Determination of the Heat of Adsorption and Desorption of a Volatile Organic Compound Under Dynamic Conditions Using Fourier‐Transform Infrared Spectroscopy

Quantitative Fourier‐transform infrared spectroscopic analysis was used for the determination of adsorption capacity of a model volatile organic compound (VOC) under dynamic conditions. The analytical method used also offers the possibility of distinguishing between reversible and irreversible adsorption as well as further detection of adsorbed VOC transformation. The obtained adsorbed amounts have been used for the determination of the heat of adsorption and the activation energy of desorption using, respectively, isosteric and temperature programmed desorption methods. The approach has been applied to explore the potential use of local clay as an adsorbent material for VOC pollutants.     

Neutron diffraction experiments in diamond and sapphire anvil cells

Diamond anvil cells (DAC) provide the highest static pressures ≥1?Mbar. Because of the low intensity of neutron sources, for a long time it was thought impossible to use DAC or other anvil cells in neutron experiments. We describe pressure cells with diamond and sapphire anvils and neutron instrumentation allowing neutron diffraction experiments to be carried out under pressures as high as 50?GPa, temperatures down to 0.1?K, and applied magnetic fields up to 7.5?T.     

Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Electrical conductivities of pyroxenite were measured between frequencies of 10^?1 and 10⁶ Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe₃O₄, Fe+FeO and Mo+MoO₂) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe₃O₄, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm³/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.     

Effect of gasketing and assembly design: a novel 10/3.5 mm multi-anvil assembly reaching perovskite pressures

A new design of multi-anvil assembly and modified gasket characteristics with octahedron and truncation edge lengths of 10 and 3.5 mm is presented for reaching pressures and temperatures over 24 GPa and 2000 °C, respectively. Partially dehydroxylated pyrophyllite half-gaskets with a tapered design fully nesting the octahedron have been employed to prevent excessive octahedron extrusion between the cubes. The assembly utilizes an axially placed thermocouple through the octahedral center, allowing two samples to be present at identical high P–T conditions on either side of the thermocouple during a run. A third sample can be used as a packing around the thermocouple, so long as that sample is inert with respect to the thermocouple and surrounding material. The temperature gradient within the sample locations has been well characterized using two-pyroxene thermometry in the CaO–MgO–SiO₂ system and numerical modeling calculations. The results indicate a good agreement in gradient shape, although the numerical model appears to under-estimate the magnitude of temperature change. The assembly maintains stable temperatures and provides low failure rates.     

Grüneisen parameter for HCP iron at extreme compression

The Thomas–Fermi approximation gives the Grüneisen parameter γ=γ_∞=1/2 for all materials at extreme compression (P→∞ or V→0). After re-analyzing the existing experimental data of volume dependence of Grüneisen parameter γ of hexagonal close-packed (HCP) iron, we find that γ=1/2+a(V/V ₀)^1/3+b(V/V ₀) ⁿ , where a, b and n are constants. Based on this new form of γ, the second Grüneisen parameter q, the Debye temperature θ_D and the shear sound velocity v _s of HCP iron are discussed in the present work. It is found that the zero pressure second Grüneisen parameter q ₀=0.654, which is consistent with the previously determined value of HCP iron for Earth's core physics from Dubrovinsky et al. The calculations for the Debye temperature and the shear sound velocity are also found to be in good agreement with the experimental data.     

High P–T Brillouin scattering study of H2O melting to 26 GPa

The properties of solid and liquid phases of H₂O at high pressure and temperature remain an active area of research. In this study, Brillouin spectroscopy has been used to determine the temperature dependence of sound velocities in H₂O as a function of pressure up to 26 GPa through the phase field of ice VII and into the liquid to a maximum temperature of 1200 K. The Brillouin shift of the quasi-longitudinal acoustic mode moves to lower frequencies upon melting at each pressure. As a test of the method, measurements of the melting of Ar by Brillouin scattering at several pressures show a similar behavior for the acoustic mode, and measured melting points are consistent with previous results. The results of H₂O melting are consistent with previously reported melting curves below 20 GPa. The data at higher pressure indicate that ice melts at a higher temperature than a number of previous studies have indicated.     

Low temperature,high pressure Raman study of SbSBr

Abstract

We have measured the Raman spectra of the quasi-one-dimensional crystal SbSBr as a function of pressure at 295, 70, 37 and 25 K.

The pressure coefficients of the observed Raman modes have been determined and used to distinguish inter-from intrachain modes. Spectral features characteristic of the ferroelectric phase have been attributed to impurities or lattice imperfections and not to the presence of the ferroelectric phase, providing indication that the para-to ferroelectric phase transition occurs below 25 K.     

Measurements of saturated basic and acidic rock electrical conductivities at lower crustal temperatures and high pressures

Abstract

Laboratory measurements of the electrical conductivity of brine saturated acidic and metabasic rocks were done at confining pressures up to 0.2 GPa, high pore pressures and temperatures of 900°C. Acidic rocks showed conductivities insufficient to explain the lower crustal high conductivity layer. Basic rocks, however, showed conductivities consistent with the high conductivity layer at those temperatures that the layer is thought to possess.     

A low-temperature high-pressure apparatus with a temperature control system

Abstract

A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm³. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.     

Electronic structure of platinum at ultrahigh pressure

Abstract

Platinum is studied, theoretically, under very high compression. The calculated equation of state is found to agree well with the recent experimental data. At V/V₀ = 0.4, where V₀ is the experimental equilibrium volume, we find a transition from the face centered cubic structure (fcc), found at ambient pressure, to the body centered cubic structure (bcc). The calculated transition pressure is 26 Mbar. The stabilization of the bcc structure is explained by the eigen value sum.