Some aspects of the analysis of coal by X-ray fluorescence spectroscopy

Bituminous coal samples from 84 distinct sources were analysed by conventional British Standards (BS) methods for phosphorus, sulphur, chlorine, ash and the ash-forming elements (calcium, silicon, aluminium, iron, sodium, magnesium, potassium, titanium and manganese). In most cases four determinations were made per element per source. Samples were crushed to ?212 μm (72 BS mesh) and pressed into aluminium cups at 20 t in^?2 (309 MPa) without binder or backing. Two pellets from each sample were analysed by wave-length dispersive X-ray fluorescence techniques, using a spectrometer equipped with a rhodium rube; the X-ray count took 60 s. The X-ray results were calibrated against the conventional results using multiple regression. The accuracy obtained was comparable with routine ‘wet chemical’ techniques. The X-ray technique is suitable for the routine determination of large numbers of samples.     

High resolution STEM/EDX spectral imaging to resolve metal distributions within ∼100 nm combustion generated ash particles

Ultrafine ash particles play an important role in establishing a sticky inner deposit layer on heat transfer surface for power plants, but it is still unclear whether a thin surface alkali coating on these ultrafine particles might control this deposition behavior. In this research, we used a high resolution FE-TEM/STEM equipped with twin SDD EDX detectors for high X-ray detection efficiency, to determine the presence and absence of surface enrichment of alkali metals on ultrafine solid fuel ash samples that had low bulk alkali compositions but high deposition rates. Results from two types of combustion generated nano-sized ash particles are presented. One was from the oxy-combustion of pulverized bituminous coal, the other from oxy-combustion of pulverized rice husks, both being burned in a 100?kW rated down-flow laboratory combustor. Elemental mapping results from STEM/EDX uncovered some surface enrichment of alkali metals in ultrafine ash particles, where it existed, as it did for combustion of rice husks. However, it was not able to discern similar alkali metal surface enrichment for the bituminous coal ultrafines that had resulted in even higher deposition rates. Since deposition rates from both of these cases lie on the same correlation with PM₁, one can conclude that although surface enrichment of alkali metals is present for some ～100?nm particles, it is not a prerequisite to achieve high inner surface deposition rates. This is in contrast to prevailing theories that point to alkali metals as “bad actors” as far as the sticky inner deposition rate is concerned.

Copyright © 2019 American Association for Aerosol Research     

Evidence for the Participation of Singlet Oxygen in the Vat–dye Photosensitized Degradation of Cellulose

A study has been made of the vat–dye photosensitized degradation of cellulose. Whilst the part played by the dyes in direct hydrogen abstraction from a cellulose substrate cannot be overlooked, it is apparent that the role played by singlet oxygen is important. The ability of a dye to produce singlet oxygen has been studied by measuring the amount of tetraphenylcyclopentadienone the dye can photo–oxidize. It would appear that the singlet oxygen is initially formed in its high energy g state by energy transfer from the triplet state of the dye to ground state molecular oxygen. Luminescence spectroscopy has been employed in order to gain information about the excited state energies of the dye molecules, and an electron spin resonance study of the dyes in rigid media has been carried out in order to obtain information about the triplet state.     

Property-composition relationships for diesel and kerosene fuels

A range of 18 diesel fuels and 21 kerosene fuels from mainly Australian petroleum and synthetic fuel sources, including coal, shale and peat, was investigated. Compositional details were defined as the weight per cent abundances of n-alkanes, branched plus cyclic saturates, single-ring aromatics, doublering aromatics and polynuclear aromatics, using both h.p.l.c. and ¹³C n.m.r. techniques. Relationships between fuel composition and a range of fuel properties were sought. Simple linear relationships between property values and compositional data were used. Explicit correlative expressions were derived using multiple linear regression analysis, with the coefficient of multiple determination, R², indicating the quality of the fit between observed and calculated property values. In most cases good correlations were achieved. For diesels the properties investigated, with R² values in parentheses, were: inverse specific gravity (0.99); ¹³C n.m.r. aromaticity (0.99); ¹H n.m.r. aromaticity (0.88); cetane index (0.97); aniline point (0.96); diesel index (0.98); and FIA-measured aromatics content (0.77). For kerosenes the properties, with R² values in parentheses, were: ¹³C n.m.r. aromaticity (0.98); ¹H n.m.r. aromaticity (0.97); smoke point (0.88); and FIA-measured aromatics content (0.94). The results are shown to be of value in assessing the potential and limitations of hydrotreating as a process for upgrading synfuels.     

Stress Analysis of Elastic-Plastic Contact Damage in Ceramic Coatings on Metal Substrates

An elastic-plastic analysis of damage in ceramic coatings on metal substrates from contacts with spherical indenters is made using finite element modeling. Computations are carried out specifically for plasma-sprayed alumina:titania on a soft steel. The algorithm assumes an elastic sphere with frictionless contact on a flat elastic-plastic layered specimen, and incrementally evaluates the expanding contact field as a function of applied load. Two key aspects of the contact field are examined: (i) the indentation stress-strain curve; (ii) the damage zone geometry. Composite coating/substrate indentation stress-strain curves are computed for two coating thicknesses, using input material parameters from iterative fits to data from control tests on free-standing coating and substrate materials. Contours of principal shear stresses, most notably those contours corresponding to yield zone boundaries in both the softer substrate and the harder coating, are mapped out in the fully plastic region. Corresponding distributions of tensile stresses are also mapped out, and are shown to correlate with the locations of transverse fractures in the coating. General implications concerning material and geometrical design of ceramic-based layer structures are discussed.     

In Situ Processing of Silicon Carbide Layer Structures

A novel route to low-cost processing of silicon carbide (SiC) layer structures is desribed. The processing involves pressureless liquid-phase cosintering of compacted power layers of SiC, containing alumina (Al₂O₃) and yttria (Y₂O₃ sintering additives to yield and yttrium aluminum garnet (YAG) second phase. By adjusting the β:α SiC phase ratios in the individual starting powders, alternate layers with distinctively different microstructures are produced: (i) "homogeneous" microstructures, with fine equiaxed SiC grains, designed for high strength; and (ii) "heterogeneous: microstructures with coarse and elongate SiC grains, designed for high toughness. By virtue of the common SiC and YAG phases, the interlayer interfaces are chemically compatible and strongly bonded. Exploratory Hertzian indetation tests across a bilayer interface confirm the capacity of the tough heterogeneous layer to inhibit potentially dangerous cracks propagating through the homogeneous layer. The potential for application of this novel processing approach to other layer architectures and other ceramic systems is considered.     

Layering garments during rest and exercise in the cold (8°C): wearer responses and comparability with selected fabric properties

How garments contribute to performance of the clothing system during wear is of interest, as is understanding the value of using fabric properties to inform end-use characteristics. To investigate the influences of layering upper-body garments, four fabrics were used to construct two first-layer garments (wool and polyester) and two outer-layer garments (wool and membrane laminate). Over six sessions, 10 moderately trained males wore each first-layer garment as a single layer and in combination with each outer-layer garment while resting, running and walking in cold environmental conditions (8 ± 1°C, 81 ± 4% RH). Here, the type of garment arrangement worn (fabric type or number of layers) had little influence on heart rate, core body temperature and change in body mass. Weighted mean covered skin temperature was warmer and weighted mean next-to-skin vapour pressure was typically higher (following the onset of exercise) with two layers versus one. Differences among fabrics for individual properties were typically overstated compared to differences among corresponding garments for physiological and psychophysical variables under the conditions of this study. These findings inform the interpretation of particular fabric properties and highlight issues to be acknowledged during development/refinement of fabric test methods.

Practitioner Summary: We examined the way in which selected fibre, fabric and garment (layering) characteristics contribute to performance of the clothing system during wear under cold conditions. Selected properties of the constituent fabrics were found to provide limited insight into how garments perform during wear under the conditions of this study.     

Processing and morphology of molecularly imprinted nylon thin films

The characterization of thin, selectively imprinted films of nylon‐6 was performed. Amino acids were used as template molecules. Spin‐cast films were prepared with sizes ranging from 2 μm to 300 nm, depending on the nylon and template concentration in the casting solution. The morphological characteristics of the film surface were examined by atomic force microscopy, and the structure within the films was observed by freeze‐fracture scanning electron microscopy. The film activity was clearly coordinated with the appearance of nanometer‐sized pores both on the surface and within the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2919–2926, 2006     

Modeling solute diffusion in aqueous polymer solutions

There are numerous models describing solute diffusion in polymer solutions. An analysis of these models demonstrates that none can provide a consistent explanation of the phenomenon observed for solutes that can be modeled as essentially solid spheres. For this reason, a new model based on a physical obstruction approach is presented. In this model, solute movement in the presence of polymer chains is assumed to be governed by the probability of the solute molecule encountering a series of openings between the chains larger than its hydrodynamic radius. The model is tested against data taken from the literature for a series of polymer solutions and solute probes and found to provide good agreement to the effects of solute size, polymer concentration, and polymer flexibility.     

Experimental Simulation of the Reactor Section of Fluid Cokers: Comparison of FCC and Fluid Coke Particles

The hydrodynamics of fluid cokers were studied in a pressurized fully cylindrical cold model of diameter 483 mm, geometrically and dynamically scaled down by a factor of ～20 from commercial units. Differential pressure fluctuations, voidage distributions, solids momentum flux distributions and steady state gas mixing behaviour in the reactor section are compared for the same operating conditions with two kinds of particles, FCC and fluid coke. The voidage distributions and core‐annular flow structures in the reactor section were similar enough that either FCC or fluid coke particles can be used for cold modelling of fluid cokers.