Thermodynamics of SmCl3 and TmCl3: Experimental Enthalpy of Fusion and Heat Capacity. Estimation of Thermodynamic Functions up to 1300 K
L. Rycerza;b and M. Gaune-Escardb a Institute of Inorganic Chemistry and Metallurgy of Rare Elements, University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland b Universite´ de Provence, IUSTI, CNRS UMR 6595, Technopoleˆ de Chateauˆ Gombert, 5 rue Enrico Fermi, 13453 Marseille Cedex 13, France Reprint requests to M. G.-E.; Fax: +33 (0)4 91 11 74 39; E-mail: [email protected]
Z. Naturforsch. 57 a, 79–84 (2002); received December 19, 2001
Heat capacities of solid SmCl3 and TmCl3 were measured by differential scanning calorimetry in the temperature range from 300 K up to the respective melting temperatures. The heat capacity of
liquid SmCl3 was also investigated. These results were compared with literature data and fitted by a polynomial temperature dependence. The temperature coefficients were given. Additionally, the
enthalpy of fusion of SmCl3 was measured. Furthermore, by combination of these results with the 0 literature data on the entropy at 298.15 K, Sm(LnCl3, s, 298.15 K) and the standard molar enthalpy
0 H of formation of form m(LnCl3, s, 298.15 K), the thermodynamic functions were calculated up to
T = 1300 K. Key words: Samarium Chloride; Thulium Chloride; Heat Capacity; Enthalpy; Entropy; Formation; Fusion; Differential Scanning Calorimetry.
Introduction preparation of a mixture in the molar ratio Tm O 2 3 :NH Cl=1:9, The enthalpies of phase transitions of lanthanide 4 sintering and chlorinating under vacuum at 600 K chlorides as well as the heat capacities of LaCl , 3 during 3 hours, CeCl , PrCl , NdCl , GdCl , DyCl , and EuCl3 have 3 3 3 3 3 sublimation of unreacted ammonium chloride at been measured and reported previously [1 - 3]. This 640 K under vacuum, work continues an investigation program on lan- thanide halides. It presents results of enthalpies of melting of crude thulium chloride, phase transitions and specific heat capacity measure- purification of crude chloride by distillation under ments of the pure lanthanide chlorides SmCl and reduced pressure (0.1 Pa). 3 TmCl performed with a SETARAM DSC 121 dif- As the product after sintering chlorinating and 3 ferential scanning calorimeter. The results are com- melting was contamined by oxychloride, TmOCl, the pared with original literature data and with literature next step of preparation was a double distillation of estimations. the crude TmCl from the less volatile residue (mainly 3 TmOCl). Details of the distillation procedure have Experimental been described in [4]. However, this method should not be used for Sample Preparation the synthesis of SmCl3 because of the decompo- sition tendency of this compound. Thus samarium Thulium chloride (TmCl3) was prepared from the trichloride was prepared by chlorinating the oxide oxide of 99.9% purity, supplied by Merck, by chlo- (Merck, 99.9%) with a current of high purity argon rinating with ammonium chloride (POCh Gliwice, (water and oxygen content less than 2 and 0.5 ppmV, Poland – pure for analysis). The synthesis included respectively) saturated with SOCl vapour in a quartz 2
the following steps: reactor, at 793 - 813 K for 24 hours. This procedure, 0932–0784 / 02 / 0100–0079 $ 06.00 c Verlag der Zeitschrift fur¨ Naturforschung, Tubingen¨ www.znaturforsch.com 80 L. Rycerz and M. Gaune-Escard · Thermodynamics of SmCl3 and TmCl3 ∆ Table 1. Chemical analysis of the lanthanide trichlorides. T i. Therefore the heat capacity of the sample is
Compound Cl Cl Ln Ln 0
Q M = ∆T m ; observed theoretical observed theoretical C =( ) ( ) p;m i s i s
mass % mass % mass % mass % M where ms is the mass of the sample and s the molar SmCl3 41.44 41.43 58.56 58.57 TmCl3 38.62 38.63 61.38 61.37 mass of the sample. The same operating conditions (e. g. initial and fi- nal temperatures, temperature increment, isothermal which revealed satisfactory, was developed empiri- delay and heating rate) are required for the two ex- cally, and no attempt was made to reduce the duration perimental runs. The original SETARAM program of the chlorinating cycle, although this may be pos- performs all necessary calculations. sible. The heat capacity measurements were performed The chemical analysis of the synthesised lan- by the “step method”. Each heating step of 5 K was thanide chlorides was performed by titration methods followed by 400 s isothermal delay. The heating rate for the chloride (mercurimetric) and lanthanide (com- was 1.5 K min 1. All experiments were started at plexometric). The results are presented in Table 1. 300 K and were performed up to 1100 K. The mass All handling of lanthanide chlorides was per- difference of the quartz cells in a particular experi- formed in an argon glove box (water content less than ment did not exceed 1 mg (mass of the cells: 400 - 2 ppmV). Continuous argon purification was achieved 500 mg). The mass of the samples was 200 - 500 mg. by forced recirculation through external molecular sieves. Results and Discussion
Differential Scanning Calorimeter (DSC) Enthalpy of Phase Transition
The enthalpies of phase transitions and heat ca- The enthalpy of fusion was determined for SmCl3. pacities were measured with a SETARAM DSC 121 As supercooling was observed in DSC cooling curves differential scanning calorimeter. The apparatus and (about 19 K), the temperature and fusion enthalpy the measurements procedure were described in details were determined from heating thermograms. in [1 - 3]. The temperature and fusion enthalpy of TmCl3 have been obtained earlier [1] by Calvet high-tempe- Measurements rature microcalorimetry, since the high melting tem- perature was beyond the experimental range of the Quartz cells (7 mm diameter and 15 mm long) DSC 121 apparatus. were filled with the lanthanide chlorides in a glove- box, sealed under vacuum and then placed into the SmCl3 DSC 121 calorimeter. SmCl was found to melt at 950 K with a corre-
Enthalpy of transition measurements were carried 3 0 H sponding enthalpy and entropy of fusion =
out with heating and cooling rates between 1 and fus m
1 0 1 1
S
47.6 k J mol and = 50.3 J mol K , 5 K min 1. fus m respectively. Our measured melting temperature of
The so-called “step method”, used for C measure- p SmCl agrees well with that measured by Poly- ments, was already described in [1, 2]. In this method, 3 achenok and Novikov [5] and that selected by small heating steps are followed by isothermal equi- Pankratz [6], although by about 5 K lower than other librations. Two correlated experiments should be car- and older literature data [7]. ried out to determine the heat capacity of the sample. The first one, with two empty containers of identical TmCl mass, and the second one with one of these loaded 3 with the sample. The heat flux is recorded as a func- TmCl melts at 1092 K with a corresponding en- 3
0 1 H
tion of time and temperature in both runs. The differ- thalpy and entropy of fusion fus m = 35.6 k J mol
0 1 1 S ence of heat flux in both runs is proportional to the and fus m = 32.6 J mol K , respectively [1]. The amount of heat (Qi) necessary to increase the temper- melting temperature and fusion enthalpy agree well ature of the sample by a small temperature increment with the reference data of Thoma [8], but this melting
82 L. Rycerz and M. Gaune-Escard · Thermodynamics of SmCl3 and TmCl3
0 0 0 3 6 2
T H T G T T
–(Gm( )– m(298.15))/ = form m = 651.101 10 + 14.978 10
3 2 1 9 3
T T T
91.27 ln T + 14.534 10 – 4.939 10 – 1.743 10
5 2 1 3
T T T T – 0.17510 + 28621 – 470.02. – 62.366 10 ln – 1015.0.
SmCl3 liquid, 950 K < T < 1300 K: SmCl3 liquid, 1190K 0 0 3 6 2 H T T C = 145.26, = 42.966 10 – 0.188 10 p;m form m 2 1 0 0 3 T T H T H – 4.268 10 – 1010.7, m( )– m(298.15) = 145.26 10 – 19.16, 0 0 3 6 2 G T T T T S = 524.911 10 + 0.188 10 m( ) = 145.26 ln – 671.02, form m 0 0 2 1 3 T T T T H T T G – 2.134 10 – 42.966 10 ln – 1009.6. –( m( )– m(298.15))/ = 145.26 ln 1 + 19160 T – 816.46. The results obtained for selected temperatures are pre- sented in Table 2. Having the thermodynamic functions for SmCl3, one can calculate the thermodynamic functions of its formation as a function of temperature. TmCl3 The formation of SmCl from the elements can be 3 The only existing literature data on the TmCl heat described by the reaction 3 capacity are the experimental data at low tempera- Sm(s) + 1.5 Cl2(g) = SmCl3(s,l), (2) tures (10 - 300 K) obtained by Tolmach et al. [15] by adiabatic calorimetry (100.10 J K 1mol 1 at 300 K). and the related thermodynamic functions of SmCl3 formation depend on the thermodynamic functions Barin and Knacke [12] as well as Knacke et al. [11] made heat capacity estimations. Our experimental of metallic Sm and chlorine gas Cl2. The latter 0 heat capacity values on TmCl3, are presented in Fig- were calculated using literature data for C and p;m 0 ure 2. They agree very well with these estimations Sm(298.15 K) [9]. The enthalpy of SmCl3 forma- 0 as with the low temperature experimental data. Un- H tion at 298.15 K, form m(SmCl3, s, 298.15 K) = fortunately we could not do measurements for liquid 1 –1025.3 kJ mol , also required in this calcula- TmCl because of limitations of the apparatus. tion, was taken from Cordfunke and Konings recent 3 Our experimental heat capacity data were fit- work [14]. ted to the polynomial (1) with the contraint that Two phase changes occur in this system described 0 C (TmCl , s, 298.15 K) be equal to the reported p;m 3 by reaction (2): the first one is the melting of SmCl3 literature value 100.00 J K 1mol 1 [15]. ! at 950 K, and the second one the solid-solid The thermodynamic functions of thulium trichlo- phase transition of Sm at 1190 K with the enthalpy ride were calculated up to 1300 K using our ex- of 3.1 kJ mol 1 [9]. Accordingly, the formation en- 0 1 perimental melting temperature and enthalpy to- H thalpy form m (kJ mol ) and the Gibbs energy of 0 1 G formation form m (kJ mol ) are described by the equations given below: SmCl3 solid, 298.15 K < T < 950 K: 0 3 6 2 H T T form m = 8.366 10 – 0.444 10 2 1 9 3 T T – 9.52710 + 3.487 10 – 1024.6, 0 3 6 2 G T T = 304.636 10 + 0.444 10 form m 2 1 9 3 T T – 4.76310 – 1.743 10 3 T T – 8.34410 ln – 1024.6. SmCl3 liquid, 950 K < T < 1190 K: Fig. 2. Molar heat capacity of TmCl . Open circles: exper- 0 3 6 2 3 H T T form m = 62.366 10 – 14.978 10 imental values, black circle: low temperature datum [15], 2 1 9 3 solid line: polynomial fitting of experimental values. T T – 9.87810 + 3.487 10 – 1015.2, L. Rycerz and M. Gaune-Escard · Thermodynamics of SmCl3 and TmCl3 83 Table 3. The calculated thermodynamic functions of TmCl3 As done for SmCl3, the thermodynamic functions of at selected temperatures from 298.15 to 1300 K. TmCl3 formation were calculated. 0 0 0 This formation from the elements can be described T C S G H TH H H G T p;m –( – )/ – m 298:15 298 form m form m K—JK 1mol 1 — — kJ mol 1 — by the reaction 298.15100.00 150.60 150.60 0.00 –996.3 –919.4 Tm(s) + 1.5 Cl2(g) = TmCl3(s,l). (3) 300 100.02 151.22 150.60 0.18 –996.3 –918.9 400 101.10 180.14 154.54 10.24 –994.1 –893.5 The thermodynamic functions of metallic Tm and 500 102.16 202.82 162.01 20.40 –991.9 –868.6 0 0 S gaseous Cl , C and (298.15 K), necessary for 600 103.20 221.53 170.41 30.67 –989.8 –844.1 2 p;m m 700 104.23 237.52 178.88 41.04 –987.8 –820.0 the calculation, were taken from [9]. The enthalpy of 800 105.26 251.51 187.11 51.52 –985.7 –796.2 0 H 900 106.29 263.96 194.97 62.10 –983.6 –772.6 TmCl3 formation, form m(TmCl3, s ,298.15 K) = 1000 107.32 275.22 202.44 72.78 –981.5 –749.3 –935.4 kJ mol 1, also required, was taken from Cord- 1092 108.27 284.70 208.97 82.69 –979.6 –728.0 funke and Konings [14]. 1092 148.53 317.30 208.97 118.29 –944.0 –728.0 1100 148.53 318.39 209.76 119.48 –943.5 –726.4 Only one phase change occurs in this system de- 1200 148.53 331.31 219.36 134.34 –937.5 –707.0 scribed by reaction (3): it is the melting of TmCl3 1300 148.53 343.20 228.43 149.19 –931.5 –688.0 at 1092 K. Accordingly, the formation enthalpy 0 1 H form m (kJ mol ) and Gibbs energy of formation gether with heat capacity data. The standard entropy 0 1 G (kJ mol ) are described by the equations 0 1 1 form m Sm(TmCl3, s, 298.15 K) = 150.60 J K mol was taken from [16]. Additionally we used the heat ca- TmCl3 solid, 298.15 K < T < 1092 K: 0 pacity value in [9] of liquid TmCl , C (TmCl ,l)= 3 p;m 3 0 3 6 2 H T T 148.53 J K 1mol 1. form m = 21.894 10 – 1.566 10 2 1 9 3 T T Our polynomial dependence of the heat capacity – 0.92810 + 0.627 10 – 1002.4, 0 3 6 2 G T T = 403.179 10 + 1.566 10 on temperature was thus used to calculate the heat form m 0 1 1 T capacity C ( )inJK mol , enthalpy increments 2 1 9 3 T T p;m – 0.464 10 – 0.363 10 0 0 1 0 T H S H ( )– (298.15 K) in kJ mol , entropy and 3 T T m m m – 21.89410 ln – 1002.4. 0 0 T H T Gibbs energy functions (Gm( )– m(298.15))/ in 1 1 JK mol , both for solid and liquid TmCl3. The TmCl3 liquid, 1092 K < T < 1300 K: corresponding equations are given below. The results 0 3 6 2 H T T = 73.348 10 – 6.693 10 for selected temperatures are presented in Table 3. form m 2 1 9 3 T T – 1.04810 + 0.627 10 – 1016.9, 0 3 6 2 G T T TmCl solid, 298.15K 3 form m 2 1 9 3 T T 0 3 5 2 – 0.52410 – 0.363 10 T T C = 97.08 + 10.254 10 – 0.12 10 , p;m 3 T T 0 0 3 – 73.348 10 ln – 1016.9. T H T Hm( )– m(298.15) = 97.08 10 6 2 2 1 T T + 5.12710 , + 0.12 10 – 29.44, In 1971 Dworkin and Bredig [17] have made 0 3 a correlation between the crystal structure of lan- T T T S ( ) = 97.08 ln + 10.254 10 m thanide chlorides and their entropy of melting. They 5 2 T + 0.0610 – 405.64, have found that for lanthanide chlorides with the 0 0 T H T –(Gm( )– m(298.15))/ = Y(OH) -type structure (LaCl , CeCl , PrCl , NdCl , 3 3 3 3 3 3 0 S T T and GdCl ) the entropy of melting (LnCl , 97.08 ln + 5.127 10 3 fus m 3 1 1 T 5 2 1 m) is about (50 4)JK mol , whereas for the T T – 0.0610 + 29440 – 502.71. lanthanide chlorides with the AlCl3-type structure (DyCl3, ErCl ) this entropy or the sum of the en- TmCl3 liquid, 1092 K < T < 1300 K: 3 0 S tropies of transition and of fusion trs m(LnCl3,s, 0 0 C S T = 148.53, T p;m trs)+ fus m(LnCl3, fus) is significantly lower and 1 1 0 0 3 equal to (314)JK mol . T H T Hm( )– m(298.15) = 148.53 10 – 43.90, 0 Tosi et al. [18] have developed these observations T T S ( ) = 148.53 ln – 721.79, m and have proposed that the melting mechanism of 0 0 T H T –(Gm( )– m(298.15))/ = trivalent metal chlorides can be classified into three 1 T 148.53 ln T + 43903 – 870.33. main types in correlation with the character of the 84 L. Rycerz and M. Gaune-Escard · Thermodynamics of SmCl3 and TmCl3 chemical bond. They have classified the lanthanide ErCl3 (AlCl3- type structure) [1], that is in excel- chlorides into three groups depending on the crystal lent agreement with the above observations (41.9 and 1 1 structure: AlCl3-, UCl3-, and PuBr3-type structure. 34.9 J K mol , respectively). Moreover, looking 0 S The AlCl3-type structure is layered and can almost at the values of the melting entropy fus m(SmCl3, 1 1 0 S T be viewed as cubic close packing of Cl ions inside T fus) = 50.3 J K mol and fus m(EuCl3, fus)= which the metal ions occupy suitable octahedral sites. 50.3 J K 1mol 1 [3], one can come to the conclu- The UCl3-type structure (also known as the Y(OH)3- sion that these chlorides both have the UCl3-type 0 S T type structure) is described as hexagonal, with each U structure, whereas TmCl3(fus m(TmCl3, fus)= 1 1 surrounded by six Cl on the corner of a trigonal prism 32.6 J K mol ) has the AlCl3-type structure. This is and further coordinated by the three coplanar Cl’s at in excellent agreement with literature data: SmCl3 and somewhat larger distance. The PuBr3-type structure EuCl3 have the UCl3-type structure [7] and TmCl3 the appears to be of a transitional type between the AlCl3- AlCl3-type structure [20]. and UCl3-type structures. In summary, the melting from the UCl3-type Acknowledgements (LaCl3, CeCl3, PrCl3, NdCl3 and GdCl3) or PuBr3- type structure (TbCl3) involves appreciably higher One of us (LR) acknowledges support from the entropies than from the AlCl3-type (ErCl3, HoCl3, Polish Committee for Scientific Research under the DyCl3). The values of this entropies are (504), Grant 3 T09A 091 18. LR also wishes to thank 1 1 (40.9) and (314)JK mol , respectively. the Institut des Systemes Thermiques Industriels 0 S We have determined previously the sum trs m + (IUSTI) for hospitality and support during this 0 S fus m for TbCl3 (PuBr3-type structure) [19] and work. [1] M. Gaune-Escard, L. Rycerz, W. Szczepaniak, and [11] O. Knacke, O. Kubaschewski, and K. Hesselmann, A. Bogacz, J. Alloys Comp. 204, 193 (1994). Thermochemical Properties of Inorganic Substances, [2] M. Gaune-Escard, A. Bogacz, L. Rycerz, and 2nd Ed. Springer-Verlag, Berlin 1991. W. Szczepaniak, J. Alloys Comp. 235, 176 (1996). [12] I. Barin, O. Knacke, and O. Kubaschewski, Thermo- [3] L. Rycerz and M. Gaune-Escard, Z. Naturforsch., in chemical Properties of Inorganic Substances, Supple- press. ment, Springer-Verlag, Berlin 1977. [4] M. Gaune-Escard, A. Bogacz, L. Rycerz, and [13] O. Kubaschewski and C. B. Alcock, Metallurgical W. Szczepaniak, Thermochim. Acta 236, 67 (1994). Thermochemistry, 5th Ed., Pergamon Press, Oxford [5] O. G. Polyachenok and G. I. Novikov, Russ. J. Inorg. 1979. Chem. 9, 42 (1964). [14] E. H .P. Cordfunke and R. J. M. Konings, Ther- [6] Z. B. Pankratz, Thermodynamic Properties of Halides, mochim. Acta 375, 17 (2001). Bull. 674, 1984 (US Bureau of Mines). [15] P. I. Tolmach, V. E. Gorbunov, K. S. Gavrichev, L. N. [7] J. A. Gibson, J. F. Miller, P. S. Kennedy, and G. W. Golyushina, and V. F. Goryushkin, Zh. Fiz. Khim. 64, Prengstorff, The Properties of the Rare Earth Metals 1090 (1990). and Compounds, compiled for The Rare Earth Reseach [16] D. M. Laptev, Physico-chemical Properties of Lan- Group (1959). thanide Chlorides and Interactions in LnCl3-LnCl2 [8] R. E. Thoma, The Rare Earth Halides, in L. Eyring Systems, Dr Sci. Thesis, Novokuznetsk, 1996 (in Rus- (ed.), Progress in the Science and Technology of the sian). Rare Earths, Pergamon, New York !966, p. 90. [17] A. S. Dworkin and M. A. Bredig, High Temp. Sci. [9] O. Kubaschewski, C. B. Alcoock, and P. J. Spencer, 3(1), 81 (1971). Materials Thermochemistry, 6th Edition, Pergamon [18] M. P.Tosi, G. Pastore, M. I. Saboungi, and D. L. Price, Press Ltd, New York 1993. Physica Scripta T39, 367 (1991). [10] J. A. Sommers and E. F. Westrum, J. Chem. Thermo- [19] L. Rycerz and M. Gaune-Escard, J. Therm. Anal. dyn. 9, 1 (1977). Calorimetry 65, (2001), in press. [20] D. H. Templeton and G. F. Carter, J. Phys. Chem. 58, 940 (1954).