The establishment of the statistical-thermodynamic model of D81-structure and its application to α-Nb5Si3

A statistical-thermodynamic model for binary nonstoichiometric A₅B₃ with D8₁-structure has been established on the basis of the grand canonical ensemble. In the model the average chemical potentials according to the composition and a new extra equation as a boundary condition are proposed for more accuracy and free experimental data calculations. The model can be used in any A₅B₃ type compounds with D8₁ structure. The establishment method of the statistical-thermodynamic model can be extended to other complicated structures. We apply the statistical-thermodynamic model to α-Nb₅Si₃ and the parameters used in the model are obtained from the first-principles' calculations. From these parameters the expression for the point defect concentrations as a function of compositions and temperatures is obtained by numeral calculations. The constitutional defects and thermal defects in α-Nb₅Si₃ are discussed.     

Critical thermodynamic evaluation and optimization of the MgO-Al2O3, CaO-MgO-Al2O3, and MgO-Al2O3-SiO2 Systems

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the MgO-Al₂O₃, CaO-MgO-Al₂O₃, and MgO-Al₂O₃-SiO₂ systems at 1 bar total pressure are presented. Optimized model equations for the thermodynamic properties of all phases are obtained that reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions. The database of the model parameters can be used along with software for Gibbs energy minimization to calculate all thermodynamic properties and any type of phase diagram section. The modified quasichemical model was used for the liquid slag phase and sublattice models, based upon the compound energy formalism, were used for the spinel, pyroxene, and monoxide solid solutions. The use of physically reasonable models means that the models can be used to predict thermodynamic properties and phase equilibria in composition and temperature regions where data are not available.     

Analysis of coupled mechanical and thermal behaviors in hot rolling of large rings of titanium alloy using 3D dynamic explicit FEM

Hot rolling of a large ring of titanium alloy (LRT) is a highly nonlinear incremental forming process with coupled mechanical and thermal behaviors (MTBs) which significantly affect microstructure and properties of the ring. In the study, a 3D coupled thermo-mechanical FE model of the process is developed and validated. Reasonable ranges of key process parameters are determined for successful simulation. Investigation and comparison are performed regarding the MTBs of LRTs with different blank sizes and the dependence of the MTBs on key process parameters using dynamic explicit FE simulation. The results obtained show that: (1) at the stable forming stage, along the radial direction of an LRT, the largest equivalent plastic strain (PEEQ) is found on the inside or outside surface, depending on the distribution ratio of feed amount. The smallest PEEQ appears in the middle layer. The highest temperature occurs in the interior of the inside or outside layer, depending on the mechanical behavior. The lowest temperature is found on the inside or outside surface, or on the end plane of the middle layer. (2) For LRTs with different blank sizes, effects of key process parameters on their MTBs are similar under different forming conditions, i.e., under the stable forming condition, a smaller n₁, a larger v, or a higher T₀ contributes to more uniform strain and temperature distributions.     

Mechanical and thermal properties of Tb2(MoO4)3 crystals

The mechanical and thermal properties of single crystal Tb₂(MoO₄)₃ have been systematically studied. The result of microhardness measurement indicates that the crystal belongs to the soft materials category. The thermodynamic parameters obtained from DTA analysis were used for determining the type of liquid-solid interface during crystal growth. Negative thermal expansion along the c-axis was observed, and this behavior was attributed to the bent Tb-O-Mo bonds. The specific heat of the crystal was measured to be 0.122 cal g⁻¹ K⁻¹ at 293.15 K. The thermal conductivity of Tb₂(MoO₄)₃ at room temperature was found to be smaller than that of representative ferroelectric LiNbO₃.     

Thermodynamic reassessment of the BaO-B2O3 system

The BaO-B₂O₃ pseudobinary system is assessed. A two-sublattice ionic solution model, (Ba²⁺) _P (O²⁻, BO₃³⁻, B₄O₇²⁻, B₃O_4.5) _Q , is adopted to describe the liquid phase. All the solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the available experimental data on both phase diagram and thermodynamic properties is obtained by using CALPHAD technique. A comparison between the calculated results and experimental data as well as a previous assessment is presented.     

Influence of La doping on elastic and thermodynamic properties of SrMoO3

The elastic and thermodynamic properties for Sr_1−xLa_xMoO₃ (x = 0.0, 0.05, 0.1, 0.15, and 0.2) with temperature have been investigated, probably for the first time, by using modified rigid ion model (MRIM). The computed results on the elastic constants (C₁₁, C₁₂, and C₄₄) are the first report on them. Using these elastic constants we have computed other elastic properties such as B, β, G′, G, E, σ, B/G ratio, Cauchy pressure (C₁₂ − C₄₄) and Lame's parameters (μ, λ). We have also reported the thermodynamic properties such as ?, f, θ_D, θ_D1, υ₀, υ₁, γ, and α. The values of Young's modulus, shear modulus and compressibility for SrMoO₃ are in good agreement with the available experimental data. The concentration (x) dependence of θ_D in Sr_1−xLa_xMoO₃ suggests that increased La doping drives the system effectively away from the strong electron-phonon coupling regime. Specific heat is reported in the wide temperature range and compared with the respective experimental data available in the literature. The thermal expansion coefficient of SrMoO₃ is in good agreement with the other theoretical data.     

The migration of ions through poly(3-octylthiophene)

Molecular dynamics (MD) simulations are used to investigate the abilities of several anions (Cl⁻, BF₄⁻, ClO₄⁻, SO₄²⁻ and PO₄³⁻) to migrate in a matrix of oxidised poly(3-octylthiophene) formed by doping the polymer. The transport of the ions is considered when it is induced both by thermal effects and by an electric field. When a degree of disorder is introduced into the lattice, the Coulomb association of the polymer and anion subsystems retains persistent lattice domains in which the ions are intercalated between the thiophene rings of the polymer backbone forming channel sites for the ions. This order seems to be a consequence of the alkyl side chains, as it is not found in unsubstituted polythiophene. Transport of the singly-charged ions occurs readily along the channels’ encountering low barriers (4 kJ mol⁻¹), but the motions of the SO₄²⁻ and PO₄³⁻ ions are precluded, presumably due to coulombic effects. Application of electric fields along the channel directions induces the motion of the SO₄²⁻ and PO₄³⁻ ions also, but applying fields perpendicular to the channel destroys the lattice order. The transport of BF₄⁻ ions in a molecular channel is simulated by twisting the poly(3-octylthiophene) into a helix and examining the migration of the ions both inside and outside the helix channel.     

Thermodynamic optimization of the Na2O-B2O3 pseudo-binary system

The Na₂O-B₂O₃ system is thermodynamically optimized by means of the CALPHAD method. A two-sublattice ionic solution model, (Na⁺¹)_P(O⁻²,BO₃ ⁻³,B₄O₇ ⁻²,B₃O_4.5)_Q, has been used to describe the liquid phase. All the solid phases were treated as stoichiometric compounds. A set of thermodynamic parameters, which can reproduce most experimental data of both phase diagram and thermodynamic properties, was obtained. Comparisons between the calculated results and experimental data are presented.     

Pitting corrosion of intermetallic compound Ni3(Si,Ti) in sodium chloride solutions

The pitting corrosion of intermetallic compound Ni₃(Si,Ti) was investigated as functions of test temperature and chloride concentration in sodium chloride solutions by using a potential step method. In addition, the pitting corrosion of solution-annealed austenitic stainless steel type 304 and pure nickel was also studied under the same experimental condition for comparison. The pitting potential obtained for the intermetallic compound decreased with increasing chloride concentration and test temperature. A critical chloride concentration below which no pitting corrosion took place was found to exist and to decrease with increasing test temperature. The specific pitting potential at the critical chloride concentration also decreased with increasing test temperature. In addition, the pitting potential at various constant chloride concentrations above the critical chloride concentration decreased with increasing test temperature. The pitting potential of Ni₃(Si,Ti) was higher than pure nickel, but lower than that of type 304.     

Preparation of SrZrO<Subscript>3</Subscript> Thermal Barrier Coating by Solution Precursor Plasma Spray

The solution precursor plasma spray (SPPS) process is capable of depositing highly durable thermal barrier coatings (TBCs). In this study, an aqueous chemical precursor feedstock was injected into the plasma jet to deposit SrZrO₃ thermal barrier coating on metal substrate. Taguchi design of experiments was employed to optimize the SPPS process. The thermal characteristics and phase evolution of the SrZrO₃ precursor, as well as the influence of various spray parameters on the coating deposition rate, microhardness, microstructure, and phase stability, were investigated. The experimental results showed that, at given spray distance, feedstock flow rate, and atomization pressure, the optimized spray parameters were arc current of 600 A, argon flow rate of 40 L/min, and hydrogen flow rate of 10 L/min. The SrZrO₃ coating prepared using the optimized spray parameters had single-pass thickness of 6.0 μm, porosity of ~18%, and microhardness of 6.8 ± 0.1 GPa. Phase stability studies indicated that the as-sprayed SrZrO₃ coating had good phase stability in the temperature range from room temperature to 1400 °C, gradually exhibiting a phase transition from t′-ZrO₂ to m-ZrO₂ in the SrZrO₃ coating at 1450 °C with increasing time, while the SrZrO₃ phase did not change.     

Fe掺BaZrS3磁性半导体的制备与研究

硫族钙钛矿是一类新兴的半导体功能材料,具有独特的电子结构与光电性质。本文采用溶胶-凝胶法结合化学气相反应的方法制备了硫族钙钛矿BaZrS₃纳米结构,并且借助掺杂的方法获得了BaZr_1-xFe_xS₃磁性半导体,并对其结构和光、磁学等性能进行研究。结果表明,对氧化物钙钛矿BaZrO₃进行硫化处理,即用同族的S元素替代O元素,样品仍然可以表现出钙钛矿结构,而且硫化处理可以起到降低带隙宽度的作用。同时用具有局域磁矩的3d过渡族金属元素,如Fe进行钙钛矿B位阳离子掺杂,通过控制Fe的掺杂量同样可以系统地调控样品的带隙宽度,而且对于BaZr_99.7Fe_0.03S₃和BaZr_99.5Fe_0.05S₃样品表现出了室温铁磁性。     

Elasticity and thermodynamic properties of α-Ta4AlC3 under pressure

First-principles calculations of the crystal structure and the elastic properties of α-Ta₄AlC₃ have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The pressure dependence of the elastic constants c_ij, the aggregate elastic moduli (B, G, E), the Poisson's ratio, and the elastic anisotropy has been investigated. Using the quasi-harmonic Debye model considering the phonon effects, the temperature and pressure dependencies of isothermal bulk modulus, and the thermal expansions, and Grüneisen parameters, as well as Debye temperatures are investigated systematically in the ranges of 0–60 GPa and 0–1500 K as well as compared to available data.     

Thermal conductivity of Ni3V–Ni3Al pseudo-binary alloys

The effect of changes in the composition and microstructure of the Ni₃V–Ni₃Al pseudo-binary alloys on their thermal conductivity has been investigated. For Ni₃V and Ni₃Al-based single-phase alloys, the thermal conductivity shows a maximum value at the stoichiometric compositions, and it decreases as the V (or Al) content of the Ni₃Al (or Ni₃V) alloy increases, following the Nordheim rule. For Ni₃V–Ni₃Al two-phase alloys, the thermal conductivity of the constituent Ni₃Al phase exhibits a smaller value than that of the Ni₃V phase. Eventually, the thermal conductivity of the two-phase alloys decreases as the Al content increases because of the increase in the volume fraction of the Ni₃Al phase with low conductivity. As the temperature increases from 293 K to 1073 K, the conductivity increases for all of the alloys but not for stoichiometric Ni₃V. However, the dependence of the thermal conductivity on the alloy composition between 293 K and 1073 K is similar. Hence, it is confirmed that the thermal conductivity of the Ni₃V–Ni₃Al pseudo-binary alloys is controlled by the composition and volume fraction of the constituent phase.     

Physical Characteristics of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>100–<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys Based on Stretching and Heating Processes Using Molecular Dynamics Simulation

The physical characteristics of Ni _x Zr_100–x proportions based on stretching and heating processes were investigated using molecular dynamics (MD) simulation. The physical characteristics included axial stretching, slip vector of dislocation nucleation, radial distribution function, Poisson’s ratio, and internal energy of thermophysical properties of the Ni _x Zr_100–x proportions. The second-moment approximation for tight-binding many-body potential was used for Ni _x Zr_100–x physical characteristics during the MD simulation. Results show that the most Zr atoms of Ni _x Zr_100–x models after axis stretching obviously move and accumulate at the outside of the Ni _x Zr_100–x models due to high-temperature softening behavior and high covalent bond strength. The Poisson’s ratios of the Ni₂₀Zr₈₀, Ni₄₀Zr₆₀, Ni₅₀Zr₅₀ Ni₆₀Zr₄₀, and Ni₈₀Zr₂₀, are 0.401, 0.397, 0.490, 0.437, and 0.385, respectively. The Ni₅₀Zr₅₀ proportion has highest Poisson’s ratio, indicating that the transverse contraction strain to longitudinal extension strain is largest than others proportions. For the thermophysical properties, the atoms of Ni₅₀Zr₅₀ in solids are orientation order.     

Ce3+-doped LaF3 nanoparticles: Wet-chemical synthesis and photo-physical characteristics “optical properties of LaF3:Ce nanomaterials”

The most effective process parameters were determined to synthesize spherical LaF₃ nanoparticles with controllable size based on ethylenediaminetetraacetic acid (EDTA) via co-precipitation technique. Thermogravimetricdifferential thermal analysis, X-ray diffraction, scanning electron microscopy, dynamic light scattering and FT-IR spectroscopy were used to characterize the resulting powders. Detailed investigations revealed that the optimal LaF₃ host nano-material was obtained when NH₄F was used as a fluoride source in the presence of EDTA at pH = 5. Furthermore, photoluminescence spectra showed an intense double emission peak at 289 and 302 nm for cerium-doped LaF₃ nanocrystals excited at 253 nm, which was assigned to the well-known 5d→4f (²F_5/2 and ²F_7/2) transitions of Ce³⁺ levels due to luminescence center mechanism. The experimental results indicate that the synthesized LaF₃:0.05Ce powders with a band gap of 5.3 eV are promising phosphors for high density scintillators.     

Thermodynamic reassessment of the BaO-B2O3 system

The BaO-B₂O₃ pseudobinary system is assessed. A two-sublattice ionic solution model, (Ba²⁺) _P (O²⁻, BO ₃ ³⁻ , B₄O ₇ ²⁻ , B₃O_4.5) _Q , is adopted to describe the liquid phase. All the solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the available experimental data on both phase diagram and thermodynamic properties is obtained by using CALPHAD technique. A comparison between the calculated results and experimental data as well as a previous assessment is presented.     

Cyclic-Oxidation Behavior of Ti3Al0.7Si0.3C2 Compounds Between 900 and 1100 °C in Air

Dense, monolithic Ti₃Al_0.7Si_0.3C₂ compounds were cyclically oxidized between 900 and 1100 °C in air for 100 h. Ti₃Al_0.7Si_0.3C₂ oxidized into rutile-TiO₂, α-Al₂O₃, and amorphous SiO₂, accompanied by the evaporation of carbon. Ti₃Al_0.7Si_0.3C₂ had good thermal shock resistance, so that adherent oxide scales formed, regardless of their thickness. The cyclic oxidation resistance of Ti₃Al_0.7Si_0.3C₂ was poorer than that of Ti₃SiC₂, Ti₃AlC₂, and Cr₂AlC. The thermal cycling did not affect the scale morphology or the oxidation mechanism that was identified in the isothermal oxidation tests, due mainly to the formation of the adherent oxide scales.     

Mechanochemical reaction between ilmenite (FeTiO3) and aluminium

A natural ilmenite (FeTiO₃) and aluminium powder have been mechanically milled together for 100 h in a laboratory ball mill. The as-milled powder and an unmilled powder of identical composition were annealed at up to 1200°C and examined by X-ray diffraction and differential thermal analysis (DTA). The unmilled sample showed aluminium melted prior to an exothermic reaction starting at 850°C. The milled powder showed no thermal activity, other than a reversible phase transition at 1067±4°C, indicating that reaction occurred within the mill. The products of both powders were the same, TiAl₃, Fe₄Al₁₃ and Al₂O₃, although in the milled powder these phases were nanocrystalline until annealing caused crystallite growth. The thermal reaction seemed to occur in two stages, formation of TiAl₃, Al₂O₃ and elemental iron followed by a slower, diffusion controlled reaction between the elemental iron and residual aluminium to form Fe₄Al₁₃. The reaction during milling was attributed to increased intermixing between the ilmenite and aluminium causing a change in the rate determining step from solid-state diffusion to another, unknown, controlling mechanism.     

Hydrogen gas sensing of Co3O4-Decorated WO3 nanowires

Co₃O₄ nanoparticle-decorated WO₃ nanowires were synthesized by the thermal oxidation of powders followed by a solvothermal process for Co₃O₄ decoration. The Co₃O₄ nanoparticle-decorated WO₃ nanowire sensor exhibited a stronger and faster electrical response to H₂ gas at 300 °C than the pristine WO₃ nanowire counterpart. The former showed faster response and recovery than the latter. The pristine and Co₃O₄-decorated WO₃ nanowire sensors showed the strongest response to H₂ gas at 225 and 200 °C, respectively. The Co₃O₄-decorated WO₃ nanowire sensor showed selectivity for H₂ gas over other reducing gases. The enhanced sensing performance of the Co₃O₄-decorated WO₃ nanowire sensor was explained by a combination of mechanisms: modulation of the depletion layer width forming at the Co₃O₄-WO₃ interface, modulation of the potential barrier height forming at the interface, high catalytic activity of Co₃O₄ for the oxidation of H₂, active adsorption of oxygen by the Co₃O₄ nanoparticle surface, and creation of more active adsorption sites by Co₃O₄ nanoparticles.     

Nanocrystalline Co3O4 fabricated via the combustion method

A facile and rapid combustion method has been used to prepare nano-crystalline Co₃O₄ spinel employing urea as a combustion fuel. The fabrication was carried out by refluxing a mixture of cobalt nitrate and urea followed by calcination, for 3 h in static air atmosphere, at 400 °C. The thermal genesis of the Co₃O₄ was explored by means of thermogravimetric and differential thermal analyses in air atmosphere in the temperature range 25–1000 °C. X-ray diffraction, Fourier transform infrared spectra, and scanning electron microscopy were used to characterize the structure and morphology of the Co₃O₄. The obtained results conrmed that the resulting oxides were comprised of pure single-crystalline Co₃O₄ nanoparticles. Moreover, various comparison experiments showed that several experimental parameters, such as the reflux time and the urea/cobalt nitrate molar ratio, play important roles in the crystallite size as well as the morphological control of Co₃O₄ powders. Consequently, the minimum crystallite size can be obtained at 12 h reflux and a urea/cobalt nitrate molar ratio of 5.