Structural and physical properties of the 6H BaRuO3 polymorph synthesized under high pressure

The single-phase 6H BaRuO₃ with the hexagonal BaTiO₃ structure was synthesized at 5 GPa and 1000 °C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) Å and c=14.0499(2) Å; the average Ru-O distance and direct Ru-Ru distance in the Ru₂O₉ dioctahedron being 1.992(6) and 2.5658(14) Å, respectively. The electrical resistivity of the 6H BaRuO₃ follows a relationship of ρ versus T^3/2 below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO₃ is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R_W and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO₃ was discussed.     

Crystal structure of the high-pressure modification of LaNbO4

Abstract

The crystal structure of the metastable LaNbO₄ high-pressure modification (HPM) has been studied by X-ray powder diffraction. It was found that the crystal structure of HPM LaNbO₄ belongs to- the room temperature BaMCF₄ -type structure (space group Cmc2₁, a = 3,941(1)Å, b= 14,460(4) Å, c = 5,681(2) Å, Z = 4).     

Continuum radiation spectroscopy in a high-pressure argon-mercury lamp

A primary study of the continuum emission from the arc of a high-intensity discharge (HID) lamp with an argon-mercury chemistry at pressures higher than is reported. Spectrally and spatially resolved calibrated continuum spectra from a vertically mounted test lamp (an MHN150 vessel filled at room temperature with 12 mg mercury and 400 mbar argon) are reported for the visible and infrared wavelength range 0.3-. These spectra were analyzed to quantify the infrared (IR) losses and to determine the temperature profile inside the lamp.     

“Vapor-liquid” equilibrium measurements and modeling for the cyclohexane + n-hexanoic acid binary system

To simulate cyclohexane to cyclohexanol oxidation reactors, the acquisition and modeling of vapor-liquid equilibria of the key components, under the process conditions, are essential. n-Hexanoic acid is a co-product of the reaction. Vapor-liquid equilibrium data are reported for the cyclohexane + n-hexanoic acid binary system at four temperatures: 413, 423, 464 and 484 K. All measurements have been carried out using an apparatus based on the “static-analytic” method, with two ROLSI™ pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng-Robinson (PR) and the Perturbed Chain Statistical Association Fluid Theory (PC-SAFT). Both models are capable of representing the experimental data, but the PC-SAFT EoS uses less binary interaction parameters.     

Viscosity of n-alkyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ionic liquids saturated with compressed CO2

The viscosity of imidazolium-based ionic liquids (ILs) saturated with gaseous, liquid and supercritical carbon dioxide (CO₂) was measured by a high-pressure viscometer at three different temperatures (25, 50, and 70 °C). The high-pressure viscosity of 1-ethyl-3-methylimidazolium ([EMIm]), 1-n-hexyl-3-methylimidazolium ([HMIm]), and 1-n-decyl-3-methylimidazolium ([DMIm]) cations with a common anion, bis(trifluoromethylsulfonyl)amide ([Tf₂N]), saturated with CO₂ was measured up to a maximum of 287 bar. As CO₂ pressure is increased the viscosity of the IL mixture dramatically decreases. While, the ambient pressure viscosity of 1-alkyl-3-methyl-imidazolium [Tf₂N] ILs increases significantly with increasing chain length, the viscosity of all the CO₂-saturated ILs becomes very similar at high CO₂ pressures. From previous vapor–liquid equilibrium data, the viscosity with concentration was determined and found to be the primary factor to describe the fractional viscosity reduction. Several predictive and correlative methods were investigated for the mixture viscosity given pure component properties and include arithmetic mixing rules, the Irving (Predictive Arrhenius) model, Grunberg equation, etc. The modified Grunberg model with one adjustable parameter provided an adequate fit to the data.     

Di-n-butyltin(IV)-catalyzed dimethyl carbonate synthesis from carbon dioxide and methanol: An in situ high pressure Sn{H} NMR spectroscopic study

The reactivity of five di-n-butyltin(IV) complexes, n-Bu₂Sn(OR)₂ (1), n-Bu₂SnO (3), [n-Bu₂Sn(OR)]₂O (4), (n-Bu₂SnO)₂(CO₂) (6) and (n-Bu₂SnO)₆[(n-Bu₂SnOR)₂(CO₃)]₂ (7) (R = CH₃), with CO₂, suggested as possible catalyst precursors and key-intermediates for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol, has been investigated using high-pressure ¹¹⁹Sn{¹H} NMR (HP-NMR) spectroscopy. Four of the five precursors studied, i.e. 3, 4, 6 and 7 give rise to an identical ¹¹⁹Sn{¹H} NMR pattern which can be explicitly attributed to the fingerprint of the dimeric form of the 1-methoxy-3-methylcarbonatotetrabutyldistannoxane {5}₂. However, with 1, a new pair of signals is observed in addition to the characteristic ¹¹⁹Sn{¹H} NMR resonances of the dimeric hemicarbonato species {2}₂ and {5}₂, which can be attributed to the in situ formation of an unprecedented species suggested to be the trinuclear carbonato di-n-butyltin(IV) complex, 8.     

High-pressure synthesis and structural behavior of sodium orthonitrate Na3NO4

Sodium orthonitrate (Na₃NO₄) is an unusual phase containing the first example of isolated tetrahedrally bonded NO₄³⁻ groups. This compound was obtained originally by heating together mixtures of Na₂O and NaNO₃ for periods extending up to >14 days in evacuated chambers. Considering the negative volume change between reactants and products, it was inferred that a high-pressure synthesis route might favor the formation of the Na₃NO₄ compound. We found that the recovered sample is likely to be a high-pressure polymorph, containing NO₄³⁻ groups as evidenced by Raman spectroscopy. The high-pressure behavior of Na₃NO₄ was studied using Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell above 60 GPa. We found no evidence for major structural transformations, even following laser heating experiments carried out at high pressure, although broadening of the Raman peaks could indicate the onset of disordering at higher pressure.     

High-pressure and high-temperature generation using diamond/sic composite anvils prepared with hot isostatic pressing

Using a hot isostatic pressing (HIP) technique, we synthesized diamond/SiC composites from diamond and Si powders. At an HIP condition of 1450 °C and 100 MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond/SiC composites. Cubes of the composites with 15 mm edge length were thereby fabricated, and an application to the second stage anvils in a Kawai-type high-pressure apparatus was attempted. A hybrid anvils system using four cubes of the composites and four of the conventional WC was introduced and heating experiments up to 1600 °C became possible. Because the diamond/SiC composites are transparent to X-rays, the present system is applicable not only to diffraction studies but also to radiographic studies that need a larger window for an X-ray image.     

Effects of High-Pressure Treatment on the Sensory Quality of White Grape Juice

The effects of high-pressure treatment on the colour (objective measurement) and sensory characteristics of white grape juice were studied during storage at 4 °C for 60 days. Grape juice was subjected to three different treatments: 400 or 500 MPa at 2 u °C, and 400 MPa at 40 °C during 10 min. Untreated juice was used as control. Colour parameters (CIE L * a * b *), hue angle (tan m 1 b */ a *), chroma {( a * 2 + b * 2 ) 1/2 }, luminosity Q *{(10 2 log( L *) + 100} and saturation S *( C */ L *) were measured. Juices were evaluated for sweetness, acidity, off-flavour and aroma. High-pressure treatments did not affect the colour parameters of juice, and similar sensory characteristics were observed in both control and treated samples on the first day. The colour and sensory characteristics of pressure-treated samples remained more stable than those of the control juice during 60 days of storage. The control juice was slightly fermented developing some changes in flavour and colour.