Above-mentioned Temperature Range Research Articles

Impact of Cr2O3 additives on the gas-sensitive properties of β-Ga2O3 thin films to oxygen, hydrogen, carbon monoxide, and toluene vapors

High-temperature β-Ga2O3:Cr2O3-based sensors sensitive to oxygen- and hydrogen-containing gases have been developed and studied. Magnetron cosputtering is the method of choice for the thin film synthesis as an industry-compatible technique. The composition-structure-properties relationship has been revealed. An introduction of 0.04–0.14 wt. % Cr leads to a significant increase in the response of the O2 sensors over the temperature range 250–400 °C. The highest response in the above-mentioned temperature range has been achieved for a Cr addition of 0.14 wt. %. An increase in the Cr content from 0.04 to 0.22 wt. % leads to a decrease in the β-Ga2O3-based sensors’ response time, especially for low O2 concentrations (≤10 vol. %). Reliable control of the β-Ga2O3:Cr2O3-based sensors’ selectivity to industry-relevant reducing gases—hydrogen, carbon monoxide, and toluene—is demonstrated. β-Ga2O3 films with a Cr incorporation content of 0.04 and 0.06 wt. % have a high response to toluene at operating temperatures 300–500 °C, while the films with 0.14 and 0.22 wt. % Cr have a high response to H2 in the range 400–500 °C. Regardless of the Cr content in β-Ga2O3 thin films, all sensors considered demonstrate a weak response to CO within the operating temperature range 250–500 °C. The results attained are of certain technological importance, i.e., in terms of the development of cost-effective methods for the synthesis of materials and systems for monitoring and control of industry-relevant gases for an environmentally friendly and sustainable growth.

AQUA: a collection of H2O equations of state for planetary models

Context. Water is one of the key chemical elements in planetary structure modelling. Due to its complex phase diagram, equations of state often only cover parts of the pressure-temperature space needed in planetary modelling. Aims. We aim to construct an equation of state of H2O spanning a very wide range, from 0.1 Pa to 400 TPa and 150 to 105 K, which can be used to model the interior of planets. Methods. We combined equations of state valid in localised regions to form a continuous equation of state spanning over the above-mentioned pressure and temperature range. Results. We provide tabulated values for the most important thermodynamic quantities: the density, adiabatic temperature gradient, entropy, internal energy, and bulk speed of sound of water over this pressure and temperature range. For better usability we also calculated density-temperature and density-internal energy grids. We discuss further the impact of this equation of state on the mass radius relation of planets compared to other popular equations of state like ANEOS and QEOS. Conclusions. AQUA is a combination of existing equations of state useful for planetary models. We show that, in most regions, AQUA is a thermodynamic consistent description of water. At pressures above 10 GPa, AQUA predicts systematic larger densities than ANEOS or QEOS. This is a feature that was already present in a previously proposed equation of state, which is the main underlying equation of this work. We show that the choice of the equation of state can have a large impact on the mass-radius relation, which highlights the importance of future developments in the field of equations of state and regarding experimental data of water at high pressures.

Thermodynamic and heat‐hydrogen transfer analyses of novel multistage hydrogen‐alloy sorption heat pump

The requirement of simultaneous heating and cooling effects at different zones of a building demands for the development of an energy-efficient air-conditioning system for heating and cooling outputs. In order to fulfil this requirement, a novel multistage hydrogen-alloy–based sorption heat pump (H-A SHP) for space air-conditioning is proposed in the present work. The proposed system produces multiple cooling and heating outputs at 20°C and 45°C, respectively, with single heat input at 160°C. A set of MmNi5, La0.8Ce0.2Ni5, MmNi4.4Al0.6, and LaNi4.6Al0.4 metal hydrides (MHs) is chosen to operate at the above-mentioned temperature range with hydrogen as working fluid. The proposed system can completely eliminate the requirement of conventional compressor because it operates using waste heat, and useful outputs (cooling-heating) result from reaction enthalpies (MH + H2 interaction). The thermodynamic and heat-hydrogen transfer analyses of H-A SHP are carried out through finite volume approach, in which heat and mass transfer equations are solved to foresee the variations in MH bed temperature, hydrogen concentration, and heat interactions during cycle operation as well as the amount of cooling and heating outputs delivered to the air-conditioning space. The numerical code is validated with experimental pressure-concentration isotherms (PCIs) measured through Sievert's apparatus. The maximum heat exchange during the cooling and heating processes, at a particular instant of time, is observed as 257.5 and 286.1 W with cooling temperature of 10°C and heating temperature of 53°C, respectively. The thermodynamic performance is estimated as 178.5 kJ of cooling effect, 265.5 kJ of upgraded heat with overall coefficient of performance (COP) of 6.8, and overall specific alloy output of 396.5 W/0.34 kg of alloy.

Estimation of bulk viscosity of dilute gases using a nonequilibrium molecular dynamics approach.

A method is proposed for the calculation of bulk viscosity, μ_{b}, of dilute gases using nonequilibrium molecular dynamics (NEMD) simulations. The method uses measurement of mechanical (P_{mech}) and thermodynamic pressure (P_{thermo}) in a NEMD simulation of an expanding fluid and then relates the bulk viscosity to them by the relation μ_{b}=(P_{mech}-P_{thermo})/∇·u[over ⃗], where ∇·u[over ⃗] is the controlled rate of expansion of the fluid per unit volume. A special emphasis is given to the fundamental physical understanding of bulk viscosity in this work. The proposed method is demonstrated for the estimation of bulk viscosity of dilute nitrogen gas in the temperature range of 200-800K. Variation of bulk viscosity with temperature is reported in the above-mentioned temperature range and is found to be in a reasonably good agreement with the data available in the literature. Furthermore, variation of bulk viscosity with pressure and volumetric expansion rate is obtained. A weak linear dependency of bulk viscosity with pressure is observed, which increases with temperature. However, no significant effect of the rate of volumetric expansion is observed until 10^{8}s^{-1}. Moreover, the effect of the direction of volumetric change (expansion vs. compression) is also demonstrated in this work.

Volumetric and Ultrasonic Study of Mixtures of Benzyl Alcohol with 1-Propanol, 2-Propanol, and 1,2-Propandiol, 1,3-Propandiol and T-butanol

Densities and speeds of sound for five binary mixtures of benzylalcohol with 1,3-propandiol, 1- propanol, 2- propanol, 1,2-propandiol and phenylethnol were measured over the entire range of composition and at five temperatures from 298.15K to 323.15K at 5K interval and atmospheric pressure using a vibrating u-tube densimeter (DSA 5000). Besides, the densities for pure compounds in the above-mentioned temperature range were measured. The experimental densities were used to calculate the excess molar volumes, isentropic compressibility changes, the excess thermal expansion coefficients, and the excess partial molar volumes at infinite dilution, The results have been used to discuss the nature and strength of intermolecular interactions in these mixtures. The calculated excess and deviations quantities are correlated with the third-order Redlich–Kister equation. As a final work we modeled the experiment results by using TM and PR EOSs. This is clear that the results with TM EOS are more acceptable than PR EOS. TM and PR EOS can successfully predict density and excess molar volume. And are unable to predict speed of sound.

Ellipsometric Method of Substrate Temperature Measurement in Low-Temperature Processes of Epitaxy of InSb Layers

The present study is aimed at solving the problem of in situ thermometry of lowtemperature processes of molecular beam epitaxy of indium antimonide. A spectral ellipsometric method for measuring the temperature of InSb epitaxial layers is proposed. The method is based on the temperature dependence of the energy positions of the critical points. The spectra of ellipsometric parameters of the material in the temperature range from 25 to 270 °C are measured. The analysis of these spectra shows that the most temperature-sensitive parameters are the spectral positions of the peaks of the ellipsometric parameter, which are manifested near the critical points E1 and E1 + Δ1. It is found that the dependences of the peak positions on temperature in the above-mentioned temperature range are linear functions with the slope factors of 0.21 and 0.10 nm/°C, respectively. These factors determine the sensitivity of the method and ensure the temperature measurement accuracy within 2–3 °C.

Modeling vapor-liquid phase equilibria of hydrogen sulfide and water system using a cubic EOS-GEX model

Vapor-liquid phase equilibria of the H2SH2O mixture were correlated by use of a cubic EOS-GEX over temperature and pressure range of 0.1–30 MPa and 278–627K. Average absolute deviations (AAD%) between the modeling results and the experimental data taken from literature for both the H2S-rich and the aqueous phases were found less than 5%. The new sets of EOS-GEX model parameters for H2SH2O mixture were evaluated from the experimental data over the above-mentioned temperature and pressure range. The proposed model was compared with the three previous published models and we discussed the advantages and the disadvantages for each of them. This study demonstrated that the advantages of the cubic EOS-GEX model in calculating phase equilibria of H2SH2O mixture over currently available models, especially at high pressures. The hydrate equilibrium, the salt effect, and the chemical reactions in the aqueous phase were not considered during phase equilibrium calculation in this study.

Temperature dependence of the heat capacity and change in the thermodynamic functions of strontium-alloyed AK1M2 alloy

The temperature dependence of the specific heat capacity and change in the thermodynamic functions of strontium-alloyed ultrahigh-purity aluminum base AK1M2 alloy have been studied in “cooling” mode over the 298.15–900 K range. Mathematical models describing the evolution of these properties of the alloys in the abovementioned temperature range with change in alloying addition concentration have been obtained. The heat capacity, enthalpy and entropy of the alloys increase with temperature, decrease with an increase in the alloying addition concentration to 0.5 wt.% and grow with a further increase in the alloying addition concentration. The Gibbs energy of the alloys has an inverse dependence: it decreases with an increase in temperature and grows with an increase in the alloying addition concentration to 0.5 wt.%.

Unmasking the Mechanism of Structural Para- to Ferroelectric Phase Transition in (NH4)2SO4.

New nontoxic and biocompatible ferroelectric materials are a subject undergoing intense study. One of the most promising research branches is focused on H-bonded organic or hybrid ferroelectrics. The engineering of these materials is based on mimicking the phase transition mechanisms of the well-known inorganic ferroelectrics. In our study, a coupled experimental and theoretical methodology was used for a precise investigation of the ferroelectric phase transition mechanism in ammonium sulfate (AS). A series of single-crystal X-ray diffraction measurements were performed in the temperature range between 273 and 163 K. The detailed inspection of the obtained static structural data, in the above-mentioned temperature range, allowed us to reveal dynamical effects at the ferroelectric phase transition. Accurate analysis of all geometrical features within the obtained crystal structures was carried out. The results were discussed in the view of previously discovered physical properties. X-ray studies were complemented by the use of quantum theory of atoms in molecules calculations and Hirshfeld surface analysis. Valence shell charge concentration analysis allowed us to find the subtle changes between charge density distribution within SO42- in para- and ferroelectric phases. H-bond interactions, geometrically classified in both AS phases, were all confirmed by the appropriate critical points. The interaction energies were estimated for the structures at 273, 233, 213, 183, and 163 K. Correlation between the geometrical approach and the results of theoretical calculations enabled us to discover the differences in interaction equilibrium between the AS phases. The mechanism of the phase transition originates from the disruption of the vibrational lattice mode between sulfate anions. Our studies resolved the problem, which was under discussion for more than 60 years.

PρT measurement and PC-SAFT modeling of N,N-dimethyl formamide, N -methyl formamide, N,N-dimethyl acetamide, and ethylenediamine from T = (293.15–423.15) K and pressures up to 35 MPa

The PρT data of N,N -dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) were measured at temperature range of (293.15–413.15) K and pressures up to 30 MPa. The same properties also were measured for N-methylformamide (NMF) and ethylenediamine (EDA) over the temperature range within (293.15 to 423.15) K and (293.15–383.15) K and at pressures up to 35 MPa and 30 MPa, respectively. The measurements at 10 K intervals and along eight isobars were done. The experimental density values were correlated with the Tait equation. Based on the obtained result, other thermodynamic properties, such as, isothermal compressibility, κT, thermal expansion coefficient, αP, and thermal pressure coefficient, γV, were calculated. Also, the PC-SAFT model was used to correlate the densities of the pure solvents at the above-mentioned temperature and pressure range. In general, both models yield comparable and satisfactorily good correlation of the high pressure and temperature density.

Liquid–vapor equilibrium and critical parameters of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate from molecular dynamics simulations

The liquid–vapor equilibrium properties of the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, often abbreviated as [bmim][PF6] or [C4mim][PF6], have been determined using a classical all-atom force field in molecular dynamics simulations. Extending our earlier work, the behavior at elevated temperatures (875–1075K) was studied to obtain the following refined estimates of the critical parameters: Tc=1105±25K, ρc=227±19kgm−3, and Pc=3.1±1.4bar. In the above-mentioned temperature range, the vapor pressure can be calculated directly with reasonable accuracy, giving us indirect access also to the enthalpy of vaporization. From these new data, several corresponding-states properties, which are believed to be generic for ionic liquids and which do not depend too sensitively on any specific potential model, can be obtained in addition to Guggenheim's reduced surface tension which we reported previously. The critical compressibility factor is found to be Zc≈0.04±0.02, Guggenheim's ratio ΔvapHapp/(RTc)≈9.9±0.5, the relative normal boiling point Tb/Tc=0.90±0.05, and Trouton's constant ΔvapS(Tb)≈71±11Jmol−1K−1. The implications of these findings are discussed.

Impact of temperature and duration of thermal treatment on different concentrations of anaerobic digested sludge: Kinetic similarity of organic matter solubilisation and sludge rheology

Municipal digested sludge is a dispersion of agglomerated particles or flocs in a liquid medium which exhibits yield stress, shear thinning behaviour and high irreversible temperature dependence.In this study, the rate of solubilisation of organic matter in digested sludge was investigated when sludge (at different solid concentrations) was exposed to thermal treatment between 50 and 80°C for 1 to 60min. The organic matter solubilisation was measured using chemical oxygen demand (COD) analysis on liquor of the thermally treated sludge. The effects of the abovementioned temperature range and heating duration on yield stress and the apparent viscosity of sludge at different solid concentrations have also been investigated.The results showed that the irreversible effect of temperature was much higher at higher concentrations, higher temperatures and longer duration of treatment. It was also observed that for any sludge concentration the kinetic of COD solubilisation, yield stress and apparent viscosity reductions followed a logarithmic correlation with duration of thermal treatment. This similarity was also pronounced in the linear relationship between solubilised COD and yield stress and apparent viscosity reductions in all tested concentrations and the durations of heat treatment. Modified form of Herschel–Bulkley was used to obtain a master curve, independent of temperature, concentration and duration of thermal treatment. Furthermore, a new model was proposed for the impact of temperature and the duration of thermal treatment on yield stress and apparent viscosity reduction.

Volumetric and ultrasonic study of mixtures of 2-phenylethanol with 1-butanol, 2-butanol, and 2-methyl-1-butanol at T = (298.15–323.15) K and atmospheric pressure: Measurement and prediction

Densities and speeds of sound for three binary mixtures 2-phenylethanol with 1-butanol, 2-butanol and 2-methyl-1-butanol were measured over the entire range of composition and at six temperatures from 298.15K to 323.15K at 5K interval and atmospheric pressure using a vibrating tube densimeter. Besides, the densities for pure compounds in the above-mentioned temperature range were measured. The experimental densities were used to calculate the excess molar volumes, VmE, isentropic compressibility change, ΔκS, the excess thermal expansion coefficients, αpE and the excess partial molar volumes at infinite dilution, V¯iE,∞. The results have been used to discuss the nature and strength of intermolecular interactions in these mixtures. The values of excess volumes and molar isentropic compressibilites over the entire composition range were negative. The calculated excess and deviations quantities are correlated with the third-order Redlich–Kister equation. Finally the predictive power of a statistically-based equation of state for volumetric properties of the studied mixtures of alcohols has been examined.

Superspin relaxation in Fe3O4/hexane magnetic fluids: A dynamic susceptibility study

We have used frequency-resolved (100Hz<f<10,000Hz) ac magnetic susceptibility measurements to directly determine the Néel and Brown relaxation times in 30-nm-size Fe3O4/hexane magnetic fluids at temperatures between 200 and 300K. Our data collected on both powder and magnetic fluid samples allow the separation of the contributions from the Néel and Brown relaxation mechanisms that act concomitantly within the above-mentioned temperature range. At all temperatures we find that the Brown relaxation times (τB) are shorter than their Néel counterparts (τN), evidence that the Brown mechanism yields the major contribution towards the system’s overall superspin dynamics. τB exhibits a steep two-order-of-magnitude decrease upon heating, from τB=1×10−3s at T=237K to τB=1.5×10−5s at T=270K, a behavior mostly driven by the heating-induced reduction of the liquid carrier’s viscosity.

Organic reactivity of alcohols in superheated aqueous salt solutions: an overview

The low dielectric constant and high self-dissociation constant of water in a temperature range between 150 and 250 °C make it a very appealing solvent for synthesis. Surprisingly, while organic chemistry in water at low temperature or around its critical point has been investigated in detail, very little seems to be known about the behaviour of organic molecules under hydrothermal conditions. The present work thus aims at shading some light on this field. As a start, we decided to investigate the reactions in which alcohols can undergo in water in the above-mentioned temperature range. Knowing that very strong salt effects on organic reactions have already been observed in super critical water, the impact of salt on the outcome of our tests was also investigated in detail.

Electrical conductivity and dynamics of quasi-solidified lithium-ion conducting ionic liquid at oxide particle surfaces

Lithium ion conducting solid-state composites consisting of lithium ion conducting ionic liquid, lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA) dissolved 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide (EMI-TFSA), denoted by [ yMLi +][EMI +][TFSA −] in this study, and various oxide particles such as SiO 2, Al 2O 3, TiO 2 (anatase and rutile) and 3YSZ are synthesized via a liquid route for the molar concentration of lithium, y, to be 1. The composite consists of SiO 2 and the ionic liquid with y = 0.2 was also prepared. The ionic liquid are quasi-solidified at the above oxide particle surfaces when x is below 40 for y = 1 and x is below 30 for y = 0.2, corresponding to the confinable thickness of the ionic liquid at the oxides' surfaces to be approximately 5–10 nm regardless of the oxide compositions. The electrical conductivities of x vol.%[ yMLi +][EMI +][TFSA -]–SiO 2, Al 2O 3, TiO 2s or 3YSZ composites are evaluated by ac impedance measurements. The quasi-solid-state composites exhibited liquid-like high apparent conductivity, e.g. 10 − 3.3 –10 − 2.0 S cm − 1 in the temperature range of 323–538 K for SiO 2–ionic liquid composites with y = 1. The self-diffusion coefficients of the constituent species of x vol.% [ yMLi +][EMI +][TFSA −] ( x is below 40, y = 0.2 and 1) − SiO 2 are evaluated by the Pulse Gradient Spin Echo (PGSE)-NMR technique in the temperature range of 298–348 K. By the quasi-solidification of the ionic liquid at SiO 2 particle surfaces, the absolute values of the diffusion coefficients of all constituent species decreased. The SiO 2 surfaces work to promote ionization of ion pair, [EMI +][TFSA −], while significant influence on the solvation coordination, [Li(TFSA) n + 1 ] n− , was not observed. The apparent transport numbers of Li-containing species both in the bulk and the quasi-solidified ionic liquid showed similar values with each other, which was evaluated to be in the range of 0.010–0.017 for y = 0.2 and 0.051–0.093 for y = 1 in the abovementioned temperature range.

Dielectric relaxation spectroscopy and electro-optical studies of a new, partially fluorinated orthoconic antiferroelectric liquid crystal material exhibiting V-shaped switching

In this paper we report the results from detailed electro-optical and dielectric studies in various antiferroelectric and ferroelectric phases of an orthoconic antiferroelectric liquid crystal (OAFLC) material . The material possesses high tilt and high spontaneous polarisation. Such an OAFLC, because of its high tilt, provides an excellent dark state. The material exhibits V-shaped switching in the SmC* phase. Dielectric studies reveal the existence of another phase during heating in the range between 78.6 and 92°C which did not appear in the DSC curve and in polarising microscopy. This phase has been identified as the SmCγ* phase and is extremely sensitive with respect to the cell conditions, aligning material, purity, etc. Three dielectric modes have been assigned in the above-mentioned temperature range and their origins are discussed.

Solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, the phase behaviour of the binary system of carbon dioxide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf 2N]) has been studied experimentally. The equipment used for the experiments is the Cailletet set-up, based on visual observations of phase transitions of systems with constant overall composition. Results are reported for carbon dioxide concentrations ranging from 12.3 to 59.3 mol%, and within temperature and pressure ranges of 310–450 K and 0–15 MPa, respectively. The data reveal an extremely high capacity of the selected ionic liquid for dissolving CO 2 gas, for example, reaching up to about 60 mol% within the above-mentioned pressure and temperature range. Also, the solubility of CO 2 in the ionic liquid [emim][Tf 2N] is compared to the solubility of CO 2 in the ionic liquid [emim][PF 6], an ionic liquid that shares the same cation.

Non-degenerate 1,2-silyl shift in silyl substituted alkyltrimethylcyclopentadienes

The five new silanes C 5Me 3RSiMe n Cl 3 − n ( n = 3, R = i-Pr ( 5); n = 2, R = i-Pr ( 6); n = 2, R = s-Bu ( 7); n = 2, R = cyclohexyl ( 8); and n = 3, R = t-Bu ( 9)) were synthesized by reaction of 1-alkyl-2,3,4-trimethylcyclopentadienyl lithium salts with appropriate chlorosilane and characterized by NMR, MS, and IR spectra. At elevated temperatures (250–360 K), all the silanes undergo a non-degenerate sigmatropic silyl rearrangement, which generates non-equivalent structures a and b. The presence of minor structure c was observed in compounds 5 and 7 only. The Diels–Alder cycloaddition of 5 with strong dienophiles tetracyanoethylene (TCNE), and dimethylacetylenedicarboxylate (DMAD) provides compounds 10 and 11, which confirmed isomers a and b, respectively. The free energy of activation of b → a isomerization for compounds 5– 8 evaluated from variable temperature NMR spectra show only marginal influence of group R on the 1,2-silyl shift rate. Moreover, in compounds 5 and 7, the process b → a was found significantly faster than b → c process in the above-mentioned temperature range.

Étude expérimentale et modélisation de la cinétique de décomposition de la pierre à chaux

Experimental study and modelling of limestone decomposition kinetics. The study of the limestone decomposition kinetics has been realized by isothermal thermogravimetry analysis in the temperature range from 820 to 900 °C, in the presence of air and CO 2 gas flow. It has been shown that in the above-mentioned temperature range, the rate of reaction is controlled by chemical step. The experimental data have been described satisfactorily by two models: the shrinking-core model and the Coats and Redfern model. The activation-energy values obtained with the two models were not significantly different. They are equal to 233.15 and 205.41 kJ mol –1, respectively, for the Coats and Redfern model and the shrinking core model. To cite this article: S. Slaoui, T. Bounahmidi, C. R. Chimie 7 (2004).