Partial pressures for several In-Se compositions from optical absorbance of the vapor

The optical absorbance of the vapor phase over various In-Se compositions between 33.3–60.99 at.% Se and 673–1418 K was measured and used to obtain the partial pressures of Se₂(g) and In₂Se(g). The results are in agreement with silica Bourdon gauge measurements for compositions between 50–61 at.%, but significantly higher than those from Knudsen cell and simultaneous Knudsen-torsion cell measurements. It is found that 60.99 at.% Se lies outside the sesquiselenide homogeneity range and 59.98 at.% Se lies inside and is the congruently melting composition. The Gibbs energy of formation of the liquid from its pure liquid elements between 1000–1300 K is essentially independent of temperature and falls between ?36 to ?38 kJ per g atomic weight for 50 and 56% Se at 1200 and 1300 K.     

Reassessment of Ni-Al and Ni-Fe-Al solidus temperatures

Solidus temperatures of the B2 NiAl phase have been determined by high-temperature differential thermal analysis for binary melt compositions Ni_xAl_100−x (45<x<57) and for ternary alloys Fe_yNi_50−yAl₅₀ (0≤y≤50). It was shown that the melting temperature of the stoichiometric Ni₅₀Al₅₀ phase is 1681 °C, which is 43 K higher than some literature data. The solidus line at the Ni-rich side of the Ni-Al phase diagram exhibits a steeper slope than that reported previously. Substituting Fe for Ni, the decrease of solidus temperature along the isoplethal section with 50 at.% Al of the ternary Ni-Fe-Al phase diagram exhibits a steep initial slope of −13 K/at.% Fe for small Fe-fractions, which changes into a nearly linear decrease with an average slope of −8.5 K/at.% Fe.     

A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species （Se（Ⅳ）, Se（Ⅵ）） at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se(IV), Se(VI), and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2–20 and 20–200 μg·L⁻¹ of Se(IV) for the fixed-time method at 30°C. The experimental and theoretical detection limits of the developed kinetic method were found to be 0.21 and 2.50 μg·L⁻¹ for the fixed-time method (3 min). All of the variables that affect the sensitivity at 645 nm were investigated, and the optimum conditions were established. The interference effect of various cations and anions on the Se(IV) determination was also studied. The selectivity of the selenium determination was greatly improved with the use of the strongly cation exchange resin such as Amberlite IR120 plus as long as chelating agents of thiourea and thiosulphate. The proposed kinetic method was validated statistically and through recovery studies in natural water samples. The relative standard deviations (RSDs) for ten replicate measurements of 2, 10, and 20 μg·L⁻¹ of Se(IV) change between 0.35% and 5.58%, while the RSDs for ten replicate measurements of 3, 6, and 12 μg·L⁻¹ of Se(VI) change between 0.49% and 1.61%. Analyses of a certified standard reference material (NIST SRM 1643e) for selenium using the fixed-time method showed that the proposed kinetic method has good accuracy. The Se(IV), Se(VI), and total inorganic selenium in lake and river water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV).     

Electromotive force study of the liquid silver-bismuth-tin alloys

The Ag−Bi−Sn alloy system has been assessed twice, so far, for its potential applications as a lead-free solder material. The first assessment was based on binary data only; the second assessment introduced ternary parameters. It was noted in conclusion that more experimental studies were needed, especially for the liquid phase. The electromotive force (emf) measurement method was used in this study to determine the thermodynamic properties of liquid Ag−Bi−Sn alloys using solid electrolyte galvanic cells as shown below: Re, Ag−Bi−Sn, SnO₂ |Yttria Stabilized Zirconia| Ni, NiO, Pt, Re, Sn, SnO₂ |Yttria Stabilized Zirconia| Ni, NiO, Pt. Alloy compositions for in vestigation were chosen along three constant Bi-to-Sn ratio lines (1/3, 1, and 3) and with the silver content changing from 10 up to 90 at.%, every 10 at.%, resulting in a total of 27 different alloy samples. The temperature of the measurements varied from 975 to 1400 K. A linear dependence of the emf on temperature was observed for all compositions, and the appropriate line equations were derived. Excess partial Gibbs energies of Sn were then calculated at 1200 K and compared with the results of the calculations of both assessments; Gibbs energy of formation of SnO₂ was determined as well. It was then shown that our new emf data fit better to the binary formalism-based calculations than to the second assessment results.     

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.     

Stable and metastable phase equilibria in the GeSe2-Se system

Stable and metastable phase equilibria in the binary system GeSe₂-Se have been investigated by means of optical and electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adiabatic calorimetry. A revised equilibrium phase diagram is presented. A not previously observed λ-type phase transition was observed near ∼420 K (147 °C) for GeSe₂. The intermediate phase, φ, which earlier had been considered as metastable, is shown to be stable through extensive annealing experiments and by adiabatic calorimetry. The φ phase, with composition near Ge₃Se₇, melts incongruently at 658±5 K (385±5 °C) to GeSe₂ and a liquid with 85±2 at.% Se. The liquidus of GeSe₂ and φ was determined by EPMA of annealed-and-quenched samples. Both a stable (φ-Se-liquid) and a metastable (GeSe₂-Se-liquid) eutectic point were observed. The stable one was observed at 480±2 K (207±2 °C) and 92.5±1.0 at.% Se, whereas the temperature of the metastable eutectic (GeSe₂-Se-liquid) was observed to be ∼10 K lower. Metastable phase equilibria, obtained on thermal evolution of glasses with different compositions, are described and discussed.     

Stable and metastable phase equilibria in the GeSe2-Se system

Stable and metastable phase equilibria in the binary system GeSe₂-Se have been investigated by means of optical and electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adiabatic calorimetry. A revised equilibrium phase diagram is presented. A not previously observed λ-type phase transition was observed near ∼420 K (147 °C) for GeSe₂. The intermediate phase, φ, which earlier had been considered as metastable, is shown to be stable through extensive annealing experiments and by adiabatic calorimetry. The φ phase, with composition near Ge₃Se₇, melts incongruently at 658±5 K (385±5 °C) to GeSe₂ and a liquid with 85±2 at.% Se. The liquidus of GeSe₂ and φ was determined by EPMA of annealed-and-quenched samples. Both a stable (φ-Se-liquid) and a metastable (GeSe₂-Se-liquid) eutectic point were observed. The stable one was observed at 480±2 K (207±2 °C) and 92.5±1.0 at.% Se, whereas the temperature of the metastable eutectic (GeSe₂-Se-liquid) was observed to be ∼10 K lower. Metastable phase equilibria, obtained on thermal evolution of glasses with different compositions, are described and discussed.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.     

High Temperature Thermodynamic Data for CdTe(c)

The high temperature heat capacity, Gibbs energy of formation, and standard enthalpy and entropy of formation at 298 K are combined with thermodynamic data for Cd and revised data for Te to provide an internally consistent data set for CdTe(c). Equations are given for the Gibbs energy of formation from Cd(g) and Te₂(g) and from the solid or liquid elements as a function of temperature. These give values similar to those used before. However, the derived enthalpy and entropy of formation are significantly different due to a revised heat capacity for CdTe(c). The standard enthalpy and entropy of formation at 298.15 K from the gases are −293262 J/mol and −200.593 J/mol K, respectively. From the solid elements they are −100270 and −4.5334.     

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 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.     

Density of liquid gold measured by a non-contact technique

Electrostatic levitation together with multi-beam laser heating and ultraviolet imaging made possible to handle a sample of liquid gold, without any contamination, and to determine its density over a large temperature range. Over the 1337–1800 K interval, the density of Au was measured as ρ(T)=1.74× 10⁴−1.44 (T−T_m) kg·m⁻³, where Tm, the melting temperature, was 1337 K. These data yield a calculated volume expansion coefficient of 8.3×10⁻⁵ K⁻¹. The values agree well with the literature values.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Effect of alloy formation in Ag?Au system on electrical double layer structure and hydrogen evolution kinetics

The variations of the zero-charge potential, specific surface charge, and free interface energy in the Ag−Au|F⁻(H₂O) system are studied with the use of impedance measurements in a wide range of alloy compositions. In terms of the concept of a finitely thick interface layer, a theoretical isotherm of the surface composition of the alloy, i.e., the concentration dependence of the activity coefficients of the components is plotted. It is shown that, in Ag−Au alloys at 298 K, gold is surface active, apparently, due to its higher hydrophilicity. The exchange current of the overall reaction of hydrogen evolution on Ag−Au alloys from aqueous sulfuric-acid solutions depends nonlinearily on the surface concentration of gold.     

Liquid-liquid equilibrium in immiscible In-Se alloys suffering metal-nonmetal transition

Electroconductivity σ(T measurements for liquid immiscible In_1-xSe_x (x = < 1/3) alloys are carried out under excess pressure of argon gas (up to 50 MPa) at temperatures up to 1200 K. In the transition region, the electroconductivities of coexisting liquids vary greatly. The liquid-liquid coexistence curve on the phase diagram of the In-Se system is determined from σ(T measurements. The coordinates of the critical point were found to bex _c = 19.2 ± 0.1 at % Se andT _c = 949 ± 1.8 K. The critical indices β and 1 — α are estimated to be 0.35 ± 0.02 and 0.87 ± 0.02, respectively. An asymmetry of the coexistence curve and the nonlinearity of its diameter are analyzed in comparison with available data for fluid metals in the vicinity of the liquid-vapor critical point.     

Phase transformation behavior and shape memory characteristics of Ti−Ni−Si alloys

Transformation behavior, microstructures and shape memory characteristics of Ti−(50−X)Ni−XSi (X=2, 4, 6 at.%) and (50−X)Ti−Ni−XSi (X=2, 5, 7, 10 at.%) alloys were investigated by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity measurements and constant load thermal cycling tests. Ti₅Si₃, Ni₁₆Ti₆Si₇ and Ni₄Ti₄Si₇ were formed in Ti−(50−X)Ni−XSi alloys, while Ti₅Si₄, Ni₃Si, Ni₃Ti₂ and Ni₃Ti₂Si were found in (50−X)Ti−Ni−XSi alloys. The total amount of silicides increased with increasing Si content, irrespective of Si content. The B2→B19 transformation occurred in Ti−(50−X)Ni−XSi alloys, and their transformation temperatures appeared to be almost constant. Transformation elongation associated with the B2→B19 transformation decreased with increasing Si content. In contrast to Ti−(50−X)Ni−XSi alloys, a transformation accompanied with structural change did not occur in (50−X)Ti−Ni−XSi alloys.     

Use of austenite corrosion-resistant steels for manufacturing medical instruments

Conclusion We recommend austenite corrosion-resistant steel 12Kh18N10T subjected to cold treatment (cooling in liquid nitrogen at −196°C), strained at 20°C with ε>50%, and tempered at 460–470°C for 60–90 min for the production of medical instruments. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 36–38, May, 1997.     

Miscibility gap and liquid-liquid equilibrium in the system In-Tl-Se

Electrical conductivity measurements were performed on liquid immiscible (In _x Tl_1−x )_0.80Se_0.20 alloys in a wide temperature range between 1200 K and the crystallization temperature under argon gas pressures up to 45 MPa. The electrical conductivity shows the same behavior as for binary liquid alloys during phase separation. It was revealed that variation of In-to-Tl ratio at constant Se content changes the properties of coexisting liquids and affects the phase-separation temperature T _S in a nonlinear manner. T _S varies from 1035 K for Tl_0.80Se_0.20 to 949 K for In_0.80Se_0.20 with a maximum at T _S =1061 K for In_0.22Tl_0.58Se_0.20. The results are analyzed in comparison with available data for binary and ternary immiscible alloys. The possible influence of sublattice dynamics on formation of the critical-point parameters is discussed.     

Structure and properties of high-temperature alloys with the effect of shape memory in the system Cu−Al−Nb

Conclusion Martensite transformation in alloys of the system Cu−Al−Nb occurs at temperatures much above 200°C. The hysteresis of the reversible martensite transformation is 108–128°C, which is less than for alloys of the system Cu−Al−Ag [3]. Alloys of the system Cu−Al−Nb possess a high effect of shape memory and an elevated ductility and strength. The degree of recovery of shape for an alloy with 2.56% Nb exceeds 90% at σ_Г MPa and δ₂₀=12.7% Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 32–34, August, 1999.     

Contribution to the thermochemistry of rare earth pnictides: The Sm-Bi system

Formation enthalpies of Sm-Bi alloys (in the complete range of compositions) and Er-Bi alloys (for a few compositions) have been measured using a direct, small-furnace, isoperibolic aneroid differential calorimeter. Typical values for the reaction in the solid state at 300 K are: Sm₂Bi,−88 ± 3; Sm₅Bi₃, −94 ± 4; Sm₄Bi₃, −104 ± 2; SmBi, −108 ± 2; SmBi₂, −76 ± 4; and ErBi, −90 ± 5 kJ/g-atom. The experimental data are briefly discussed, compared with those of similar rare earth compounds, and found to be in good agreement with those computed according to the Miedema model and, for the rare earth-rich alloys, also with those calculated according to the Kubaschewski suggestion based on the so-called “effective coordination number” in alloys.