简介概要

Thermodynamic reassessment of Ga-Hg and Mg-Hg systems

来源期刊:中南大学学报(英文版)2009年第1期

论文作者:冯艳 彭超群 王日初 刘华山

文章页码:32 - 37

Key words:Ga-Hg system; Mg-Hg system; intermetallic phases; thermodynamic assessment; phase diagram; CALPHAD

Abstract: The Ga-Hg binary system was thermodynamically assessed by the CALPHAD method, but only configuration contributions were considered to the entropy of the liquid. The Mg-Hg binary system has not been assessed yet. In the assessments of the Ga-Hg and Mg-Hg binary systems, solutions including liquid and hcp (Mg) were treated as substitution solutions, of which the excess Gibbs energies were formulated with the Relich-Kister polynomial. The intermetallic phases in the Mg-Hg binary system, Mg3Hg, Mg5Hg2, Mg2Hg, Mg5Hg3, MgHg, and MgHg2, were described as stoichiometric compounds. Based on the reported experimental data and thermodynamic properties of the phase diagram, sets of self-consistent parameters describing all phases in the Ga-Hg and the Mg-Hg binary systems were obtained.



详情信息展示

J. Cent. South Univ. Technol. (2009) 16: 0032-0037

DOI: 10.1007/s11771-009-0005-7

Thermodynamic reassessment of Ga-Hg and Mg-Hg systems

FENG Yan(冯 艳), WANG Ri-chu(王日初), PENG Chao-qun(彭超群), LIU Hua-shan(刘华山)

(School of Materials Science and Engineering, Central South University, Changsha 410083, China)

                                                                                                

Abstract: The Ga-Hg binary system was thermodynamically assessed by the CALPHAD method, but only configuration contributions were considered to the entropy of the liquid. The Mg-Hg binary system has not been assessed yet. In the assessments of the Ga-Hg and Mg-Hg binary systems, solutions including liquid and hcp (Mg) were treated as substitution solutions, of which the excess Gibbs energies were formulated with the Relich-Kister polynomial. The intermetallic phases in the Mg-Hg binary system, Mg3Hg, Mg5Hg2, Mg2Hg, Mg5Hg3, MgHg, and MgHg2, were described as stoichiometric compounds. Based on the reported experimental data and thermodynamic properties of the phase diagram, sets of self-consistent parameters describing all phases in the Ga-Hg and the Mg-Hg binary systems were obtained.

Key words: Ga-Hg system; Mg-Hg system; intermetallic phases; thermodynamic assessment; phase diagram; CALPHAD

                                                                                                           

1 Introduction

Magnesium alloys are used extensively as a sort of anode materials in the seawater battery system for its good performances such as rapid activation, high cell voltage-wide voltage range, and high power density capability [1-4]. As is known, pure magnesium electrode can be polarized easily by a protective oxide or hydroxide film. It has been reported that the alloying elements Ga and Hg can enhance the electrochemical activity of the Mg anodes because they can produce uniform dissolution of Mg anodes in environments containing aggressive ions [5-6]. Moreover, the addition of Ga in the Mg-Hg alloys can decrease the driving force of the galvanic couple corrosion and enhance the corrosion resistance and the electrode efficiency of the Mg-Hg anode materials [7]. In order to design alloy and better understand the mechanisms of Ga and Hg activating the Mg anode materials, the thermodynamic assessments of the Ga-Hg and Mg-Hg binary systems are necessary.

A review of the literature data on the Ga-Hg system, which includes publications before 1993, has been presented by GUMINSKI and ZABDYR [8]. Three thermodynamic models were published for the Ga-Hg liquid phase [9]. Using tetrahedral approximation for the Ga-Hg liquid phase, GUBBELS [9] calculated the most consistent results in extrapolation of the Ga-Hg-In ternary system, but only configuration contributions were considered to the entropy of the liquid. The newest review of the Mg-Hg binary system was reported by NAYEB-HASHEMI and CLARK [10], who summarized the publications before 1987. There has not any thermodynamic assessment on the Mg-Hg binary system yet.

In view of these, the thermodynamic reassessments of the Ga-Hg and Mg-Hg binary systems were performed in the present work.

2 Evaluation of experimental data

2.1 Experimental data of Ga-Hg binary system

The liquidus in the Ga-Hg diagram was determined using thermal analysis [9, 11-14]. These data are consistent and used in the optimization. There is a miscibility gap in the liquid of the Ga-Hg binary system and no intermetallics exist. The largest solid solubility of Hg in orthorhombic (Ga) was 0.02%, determined by measuring the residual electric resistivity of the Hg-rich alloys [15]. The largest solid solubility of Ga in rhombohedral (Hg) was determined using the same method [16].

By calorimetric measurements, mixing enthalpies of the Ga-Hg liquid at 478 and 513 K were determined [11,17-19]. These data are consistent except the larger values on the Ga-rich region in Refs.[11,17-18], which were confirmed by ZHANG and GUO [20] using calculation. So the symmetric mixing enthalpy of the Ga-Hg liquid in the whole composition range was not accepted in this optimization [19]. Due to lack of other new experimental data, no temperature dependence of the mixing enthalpy of the Ga-Hg liquid was considered in this optimization.

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