The effect of the regular solution model in the condensation of protoplanetary dust

We utilize a chemical equilibrium code in order to study the condensation process which occurs in protoplanetary discs during the formation of the first solids. The model specifically focuses on the thermodynamic behaviour on the solid species assuming the regular solution model. For each solution, we establish the relationship between the activity of the species, the composition and the temperature using experimental data from the literature. We then apply the Gibbs free energy minimization method and study the resulting condensation sequence for a range of temperatures and pressures within a protoplanetary disc. Our results using the regular solution model show that grains condense over a large temperature range and therefore throughout a large portion of the disc. In the high temperature region (T > 1400 K) Ca-Al compounds dominate and the formation of corundum is sensitive to the pressure. The mid-temperature region is dominated by Fe(s) and silicates such as Mg2SiO4 and MgSiO3 . The chemistry of forsterite and enstatite are strictly related, and our simulations show a sequence of forsterite-enstatite-forsterite with decreasing temperature. In the low temperature regions (T < 600 K) a range of iron compounds and sulfides form. We also run simulations using the ideal solution model and see clear differences in the resulting condensation sequences with changing solution model In particular, we find that the turning point in which forsterite replaces enstatite in the low temperature region is sensitive to the solution model. Our results show that the ideal solution model is often a poor approximation to experimental data at most temperatures important in protoplanetary discs. We find some important differences in the resulting condensation sequences when using the regular solution model, and suggest that this model should provide a more realistic condensation sequence.Comment: MNRAS: Accepted 2011 February 16. Received 2011 February 14; in original form 2010 July 2

Application of 57Fe Mössbauer spectroscopy as a tool for mining exploration of bornite (Cu5FeS4) copper ore

Nuclear resonance methods, including Mössbauer spectroscopy, are considered as unique techniques suitable for remote on-line mineralogical analysis. The employment of these methods provides potentially significant commercial benefits for mining industry. As applied to copper sulfide ores, Mössbauer spectroscopy method is suitable for the analysis noted. Bornite (formally Cu5FeS4) is a significant part of copper ore and identification of its properties is important for economic exploitation of commercial copper ore deposits. A series of natural bornite samples was studied by 57Fe Mössbauer spectroscopy. Two aspects were considered: reexamination of 57Fe Mössbauer properties of natural bornite samples and their stability irrespective of origin and potential use of miniaturized Mössbauer spectrometers MIMOS II for in-situ bornite identification. The results obtained show a number of potential benefits of introducing the available portative Mössbauer equipment into the mining industry for express mineralogical analysis. In addition, results of some preliminary 63,65Cu nuclear quadrupole resonance (NQR) studies of bornite are reported and their merits with Mössbauer techniques for bornite detection discussed

Sourcing limestone masonry for restoration of historic buildings: a spectroscopic study

This study presents a combined Fourier transform (FT) mid-infrared, laser Raman and Commission internationale d’éclairage (CIE) L*a*b*system analysis of quarry-derived impure limestone and fallen masonry from a medieval listed building situated in the south east of England, to ascertain how spectroscopic information can be collectively employed to identify the most exacting possible replacement stone source.Data shows that subtle differences in [Al] and [Fe3+] octahedral and tetrahedral site occupancy in glauconite group clays registered in the mid-infrared [3530 cm−1/3620 cm−1] absorption ratio exerts some influence on L*Cab*hab*values. Increases in L*and Cabare associated with decreasing clay content. Theoverall weakness of correlations between infrared and visible range spectral attributes indicates multiple contributing sources to overall color. Evidence indicates that the degree of laser Raman induced background noise is related to the overall calcite content and that activators of fluorescence at 785 nmexcitation wave length may also contribute to rock color. The results are utilized to define closest matching quarry samples to the fallen masonry

A lumped bubble capacitance model controlled by matrix structure to describe layered biogenic gas bubble storage in shallow subtropical peat

Methane (CH4) accumulates in the gaseous phase in peat soils, being released to the atmosphere at rates higher than those for diffusion and plant‐mediated pathways. An understanding of the mechanisms regulating gas bubble storage in peat remains incomplete. We developed a layered capacitance model to compare the bubble storage ability of peat over different depths. A peat monolith (0.395 m × 0.243 m × 0.247 m) was collected from the U.S. Everglades and kept submerged for 102 days from a condition of minimum bubble storage to bubble saturation. Time‐lapse electromagnetic wave velocity and power spectrum data were used to estimate changes in both gas content and relative average dimensions of stored bubbles with depth. Bubble capacitance, defined as the increase in volumetric gas content (m3 m−3) divided by the corresponding pressure (Pa), ranges from 3.3 × 10−4 to 6.8 × 10−4 m3 m−3 Pa−1, with a maximum at 5.5 cm depth Bubbles in this hotspot were larger relative to those in deeper layers, while the decomposition degree of the upper layers was generally smaller than that of the lower layers. X‐ray computed tomography on peat sections identified a specific depth with a low void ratio, and likely regulating bubble storage. Our results suggest that bubble capacitance is related to (1) the difference in size between bubbles and peat pores, and (2) the void ratio. Our work suggests that changes in bubble size associated with variations in water level driven by climate change will modify bubble storage in peat soils

Phase transition and anomalous electronic behavior in layered dichalcogenide CuS (covellite) probed by NQR

Nuclear quadrupole resonance (NQR) on copper nuclei has been applied for studies of the electronic properties of quasi-two-dimensional low-temperature superconductor CuS (covellite) in the temperature region between 1.47 and 290 K. Two NQR signals corresponding to two non-equivalent sites of copper in the structure, Cu(1) and Cu(2), has been found. The temperature dependences of copper quadrupole frequencies, line-widths and spin-lattice relaxation rates, which so far had never been investigated so precisely for this material, altogether demonstrate the structural phase transition near 55 K, which accompanies transformations of electronic spectrum not typical for simple metals. The analysis of NQR results and their comparison with literature data show that the valence of copper ions at both sites is intermediate in character between monovalent and divalent states with the dominant of the former. It has been found that there is a strong hybridization of Cu(1) and Cu(2) conduction bands at low temperatures, indicating that the charge delocalization between these ions takes place even in 2D regime. Based on our data, the occurrence of energy gap, charge fluctuations and charge-density waves, as well as the nature of phase transition in CuS are discussed. It is concluded that some physical properties of CuS are similar to those of high-temperature superconductors (HTSC) in normal state.Comment: to be publishe

Non-aqueous sol-gel synthesis through a low-temperature solvothermal process of anatase showing visible-light photocatalytic activity

A novel, facile method based on a non-aqueous sol-gel solvothermal process has been developed to synthesise spherical TiO2 nanoparticles (NPs) in one pot. The reaction between titanium(IV) tert-butoxide (Ti[OC(CH3)(3)](4)) and benzyl alcohol was a simple process, which resulted in the formation of highly crystalline titania NPs with a small size of only 6 nm, and with a correspondingly high surface area. The chemical formation mechanism of the metal oxide NPs has been proposed, and the degree of surface hydroxyls (-OH groups) has been examined. The products of the synthesis were characterised by X-ray powder diffraction (XRPD) using the advanced whole powder pattern modelling (WPPM) method, high-resolution transmission electron microscopy (HR-TEM), thermo-gravimetric analysis (TGA), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The photocatalytic activity (PCA) was evaluated in both the liquid-solid phase, by monitoring the degradation of an organic dye (methylene blue (MB)) under UV-light irradiation, and in the gas-solid phase, by following the degradation of 2-propanol under UV and visible-light exposures. The synthesized titania powders not only exhibited excellent photocatalysis in the liquid-solid phase (under UV irradiation), but also possessed a superior PCA in the gas-solid phase under a visible-light exposure. The effects on the PCA of the very small crystalline domain size, surface composition and the presence of organic molecules due to the synthesis process of the TiO2 NPs were shown to account for this behaviour

NIR Spectroscopy of Selected Iron (II) and Iron (III) Sulphates

A problem exists when closely related minerals are found in paragenetic relationships. The identification of such minerals cannot be undertaken by normal techniques such as X-ray diffraction. Vibrational spectroscopic techniques may be applicable especially when microtechniques or fibre-optic techniques are used. NIR spectroscopy is one technique which can be used for the identification of these paragenetically related minerals and has been applied to the study of selected iron(II) and iron(III) sulphates. The Near–IR spectral regions may be conveniently divided into four regions (a) the high wavenumber region > 7500 cm-1 (b) the high wavenumber region between 6400 and 7400 cm-1 attributed to the first overtone of the fundamental hydroxyl stretching mode (c) the 5500-6300 cm-1 region attributed to water combination modes of the hydroxyl fundamentals of water, and (d) the 4000-5500 cm-1 region attributed to the combination of the stretching and deformation modes of the iron(II) and iron(III) sulphates. The minerals containing iron(II) show a strong, broad band with splitting, around 11000-8000 cm-1 attributed to 5T2g --> 5Eg transition. This shows the ferrous ion has distorted octahedral coordination in some of these sulphate minerals. For each of these regions, the minerals show distinctive spectra which enable their identification and characterisation. NIR spectroscopy is a less used technique which has great application for the study of minerals, particularly minerals which have hydrogen in the structure either as hydroxyl units or as water bonded to the cation as is the case for iron(II) and iron(III) sulphates. The study of minerals on planets is topical and NIR spectroscopy provides a rapid technique for the distinction and identification of iron(II) and iron(III) sulphates minerals