Identifying sources and processes controlling the sulphur cycle in the Canyon Creek watershed, Alberta, Canada

Sources and processes affecting the sulphur cycle in the Canyon Creek watershed in Alberta (Canada) were investigated. The catchment is important for water supply and recreational activities and is also a source of oil and natural gas. Water was collected from 10 locations along an 8?km stretch of Canyon Creek including three so-called sulphur pools, followed by the chemical and isotopic analyses on water and its major dissolved species. The δ(2)H and δ(18)O values of the water plotted near the regional meteoric water line, indicating a meteoric origin of the water and no contribution from deeper formation waters. Calcium, magnesium and bicarbonate were the dominant ions in the upstream portion of the watershed, whereas sulphate was the dominant anion in the water from the three sulphur pools. The isotopic composition of sulphate (δ(34)S and δ(18)O) revealed three major sulphate sources with distinct isotopic compositions throughout the catchment: (1) a combination of sulphate from soils and sulphide oxidation in the bedrock in the upper reaches of Canyon Creek; (2) sulphide oxidation in pyrite-rich shales in the lower reaches of Canyon Creek and (3) dissolution of Devonian anhydrite constituting the major sulphate source for the three sulphur pools in the central portion of the watershed. The presence of H(2)S in the sulphur pools with δ(34)S values ～30?‰ lower than those of sulphate further indicated the occurrence of bacterial (dissimilatory) sulphate reduction. This case study reveals that δ(34)S values of surface water systems can vary by more than 20?‰ over short geographic distances and that isotope analyses are an effective tool to identify sources and processes that govern the sulphur cycle in watersheds.     

Interfacial phenomena in microwave sintering

Microwave sintering of ceramics appears to offer some valuable advantages when compared to conventional sintering, including the potential for manipulation of microstructures. Although considerable work has been done on the bulk effects of microwave sintering, effects on grain boundaries and interfacial phenomena have received little attention. This paper is a review of the published work on the interfacial effects that occur during microwave sintering, with an emphasis on studies of zirconia ceramics.     

Interdimensional degeneracies in van der Waals clusters and quantum Monte Carlo computation of rovibrational states

Quantum Monte Carlo estimates of the spectrum of rotationally invariant states of noble gas clusters suggest interdimensional degeneracy in N-1 and N+1 spatial dimensions. We derive this property by mapping the Schrodinger eigenvalue problem onto an eigenvalue equation in which D appears as a continuous variable. We discuss implications for quantum Monte Carlo and dimensional scaling methods.     

Voltammetric behavior of the iron(II)-(III) and cerium(III)-(IV) couples in potentiometric titrations at constant current and amperometric titrations with two indicator electrodes

The voltammetric behavior at the rotated platinum electrode of the iron(II)-(lII) and cerium (III)-(IV) couples in sulfuric and hydrochloric acids has been investigated The iron and cerium couples are not reversible at a platinum electrode when current flows in the system, and the current-potential curves deviate considerably from those predicted on the basis of reversibility Titration curves for potentiometric titrations at constant current using one and two indicator electrodes are predicted from the current-potential curves and compared with the experimental curves.The degree of reversibility of the iron couple depends greatly on the pretreatment of the electrode The current-potential curves of the iron couple at a platinum electrode coated with a monomolecular film of platinum oxide approach reversibility while those at a clean electrode are highly irreversible Experimental and calculated titration lines for amperometric titrations using two indicator electrodes are compared, and the effects of medium and applied e.m.f. upon the characteristics of the titration curves are considered.     

Vitamine

Ohne Zusammenfassung     

Clathrate and inclusion compounds. 14. Variable temperature vibrational spectroscopic studies of monosubstituted cyclohexane guests in thiourea

Infrared and Raman spectra over the temperature range room temperature to 74K have been recorded for a range of inclusion compounds of thiourea containing monosubstituted cyclohexanes C₆H₁₁X (X =Cl,Br,I,CN,NCO) as guests. The liquid phase of all the cyclohexanes consists of an equilibrium mixture of axial and equatorial conformers, with the equatorial conformer being the more abundant. At room temperature the chloro, bromo and cyano substituted guests exist predominantly as the axial conformer, whereas the iodo and isocyanato substituted guests exist as a mixture of both conformers, but with the axial conformer being the more abundant. The iodocyclohexane inclusion compound was the only one to display a temperature dependent change in the intensity ratio of the conformer bands. This could be due to a change in the conformer ratio or to a structural phase change. J. E. D. Davies and V. A. Tabner,J. Incl. Phenom.,31, 99 (1998). Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 988–992, September–October, 1999.     

Single-step synthesis and interface tuning of core–shell metal–organic framework nanoparticles

Control over the spatial distribution of components in metal–organic frameworks has potential to unlock improved performance and new behaviour in separations, sensing and catalysis. We report an unprecedented single-step synthesis of multi-component metal–organic framework (MOF) nanoparticles based on the canonical ZIF-8 (Zn) system and its Cd analogue, which form with a core–shell structure whose internal interface can be systematically tuned. We use scanning transmission electron microscopy, X-ray energy dispersive spectroscopy and a new composition gradient model to fit high-resolution X-ray diffraction data to show how core–shell composition and interface characteristics are intricately controlled by synthesis temperature and reaction composition. Particle formation is investigated by in situ X-ray diffraction, which reveals that the spatial distribution of components evolves with time and is determined by the interplay of phase stability, crystallisation kinetics and diffusion. This work opens up new possibilities for the control and characterisation of functionality, component distribution and interfaces in MOF-based materials.

Core–shell metal–organic framework nanoparticles have been synthesised in which the internal interface and distribution of components is found to be highly tunable using simple variations in reaction conditions.