Thermodynamic determination of the stability area of boehmite in Al2O3-Na2O-H2O and Al2O3-H2O systems

Panias, D; Paspaliaris, I

dc.contributor.author	Panias, D	en
dc.contributor.author	Paspaliaris, I	en
dc.date.accessioned	2014-03-01T01:48:48Z
dc.date.available	2014-03-01T01:48:48Z
dc.date.issued	1999	en
dc.identifier.issn	00442658	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/25598
dc.relation.uri	http://www.scopus.com/inward/record.url?eid=2-s2.0-0033349647&partnerID=40&md5=a235b76c48d44e47700051d122bf1f24	en
dc.subject.other	Alumina	en
dc.subject.other	Crystallization	en
dc.subject.other	Phase transitions	en
dc.subject.other	Reaction kinetics	en
dc.subject.other	Sodium compounds	en
dc.subject.other	Supersaturation	en
dc.subject.other	Thermodynamic stability	en
dc.subject.other	Boehmite	en
dc.subject.other	Sodium hydroxide	en
dc.subject.other	Bauxite deposits	en
dc.title	Thermodynamic determination of the stability area of boehmite in Al2O3-Na2O-H2O and Al2O3-H2O systems	en
heal.type	journalArticle	en
heal.publicationDate	1999	en
heal.abstract	In the system Al2O3-Na2O-H2, boehmite (γ-AlOOH) is considered to be a stable phase at temperatures higher than 100 °C. At lower temperatures the stable phase is either gibbsite or bayerite (Al(OH)3). This observation is based on previous experimental findings concerning the crystallization of the various aluminum hydroxides or oxidehydroxides phases during aluminum hydrolysis or aluminum oxide hydroxylation in aqueous systems. In this work a thermodynamic analysis of the transformation reaction of gibbsite to boehmite is presented. This analysis has shown that boehmite is the thermodynamically stable phase in the system Al2O3-H2O at temperatures as low as 59.9±6.6 °C. In the system Al2O3Na2O-H2O, it has been proved that the stability area of boehmite depends on the sodium hydroxide concentration. It is extended to the lower temperatures as the sodium hydroxide concentration increases. In the case of a 6 m sodium hydroxide solution, boehmite can be considered as a stable phase at temperatures as low as 49.4±6.6 °C. The disagreement between the conclusions of the thermodynamic analysis and the previous experimental findings is attributed to the significant kinetic inhibitions of the chemical reactions taking place during boehmite crystallization under atmospheric conditions. Finally, in this paper a procedure to calculate theoretically the water activity in supersaturated sodium aluminate solutions based on the Bromley monoparametric equation is presented. For the first time, a value for the characteristic constant B of the Bromley equation for NaAl(OH)4 is presented here.	en
heal.publisher	Verlag fuer Kunst und Touristik GmbH, Leipzig, Germany	en
heal.journalName	Erzmetall: Journal for Exploration, Mining and Metallurgy	en
dc.identifier.volume	52	en
dc.identifier.issue	11	en
dc.identifier.spage	585	en
dc.identifier.epage	595	en