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Section I: Basic and Applied Research

Thermodynamic Description of SrO-Al2O3 System and Comparison with Similar Systems Xinyu Ye, Weidong Zhuang, Jingfang Wang, Wenxia Yuan and Zhiyu Qiao

(Submitted August 13, 2006) The Al2O3-SrO binary system has been studied using the CALPHAD technique in this paper. The modeling of Al2O3 in the liquid phase is modified from the traditional formula with the 2liquid phase represented by the ionic two-sublattice model as (Al3+, Sr2+)P ( AlO1
2 , O )Q. Based on the measured phase equilibrium data and experimental thermodynamic properties, a set of thermodynamic functions has been optimized using an interactive computer-assisted analysis. The calculated results are compared with experimental data. A comparison between this system and similar systems is also given.

Keywords

phase diagram, SrO-Al2O3, thermodynamic properties

2. Experimental Information 2.1 Phase Diagram and Intermediate Compounds

1. Introduction The SrO-Al2O3 system is of interest because of the use of the intermediate compounds for hydraulic cements, laser matrices, and long-duration photoluminescence or thermoluminescence pigments.[1] But comparing with the magnesium and calcium counterparts, the knowledge of phase diagram of strontium aluminates is quite limited. Fortunately, with the help of the powerful CALPHAD technique, it is possible to obtain consistent thermodynamic description of such system from dispersed and scarce experimental information, to guide the synthesis of proper compounds to satisfy the practical requirements. Inspired by the work of re-evaluation of the liquid phases in the CaO-Al2O3 and MgO-Al2O3 systems by Mao et al.,[2] we have already thermodynamically assessed the BaO-Al2O3 system.[3] The aim of the present work is to review the experimental studies of another one of alkali earth aluminates, i.e., SrOAl2O3 system in order to provide a consistent thermodynamic description for the system with the new liquid model proposed by Mao et al.[2] and to compare the thermodynamic properties with correlative systems.

Xinyu Ye and Weidong Zhuang, National Engineering Research Center for Rare Earth Materials, General Research Institute for Nonferrous Metals, and Grirem Advanced Materials Co. Ltd, Beijing 100088, China; Jingfang Wang and Wenxia Yuan, School of Applied Science, University of Science & Technology Beijing, Beijing 100083, China; Zhiyu Qiao, School of Metallurgy and Ecological Engineering, University of Science & Technology Beijing, Beijing 100083, China; Contact e-mail: [email protected]

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By comparison with the closely related and better-known system CaO-Al2O3, the SrO-Al2O3 phase diagram has many uncertainties, even the melting points and, more importantly, the existence of some compounds. In the system, four intermediate compounds, i.e., SrO  6Al2 O3 , SrO  2Al2 O3 , SrO  Al2 O3 , and 3SrO  Al2 O3 have been proven to exist for a long time.[4-8] Then, Dear[9] reported the presence of a new compound with formula 5SrO Æ Al2O3. However, the formula was modified to be 4SrO Æ Al2O3