Thermodynamic properties of SmFeO3(s) and Sm3Fe5O12(s)

The enthalpy increments and the standard molar Gibbs energy (G) of formation of SmFeO₃(s) and Sm₃Fe₅O₁₂(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A λ-type transition, related to magnetic order-disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at ∼673 K for SmFeO₃(s) and at ∼560 K for Sm₃Fe₅O₁₂(s). Enthalpy increment data for SmFeO₃(s) and Sm₃Fe₅O₁₂(s), except in the vicinity of λ-transition, can be represented by the following polynomial expressions:

Thermodynamic investigation of the aluminum-chromium system

In the course of a thorough investigation of the Al-Cr-Nb ternary system, the intermetallic compounds of the Al-Cr system were investigated by direct reaction calorimetry at high temperatures. New enthalpies of formation were determined and compared with literature data. X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), and differential thermal analysis (DTA) were carried out on calorimetric products as well as on heat-treated alloys. A eutectoid decomposition of the Al₁₁Cr₂ phase

Evaluation of off-diagonal diffusion coefficient from phase diagram information

A theoretical investigation in order to clarify the physico-chemical meaning involved in off-diagonal multicomponent diffusion coefficients has been carried out. From a mathematical expression for the diffusion coefficients of interstitial elements in Fe-Metal-C or Fe-Metal-N ternary solid solutions, it was found that the off-diagonal diffusion coefficient of the interstitial element (C) could be evaluated from phase diagram information on isopotential curves of that element resulting in the following relation:

Activities in the FeTiO<Subscript>3</Subscript>-NiTiO<Subscript>3</Subscript> Solid Solution from Alloy-Oxide Equilibria at 1273 K

Nine tie-lines between Fe-Ni alloys and FeTiO₃-NiTiO₃ solid solutions were determined at 1273 K. Samples were equilibrated in evacuated quartz ampoules for periods up to 10 days. Compositions of the alloy and oxide phases at equilibrium were determined by energy-dispersive x-ray spectroscopy. X-ray powder diffraction was used to confirm the results. Attainment of equilibrium was verified by the conventional tie-line rotation technique and by thermodynamic analysis of the results. The tie-lines are skewed toward the FeTiO₃ corner. From the tie-line data and activities in the Fe-Ni alloy phase available in the literature, activities of FeTiO₃ and NiTiO₃ in the ilmenite solid solution were derived using the modified Gibbs-Duhem technique of Jacob and Jeffes [K.T. Jacob and J.H.E. Jeffes, An Improved Method for Calculating Activities from Distribution Equilibria, High Temp. High Press., 1972, 4, p 177-182]. The components of the oxide solid solution exhibit moderate positive deviations from Raoult’s law. Within experimental error, excess Gibbs energy of mixing for the FeTiO₃-NiTiO₃ solid solution at 1273 K is a symmetric function of composition and can be represented as:

Study of fracture and erosive wear of plasma sprayed coatings

Double cantilever beam (DCB) and short bar (SB) specimens were used to determine the critical strain energy release rate (G _IC) of plasma-sprayed coatings ofZrO ₂-base ceramic and WC-Co coatings. Erosion rates were measured for various erosive conditions. By comparing theG _Ic data and erosion rate (E _v) data with X- ray diffraction and fractographic analysis, fracture and erosion mechanisms of plasma-sprayed coatings were proposed. Based on the erosion models for brittle materials, a proportional relationship between the erosion rate,E _v, andG _IC was derived as follows:

Gibbs Energy of Formation of MnO: Measurement and Assessment

Based on the measurements of Alcock and Zador, Grundy et al. estimated an uncertainty of the order of ±5 kJ mol⁻¹ for the standard Gibbs energy of formation of MnO in a recent assessment. Since the evaluation of thermodynamic data for the higher oxides Mn₃O₄, Mn₂O₃, and MnO₂ depends on values for MnO, a redetermination of its Gibbs energy of formation was undertaken in the temperature range from 875 to 1300 K using a solid-state electrochemical cell incorporating yttria-doped thoria (YDT) as the solid electrolyte and Fe + Fe_1 − δO as the reference electrode. The cell can be presented as

Kinetics of ferrite formation in low-carbon alloy Fe-9% Cr

Conclusions  1. The formation of ferrite in low-carbon Fe-9% Cr alloys seems to obey the kinetic theory of Khan, which is confirmed by the transformation fromn=4 (nucleation over grain boundaries) ton=1 (growth without the appearance of new centers). 2. The time of the transformation to a specified degreef can be described quite satisfactorily by an equation of the form

High stress abrasive wear behavior of sillimanite-reinforced Al-alloy matrix composite: A factorial design approach

An attempt has been made to explore the possibility of using a natural mineral, namely sillimanite, as dispersoid for synthesizing aluminum alloy composite by solidification technique. The abrasive wear behavior of this composite has been studied through factorial design of experiments. The wear behavior of the composite (Y _composite) and the alloy (Y _alloy) is expressed in terms of the coded values of different experimental parameters like applied load (x ₁), abrasive size (x ₂), and sliding distance (x ₃) by the following linear regression equations:

Kinetics of iron removal from metallurgical grade silicon with pressure leaching

In this paper, the kinetics of pressure leaching for purification of metallurgical grade silicon with hydrochloric acid was investigated. The effects of particle size, temperature, total pressure, and concentration of hydrochloric acid on the kinetics and mechanism of iron removal were studied. It was found that the reaction kinetic model followed the shrinking core model, and the apparent activation energy of the leaching reaction was 46.908 kJ/mol. And the apparent reaction order of iron removal with pressure leaching was 0.899. The kinetic equation was ob-tained and the mathematical model of iron removal from metallurgical grade silicon (MG-Si) was given as follows: 1-2/3x-(1-x)2/3=exp(5.1654-4811.4591/T+1.287lnp+1.046ln[C])·t/r02· The values calculated from the equation were consistent with the experimental results.     

A New Finding About Conditions for More Than One Kirkendall Marker Plane in Binary Single Phase Diffusion Couples

It is now well known that there are experimental results of bifurcate, trifurcate or more Kirkendall marker planes (K-plane) in a multiple phase diffusion couple (M-couple). In the case of Au-Zn binary alloy system, for example, even in a β’/β’ single phase diffusion couple (S-couple) there is a possibility of the bifurcate K-planes because the ratio R = D _Zn/D _Au of the intrinsic diffusion coefficients in the β’ phase is smaller than 1 in the Au rich side and larger than 1 in the Zn rich side. It has been reported that the positions of the K-planes in a diffusion zone can be found graphically as intersections between the plot of marker moving distance \(2t\upsilon_{\text{k}}^{\text{D}}\) versus X _k and the plot of a straight line \(2t\upsilon_{\text{k}}^{\text{EX}}\) versus X _k. Here, \(\upsilon_{\text{k}}^{\text{D}}\) is the marker velocity with respect to the volume fixed frame of reference (V-frame) defined by,

$$\upsilon_{\text{k}}^{\text{D}} = \upsilon_{\text{k}} - \upsilon_{\text{V}} = V_{\text{B}} \left( {D_{\text{B}}^{\text{V}} - D_{\text{A}}^{\text{V}} } \right)\left( {\frac{{\partial C_{\text{B}} }}{\partial X}} \right),$$

and \(\upsilon_{\text{k}}^{\text{Ex}}\) is that determined experimentally by the following equation,

$$\upsilon_{\text{k}}^{\text{Ex}} = \upsilon_{\text{k}} - \upsilon_{0} = \frac{{X_{k} - X_{0} }}{2t}.$$

In this work, we studied the alignments of multiple markers (M-Ms) after diffusion anneal embedded in a S-couple for widely different constant values of ratio of intrinsic diffusion coefficients, R = D _B /D _A, with respect to the mole fixed frame of reference (N-frame) by our numerical technique taking the change in molar volume into account. For this purpose, new two plots to know the K-plane(s) for the N-flame were derived. A possibility was indicated that Kirkendall markers can locate not only at the intersection(s) between these new two plots but also at an unexpected place where the intersection cannot be found.

     

Thermodynamic Interactions of Si and Ti in Liquid Cu

The activity coefficients of titanium in liquid Cu-Ti at 1623 and 1673 K were measured by equilibrating the liquids with Ti₃O₅ in a oxygen partial pressure controlled by C(s)/CO(g) equilibrium. Furthermore, the thermodynamic interaction parameter of silicon on titanium and the self-interaction parameter of titanium in liquid Cu-Ti-Si at 1773 K were determined by equilibrating the 58 mass% TiO₂-42 mass% CaF₂ slag with Cu-Si-Ti liquids. And the interaction parameters e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} and e_\textTi^\textSi e_{\text{Ti}}^{\text{Si}} obtained using a multiple regression were as large as −69.32 and 15.44 respectively. Based on the above determined value of e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} , the relationship between Henrian constant of titanium in liquid Cu-Ti melt, \upgamma_{\textTi(\texts)}⁰ \upgamma_{{{\text{Ti}}({\text{s}})}}^{0} , from 1473 to 1923 K was evaluated, and is expressed as:

Quasi-Ternary System Ag2Se-CdSe-Ga2Se3

Phase equilibria in the quasi-ternary system Ag₂Se-CdSe-Ga₂Se₃ were investigated by differential thermal and x-ray phase analysis methods. Phase diagrams of nine vertical sections were constructed. The boundaries of seven single-phase fields were determined which are solid solution ranges of system components and intermediate phases. We constructed the isothermal section at 820 K and the liquidus surface projection, and have determined the position in the system of six invariant processes with the participation of liquid: $ {\text{L}}_{{{\text{U}}_{1} }} + {\upzeta} {\leftrightarrows} {\upbeta} + {\upeta} $ L U 1 + ζ ? β + η (1145 K), $ {\text{L}}_{{{\text{U}}_{ 2} }} + \upzeta \leftrightarrows \upgamma + \upeta $ L U 2 + ζ ? γ + η (1138 K), $ \text{L}_{{U_{3} }} + \upeta \leftrightarrows \updelta + \upgamma $ L U 3 + η ? δ + γ (1113 K), $ {\text{L}}_{{{\text{E}}_{ 1} }} \leftrightarrows \upbeta + \updelta + \upeta $ L E 1 ? β + δ + η (1083 K), $ {\text{L}}_{{{\text{E}}_{ 2} }} \leftrightarrows \upalpha + \upbeta + \upvarepsilon $ L E 2 ? α + β + ε (969 K), $ {\text{L}}_{{{\text{E}}_{ 3} }} \leftrightarrows \upbeta + {\updelta} + \upvarepsilon $ L E 3 ? β + δ + ε (963 K). Two invariant processes in the sub-solidus part, $ \upbeta + \updelta \leftrightarrows \upeta + \uplambda $ β + δ ? η + λ and $ \upbeta + \updelta \leftrightarrows \upvarepsilon + \uplambda $ β + δ ? ε + λ at 968 and 938 K, respectively, were investigated as well.     

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.     

Transformations of Carbides During Tempering of D3 Tool Steel

The studies were performed on D3 tool steel hardened after austenitizing at 1050 °C during 30 min and tempering at 200-700 °C. Based on the diffraction studies performed from the extraction replicas, using electron microscopy, it was found that after 120-min tempering in the consecutive temperatures, the following types of carbides occur: $$ 200\;^\circ {\text{C}} \to \upvarepsilon + \upchi + {\text{ Fe}}_{ 3} {\text{C}},\quad 3 50\;^\circ {\text{C}} \to \upvarepsilon + \upchi + {\text{ Fe}}_{ 3} {\text{C,}} $$ $$ 500\;^\circ {\text{C}} \to \upchi + {\text{ M}}_{ 3} {\text{C }} + {\text{ M}}_{ 7} {\text{C}}_{ 3} ,\quad 600\;^\circ {\text{C}} \to \upchi + {\text{ M}}_{ 3} {\text{C }} + {\text{ M}}_{ 7} {\text{C}}_{ 3} , $$ $$ 700\;^\circ {\text{C}} \to {\text{M}}_{ 3} {\text{C }} + {\text{ M}}_{ 7} {\text{C}}_{ 3} . $$ Apart from higher mentioned carbides, there are also big primary carbides and fine secondary M₇C₃ carbides occurring, which did not dissolve during austenitizing.     

Partial Thermodynamic Properties of <Emphasis Type="Italic">γ</Emphasis>′-(Ni,Pt)<Subscript>3</Subscript>Al in the Ni-Al-Pt system

Measurements were made to determine how Pt influences the partial thermodynamic properties of Al and Ni in γ′-(Ni,Pt)₃Al and liquid in the Ni-Al-Pt system. The activities of Al and Ni were measured with a multiple effusion-cell mass spectrometer (multi-cell KEMS). For a constant X _Al = 0.24, adding Pt, from X _Pt = 0.02-0.25, reduces a(Al) almost an order of magnitude, from 2 × 10⁻⁴ to 2 × 10⁻⁵, at 1560 K. This occurred for of −203 ± 10 kJ mol⁻¹ and the a(Al) decrease was due to increasing from −60 to −40 J mol⁻¹ K⁻¹ with Pt addition. The large negative and indicate Al-atoms are highly ordered in γ′-(Ni,Pt)₃Al. Nickel activity, a(Ni), remained essentially constant, ∼0.7, indicating an increasing ternary interaction between Ni-atoms and (Al + Pt)-atoms with Pt addition, where γ_Ni increased from about 0.7 to 1.2. This is supported by in the range 6.1-7.1 ± 1.5 kJ mol⁻¹ at 1520 K, and a positive , which suggest disorder on the Ni-lattice. For a consistent X _Al = 0.27, adding Pt, from X _Pt = 0.10–0.25, also reduces a(Al) but only by a factor of about 3, while a(Ni) remained essentially constant, with γ_Ni increasing from about 0.7 to 0.95. A dramatic change in the mixing behavior was observed between the and 0.27 series of alloys, where and are seen to increase about 50 kJ mol⁻¹ and 20 J mol⁻¹ K⁻¹ at T = 1566 K, respectively. In contrast, decreased about 16 kJ mol⁻¹ at T = 1520 K and changed from a positive to a negative value. This article was presented at the Multi-Component Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12–16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.