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The L-tryptophan sublimation was studied by high-temperature mass spectrometry in the temperature range 395–493 K. The compound evaporates congruently in the form of monomeric molecules. The saturated vapor pressure at 485 K was determined by the Knudsen effusion method. In combination with mass spectrometric data, the pressure equation ln (p, Pa) = –(19943±304)/T + (40.568±0.688) is recommended for the temperature range 395–493 K. The enthalpy of 167.5±1.6 kJ/mol for sublimation at 298.15 K was determined on the basis of the second and third laws of thermodynamics.

The materials typically used for oxygen transport membranes, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) tend to decompose due to their low thermochemical stability under reducing atmosphere. Fe- and Co-doped SrTiO3 (SrTi1-x-yCoxFeyO3-δ, x + y ≤ 0.35) (STCF) materials showing an oxygen transport comparable to LSCF have great potential for application in ion-transport-devices. In this study, the thermochemical stability of pure perovskite-structured STCF was investigated after annealing in a syngas atmosphere at 600–900 °C. The phase composition of the materials after annealing was characterized by means of X-ray diffraction (XRD). The thermodynamic activities of SrO, FeO, and CoO in the STCF materials were evaluated using Knudsen effusion mass spectrometry (KEMS). Co-doped SrTiO3 (STC) materials were not stable after annealing in the syngas atmosphere above 5 mol% Co-substitution. Ruddlesden-Popper-like phases and SrCO3 were detected after annealing at 600 °C. In contrast, Fe substitution (STF) showed good stability after annealing in syngas upto 35 mol% substitution.

In the temperature range of 388–506 K in saturated vapor over 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImTfO) ionic liquid along with the monomer neutral ionic pairs (NIP) C+A–, where C+ is EMIm+ (cation) and A– is TfO– (anion), the dimers (C+A–)2 were registered with a fraction of 0.5% for the first time. The corresponding associative ions C2A+ and C3A2+ formed as a result of attachment of the cation C+ to the monomer and dimer NIPs were also found. The evaporation enthalpies ΔvH°(298.15 K) = 128 ± 5 kJ mol–1 (monomer) and ΔvH°(298.15 K) = 161 ± 9 kJ mol–1 (dimer) were determined. The enthalpy of formation of the monomer and dimer NIP of EMImTfO at 298.15 K in the state of ideal gas were derived from the evaporation enthalpies: –1033 ± 50 kJ mol–1 and –2160 ± 50 kJ mol–1, respectively. The desorption enthalpies ΔdesH°(T) of the C+, C2A+, and C3A2+ cations were found to be 164 ± 5 kJ mol–1 (435 K), 159 ± 7 kJ mol–1 (435 K), and 152 ± 21 kJ mol–1(457 K), respectively. The equilibrium constants of the heterophase ion-molecular reactions were measured and the formation enthalpies of associative ions were calculated: ΔfH°(C2A+, 298.15 K) = –493 ± 50 kJ mol–1 and ΔfH°(C3A2+, 298.15 K) = –1631 ± 50 kJ mol–1.

The thermodynamic activity of lithium was measured by Knudsen Effusion Mass Spectrometry (KEMS) within the Cu-Li-Sn system in the liquid region. For this purpose, eleven samples were studied between 773 and 1078 K in the Sn-rich part of the Cu-Li-Sn phase diagram. Mixing enthalpies, entropies and Gibbs energies were derived directly from the measured thermodynamic activity. The measured thermodynamic activities of Li were fitted to the Redlich-Kister-Muggianu (RKM) sub-regular solution model, by taking ternary interactions into account, using a mathematical regression procedure. Thereby, the partial and integral excess thermodynamic properties, the activities of Li, Cu and Sn and the ternary interaction L-parameters, as a function of temperature, were obtained.

Ion-molecular equilibria LaI4– + LnI3 = LnI4– + LaI3, Ln2I7– = LnI3,cr + LnI4– (Ln = Ce, Pr, Gd, Tb, Tm, and Lu), and 3LaBr4– + 4LaI3 = 3LaI4– + 4LaBr3 in vapors over the LaI3-CeI3-PrI3-GdI3, LaI3-GdI3-TbI3-TmI3, and LaI3-LaBr3 mixtures and the pure lanthanide triiodides were studied in the temperature range of 700–1050 K by Knudsen effusion mass spectrometry. The equilibrium constants were measured and the reaction enthalpies were calculated by the techniques of the second and third laws of thermodynamics. The standard formation enthalpies of ions, ΔfH°(298.15 K) (in kJ mol–1), were determined to be –832 ± 21 (LaI4–), –834 ± 23 (CeI4–), –834 ± 25 (PrI4–), –812 ± 24 (GdI4–), –813 ± 25 (TbI4–), –817 ± 23 (TmI4–), –806 ± 25 (LuI4–), –1399 ± 45 (La2I7–), –1402 ± 46 (Ce2I7–), –1417 ± 47 (Pr2I7–), –1356 ± 47 (Gd2I7–), –1365 ± 47 (Tb2I7–), –1366 ± 46 (Tm2I7–), and –1322 ± 47 (Lu2I7–).

Sublimation of 1,3,3,6′-tetramethyl-8′-formyl-spiroindoline-2,2′-[2H] -chromene (SP-1) and 3,6′-dimethyl-8′-formyl-spiro (4-oxo-3,4-dihydro-2H-1,3-benzoxazine)-2,2′-[2H] -chromene (SP-2) was studied by Knudsen effusion mass spectrometry in the temperature range 309–363 K and 331–384 K, respectively. It has been shown that, in the temperature range under study, both spiropyrans are thermally stable and sublime congruently in the form of monomeric molecules. The dependences of the saturated vapor pressure (Pa) on temperature are described by the equations: lg p (SP-1) = – (6.239±0.093)∙103∙T–1+ (15.832±0.278), lg p (SP-2) = – (6.625±0.111)∙103∙T–1 + (15.459±0.312). The sublimation enthalpies have been evaluated by the second law method as ΔsH°(298.15 K) = 119±5 kJ∙mol–1 (SP-1) and ΔsH°(298.15 K) = 128±5 kJ∙mol–1 (SP-2). The enthalpies of formation of spiropyran molecules in the ideal gas state, ΔfH°g(298.15 K) = 199±9 kJ∙mol–1 (SP-1) and ΔfH°g(298.15 K) = –296±10 kJ∙mol–1 (SP-2), have been calculated using isodesmic reactions method implying quantum chemical calculations. Combining the latter values with the corresponding sublimation enthalpies the enthalpies of formation for crystalline state spiropyrans were determined: ΔfH°cr(298.15 K) = 80±10 kJ∙mol–1 (SP-1) and ΔfH°cr(298.15 K) = –424±11 kJ∙mol–1 (SP-2).

A multi-technique approach based on Knudsen effusion mass spectrometry, gas phase chromatography, mass spectrometry, NMR and IR spectroscopy, thermal analysis, and quantum-chemical calculations was used to study the evaporation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4). The saturated vapor over BMImBF4 was shown to have a complex composition which consisted of the neutral ion pairs (NIPs) [BMIm+][BF4−], imidazole-2-ylidene C8N2H14BF3, 1-methylimidazole C4N2H6, 1-butene C4H8, hydrogen fluoride HF, and boron trifluoride BF3. The vapor composition strongly depends on the evaporation conditions, shifting from congruent evaporation in the form of NIP under Langmuir conditions (open surface) to primary evaporation in the form of decomposition products under equilibrium conditions (Knudsen cell). Decomposition into imidazole-2-ylidene and HF is preferred. The vapor composition of BMImBF4 is temperature-depended as well: the fraction ratio of [BMIm+][BF4−] NIPs to decomposition products decreased by about a factor of three in the temperature range from 450 K to 510 K.

The results of systematic investigations of the molecular and ionic sublimation of lanthanide triiodides LnI3 (Ln = La–Lu) by Knudsen effusion mass spectrometry are summarized. The LnI3 monomer and Ln2I6 dimer molecules as well as the associated LnI4– and Ln2I7– ions are the main constituents of saturated vapor. The total fraction of ions is negligible compared to that of neutral species. The partial vapor pressures of the molecules and the equilibrium constants of ion-molecular reactions are determined. On the basis of a joint analysis of all vaporization thermodynamics data obtained in the period from 1952 to 2020, the sublimation enthalpies ΔsHo(298.15 K) of LnI3 in the form of monomer and dimer molecules are recommended. The standard thermochemical properties such as the formation enthalpy and atomization/dissociation enthalpy of the molecules and ions are obtained. The variation of these properties along the lanthanide series is discussed.

(La,Sr)(Co,Fe)O3-δ is very common as cathode material in SOFC applications. Sr in this type of cathode material is very reactive to form secondary phases with other oxides, which affect micro-structures and properties of the cathode materials, GDC layers and ZrO2-based electrolytes. The Sr-related degradation issues, Cr poisoning and volatile Sr species formation, are studied. As supplement to existing experimental knowledge on Cr poisoning, specific thermodynamic aspects for Cr poisoning are discussed. The thermodynamic calculations show that the partial pressure pCrO3 has a stronger temperature dependence than pCrO2(OH)2, and when considering the reaction between SrO and CrO3(g), dependent on different pCrO3 and pO2, different Sr–Cr–O compounds SrCrO4, SrCrO3, Sr3Cr2O8 or Sr2CrO4 could be formed. In addition, thermodynamic calculations show that in the presence of water vapor, formation of volatile Sr(OH)2 is possible as well. pSr(OH)2 depends on temperature, pH2O and SrO activity and can be of the same order of magnitude as pCrO2(OH)2. Volatile Sr(OH)2 can diffuse through the porous GDC layer and react with ZrO2-based electrolytes to form SrZrO3 precipitates. The reaction between gaseous Sr species and 8YSZ sheet is studied experimentally. The surface of the 8YSZ sheet is investigated by SEM coupled with EDS, confirming the deposition of Sr.

The sublimation of solid gadolinium and thulium triiodides was studied by Knudsen effusion mass spectrometry. The partial vapor pressures [atm] of the monomer and dimer molecules were determined as: ln p (GdI 3 ) = −(32.31 ± 0.18) × 10 3 / T + (21.38 ± 0.21) for 777–946 K; ln p (Gd 2 I 6 ) = −(38.07 ± 0.42) × 10 3 / T + (24.49 ± 0.47) for 843–946 K; ln p (TmI 3 ) = −(31.84 ± 0.25) × 10 3 / T + (21.88 ± 0.29) for 760–965 K; and ln p (Tm 2 I 6 ) = −(38.23 ± 0.27) × 10 3 / T + (25.71 ± 0.43) for 799–965 K. In addition, the trimers Gd 3 I 9 and Tm 3 I 9 were detected in very small fractions. On the basis of a joint analysis of all available data in literature, the sublimation enthalpies [kJ mol −1 ] at 298.15 K are recommended as 283 ± 9 (GdI 3 ), 336 ± 16 (Gd 2 I 6 ), 366 ± 50 (Gd 3 I 9 ), 276 ± 3 (TmI 3 ), 330 ± 6 (Tm 2 I 6 ), and 354 ± 50 (Tm 3 I 9 ). The standard formation enthalpies [kJ mol −1 ] of the gaseous species at 298.15 K are −341 ± 9 (GdI 3 ), −912 ± 16 (Gd 2 I 6 ), −1506 ± 50 (Gd 3 I 9 ), −344 ± 5 (TmI 3 ), −909 ± 7 (Tm 2 I 6 ), and −1506 ± 50 (Tm 3 I 9 ).

A mass spectrometric method for the determination of the electron work function based on analysis of thermochemical cycles including molecules and ions has been described. Application of this method for calculation of the electron work functions of lanthanum, cerium, and praseodymium triiodides gave 3.8±0.3 eV for LaI3, 3.5±0.3 eV for CeI3, and 2.8±0.3 eV for PrI3.

This work was supported by the Ministry of science and higher education of the Russian Federation in the framework of Government order (№ FZZW-2020-0007). The authors are grateful to Ph.D. N.L. Pechnikova and Dr. V.V. Aleksandriiskii (Research Sharing Center of the Ivanovo State University of Chemistry and Technology) for the synthesis of TPP and the study of the NMR spectrum, respectively, Ph.D. D.V. Tyurin (Department of Chemistry and Technology of Higher Molecular Compounds of the Ivanovo State University of Chemistry and Technology) for the MALDI spectrum of TPP and Ph.D. A.A. Gushchin (Department of Industrial Ecology of the Ivanovo State University of Chemistry and Technology) for the analysis of TPP sample by the high performance liquid chromatography. The authors also thank Ph.D. M.S. Gruzdev (Research Sharing Center of the Institute of Solution Chemistry RAS, Ivanovo) and Ph.D. D.N. Sergeev (Forschungszentrum Julich, IEK-2, Germany) for measuring the heat capacity of TPP in the temperature ranges 169–302 K and 328–568 K, respectively.

The Sm, Eu, and Yb tri- and dichlorides were investigated by Knudsen effusion mass spectrometry. It was found out by the analysis of mass spectra and ionization efficiency curves that the vapor composition is complex due to the partial high temperature decomposition/disproportionation of the samples. Up to five vapor species were identified for both LnCl3 (LnCl3, LnCl2, Ln2Cl4, Ln2Cl5, and Ln2Cl6) and LnCl2 (LnCl3, LnCl2, LnCl, Ln, and Ln2Cl4). The quantitative evaluation of vapor composition was made. It indicates that the disproportionation of SmCl2 and EuCl2 is negligible in the temperature range studied whereas that of YbCl2 and the decomposition of SmCl3 and YbCl3 cannot be neglected.

The molecular and ionic sublimation of neodymium, dysprosium, holmium, and erbium triiodides was studied by Knudsen effusion mass spectrometry. The monomer LnI3, dimer Ln2I6, and trimer Ln3I9 molecules and the ions LnI4– and Ln2I7– were found to be constituents of the saturated vapors in each case. The partial pressures of the vapor species and the equilibrium constants of the ion-molecular reactions were calculated. On the basis of a joint analysis of all literature data, the sublimation enthalpies ΔsHo(298.15 K)/(kJ mol−1) are recommended as 293 ± 3 (NdI3), 387 ± 30 (Nd2I6), 281 ± 3 (DyI3), 353 ± 12 (Dy2I6), 281 ± 3 (HoI3), 352 ± 6 (Ho2I6), 278 ± 4 (ErI3), and 350 ± 30 (Er2I6). The standard formation enthalpies ΔfHo(298.15 K)/(kJ mol−1) of the molecules and ions were determined to be −346 ± 5 (NdI3), −891 ± 30 (Nd2I6), −815 ± 23 (NdI4–), −1379 ± 46 (Nd2I7–), −336 ± 4 (DyI3), −880 ± 12 (Dy2I6), −811 ± 23 (DyI4–), −1360 ± 46 (Dy2I7–), −342 ± 4 (HoI3), −894 ± 7 (Ho2I6), −814 ± 23 (HoI4–), −1372 ± 46 (Ho2I7–), −341 ± 5 (ErI3), −888 ± 30 (Er2I6), −819 ± 23 (ErI4–), and −1377 ± 46 (Er2I7–).

The molecular and ionic composition of vapor over EMImNTf2 ionic liquid was studied by Knudsen effusion mass spectrometry. Along with the neutral ionic pairs the positive C+, C2A+, and negative A−, CA2− ions (where C+ is the EMIm+ cation and A− the NTf2− anion) were observed under equilibrium conditions for the first time. The total fraction of ionic vapor species was found to be 10− 9–10− 11 in the temperature range of 437–519 K.

The thermal emission of alkali metal ions from Al30-pillared montmorillonite in comparison with its natural form was studied by mass spectrometry in the temperature range 770–930 K. The measurements were carried out on a magnetic mass spectrometer MI-1201. For natural montmorillonite, the densities of the emission currents (j) decrease in the mass spectrum in the following sequence (T = 805 K, A/cm2): K+ (4.55 · 10−14), Cs+ (9.72 · 10−15), Rb+ (1.13 · 10−15), Na+ (1.75 · 10−16), Li+ (3.37 · 10−17). For Al30-pillared montmorillonite, thermionic emission undergoes temperature-time changes. In the low-temperature section of the investigated range (770–805 K), the value of j increases substantially for all ions in comparison with natural montmorillonite (T = 805 K, A/cm2): Cs+ (6.47 · 10−13), K+ (9.44 · 10−14), Na+ (3.34 · 10−15), Rb+ (1.77 · 10−15), and Li+ (4.59 · 10−16). A reversible anomaly is observed in the temperature range 805–832 K: with increasing temperature, the value of j of alkaline ions falls abruptly. This effect increases with increasing ionic radius of M+. After a long heating-up period, this anomaly disappears and the lnj-1/T dependence acquires a classical linear form. The results are interpreted from the point of view of the dependence of the efficiency of thermionic emission on the phase transformations of pillars.

The gas phase equilibria Ba + LnX = BaX + Ln (Ln = Sm, Eu, Yb; X = Cl, Br, I) were investigated by Knudsen effusion mass spectrometry using a low energy of ionizing electrons to avoid fragmentation processes. The BaX molecules were used as references with well-established bond energies. The atomization enthalpies ΔatH0° of the LnX molecules were determined to be 427 ± 9 (SmCl), 409 ± 9 (EuCl), 366 ± 9 (YbCl), 360 ± 10 (SmBr), 356 ± 13 (EuBr), 316 ± 9 (YbBr), 317 ± 10 (SmI), 293 ± 10 (EuI), and 283 ± 10 (YbI) kJ·mol−1.

An approach for the determination of atomization energies based on the extrapolated difference technique in the framework of Knudsen effusion mass spectrometry is proposed. Its essence is the use of thermodynamic data for the determination of the appearance energy of fragment ions of a reference and a special mathematical treatment of the ionization efficiency functions. The advantages of this approach are demonstrated for the cases of incongruently vaporizing lanthanide bromides that suffer from decomposition or disproportionation at high temperatures. The atomization energies for SmBr2 (7.78 ± 0.12 eV), EuBr2 (7.51 ± 0.11 eV), YbBr2 (7.25 ± 0.13 eV), SmBr3 (11.09 ± 0.10 eV), and YbBr3 (10.23 ± 0.09 eV) molecules have been determined for the first time.

RATIONALE The vaporization of Sm, Eu, and Yb tri- and dibromides is accompanied by decomposition and disproportionation reactions. These result in complex vapor compositions whose analysis is an intricate problem for experimentalists. Approaches have been developed to interpret mass spectra and accurately determine the vapor composition of thermally unstable compounds. METHODS A sector type magnet instrument was used. A combined ion source allowed the study of both the molecular and ionic vapor compositions in the electron ionization (EI) and the thermionic emission (TE) modes. The methodological approaches were based on a joint analysis of the ionization efficiency functions, the temperature and time dependences of the ion currents, and special mathematical data evaluation. RESULTS The vaporization of SmBr3, YbBr3, SmBr2, EuBr2, and YbBr2 was studied in the temperature range of 850–1300 K. An initial stage of incongruent vaporization was observed in the case of the tribromides, SmBr2, and YbBr2. This eventually changed to a congruent vaporization stage. Various neutral (Ln, Br, Br2, LnBr, LnBr2, LnBr3, Ln2Br4, Ln2Br5, and Ln2Br6) and charged (Br–, LnBr3–, LnBr4–) species were detected at different vaporization stages. CONCLUSIONS The quantitative vapor composition of Sm, Eu, and Yb tri- and dibromides was determined. It was found that only EuBr2 was stable in the studied temperature range. The developed approaches can be useful in the case of other thermally unstable compounds.

The vaporization of Al-Dy-O mixtures has been investigated by the Knudsen effusion mass spectrometry technique. The saturated vapor has been found to consist of the atoms Al, O and the molecules AlO, Al2O, DyO. At the initial stage the vaporization of Dy2O3 and Al2O3-Dy2O3 mixtures was found to be incongruent and accompanied by some loss of oxygen. An attainment of congruently vaporizing composition and equilibrium state takes quite a long time. The activities of binary oxides have been measured at T = 2130 K. The Gibbs energies and enthalpies have been derived for formation of the compounds Dy4Al2O9, DyAlO3 and Dy3Al5O12 from sesquioxides.

Vaporization of thermally unstable SmBr3, YbBr3, SmBr2, EuBr2, and YbBr2 is investigated by the high temperature mass spectrometry. It is found that the composition of vapor phase changes in the course of vaporization due to thermal decomposition of tribromides and disproportionation of dibromides. The neutral (Ln, Br, Br2, LnBr, LnBr2, LnBr3, Ln2Br4, Ln2Br5, and Ln2Br6) and charged (Br–, LnBr3 –, LnBr4 –) species are present in vapor at various vaporization stages. Eventually for each sample studied the vaporization approaches steadiness when the LnBr2 molecules are predominant in the vapor.

Vaporization of five liquid binary Li-Sn alloys (molar fractions x Li = 0.1; 0.2; 0.3; 0.4; and 0.5) as well as pure Li have been investigated in the temperature range 576-1040 K by Knudsen effusion mass spectrometry (KEMS). The Thermodynamic activity of lithium was determined by the ratio of ion current intensities measured over the alloy and the pure metal. The activity of tin was determined by Gibbs-Duhem integration. The results were approximated by Redlich-Kister sub-regular solution model and compared with the available literature data.

Vaporization of ternary Al-Cr-Fe and binary Al-Fe, and Cr-Fe alloys has been investigated in the temperature range 1234-1608 K by Knudsen effusion mass spectrometry (KEMS). The atoms Al, Cr, and Fe were found to be the only vapor species. Partial pressures of the elements were evaluated from the measured ion intensities and thermodynamic activities of the alloy components were determined by pressure ratio method (p/p°). Reliable partial and integral molar enthalpies, entropies and Gibbs energies for all the components have been obtained for the systems under investigation. The partial molar enthalpies and entropies were found to be nearly temperature independent over the wide temperature range investigated.

A new approach to determine the work function for ionic crystals by Knudsen Effusion Mass Spectrometry was suggested. The method was successfully tested on the alkali halide metals MX (M = Na, K, Rb, Cs; X = F, Cl, Br, I).

The molecular and ionic composition of vapor over cerium triiodide was studied by Knudsen effusion mass spectrometry. In the saturated vapor over CeI3the monomer, dimer, and trimer molecules and the negative ions I−,CeI4-, andCe2I7-were identified in the temperature range of 753–994 K. The partial pressures of CeI3, Ce2I6, and Ce3I9were determined and the enthalpies of sublimation,ΔsH°(298.15 K) in kJ·mol−1, in the form of monomers (298±9), dimers (415±30), and trimers (423±50) were obtained by the second and third laws of thermodynamics. The enthalpy of formation,ΔfH°(298.15 K) in kJ·mol−1, of the CeI3(-371±9), Ce2I6(-924±30), and Ce3I9(-1585±50) molecules and theCeI4-(-857±19) andCe2I7-(-1451±50) ions were calculated. The electron work function,φe=3.3±0.3 eV, for the CeI3crystal was evaluated.

The vaporization of Al–Dy–O mixtures has been investigated by the Knudsen effusion mass spectrometry technique. The saturated vapor has been found to consist of the atoms Al, O and the molecules AlO, Al 2 O, DyO. At the initial stage the vaporization of Dy 2 O 3 and Al 2 O 3 –Dy 2 O 3 mixtures was found to be incongruent and accompanied by some loss of oxygen. An attainment of congruently vaporizing composition and equilibrium state takes quite a long time. The activities of binary oxides have been measured at T = 2130 K. The Gibbs energies and enthalpies have been derived for formation of the compounds Dy 4 Al 2 O 9 , DyAlO 3 and Dy 3 Al 5 O 12 from sesquioxides.

Molecular and ionic sublimation of gadolinium and terbium tribromides in Knudsen and Langmuire modes was studied by the method of high-temperature mass-spectrometry. On the basis of obtained enthalpies of sublimation and ion-molecule reactions the enthalpies of formation of LnBr3 and Ln2Br6 molecules and LnBr4− and Ln2Br7− negative ions were determined. For the first time the electron work function for crystals of the studied tribromides was calculated.

The Knudsen effusion mass spectrometric technique was used to study vapor species over praseodymium triiodide. The monomer, PrI 3 , and dimer, Pr 2 I 6 , molecules and the negative ions, PrI 4 − and Pr 2 I 7 − , were observed in saturated vapor in the temperature range from 856 K to 1048 K. The partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation obtained using the second and the third laws of thermodynamics (Δ s H °(298.15 K) = 291 ± 4 kJ mol −1 for PrI 3 , and Δ s H °(298.15 K) = 400 ± 30 kJ mol −1 for Pr 2 I 6 ). The equilibrium constants for various ion molecular reactions were measured and the enthalpies of reactions obtained. The enthalpies of formation, Δ f H °(298.15 K) kJ mol −1 , of gaseous molecules and ions were calculated and are as follows: −374 ± 6 (PrI 3 ), −929 ± 30 (Pr 2 I 6 ), −867 ± 30 (PrI 4 − ), −1432 ± 50 (Pr 2 I 7 − ).

The vaporization of the NaI-PrI3 quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI)n and (PrI3)n molecules (n = 1, 2) and Na+(NaI)n(n = 0–4) and I−(PrI3)n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI4, Na2PrI5, NaPrI3+, Na2PrI4+, Na3PrI5+, Na4PrI6+, NaPrI5−, and NaPr2I8−). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.

The molecular and ionic composition of vapor over holmium tribromide was studied by high-temperature mass spectrometry under the conditions of sublimation from a Knudsen effusion cell and from the open single crystal surface. The partial pressures of HoBr3 and Ho2Br6 in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The intensities of lines in the electron impact mass spectra and their temperature dependences were different under Knudsen and Langmuir conditions, which was evidence of superthermal vibrational-rotational excitation of molecules sublimed from the open surface. The enthalpies and activation energies of sublimation of HoBr3 crystals as monomers and dimers were calculated. The emission of HoBr4− and Ho2Br7− negative ions was observed under both sublimation conditions. Ion-molecular equilibria in the LaBr3-HoBr3 system were studied. The enthalpies of formation of the HoBr3 and Ho2Br6 molecules and HoBr4− and Ho2Br7− negative ions in the gas phase were calculated.

The thermodynamic activities of sodium iodide and praseodymium triiodide in NaI-PrI3 binary system melts at 900 K were determined by high-temperature mass spectrometry. The activities were used to calculate the excess integral Gibbs energy of melt formation. A negative deviation of the system from the behavior of an ideal melt was observed.

The vaporization of praseodymium triiodide was studied by high-temperature mass spectrometry. Monomeric (PrI3) and dimeric (Pr2I6) molecules and the PrI 4 − and Pr2I 7 − negative ions were recorded in saturated vapor over the temperature range 842–1048 K. The partial pressures of neutral vapor components were determined. The enthalpies of sublimation Δs H o(298.15 K) in the form of monomers (291 ± 10 kJ/mol) and dimers (400 ± 30 kJ/mol) were calculated by the second and third laws of thermodynamics. The equilibrium constants of ion-molecular reactions were measured and the enthalpies of the reactions determined. The enthalpies of formation Δf H o(298.15 K) of molecules and ions in the gas phase were calculated (−373 ± 11, −929 ± 31, −865 ± 25, and −1433 ± 48 kJ/mol for PrI3, Pr2I6, PrI 4 − , and Pr2I 7 − , respectively).

The thermodynamic properties of the congruently melting Cs3CeCl6 compound, which is known to exist in the CeCl3-CsCl system, were studied by differential scanning calorimetry and Knudsen effusion mass spectrometry. The heat capacity of solid and liquid Cs3CeCl6 was measured as a function of temperature in the range (300 to 1100) K. The thermodynamic activities of CsCl and CeCl3 were determined in the twophase field {Cs3CeCl6(s) + liquid}. These data were used to calculate the whole set of thermodynamic functions for the solid and liquid compound as well as the temperature variation of the Gibbs free energy and enthalpy of compound formation according to the reaction CeCl3(s,l) + 3CsCl(s,l) ) Cs3CeCl6(s,l). Several compounds may exist in LnX3-MX mixtures (Ln ) lanthanide, X ) halide, M ) alkali metal). These systems have relatively simple phase diagrams when they include the lighter alkali metal halides (LiX and NaX), while those with KX, RbX, and CsX exhibit generally several compounds of stoichiometry, M3LnX6 ,M 2LnX5, and MLn2X7. The stability of these compounds depends on the nature of both cations (lanthanide Ln, alkali M) and anions X. 1-3 We have paid much attention to the M3LnX6 stoichiometric compounds that exist in most LnX3-MX systems 4-11 and have a more extended stability range than those of other stoichiometry. These congruently melting compounds were found 12 to exist also in the CeCl3-MCl systems (M ) K, Rb, and Cs). The present work reports on the thermodynamic properties of the Cs3CeCl6 compound. It has been established earlier that this compound is metastable at ambient temperature. 12,13 It undergoes a solid-solid state transition at 676 K and melts congruently at 1078 K with the respective enthalpies (7.8 ( 0.4 and 67.4 ( 0.8) kJ · mol -1 . 2,3,14 Its formation enthalpy from the system componentssCsCl and CeCl3swas determined as -26.0 kJ · mol -1 at 298.15 K 12 by solution calorimetry.

The development of an accurate thermodynamic model description for the system Fe–Al–Cr is hampered by the sparseness of thermodynamic data in this ternary system. This compelled us to measure activities in the system Fe–Al–Cr using the Knudsen Effusion Mass Spectrometry technique. We investigated two samples with target compositions 45.1Fe–39.8Al–15.1Cr (at.%) and 49.9Fe–19.9Al–30.2Cr (at.%) in the temperature range between 1150 K and 1550 K. We combined these measurements with a revised thermodynamic model description for this system based on the so-called Calphad approach. This approach allows us to predict thermodynamic properties in the ternary system from the Gibbs energy formulations of the binary subsystems. This combination was used to discriminate between the quality of the sparse experimental activity data available in the literature and our own experimental data. We found that additional iron activity measurements are necessary in the binary system Fe–Al. Additional activity measurements of iron, aluminum and chromium are also necessary in a compositional region close to this system. We show preliminary calculations of the on-diagonal thermodynamic factors, which appear to be largest in the compositional region close to the system Fe–Al. For a composition in the ternary system they decrease in the order aluminum, iron, chromium.

The molecular and ionic vaporization of cerium tribromide from the effusion cell (Knudsen conditions) and the open surface of a CeBr3 single crystal (Langmuir conditions) were studied by high-temperature mass spectrometry. The CeBr3 and Ce2Br6 molecules and the CeBr4− and Ce2Br7− negative ions were observed as vapor constituents. The partial pressures of the molecules in saturated vapor and the ratio between the vaporization coefficients of monomers and dimers under free vaporization conditions were determined. The enthalpies and the activation energies of sublimation in the form of monomers and dimers were measured. Ion–molecular equilibria with the participation of negative ions were studied. The enthalpies of formation of molecules and ions in the gas phase were obtained.

The method of high-temperature mass spectrometry is used for studying the composition of saturated vapor over cerium and praseodymium tribromides. Monomer and dimer molecules are found in the temperature ranges of 789–994 K and 804–957 K for cerium and praseodymium, respectively. The partial pressures of vapor components are determined, p(Pa), the temperature dependences of which are approximated by the equations $$ \begin{gathered} \log p(CeBr_3 ) = ( - 14.63 \pm 0.08) \times 10^3 /T + (14.54 \pm 0.09), T = 789 - 994 K; \hfill \\ \log p(Ce_2 Br_6 ) = ( - 19.72 \pm 0.61) \times 10^3 /T + (17.60 \pm 0.64), T = 918 - 980 K; \hfill \\ \log p(PrBr_3 ) = ( - 14.13 \pm 0.12) \times 10^3 /T + (14.09 \pm 0.14), T = 804 - 957 K; \hfill \\ \log p(Pr_2 Br_6 ) = ( - 18.90 \pm 0.50) \times 10^3 /T + (17.15 \pm 0.53), T = 903 - 955 K. \hfill \\ \end{gathered} $$ The values of pressure of vapor components are used along with literature data for the calculation of enthalpies of sublimation in the form of monomer and dimer molecules by the procedures of the second and third laws of thermodynamics. Based on analysis of the results, thermodynamic parameters of monomer and dimer molecules (in kJ mol−1) are recommended, $$ \begin{gathered} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (CeBr_3 , 298.15) = 305 \pm 5, \Delta _s H^0 (PrBr_3 , 298.15) = 293 \pm 5, \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (Ce_2 Br_6 , 298.15) = 410 \pm 28, \Delta _s H^0 (Pr_2 Br_6 , 298.15) = 403 \pm 28, \hfill \\ \,\,\,\,\,\,\,\Delta _f H^0 (CeBr_3 , gas, 298.15) = - 587 \pm 6, \Delta _f H^0 (PrBr_3 , gas, 298.15) = - 597 \pm 7, \hfill \\ \Delta _f H^0 (Ce_2 Br_6 , gas, 298.15) = - 1372 \pm 28, \Delta _f H^0 (Pr_2 Br_6 , gas, 298.15) = - 1378 \pm 28. \hfill \\ \end{gathered} $$

The molecular and ionic composition of saturated vapor over lanthanum triiodide was studied by Knudsen effusion mass spectrometry. The (LaI3)n molecules (n = 1–3) and the [I(LaI3)n]− ions (n = 0–4) were observed. The partial pressures of the molecules were determined and the enthalpies of sublimation, ΔsH° (298.15 K) in kJ mol−1, in the form of monomers (304 ± 7), dimers (428 ± 25), and trimers (455 ± 50) were obtained by the second and third laws of thermodynamics. The enthalpy of formation, ΔfH° (298.15 K) in kJ mol−1, of the LaI3 (−376 ± 10), La2I6 (−932 ± 25), La3I9 (−1585 ± 50) molecules and the LaI4− (−841 ± 24), La2I7− (−1486 ± 32) ions were determined. The electron work function, φe = 3.5 ± 0.3 eV, for the LaI3 crystal was calculated from the thermochemical cycle.

The enthalpy stability of the LaCl4− and LuCl4− ions is assessed using high-temperature mass spectrometry. The enthalpy of Cl− detachment is determined to be ΔrH0(298.15 K) = 332 ± 10 kJ/mol for LaCl4− and 359 ± 10 kJ/mol for LuCl4−.

The experimentally measured values of the EuBr2 sublimation enthalpy and EuBr3– desorption enthalpy were used to construct a thermochemical cycle to determine the work function φe = 405 ± 39 kJ·mol–1 (4.2 ± 0.4 eV) for europium dibromide.

The composition of saturated vapor over thulium trichloride is studied using the method of high-temperature mass spectrometry. Neutral (TmCl3) n and charged Cl–(TmCl3) n associates up to n= 5 and 8, respectively, have been registered for the first time in the temperature range from 868 to 1110 K. Partial pressures p(atm) of the vapor components are determined. The second and third laws of thermodynamics are used to calculate the sublimation enthalpies Δ s H° (298 K) in the form of monomeric and associated molecules, as well as the enthalpies of formation Δ f H° (298 K) of gaseous molecules and ions.

A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl(3) and SmCl(3). Monomer, dimer, and trimer (Sm(3)Cl(9)) molecules, and LnCl(4-), Ln(2)Cl(7-), Ln(3)Cl(10-) (Ln = Ce, Sm) negative ions, were observed in saturated vapor in the temperature range 958-1227 K. Partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation (Delta(s)H, 298 K, kJ.mol(-1)) to monomers and associated molecules obtained: 328 +/- 6 (CeCl(3)), 306 +/- 6 (SmCl(3)), 453 +/- 16 (Ce(2)Cl(6)), 408 +/- 12 (Sm(2)Cl(6)), and 468 +/- 40 (Sm(3)Cl(9)). Equilibrium constants for various chemical reactions were measured and the enthalpies of reactions obtained using the second and third laws of thermodynamics. The enthalpies of formation (Delta(f)H, 298 K, kJ.mol(-1)) of molecules and ions have been calculated as follows: -730 +/- 6 (CeCl(3)), -722 +/- 6 (SmCl(3)), -1663 +/- 16 (Ce(2)Cl(6)), -1649 +/- 13 (Sm(2)Cl(6)), -2617 +/- 40 (Sm(3)Cl(9)), -1250 +/- 15 (CeCl(4)(-)), -1252 +/- 15 (SmCl(4-)), -2184 +/- 35(Ce(2)Cl(7-)), -2172 +/- 26 (Sm(2)Cl(7-)), -3183 +/- 43 (Ce(3)Cl(10-)), and -3147 +/- 43 (Sm(3)Cl(10-)).

A Knudsen-cell mass spectrometric technique was used to study a composition of saturated vapour over terbium and thulium trichlorides. For the first time the various neutral (LnCl 3 ) n and charged Cl - (LnCl 3 ) n (Ln = Tb, Tm, n = 1-8) species have been found in the temperature range between 900 and 1100 K. The partial vapour pressures of neutral constituents have been measured and the sublimation (Δ s H°) and the formation (Δ f H°) enthalpies of gaseous molecules and ions have been determined by means of the second and third laws of thermodynamics. The recommended values of Δ s H° (298 K)/kJ mol -1 are as follows: 290 ± 6 (TbCl 3 ), 291 ± 5 (TmCl 3 ), 365 ± 20 (Tb 2 Cl 6 ), 361 ± 10 (Tm 2 Cl 6 ), 414 ± 40 (Tb 3 Cl 9 ), 419 ± 15 (Tm 3 Cl 9 ), 400 ± 20 (Tm 4 Cl 12 ), 365 ± 60 (Tm 5 Cl 15 ). The values of Δ f H° (298 K)/kJ mol -1 are as follows: -709 ± 6 (TbCl 3 ), -697 ± 6 (TmCl 3 ), -1632 ± 15 (Tb 2 Cl 6 ), -1615 ± 10 (Tm 2 Cl 6 ), -2582 ± 40 (Tb 3 Cl 9 ), -2545 ± 15 (Tm 3 Cl 9 ), -3552 ± 20 (Tm 4 Cl 12 ), -4575 ± 50 (Tm 5 Cl 15 ), -1233 ± 20 (TbCl - 4 ), -1239 ± 16 (TmCl - 4 ), -2180 ± 35 (Tb 2 Cl - 7 ), -2151 ± 22 (Tm 2 Cl - 7 ), -3138 ± 40 (Tb 3 Cl - 10 ), -3093 ± 23 (Tm 3 Cl - 10 ), -4161 ± 50 (Tb 4 Cl - 13 ), -4105 ± 24 (Tm 4 Cl - 13 ), -5139 ± 60 (Tb 5 Cl - 16 ), -5022 ± 60 (Tm 5 Cl - 16 ), -6097 ± 25 (Tm 6 Cl - 19 ), -8083 ± 80 (Tm 8 Cl - 25 ).

The vaporization of Sm, Eu, and Yb tri- and dibromides is accompanied by decomposition and disproportionation reactions. These result in complex vapor compositions whose analysis is an intricate problem for experimentalists. Approaches have been developed to interpret mass spectra and accurately determine the vapor composition of thermally unstable compounds.A sector type magnet instrument was used. A combined ion source allowed the study of both the molecular and ionic vapor compositions in the electron ionization (EI) and the thermionic emission (TE) modes. The methodological approaches were based on a joint analysis of the ionization efficiency functions, the temperature and time dependences of the ion currents, and special mathematical data evaluation.The vaporization of SmBr3 , YbBr3 , SmBr2 , EuBr2 , and YbBr2 was studied in the temperature range of 850-1300 K. An initial stage of incongruent vaporization was observed in the case of the tribromides, SmBr2 , and YbBr2 . This eventually changed to a congruent vaporization stage. Various neutral (Ln, Br, Br2 , LnBr, LnBr2 , LnBr3 , Ln2 Br4 , Ln2 Br5 , and Ln2 Br6 ) and charged (Br(-), LnBr3 (-), LnBr4 (-)) species were detected at different vaporization stages.The quantitative vapor composition of Sm, Eu, and Yb tri- and dibromides was determined. It was found that only EuBr2 was stable in the studied temperature range. The developed approaches can be useful in the case of other thermally unstable compounds.

The content of saturated vapors above europium dibromide and Eu-EuBr2, Eu-Ba-BaBr2, EuBr2-LaBr3 systems is investigated by means of high-temperature mass-spectrometry in the electron ionization and thermoionic emission regimes. On the basis of the measured equilibrium constants for reactions with participation of molecules and negative ions, the enthalpies of formation ΔfH298° (kJ/mol) are determined using the method of the third law of thermodynamics: −59 ± 13 (EuBr), −349 ± 19 (EuBr2), and −861 ± 24 (EuBr3−).

The vaporization process of ytterbium di- and tribromide was studied using high-temperature mass spectrometry over the temperature range of 850 to 1300 K. It was ascertained that, at the early vaporization stages, the vapor contained molecules YbBr3, YbBr2, YbBr, Br2, Yb2Br2, Yb2Br3, Yb2Br4, Yb2Br5, Yb2Br6, and atoms Yb and Br. The partial pressures of all components of saturated vapor were calculated. It was found that vapor composition reflected the course of the reactions of decomposition of tribromide and disproportionation of dibromide in the condensed phase. It was concluded that vaporization of di- and tribromide was incongruent at the initial stages; vaporization of both agents acquired a congruent character with the Yb: Br = 1.0: 1.9±0.2 ratio with time.

A procedure for determining the formation enthalpies of LnXn (n = 1-3) molecules of thermally unstable lanthanide diand trihalides that is based on measuring the equilibrium constants of reactions in Ln-X systems of various content and solving a system of thermochemical equations is suggested. The proce� dure is used to determine the enthalpies of formation ΔfH of molecules and negative ions found in the vapors of ytterbium bromides: YbBr (20 ± 3), YbBr2 (-135 ± 10), YbBr3 (-233 ± 12), (-615 ± 31), and (-766 ± 23) kJ/mol.

The vaporization process of europium dibromide was studied using high-temperature mass spectrometry. It was ascertained that saturated vapor in temperature range of 1049–1261 K was represented mainly by EuBr2 molecules; the fraction of dimer molecules Eu2Br4 was less than 1%. Heat capacities of solid and liquid europium dibromide, as well as the melting enthalpy were measured by means of differential scanning calorimetry in temperature range 300–1100 K; using these data thermodynamic functions for EuBr2 in condensed state were calculated. For all experimental data, including the literature data, thermodynamic characteristics of the vaporization of europium dibromide were determined using a unified set of thermodynamic functions according to the methods of the second and third laws of thermodynamics. The value of ΔsHo(298.15 K) = 354 ± 5 kJ/mol was recommended for the reaction of sublimation of EuBr2(cr.) = EuBr2.