A. Bogacz

Enthalpies of phase transition in the lanthanide chlorides LaCl3, CeCl3, PrCl3, NdCl3, GdCl3, DyCl3, ErCl3 and TmCl3

Abstract The enthalpies of phase transition in the lanthanide chlorides have been measured with a differential scanning calorimeter and also with a Calvet-type microcalorimeter to within an experimental error of ±2%. The molar enthalpies of fusion of LaCl 3 , CeCl 3 , PrCl 3 , NdCl 3 , GdCl 3 , DyCl 3 , ErCl 3 and TmCl 3 are 55.7, 55.5, 52.1, 48.1, 40.6, 22.8, 31.1 and 35.6 kJ mol −1 respectively. The existence of a solid-solid phase transition was found in DyCl 3 and ErCl 3 at 611 and 1025 K with a molar enthalpy of transition of 1.4 and 5.3 kJ mol −1 respectively. A significant difference (8.5 kJ mol −1 ) between the absolute values of molar enthalpies of crystallization and fusion was found for LaCl 3 at 1124±3 K; this unusual behaviour was explained by an “after-fusion” effect. The entropies of fusion are discussed in terms of structural types of the lanthanide chlorides.

Heat capacity of LaCl3, CeCl3, PrCl3, NdCl3, GdCl3, DyCl3

Abstract Heat capacities of LaCl3, CeCl3, PrCl3, NdCl3, GdCl3, DyCl3 have been measured by differential scanning calorimetry in the temperature range from 300 K to melting temperatures of the compounds. Heat capacities of liquid PrCl3, NdCl3, GdCl3, DyCl3 have also been registered. These results have been compared with literature data and fitted by a linear temperature dependence. The temperature coefficients have been given.

Calorimetric investigation of NdCl3MCl liquid mixtures (where M is Na, K, Rb, Cs)

Abstract The molar enthalpies of mixing ΔmixHm in the liquid NaClNdCl3, KClNdCl3, RbClNdCl3 and CsClNdCl3 binary systems have been measured over the whole composition range at 1124, 1065, 1122 and 1122 K, respectively, with an accuracy of about 6%. The apparatus used was a Calvet-type high-temperature microcalorimeter and mixing of the two liquid components was obtained by the break-off ampoule technique. In the investigated systems, the enthalpies of mixing are negative with minimum values at about −5.7, −16.6, −20.2 and −23.4 kJ mol−1, respectively, at χNdCl3 = 0.4. These values are almost identical, within the experimental accuracy, to those in other previously investigated MClLnCl3 mixtures. The molar enthalpies of formation ΔfHm(K3NdCl6, 1, 1065)/kJ mol−1, ΔfHm(Rb3NdCl6, 1, 1122)/kJ mol−1 and ΔfHm(Cs3NdCl6, 1, 1122)/kJ mol−1, according to the reaction 3 MCI(1) + LnCl3(1)= M3LnCl6(1), are equal to −55.2, −68.8 and −80.8 kJ mol−1, respectively. The least-squares coefficients A, B, C, D, E of the equation for the interaction parameter λ= A + Bχ + Cχ2 + Dχ3 + Eχ4χ4 (in kJ mol−1) are presented.

Entropies of phase transitions in the M3LnCl6 compounds (MK, Rb, Cs; LnLa, Ce, Pr, Nd) and K2LaCl5

Abstract The molar enthalpies of the solid-solid and solid-liquid phase transitions were determined by differential scanning calorimetry for the compounds K2LaCl5, Rb3LaCl6, Cs3LaCl6, K3CeCl6, Rb3CeCl6, Cs3CeCl6, K3PrCl6, Rb3PrCl6, Cs3PrCl6, K3NdCl6, Rb3NdCl6 and Cs3NdCl6. The K3LnCl6 (LnCe, Pr, Nd) and Rb3LaCl6 compounds, which do not exist at room temperature, are formed at high temperature with a considerable loss of enthalpy (48–55 kJ mol−1) compensated by a high gain in entropy (63–65 J mol−1 K−1). The Cs3LnCl6 (LnLa, Ce, Pr, Nd) compounds are stable at ambient temperature; they undergo a transition in the solid state with a corresponding enthalpy and entropy of 7.4–7.8 kJ mol−1 and 10.9–11.2 J mol−1 K−1. The calorimetric measurements show that Rb3CeCl6, Rb3PrCl6 and Rb3NdCl6 are also probably stable at room temperature. The enthalpies and entropies of fusion are reported for all the compounds mentioned above.

Formation enthalpies of the MBrLaBr3 liquid mixtures (M = Li, Na, K, Rb, Cs)

Abstract Molar enthalpies of mixing of the LiBrLaBr 3 , NaBrLaBr 3 , KBrLaBr 3 , RbBrLaBr 3 and CsBrLaBr 3 systems have been measured with a Calvet-type high-temperature microcalorimeter. The enthalpies decrease gradually from −0.67 kJ mol −1 for the lithium system through −4.32, −10.73 and −14.97 kJ mol −1 for the sodium, potassium, and rubidium systems to −16.81 kJ mol −1 for that of cesium at the composition of the 3 MBr·LaBr 3 compound. The results have been discussed in terms of the conformal solution theory of Davis as well as in terms of relative ionic potentials.

Enthalpies of mixing in the DyCl3-NaCl, DyCl3-KCl and DyCl3-PrCl3 liquid systems

Abstract The molar enthalpies of mixing ( Δ mix H m ) in the DyCl 3 -NaCl, DyCl 3 -KCl and DyCl 3 -PrCl 3 liquid binary systems were measured at temperature of 1100, 1070 and 1074 K respectively over the whole composition range under argon at atmospheric pressure. The apparatus used was a Calvet-type high temperature microcalorimeter and mixing of the two liquid components was achieved by the ampoule break-off technique; the experimental uncertainties were about 6% (DyCl 3 -NaCl, DyCl 3 -KCl) and 10% (DyCl 3 -PrCl 3 ). For the first two systems, the enthalpies of mixing are negative over the whole composition range, with minima at x DyCl 3 ≈ 0.3 of about −8 and −21 kJ mol −1 respectively. In the DyCl 3 -PrCl 3 system the enthalpy-of-mixing values are positive, with a maximum at x DyCl 3 ≈ 0.4 of about 760 J mol −1 . The least-squares coefficients A , B , C , and D of the equation for the interaction parameter λ (kJ mol −1 ) = A + Bx + Cx 2 + Dx 3 are presented.

Calorimetric investigation of PrCl3NaCl and PrCl3KCl liquid mixtures

Abstract The present work is part of the thermodynamic research performed on the LnCl 3 MCl systems (where Ln is lanthanide and M is alkali metal). The molar enthalpies of mixing Δ mix H m in the NaClPrCl 3 and KClPrCl 3 liquid binary systems were measured at 1122 K over the whole composition range under argon at atmospheric pressure, with an accuracy of about 6%. The apparatus used was a Calvet-type high-temperature microcalorimeter and mixing of the two liquid components was obtained by the break-off ampoule technique. In the systems, the enthalpies of mixing values are negative, with a minimum value of about −7 and −16 kJ mol −1 for NaClPrCl 3 and KClPrCl 3 , respectively, at χ PrCl 3 ≈Fl 0.4. These values are very similar to those relative to the systems MClLnCl 3 previously investigated. The molar enthalpies of formation Δ f H m (K 3 PrCl 6 , 1, 1122 K)/kJ mol −1 , Δ f H m (Rb 3 PrCl 6 , 1, 1122 K)/kJ mol −1 and Δ f H m (Cs 3 PrCl 6 , 1, 1122 K)/kJ mol −1 , according to the reaction 3MCl(1) + PrCl 3 (1) = M 3 PrCl 6 (1), are equal to −55.9, −66.4, and −80.4 kJ mol −1 respectively, and are almost identical (in the limits of experimental uncertainty) to those of the compounds M 3 LnCl 6 (where M is K, Rb, Cs, and Ln is La, Ce, Nd) previously investigated. The least-squares coefficients A, B, C, D and E of the equation for the interaction parameter λ = A + B χ + C χ 2 + D χ 3 + E χ 4 (in kJ mol −1 are presented.

Electrical conductivity of molten LnCl3 and M3LnCl6 compounds (Ln La, Ce, Pr, Nd; M K, Rb, Cs)

Abstract The electrical conductivities of molten lanthanide chlorides LnCl 3 and definite compounds M 3 LnCl 6 (where Ln  La, Ce, Pr, Nd and M  K, Rb, Cs) have been determined. The conductivities were well represented as quadratic functions of temperature. The molar conductivities for pure lanthanide chlorides were derived and represented well by an Arrhenius-type function of temperature. Electrical conduction in investigated melts was discussed on the basis of complex formation and polymerization.

Enthalpies of mixing in PrCl3CaCl2 and NdCl3CaCl2 liquid systems

Abstract The molar enthalpies of mixing Δ mix H m in the PrCl 3 CaCl 2 and NdCl 3 CaCl 2 liquid binary systems were measured at 1073 K over the whole composition range under argon at atmospheric pressure. The apparatus used was a Calvet-type high-temperature micro-calorimeter and mixing of the two liquid components was obtained by the break-off ampoule technique. In both systems the plots of enthalpies of mixing versus composition were “S-shaped” curves. The enthalpy of mixing values are positive for NdCl 3 - and PrCl 3 -rich compositions, and negative for other compositions. These values are very small (from about −200 to about 180 J mol −1 ). In the PrCl 3 CaCl 2 and NdCl 3 CaCl 2 liquid binary systems,Δ mix H m ≈0 at χ PrCl 3 ≈ 0.6 and at χ NdCl 3 ≈ 0.4, respectively. These results are discussed in terms of equilibrium between the LnCl 3 (where Ln is Pr, Nd) polymers and anionic complexes as a function of the composition of the melts.

Calorimetric investigations of the MBr−NdBr3 melts (M=Li, Na, K, Cs)

Present work is a part of thermodynamic research program on the MX−LnX3 system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr−NdBr3, NaBr−NdBr3 and KBr−NdBr3 liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atXNdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals.Molar enthalpies of solid-solid and solid-liquid phase transitions of K3NdBr6 and Cs3NdBr6 have been also determined by differential scanning calorimetry (DSC). K3NdBr6 is formed at 689 K from KBr and K2NdBr5 with enthalpy of 44.0 kJ·mol−1 whereas Cs3NdBr6 is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol−1. Enthalpies of melting have been also determined.ZusammenfassungVorliegende Arbeit ist ein Teil eines thermodynamischen Forschungsprogrammes an MX−LnX3-Systemen (M=Alkalimetall,X=Cl, Br undLn=Lanthanid). Mittels direkter Kalorimetrie wurden die molaren Mischungsenthalpien in den flüssigen binären Systemen LiBr−NdBr3, NaBr−NdBr3 und KBr−NdBr3 bei 1063 K im gesamten Konzentrationsbereich bestimmt. Die untersuchten Systeme sind generell durch negative Mischungsenthalpien mit einem Minimum beiXNdBr3≈0.3–0.4 gekennzeichnet. Diese Enthalpien sinken mit abnehmendem Alkalimetallradius.Mittels DSC wurden weiterhin die molaren Enthalpien für Feststoff-Feststoff- und für Feststoff-Flüssigkeits-Umwandlungen von K3NdBr6 und Cs3NdBr6 ermittelt. K3NdBr6 wird bei 689 K aus KBr und K2NdBr5 mit einer Enthalpie von 44.0 kJ/mol gebildet, während Cs3NdBr6 bei Raumtemperatur stabil ist und im Festzustand bei 731 K einer Phasenumwandlung mit einer Enthalpie von 8.8 kJ/mol unterliegt. Die Schmelzenthalpien wurden ebenfalls ermittelt.