transformation of theta into alpha -alumina. (C) 2001 E lsevier Science Ltd. All rights reserved.