Preparation Of Flaky Alumina By Molten Salt Synthesis And Its Morphologies Control

Flaky alumina is an important special alumina powder material,which not only has the excellent properties of extreme hardness,corrosion resistance and high temperature resistance,but also has special two dimension platelets structure,which attach it special mechanical structure properties,fine adhesive ability,and special light reflection.Therefore,it has been widely used in the fields such as ceramics reinforcements,grinding medium,and pearlescent pigments,etc.Basing on the flaky alumina prepared by molten salts synthesis and changing some processing factors,such as molten salts,additives,surfactants,calcination conditions,and reaction pH values,this paper investigated the morphologies transformation course and growth mechanism of flaky alumina,which combined with phases transformations and morphologies.Research results was listed as follows:Processing conditions,such as molten salts kinds and amounts,heating conditions and reaction pH values,had great effects on the morphologies of flaky alumina.Adding chloride molten salts was helpful to obtain flaky alumina product with larger diameter and led to the change of diameter increasing firstly and then decreasing when increasing molten salts amounts.Increasing calcination temperature and holding time promoted alumina nucleus attaching on surface consumed by flaky alumina growth during the formation of ?-Al2O3,which was helpful to obtain flaky alumina with smooth surface morphologies,while it created little effect on diameter and thickness.The non-thermal effect of microwave promoted alumina growth so that diameter and thickness increased,while calcination temperature and holding time created little effect on diameter and thickness of flaky alumina.Under acidic conditions precursors with small particles and low crystallinity would be obtained,which was beneficial to gain flaky products with average size and excellent morphologies.Although increasing pH values increased precursor crystallinity and products diameter,the size distribution was lowered.Moreover,different kinds additives in preparation would had great effects on the morphologies of flaky alumina.The absorption mechanism and lattice replacement mechanism created by adding metal ions with different radius had great influence on the morphologies of final flaky products.Adding Zn2+ helped to gain the flaky products with with average size and excellent morphologies,and lowered the diameter and thickness of flaky products finitely.Adding Ti4+ decreased the tendency of anisotropy growth,and led to the tendency of diameter increasing firstly and then decreasing,while thickness increasing constantly.The existence form of different titanium additive also had great effect on the course of titanium diffusion into alumina crystal,and led to different morphologies products.The kinds of surfactants and processing pH values also had obvious influence on the final flaky products.Adding little amount of surfactant would reduce diameter and thickness obviously,and it helped to gain flaky alumina products with average size and completed shape.Flaky alumina with better morphologies would be obtained under acidic conditions by adding surfactant CTAB and PEG,however,adding SDBS surfactant gained impure products because of the second nucleation of aluminum hydroxide.