Phase diagram study and thermodynamic modeling of the Na2O–Al2O3–ZrO2 system

The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was experimentally studied at 1500°C–1650°C by a classical equilibration/quenching method and differential thermal analysis followed by X-ray diffraction phase analysis and electron probe micro-analysis. A sealed Pt crucible was utilized to prevent the volatile loss of Na₂O during high-temperature phase equilibrium experiments and the hydration upon quenching. The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was revealed for the first time. Based on the present experimental data and available binary modeling results in literature, the thermodynamic modeling of the ternary system was performed using the Calculation of Phase Diagram method and the phase diagram of the entire the Na₂O–Al₂O₃–ZrO₂ system was constructed and the optimized thermodynamic properties for all solids and liquid phase within the ternary system were obtained.     

Thermochemistry of the ZrO2–SrO System: From enthalpies of formation and heat capacities of the compounds to the phase diagram

The thermodynamics of the ZrO₂–SrO system is of interest for the optimization of synthesis and applications of functional materials and high-temperature structural ceramics. Earlier data on phase relationships and thermodynamic properties of the system are unfortunately scattered and inconsistent. In this study, the compounds Sr_n+1Zr_nO_3n+1 (n = 3, 2, and 1) were prepared by solid-state reaction. Their heat capacities from 573 to 1273 K were measured by differential scanning calorimetry and their enthalpies of formation from component oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. The CALPHAD method was used to assess the ZrO₂–SrO system, using both available literature data and our new measurements. A self-consistent thermodynamic database and the calculated phase diagram of the ZrO₂–SrO system are provided. This work is a prerequisite for accurate predictions of the relationships among the composition, temperature, and microstructure of complex functional and structural materials containing ZrO₂ and SrO.     

Experimental and thermodynamic modeling study of phase equilibria in the PbO–NiO–SiO2 system

An integrated experimental and thermodynamic modeling investigation of the phase equilibria in the PbO–NiO–SiO₂ system in air and also in equilibrium with liquid metal has been undertaken to better characterize the chemical reactions taking place in the Ni-containing Pb processing slags. New experimental phase equilibria data at 720°C–1740°C were obtained for this system using high-temperature equilibration of synthetic mixtures with predetermined compositions in sealed silica ampoules or in Au/Pt–Ir foils, a rapid quenching technique, and electron probe x-ray microanalysis of the equilibrated phase compositions. Phase equilibria and liquidus isotherms in the quartz/tridymite/cristobalite (SiO₂), olivine (Ni₂SiO₄), monoxide (NiO), Ni-barysilite (Pb₈NiSi₆O₂₁), massicot (PbO), and di-lead silicate (Pb₂SiO₄) primary phase fields were revealed and the extent of the high-SiO₂ two-liquid immiscibility gap in equilibrium with cristobalite was determined. New experimental data were used in the development of a thermodynamic database describing this ternary system. Also, modeling revision of the NiO–SiO₂ binary system was conducted, resulting in a smaller miscibility gap in ternary systems that was closer to the experimental results.     

Structure of the phase diagram of the 2-methyl-1,3-butadiene–2-methyl-2-butene–acetonitrile–water system

The structure of the liquid–liquid–vapor diagram of the industrially important four-component system 2-methyl-1,3-butadiene–2-methyl-2-butene–acetonitrile–water has been determined. A model of the phase equilibrium has been derived from experimental data. The evolution of the three-phase immiscibility region in the concentration simplex has been investigated.     

Solid solutions in ternary phase diagram CeO2–ZrO2–Er2O3 using pyrolitic precursors

Abstract

ZrO₂ based ceramics have important technological properties with interesting industrial applications. In the present paper erbia is investigated as a potential replacement for yttria in zirconia based ceramics. Several compositions in the ternary CeO₂–ZrO₂–Er₂O₃ system and to the binary system CeO₂–Er₂O₃, not yet reported, were prepared. Owing to the low reactivity of cerium and erbium oxides, all the powders were prepared from highly reactive powder precursors which could attain equilibrium in short processing times. The method was based on the pyrolysis of soluble salts, according to a technique already previously applied to obtain shorter firing times and lower firing temperatures. The presence of two solid solutions in CeO₂–Er₂O₃ and in CeO₂–ZrO₂–Er₂O₃ systems was stated and its limits were reported.     

Thermodynamic prediction of the nonstoichiometric phase Zr1–zCezO2–x in the ZrO2–CeO1.5–CeO2 system

A thermodynamic estimation of the ZrO₂–CeO₂ and ZrO₂–CeO_1.5 systems, as well as the cubic phase in the CeO_1.5–CeO₂ system has been developed and the complex relation between the nonstoichiometry, y, in Ce_zO_2–y and the oxygen partial pressure at different temperatures is evaluated. The behavior of the nonstoichiometry phase Zr_1–zCe_zO_2–x is described based on the thermodynamic estimation in the ZrO₂–CeO₂, CeO_1.5–CeO₂ and ZrO₂–CeO_1.5 systems. Additionally, the interdependence among miscellaneous factors, which can be used to describe the change in oxidation states of cerium such as the oxygen partial pressure, the CeO_1.5 fraction in CeO_1.5–CeO₂ in the quasi-ternary system, the nonstoichiometry y and the difference between the activity of CeO₂ and CeO_1.5 are predicted. The calculated results are found to be very useful to explain the influence of pressureless sintering at different O₂ partial pressures on the mechanical properties of CeO₂-stabilised ZrO₂ ceramics     

A kinetic study of the quartz–cristobalite phase transition

Cristobalite is a common silica polymorph in ceramics, as it can crystallize in SiO₂-rich systems during high temperature processes. Its occurrence in final traditional ceramic bodies remarkably affects their thermal expansion, thus playing an important role in the shrinkage upon cooling. The quartz–cristobalite transformation kinetics is investigated by in-situ isothermal X-ray powder diffraction experiments and then correlated to the average particle size (〈d〉) of the starting quartz using a model here developed. An Avrami-like rate equation, i.e. α(t) = 1 ? exp(? k × t)ⁿ, in which the n-term is assumed to account for the dependence on the average particle size, has provided the best fitting of theoretical to experimental data, yielding activation energy values that range from 181 to 234 kJ mol^?1, and exponential n-coefficients from 0.9 to 1.5. Ex-situ observations have demonstrated that the formation of cristobalite from quartz after 50 min, 2, 4 and 6 h at 1200 and 1300 °C, exhibits a remarkable dependence on 〈d〉 of quartz, showing comparable behaviours in the case of 〈d〉 equal to 15.8 and 28.4 μm, but significant differences for 〈d〉 of 4.1 μm. The formation of cristobalite is boosted remarkably at temperature higher than 1200 °C, with an increase by weight even of 500%, with respect to its content at lower temperature. The method of sample preparation (dry powder, wet powder and tablet of compressed dry powder) seems to influence the results only at temperature > 1200 °C and in the case of fine powder.     

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

Tantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high-performance photonic and photoelectric components. However, successful attainment of feature control in tantalum-doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro- and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li₂O–Ta₂O₅–SiO₂ ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li₂O–Ta₂O₅–SiO₂ ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO₆ octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta⁵⁺ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li₂O–Ta₂O₅–SiO₂ ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials.     

Subsolidus phase relations in the SnO2–CuSb2O6 binary system

The SnO₂–CuSb₂O₆ binary system plays a significant role in the SnO₂–Sb₂O₃–CuO ternary system, delimiting the compositional ranges and their sensor and catalytic properties. The initial compositions expressed as (1−x) SnO₂–xCuSb₂O₆ were treated both non-isothermally using DTA up to 1500 °C and iso-thermally at temperatures between 1000 and 1200 °C. Phase analysis of the samples was determined by XRD and IR spectroscopy. It was established that SnO₂–CuSb₂O₆ is a pseudobinary system with a solid solubility limit of the end members. The determined lattice parameters of the unit cell of the obtained rutile and trirutile solid solutions obeyed Vegard's rule. From IR spectral investigations it was inferred that Sn⁴⁺ might be preferentially incorporated on Sb⁵⁺ sites into the CuSb₂O₆ lattice.     

In-situ determination of the HfO2–Ta2O5-temperature phase diagram up to 3000°C

The previously unknown experimental HfO₂–Ta₂O₅-temperature phase diagram has been elucidated up to 3000°C using a quadrupole lamp furnace and conical nozzle levitator system equipped with a CO₂ laser, in conjunction with synchrotron X-ray diffraction. These in-situ techniques allowed the determination of the following: (a) liquidus, solidus, and invariant transformation temperatures as a function of composition from thermal arrest experiments, (b) determination of equilibrium phases through testing of reversibility via in-situ X-ray diffraction, and (c) molar volume measurements as a function of temperature for equilibrium phases. From these, an experimental HfO₂–Ta₂O₅-temperature phase diagram has been constructed which is consistent with the Gibbs Phase Rule.     

SnO2–polyaniline composites for the desensitization of Al/SnO2 thermite composites

Nanothermites consisting of a reducing metal and a metal oxide nanopowder represent a new generation of energetic materials in pyrotechnics due to their impressive reactive properties. However, their extreme sensitivity regarding electrostatic discharge appears to be detrimental to their future practical applications. Herein, the mitigation of the sensitivity thresholds of the aluminium/tin (IV) oxide energetic nanocomposite is successfully achieved by using a conducting polymer, polyaniline (PAni). PAni was introduced within the thermite by the chemical polymerization of an oxidizer/PAni hybrid matrix. The SnO₂–PAni composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, electrical conductivity measurements, and transmission electron microscopy. The derived Al/SnO₂–PAni thermites were investigated in terms of sensitivities and reactivity. Results revealed gradual desensitization of the Al/SnO₂ thermite as a function of the concentration of PAni for both the electrostatic discharge (0.14–1212 mJ) and friction (216–360 N) tests while maintaining reactive energetic composites. This work presents a way for the preparation of insensitive and reactive energetic formulations. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48947.     

The influence of microstructure and phase composition of glass ceramics in the VO2–V2O5–P2O5–Cu2O–SnO2 system on the electrical properties related to the metal–semiconductor phase transition

Phase composition, microstructure and electrical conductivity of glass ceramics in the VO₂–V₂O₅–P₂O₅–SnO₂ and VO₂–V₂O₅–P₂O₅–Cu₂O–SnO₂ systems have been studied. Only crystalline phases VO₂, SnO₂ and vanadium phosphate glass of the V₂O₅–P₂O₅ system have been found in glass ceramic compositions in the VO₂–V₂O₅–P₂O₅–SnO₂ system. Besides the above-mentioned phases, probably the X-ray lines of V₃O₅, V₄O₇, V₅O₉, V₆O₁₁, V₇O₁₃, V₄O₉, V₆O₁₃, V₂O₅, SnO₂, SnO, Sn₂O₃, Sn₃O₄ and CuO phases are observed in the X-ray spectra of glass ceramics in the VO₂–V₂O₅–P₂O₅–Cu₂O–SnO₂ system. According to SEM/EDS data, these phases were observed as submicrometer fine-crystalline inclusions in glass on the surface of VO₂ crystallites and between them. The formation of these phases was caused by the redox processes in the liquid phase during glass ceramics synthesis. The important role of tin oxides possessing high electrical conductivity and vanadium oxides exhibiting a low temperature of metal–semiconductor phase transition in the stabilization of glass ceramics electrical properties related to the phase transition in VO₂ has been established.     

Influence of La3+ additions on the phase behaviour and antibacterial properties of ZrO2–SiO2 binary oxides

The present study reports the influence of lanthanum (La³⁺) content on the phase stability and antibacterial activity of ZrO₂–SiO₂ binary oxides. Four different concentrations of La³⁺ additions in ZrO₂–SiO₂ binary oxides were synthesized using a sol–gel technique. Heat treatment of the synthesized powders resulted in the formation of t-ZrO₂ phase at 1000 °C. Heat treatment beyond 1000 °C resulted in the phase degradation of t-ZrO₂ to yield m-ZrO₂ and ZrSiO₄. Results from antibacterial tests confirmed the potential activity of La³⁺ doped ZrO₂–SiO₂ binary oxides in countering the microbial invasion.     

Palygorskite and SnO2–TiO2 for the photodegradation of phenol

The photocatalytic removal of phenol was studied using palygorskite-SnO₂–TiO₂ composites (abbreviated as Paly-SnO₂–TiO₂) under ultraviolet radiation. The photocatalysts were prepared by attachment of SnO₂–TiO₂ oxides onto the surface of the palygorskite by in situ sol–gel technique. The products were characterized by XRD, TEM and BET measurements. SnO₂–TiO₂ nanoparticles, with an average diameter of about 10 nm, covered the surface of the palygorskite fibers without obvious aggregation. Compared with palygorskite-titania (Paly-TiO₂), palygorskite-tin dioxide (Paly-SnO₂), and Degussa P25, Paly-SnO₂–TiO₂ and SnO₂–TiO₂ exhibited much higher photocatalytic activity. The photodecomposition of phenol was as high as 99.8% within 1.5 h. The apparent rate constants (k_app) for Paly-SnO₂–TiO_2, TiO₂, and P25 were measured. Paly-SnO₂–TiO₂ showed the highest rate constant (0.03435 min^?1). The chemical oxygen demand (COD) of the phenol solution was reduced from 220.2 mg/L to 0.21 mg/L, indicating the almost complete decomposition of phenol. Reusability of the photocatalyst was proved.     

Heterostructural phase diagram of Ga2O3–based solid solution with Al2O3

Ga₂O₃, which is emerging as semiconductor material due to the ultra-wide bandgap, has tunability in bandgap and lattice constant by alloying Al. However, successful control of alloying phase is still challenging due to its heterostructural nature and rich polymorphs. Here, we identified the thermodynamic phase diagram of heterostructural (Al_xGa_1-x)₂O₃ alloy. Using density-functional theory (DFT) calculations and regular solution model, we calculated the Gibbs-free energy of mixing of heterostructural polymorphs. Based on the calculation, we show the phase diagram of (Al_xGa_1-x)₂O₃ alloy system with a markedly increased metastability than the isostructural alloy, which can make a vast phase space for homogeneous single-phase alloys. We also investigated the correlation between the bandgap and lattice constant within these systems using hybrid DFT calculations, which can guide the device design of Ga₂O₃ power electronics.