Clifford E. Myers

Selective Deposition of TiSi2 from H 2 ‐ TiCl4 Gas Mixtures and Si: Aspects of Thermodynamics Including Critical Evaluation of Thermochemical Data in the Ti‐Si System

Chemical vapor deposition (CVD) of TiSi 2 from TiCl 4 , H 2 , and substrate silicon has been investigated thermodynamically. From a critical evaluation of the thermochemical data, an assessment of the Ti-Si binary phase diagram has been performed. This is the basis of a new set of thermodynamic values for the titanium silicides, which have been used in the calculations. As a comparison, two other common data sets have also been used. The results from the calculations showed that the trends in selectivity as well as substrate etching were not affected by the choice of the silicide data

Thermodynamic mixing functions and phase equilibria in the nickel-chromium system by high-temperature Knudsen cell mass spectrometry

Thermodynamic excess functions of nickel-chromium alloys in the body-centered cubic (bcc) phase have been investigated by computer-aided Knudsen cell mass spectrometry in the tem-perature range of 1300 to 1650 K. Activities, as well as molar excess Gibbs energies, enthalpies, and entropies, were obtained from the ion intensities as a function of composition by fitting to a subregular solution model [2-parameter thermodynamically adapted power (TAP) series:CHn in J/mol,CH1= 3900,CH1= 44,610;CSn in J/mol-K,C = 9.71, c= 13.52]. Based upon these data, the phase diagram has been recalculated.

Vaporization thermodynamics and heat capacities of Cr3Ge and Cr5Ge3

Abstract Thermodynamic stabilities of two chromium germanides Cr 3 Ge and Cr 5 Ge 3 have been studied by means of high-temperature Knudsen effusion mass spectrometry (KEMS) and differential scanning calorimetry (DSC). Thermodynamic activities of Cr and Ge have been measured over the Cr 3 Ge single phase and over two-phase mixtures of (Cr) solid solution+Cr 3 Ge and Cr 3 Ge+Cr 5 Ge 3 in a temperature range of approximately 1400–1600 K by direct comparison with solid Cr and liquid Ge metals. The standard free energies of formation of the chromium germanides at high temperature were determined from the activity data. Heat capacities of Cr 0.75 Ge 0.25 and Cr 0.63 Ge 0.37 were measured by DSC in the temperature range of 300–700 K. Standard enthalpies of formation of Cr 0.75 Ge 0.25 and Cr 0.63 Ge 0.37 at 298 K were calculated by the third-law method with the use of literature absolute entropy and estimated high-temperature heat capacity data. The results obtained are: Cr 0.75 Ge 0.25 , −19.3±2.5 kJ; Cr 0.63 Ge 0.37 , −12.3±2.5 kJ. The results are compared with previously reported measurements.

Thermodynamics and phase equilibria in the AlMn system

Abstract The AlMn system has been investigated by Knudsen cell-mass spectrometry in the temperature range 1100–1275 K and composition range 42–62 at.% manganese. Thermodynamic activities were obtained by direct comparison with the elements. The variation of manganese activity with composition at 1175 K was found to be in accordance with the published phase diagram. The free energies of phase formation at 1175 K were calculated as: for Al0.67Mn0.43 (γ2), − 3790 cal (g-atom)−1; for Al0.50Mn0.50 (γ), − 3860 cal (g-atom)−1; for Al0.45Mn0.55 (E), −3890 cal (g-atom)−1.

Vaporization behavior of V3P(s)

Abstract The vaporization behavior of V3P has been studied by mass-loss effusion in the temperature range 1830–1900 K. The vaporization is kinetically inhibited, and vaporization under grossly non-equilibrium conditions is congruent. As equilibrium is approached, the vaporization becomes incongruent with phosphorus being lost preferentially. Data from runs which are at equilibrium yield a standard enthalpy of formation ΔHf,298.15o = − 49.7 ± 1.0 kcal mol − 1 for V3P(s).

Vaporization thermodynamics and heat capacities of Ti5Ge3 and Ti6Ge5

Abstract Thermodynamic stabilities of titanium germanides Ti 5 Ge 3 and Ti 6 Ge 5 have been studied by means of high-temperature Knudsen effusion mass spectrometry (KEMS) and differential scanning calorimetry (DSC). Thermodynamic activities of Ti and Ge have been measured over the two-phase mixtures of Ti 5 Ge 3 +Ti 6 Ge 5 in a temperature range of ca. 1680–1880 K by direct comparison with solid Ti and liquid Ge metals. The standard free energies of formation of Ti 5 Ge 3 and Ti 6 Ge 5 at high temperature were determined from the activity data. Heat capacities of Ti 5 Ge 3 and Ti 6 Ge 5 were measured by DSC in the temperature region 300–700 K. Standard enthalpies of formation of Ti 5 Ge 3 and Ti 6 Ge 5 at 298 K were calculated by the third-law method with the use of estimated absolute entropy and high-temperature heat capacity data. The results obtained are: 1 8 Ti 5 Ge 3 , −69.8±5 kJ; 1 11 Ti 6 Ge 5 , −70.1±5 kJ. The results obtained in this work are compared with previous estimates and measurements.

The heat capacities of V3P and V3Si

The heat capacities of V3P and V3Si were measured in the temperature range from 150–350 K. At 298.15 K, we find Cp(V3P)=22.3±.2 J/g atom K and Cp(V3Si)=22.6±0.2 J/g atom K. At 150 K the heat capacity of V3P is 6% smaller than that of V3Si. Our data provide support for a value of 25.6 J/g atom for the standard entropy of V3Si at 298.15 K, and result in an estimated value of 23.5 J/g atom for the standard entropy of V3P at 298.15 K.

Vapor pressures and sublimation thermodynamics of GdCl3, TbCl3 and DyCl3

Abstract The vapor pressures of gadolinium trichloride, terbium trichloride and dysprosium trichloride were measured by mass loss effusion from stainless steel cells at temperatures near 1000 K. The third law enthalpies of sublimation at 298.15 K are as follows: GdCl3, 37.5 ± 1.5 kK; TbCl3, 36.6 ± 1.5 kK; DyCl3, 37.4 ± 1.5 kK. These results are discussed in relation to crystal structures, hard sphere ion and thermochemical lattice energies, and bonding models for the solids.

Sublimation pressures and thermodynamics of praseodymium trichloride

Abstract The sublimation pressures of praseodymium trichloride, PrCl 3 , were measured by mass loss effusion from graphite and stainless steel cells. There was evidence of diffusion through the walls of the graphite cell. The third law enthalpy of sublimation based on the data from the stainless steel cell only is ΔH 0 III 298.15 / R = 39.4 ± 1.5 kK.

Thermodynamics of phase formation in the V–Ge system

Abstract Vaporization thermodynamics in the vanadium-rich portion of the vanadium–germanium system has been studied by high temperature Knudsen effusion mass spectrometry. Thermodynamic activities of V and Ge have been measured over the two-phase mixtures of V+V 3 Ge and V 3 Ge+V 5 Ge 3 in a temperature range of ca. 1750–1980 K, and Ge activity was measured over the V 5 Ge 3 +V 11 Ge 8 mixture. The activities were measured by direct comparison with solid V and liquid Ge metals. The standard free energies of formation of V 3 Ge and V 5 Ge 3 at high temperature were determined from the activity data. The standard free energies of formation were then combined with published heat capacity and standard molar entropy data, and used in a third-law evaluation of the standard enthalpies of formation at 298 K of all the four intermediate compounds in this system. The results obtained are: 1 4 V 3 Ge, −36.2±2.5 kJ; 1 8 V 5 Ge 3 , −45.9±2.5 kJ; 1 19 V 11 Ge 8 , −45.5±3.0 kJ; 1 48 V 17 Ge 31 , −35.0±3.0 kJ. The results obtained in this work are compared with previous estimates and measurements.