Structural and morphological features of disperse alumina synthesized using aluminum nitrate nonahydrate

Abstract

Transformation of Al(NO3)3∙9H2O (upon heating in the range of 20-1200 oC) into blends of amorphous and crystalline boehmite (210-525 oC), amorphous alumina and crystalline gamma-Al2O3 (850 oC), and crystalline alfa-Al2O3 (1100 oC) was analyzed using XRD, HRTEM, IR spectroscopy, thermogravimetry and low-temperature nitrogen adsorption. Boehmite consists of nanoparticles of 6-10 nm in diameter and part of them has crystalline structure observed in HRTEM images, despite they are XRD amorphous. The nanoglobules are surrounded by amorphous aluminum hydroxide with chains of –AlO(H)–O–AlO(H)– of 1-5 nm in length. Heating of samples at 350-525 oC gives mesoporous aluminum hydroxide with a relatively narrow pore size distribution. An increase in calcination temperature to 850 oC decreases the porosity of alumina composed of amorphous and crystalline (gamma-Al2O3) phases. Calcination at 1100 oC gives alfa-Al2O3 with strongly decreased porosity of aggregates.