Practical remarks concerning phase diagrams determination on the basis of differential scanning calorimetry measurements

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1 J Therm Anl Clorim ( : DOI 1.17/s Prcticl remrks concerning phse digrms determintion on the bsis of differentil scnning clorimetry mesurements Leszek Rycerz Received: 15 October 212 / Accepted: 21 Februry 213 / Published online: 26 Mrch 213 Ó The Author(s 213. This rticle is published with open ccess t Springerlink.com Phse digrms of binry systems t constnt pressure re representtions of one- nd two-phse regions with their boundries being functions of temperture nd concentrtion. The most populr techniques used in determintion of phse digrms re therml nlysis (TA, differentil therml nlysis (DTA nd differentil scnning clorimetry (DSC. The first of them, bsed on recording of cooling curves, hs no significnt mening nowdys; however, it is still used, especilly in didctics. Actully DTA nd DSC re widely used in phse digrms determintion. DSC hs n dvntge over DTA, becuse in ddition to temperture it gives precise vlue of enthlpy of therml effect. Two types of DSCs must be distinguished: the het flux DSC nd the power compenstion DSC. The chrcteristic feture of ll DSC mesuring systems is the twin-type design nd the direct in-difference connection of the two mesuring systems which re of the sme kind. It is the decisive dvntge of the differentil principle tht, in first pproximtion, disturbnces such s temperture vritions in the environment of the mesuring system nd the like, ffect the two mesuring systems in the sme wy nd re compensted when the difference between the individul signls is formed [1]. The differentil signl is the essentil chrcteristic of ech DSC. Another chrcteristic which distinguishes it from most clssic clorimeters is the dynmic mode of opertion. The DSC cn be heted or cooled t preset heting or cooling rte. A chrcteristic common to Prcticl remrks concerning phse digrms determintion on the bsis of DSC mesurements re illustrted by numerous exmples of binry lnthnide hlide lkli hlide systems. L. Rycerz (& Chemicl Metllurgy Group, Fculty of Chemistry, Wroclw University of Technology, Wrocłw, Polnd e-mil: leszek.rycerz@pwr.wroc.pl both types of DSC is tht the mesured signl is proportionl to het flow rte (in opposition to clssicl clorimeters where het flow is mesured. This fct directly mesured het flow rtes enbles the DSC to solve problems rising in mny fields of ppliction [1]. In the het flux DSC defined exchnge of the het to be mesured tkes plce vi therml resistnce. The mesurement signl is the temperture difference; it describes the intensity of the exchnge nd is proportionl to the het flow rte. There re two min types of the het flux DSC: the disc-type mesuring system with solid smple support (disc nd the cylinder-type mesuring system with integrted smple cvities. Het flux DSCs with disctype mesuring system re vilble for tempertures between -19 nd 1,5 C[1]. In the het flux DSC with cylindertype mesuring system, the outer surfces of ech smple continer re in contct with gret number of thermocouples connected in series between the continer nd furnce cvity. The thermocouples bnds or wires re the dominting het conduction pth from the furnce to smples. Both smple continers re thermlly decoupled; het exchnge tkes plce only with prts of the mssive furnce. These pprtuses re vilble for temperture rnge between -19 nd 1,5 C [1]. The power compenstion DSC belongs to the clss of het-compensting clorimeters. The het to be mesured is compensted with electric energy, by incresing or decresing n djustble Joule s effect. The mesuring temperture rnge extends from -175 to 725 C[1]. Differentil scnning clorimetry is reltive technique. Becuse of its dynmic temperture chrcteristics, the mesurements re not mde in therml equilibrium. The reltive dt must be converted to bsolute vlues by clibrtion procedure requiring the employment of stndrds whose property vlues nd their ssocited uncertinties re known nd estblished following metrologicl procedure [2].

2 232 L. Rycerz Results presented in this work were obtined with Setrm DSC 121, which is cylinder-type scnning clorimeter. Its temperture scle ws clibrted in ccordnce with clibrtion procedure recommended by IUPAC Technicl Report concerning clibrtion stndrds for DSC [2]. Temperture correction coefficients were clculted nd subsequently used by pprtus softwre. Enthlpy clibrtion ws performed by the so-clled Joule effect. Identicl, stndrd-heting elements (resistivity of ech equl 1 X plced in lumin protection tubes were introduced into constnt temperture zone of the clorimetric block. One of them generted therml impulses (P of 2 mw during 2 s. Ech impulse ws followed by stbiliztion of clorimeter during 6 s. A computer recorded the vlue of the therml effect (Q introduced into clorimeter. The vlue of clorimeter constnt K t temperture T is described by n eqution: K ¼ Q P t : Such clibrtion ws crried out t defined tempertures by the so-clled step method (DT = 5 K over the entire temperture rnge of clorimeter work. As result the clibrtion curve, i.e. clorimeter constnt dependence on temperture, K(lV mw -1 = f(t, ws obtined. This dependence ws utomticlly used during dt tretment by originl softwre of SETARAM. The mximum of reltive error of enthlpy of phse trnsition determintion did not exceed 1 %. Clibrtion of pprtus by Joule effect ws checked by mesurements of tempertures nd enthlpies of phse trnsitions of stndrd substnces. Results obtined (differences in fusion tempertures less thn 1 K, differences in enthlpies of fusion less thn.5 % confirmed correct work of clorimeter. Tempertures of the invrint points were determined s et, temperture of liquidus ws determined s T pek. Unfortuntely, enthlpy obtined in DSC mesurements tell us nothing bout the kind of rection by which it is generted. Therefore, DSC technique must be supported by dditionl technique such s X-ry crystllogrphy. A further development is the ppliction of high-temperture X-ry techniques. Other methods pplied in phse digrm determintions re high-temperture microscopy, mesurement of electricl conductivity nd metllogrphic methods (in cse of lloys. The correct phse digrm determintion depends on mny fctors. Of course the method used is importnt, but primrily it depends on purity of components, proper preprtion of the smples, correct mesurements nd nlysis of obtined dt, nd supplementry methods such s for exmple X-ry diffrction. Lets ssume tht ll other requirements for correct phse digrm determintion re fulfilled nd only correct nlysis of DSC curves should be done. In generl one cn observe chrcteristic dependence between topology of phse digrm nd shpe of DSC curves. Let us tke the phse digrm of the binry system with incongruently melting compound (Fig. 1. If pure components undergo only melting one pek on DSC curve will be observed. It will be less or more unsymmetricl nd return to bse line will pper fter it. For isopleth b two therml effects will be observed on DSC heting curve. The first corresponding to incongruent melting nd second one, with chrcteristic shpe of longer or shorter til, corresponding to the liquidus. For smple with composition c three effects relted to eutectic, incongruent melting nd liquidus will pper. Due to physicl resons return to the Fig. 1 Correltion between topology of phse digrm nd shpe of DSC curves b c d e T A X B

3 Prcticl remrks concerning phse digrms determintion 233 Fig. 2 DSC curves for the system CeBr 3 LiBr x(cebr 3 =,73 x(cebr 3 =,35 x(cebr 3 =,274 T liq = 762 K T liq =? T liq = 942 K = 673 K = 673 K = 674 K x(cebr 3 =,221 x(cebr 3 =,163 x(cebr 3 =,1 T liq =? T liq = 759 K T liq = 783 K = 674 K = 674 K = 672 K bseline will tke plce fter liquidus effect. The shpe of pure eutectic effect (d is identicl to those of pure components. Finlly for the smple with mole frction e two peks, relted to eutectic nd liquidus, will be present on DSC curve. Now let us look on rel DSC curves for the CeBr 3 LiBr system (Fig. 2 [3]. Looking on the shpe of DSC curves one cn conclude tht it is simple eutectic system. Two peks re observed in lmost ll thermogrms. The first t constnt temperture ( K is undoubtedly relted to the eutectic. The second one, with chrcteristic til shpe, corresponds to the liquidus. It is well visible for compositions fr wy from eutectic composition. For smples with compositions mowing to the eutectic composition it strts to be more close to the eutectic effect nd less visible. Finlly, for some compositions round eutectic (Fig. 2 molr frction of CeBr 3 rnging from.274 up to.22 it is so smll tht it is not visible in DSC curves. Conclusion coming from such results is cler. It is impossible to determine eutectic composition directly from experimentl curves. However, eutectic hs strictly defined composition nd cnnot be situted t different mole frctions. Should the eutectic composition be tken rndomly from the rnge of compositions where liquidus effect is not visible? Of course, not. Proper determintion of eutectic composition requires cretion of the so-clled Tmmnn digrm, i.e. dependence of molr enthlpy relted to the eutectic effect on mole frction. As consequence of the lever rule nd the fct tht it is lwys the sme liquid tht is initilly formed (with the eutectic composition, the size of the integrted eutectic signl (D r H should descend linerly by mole frction on either side of the eutectic point. This is the bsis for the Tmmnn digrm [4, 5]. The Tmmnn plot should strt t whtever the left nd the right endpoints of the eutectic line re. This only corresponds to x = nd x = 1 if the left nd right phses hve negligible solid solubility. This mens tht the plot cn give us informtion on both the eutectic composition nd the solid solubilities t T eutectic. (The ltter re typiclly the mximum solubilities. Results for the CeBr 3 LiBr system (Tmmnn digrm nd phse digrm re presented in Fig. 3. The intercept of stright lines in Tmmnn digrm gives mole frction of CeBr 3, x(cebr 3 =.249 for eutectic composition. These lines cross the composition xis t x(cebr 3 = nd 1. This mens tht the formtion of solid solutions on both sides of the system is negligible. Tmmnn plot constructed for the YbCl 2 NCl system (Fig. 4 gives informtion bout eutectic composition [x(ybcl 2 =.559] nd informs bout formtion of solid solution of YbCl 2 in NCl [6]. Limit of solubility t eutectic temperture corresponds to mole frction of YbCl 2 equl.. Tmmnn digrm cn be lso used for determintion of stoichiometry of incongruently melting compound. Figure 5 presents phse digrm of TbBr 3 RbBr binry system [7] nd Tmmnn digrm used for determintion of TbBr Rb 3 TbBr 6 eutectic composition nd stoichiometry of incongruently melting RbTb 2 Br 7 compound. Mole frction of TbBr 3, x(tbbr 3 =.658 is in quite good greement with rh/kj mol 1 Δ x eut = x(cebr 3 Fig. 3 Tmmn nd phse digrms for the CeBr 3 LiBr system [3]

4 234 L. Rycerz 15 = 718 K 85 T liq = 97 K = 729 K 65 Δ r H/kJ mol = 715 K =.351 heting rte = 5 K min 1 T liq = 986 K.5 1 x(ybcl 2 = 86 K Fig. 4 Tmmn nd phse digrms for the YbCl 2 NCl system theoreticl vlue (.666 corresponding to the stoichiometry of RbTb 2 Br 7 compound. Sometimes it is difficult or even impossible to crete Tmmnn digrm. Such sitution tkes plce in the cse of determintion of Rb 3 TbBr 6 RbTb 2 Br 7 eutectic composition (Fig. 5 [7]. In the very nrrow temperture rnge K, severl phse equilibri tke plce over the whole composition rnge. However, their number is difficult to pprecite over the composition rnge.25 \ x(tbbr 3 \.666. For this reson more detiled investigtions on this composition rnge were performed by running DSC scns t fr smller heting rtes (1 nd.2 K min -1. Indeed the therml events merged in Fig. 6, b were deconvoluted upon slower heting t 1 K min -1 (Fig. 7 nd even reveled more detils t.2 K min -1 (Fig. 7b, c. For mixtures in the composition rnge.25 \ x(tbbr 3 \.445, n dditionl effect t 718 K ws visible in ddition rh/kj mol 1 Δ K 887 K 728 K Rb 3 TbBr 6 eutectic RbBr Rb 3 TbBr K 712 K incongruent melting RbTb 2 Br K 83 K RbTb 2 Br 7 x =.117 x = x(tbbr 3 Fig. 5 Tmmn nd phse digrms for the TbBr 3 RbBr system [7] =.583 heting rte = 5 K min 1 Fig. 6 DSC heting curves for selected xtbbr 3 (1 - xrbbr mixtures (x =.351 nd.583 to the liquidus nd Rb 3 TbBr 6 trnsition t 728 K but merged with the ltter under stndrd heting conditions (5 K min -1. In n ttempt to seprte these events, further experimenttion ws performed t slower heting rtes [7]. While t 1 K min -1 the phse trnsition occurred seprtely, the nticipting effect t 718 K ws found to be superimposition of two effects nd could not be fully resolved even upon very slow heting (.2 K min -1, s shown in Fig. 7b. However, even so, two chrcteristic tempertures (712 nd 719 K were determined in ll smples in the composition rnge.25 \ x(tbbr 3 \.666 nd only one (712 K t compositions beyond. Effect t 712 K ws ssigned to the solid solid trnsition of the RbTb 2 Br 7 compound. Accordingly the therml event t 719 K should be relted to the formtion of eutectic mixture of Rb 3 TbBr 6 nd RbTb 2 Br 7. The evlution of this eutectic mixture composition from n enthlpy versus composition plot, s explined bove, would not be relible in view of the merged nd non-seprble enthlpy effects observed in the nrrow temperture rnge K. An lternte method ws used insted. The globl enthlpy relted to the overlpping effects, DH m (globl, ws determined from DSC thermogrms obtined t heting rte of 5 K min -1. The enthlpy relted to the eutectic, DH m (eutectic cn be clculted s: DH m ðeutecticþ ¼ DH m ðgloblþ D trs H m ðrb 3 TbBr 6 Þ D trs H m ðrbtb 2 Br 7 Þ: The contribution of the enthlpy of trnsition, D trs H m (Rb 3 TbBr 6 solid solid trnsition, to the globl enthlpy could be determined from Tmmnn digrm s shown in b

5 Prcticl remrks concerning phse digrms determintion = 716 K = 728 K Δ rh/kj mol b c =.351 heting rte = 1 K min x(tbbr 3 = 712 K T pek = 719 K Fig. 8 Grphicl evlution of the therml effect relted to Rb 3 TbBr 6 RbTb 2 Br 7 eutectic: open circles enthlpy relted to the Rb 3 TbBr 6 trnsition t 728 K (, open tringles enthlpy relted to the RbTb 2 Br 7 trnsition t 712 K (c, open dimonds globl enthlpy in composition rnge.25 B x B.666, blck dimonds enthlpy relted to the Rb 3 TbBr 6 RbTb 2 Br 7 eutectic with T eut = 718 K (b =.351 heting rte =.2 K min 1 = 712 K =.583 heting rte =.2 K min 1 T pek = 719 K Fig. 7 DSC heting curves for selected xtbbr 3 (1 - xrbbr mixtures (x =.351 nd.583 Fig. 8. The effect t 728 K only results from the solid solid phse trnsition in Rb 3 TbBr 6 t x(tbbr 3 B.25 (Fig. 5 nd the relted enthlpy vries linerly with composition with the mximl vlue kj mol -1 t x(tbbr 3 =.25. The liner dependence must occur lso for x(tbbr 3 [.25. The therml effect relted to this trnsition disppers t x(tbbr 3 *.445, thus t x(tbbr 3 =.445 this enthlpy must be. Using the enthlpy vlues t x(tbbr 3 =.25 (1.974 kj mol -1 ndx(tbbr 3 =.445 ( kj mol -1 (blck circles in Fig. 8 D trs H m (Rb 3 TbBr 6 ws fitted to the liner eqution (.25 B x(tbbr 3 B.445 nd plotted ginst x(tbbr 3 in Fig. 8 (dshed line. The contribution of D trs H m (RbTb 2 Br 7 to the globl enthlpy ws described in similr wy (Fig. 8c. The therml effect t 712 K only results from the solid solid phse trnsition in RbTb 2 Br 7 t.666 B x(tbbr 3 \ 1(Fig.5. The corresponding enthlpy is liner function of x(tbbr 3 with the mximl vlue kj mol -1 t x(tbbr 3 =.666. The therml effect relted to this b c trnsition disppers t x(tbbr 3 =.25 thus t x(tbbr 3 =.25 this enthlpy must be. The enthlpy vlues t x(tbbr 3 =.25 ( kj mol -1 nd x(tbbr 3 =.666 (5.453 kj mol -1 (blck tringles in Fig. 8c resulted in the liner eqution of the D trs H m (RbTb 2 Br 7 in the molr frction rnge.25 B x(tbbr 3 B.666 s displyed in Fig. 8c (broken line. It ws then possible to clculte the enthlpy chnge relted to the Rb 3 TbBr 6 RbTb 2 Br 7 eutectic (Fig. 8b. The eutectic composition [x(tbbr 3 =.449] ws determined from the intercept of the two liner prts in Fig. 8b. Sometimes very interesting phenomen in form of exoeffects re observed on DSC curves. Such sitution ws observed in the CeBr 3 CsBr system [8]. Phse digrm of this system is presented in Fig. 9. For smples with composition.25 \ x(cebr 3 \.666 (Fig. 9 on primry heting curves (heting rte 5 K min -1, n endothermic effect ws visible t 685 K t ll compositions, which ws ssessed to possible decomposition of Cs 2 CeBr 5 into the djcent Cs 3 CeBr 6 nd CsCe 2 Br 7 compounds. However, on subsequent cooling, the formtion of Cs 2 CeBr 5 ws not observed (Fig. 1 nd it is likely tht metstble mixture K 712 K Cs 3 CeBr 6 75 K 685 K Cs2 CeBr x(cebr 3 Fig. 9 Phse digrm of the CsBr CeBr 3 system [8] 841 K CsCe 2 Br K

6 236 L. Rycerz Fig. 1 Experimentl curves [8]: primry heting/cooling (5 K min -1 ; b secondry heting (5 K min -1 ; c Cs 3 CeBr 5 formtion on slow cooling (.1 K min -1 ; d subsequent heting Het flow/mw K K 713 K K 768 K 4 b 685 K K 685 K K 764 K 753 K 764 K c 555 K 25 2 d 685 K of Cs 3 CeBr 6 nd CsCe 2 Br 7 exists down to room temperture insted. Solid-stte rections, such s the formtion or decomposition of compounds in the solid stte, cn be considered s specil kind of reconstructive trnsition in which the rrngement of the ions is drsticlly chnged. Ions hve to move from one site to nother pssing strong potentil wlls of other ions. The resulting kinetic hindrnce cn cuse gret difference between rection tempertures, mesured in DSC heting nd cooling runs (therml hysteresis [9]. In extreme cses during cooling experiments the undercooling cn become so strong tht the rection does not occur in the DSC time-scle. Due to kinetic resons, the compound formtion during cooling does not tke plce nd metstble mixture of other compounds exists insted. Thus secondry heting runs were performed t heting rte 5 K min -1 nd this time n exothermic effect ws observed first t bout 585 K which ws followed by n endothermic effect (Fig. 1b occurring t temperture identicl to tht of decomposition previously observed (685 K. But on this secondry cooling curve, the effect t 685 K (compound formtion ws once gin not visible. So, we decided to het once gin one smple up to melting nd to cool it down to room temperture, but t very low cooling rte (.1 K min -1. This time the effect corresponding to the compound formtion ws observed t bout 655 K (Fig. 1c. As the compound ws formed during cooling, no exothermic effect ws present in subsequent heting DSC curve (Fig. 1d. Another problem with interprettion of DSC curves rises sometimes in the cse of existence of incongruently melting compounds [1]. This difficulty cn be exemplified by the phse digrm of DyBr 3 RbBr system (Fig. 11 [11]. Becuse of the lrge temperture difference of the melting point of Rb 3 DyBr 6 (1,59 K nd the potentil eutectic formed by Rb 2 DyBr 5 compound (bout 7 K during cooling lrge mount of Rb 3 DyBr 6 crystllizes from the melt bove the temperture incongruent melting of Rb 2 DyBr 5 (presumbly 734 K. The crystls seprte from the melt nd, therefore, the formtion of Rb 2 DyBr 5 is not complete. As consequence, ll other effects t lower tempertures, nmely the eutectic nd phse trnsition of Rb 3 DyBr 6 will pper lso in the rnge of compositions where the bove-mentioned temperture difference is lrge. Thus, the quenched smples hve to be nneled to get equilibrium conditions [1]. We hve performed the nneling of the smples with molr frction of the DyBr 3 rnging from.25 to.4 t temperture 78 K during 78 h. The curves of the smples with x(dybr 3 =.283 nd x(dybr 3 =.376 without nneling nd fter nneling, obtined with heting rte 1 K min -1, re presented in Fig. 12. For the smples with molr frction x(dybr 3 \.333 effect t bout 7 K (potentilly relted to the Rb 2 DyBr 5 eutectic disppers (Fig. 12, b. For the smples with molr frction x(dybr 3 [.333 disppers effect t temperture of bout 717 K (Fig. 12c, d corresponding to the K K 726 K 159 K Rb 3 DyBr K Rb 2 DyBr K 748 K x(dybr 3 RbDy 2 Br K 1152 K Fig. 11 Phse digrm of DyBr 3 RbBr system [11]: blck dimonds dditionl effects tht were observed in DSC curves obtined for smples without nneling

7 Prcticl remrks concerning phse digrms determintion 237 b 699 K 717 K 733 K 719 K 735 K c 717 K 733 K d 738 K Het flow/mw 699 K 73 K e f 698 K 75 K 748 K Fig. 12 DSC heting curves for DyBr 3 RbBr [11] without (, c, e nd fter (b, d, f nneling t 78 K during 48 h: (, b x =.283; (c, d x =.376; (e, f x =.76. Heting rte 1 K min -1 (indicted tempertures re onset tempertures phse trnsition of Rb 3 DyBr 6. These nneling experiments confirmed existence of incongruent melting t 737 K (men vlue from ll pproprite curves Rb 2 DyBr 5 compound. Effect t lower temperture (72 K is relted to the eutectic formed by Rb 2 DyBr 5. In the composition rnge.5 \ x(dybr 3 \ 1. two endothermic peks were present in ll heting curves in ddition to liquidus. The temperture of first effect corresponds very well with effect observed for smples with molr frction of DyBr 3.33 \ x(dybr 3 \.5 (bout 72 K. The second effect occurs t bout 75 K nd suggests existence of nother incongruently melting compound. However, existence of this compound should influence effect t lower temperture (72 K. At composition of this compound effect t 72 K, relted to the eutectic, should dispper. But once gin we hve the sitution of lrge difference between melting temperture of DyBr 3 (1,152 K nd temperture of incongruent melting of this hypotheticl compound (75 K. Anneling of the smples ws performed t 78 K during 78 h. As result of this nneling the therml effect t 72 K disppered in the smples with x(dybr 3 [.666 (Fig. 12e, f, thus confirming existence of RbDy 2 Br 7 incongruently melting compound. Conclusions 1. There is chrcteristic dependence between topology of phse digrm nd shpe of DSC curves. 2. Tmmnn digrm is outcome from the theory of phse digrms nd predicts, through ppliction of the lever rule the vrition of enthlpy ssocited with first-order trnsformtion s function of concentrtion. Regrettbly, this plot is seldom used or merely overlooked, lthough it provides vluble informtion nd is known from beginning of XX century. 3. Kinetic hindrnce which cn pper in the cse of solid-stte rections, such s the formtion or decomposition of compounds in the solid stte, cn led to the metstble phses formtion. 4. Existence of incongruently melting compounds cn cuse difficulties with interprettion of DSC curves. Becuse of the lrge temperture difference of the melting point of neighbouring congruently melting compound nd eutectic, during cooling lrge mount of this congruently melting compound crystllizes from the melt bove the temperture of incongruent melting. The crystls seprte from the melt nd,

8 238 L. Rycerz therefore, the formtion of incongruently melting compound is not complete. As consequence, ll other effects t lower tempertures will pper lso in the rnge of compositions where the bove-mentioned temperture difference is lrge. Thus, the quenched smples hve to be nneled to get equilibrium conditions. Acknowledgments The work ws finnced by sttutory ctivity subsidy from the Polish Ministry of Science nd Higher Eduction for the Fculty of Chemistry of Wroclw University of Technology. Open Access This rticle is distributed under the terms of the Cretive Commons Attribution License which permits ny use, distribution, nd reproduction in ny medium, provided the originl uthor(s nd the source re credited. References 1. Hohne GWH, Hemminger W, Flmmersheim HJ. Differentil scnning clorimetry. An introduction for prctitioners. Heidelberg: Springer; Dell Gtt G, Richrdson MJ, Srge SM, Stolen S Stndrds. Clibrtion nd guidelines in microclorimetry. Prt 2. Clibrtion stndrds for differentil scnning clorimetry (IUPAC technicl report. Pure Appl Chem. 26;78(7: Ingier-Stock E, Rycerz L, Gdzuric S, Gune-Escrd M. Therml nd conductometric studies of the CeBr 3 MBr binry systems (M=Li, N. J Alloys Comp. 28;45: Findly A. The phse rule nd its pplictions. New York: Longmns, Green nd Co.; Guenet JM. Contributions of phse digrms to the understnding of orgnized polymer-solvent systems. Thermochim Act. 1996; 284: Rycerz L. Phse digrm of the YbCl 2 NCl binry system (unpublished results. 7. Rycerz L, Gune-Escrd M. Phse digrm of the TbBr 3 RbBr binry system: thermodynmic nd trnsport properties of the Rb 3 TbBr 6 compound. Inorg Chem. 27;46: Rycerz L, Ingier-Stock E, Gune-Escrd M. Phse digrm nd electricl conductivity of the CeBr 3 CsBr binry system. J Therm Anl Clorim. 29;97: Seifert HJ. Ternry chlorides of the trivlent lte lnthnides. J Therm Anl Clorim. 26;83: Sebstin J, Seifert HJ. Ternry chlorides in the systems ACl/ YbCl3 (A=Cs, Rb, K. Thermochim Act. 1998;318: Chojnck I, Rycerz L, Berkni M, Gune-Escrd M. Phse digrm nd electricl conductivity of the DyBr 3 RbBr binry system. J Therm Anl Clorim. 212;18(2: doi:1.17/s