Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃-SiO₂ and CrO-Cr₂O₃-SiO₂-Al₂O₃ systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

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⁻, 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.     

Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10^?3 atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Phase Relations in the Systems SrO-Y2O3-CuO-O2 and CaO-Y2O3-CuO-O2 at 1173 K

Phase relations in the systems SrO-Y₂O₃-CuO-O₂ and CaO-Y₂O₃-CuO-O₂ at 1173 K were estab-lished by equilibrating different compositions in flowing oxygen gas at a pressure of 1.01 × 10⁵ Pa. The quenched samples were examined by optical microscopy, X-ray diffraction (XRD), energy dis-persive analysis of X-rays (EDAX), and electron spin resonance (ESR). In the system SrO-Y₂O₃-CuO-O₂, except for the limited substitution of Y₃+ for Sr₂+ ions in the ternary oxide Sr₁₄ Cu₂₄O₄₁, no new quaternary phase was found to be stable. The compositions corresponding to the solid solution Sr_14-xY_xCu₂₄O₄₁ and the compound SrCuO₂+δ lie above the plane containing SrO, Y₂O₃, and CuO, displaced towards the oxygen apex. However, in the system CaO-Y₂O₃-CuO-O₂ at 1173 K, all the condensed phases lie on the plane containing CaO, Y₂O₃, and CuO, and a new quaternary oxide YCa₂Cu₃O_6.5 is present. The quaternary phase has a composition that lies at the center of the non-stoichiometric field of the analogous phase YBa₂Cu₃O_7-δ in the BaO-Y₂O₃-CuO-O₂ system. The com-pound YCa₂Cu₃O_6.5 has the tetragonal structure and does not become superconducting at low temperature. Surprisingly, phase relations in the three systems CaO-Y₂O₃-CuO-O₂, SrO-Y₂O₃-CuO-O₂, and BaO-Y₂O₃-CuO-O₂ are found to be quite different.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃-SiO₂ and CrO-Cr₂O₃-SiO₂-Al₂O₃ systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.     

Experimental and computational investigations on the AlH3/AlF3 system

The possibility of changing the thermodynamic properties of AlH₃, alane, by fluorine anion substitution has been investigated by experimental measurements, ab initio calculations and thermodynamic modelling. No solid solution phases are observed experimentally. In accordance to this the calculations give a positive free energy of mixing for all compositions, showing that a mixed phase is not thermodynamically favourable. Thus fluorine anion substitution does not seem feasible for the alane system.     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

Influence of B2O3 additives on microstructure and electrical properties of ZnO-Bi2O3-Sb2O3-based varistors

B₂O₃-doped ZnO-Bi₂O₃-Sb₂O₃-based varistors were fabricated by conventional ceramic technique. The microstructure and electrical properties were investigated by SEM, XRD and electrical measurements. With the addition of B₂O₃, the liquid-assisted sintering based on Bi₂O₃ was improved, and the Bi₂O₃-B₂O₃ glass and Zn₃(BO₃)₂ phase were formed on the grain boundaries. The doping of B₂O₃ markedly improved the varistor performance of the ZnO-Bi₂O₃-Sb₂O₃-based varistors. The nonlinear coefficient of the sample with 3.5 mol% B₂O₃ sintered at 1100 °C reached 56 and the leakage current was only 0.3 μA.     

Mechanochemical synthesis of Al2O3-TiB2 nanocomposite powder from Al-TiO2-H3BO3 mixture

Alumina-titanium diboride nanocomposite (Al₂O₃-TiB₂) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO₂, B₂O₃ and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al₂O₃-TiB₂ nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size.     

Complex impedance analysis of (Y2O3 + CeO2)-YCr0.5Mn0.5O3 composite NTC ceramics

Ceramic compositions based on (aY₂O₃ + bCeO₂)-0.4YCr_0.5Mn_0.5O₃ (a + b = 0.6) were prepared by conventional solid state reaction at 1200 °C, and sintered under air atmosphere at 1600 °C. For 0 ≤ a < 0.6, XRD patterns have shown that the major phases presented in the calcined powders are Y₂O₃, CeO₂ and orthorhombic perovskite YCr_0.5Mn_0.5O₃ phase, respectively. SEM and EDAX observations confirm the YCr_0.5Mn_0.5O₃ phases mostly exist at the grain, whereas the Y₂O₃ and CeO₂ phases mainly exist at the grain boundaries. Complex impedance analysis shows that, for 0 < a ≤ 0.6, single semicircular arc whose shape does not show any change with temperature. Nevertheless, for a = 0, two overlapping semicircular arcs are observed at and above 300 °C. The grain boundary properties exhibit thermistor parameters with a negative temperature coefficient characteristic. The relaxation behavior and conduction for the grain boundary could be due to a space-charge relaxation mechanism and oxygen vacancies, respectively.     

CVD deposition and characterization of coloured Al2O3/ZrO2 multilayers

Coloured Al₂O₃/ZrO₂ multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO₂ process used in the multilayer, with ZrCl₄ as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO₂ phases. However by adding a relatively small amount of AlCl₃ during such a process results in ZrO₂ layers being composed of predominantly tetragonal ZrO₂ phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO₂ phase seem to be less perfect with existence of larger grains of ZrO₂ which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al₂O₃ layers.It is believed that, in the studied Al₂O₃/ZrO₂ multilayers, the observed tetragonal ZrO₂ phase is the result of a size effect, where small enough ZrO₂ crystallites energetically favor the tetragonal phase. However as the ZrO₂ crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO₂ phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO₂ based ceramics.     

La2O3含量对Al2O3/Cu基复合材料组织与性能的影响

以La₂O₃粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La₂O₃对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明：添加La₂O₃可获得纳米Al₂O₃颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa₂O₃,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La₂O₃,其导电率提高10.1%,磨损量减小36.6%。     

Thermodynamic assessment of ZnO-SiO2 system

ZnO-containing slags are common in pyrometallurgical processing of the base metals and steel. This caused the interest to the thermodynamics of the ZnO-SiO₂ system. A complete literature survey, critical evaluation of the available experimental data and a thermodynamic optimization of the phase equilibria and thermodynamic properties of the system ZnO-SiO₂ at 1.013×10⁵ Pa are presented. The molten oxide was described as an associate solution. The properties of liquid were reassessed and enthalpy term of the Gibbs energy of solid Zn₂SiO₄ was re-fitted to be compatible with the new data in the willemite primary phase field. The thermodynamic data set agrees well with the recent experimental observations. It can be used for predicting, e.g., the thermodynamic properties and the domains of the phase diagram, like critical point of the liquid miscibility gap, with a better accuracy than using the previous assessments. A set of optimized model parameters were obtained, reproducing the reliable thermodynamic and phase equilibrium data within their experimental errors from 298 K to liquidus temperatures, over the entire composition range. The created database can be used in a Gibbs energy minimization software to calculate the thermodynamic properties and the phase diagram sections of interest.     

Phase relationships in the systems RE2O3-Al2O3-SiO2 (RE = rare earth element, Y, and Sc)

A literature survey and recent results on phase relationships in the quasi-ternary systems RE₂O₃-Al₂O₃-SiO₂ are given. The investigated systems exhibit extended ternary solid solutions, RE_9.33+2x(Si_{1_x}Al_xO₄)₆O₂ (withx up to ~0.33) and/or RE₄Al_{2(1_X)}Si_2xO_9+x (withx up to ~0.3), which are based on the quasi-binary phases RE_9.33(SiO₄)₆O₂ and RE₄A1₂O₉, respectively. The former is encountered only in systems with laige RE³⁺ ions (e.g., La³⁺), whereas the latter is found in systems with small RE³⁺ ions (e.g., Yb³⁺); in systems with medium-sized KE³⁺ ions (e.g., Gd³⁺) both types exist Quasi-ternary compounds are known only in the La, Ce, and Sc systems. Severe discrepancies in reported ternary eutectic temperatures led to a need for their accurate redeteimination.