final calcination temperature alternatively one can use a separate intermediate drying at 100 u00b0 to 200 u00b0 c for about 0 5 to 4 hours two different types of aluminum oxide were used for the following examples their properties are shown in table i below table 1______________________________________properties of aluminum oxide aluminum oxide i aluminum oxide ii______________________________________manufacturer norton rhone poulenctype sa 6276 spheralite 501aspecific surfacearea 200 m sup 2 g 320 m sup 2 gbulk density 420 590 g liter 800 g literpore volume 0 9 1 ml g 0 45 ml gwater uptake 90 g 100 g al sub 2 o sub 3 52 g 100 g al sub 2 o sub 3granule diameter 3 mm 3 mm______________________________________ 1 kg aluminum oxide i was impregnated with 8 by weight potassium tungstate using pore volume impregnation the details of the process were as follows the aluminum particles were first calcined in air for 4 hours at 455 u00b0 c the potassium tungstate solution was made by suspending 66 6 g tungstic acid in 500 ml water and dissolving 29 9 g potassium hydroxide in 450 ml water the two components were mixed and heated to 95 u00b0 c with stirring a clear solution formed the solution was sprayed over granules in a rotating coating pan the volume of the impregnating solution was about 110 of the experimentally determined water uptake of the particles used the impregnated granules.