Comparative Study of Influence of Anions on Thermal Behavior of nanosized Alumina

Abstract

Nanoalumina precursors homogeneously precipitated from aluminum nitrate and aluminum chloride were investigated for their thermal transitions and structural transformations. From both the monovalent anionic salts under identical reaction conditions, alumina precursors derived were same i.e. pseudoboehmite but their thermal behavior was different. Pseudoboehmite prepared from nitrate was amorphous and prone to dehydroxylation and subsequent calcination while pseudoboehmite prepared from chloride had relatively higher crystallinity and delayed dehydroxylation and calcination. In case of nitrate, life duration of gamma alumina was brief i.e. up to 350^oC whereas it in case of chloride it showed off at 375 and persisted up to 800^oC. Consequently, complete formation of alpha alumina occurred at 1150^oC in the former case while alpha phase was in process of its conversion from theta phase in this temperature regime in the latter case. DTA-TG, XRD, SEM, etc. were carried out for the characterization.

Keywords: aluminum hydroxide, boehmite, pseudoboehmite, metastable polymorphs, corundum