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.     

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.     

Up-Date of a Thermodynamic Database of the ZrO<Subscript>2</Subscript>-Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System for TBC Applications

The thermodynamic database of the ZrO₂-Gd₂O₃-Y₂O₃-Al₂O₃ system is up-dated taking into account new data on lattice stabilities of ZrO₂, Gd₂O₃ and Y₂O₃ and heat capacity measurements for the monoclinic phase Gd₄Al₂O₉ and phase with garnet structure Gd₃Al₅O₁₂. New data for the heat capacities of Gd₂Zr₂O₇ (pyrochlore) and GdAlO₃ (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr_1−x Gd _x )O_2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd₄Al₂O₉ phase from a peritectic one to a congruent one in the Gd₂O₃-Al₂O₃ system. Correspondently, in the ternary system ZrO₂-Gd₂O₃-Al₂O₃, the melting character of the three-phase assemblage Gd₂O₃ (B), Gd₄Al₂O₉ and GdAlO₃ changed from eutectic to transition type U. The T ₀-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO₂-Gd₂O₃-Y₂O₃ system.     

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.     

Phase Relations in the ZrO<Subscript>2</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> System: Experimental Study and Advanced Thermodynamic Modeling

Phase equilibria in the ZrO₂-Nd₂O₃-Y₂O₃ system at 1523-1873 K have been investigated by x-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Temperatures of phase transformations were determined by differential thermal analysis. Temperatures of invariant reactions in the ZrO₂-Nd₂O₃ system F = A + Pyr and H = F + A were determined as 1763 and 2118 K respectively and thermodynamic parameters of phases were re-assessed. Phase transformations in ternary systems were determined at 1732 K for composition ZrO₂-48.46Nd₂O₃-5.38Y₂O₃ (mol%) and at 1744 and 1881 K for composition ZrO₂-79.09Nd₂O₃-2.75Y₂O₃ (mol%). They were interpreted using XRD investigation before and after DTA as Pyr + B → F, Pyr → F and A → B, respectively. The solubility of the Y₂O₃ in pyrochlore phase was found to exceed 10 mol%. The thermodynamic parameters of the ZrO₂-Nd₂O₃-Y₂O₃ system were reassessed taking into account solubility of Y₂O₃ in the Nd₂Zr₂O₇ pyrochlore phase (Pyr). It is assumed that Y³⁺ substitutes Nd³⁺ and Zr⁴⁺ in their preferentially occupied sublattices. Ternary parameter was introduced into fluorite phase (F) for better reproducing of phase equilibria. Mixing parameters were reassessed for phase A (Nd₂O₃ based solution), monoclinic phase B and cubic phase C (Y₂O₃ based solution). The isothermal sections calculated for the ZrO₂-Nd₂O₃-Y₂O₃ system are in the reasonable agreement with experimental results.     

Thermal and structural role of additives in P<Subscript>2</Subscript>O<Subscript>5</Subscript>-ZnO-Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> glass for low expansion sealing materials

A glass based on the P₂O₅-ZnO-Sb₂O₃ ternary system was modified with various additives, such as RO (R=Ca, Ba and Mn), B₂O₃ and V₂O₅, for low temperature and low expansion sealing materials. The glass transition temperature (T_g) and coefficient of thermal expansion (CTE) were monitored and reduced with additive compositions of RO. Additional incorporation of B₂O₃ at the expense of RO also showed a similar result. Significant improvement was observed when the glass was modified with V₂O_5. A glass showing T_g<350 °C along with CTE<65×10⁻⁷/°C was found, suggesting a high potential for low temperature sealing materials especially for display applications. The role of the quaternary element within the glass is discussed, along with the structural effect using Raman spectroscopy.     

Dielectric properties of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films deposited onto Ti and TiO<Subscript>2</Subscript> layer

The present study describes the dielectric properties of RF sputtered Ta₂O₅ thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO₂. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta₂O₅ thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta₂O₅ fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta₂O₅/Ti/Si/Cu and Cu/Ta₂O₅/TiO₂/Si/Cu) indicated that the amorphous Ta₂O₅ grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10⁻¹–10⁻⁴ A/cm²), whereas a relatively low dielectric constant (−10) and low leakage current (−10⁻¹⁰ A/cm²) were observed in the amorphous Ta₂O₅ deposited on the TiO₂ buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta₂O₅ thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta₂O₅/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta₂O₅/TiO₂ film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

Thermodynamic Calculation of HfB<Subscript>2</Subscript> Volatility Diagram

The thermodynamics of the oxidation of HfB₂ at temperatures of 1000, 1500, 2000, and 2500 K have been studied using volatility diagrams. Both the equilibrium oxygen partial pressure ( P_\textO2 P_{{{\text{O}}_{2} }} ) for the HfB₂(s) to HfO₂(s) plus B₂O₃(l) and the partial pressures of B-O vapor species formed due to B₂O₃(l) volatilization increase with increasing temperature. Vapor pressures of the predominant gaseous species also increase with P_\textO2 P_{{{\text{O}}_{2} }} . At 1000 K, the predominant vapor transition sequence is predicted be BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g) with increasing P_\textO2 P_{{{\text{O}}_{2} }} , and the predominant gas is BO₂(g) with a pressure of 1.27 × 10⁻⁶ Pa under the condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa. At higher temperatures of 1500, 2000, and 2500 K, the system undergoes vapor transitions in the same sequence of B(g) → BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g). Under the same condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa, the predominant vapor species is B₂O₃(g) with pressures of 2.38, 4.49 × 10³, and 3.55 × 10⁵ Pa, respectively. Volatilization of B₂O₃(l) may produce porous HfO₂ scale, which is consistent with the experimental observations of HfB₂ oxidation in air. The present volatility diagram of HfB₂ shows that HfB₂ exhibits oxidation behavior similar to ZrB₂, and factors other than volatility of gaseous species affect the oxidation rate.     

Influence of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the properties of KBT-NBT-BT lead-free piezoelectric ceramics

0.144(K0.5Bi0.5)TiO3-0.85(Na0.5Bi0.5)TiO3-0.006BaTiO3(KBT-NBT-BT) lead-free piezoelectric ceramics were prepared using a conventional solid state method.The influence of Sb2O3 doping on the crystal phase,surface microstructure and properties of the KBT-NBT-BT lead-free piezoelectric ceramics were investigated using X-ray diffraction(XRD),scanning electron microscope(SEM) and other analytical methods.The results show that all compositions are of pure perovskite structure solid states.Sb2O3 doping does not influence the microstructure of KBT-NBT-BT lead-free piezoelectric ceramics obviously in the Sb2O3 doping range of 0.1-0.5 wt.%.Sb2O3 functions as a donor when doped small amount,while functions as a acceptor when doped large amount.The piezoelectric strain constant(d33) increases first and then decreases;the dielectric constant(ε3T3/ε0) and the dielectric loss(tanδ) decrease continuously when the amount of Sb2O3 dopant increases.When the doping amount of Sb2O3 is 0.1 wt.%,the KBT-NBT-BT piezoelectric ceramics with good comprehensive properties are obtained,whose d33,ε3T3/ε0 and tanδ are 147 pC/N,1510 and 4.2%,respectively.     

Oxidation Behavior of TiAl<Subscript>3</Subscript>/Al Composite Coating on Orthorhombic-Ti<Subscript>2</Subscript>AlNb Based Alloy at Different Temperatures

This paper reports the oxidation behavior of TiAl₃/Al composite coating deposited by cold spray. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The oxidation kinetics of the coating was tested at 650, 800, and 950 °C, respectively. The parabolic rate constant for the coating oxidized at 650 °C was k _p = 7.2 × 10⁻² mg·cm⁻²·h^−1/2 for the tested 1200 h. For the coating oxidized at 800 °C, the oxidation kinetics could be separated into two stages with k _p value of 39.8 × 10⁻² mg·cm⁻²·h^−1/2 for the initial 910 h and 17.7 × 10⁻² mg·cm⁻²·h^−1/2 for the stage thereafter. For the coating oxidized at 950 °C, the oxidation kinetics can be separated into three stages with k _p of 136.9 × 10⁻² mg·cm⁻²·h^−1/2 in the first 100 h, followed by 26.9 × 10⁻² mg·cm⁻²·h^−1/2 from 100 to 310 h, and 11.8 × 10⁻² mg·cm⁻²·h^−1/2 from 310 to 1098 h. XRD, SEM, and EPMA were used to study the microstructure of the coating. The results indicated that the oxidation took place throughout the entire coating instead of only at the surface. The aluminum phase in the composite coating was soon oxidized to Al₂O₃ in all tested cases. The aluminum in TiAl₃ phase was depleted gradually and oxidized to Al₂O₃ along with the degradation of TiAl₃ to TiAl₂ and TiAl as the temperature increased and time proceeded. AlTi₂N was also a typical oxidation product at temperature higher than 800 °C. The experimental results also indicated that the protection of the coating was attributed greatly to the interlayer formed between the coating and the substrate.     

The effect of heat treatment on the corrosion resistance of 440C stainless steel in 20% HNO<Subscript>3</Subscript> + 2.5% Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript> solution

The effect of heat treatment on the corrosion resistance of 440C stainless steel was investigated in a 20% HNO₃ + 2.5% Na₂Cr₂O₇ solution using electrochemical noise (ECN) measurements, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) examinations. The noise resistance (Rn), which has been found to be inversely related to the localized corrosion rate, was measured to be 5.7E + 08 Ω-cm², 4.2E + 08 Ω-cm², and 3.7E + 04 Ω-cm² for the oil-quenched, air-quenched, and vacuum furnace cooled (VFC) samples, respectively, after 1200 s exposures. The Rn for all heat treat conditions stabilized within a range of 1.0E + 07 Ω-cm² to 3.2E + 08 Ω-cm² after 2 h exposures. The EIS response showed a polarization resistance (R _p) on the order of 6.6E + 04 Ω-cm², 5.3E + 04 Ω-cm², and 1.1E + 04 Ω-cm² for the oil-quenched, air-quenched, and VFC samples, respectively, after 2 h exposures. The EIS data are in good agreement with ECN data and indicate that after longer exposures, general corrosion mechanisms dominate and the corrosion rates are comparable. SEM examinations of specimens subjected to 1200 s exposures revealed that severity of pitting and intergranular corrosion damage was consistent with trends in the Rn data. Specifically, the electrochemical noise data as well as SEM examinations of specimens revealed a higher localized corrosion resistance of the hardened specimens during the early stages of passivation. This greater resistance to localized corrosion can be attributed to an increased stability of the natural passive film resulting from a higher concentration of chromium atoms in solution for the martensite phase.     

Electronic structures of new tunnel barrier spinel MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: first-principles calculations

The electronic structures of spinel MgAl2O4 and MgO tunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl2O4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5. 10 eV for MgAl2O4 and 4. 81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point (△ band), the coherent tunneling effect might be expected to appear in MgAl2O4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2. 9 J. m-2) and MgAl2O4 (2. 27 J·m-2) on the {100}orientation, and the smaller lattice mismatch between MgAl2O4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl2O4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.     

Phase Relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> System in the Solid State. The Crystal Structure of AlVO<Subscript>4</Subscript>

Phase relations in the ternary oxide system Al₂O₃-V₂O₅-MoO₃ in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al₂O₃-V₂O₅-MoO₃ system, there exist seven phases, that is Al₂O₃, V₂O_5(s.s.), MoO₃, AlVO₄, Al₂(MoO₄)₃, AlVMoO₇, and V₉Mo₆O₄₀. Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO₄ has been refined from x-ray powder diffraction data. Its space group is triclinic, , Z = 6, with a = 0.65323(1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, α = 96.175(2)°, β = 107.234(3)°, γ = 101.404(3)°, V = 0.42555 nm³. The crystal structure of the compound is isotypic with FeVO₄. Infrared (IR) spectra of AlVO₄ and FeVO₄ are compared.     

Solvothermal synthesis and thermoelectric properties of skutterudite compound Fe（0.25）Ni（0.25）Co（0.5）Sb3

Nanostructured skutterudite-related compound Fe_0.25Ni_0.25Co_0.5Sb₃ was synthesized by a solvothermal method using FeCl₃, NiCl₂, CoCl₂, and SbCl₃ as the precursors and NaBH₄ as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m⁻¹·K⁻¹ at room temperature and decreases to 1.57 W·m⁻¹·K⁻¹ at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure of merit of 0.15 is obtained at 673 K.     

Surface modification of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> with Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> for lithium ion batteries

Cr 2 O 3-coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr 2 O 3 does not affect the LiNi 1/3 Co 1/3 Mn 1/3 O 2 crystal structure (α-NaFeO 2 ) of the cathode material compared to the pristine material, the surfaces of LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples are covered with Cr 2 O 3 well, and the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with Cr 2 O 3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with 1.0 wt.% Cr 2 O 3 at 0.5C reaches 169 mAh·g 1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 is only 160.8 mAh·g 1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.     

Phase Equilibria in the System Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-CoO and Gibbs Energy of Formation of Ca<Subscript>3</Subscript>CoAl<Subscript>4</Subscript>O<Subscript>10</Subscript>

An isothermal section of the system Al₂O₃-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca₃CoAl₄O₁₀, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca₃CoAl₄O₁₀ in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: From the emf of the cell, the standard Gibbs energy change for the Ca₃CoAl₄O₁₀ formation reaction, CoO + 3/5CaAl₂O₄ + 1/5Ca₁₂Al₁₄O₃₃ → Ca₃CoAl₄O₁₀, is obtained as a function of temperature: /J mol⁻¹ (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca₃CoAl₄O₁₀ from its component binary oxides, Al₂O₃, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca₃CoAl₄O₁₀ at 298.15 K are evaluated. Chemical potential diagrams for the system Al₂O₃-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.     

<Superscript>63</Superscript>Cu NMR spectra,magnetic susceptibility,and transmission electron microscopy of the rapidly quenched alloy Ti<Subscript>50</Subscript>Ni<Subscript>25</Subscript>Cu<Subscript>25</Subscript>

Methods of transmission and scanning electron microscopy and nuclear magnetic resonance (NMR) at ⁶³Cu nuclei, as well as measurements of the static magnetic susceptibility χ(T) have been used to study a shape-memory alloy (SMA) Ti₅₀Ni₂₅Cu₂₅, which experiences a thermoelastic martensite transformation. The alloy was obtained from an amorphous ribbon in a bimodal nano- and submicrocrystalline state via a crystallization annealing for 1 h at 770 K with a subsequent quenching to room-temperature water. The resultant B2 austenite is characterized by a fine structure of the ⁶³Cu NMR spectra, which is connected with the different distribution of ⁶³Cu atoms on the second coordination shell. The evolution of the shape of the spectra with decreasing temperature reveals a structural transition B2 → B19. In addition, the ⁶³Cu NMR spectra, just as the transmission electron microscopy, indicate the presence of phase separation in the alloy, with the precipitation of a TiCu (B11) phase. The temperature dependence of the static magnetic susceptibility χ(T) also indicates the occurrence of a structural transition and has a hysteretic nature of “stepped” type. The discovered stepped nature of the χ(T) dependence is explained by the bimodal size distribution of grains of the B2 phase due to the size effect of the martensitic transformation.     

Porous Y<Subscript>2</Subscript>O<Subscript>3</Subscript> microcubes: synthesis and characterization

In this work, a facile route using a simple solvothermal reaction and sequential heat treatment process to prepare porous Y₂O₃ microcubes is presented. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), energy dispersive spectrometer (EDS), thermogravimetric analysis (TG), and differential thermal analysis (DTA). The thermal decomposition process of the Y₂O₃ precursor was investigated. SEM results demonstrated that the as-prepared porous Y₂O₃ microcubes were with an average width of about 20 μm and thickness of about 8 μm. It was found that the morphology of the Y₂O₃ precursor could be readily tuned by varying the molar ratio of S₂O₈²⁻ to Y³⁺. Y₂O₃:Eu³⁺ (6.6%) microcubes were also prepared and their photoluminescence properties were investigated.