Phase equilibria in the cobalt oxide-copper oxide system

Thermodynamic properties were determined for the system cobalt oxide-copper oxide by means of an electromotive force (EMF) measurement techniques using galvanic cells with calciastabilized zirconia (CSZ) as the solid electrolyte and with air as the reference electrode according to the following schemes: CuO, Cu₂O | CSZ | air and CoO-CuO, Cu₂O CSZ | air for composition variables y=X_Cu/(X_Co+X_cu equal to 0.05, 0.15, 0.25, 0.35, 0.45, 0.667, and 0.8; and within the temperature interval 1200–1350 K. Thermodynamic properties calculated directly from EMF values were combined with the available literature data on phase equilibria, and thermodynamic properties of solid phases in the Co-Cu-O system were assessed. Both terminal solid solutions, (Co,Cu)O and (Cu,Co)O, were described by a sublattice model with Redlich-Kister excess term. The interaction parameters for both (Co,Cu)O and (Cu,Co)O solid solutions and the Gibbs energy of formation for the intermediate phase Cu₂CoO₃ were obtained. The Gibbs energies of fictive end-members: monoclinic “CoO” and “CuO” with rock salt structure were derived as well. The phase diagrams were calculated using the assessed thermodynamic parameters. The (T, y) phase diagram was calculated for existence under ambient air. The property diagrams log₁₀P(O₂) versus composition and activity of CuO versus composition were calculated at 1273 K. The results of our calculations were in a good agreement with available experimental data. This paper was presented at CALPHAD XXX International Conference on Phase Diagram Calculations in York, UK, May 27–June 1, 2001, and appeared in the Conference Abstracts on Page 75.     

Phase equilibria in the Al---Cr system

The Al---Cr system has been reviewed for Cr content up to 40 at.%. In this system several intermetallic compounds are formed by peritectic reactions. From the temperature of transformation and the composition of the phases, the nature of the invariant transformations is discussed. Transmission electron microscopy studies were performed on samples forming these compounds. A detailed structural interpretation is given for the phase θ-Al₇Cr. A new structure is proposed for Al₄Cr similar to that of the μ-Al₄Mn phase of which the crystal structure is known. The phase Al₅Cr (or Al₁₁Cr₂) was found to be orthorhombic and not monoclinic, as had been previously proposed. The existence of a cubic structure for the Al₉Cr₄ phase was confirmed.

On account of previous results, we should point out that the phases θ-Al₇Cr, Al₄Cr and Al₅Cr present characteristic features of pseudoicosahedral symmetry of the Al₄Cr icosahedral phase: it has been verified in the case of θ and μ that the same type of atomic cluster may be considered in order to describe these structures, i.e. 12 atoms located at the vertices of deformed icosahedra (either 12Al or 11Al + 1Cr or 10Al + 2Cr) whose centres are occupied by a Cr atom.

The reason for such an investigation originated from a study of the Al---Cr---Ni system for which the observed ternary structures appeared incoherent with those given for the binary Al---Cr system. This second study will be reported elsewhere.     

Phase equilibria in the Co-rich Co-Al-W-Ti quaternary system

We determined phase equilibria in the Co-rich Co-Al-W-Ti quaternary system at a temperature range between 900 °C and 1200 °C with a close attention to the thermodynamic stability of the γ′-Co₃(Al, W, Ti) (L1₂) phase, based on micro-structure observation and electron microprobe analysis on bulk alloy samples heat-treated for periods up to 2000 h. In the quaternary system the single phase field of γ′ extends from the Co-Ti binary edge to a composition of Co-5Al-8.5W-8Ti (in at.%) at 900 °C. At the tip of the single phase field, the γ′ phase is in equilibrium with the γ-Co (A1), Co₂AlTi (L2₁) and Co₃W (D0₁₉) phases. The constructed vertical section of phase diagram between Co-9.4Al-9.6W and Co-16.5Ti indicates that there is a narrow composition range around Co-4.5Al-5.4W-7.5Ti in which the γ single phase field exists at high temperatures above 1200 °C and two-phase of γ+γ′ is thermodynamically stable at low temperatures below 1100 °C.     

Co-Cu-Zn三元系相平衡的实验研究

本实验通过采用电子探针显微分析和X-ray衍射分析方法实验研究了Co-Cu-Zn三元体系在800°C和1000°C时的相平衡。在这两个等温截面中均未发现三元化合物。在800°C等温截面,Co在β-CuZn相中的固溶度为32.36%,Cu在β1-CoZn相中的固溶度为5.28%。除此之外,γ-Co5Zn21和γ-Cu5Zn8具有相同的晶体结构,因此,它们之间形成了一个贯穿连续固溶体相。1000°C的等温截面中,β-CuZn相、β1-CoZn相、γ-Co5Zn21相、γ-Cu5Zn8相都消失了。随着温度从800°C上升到1000°C,液相区域增大。     

Ni-Al-Sn三元系相平衡的实验研究

采用电子探针显微分析和X-ray衍射分析方法实验研究了Ni-Al-Sn三元体系在800°C和1000°C时的相平衡。结果表明：(1) Ni-Al-Sn三元体系在800°C和1000°C时均未发现三元化合物;(2) Ni-Al侧包含NiAl、Ni3Al、Al3Ni和Al3Ni2四个化合物,其中800°C时,Sn在NiAl和Ni3Al中的固溶度在分别为3.1和14.7 at.%,在1000°C时分别为3.0和8.0 at.%。而Sn在Al3Ni和Al3Ni2相中几乎没有固溶度;(3) Ni-Sn侧包含Ni3Sn(r)、Ni3Sn(h)和Ni3Sn2(h)三个化合物相。800°C时,Ni3Sn(r)相的固溶度为4.2 at.%,1000°C时,Ni3Sn(r)相转变为Ni3Sn(h)相,拥有5.5 at.% 的固溶度。另外,800°C时,Al在Ni3Sn2(h)相中的固溶度为8.4 at.%,1000°C时为12.1 at.%;(4) Ni-Al-Sn三元体系Al-Sn侧为相互贯通的液相区域,实验测得的Ni在Al-Sn侧的溶解度约为1 at.%。     

Phase equilibria in the binary Rh–Ti system

The present study of the binary Ti–Rh system provides a revised phase diagram clarifying controversial results in the literature. Various experimental methods were applied: electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The tie-lines of two-phase equilibria and the second-order transition A2/B2 were identified by means of diffusion couple experiments and by analysis of annealed bulk alloys. The diffusion couple experiments revealed two phenomena which were identified as pseudo-interfaces: one associated with crossing the stoichiometric composition of the B2 phase; a second between pure Rh and the Rh-rich solution.     

Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti₅(Si,Ga)₃ and β (Ti-base solid solution) and a narrow one of Ti₂Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti₅(Si,Ga)₃ and L↔β+Ti₂Ga and to the L+Ti₅(Si,Ga)₃↔Ti₂Ga peritectic reaction. The three-phase region (β+Ti₅(Si,Ga)₃+Ti₂Ga) results from the four-phase eutectic reaction L↔β+Ti₅(Si,Ga)₃+Ti₂Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti₅Si₃ and of both the elements in Ti are given.     

Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti₅(Si,Ga)₃ and β (Ti-base solid solution) and a narrow one of Ti₂Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti₅(Si,Ga)₃ and L↔β+Ti₂Ga and to the L+Ti₅(Si,Ga)₃↔Ti₂Ga peritectic reaction. The three-phase region (β+Ti₅(Si,Ga)₃+Ti₂Ga) results from the four-phase eutectic reaction L↔β+Ti₅(Si,Ga)₃+Ti₂Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti₅Si₃ and of both the elements in Ti are given.     

Co-Ti-Ta三元系富Co区的相平衡

研究Co-Ti-Ta三元系富Co区的相平衡。显微组织和XRD分析以及EDS检测结果表明,在1000～1200℃温度范围内,L12结构Co3Ti相和Laves_36_Co3Ta相与α-Co构成相平衡。Co3Ti相中Ta的固溶度超过10%,Ta的加入使Co3Ti相更稳定。根据实验结果构建Co-Ti-Ta三元系富Co区在1000、1100和1200℃等温截面图。     

Phase equilibria in the lead-copper (Pb-Cu) liquid system

The shape of the liquid-liquid coexistence curve of the Pb-Cu system with a miscibility gap has been determined by the γ-ray attenuation technique. According to the authors’ measurements, the coordinates of the critical point are T _C=1253.7±1.5K, X _C=37.2±0.3 at.% Pb. the critical exponent β of the coexistence curve equals 0.315±0.005, which agrees closely with the nonclassical value. Near the critical point the values (X ₁+X ₂)/2 (X ₁ and X ₂ are the concentrations of the phases in equilibrium with each other) exhibit a departure from the law of the rectilinear diameter.     

Phase equilibria in the lead-copper (Pb-Cu) liquid system

The shape of the liquid-liquid coexistence curve of the Pb-Cu system with a miscibility gap has been determined by the γ-ray attenuation technique. According to the authors’ measurements, the coordinates of the critical point are T _C=1253.7±1.5K, X _C=37.2±0.3 at.% Pb. the critical exponent β of the coexistence curve equals 0.315±0.005, which agrees closely with the nonclassical value. Near the critical point the values (X ₁+X ₂)/2 (X ₁ and X ₂ are the concentrations of the phases in equilibrium with each other) exhibit a departure from the law of the rectilinear diameter.     

Phase equilibria in the Al–Mo–Si system

The ternary Al–Mo–Si phase diagram was investigated by a combination of optical microscopy, powder X-ray diffraction (XRD), differential thermal analysis (DTA), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Ternary phase equilibria were investigated within two isothermal sections at 600 °C for the Mo-poor part and 1400 °C for the Mo-rich part of the phase diagram. The solubility ranges of several phases including MoSi₂ (C11_b) as well as Mo(Si,Al)₂ with C40 and C54 structure were determined. The binary high temperature phase Al₄Mo was found to be stabilized at 600 °C by addition of Si. DTA was used to identify 9 invariant reactions and thus constructing a ternary reaction scheme (Scheil diagram) in the whole composition range. A liquidus surface projection was constructed on basis of the reaction scheme in combination with data for primary crystallization from as-cast samples determined by SEM measurements.     

Phase equilibria in the Nb-Ga-As system below 1000 °C

The Nb-Ga-As solid state equilibrium phase diagram was determined at 600 °C with the use of powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), and scanning electron microscopy (SEM). No ternary Nb-Ga-As phases were found, and limited solid solubilities were measured in the constituent binary Nb-Ga and Nb-As compounds. The phases GaAs, NbGa₃, and NbAs coexist with each other to form a three-phase equilibrium that dominates the GaAs side of the phase diagram. The phase diagram is in agreement with interfacial reaction studies, which have shown that NbGas and NbAs are the stable phases when Nb thin films are reacted to completion on GaAs.     

Phase equilibria in the Co-Ti portion of the Co-Al-Ti ternary system

Phase equilibria of 900, 1000, and 1100 °C in the Co-Ti portion of the Co-Al-Ti system were mainly determined by energy dispersion x-ray spectroscopy. On the Ti-Al side, the β-Ti (A2) phase region is extended by the addition of Co and the β-Ti + AlTi₃ (D0₁₉) two-phase region appears in the ternary equilibrium, while the AlTi (L1₀), AlTi₃, and β-Ti phases show very low solubility of Co. It was found that the two ternary intermetallic compounds, Co₂AlTi (L2₁) and CoAl₂Ti (D8 _a ), exist over a wide solubility range along the CoAl(B2)-CoTi (B2) and CoAl₃-CoTi₃ sections, respectively. The ordering transition and the phase separation due to ordering of the β-Ti, CoAl, or CoTi and Co₂AlTi phases fundamentally possessing the bcc structure are also discussed.     

Phase equilibria in the α-Ti-Al-Si region of the Ti-Si-Al system

An experimental investigation of the phase relations in the titanium (Ti)-aluminum (Al)-silicon (Si) system was undertaken by differential thermal analysis, x-ray diffraction, metallography, and microprobe analysis. The present measurements when combined with those from an earlier investigation at this laboratory provide data for 56 alloy compositions in the Ti-Al-Si system. The combined results allowed the construction of a solidus projection, a melting diagram including both solidus and liquidus, partial isothermal sections at 1270 °C and 1250 °C, three isopleths with a constant percentage of one or another component, and a reaction scheme.     

Phase equilibria in the Co-Ti portion of the Co-Al-Ti ternary system

Phase equilibria of 900, 1000, and 1100 °C in the Co-Ti portion of the Co-Al-Ti system were mainly determined by energy dispersion x-ray spectroscopy. On the Ti-Al side, the β-Ti (A2) phase region is extended by the addition of Co and the β-Ti + AlTi₃ (D0₁₉) two-phase region appears in the ternary equilibrium, while the AlTi (L1₀), AlTi₃, and β-Ti phases show very low solubility of Co. It was found that the two ternary intermetallic compounds, Co₂AlTi (L2₁) and CoAl₂Ti (D8 _a ), exist over a wide solubility range along the CoAl(B2)-CoTi (B2) and CoAl₃-CoTi₃ sections, respectively. The ordering transition and the phase separation due to ordering of the β-Ti, CoAl, or CoTi and Co₂AlTi phases fundamentally possessing the bcc structure are also discussed.     

Phase equilibria of the constituent ternaries of the Mg-Al-Ca-Sr system

Thermodynamic modeling of the Al-Ca-Sr, Mg-Ca-Sr, Mg-Al-Ca and Mg-Al-Sr systems was conducted using the modified quasichemical model. A self-consistent database has been established for these systems. Mg-Al-Ca and Mg-Al-Sr ternary systems were studied experimentally through microstructure characterization, phase identification, and thermal analysis and thermodynamic modeling based on these experimental findings. It has been observed that the intermetallic compounds in the Mg-Ca, Mg-Sr, Al-Ca, and Al-Sr binary systems dissolve the third component in the respective ternary phase diagrams. In addition, two ternary compounds, Mg₅₆Al₄₀Sr₄ and Mg₂Al₄Ca₃, have been reported.