High-temperature Equilibrium Research Articles

Headspace conditions and ingredients can affect artefactual benzene formation in beverages

A headspace sampling-gas chromatography/mass spectrometry (HS-GC/MS) method using mild HS conditions (40 °C, 30 min) was established, validated in terms of specificity, linearity (1.75–87.65 ng mL−1), precision (0.3–9.1% RSD), and accuracy (81.1–117.7%); and applied for the monitoring of 900 commercial beverage samples of six different types. These mild (low-temperature) conditions were compared with 1) optimized (high-temperature) conditions and 2) a liquid-phase microextraction method involving no heat treatment. This method was desirable because a high equilibrium temperature induced artefactual benzene formation from benzoate and ascorbic acid. In a 2IV8-3 fractional factorial design, eight variables—ascorbic acid, benzoate, benzaldehyde, Cu2+, Fe2+, riboflavin, pyridoxine, and heat treatment—were tested as potential factors affecting benzene formation. All variables except Fe2+ and pyridoxine significantly affected benzene formation, both individually and interactively. The present study suggests an accurate and reliable method for benzene analysis and provides strategies to prevent unintentional benzene formation in beverages.

Excellent Temperature-Control Based on Reversible Thermochromic Materials for Light-Driven Phase Change Materials System

Light-driven phase change materials (PCMs) have received significant attention due to their capacity to convert visible light into thermal energy, storing it as latent heat. However, continuous photo-thermal conversion can cause the PCMs to reach high thermal equilibrium temperatures after phase transition. In our study, a novel light-driven phase change material system with temperature-control properties was constructed using a thermochromic compound. Thermochromic phase change materials (TC-PCMs) were prepared by introducing 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) and bisphenol A (BPA) into 1-hexadecanol (1-HD) in various proportions. Photo-thermal conversion performance was investigated with solar radiation (low power of 0.09 W/cm2) and a xenon lamp (at a high power of 0.14 W/cm2). The TC-PCMs showed a low equilibrium temperature due to variations in absorbance. Specifically, the temperature of TC-PCM180 (ODB-2, bisphenol A and 1-HD ratio 1:2:180) could stabilize at 54 °C approximately. TC-PCMs exhibited reversibility and repeatability after 20 irradiation and cooling cycles.

A method to predict the glass transition temperature in metallic glasses from properties of the equilibrium liquid

The glass transition temperature, Tg, is important for predicting glass formation and stability and for designing processing steps for tailoring the glass to specific applications. It is conventionally determined from measurements of the shear viscosity or specific heat. This requires that the glass first be made, significantly limiting the use of this parameter for the prediction of glass formation. Further, viscosity or specific heat measurements can only be made for glasses that have a high stability against crystallization at Tg. It is demonstrated here that it is possible to accurately predict Tg from measurements of the shear viscosity and thermal expansion coefficient of the high temperature equilibrium liquid. In addition to the practical usefulness of this, the connection between the glass transition and the properties of the equilibrium liquid may shed light into the processes that determine glass formation in metallic alloys and of the nature of the glass transition.

Experimental carbonatite/graphite carbon isotope fractionation and carbonate/graphite geothermometry

Abstract Carbon isotope exchange between carbon-bearing high temperature phases records the carbon (re-) processing in the Earth's interior, where the vast majority of global carbon is stored. Redox reactions between carbonate phases and elemental carbon govern the mobility of carbon, which then can be traced by its isotopes. We determined the carbon isotope fractionation factor between graphite and a Na2CO3-CaCO3 melt at 900–1500 °C and 1 GPa; The failure to isotopically equilibrate preexisting graphite led us to synthesize graphite anew from organic material during the melting of the carbonate mixture. Graphite growth proceeds by (1) decomposition of organic material into globular amorphous carbon, (2) restructuring into nano-crystalline graphite, and (3) recrystallization into hexagonal graphite flakes. Each transition is accompanied by carbon isotope exchange with the carbonate melt. High-temperature (1200–1500 °C) equilibrium isotope fractionation with type (3) graphite can be described by Δ 13 C c a r b o n a t e - g r a p h i t e = 3.17 ( ± 0.07 ) · 10 6 T 2 (temperature T in K). As the experiments do not yield equilibrated bulk graphite at lower temperatures, we combined the ≥1200 °C experimental data with those derived from upper amphibolite and lower granulite facies carbonate-graphite pairs (Kitchen and Valley, 1995; Valley and O'Neil, 1981). This yields the general fractionation function Δ 13 C c a r b o n a t e - g r a p h i t e = 3.37 ± 0.04 · 10 6 T 2 usable as a geothermometer for solid or liquid carbonate at ≥600 °C. Similar to previous observations, lower-temperature experiments (≤1100 °C) deviate from equilibrium. By comparing our results to diffusion and growth rates in graphite, we show that at ≤1100 °C carbon diffusion is slower than graphite growth, hence equilibrium surface isotope effects govern isotope fractionation between graphite and carbonate melt and determine the isotopic composition of newly formed graphite. The competition between diffusive isotope exchange and growth rates requires a more careful interpretation of isotope zoning in graphite and diamond. Based on graphite crystallization rates and bulk isotope equilibration, a minimum diffusivity of Dgraphite = 2 × 10−17 m2s−1 for T > 1150 °C is required. This value is significantly higher than calculated from experimental carbon self-diffusion constants (∼1.6 × 10−29 m2 s−1) but in good agreement with the value calculated for mono-vacancy migration (∼2.8 × 10−16 m2 s−1).

Electric field effects on the growth of flame-synthesized nanosilica: a two-stage modeling

Electric field effects on the kinetics of SiO2 formation, and the growth of silica nanoparticles formed in the flame (fumed silica) are studied theoretically and computationally, considering combustion of SiCl4 in the H2/O2 flame. An existing mechanism for the gas-phase part of this flame synthesis reaction is improved and used to derive instantaneous concentrations of the involved species. Quantum (DFT) computations are used to obtain thermodynamic data required for the calculation of equilibrium concentrations and reaction rate constants, assuming an overall (high temperature) equilibrium state. Kinetics equations based on a modified 43-step 24-species mechanism are established and solved to obtain concentrations at different temperatures and EF strengths. These concentrations are used as inputs for the Monte Carlo simulation of the growth of silica nanoparticles, considering also possibility of atomic displacements and vacancies. Effects of homogeneous electric field of different strengths on the growth of silica nanoparticles are investigated. Results of this study show that electric field changes the preferences of different paths of the mechanism of this flame synthesis reaction and changes composition of the flame via controlling orientation of the dipolar species, which consequently determine characteristics of the grown silica nanoparticles. Furthermore, EF effect is larger at lower temperatures.

Electrical resistivity of liquid expanded metals by Ziman approach

Transport properties of metals near the critical points were intensively studied. Using quantum dynamics simulations, we consider the structures of liquid aluminum and copper at high equilibrium temperatures and strong expansion. On the other hand, we carry out classical molecular dynamics simulations using the embedded atom method interatomic potentials. Both approaches provide data for resistivity calculations based on the well-known Ziman–Evans formula. The results of these calculations show a weak dependence on the used methods of ion structure computations. Also, we demonstrate that an effect of electron exchange and correlation is taken into account in electron–ion screening function, makes electric resistivity smaller in all considered situations.

Predissociation Measurements of Bond Dissociation Energies.

A fundamental need in chemistry is understanding the chemical bond, for which the most quantitative measure is the bond dissociation energy (BDE). While BDEs of chemical bonds formed from the lighter main group elements are generally well-known and readily calculated by modern computational chemistry, chemical bonds involving the transition metals, lanthanides, and actinides remain computationally extremely challenging. This is due to the simultaneous importance of electron correlation, spin-orbit interaction, and other relativistic effects, coupled with the large numbers of low-lying states that are accessible in systems with open d or f subshells. The development of efficient and accurate computational methods for these species is currently a major focus of the field. An obstacle to this effort has been the scarcity of highly precise benchmarks for the BDEs of M-X bonds. For most of the transition metal, lanthanide, or actinide systems, tabulated BDEs of M-X bonds have been determined by Knudsen effusion mass spectrometric measurements of high-temperature equilibria. The measured ion signals are converted to pressures and activities of the species involved in the equilibrium, and the equilibrium constants are then analyzed using a van't Hoff plot or the third-law method to extract the reaction enthalpy, which is extrapolated to 0 K to obtain the BDE. This procedure introduces errors at every step and ultimately leads to BDEs that are typically uncertain by 2-20 kcal mol-1 (0.1-1 eV). A second method in common use employs a thermochemical cycle in which the ionization energies of the MX molecule and M atom are combined with the BDE of the M+-X bond, obtained via guided ion beam mass spectrometry, to yield the BDE of the neutral, M-X. When accurate values of all three components of the cycle are available, this method yields good results-but only rarely are all three values available. We have recently implemented a new method for the precise measurement of BDEs in molecules with large densities of electronic states that is based on the rapid predissociation of these species as soon as the ground separated atom limit is exceeded. When a sharp predissociation threshold is observed, its value directly provides the BDE of the system. With this method, we are able in favorable cases to determine M-X BDEs to an accuracy of ∼0.1 kcal mol-1 (0.004 eV). The method is generally applicable to species that have a high density of states at the ground separated atom limit and has been used to measure the BDEs of more than 50 transition metal-main group MX molecules thus far. In addition, a number of metal-metal BDEs have also been measured with this method. There are good prospects for the extension of the method to polyatomic systems and to lanthanide and actinide-containing molecules. These precise BDE measurements provide chemical trends for the BDEs across the transition metal series, as well as crucial benchmarks for the development of efficient and accurate computational methods for the d- and f-block elements.

High Temperature Equilibrium and Growth Shape of Small Particles: The Case of Thallium

The temperature dependence of the equilibrium shape and growth shape of small thallium particles is studied in situ by ultrahigh vacuum scanning electron microscopy. Pronounced anisotropic surface roughening and surface melting is observed and compared with earlier studies of four metals with different crystal structures illustrating significant differences in disordering behavior. A comparison with theoretical 0 K equilibrium shapes shows that these do not allow in general prediction of the equilibrium and growth shapes at high temperatures.

Phase equilibria and liquidus surface of CaO-SiO2–5 wt%MgO-Al2O3-TiO2 slag system

The lack of phase equilibria relations and liquidus surface thermodynamic information for CaO-SiO2–5 wt%MgO-Al2O3-TiO2 system has seriously restricted the comprehensive utilization of the titanium resources. In present study, the phase equilibrium relationships were investigated for CaO-SiO2–5 wt%MgO-Al2O3-TiO2 phase diagram system at 1300 °C and 1400 °C using the high temperature equilibrium technique followed by X-Ray Fluoroscopy (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscope (EDX) analysis. In the composition range studied, the liquid phase, melilite solid solution phase and CaO·TiO2 phase were found. The two-phase equilibrium of liquid coexisting with CaO·TiO2 phase was intensively dicussed, and the spatial liquidus surfaces at 1300 °C, 1400 °C and 1450 °C (data from literatures only) for liquid coexisting with CaO·TiO2 phase were first constructed in CaO-SiO2–5 wt%MgO-Al2O3-TiO2 tetrahedral phase diagram, which can realize a visual understanding of the phase relation change trendency in 3-dimensional space.

Experimental calibration of clumped isotope reordering in dolomite

Dolomite clumped isotope compositions are indispensable for determining the temperatures and fluid sources of dolomitizing environments, but can be misleading if they have modified since formation. Carbonate Δ47 values are susceptible to resetting by recrystallization during diagenesis, and, even in the absence of dissolution and reprecipitation reactions, alteration by solid-state reordering during prolonged residences at elevated temperatures. In order to understand the potential of dolomite Δ47 values to preserve the conditions of dolomitization in ancient sections, the kinetic parameters of solid-state reordering in this phase must be determined. We heated mm-sized crystals of near-stoichiometric dolomite in a René-type cold seal apparatus at temperatures between 409 and 717 °C for 0.1–450 h. In order to prevent the decarbonation of dolomite to calcite, periclase, and CO2 at these conditions, the system was pressurized with CO2 to 0.45–0.8 kbar. Over the course of 31 temperature-time points and 128 individual Δ47 measurements of powdered dolomite crystals from these points, we observed the evolution of dolomite Δ47 values from the initial (unheated) composition of the crystals (0.452 ± 0.004‰, corresponding to a formation temperature of ∼145 °C) towards high-temperature equilibrium distributions. Complete re-equilibration occurred in the 563–717 °C experiments. As with previous heating experiments using calcite and apatite, dolomite Δ47 exhibited complex reordering behavior inadequately described by first-order Arrhenian-style models. Instead, we fit the data using two published models for clumped isotope reordering: the transient defect/equilibrium defect model of Henkes et al. (2014), and the exchange-diffusion model of Stolper and Eiler (2015). For both models, we found optimal reordering parameters by using global least-squares minimization algorithms and estimated uncertainties on these fits with a Monte Carlo scheme that resampled individual Δ47 measurements and re-fit the dataset of these new mean values. Because the exact Δ47–T relationship between 250 and 800 °C is uncertain, we repeated these fitting exercises using three published high-temperature Δ47–T calibrations. Regardless of calibration choice, dolomite Δ47 rate constants determined using both models are resolvably slower than those of calcite and apatite, and predict that high-grade dolomite crystals should preserve apparent equilibrium blocking temperatures of between ∼210 and 300 °C during cooling on geologic timescales. Best agreement between model predictions and natural dolomite marbles was found when using the exchange-diffusion model and the ab initio Δ63–T calibration of Schauble et al. (2006), projected into the Δ47 reference frame by Bonifacie et al. (2017). Therefore, we recommend modeling dolomite Δ47 reordering using the exchange-diffusion model and this parameter set. In simple heating scenarios, the two models disagree. The transient defect/equilibrium defect model suggests that dolomite fabrics resist detectable reordering at ambient temperatures as high as 180 °C for tens of millions of years, while the exchange-diffusion model predicts incipient partial reordering perhaps as low as 150 °C. In either case, barring later recrystallization, dolomite Δ47 values should be faithful recorders of the conditions of dolomitization in sedimentary sections buried no hotter than ∼150 °C for tens of millions of years.

Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b.

To constrain the formation history of an exoplanet, we need to know its chemical composition1-3. With an equilibrium temperature of about 4,050 kelvin4, the exoplanet KELT-9b (also known as HD195689b) is an archetype of the class of ultrahot Jupiters that straddle the transition between stars and gas-giant exoplanets and are therefore useful for studying atmospheric chemistry. At these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms5. However, despite being the most abundant transition metal in nature, iron has not hitherto been detected directly in an exoplanet because it is highly refractory. The high temperatures of KELT-9b imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium5 and cloud-free6,7, and it has been predicted that spectral lines of iron should be detectable in the visible range of wavelengths5. Here we report observations of neutral and singly ionized atomic iron (Fe and Fe+) and singly ionized atomic titanium (Ti+) in the atmosphere of KELT-9b. We identify these species using cross-correlation analysis8 of high-resolution spectra obtained as the exoplanet passed in front of its host star. Similar detections of metals in other ultrahot Jupiters will provide constraints for planetary formation theories.

Microwave-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks chemically linked to SiC nanoparticles

Microwave (MW)-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) interpenetrating polymer networks (SMP-IPNs) were prepared through in situ polymerization. Silicon carbide (SiC) nanoparticles were modified by 3-(methacryloyloxy) propyltrimethoxysilane (KH570). 3-(Methacryloyloxy) propyltrimethoxysilane was covalently bonded on the surface of SiC through the reaction of silanol and the methoxy groups. The polymerization of acrylic acid (AA) using N,N′-methylenebis (2-propenamide) (MBA) as cross-linker in PVA solution was initiated through the double bonds of KH-570 grafted on SiC, leading to a PAA polymer network cross-linked with MBA. The PVA molecular chains run through the PAA cross-linking network and form an IPN structure. Therefore, SiC as a strong MW absorbing material could be chemically cross-linked into polymer matrix. The effect of composition on the properties of SMP-IPN was studied using dynamic mechanical analysis, dielectric properties and shape memory effect (SME) test. The results showed that the introduction of SiC in IPNs not only provided samples with excellent MW-induced shape memory effect (SME), but also caused a higher equilibrium temperature under MW irradiation. Moreover, both SiC content and applied MW power affected the shape recovery properties of PVA/PAA interpenetrating composites. MW-induced SMPs offered great advantages such as fast recovery, high recovery rate, and remote actuation. This study provides the potential applications of the fast and environmentally friendly SMPs used as MW-responsive sensors, implantable devices, etc.

MASCARA-2 b

In this paper we present MASCARA-2 b, a hot Jupiter transiting the mV = 7.6 A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million flux measurements of the star, corresponding to a total of almost 3000 h of observations, revealing a periodic dimming in the flux with a depth of 1.3%. Photometric follow-up observations were performed with the NITES and IAC80 telescopes and spectroscopic measurements were obtained with the Hertzsprung SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of 3.4741119-0.000006+0.000005 days at a distance of 0.057 ± 0.006 au, has a radius of 1.83 ± 0.07 RJ and place a 99% upper limit on the mass of <17 MJ. HD 185603 is a rapidly rotating early-type star with an effective temperature of 8980-130+90 K and a mass and radius of 1.89-0.05+0.06 M⊙, 1.60 ± 0.06 R⊙, respectively. Contrary to most other hot Jupiters transiting early-type stars, the projected planet orbital axis and stellar spin axis are found to be aligned with λ = 0.6 ± 4°. The brightness of the host star and the high equilibrium temperature, 2260 ± 50 K, of MASCARA-2 b make it a suitable target for atmospheric studies from the ground and space. Of particular interest is the detection of TiO, which has recently been detected in the similarly hot planets WASP-33 b and WASP-19 b.

HATS-50b through HATS-53b: Four Transiting Hot Jupiters Orbiting G-type Stars Discovered by the HATSouth Survey*

Abstract We report the discovery of four close-in transiting exoplanets (HATS-50b through HATS-53b), discovered using the HATSouth three-continent network of homogeneous and automated telescopes. These new exoplanets belong to the class of hot Jupiters and orbit G-type dwarf stars, with brightness in the range V = 12.5–14.0 mag. While HATS-53 has many physical characteristics similar to the Sun, the other three stars appear to be metal-rich ( ), larger, and more massive. Three of the new exoplanets, namely HATS-50b, HATS-51b, and HATS-53b, have low density (HATS-50b: , ; HATS-51b: , ; HATS-53b: , ) and similar orbital periods ( days, days, days, respectively). Instead, HATS-52b is more dense (mass and radius ) and has a shorter orbital period ( days). It also receives an intensive radiation from its parent star and, consequently, presents a high equilibrium temperature ( K). HATS-50 shows a marginal additional transit feature consistent with an ultra-short-period hot super Neptune (upper mass limit 0.16 ), which will be able to be confirmed with TESS photometry.

Evaluating baddeleyite oxygen isotope analysis by secondary ion mass spectrometry (SIMS)

Two baddeleyite megacrysts were evaluated as potential reference materials (RMs) for SIMS oxygen isotope analysis, and utilized to understand and calibrate instrumental mass fractionation (IMF). A baddeleyite crystal (S0045) from the Phalaborwa carbonatite, South Africa has a mean δ18OVSMOW = +4.6 ± 0.3‰ (range 0.75‰) measured using laser fluorination gas source mass spectrometry (LF-GMS) and one (S0069) from the Mogok metamorphic belt, Myanmar has δ18OVSMOW = +22.2 ± 0.4‰ (range 0.89‰). SIMS standardization utilizing these inherently heterogeneous RMs is possible by analyzing a number of crystal fragments and utilizing one of them lying at the median of the range. Metamictization, lattice orientation, and chemical composition do not appear to be significant (<0.5‰) variables in matrix matching of RMs and unknowns. Propagation of errors while utilizing the imperfect RMs results in 10 μm diameter spot uncertainties of about ±0.3‰ (2σ).SIMS oxygen isotope analysis of co-crystalline zircon and baddeleyite from the 2.2 Ga Duck Lake sill (DLS) in the Northwest Territories, Canada, yield predominant δ18OVSMOW modes of +6.0‰ and +3.2‰, respectively. This difference is consistent with preserving high-temperature isotopic equilibrium between zircon and baddeleyite. DLS baddeleyite δ18O data as a whole are negatively skewed (to 0.0‰), and interpreted to reflect low temperature, open-system behaviour. Zircon δ18O are less affected, but also show hints of the same influences of secondary alteration and oxygen isotope exchange.

Phase Equilibrium Investigation for CaO-SiO&lt;sub&gt;2&lt;/sub&gt;-5wt.%MgO-20wt.%Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-TiO&lt;sub&gt;2&lt;/sub&gt; System Relevant to Ti-bearing Slag System

In order to resolve the lack of thermodynamic information for the comprehensive unilization of Ti-bearing blast furnace slag, the phase diagram relevant to the Ti-bearing slag composition was widely investigated. In the present work, the phase equilibrium relationships were investigated for the CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 phase diagram system. The equilibrium phases were experimentally determined at 1300°C and 1400°C using the high temperature equilibrium technique followed by X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscope (EDX) analysis. The liquid phase (L), melilite solid solution ((2CaO·MgO·2SiO2, 2CaO·Al2O3·SiO2)ss) phase, perovskite (CaO·TiO2) phase, Al–Ti diopside phase and pseudobrookite solid solution (MgO·TiO2, Al2O3·TiO2)ss phase were found. Based on the experimental results, the 1300°C to 1500°C liquidus lines and phase diagram were constructed for the specified region of the CaO-SiO2-5wt.%MgO-20wt.%Al2O3-TiO2 system.

Solid Phase Equilibrium Relations in the CaO-SiO2-Nb2O5-La2O3 System at 1273 K

Silicate slag system with additions Nb and RE formed in the utilization of REE-Nb-Fe ore deposit resources in China has industrial uses as a metallurgical slag system. The lack of a phase diagram, theoretical, and thermodynamic information for the multi-component system restrict the comprehensive utilization process. In the current work, solid phase equilibrium relations in the CaO-SiO2-Nb2O5-La2O3 quaternary system at 1273 K (1000 °C) were investigated experimentally by the high-temperature equilibrium experiment followed by X-ray diffraction, scanning electron microscope, and energy dispersive spectrometer. Six spatial independent tetrahedron fields in the CaO-SiO2-Nb2O5-La2O3 system phase diagram were determined by the Gibbs Phase Rule. The current work combines the mass fraction of equilibrium phase and corresponding geometric relation. A determinant method was deduced to calculate the mass fraction of equilibrium phase in quaternary system according to the Mass Conservation Law, the Gibbs Phase Rule, the Lever’s Rule, and the Cramer Law.

A dearth of small particles in the transiting material around the white dwarf WD 1145+017

White dwarf WD 1145+017 is orbited by several clouds of dust, possibly emanating from actively disintegrating bodies. These dust clouds reveal themselves through deep, broad, and evolving transits in the star's light curve. Here, we report two epochs of multi-wavelength photometric observations of WD 1145+017, including several filters in the optical, K$_\mathrm{s}$ and 4.5 $\mu$m bands in 2016 and 2017. The observed transit depths are different at these wavelengths. However, after correcting for excess dust emission at K$_\mathrm{s}$ and 4.5 $\mu$m, we find the transit depths for the white dwarf itself are the same at all wavelengths, at least to within the observational uncertainties of $\sim$5%-10%. From this surprising result, and under the assumption of low optical depth dust clouds, we conclude that there is a deficit of small particles (with radii $s \lesssim$ 1.5 $\mu$m) in the transiting material. We propose a model wherein only large particles can survive the high equilibrium temperature environment corresponding to 4.5 hr orbital periods around WD 1145+017, while small particles sublimate rapidly. In addition, we evaluate dust models that are permitted by our measurements of infrared emission.

Inclusion evolution in 50CrVA spring steel by optimization of refining slag

In order to control the CaO-Al2O3-SiO2-MgO system inclusions in 50CrVA spring steel in a lower melting temperature region, high temperature equilibrium experiments between steel and slag were performed in the laboratory, under the conditions of the initial slag basicity within 3–7 and the content of Al2O3 between 18–35 mass%, to investigate the formation and evolution of this type of inclusion. The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al2O3 content in slags, and CaO-Al2O3-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al2O3 content in slags. The most favorable composition for the refining slag is composed of 51–56 mass% CaO, 9–13 mass% SiO2, 20–25 mass% Al2O3 and 6 mass% MgO. In this case, the inclusions in 50CrVA spring steel are mostly in the low melting point regions, in which their plasticities are expected to improve during steel rolling. The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed. It is also found that adding around 11 mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion. Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching

Herein, we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical-potential space (SCPS) of CZTS at an elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of VCu−−ZnCu+ complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like ZnCu+ antisites are involved in the formation of VCu−−ZnCu+ complex making CuZn− dominant and providing p-type conductivity even for Cu-poor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS due to nearly constant concentration of dominant charged defects. The calculations for the full equilibrium and quenching indicate that hole concentration is strongly dependent on the annealing temperature and decreases substantially after the drastic cooling. This means that the precise control of annealing temperature and post-annealing cooling rate are critical for tuning the electrical properties of CZTS.