Development of a trace gas stable isotope capture system in a mobile laboratory for temporal and spatial sampling of field and laboratory experiments

We describe the development of a novel mobile field laboratory, purposely designed for the automated capture and subsequent stable isotopic analyses of multiple gas samples. The multiple capture system is integrated into a mobile laboratory that is fully capable of measuring the concentration of carbon dioxide, methane and nitrous oxide trace gases in a flow-through system connected to a gas chromatograph fitted with both electron capture and flame ionisation detectors. The capture of gases is achieved by routing samples through a series of 135 mL gas flasks that are sealed by micro-solenoid valves triggered by a timing system. Trace gas light stable isotope ratio mass spectrometry can then be carried out on gas samples collected by the system (NERC (15)N Stable Isotope Facility). The excitingly unique potential of the system to the ecological research field is that it will allow the collection of cyclical data for three different trace gases both in real-time and in situ. We present data arising from the validation of this mobile system as well as a preliminary experimental assessment of this technique. This technique was used to measure delta(13)C in CO(2) and CH(4) in soil gases released from waterlogged cores and delta(13)C-CH(4) values were significantly depleted in wet cores compared with dry ones (p < 0.001).     

A model for light impurities in metals

The feasibility of studying the energetics of light impurities in metallic hosts by treating the impurity ion plus its screening cloud as a unit, or “quasi-atom”, is explored. In the simplest approximation the energy of the impurity is given in terms of the local host electron density. This approach is tested against results taken from the literature for the energy of light atoms in inhomogeneous electronic environments. Corrections to the simplest approximation are discussed.     

Surface structure of liquid Li and Na: an ab initio molecular dynamics study

Molecular dynamics simulations of the liquid-vapor interfaces of liquid metals have been performed using first principles methods. Results are presented for liquid lithium and sodium near their respective triple points, for samples of 2000 particles in a slab geometry. The atomic density profiles show a pronounced stratification extending several atomic diameters into the bulk, which is similar to that already experimentally observed in liquid K, Ga, In, and Hg.     

Penalty-based sequencing strategy implemented within a knowledge-based system

A hot dip coating line (HDCL) is used to coat steel coils with a corrosion-resistant coating. The sequencing of the coils going into a HDCL is important to ensure that the required coating quality of each coil is achieved and that production through the facility is maximised. In this paper, the logic used in a knowledge-based sequencing system for a HDCL will be outlined. Also, how the original knowledge-based system logic was modified to include a penalty-based heuristic sequencing strategy that resulted in much-improved HDCL coil sequences will be discussed. The enhanced version of this system has been in routine use since January 1994.     

CoMFA Analysis of Biodegradability

Abstract

CoMFA (comparative molecular field analysis) has been used to correlate the biodegradability of several classes of compounds. The technique uses an atomic probe to detect the steric and electrostatic fields around a molecule. Good cross-validated correlations were obtained for some series (alcohols, carboxylic acids and linear alkyl benzene sulphonates). Correlations were weaker for esters and benzene sulphonates, and were non-existent for phenols. These results may reflect the unreliability of biodegradation data, but may also be a result of molecular misalignment in the CoMFA procedure. CoMFA appears to be a potentially very useful method for the prediction of biodegradability.     

Inhibition of metal dusting of Alloy 800H by laser surface melting

Metal dusting is a catastrophic carburisation phenomenon that occurs at temperatures of 450-850 °C in atmospheres of high carbon activity. The resistance of alloys to corrosion, including metal dusting, relies on the formation of a dense, adherent oxide layer that separates the alloy from the corrosive environment. For such an oxide layer to be protective, it must achieve full surface coverage, be crack-free and be established before significant material degradation has occurred. Formation of a protective oxide scale can be enhanced by increasing the population of rapid diffusion paths for the protective elements (e.g. Cr and Al) to reach the alloy surface.In this work, laser surface melting has been used to improve the metal dusting resistance of Alloy 800H by creating a rapid solidification microstructure and, thereby, increasing the density of rapid diffusion paths. Oxidation during laser processing has been found to be detrimental to metal dusting resistance. However, it has been demonstrated that the resulting oxide can be removed without compromising metal dusting resistance.Results of exposure to a metal dusting atmosphere (20% H₂ and 80% CO at 650 °C) are presented. Samples have been examined in plan and cross-section using optical and scanning electron microscopy (SEM). Selected samples were also examined by electron probe microanalysis (EPMA) and X-ray diffraction (XRD).