Vapor pressure of SeO2 (s) and optical density of SeO2 (g)

The optical density of the vapor generated by SeO₂ (s) between about 416 and 505 K has been measured between 400 and 200 nm for optical path lengths of 10.14 and 10.15 cm and temperatures of 533, 733, 1133, and 1420 K. A pressure of oxygen of about 0.7 to 0.9 atm was present in the cells and that of Se₂ was below the minimum detectable of about 0.001 atm. For one cell, complete vaporization occurred at 481.5 K and a vapor pressure of 5.02 × 10⁻³ atm was calculated from the weight of SeO₂ (s), the volume profile of the optical cell, and the temperature distribution along the cell. Assuming Beer’s law is obeyed for a number of vibronic peaks, the vapor pressure is obtained as log₁₀ P (atm)=−5705/T+9.5443 in close agreement with two studies with fused silica Bourdon gauges. Beer’s law constants relating the pressure to the optical density at various wavelengths are obtained for the optical path temperatures listed above. Thermodynamic data previously published for solid and liquid SeO₂ need be changed only slightly to be consistent with the present vapor pressure. We obtain a standard enthalpy of sublimation at 298 K of 112.70 kJ/mol and standard entropies at 298 K of 258.72 and 66.693 J · mol⁻¹ · K⁻¹ for, respectively, gaseous and solid SeO₂.     

Vapor pressure measurements of arsenic and arsenic trioxide over condensed phases

The solid-vapor relations for arsenic in the temperature range from 680 to 840 K and the liquid-vapor relations for arsenic trioxide in the temperature range from 650 to 740 K were determined by direct vapor pressure measurements carried out with a quartz gauge. The resulting InP (total) vsT are : InP (atm) = 2545.1/T + 22.27 InT− 154.02 (for arsenic) and InP (atm) = −50983/T + 6.869 (for arsenic trioxide). Calculated enthalpy of vaporization (ΔH_v,T ⁰) for arsenic trioxide and enthalpy of sublimation (ΔH_s,298 ⁰) for arsenic are 42.36 kJ/mol and 156.13 kJ/mol, respectively.     

Vapor pressure measurements of arsenic and arsenic trioxide over condensed phases

The solid-vapor relations for arsenic in the temperature range from 680 to 840 K and the liquid-vapor relations for arsenic trioxide in the temperature range from 650 to 740 K were determined by direct vapor pressure measurements carried out with a quartz gauge. The resulting InP (total) vsT are : InP (atm) = 2545.1/T + 22.27 InT− 154.02 (for arsenic) and InP (atm) = −50983/T + 6.869 (for arsenic trioxide). Calculated enthalpy of vaporization (ΔH_v,T ⁰) for arsenic trioxide and enthalpy of sublimation (ΔH_s,298 ⁰) for arsenic are 42.36 kJ/mol and 156.13 kJ/mol, respectively.     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

Diagrams of Chemical and Electrochemical Stability of Thermal-Diffusion Zinc Coatings

Cutsets are calculated for the Zn-Fe-O system phase diagram at 700 and 298 K and the Zn-Fe-H₂O system potential-pH diagram at 298 K, 1 atm (air), and a _i = 10⁻⁶ mol/l with zinc excess (C _Zn ^al > C _Zn ^cr ) or deficiency (C _Zn ^al < C _Zn ^cr ) in the alloy surface layer of the Zn-Fe alloy. Thermodynamics of corrosion-electrochemical behavior of different phases in thermal-diffusion zinc coatings are discussed. __________ Translated from Zashchita Metallov, Vol. 41, No. 5, 2005, pp. 508–514. Original Russian Text Copyright ? 2005 by Tyurin, Galin.     

Accelerated Corrosion of Fe–xCr–10Al Alloys Containing 0–20 at.% Cr Induced by Sulfur and Chlorine in a Reducing Atmosphere at 600 °C

The corrosion behavior of five Fe–xCr–Al alloys with a constant Al content of 10 at.% and Cr contents ranging from 0 at.% to 20 at.% was examined at 600 °C in a H₂–HCl–H₂S–CO₂ gas mixture providing 3.7 × 10⁻²² atm O₂, 2.4 × 10⁻¹⁴ atm Cl₂ and 3.9 × 10⁻⁹ atm S₂. All the alloys formed duplex scales containing an outermost layer of iron oxide plus an inner layer composed of mixtures of the oxides of all the alloy components. Besides, a region of internal attack of Al or Al + Cr, whose depth decreased with increasing Cr content, formed in all the alloys. The simultaneous presence of chlorine and sulfur in the gas mixture significantly accelerated the corrosion of all the alloys with respect to their oxidation in a simpler H₂–CO₂ mixture providing the same oxygen pressure, by forming thick and cracked scales. The effect was particularly large for the high-Cr alloys due to their inability to form external protective alumina scales in the present gas mixture.     

Reanalysis of solidus points and Te chemical potential for Te-rich CdTe(s)

The author’s previously published partial pressures of tellurium over tellurium-rich CdTe are reanalyzed to yield new solidus points as well as temperatures and partial pressures for compositions within the homogeneity range. Although the results are qualitatively the same as before, they are more satisfactory in that some thermodynamic inconsistencies have been removed. The composition range of the CdTe phase extends slightly beyond the equal atom fraction,X _Te=0.5, to a Te-rich composition of (X _Te−0.5)=(1 to 7)×10⁻⁵. The data are in fair agreement with that obtained from total pressure measurements at generally higher compositions. Since both types of measurement are near the limits of attainable accuracy, their agreement would seem to confirm the essential correctness of both.     

Thermodynamic Calculation of HfB<Subscript>2</Subscript> Volatility Diagram

The thermodynamics of the oxidation of HfB₂ at temperatures of 1000, 1500, 2000, and 2500 K have been studied using volatility diagrams. Both the equilibrium oxygen partial pressure ( P_\textO2 P_{{{\text{O}}_{2} }} ) for the HfB₂(s) to HfO₂(s) plus B₂O₃(l) and the partial pressures of B-O vapor species formed due to B₂O₃(l) volatilization increase with increasing temperature. Vapor pressures of the predominant gaseous species also increase with P_\textO2 P_{{{\text{O}}_{2} }} . At 1000 K, the predominant vapor transition sequence is predicted be BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g) with increasing P_\textO2 P_{{{\text{O}}_{2} }} , and the predominant gas is BO₂(g) with a pressure of 1.27 × 10⁻⁶ Pa under the condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa. At higher temperatures of 1500, 2000, and 2500 K, the system undergoes vapor transitions in the same sequence of B(g) → BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g). Under the same condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa, the predominant vapor species is B₂O₃(g) with pressures of 2.38, 4.49 × 10³, and 3.55 × 10⁵ Pa, respectively. Volatilization of B₂O₃(l) may produce porous HfO₂ scale, which is consistent with the experimental observations of HfB₂ oxidation in air. The present volatility diagram of HfB₂ shows that HfB₂ exhibits oxidation behavior similar to ZrB₂, and factors other than volatility of gaseous species affect the oxidation rate.     

Phase composition and magnetic properties of nanocrystalline SmFe11 ? xGaxC1.25 (2 ≤ x ≤ 5) alloys

As-cast and rapidly quenched alloys (RQAs) SmFe_{11 − x} Ga _x C_1.25 (2 ≤ x ≤ 5) have been studied. The RQAs were prepared by melt spinning on a steel wheel rotating at a velocity V = 10−40 m/s. Fragments of the RQAs were annealed in a vacuum at T _ann = 500−850°C. The as-cast alloys are multiphase; the maximum volume fraction in them corresponds to the Sm₂(Fe, Ga)₁₇C compound with a rhombohedral structure. The rapid quenching leads to the formation of the Sm(Fe, Ga)₁₁C compound (1: 11) with a tetragonal BaCd₁₁-type structure; the maximum volume fraction of the compound is reached in the alloy with x = 3 quenched to a wheel rotating at V = 30 m/s. The melt spinnins of the alloys with x = 2−4 at V = 40 m/s is accompanied by their substantial amorphization. During annealing, the amorphous phase crystallizes mainly with the formation of the 1: 11 phase. A nonequilibrium phase diagram of the alloys quenched at V = 40 m/s and annealed at T _ann = 500−850°C has been constructed. The 1: 11 compound has a single-phase region near x = 3 at T _ann ≥ 600°C. As the volume fraction of the 1:11 phase increases, the coercive force H _c of nanocrystalline RQAs increases. The maximum coercive force is observed for the SmFe₈Ga₃C_1.25 alloy quenched at V = 40m/s and subsequently annealed at 700°C; it is 0.8 and 12 kOe at 293 and 50 K, respectively. The high coercive force obtained indicates that the Sm(Fe, Ga)₁₁C phase is magnetically uniaxial and has a high magnetic anisotropy energy. The magnetic anisotropy constant K ₁ of the compound at T = 50 K was estimated to be 3.1 × 10⁷ erg/cm³.     

Thermal Expansion and Phase Stability Investigations on Cs-Substituted Nanocrystalline Calcium Hydroxyapatites

The high-temperature phase stability of Ca_10−x Cs _x (PO₄)₆(OH)₂, (x = 0–3) compositions synthesized by various wet chemical methods was investigated. The thermal expansion property of Ca₁₀(PO₄)₆(OH)₂ (abbreviated as CaHAp) and Cs-substituted CaHAp was measured by high-temperature XRD and dilatometry. The average crystallite size of the powders synthesized by wet chemical methods was found to be 10–50 nm range as shown by XRD and TEM. Up to 30 mol% Cs loading was observed to show only the apatite phase by XRD when the apatite powder was nanocrystalline in nature. However, high-temperature stability of the Cs-substituted system is limited to ≤5 mol%. Cs₃(PO₄) is observed to be separated out on heating the material above 773 K for compositions substituted with more than 5 mol% of Cs in the Ca-sublattice. The coefficient of thermal expansion measured by HTXRD is α_a = 12.42 × 10⁻⁶ K⁻¹, α_c = 14.98 × 10⁻⁶ K⁻¹; and α_a = 12.62 × 10⁻⁶ K⁻¹, α_c = 12.57 × 10⁻⁶ K⁻¹ for CaHAp and Ca_9.78Cs_0.2(PO₄)₆(OH)_1.96, respectively, in the temperature range of 298-1083 K. Bulk thermal expansion measurements are seen to be in agreement with the lattice expansion results.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Oxygen-free precursor for chemical vapor deposition of gold films: thermal properties and decomposition mechanism

Thermal properties of oxygen-, phosphorus-, and halogen-free dimethylgold(III) diethyldithiocarbamate complex (CH₃)₂AuS₂CN(C₂H₅)₂ (gold, dimethyl(diethylcarbamodithioato -S,S′)-) having excellent storage stability and the mechanism of its decomposition to elemental gold were studied. Saturated vapor pressure was found to be ~10⁻³–10⁻¹ Torr at 50–90°C. Decomposition of the vapor on the surface starts at T = 210°C. The temperature dependence of gas phase composition was studied using the original mass spectrometric technique, it was established that the decomposition of the compound on the surface in vacuum follows three main pathways. Two of them result in the formation of elemental gold, saturated C2–C4 alkanes and (1) protonated ligand or (2) methylated ligand. The third one results in elemental gold and gaseous products: C2–C3 alkylmercaptanes and CH₃SCN(C₂H₅)₂. The formation of gold as a sole solid product within the temperature range 210–240°C was confirmed by X-ray photoelectron spectroscopy analysis. It was shown that the compound exhibits the best combination of volatility, thermal, and storage stability among volatile organogold complexes and thus it may be a promising precursor for obtaining gold films by chemical vapor deposition.     

Surface tension and thermodynamic properties of liquid Ag-Bi solutions

With the maximum bubble pressure method, the density and surface tension were measured for five Ag-Bi liquid alloys (X _Bi=0.05, 0.15, 0.25, 0.5, and 0.75), as well as for pure silver. The experiments were performed in the temperature range 544–1443 K. Linear dependences of both density and surface tension versus temperature were observed, and therefore the experimental data were described by linear equations. The density dependence on concentration and temperature was derived using the polynomial method. A similar dependence of surface tension on temperature and concentration is presented. Next, the Gibbs energy of formation of solid Bi₂O₃, as well as activities of Bi in liquid Ag-Bi alloys, were determined by a solid-state electromotive force (emf) technique using the following galvanic cells: Ni, NiO, Pt/O ⁻²/W, Ag _X Bi _(1−X), Bi ₂ O _3(s). The Gibbs energy of formation of solid Bi₂O₃ from pure elements was derived: =−598 148 + 309.27T [J · mol⁻¹] and =−548 008 + 258.94T [J · mol⁻¹]; the temperature and the heat of the α → δ transformation for this solid oxide were calculated as 996 K and 50.14 J · mol⁻¹. Activities of Bi in the liquid alloys were determined in the temperature range from 860–1075 K, for five Ag-Bi alloys (X _Ag=0.2, 0.35, 0.5, 0.65, 0.8), and a Redlich-Kister polynomial expansion was used to describe the thermodynamic properties of the liquid phase. Using Thermo-Calc software, the Ag-Bi phase diagram was calculated. Finally, thermodynamic data were used to predict surface tension behavior in the Ag-Bi binary system.     

Surface tension and thermodynamic properties of liquid Ag-Bi solutions

With the maximum bubble pressure method, the density and surface tension were measured for five Ag-Bi liquid alloys (X _Bi=0.05, 0.15, 0.25, 0.5, and 0.75), as well as for pure silver. The experiments were performed in the temperature range 544–1443 K. Linear dependences of both density and surface tension versus temperature were observed, and therefore the experimental data were described by linear equations. The density dependence on concentration and temperature was derived using the polynomial method. A similar dependence of surface tension on temperature and concentration is presented. Next, the Gibbs energy of formation of solid Bi₂O₃, as well as activities of Bi in liquid Ag-Bi alloys, were determined by a solid-state electromotive force (emf) technique using the following galvanic cells: Ni, NiO, Pt/O ⁻²/W, Ag _X Bi _(1−X), Bi ₂ O _3(s). The Gibbs energy of formation of solid Bi₂O₃ from pure elements was derived: =−598 148 + 309.27T [J · mol⁻¹] and =−548 008 + 258.94T [J · mol⁻¹]; the temperature and the heat of the α → δ transformation for this solid oxide were calculated as 996 K and 50.14 J · mol⁻¹. Activities of Bi in the liquid alloys were determined in the temperature range from 860–1075 K, for five Ag-Bi alloys (X _Ag=0.2, 0.35, 0.5, 0.65, 0.8), and a Redlich-Kister polynomial expansion was used to describe the thermodynamic properties of the liquid phase. Using Thermo-Calc software, the Ag-Bi phase diagram was calculated. Finally, thermodynamic data were used to predict surface tension behavior in the Ag-Bi binary system.     

Oxidation Behavior of TiAl<Subscript>3</Subscript>/Al Composite Coating on Orthorhombic-Ti<Subscript>2</Subscript>AlNb Based Alloy at Different Temperatures

This paper reports the oxidation behavior of TiAl₃/Al composite coating deposited by cold spray. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The oxidation kinetics of the coating was tested at 650, 800, and 950 °C, respectively. The parabolic rate constant for the coating oxidized at 650 °C was k _p = 7.2 × 10⁻² mg·cm⁻²·h^−1/2 for the tested 1200 h. For the coating oxidized at 800 °C, the oxidation kinetics could be separated into two stages with k _p value of 39.8 × 10⁻² mg·cm⁻²·h^−1/2 for the initial 910 h and 17.7 × 10⁻² mg·cm⁻²·h^−1/2 for the stage thereafter. For the coating oxidized at 950 °C, the oxidation kinetics can be separated into three stages with k _p of 136.9 × 10⁻² mg·cm⁻²·h^−1/2 in the first 100 h, followed by 26.9 × 10⁻² mg·cm⁻²·h^−1/2 from 100 to 310 h, and 11.8 × 10⁻² mg·cm⁻²·h^−1/2 from 310 to 1098 h. XRD, SEM, and EPMA were used to study the microstructure of the coating. The results indicated that the oxidation took place throughout the entire coating instead of only at the surface. The aluminum phase in the composite coating was soon oxidized to Al₂O₃ in all tested cases. The aluminum in TiAl₃ phase was depleted gradually and oxidized to Al₂O₃ along with the degradation of TiAl₃ to TiAl₂ and TiAl as the temperature increased and time proceeded. AlTi₂N was also a typical oxidation product at temperature higher than 800 °C. The experimental results also indicated that the protection of the coating was attributed greatly to the interlayer formed between the coating and the substrate.     

Mechanical and tribological properties of plasma-sprayed Cr3C2-NiCr, WC-Co, and Cr2O3 coatings

Mechanical properties such as Young’s moduli and fracture toughness of plasma-sprayed Cr₃C₂-NiCr, WC-Co and Cr₂O₃ coatings were measured. The tribological properties of the three kinds of coatings were investigated with a block-on-ring self-mated arrangement under water-lubricated sliding. Furthermore, the influences of the mechanical properties on the tribological properties of the coatings were also examined. It was found that the Young’s moduli, bend strengths and fracture toughness of the coatings were lower than the corresponding bulk materials, which may be attributed to the existence of pores and microcracks in the coatings. Among the three kinds of coatings, the magnitude of wear coefficients, in decreasing order, is Cr₃C₂-NiCr, WC-Co and Cr₂O₃, and the wear coefficient of Cr₂O₃ coating was less than 1 × 10⁻⁶mm³N⁻¹m⁻¹. The wear mechanisms of the coatings were explained in terms of microcracking and fracturing, and water deteriorated wear performance of the coatings. The higher the fracture toughness and the lower the porosity and length of microcracking of the coating, the more the wear-resistance of the coating.     

Effects of dopant content on optical and electrical properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript>: W transparent conductive films

The In2O3:W (IWO) films with different W content were deposited on glass substrate using direct current sputtering method. The structure, surface morphology, and optical and electrical properties were investigated. Results showed that both the carrier concentration and carrier mobility were increased with the doping of W. The IWO film with the lowest resistivity of 1. 0× 10-3 Ω· cm, highest carrier mobility of 43. 7 cm2. W-1. s-1 and carrier concentration of 1. 4× 1020 cm-3 was obtained at the content of 2. 8 wt. ％. The average optical transmittance from 300 nm to 900 nm reached 87. 6％.     

Investigation on Oxygen Chemical Diffusion Properties of Perovskite Oxides (La1?x Pr x )0.6Sr0.4Co0.8Fe0.2O3?δ

Perovskite oxide samples of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (x = 0.2, 0.4, 0.6, 0.8) are obtained by solid-state reaction method. The oxygen chemical diffusion properties of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ are determined by electrical conductivity relaxation technique. The results show that the conductivity of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ increases with the increase of oxygen partial pressure. The (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ samples have a high oxygen chemical diffusion coefficient, which decreases linearly with a decrease in temperature and an increase in Pr content. The oxygen chemical diffusion coefficient D _chem remains fairly constant at high PO₂. The oxygen chemical diffusion coefficient is the highest for (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ with x = 0.2, and attains a value of 9.41 × 10⁻⁵ cm² s⁻¹ at 600 °C. This shows the material’s promise as a cathode material for intermediate temperature solid oxide fuel cells.     

Surface Plasmon Resonance Tunability in Au?VO2 Thermochromic Nano-composites

A new type of photo-active nano-composite material appropriate for Ultra-fast Nonlinear Optical χ⁽³⁾ (ω) applications has been synthesized and optically characterized. Compared to standard noble metal particles- oxide nano-composites exhibiting a superior effective χ⁽³⁾ (ω) due to the enhancement of the local electric field, these Au−VO₂ nano-composites display an additional reversibly tunable surface plasmon frequency under external temperature stimuli. Such a smart plasmon tunability is correlated to the Mott’s type semiconducting/metallic 1st order transition of the host VO₂ matrix. The nano-gold surface plasmon wavelength shifts reversibly from 645 nm to 598nm when the Au−VO₂ nano-composites temperature varies from 25°C to 120°C.     

Metal-oxide heterophase structures formed at low temperature activation of iron. 2. IR spectroscopy

Low-temperature activation of iron is observed during its isothermal oxidation at a temperature of 300°C and an oxygen pressure of 10⁻² Torr. A 1-h treatment provides the maximum gain in the oxide layer thickness for this oxygen pressure. According to IR spectroscopic data, the amount of Fe₃O₄ in the oxide reaches the maximum in the oxygen pressure interval from 10⁻³ to 10⁻² Torr and decreases with a further increase in the oxygen pressure. In contrast, the haematite content increases with an increase in the oxygen pressure. In the latter case, first, the content of the α-Fe₂O₃ phase increases to reach its maximum at pressures from 5×10⁻³ to 10⁻² Torr, while the phase of haematite γ-Fe₂O₃ appears at 0.1 Torr. This confirms the earlier assumption that the haematite islets layer plays the decisive roles in the low-temperature activation and the active-passive transition of iron. Original Russian Text ? V.A. Kotenev, N.P. Sokolova, A.M. Gorbunov, A.Yu. Tsivadze, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 6, pp. 630–634.