Search

The pure ternary phases on the line Yb2O3-SeO2 in thermodynamical equilibrium have been synthesized by solid state reaction and characterized using X-ray powder diffraction and IR-spectroscopy. There exist three phases: Yb2SeO5, Yb2Se3O9 and Yb2Se4O11, the last one with a homogeneiety range extending a higher SeO2-content. The thermal decompositions have been determined by total pressure measurements, and the thermodynamical data of the compounds have been derived. The phase diagram and the phase barogram have been established using the results of thermal analysis and total pressure measurements.

The solution enthalpies have been determined for the ternary phases RE2SexO3+2x existing on the pseudo-binary section RE2O3-SeO2 and for RE2O3 and SeO2 in 4n HCl (RE =Nd, Sm, Y). From these date the enthalpies of formation of the ternary phases have been derived via suitable solution schemes on the basis of the known enthalpies of formation of RE2O3 and SeO2.

The thermodynamical data of solid Lanthanum Aluminium Bromide LaAl3Br12 have been obtained by determination of the decomposition equilibria from total pressure measurements. For different compositions LaBr3/AlBr3, the barogram of the binary system LaBr3-AlBr3 was constructed and from this and DTA the melting diagram was determined. The chemical trans­ port of LaBr3 with AlBr3 is suggesting the existence of two gaseous complexes LaAl3Br12 and LaAl2Br9. The data are: ΔH°B(LaAl3Br12,f,298) =-587,2 ± 7 kcal/mol, S°(LaAl3Br12,f,298) = 179,3 ± 7 cal/K·mol; ΔH°B(LaAl3Br12,g,298) =-548,7 ± 5 kcal/mol, S°(LaAl3Br12,g,298) = 239,4 ± 6 cal/K·mol; ΔH°B(LaAl2Br9,g,298) =-619,7 ± 5,5 kcal/mol, S°(LaAl2Br9,g,298) = 212,0 ± 7 cal/K·mol. From solution calorimetric measurements follows the enthalpy of formation of the solid com­plexes: ΔH°B(LaAl3Br12,f,298) =-590,9 ± 3 kcal/mol.

Five phases exist in the system Co-Si: Co3Si, α- and β-Co2Si, CoSi and CoSi2. The phases α-Co2Si and CoSi could be prepared by chemical transport with iodine as transport agent in the temperature range between T1 (700 °C) and T2 (900 °C). In a attempted systematic clarification of the chemical transport reactions of all phases in the system, the effective transport equilibria were determined. Thermodynamic data show satisfactory agreement between calculation and experiment.

Pseudoternary System Bi2O3/Bi2Se3/Bi2Te3, Phase Diagram, Thermodynamic Data The phase diagram of the pseudoternary system Bi2O3/Bi2Se3/Bi2Te3 is found to include a quaternary solid solution Bi2O2 (TexSe1-x) and ternary, intermetallic mixed crystals Bi2(TexSe1-x)3. Using thermodynamic modeling of the solid solutions it is possible to calcu­ late complex heterogeneous equilibria between all phases of this phase diagram. As a result we can thermodynamically describe the observed phase relations: Bi2(TexSe1-x)3 ⊿H°m(298) = 0; ⊿S°m(298) = R[xlnx + (1-x)ln(1-x)] Bi2O2(TexSe1-x) ⊿H°m(298) = Ω · x(1-x); O⊿S°m(298) = R/4 [xlnx + (1-x)ln(1-x)] Ω = 0,6 kcal/mol

The phase relations in the quaternary system Bi/Se/O/Cl have been studied and the existence of several new compounds in the pseudotemary area Bi2O3/Bi2Se3/BiCl3 has been established by solid state and chemical vapour transport reactions. The phase diagram is derived from X-ray powder diffraction and thermal analysisdata, and from measurements of the decomposition pressure behaviour. Three new quaternary phases with different compositions exist in the system: Bi4O4SeCl2, Bi10O12SeCl4 and Bi22O28SeCl8. By estimation of the thermodynamic data of the quaternary phases it is possible to calculate complex heterogeneous chemical equilibria between all the binary, ternary and quaternary compounds of the phase diagram. As a result, we can describe thermodynamically the observed phase relations and the direction of thermal decomposition of the respective compounds.

Five phases exist in the system Fe-Si: Fe3Si, Fe2Si, Fe5Si3, FeSi, α-and β-FeSi2. All phases could be prepared by chemical transport with iodine as transport agent in the temperature range between T1 (700 °C) and T2 (1030 °C). In a attempted systematic clarification of the chemical transport reactions of all phases in the system, the effective transport equilibria were determined. Thermodynamic calculations show satisfactory agreement between calcula­tion and experiment.

The thermodynamical data of ammonium neodymium iodides (NH4)3NdI6 and (NH4)2NdI5 were derived by the determination of their decomposition equilibria by total pressure measurements. Moreover, solution calorimetry was applied. The enthalpies of formation of these phases were calculated from their heats of solution and from the enthalpies of formation and the heats of solution of N dl3 and NH4I in 4n HI (aq.) at 298 K. Data by total pressure measurement: ⊿H°B(NH4)3NdI6,f,298) = -306,7 ± 4,9 kcal/mol; S°((NH4)3NdI6,f,298) = 152,8 ± 5,7 cal/K·mol; ⊿H°B(NH4)2NdI5,f,298) = -260,9 ± 4,2 kcal/mol; S°((NH4)2NdI3,f,298) = 114,3 ± 4,7 cal/K·mol. Data by solution calorimetry: ⊿H°B(NdI3,f,298) = -154,3 ± 2,0 kcal/mol; ⊿H°B((NH4)3NdI6,f,298) = -299,6 ± 3,2 kcal/mol; ⊿H°B((NH4)2NdI5,f,298) = -255,2 ± 2,8 kcal/mol.

The thermal decomposition equilibria of ammonium neodymium bromides (NH4)3NdBr6, (NH4)2NdBr5 and NH4Nd2Br7 have been investigated by total pressure measurements. The thermodynamical data of these solid phase complexes have been derived from the decomposition functions. The standard enthalpies of solution in 4N HBr (aq.) of (NH4)3NdBr6, (NH4)2NdBr5, NH4Nd2Br7, NdBr3 and Nd2O3 were measured. On the basis of these values and tabulated data, the standard enthalpies at 298 K of the ammonium neodymium bromides were derived and compared with the results obtained from the total pressure measurements. Data by total pressure measurement: ΔH°B((NH4)3 NdBr6,f,298) = -399,1 ± 4,9 kcal/mol; S°((NH4)3NdBr6,f,298) = 153,4 ± 7,4 cal/K.mol; ΔH°B((NH4)2NdBr5,f,298) = -343,0 ± 4,4 kcal/mol; S°((NH4)2,NdBr5,f,298) = 109,9 ± 6,8 cal/K.mol; ΔH°B(NH4Nd2Br7,f,298) = -484,0 ± 5,1 kcal/mol; S°(NH4Nd2Br7,f,298) = 127,9 ± 6,6 cal/K.mol. Data by solution calorimetry: ΔH°B(NdBr3,f,298) = -208,7 ± 1,6 kcal/mol; ΔH°B((NH4)3- NdBr6,f,298) = -404,8 ± 2,7 kcal/mol; ΔH°B((NH4)2NdBr5,f,298) = -344,2 ± 2,4 kcal/mol; ΔH°B(NH4Nd2Br7,f,298) = -482,7 ± 3,7 kcal/mol.

GeTe, SnTe, and PbTe have been prepared by chemical transport reactions with iodine as transport agent in the temperature range between T2(800 - 700°C) and T1(700 - 500°C). The effective transport equilibria were determineted. Total pressure measurements in the system Ge- Te-I give the coexistence equlibria for condensed phases, and also for the gasphase equilibra. GeTe4 exists only as a metastable phase at lower temperatures and decom poses near 260°C in GeTe and Te. Thermodynamic calculations show satisfactory agreement between calculation and experiment

The evaporation of LaCl3, LaBr3 and Lal3 was investigated in closed tubes under argon atmosphere and correlated with data in the literature. The enthalpies and entropies of evaporation were derived from the temperature functions of pressure: ΔH°(v, LaCl3, T) = 48,5 ± 2 kcal/mol, ΔS°(v, LaCl3, T) = 22,0 ± 3 cal/K-mol ΔH°(v, LaBr3, T) = 48,0 ± 2 kcal/mol, ΔS°(v, LaBr3, T) = 24,0 ± 2 cal/K-mol ΔH° (v , Lal3, T) = 49,5 ± 2 kcal/mol, ΔS°(v, Lal3,T) = 29,0 ± 2 cal/K-mol

The phase diagram of the pseudobinary sytem Bi2Te3/BiBr3 was investigated by DTA, total pressure measurements and X-ray phase analysis. Only BiTeBr exists as a ternary phase in this system. The compound melts congruently at 526 °C. The heat of formation and standard entropy were calculated from vapor pressure data: ΔH(BiTeBr, f, 298) = (-30,4 ± 1,4) kcal/mol; S°(BiTeBr, f, 298) = (36,2 ± 2,9) cal/K·mol.

The phase diagram of the pseudobinary sytem Bi2Te3/BiCl3 was investigated by DTA, total pressure measurements, and X-ray phase analysis. Only BiTeCl exists as a ternary phase in this system. The compound melts incongruently at 430 °C. The heat of formation and the standard entropy of BiTeCl were calculated from vapor pressure data: ΔH°B (BiTeCl, f, 298) = (-39,5 ± 1,6) kcal/mol; S° (BiTeCl, f, 298) = (34,4 ± 2,7) cal/K· mol. The heat of formation of BiCl3 was determined on the basis of the heat of solution of BiCl3 and Bi2O3, and the heat of formation of Bi2O3: ΔH°B (BiCl3, f, 298) = (-95,9 ± 0,9) kcal/mol.

The thermodynamical data of solid and gaseous aluminium neodymium chloride have been obtained by determination of the decomposition equilibria (of solid) from total pressure measurements and chemical transport reactions (gaseous). The melting diagram was determined by DTA. The enthalpy of formation of the solid phase was calculated from their heats of solution and from the enthalpies of formation and the heats of solution of NdCl3 and AlCl3. Data by total pressure measurement: ΔH°B |(NdAl3Cl12,f,298) = -749,6 ± 2,5 kcal/mol; S°(NdAl3Cl12,f,298) = 118,2 ± 3,0 cal/K·mol. Data by solution calorimetry: ΔH°B(NdAl3Cl12,f,298) = -748,6 ± 1,3 kcal/mol. Data by chemical transport: ΔH°B(NdAl3Cl12,g,298) = -701,5 ± 3,0 kcal/mol; S°(NdAl3Cl12,g,298) = 215,0 ± 4,0 cal/K-mol.

The heterogeneous reactions: OsO4,s =OsO4,g, 2OsO2,s = Oss + OsO4,g, Oss + 3OsO4,g = 4OsO3,g, OsO2,s + OsO4,g = 2OsO3,g and the homogeneous reaction OsO4,g = OsO3,g + 1/2 O2,g were determined by total pressure measurements. From this and from chemical transport reactions of OsO2 and Os with Osmium tetroxide, the enthalpy of formation of gaseous OsO3 was computed to ΔH°B(OsO3,g,298) = -40,0 ± 3 kcal/mol.

The thermal decomposition equilibria of ammonium europium chlorides (NH4)3EuCl6, (NH4)2EuCl5 and NH4Eu2Cl7 have been investigated by total pressure measurements in a membrane zero manometer. The thermodynamic data of these solid phases have been derived from the decomposition functions. The standard enthalpies of solution in 4n HCl (aq.) of (NH4)3EuCl6, (NH4)2EuCl5, NH4Eu2Cl7, EuCl3 and Eu2O3 were measured. On the basis of these values and tabulated data, the standard enthalpies at 298 K of the ammonium europium chlorides were derived and compared with the obtained results from the total pressure measurements.

The thermodynamical data of ammonium neodymium chlorides (NH4)2NdCl5 and NH4Nd2Cl7 were derived by the determination of their decomposition equilibria by total pres­sure measurements. Moreover, solution calorimetry was applied. The enthalpies of formation of these phases were calculated from their heats of solution and from the enthalpies of formation and the heats of solution of NdCl3 and NH4Cl. Data by total pressure measurement: ΔH°B((NH4)2NdCl5,f,298) = - 412,5 ± 3,6 kcal/mol; S°((NH4)2NdCl5 f 298) = 80,1 ± 5,8 cal/K · mol; ΔH°B(NH4Nd2Cl7,f,298) = -579,5 ± 3,5 kcal/mol; S°(NH4Nd2Cl7,f,298) 101,8 ± 5,6 cal/K mol. Data by solution calorimetry: ΔH°B(NdCl3,f,298) = -251,2 ± 0,7 kcal/mol; ΔH°B((NH4)2NdCl5,f,298) = -405,5 ± 1,0 kcal/mol; ΔH°B(NH4Nd2Cl7,f, 298) = -576,8 ± 1,7 kcal/mol.

We determined the decomposition equilibria of ammonium samarium chlorides (NH4)2SmCl5 and NH4Sm2Cl7 by total pressure measurements and derived their thermody­ namical data from the decomposition functions. The enthalpies of formation were compared with the results of the solution calorimetry. The heats of solution of all solid phases in the system SmCl3-NH4Cl and of Sm2O3 were measured in 4n HCl. The enthalpies of formation of ammonium samarium chlorides were derived from the enthalpies of formation of SmCl3 and of NH4Cl and their heats of solution. Data by total pressure measurement ΔH°B((NH4)2SmCl5,f,298) =-407,7 ± 2,9 kcal/mol; S0((NH4)2SmCl5,f,298) = 84,0 ± 4,5 cal/K-mol; ΔH°B((NH4)Sm2Cl7,f,298) = -576,8 ± 3,4 kcal/mol; S°(NH4Sm2Cl7,f,298) = 98,1 ± 5,5 cal/K-mol. Data by solution calorimetry ΔH°B(SmCl3,f,298) = -248,1 ± 0,8 kcal/mol; ΔH°B((NH4),SmCl5,f,298) = -404 ,3 ± 1,1 kcal/mol; ΔH°B(NH4Sm9Cl7,f,298)= -572,3 ± 1,8 kcal/mol.

The decomposition equilibria of Ammonium Lanthanum Halides (NH4)2LaX5 were determined by total pressure measurements in a membrane zero manometer. The phases (NH4)2LaX5 decompose in one step to give solid LaX3 and gaseous NH3 and HX. From the decomposition functions the enthalpies of formation and the standard entropies of the phases are derived. ΔH°B (NH4)2LaCl5,f,298) = -411 ,7 ± 2,2 kcal/mol; S°((NH4)2LaCl5,f,298) = 86,7 ± 2,3cal/Kmol; ΔH°B (NH4)2LaBr5,f,298) = -351,6 ± 3,8 kcal/mol; S°((NH4)2LaBr5,f,298) = 101,1 ± 1,8 cal/Kmol; ΔH°B (NH4)2LaI5,f,298)= -268 ,9 ± 3,9 kcal/mol; S°((NH4)2LaI5,f,298) = 115,5 ± 4,3 cal/Kmol.