On the structural and magnetoelectrical characterization of epitaxial SrRuO3 thin films grown on (001) SrTiO3 substrates

High-quality epitaxial thin films of the ferromagnetic metallic oxide SrRuO₃ (SRO) were fabricated by dc-sputtering at high oxygen pressure and their structural and magnetoelectrical properties were carefully studied. The films featured a Curie temperature T_C ～ 160 K and a magnetic moment of ～0.7 μ_B per Ru ion. The temperature dependent magnetization could be well described by the scaling relation M(T) ∝ (T_C ? T)^β with a critical exponent β = 0.53 over the entire ferromagnetic temperature range. A negative magnetoresistance, MR, on the order of a few percent was found up to room temperature. MR showed a maximum of ～4% right at T_C where a kink structure of the resistivity, ρ, at zero field was flattened out on magnetic field application. This ρ contribution could be related to scattering due to orientational disorder of the Ru magnetic moments which become aligned by an external magnetic field. In addition, an equally strong MR effect, related to localization phenomena, could be observed at lower temperature. Particularly, the second MR peak at ～35 K might be related to a Fermi-liquid to non-Fermi-liquid crossover. A scaling behavior dρ/dT ∝ |T ? T_C|^α was observed only above T_C. Here, values for the exponent α ≈ ?0.4 and α ≈ ?1.4 were obtained in zero field and in a field of 9 T, respectively. The commonly observed ρ minimum, appearing at low temperatures (～3 K in the present case), is correlated with the structural disorder of the SRO films and is believed to have its origin in quantum corrections to the conductivity (QCC).     

Surface tension and viscosity of molten vanadium measured with an electrostatic levitation furnace

Surface tension and viscosity of molten vanadium were measured over a wide temperature range by the oscillating drop method in an electrostatic levitation furnace. Over the (2023 to 2517) K temperature range, the surface tension can be expressed as γ(T)/(10^?3 N/m) = 1935 ? 0.27 {(T ? T_m)/K} with T_m = 2183 K. Over the same temperature span, the viscosity can be expressed as η(T)/(10^?3 Pa · s) = 1.23exp[2.27 · 10⁴/(RTK^?1)], where R is the gas constant.     

Observation of possible quantum interference effects in SrRuO3 epitaxial thin films grown by high-oxygen pressure dc sputtering

A careful study of the electronic transport and magnetotransport properties of metallic ferromagnetic SrRuO₃ (SRO) thin films is reported. Epitaxial (～150 nm) SRO films were grown on (001)-oriented SrTiO₃ (STO) substrates by dc sputtering technique at high oxygen pressure. Resistivity measurements were performed up to temperatures as low as 2 K in magnetic fields strengths of up to 9 T, applied perpendicular to the film plane. The films featured excellent metallic behavior at room temperature, with a resistivity, ρ(300 K) < 600 μΩ cm. The presence of minima in the ρ–T plots at ～4 K was clearly detected from these measurements. The 9 T magnetic field did not remove the minima signaling its nonmagnetic origin In addition, the ρ(μ₀H = 9 T,T) minima was slightly shifted to higher temperature and the ρ(μ₀H = 9 T,T ≤ 4 K) was larger when it was compared with ρ(μ₀H = 0 T,T ≤ 4 K). Increasing relevance of quantum corrections to the conductivity as the temperature is lowered has been invocated as possible cause of this anomalous electrical behavior. In this case, effects arising from quantum interference of the electronic wavelength are expected. Weak localization and renormalized electron–electron interaction have been considered as possible sources giving rise to quantum correction to the conductivity.     

Thermodynamic properties of tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate fromT → 0 toT = 340 K

The temperature dependence of the standard molar heat capacity C_{p, m}^oof samples of crystalline tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate was measured in an adiabatic low-pressure calorimeter between T =  4.8 K and T =  340 K and from T =  5.8 K to T =  340 K, respectively, mostly to within a precision of 0.2 per cent. For tetraphenylphosphonium perchlorate, an anomalous change of the heat capacity in the range T =  125 K to T =  185 K, probably arising from the excitation of hindered rotations of atomic groups, was found and its thermodynamic characteristics were determined. No such anomaly was observed for tetraphenylarsonium perchlorate. The data obtained were used to calculate the thermodynamic functions C_{p, m}^o(T) / R, Δ₀^TH_m^o / R·K, Δ₀^TS_m^o / R, and Φ_m^o = Δ₀^TS_m^o − Δ₀^TH_m^o / T(where R is the universal gas constant) of the compounds between T →  0 and T =  340 K.     

Thermodynamics of dibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin fromT = 5 K toT = 490 K

In adiabatic low-pressure and dynamic calorimeters the temperature dependence of the standard molar heat capacity C_{p, m}^oof dibenzo- p -dioxin and 1,2,3,4-tetrachlorodibenzo- p -dioxin have been determined at temperatures in the range T =  5 K to T =  490 K: from T =  5 K to T =  340 K with an accuracy of about 0.2 per cent and with an accuracy of 0.5 per cent to 1.5 per cent between T =  340 K and T =  490 K. The temperatures, enthalpies, and entropies of melting of the above compounds have been determined. The experimental data were used to calculate the thermodynamic functions C_{p, m}^o / R, Δ₀^TH_m^o / (R·K), Δ₀^TS_m^o / R, and Φ_m^o = Δ₀^TS_m^o − Δ₀^TH_m^o / T(where R is the universal gas constant) in the range T →  0 to T =  490 K. The isochoric heat capacity C_{V, m}of both dioxins has been estimated over the range T →  0 to T_fus. The effect of substitution of four hydrogen atoms by chlorine atoms on the lattice and atomic components of the isochoric heat capacity was considered.     

Hydrogen production from hydrogen sulfide using membrane reactor integrated with porous membrane having thermal and corrosion resistance

Using mathematical model and experimental method, the thermal decomposition of hydrogen sulfide in membrane reactor with porous membrane which has Knudsen diffusion characteristics was investigated. With mathematical model, the effect of characteristics of membrane reactor and operating conditions on H₂ concentration in the permeate chamber, y_H2, which increases at higher reaction temperature, lower pressure and higher ratio of cross-sectional area of the permeate chamber to that of the reactor, was evaluated. The reaction experiments with ZrO₂–SiO₂ porous membrane were carried out under the following conditions: temperature T, 923–1023 K; pressure in the reactor p^R_T, 0.11–0.25 MPa absolute; pressure in the permeate chamber p^P_T, 5 kPa absolute and inlet flow rate of H₂S f⁰_H2S, 3.2×10⁻⁵–1.5×10⁻⁴ mol/s. At p^R_T=0.11 MPa and f⁰_H2S=6.4×10⁻⁵, y_H2 increased from 0.02 at T=923 K to 0.15 at 1023 K. With the experimental condition, p^R_T=0.11, T=1023 K and f⁰_H2S=3.2×10⁻⁵, y_H2 was 0.22. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.     

Photolysis of glyoxal in air

The photolysis of glyoxal in synthetic air was investigated in a quartz cell at 298 K using three types of UV sources (TL/12 lamps (275–380 nm), TL/03 lamps (390–470 nm) and mercury lamps (254 nm)) and products were identified and quantitatively analyzed using long-path FTIR spectroscopy. For all light sources, the observed products were CO, HCHO and HCOOH. Absolute quantum yields were determined using Cl₂ and Br₂ as actinometers. Photolysis in the first absorption band of glyoxal, using TL/12 lamps, provided an overall quantum yield of Φ_T = 0.97 ± 0.05, independent of total pressure ranging from 100 to 700 Torr air. The absolute quantum yields obtained with the TL/03 lamps, covering the second absorption band of glyoxal, showed dependency on total pressure, ranging from Φ_T = 0.12 at 100 Torr to Φ_T = 0.042 at 700 Torr, which can be expressed as a Stern–Volmer-type equation 1/Φ_T = (6.80 + 251.8) × 10⁻⁴ × P (Torr).By combining the product yields with literature data, we deduced the detailed picture of glyoxal photolysis, including the dependency of the quantum yield of each particular channel: CHOCHO + hν → 2HCO (Φ₁); CHOCHO + hν → H₂ + 2CO (Φ₂); CHOCHO + hν → H₂CO + CO (Φ₃) on the applied wavelength. The product quantum yields indicate that dissociation into two HCO radicals is the most important pathway under atmospheric conditions. The mean photolysis rate was measured under solar radiation in the EUPHORE outdoor chamber to be J_obs = 1.04 ± 0.10 × 10⁻⁴ s⁻¹, corresponding to a mean effective quantum yield ϕ_eff = 0.035 ± 0.007. Although glyoxal has a very low effective quantum yield, photolysis remains an important removal path in the atmosphere.     

Synthesis,structure, and property of a triruthenium cluster having a μ-alkyl ligand: Transformation of a μ3(⊥)-alkyne ligand into a μ-alkyl ligand via a μ3-vinylidene complex

A triruthenium μ-alkyl complex, (Cp¹Ru)₃(μ-η²-HCHCH₂R)(μ-CO)₂(μ₃- CO) (2a, R = Ph; 2b, R = ^tBu, Cp¹ = η⁵-C₅Me₅), which contains a two-electron and three-center interaction among Ru, C, and H atoms, has been synthesized by the reaction of a perpendicularly coordinated 1-alkyne complex, {Cp¹Ru(μ-H)}₃(μ₃-η²:η²(⊥)-RCCH) (1a; R = Ph, 1b; R = ^tBu), with carbon monoxide. A diffraction study for 2b clearly represented the bridging neohexyl group on one Ru–Ru edge. This μ-alkyl group exhibited dynamic behavior resulting in site-exchange of the α-hydrogen atoms between the terminal and bridging positions, which was synchronized with the migration of the μ-alkyl groups between the two ruthenium atoms. The agostic C–H bond was readily cleaved upon pyrolysis. Whereas the μ-phenethylidene intermediate resulting from the σ-C–H bond cleavage has never been observed, a μ₃-phenethylidyne complex, {Cp¹Ru(μ-CO)}₃(μ₃-CCH₂Ph) (7a), and a μ₃-methylidyne complex, {Cp¹Ru(μ-CO)}₃(μ₃-CH) (8), were obtained by the successive C–H/C–H and C–H/C–C bond cleavages at the μ-alkyl moiety, respectively.     

Development of a headspace-gas chromatography (HS-GC-PID-FID) method for the determination of VOCs in environmental aqueous matrices: Optimization,verification and elimination of matrix effect and VOC distribution on the Fortaleza Coast,Brazil

An analytical protocol combining a headspace technique with gas chromatography and detection by photoionization detector and flame ionization detector (HS-GC-PID-FID) was developed. This procedure was used to measure volatile organic compounds (VOCs) in environmental aqueous matrices and was applied in determination of VOCs on the coast of Fortaleza, Brazil. At optimum operating conditions, analytical figures of merit such as linearity (R ranged from 0.9983 to 0.9993), repeatability (5.62 to 9.63% and 0.02 to 0.19% for the quantitative and qualitative analyses, respectively), detection limits (0.22 to 7.48 μg L⁻¹) and sensibility were estimated. This protocol favors a fast sampling/sample preparation (in situ), minimizes the use of laboratory material, eliminates the matrix effect from environmental samples, and can be applied to river, estuarine and oceanic waters. The advantage of detectors in series is that a low sensitivity in detection in one is compensated by the other. Toluene was the most abundant VOC in the studied area, with an average concentration of 1.63 μg L⁻¹. It was followed by o-xylene (1.15 μg L⁻¹), trichloroethene (1.08 μg L⁻¹), benzene (0.86 μg L⁻¹), ethylbenzene (0.74 μg L⁻¹), carbon tetrachloride (0.55 μg L⁻¹), m/p-xylene (0.48 μg L⁻¹) and tetrachloroethene (0.46 μg L⁻¹), compounds which are very commonly detected in urban runoff from most cities. The results of the VOC distribution showed that port activity was not the main source of VOCs along the Fortaleza Coast, but that the contribution from urban runoff seemed more significant.     

Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Thermodynamic study on the sublimation of 1,2-diphenylethane and of 3-phenylpropiolic acid

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline compounds: 1,2-diphenylethane (bibenzyl), between T =  289.16 K and T =  303.20 K, and of 3-phenylpropiolic acid between T =  329.15 K and T =  343.15 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by the Clausius–Clapeyron equation. From these results the standard, p^o =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K, were calculated:     

Ab initio calculations and mechanism of two proton migration reactions of ethoxy radical

We present a direct ab initio and density functional theory dynamics study of the thermal rate constants of the two H-migration reactions of C₂H₅O radical. MPW1K/6-31+G(d,p) methods were employed to optimize the geometries of all stationary points and to calculate the minimum energy path (MEP). The energies of all the stationary points were refined at the QCISD(T)/aug-cc-pVTZ level of theory. The thermal gas phase rate constants were evaluated based on the energetics from the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory using both microcanonical variational transition state theory (μVT) and canonical variational transition state theory (CVT) with the Eckart tunneling correction in the temperature range of 200–2500 K. The extended Arrhenius expression fitted from the μVT/Eckart rate constants of 1,2 H-shift and 1,3 H-shift reactions of C₂H₅O radical in the temperature range of 200–2500 K are k = 3.90 × 10⁻³¹T^12.4e^{(−2.13 × 103/T)} and k = 2.83 × 10⁻²⁹T^11.9e^{(−2.24 × 103/T)} s⁻¹, respectively. The two isomerization rate constants exhibited positive temperature dependence in the calculated temperature region. The variational effects for the two isomerizations of ethoxy radical are small and the tunneling effects are important in the low temperature range. The titled reactions are minor and not essential compared to the decomposition pathways of ethoxy radical.     

Enantiomeric separation of a melatonin agonist Ramelteon using amylose-based chiral stationary phase

A new simple isocratic chiral liquid chromatographic method was developed for the enantiomeric purity of Ramelteon[(S)-N-[2-(1,6,7,8-tetrahydro-2H-indeno[5,4-b]furan-8-yl) ethyl]-propionamide], a melatonin agonist in bulk drugs. The chromatographic separation was achieved on Chiralpak AD-H, 250 mm × 4.6 mm, 5 μm column using a mobile phase system consisting of n-hexane, ethanol and methanesulfonic acid in the ratio of 900:100:0.1 (v/v/v). The mobile phase was pumped on the column at the flow rate of 1 mL min^?1. Addition of methane sulfonic acid in the mobile phase enhanced chromatographic efficiency and resolution between the enantiomers. The resolution between the enantiomers was found to be more than four. The developed method was subsequently validated and proved to be accurate and precise. The experimentally established limit of detection and quantification of (R)-enantiomer were found to be 25.5 and 77.2 ng ml^?1, respectively, for 20 μl injection volumes. The percentage recovery of (R)-enantiomer was ranged from 98.5 to 101.9 in bulk drug samples of Ramelteon. The stability of Ramelteon sample in analytical solution was checked for about 48 h at room temperature and was found to be stable for about 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of (R)-enantiomer in drug substance.     

Modeling of thermal and chemical non-equilibrium in a laser-induced aluminum plasma by means of a Collisional-Radiative model

A 0D numerical approach including a Collisional-Radiative model is elaborated in the purpose of describing the behavior of the nascent plasma resulting from the interaction between a 4 ns/65 mJ/532 nm Q-switched Nd:YAG laser pulse and an aluminum sample in vacuum. The heavy species considered are Al, Al⁺, Al²⁺ and Al³⁺ on their different excited states and free electrons. The translation temperatures of free electrons and heavy species are assumed different (T_e and T_A respectively). Numerous elementary processes are accounted for as electron impact induced excitation and ionization, elastic collisions, multiphoton ionization and inverse Bremsstrahlung. Atoms passing from the sample to gas phase are described by using classical vaporization theory so that the surface temperature is arbitrarily limited to values less than the critical point one at 6700 K. The laser flux density considered in the study is therefore moderate with a fluence lower than 7 J cm^? 2.This model puts forward the major influence of multiphoton ionization in the plasma formation, whereas inverse Bremsstrahlung turns out to be quasi negligible. The increase of electron temperature is mainly due to multiphoton ionization and T_e does not exceed 10,000 K. The electron induced collisions play an important role during the subsequent phase which corresponds to the relaxation of the excited states toward Boltzmann equilibrium. The electron density reaches its maximum during the laser pulse with a value ≈ 10²², 10²³ m^? 3 depending highly on the sample temperature. The ionization degree is of some percents in our conditions.     

Thermodynamic study on the sublimation of six methylnitrobenzoic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T =  357.16 K and T =  371.16 K; 2-methyl-6-nitrobenzoic acid, between T =  355.16 K and T =  369.16 K; 3-methyl-2-nitrobenzoic acid, between T =  371.16 K and T =  385.14 K; 3-methyl-4-nitrobenzoic acid, between T =  363.21 K and T =  379.16 K; 4-methyl-3-nitrobenzoic acid, between T =  363.10 K and T =  377.18 K; 5-methyl-2-nitrobenzoic acid, between T =  355.18 K and T =  371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p^o =  10⁵Pa, molar enthalpies Δ_cr^gH_m^o, entropies Δ_cr^gS_m^oand Gibbs energies Δ_cr^gG_m^oof sublimation at T =  298.15 K, were derived:     

Potential energy surface and rate constant of the inversion substitution reactions CH3X + O2 → CH3O2• + X• (X = SH,NO2)

The temperature dependence of the rate constant of the inversion substitution reactions CH₃X + O₂ → CH₃O₂^? + X^? (X = SH, NO₂), can be expressed as k = 6.8 × 10^–12(T/1000)^1.49exp(–62816 cal mol^–1/RT) cm³ s^–1 (X = SH) and k = 6.8 × 10^–12(T/1000)^1.26 × × exp(–61319 cal mol^–1/RT) cm³ s^–1 (X = NO₂), as found with the use of high-level quantum chemical methods and the transition state theory.     

Novel Co complex with high transformation temperature of valence tautomerism

The preparation and characterization of [Co^II-HS(dpa)(3,5-DBSQ)₂] are presented first time. From the magnetic curve, the phase transition temperatures, T_c is 380 K. To our knowledge, the T_c value is the highest among the species exhibiting thermal valence tautomerism. After illumination with 532 nm light at 5 K, the magnetization values increase from μ_eff=1.73 to 2.0μ_B, showing valence tautomerism. The metastable state will recover to the original state with the increase of temperature. The alternate illumination with 532 and 830 nm light at 5 K can induce a reversible change in magnetization. The quick response to light means that this compound can be used for the development of optical–magnetic switch.     

Thermodynamic study on the sublimation of 3-phenylpropionic acid and of three methoxy-substituted 3-phenylpropionic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T =  305.17 K and T =  315.17 K; 3-(2-methoxyphenyl)propionic acid, between T =  331.16 K and T =  347.16 K; 3-(4-methoxyphenyl)propionic acid, between T =  341.19 K and T =  357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T =  352.18 K and T =  366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation Δ_cr^gH_m^owere derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p ^∘  =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:     

Thermodynamic study on the sublimation of succinic acid and of methyl- and dimethyl-substituted succinic and glutaric acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T =  360.11 K and T =  375.14 K; methylsuccinic acid, between T =  343.12 K and T =  360.11 K; 2,2-dimethylsuccinic acid, between T =  350.11 K, and T =  365.11 K; 2-methylglutaric acid, between T =  338.38 K and T =  347.63 K; and 2,2-dimethylglutaric acid between T =  342.18 K and T =  352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, p^o =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived: