Several Factors Affecting Faster Rates of Gibbsite Formation

A rigorous study of the experimental conditions for the obtention of several aluminum hydroxide gels was performed. To obtain different alumina hydrate phases, some of the key factors which affect the rates of formation like precipitation temperature, ammonia concentration, and aging and pH conditions were studied. The alumina hydrates obtained such as amorphous gels, boehmite, bayerite, and gibbsite were calcined under controlled conditions, to yield the final δ- and α-aluminas. Either the intermediate alumina hydrates or the final alumina oxides were structurally characterized using SEM, TG, XRD, and nitrogen physisorption (BET areas and pore distributions) techniques in order to understand the key factors that control faster rates of hydrates formation. Large amounts of gibbsite were obtained under aging times of 1 week, compared with the reported several months. Then, pure α-Al 2 O 3 with surface areas of about 40 m 2 /g was easily obtained from gibbsite. α-Al 2 O 3 with less than 10 m 2 /g was usually obtained from bayerite.