Precipitation of the ultrafine equiaxial near-spherical gibbsite with low oil absorption value by adding mixed seeds

Abstract

Ultrafine, near-spherical gibbsite with a low oil-absorption value hold significant potential for use in advanced flame-retardant fillers, polishing materials and dense alumina-bearing ceramics owing to its regular morphology, high dispersibility and good flowability. In this study, ultrafine equiaxial near-spherical gibbsite with a medium particle size (d₅₀) of 359 nm and an oil-absorption values of 25.0 mL/100 g was precipitated by seeded precipitation from sodium aluminate solution. The mixed seeds, comprising bayerite and gibbsite, were prepared by the addition of NaHCO₃, Al₂(SO₄)₃, and H₂O₂, respectively. A high bayerite content in the NaHCO₃-induced seeds, combined with significant supersaturation fluctuations, enabled a precipitation efficiency exceeding 51 % at an initial temperature of 80 °C for 35 h. Preferential growth of the (110), (100), and (001) planes occurred during the early stage, followed by the emergence of the (101) and (112) planes in the mid-to-late stage. High supersaturation from bayerite dissolution and adsorption of Al(OH)₄⁻ ions promoted the development of (001), (110), (100), (101), and (112) planes, resulting in the formation of equiaxial near-spherical gibbsite. Furthermore, the low surface energy and high zeta potential of the well-crystallized gibbsite precipitated from NaHCO₃-induced seeds contributed to its low oil absorption. These findings indicate that the presence of bayerite in seeds, elevated interfacial supersaturation, and high temperature collectively facilitate the formation of ultrafine, equiaxial, near-spherical gibbsite.