D0I:10.13374/j.issm1001-053x.1989.06.034 第11卷第6期 北京料技大学学报 Vol.11 No.6 1989年11月 Journal of University of Science and Technology Beijing Nov,1989 Measurement and Calculation of ReCla-LiCl (Re:La,Ce)Phase Diagrams' Qiao Zhiyu（乔芝郁)，Wang Mingsheng（王明生)， Zheng Chaog4i(郑朝贵)，◆◆Duan Shuzhen(段淑贞) ABSTRACT:In this paper the phasc diagrams of LaCl3-LiCl and CeCIs-LiCl systems have been experimentally determined and theoretically calculated.Both are simple eutectic systems.The eutectic points are at 25mol%LaCls,508C and 27mol%CeCl3,494C,respectively.The optimized phase diagrams and thermodynamical data of LaCls-LiCl and CeCls-LiCl systems with self consistency are a better basis for constructing ternary phase diagrams. KEY WORDS,phase diagram,measurement and calculation,rare earth element, ReCl3-LiCl Rare earth metals play an increasing important role in various fields of contemporary science and technology.As well known,molten salt electrolysis was widely used for the production of rare earth metals and their alloys.More- over,phase diagrams are the most important data for fused electrolytes.Dealing with the binary phase diagrams involving rare earth chlorides,not a few papers have been published.However,there is still no LaCl,-Licl phase diagram available in literature.For the CeCls-LiCl phase diagram reported very recently by Chai et al.t,just shown in Fig.2,there are not enough measured liquidus data over the CeCl3-rich side. As one of the systematic studies on the measurement and calculation of phase diagrams involving rare earth chlorides,the present work was undertaken to determining the accurate liquidus of the LaCl3-LiCl and CeCl,-LiCl binary systems as well as to optimize their phase diagrams and thermodynamic data. The Project Supported by National Natural Science Fundation of China Manuscript Received April 6,1989 .Dept.of Physical Chemistry ···Dept.of Chemistry,Peking University 598
第 卷第 期 年 月 北 京 科 技 大 学 李 报 一 召 。 一 夏 ’ 、 ， 一 ，，目产 夕 乔芝郁 ， 牙 夕 ， 夕 王 明 生 ，二 尸 夕 夕 郑朝 责 ，… ， “ 段 淑 贞 一 一 一 · 写 ， ， ， · 一 一 ， ， ， 一 一 犷 一 ， 。 ， 一 ， · ， 一 一 ‘ ， · ， 一 ， 一 一 丁 《， ， 二 盆 … ， 声 DOI ：10．13374／j ．issn1001－053x．1989．06．034
1 Experimental 1.1 Chemicals The chemical LiCl was of analytical reagent grade and dried in the same way as in Ref.[2]and Ref.[3. LaCls.7H2O with high purity were used.According to the mechanism of dehydration of LaCls7H2O and CeCl,7H2Ot4),they were dehydrated under the dry HCl atmosphere which pressure was less than 1 atm (101kPa)by slow heating to the following temperatures and kept at these temperatures for 5h each: 80°C,130°C,185°C,300°Cand80C,125°C,145°C,200°C,300°C,respectively· 1.2 Data Measurements Melting points and phase transition temperatures were measured by differential thermal analysis technique.A 100 mg sample of the required composition of LiCl and ReCla was weighted out into a clean,dry quartz crucible in a high purity nitrogen atmosphere.Then the quartz crucible was sealed and the sample was melted.After cooling,the samples were annealed at 350C for 12h. The DTA measurements were carried out on heating or cooling in purified nitrogen atmosphere using a NiCr-NiSi thermocouple and a-Al2Os powder as reference material.The DTA temperatures were calibrated using the following solid-solid or solid-liquid transition points:KNO3 (334C),Zn (419.7C),SiOz (573°C),KzS04(583°C),NaC1(801°C).In order to avoid the effect of supercooling up on the measured accuracy the heating curves were generally used to determine the liquidus temperatures.Typical heating rate was 10C/min. The onset of the DTA peak was used as the phase transition temperature. 2 Measured Results 2.1 Melting Points of Pure Components The measured melting point of LiCl was 610C,which agreed very well with Ref5).The obtained melting point of CeCls was 815+3C which was in agree- ment with Ref.5],but a little higher than the reported value in Ref.1).The melting points of LaCls gived in Ref.5]and Ref.C6]are 855C and 850C which are by 20C and 25C lower than that found recently in Ref.7]and Ref.C8]. The reason suggested in Ref.9]was due to impurities of the LaCla.We paid much attention to purities and dehydration of the LaCis and measured several times.The melting point of LaCla was found to be 8753C which agreed very well with that reported in Ref.[7-9]. 599
三 。 卜 · 〔 〕 〔 〕 。 · 了 · ， 饰 主 ， ‘ “ ， “ ， 企 “ ， “ ， ， “ ， “ ， ， “ ， 、 。 一 。 ， 。 任 ， · 一 一 一 一 一 “ ， ， “ ， 声 ， “ 。 立 “ · 电气 、 “ ， 立 〔 〕 · 士 “ 〔 〕 ， 〔 〕 。 。 〔 〕 〔 〕 “ “ “ 〔 〕 〔 〕 。 〔 〕 士 “ 了 · 〔 一 〕
2.2 CeCl,-LICI Phase Diagram Our experimental results were shown in Table I and Fig.1.It is a simple eutectic system with an eutectic point at 27 mol%CeCl,and 494C which is by 28°C higher than that reported in Ref.〔l). Table 1,The DTA measured data of the CeCl,-Licl system Composition Liquidus Eutectic Compcsition Liquidus Eutectic of CeCls of CeCl, mol%wt% C mol%wt% C 9.337.3 585 494 29.070.3 516 494 10.039.1 566 494 38.278.2 590 494 11.1 42.0 583 496 41.880.7 608 494 13.046.6 566 494 46.483.4 641 494 18.757.3 538 494 48.084.3 644 494 20.660.1 532 494 57.688.8 672 494 22.362.5 514 492 61.590.3 722 494 24.164.9 500 494 69.493.0 765 494 25.366.3 518 490 86.897.4 796 494 100 100 815 2.3 LaCls-LICI Phase Diagram As shown in Table 2 and Fig.2,the system is also a simple eutectic one with an eutectic point at 25 mol%LaCls and 508C. Table 2. The DTA measured data of the LaCl,-LICI systom Composition Liquidus Eutectic Composition Liquidus Eutectic of LaCls of LaCl, mol%wt% C mol%wt% C 3.7 18.2 606 506 30.771.9 574 506 7.7 32.5 586 505 33.074.0 585 508 10.841.1 565 506 36.977.2 628 511 13.246.9 560 508 50.085.2 681 508 17.455.0 552 508 51.2 85,9 690 506 20.359.6 524 508 54.687.4 710 508 21.763.8 518 508 62.890.7 716 506 26.968.1 526 508 65.491.6 718 508 28.669.8 532 508 79.595.7 798 506 100 100 875 600
乏 一 一 一户卜。 。 。 。 。 〔 〕 。 · · “ 。 一 丫 写 肠 肠 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 一 一 · ， 纬 于 卜 一 丫 写 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。
3 Optimization and Calculation 3.1 Method For A-B liquid solution the molar Gibbs free energy Gm is G.=XOG+XG+RT(XInX+XalnX)+G. (1) XA+XB=1 (2) where G:and X are the standard free energy of component i in liquid state and mole fraction of component i,respectively,EGm is the excess molar Gibbs free energy.For different theoretical models and empirical formulas the EGm expre- ssions are different from each other.In our case as a general formula EGm is expressed as G。=8h,-TS)XX6 (3) where a,A are the positive integral powers;a and B are related to the molar enthal- py of mixing and excess molar entropy of mixing: H:=∑∑h.BXAX Sm=D∑Sa6XgXg It is clear that if a=1,B=1 and a=1,B=2 the formula (3)wcu!d be redu- ced to the regular solution model and subregular solution model,respectively.In this paper u=1,B=2,are chosen for coupling the phase diagram and thermo- dynamic data. With reference to [10-12],the expressions of 5G.for the CeCla-LiCl and LaCla-LiCl binary systems were obtained. 1000 1000r Calculated 900 -Caleulated 900 75 ◆Measured 815 Measured 800 800 700 700 6000 610 600 494 508 500 27 500 25 400 400 0 20 40 60 80 100 0 20 40 60 80 LiCl ,100 若…mol% CeCl3 Licl mol% aCh Fig.1 LiCl-CeCl,system Fig.2 LiCl-LaCl,system 601
。 人 一 扭 。 ’ 。 二 旦 ， 十 昙口 ， 尤 ， ， 。 。 十 “ 。 二 “ ， ， ， ， · 。 、 · 二 民 二 二 兄 。 ， 一 了 。 ， 叉 睿 夕 ， 刀 皿 月 岔 乙 艺 。 。 ， 皿 男 尹 。 二 兄 。 ， 且 百 声 ， 刀 ， 刀 二 ’ 住 ， ， 、 ‘ 手二 以 ， 刀 ， 二 。 〔 一 〕 ， ￡ 。 。 一 。 一 犷 手 · · 驴 卜尸任。﹄己﹄。 护妇‘。口‘ 卜岳 一‘ 口月 』一 扮 监产尸 卜 ’ 理 才 愧卜 、 口 尸一 只产 百 弓 蔺 。 】 一 沪产 ， 心 。 口 夕 产 月 卜， 咬 一 山一产 川 一 叫曦出 知 习 枯 一 。 一 丫
3.2 CeCl3-LiCl System The excess molar Gibbs free energies of mixing at different compositions for CeCl,-LiCl binary system at To=1098K bave been measured using e.m.f. method by Egan et al.1.The G expression as follows was simulated by least square regression analysis using subregular solution model eG.,r。=Xcc1,(1-Xcc1,)(-12895.7+5569.2Xcec1,) J/mol S.could be estimated as follows from theG.values and our reliable measured phase diagram data using subregular solution model S.=Xcc1,(1-Xcc1,)(12.16-26.8Xcc1,) J/mol.K Thus,the G.at temperature T will be obtained. The calculated phase diagram of CeCl,-LiCl is in good agreement with our measured one shown in Fig.1. 3.3 LaCls-LICI System The integral enthalpies of mixing H for the LaCl,-LiCl binary system has been determined calorimetrically by Papatheodorou and Ostvold [ H=XLc1,(1-Xc1,）（-9623,7+418Xzc1, J/mol From the H values and our reliable measured phase diagram data "S.could be estimated. S.=Xzc,(1-Xc1,)(0.4065+13.155Xc1,) J/molK As shown in Fig.2.,the calculated phase diagram of LaCla-LiCl agreed well with our measured one. REFERENCES 1 Chai Liang,Zheng Chaogui.Proceedings of Fifth Symposfum on Phase Diagrams,The Chinese Physical Soclety,Wuhan,1977,Vol.3 2 Qiao Zhiyu,Sangester J,Pelton A D.CHLPHAD,1987;11(2):277 3 Qiao Zhiyu,Wang Mingsheng,Zheng Chaogui,Duan Shuzhen.Acta Metallurgical Silica,1989;25 (4):B234 4 Su Mianzeng.Li Peigen.HUAXUE TONGBAO (Chemistry),1964 4 34 5 Barin I,Knacke O,Kubaschewski O.Thermodynamical Properties of Inorganic Substance and Supplement,Springer-verlag,N.Y.1973,1977 6 Morozov I S,Shevtsova Z N.Zhur.Neorg.Khim.,1957;(2):1640 7 Blachnik R,Alberts G.Thermochimica Acta,19831 64:317 602
。 亡 一 心 ， 一 二 一 · · · 君 ‘ ， 一 一 · · · 一 ￡ · 二 万 一 。 。 一 。 一 一 · 。 。 一 · ， 君 “ · 。 一 一 心 丫 留 一 ‘ 份 。 一 。 ， 一 。 一 二 ， 。 一 凡 一 凡 。 ， 瓜 。 二 · 一 ， 一 。 ， 一 ， 了 夕， 夕 ‘ “ 二 。 夕 ， 了 ， ， ， 。 ， ， 。 万 ， 住 ， ， ， 五 。 万 。 “ 夕‘ ‘ ， ， ， ， ‘ · ， ， ， 了 一 ， 一 一 ， ， 。 夕 成 ， ， ， 巾 而 用 ，