# Synthesis of Beta Alumina from Aluminum Hydroxide Precursor Formed by Gel to Crystallite Conversions

Kutty, TRN and Jayaraman, V and Periaswami, G (1996) Synthesis of Beta Alumina from Aluminum Hydroxide Precursor Formed by Gel to Crystallite Conversions. In: Materials Research Bulletin, 31 (9). pp. 1159-1168.

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## Abstract

A novel method is reported for the preparation of phase-pure $\beta"$-(Na) alumina by the gel to crystallite conversion technique. Coarse gels of hydrated alumina, $Al_20_3.YH_20(8O<Y<120)$, were reacted with sodium hydroxide solution in ethanol, yielding crystalline $Na_x,Al0_x,(OH)_{3-x}(0.17 < x < 0.23)$ having the gibbsite structure with inserted sodium ions. Thermal decomposition of this precursor above 573 K yielded the intermediate $Na_x,AlO_{1+x},(OH)_{1-x}$, with the boehmite structure. At higher temperatures this intermediate gave rise to \gamma-alumina, $Na_xA1_20_{3-x}(0H)_{3x}$ and $NaAl_{7/3}O_4$ with the defect spinel structure. It is proposed that because of the cubic close packing of oxygen ions present in the intermediate alumina, formation of $\beta"$- alumina takes place above 1273 K as a continuous solid-state process with minimal rearrangement of the close packed oxide ions. The $\beta"$-alumina phase thus formed is free of intergrowths of the $_\beta$-phase, as revealed by HREM and is stable up to near-melting conditions.

Item Type: Journal Article Materials Research Bulletin Elsevier Copyright of this article belongs to Elsevier. Oxides;Chemical synthesis;Eelectron microscopy;X-ray diffraction;Ionic conductivity Division of Chemical Sciences > Materials Research Centre 03 Jan 2007 19 Sep 2010 04:33 http://eprints.iisc.ac.in/id/eprint/9190