Thermodynamic optimization and calculation of phase diagrams of YbCl3-MCl (M=Na, K, Rb, Cs)

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JOURNAL OFRAREEARTHS,Vo1.26,No. Aug.200&p.552 www.re-j‘0111Tad.tom Thermodynamic optimization and calculation of phase diagrams of YbCI3-MCI(M=Na,K,Rb,Cs) SUN Yimin(孙益民) ,YAO Yongxiang(姚永香) ,HU Juan(胡娟) ,MENG Xiangzhen(孟祥珍) , GAO Tianyi(高天铱) ,QIAO Zhiyu(乔芝郁) rJ.CollegeofChemistry andMaterialsScience,AnhuiNormalUniversity,Wuhu 241000,China;2.DepartmentofPhysicalChemistry,University ofScience andTech- nologyBeijing,BeUmg100083,China) 

Received 16 September 2007;revised 26 October 2007 

Abstract:YbCl3-MC1(M=Na,K,Rb,Cs)systems were optimized and calculated using the CALPHAD(ChLculati0n 0f PHAse Diagram) technique.The modifled quasi—chemical model in the pair—approximation for short-range ordering was used to describe the Gibbs energies of liquid phase in the systems.On the basis of the measured phase diagram data and experimental thermodynamic properties,a series of ther- modynamic tractions were optimized and calculated through an interactive computer-assisted analysis.Furthermore.some reasonable dis. cussions on the thermodynamic parameters for these s ̄ong interaction binary systems were carried out.111e results showed that the opti. mized parameters and experimental data are thermodynamically self-consistent. 

Keywords:phase diagram;YbC13--MCI systems;modified quasi・-chemical model;thermodynamic properties;rare earths 

Phase diagrams have played an increasingly important role in various fields such as material design.In numerous applications,molten salt electrolysis is widely used to pro— duce rare earth metals and their alloys.Thus,the data and parameters of the YbC1 .MCl(M=Na,K,Rb,Cs)systems are the basic reference for the production of metallic ytter- bium anditsalloys. In continuation with the previous study ‘ .thermody. namic optimization of the YbCl3.MCl(M=Na,K,Rb,Cs) systems is carried out in this article.The YbCl .NaCl system was measured by Drobot and Korshunov_『J.and only an in— congruently melted compound N YbC16 was found in the system.Buchel D and Seifert H JL measured this system again by means of D and X.ray diffraction and found that two types of compounds existed,Na3YbC16 and NaYbC14.The phase diagram of the YbC11一KC1 system was also studied by two groups.Novikov G L et a1. investi— gated this system and found only an incongruenfly melted compound K3YbC16;Sebastian and Sei ̄a H J Lioj measured this system by means of DTA and XRD.and found four types of compounds:two incongruenfly melting compounds K2YbC15 and KYb2C17,a congruently melted compound K3YbC16 and compound K3Yb2C19.The phase diagrams of the YbCl1.RbC1 system were determined by Sebastian and SeifeaH J【 bymeans ofDTAandXRDandthe existence of compounds Rb3YbC16,Rb:YbC15,and RbYb2C17 was confirmed in the YbC13。RbC1 systems.The phase diagram of the YbC13一CsC1 system was determined by Von R Blachnik and SeHe D in the 1970s[ ”.but later it was deter. 

minedby SebastianandSeifertHj[1O】bymeans ofDTAand 

XRD.There are three incongruenfly melted compounds, Cs2YbC15,Cs3Yb2C19,and CsYb2C17,and a congruently melted compound Cs3YbC16.In principle,we will review all experimental data from diferent literatures and a general evaluation will be given after considering several impacts on theliteratures.Infact,wetakeinallthe experimental datain the database for optimization by setting different weights. Evidently,more recently published data obtained by im- proved methods and higher measuring accuracy will be given more weight.In practice,all data with different weights were put together into one file for optimization. 

1 Model Several theoretical models based on the thermodynamics of liquid solution were established to resolve the thermody— namic properties of liquid phase.However,the previous models could not describe the thermodynamic properties of binary systems with strong interaction.Pelton A D and Blander M[ ]modified Guggenheim’s quasi.chemical theory[ ' 引.The energy of pair formation is expanded in 

terms of pair fraction rather than component fractions,and 

Foundation item:Project supported by Key Project Foundation of Namrfl Science of Anhui Education Committee(KJ2008A083) Corresponding author:SUN Yimin(E—mail:mysun@mail.ahnu.edu.cn;Te1.:+86—553-3399366) 

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