THE EFFECT OF LANTHANUM AND BARIUM ADDITIVES ON THE THERMAL STABILIZATION OF GAMMA-AL2O3

The effect of La and Ba additives on the thermal stabilization of gamm a-Al2O3 was investigated through total-surface-area measurements. The parameters considered were additive content, calcination temperature, and calcination period. The effect of precalcination was also studied. It was found that thermal stabilization caused by 3 wt% La and Ba is superior to 6 wt% La or Ba, and the positive effect of 3 wt% La and 3 wt% Ba are almost identical. The nearly threefold increase in the tota l surface area of 3 wt% La or Ba doped samples calcined above the gamm a - alpha phase-transition temperature indicates that the aluminate co mplexes formed with La or Ba during phase transition impart thermal re sistance to sintering. Aluminate formation at these temperatures is ve rified by XRD measurements. Precalcination at 723 K stabilizes the gam ma-Al2O3 structure, leading to higher surface areas in the undoped sam ple upon sintering.