Critical Systematic Evaluation and Thermodynamic Optimization of the Fe-RE System: RE = Gd,Tb, Dy,Ho, Er,Tm, Lu,and Y

As the second part of the thermodynamic study of binary Fe-RE system, critical evaluations and optimizations of all available phase diagrams and thermodynamic data for the Fe-heavy RE (heavy RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) systems were conducted to obtain reliable thermodynamic functions of all the phases in the systems. In the thermodynamic modeling of the heavy RE systems, systematic variations in the phase diagrams and thermodynamic properties such as the enthalpy of mixing in the liquid state and enthalpy of formation of solid compounds with the atomic number of lanthanide series were observed. These systematic trends were incorporated in the optimization of the Fe-heavy RE system to resolve inconsistencies between available experimental data and to estimate unknown thermodynamic properties. The systematic trends in thermodynamic properties of solid and liquid phases and phase diagram of the entire Fe-RE systems were summarized.     

Thermodynamic Optimization of the Sc-X (X = La, Li, Ca, Cr) Systems

The Sc-X (X = La, Li, Ca, Cr) systems have been thermodynamically assessed by means of the CALPHAD (CALculation of PHAse Diagram) method. For each of the binary systems, a set of self-consistent thermodynamic parameters has been obtained. Comparisons between the calculated and measured phase diagrams show that the experimental data are satisfactorily accounted for by the present thermodynamic modeling.     

Critical Systematic Evaluation and Thermodynamic Optimization of the Mn-RE System (RE = Tb,Dy, Ho,Er, Tm and Lu) with Key Experiments for the Mn-Dy System

Critical evaluation and optimization of all available phase diagrams and thermodynamic data for the Mn-RE (RE = Tb, Dy, Ho, Er, Tm, and Lu) systems has been conducted to obtain reliable thermodynamic functions of all the phases in the systems. Key experiments for the Mn-Dy system were performed using DSC and solution calorimeter. In the thermodynamic modeling, it is found that the Mn-RE systems show systematic changes in the phase diagrams and thermodynamic properties such as enthalpy of mixing in liquid state in the order of periodic number in the lanthanide series. The systematic thermodynamic modeling approach for RE elements allow to resolve inconsistencies in the experimental data and estimate unknown thermodynamic properties and phase equilibria of Mn-RE system.     

High Temperature Thermodynamics of RE(La,Ce,Pr,Y,Tb)-S-F Systems

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Thermodynamic Optimization and Calculation of the HoCl3-MCl (M = Na, K, Rb, Cs) Systems

According to measured experimental phase diagram data and thermodynamic data, the HoCl₃-MCl (M = Na, K, Rb, Cs) phase diagrams were determined by the CALPHAD technique. The Gibbs energies of liquid phases in these systems have been optimized and calculated by the modified quasi-chemical model in the pair-approximation for short-range ordering. A series of thermodynamic functions have been optimized and calculated on the basis of an interactive computer-assisted analysis. The results show that the thermodynamic properties and phase diagrams are self-consistent. The optimized results for the systems are discussed.     

Thermodynamic Assessment of the Fe-Y System

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RE(RE=Y,La,Ce,Lu)对TiAl性能影响的计算研究

基于密度泛函理论的第一性原理,探讨了稀土金属元素RE(RE=Y,La,Ce,Lu)合金化对TiAl力学性能的影响。通过计算TiAl合金形成能发现:富Al(Ti8Al7Al)晶体结构比富Ti(Ti_7Al_8Ti)晶体结构更稳定,稀土金属元素RE合金化TiAl合金晶体结构的能量比合金化前有所下降,合金化可提高体系的结构稳定性。通过态密度、Bander电荷密度等分析,发现稀土金属元素RE合金化提高TiAl力学性能的根本原因是:合金化元素RE的电子与周围的Ti原子产生了电荷转移,导致Ti原子失电子数增加,使Ti-Al之间离子性相互作用减弱,共价性相互作用增强,增加TiAl的结构稳定性。同时,RE合金化可降低TiAl合金体系的脆性,增加体系的韧性,其中作用效果从大到小依次是:YCeLaLu。     

Effect of the Rare-Earth Addition (R = Ce,Sm) on the Phase Equilibria and Microstructure of Ni-Al Alloys

The peculiarities in the phase formation in the Al-rich region of the Ce-Ni-Al and Sm-Ni-Al ternary systems have been investigated by means of optical and scanning electron microscopy, electron probe microanalysis and x-ray powder diffraction (XRD) study. The following ternary phases have been identified: Ce₄Ni₆Al₂₃ (τ₁, mS66-Y₄Ni₆Al₂₃), CeNiAl₄ (τ₃, oS24-YNiAl₄), Sm₃Ni₅Al₁₉ (τ₂, oS108-Gd₃Ni₅Al₁₉), Sm₄Ni₆Al₂₃ (τ₁, mS66-Y₄Ni₆Al₂₃) and SmNiAl₄ (τ₃, oS24-YNiAl₄). Moreover, a temperature of 622 °C ± 1 has been established for the ternary eutectic reaction L ? (Al) + NiAl₃ + αCe₃Al₁₁ using a differential scanning calorimeter (DSC). The general characteristics of the sections are discussed in comparison with those of other R-Ni-Al systems (R = rare earths).     

Phase Relations in SiC-AlN-R2O3 (R = Nd, Gd, Yb, Y) Systems

The phase relations in SiC-AlN-R₂O₃ (R = Nd, Gd, Yb, Y) systems were determined by XRD and EPMA analyses of the solid-state reacted samples from powder mixtures of SiC, AlN and various R₂O₃. Subsolidus phase diagrams of these systems were established. In the Nd-system by Si-C partially substituted for Al-N in Nd₂AlO₃N, the formation of solid solution with formula Nd₂Al_1?x Si _x O₃N_1?x C _x (x = 0-0.5) was first found. Impurities of Al₂O₃ and SiO₂ from AlN and SiC starting powders respectively often caused the formation of some salt compounds, RAP type (R = Nd) and RAM type (R = Gd, Yb, Y), in corresponding systems. Mechanism of the reactions of forming salt compounds and their relations with rare earth oxides series are discussed.     

First-Principles Calculations of the Dynamical and Thermodynamic Properties of Yttrium Compounds YX (X = N,P, As and Sb)

The structural, dynamical and thermodynamical properties of the yttrium pnictides YN, YP, As and YSb compounds in the NaCl (B1) stable phase and the CsCl (B2) unstable phase structures are studied by performing ab initio calculations with the help of the generalized gradient approximation (GGA). The computed lattice parameters; lattice constants, static bulk modulus and corresponding first-order pressure derivative of the bulk modulus are obtained in the two structures NaCl and CsCl and compared with other theoretical and experimental values. The transition pressure from B1 type to B2 type phases is presented and it is about 171, 72, 75 and 34 GPa for YN, YP, YAs and YSb compounds respectively. To obtain the dispersion relation curves and density of states we used the linear-response approach to the density functional theory in both structures. The values of phonon frequencies are used to obtain the thermodynamic quantities such as entropy and heat capacity as function of temperature at different pressures.     

Phase Equilibria in the Zn-Rich Corner of the Zn-Cu-Ti-RE (Ce,La) Systems at 450 °C

The Zn-rich corner of the Zn-Cu-Ti-RE(Ce, La) quaternary systems at 450 °C have been experimentally investigated by scanning electron microscopy coupled with energy dispersive x-ray spectrometer and x-ray diffraction. The liquid containing phase regions have been well identified in these two systems. The ternary compound τ (Cu₂TiZn₂₀) can equilibrate with all phases in the Zn-rich corner of these two systems. Neither Ce nor La can dissolve into TiZn₁₆, ε(CuZn₄) and τ(Cu₂TiZn₂₀). While the solubility of Cu in CeZn₁₁ and LaZn₁₃ can reach 2.9 at.% and 5.0 at.%, respectively. The results can help to design and analyze the Zn-Cu-Ti-RE alloys.     

Structural and corrosion characterization of biodegradable Mg–RE (RE=Gd,Y, Nd) alloys

Binary Mg–Gd (up to 5% Gd in mass fraction), Mg–Nd (up to 9% Nd in mass fraction) and ternary Mg–Gd-Y (up to 5% Gd, 1% Y) alloys with precisely determined contents of cathodic impurities (Fe, Ni, Cu, Co) were studied. The alloys were studied in the as-cast state (cooling rate of 500 K/min) and after solution heat treatment (T4). Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution (9 g/L NaCl) was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine α-Mg dendrites and eutectic Mg–RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg–Gd alloys. For this reason, the T4 heat treatment of the Mg–Gd alloy led to the formation of a new cuboidal Mg₅Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg–Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg–Gd alloys. Its effect on the corrosion of Mg–Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.     

Phase Relations in Si-Al-M-O-C (M = Zr,Mg) Systems

The present work determined the phase relations in Si-Al-M-O-C (M = Zr, Mg) systems, involving SiC-Al₂O₃-ZrO₂, SiC-Al₂O₃-MgO, SiC-SiO₂-Al₂O₃-ZrO₂ and SiC-SiO₂-Al₂O₃-MgO systems by XRD phase analyses of the solid-state reacted samples from powder mixtures of SiC, Al₂O₃, ZrO₂, MgO and SiO₂. Within these systems, SiC was respectively compatible with other neighboring phases, forming a set of four-phase compatibility tetrahedrons. The subsolidus phase diagrams of the SiC-SiO₂-Al₂O₃-ZrO₂ and SiC-SiO₂-Al₂O₃-MgO quaternary systems were presented.     

Effects of RE^3＋（RE=La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） on the luminescence of Sr2MgSiO5：Eu^2＋ phosphors

Sr2MgSiO5:Eu2+phosphors were synthesized through a high temperature solid state reaction method.The phase and luminescence properties of the samples were characterized by X-ray diffraction(XRD) and a luminescence spectrometer.The effects of RE3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) on the luminescent properties of the samples were studied.The results show that the luminescence spectrum of Sr2MgSiO5:Eu2+ is a broad band composed of two emission peaks,at 460 and at 530 nm under near-ultraviolet excitation.Rare earth ions Re3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) have great influence on the emission of Sr2MgSiO5:Eu2+ phosphors.The La3+ ion in Sr2MgSiO5:Eu2+ phosphors greatly enhances the emission at 460 and 530 nm.     

Application of Solid Electrolyte Cells to Study of Thermodynamic Properties of RE－O－F Systems

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Effect of RE element Y on properties of Ti(C, N)-based cermet

The effect of RE element Y on the microstructure and properties of Ti(C, N)-based cermet has been investigated. Yttrium can refine the particles of carbide phase because it can purify the interface between binder phase and carbide phase, and increase the thickness of rim phase slightly. The effect is in the most evidence when the mass fraction of Y is 0.8% and when the transverse rupture strength and the hardness of Ti(C, N)-based cermet are maximal.