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Gas pycnometry and mercury porosimetry are used to investigate the porous network of Gilsocarbon nuclear graphite samples that are representative of the material present in the cores of UK Advanced Gas-Cooled reactors at different stages of the reactors' operational lifetimes. Irradiation and radiolytic oxidation change the pore volume of nuclear graphite and the relative ratios of open (coolant gas accessible) and closed pore volume. Particular focus has been paid to the deformation of the Gilsocarbon graphite observed during mercury intrusion at high pressure, which has previously marred the use of porosimetry to characterise this material. The results show clear trends in the evolution of the Gilsocarbon graphite porous space. Semi-quantitative deductions are made that will assist the modelling of the evolution of the pore space in the context of the safe extension of the reactors' working lifetimes. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: A range of calcium carbonate-based tablets and paper coating layers, with latex or starch as binder, were prepared. Their dry porous structures were analysed by mercury porosimetry. Some of these samples were also examined by electron microscopy. The porous space of these structures has been simulated using a network model named Pore-Cor, which creates network structures with percolation behaviour and porosity matching those of the experimental sample. Representative particles were grown between the cubic pores and cylindrical throats of the void network model until they touched up to four of the adjacent void features. The sizes of these representative particles, or skeletal elements, have been previously shown to be realistic for the case of unconsolidated sand and glass beads. The size distributions of these skeletal elements were compared with each other and with experiment using a Mann–Whitney test. The sizes of the skeletal elements were found to increase with the particle size of the calcium carbonate powder. The properties of the binders, used in the paper coating formulations, were found to have a major influence on the sizes of the skeletal elements, whose sizes also increased with coating thickness. These findings give insights into the wet structure and the drying process of paper coatings. [Copyright &y& Elsevier]

In nuclear graphite, the wide range of void sizes precludes a full characterisation of pore volume by means of a single technique. A novel multi-technique approach, consisting of pycnometry, low pressure gas adsorption and mercury porosimetry is presented. The approach is validated for two nuclear-grade graphites designed for use in Generation IV nuclear reactors, namely IG-110 and IG-430. Damage and deformation caused to the structure of the graphite by mercury intrusion is estimated by consecutive intrusion experiments. The damage is assumed to be caused by the highest applied pressures of mercury. It is compensated by substituting that part of the percolation curve with one derived from adsorption measurements. The various measurements are inverse modelled in a way which intelligently bridges the size gap between the techniques. The resulting complete non-hierarchical pore structure covers sizes spanning 4 orders of magnitude. The new approach resolves the long standing issues associated with performing porosimetry on graphitic samples, and fills the gap in knowledge for the assessment of multilevel porosity within graphite. As an example of the possible applications of the resulting void network structure, we calculated the air network flow capacity, related to absolute permeability, for the two graphite samples. [ABSTRACT FROM AUTHOR]

Abstract: The cores of the fourteen Advanced Gas-cooled nuclear Reactors (AGRs) within the UK comprise Gilsocarbon graphite, a manufactured material surrounded predominantly by CO2 at high pressure and temperature to provide heat exchange. The intense ionising radiation within the reactors causes radiolytic oxidation, and the resulting mass loss is a primary factor in determining reactor lifetime. The void structure of the porous Gilsocarbon graphite affects the permeability and diffusion of the carbon dioxide, and the sites of oxidation. To model this void structure, the porosities and densities of ten virgin Gilsocarbon graphite samples have been measured by powder and helium pycnometry. For comparison, results are also presented for highly ordered pyrolytic graphite (HOPG), and a fine-grained Ringsdorff graphite. Samples have been examined at a range of magnifications by electron microscopy. Total porosities and percolation characteristics have been measured by standard and cyclic mercury porosimetry up to an applied mercury pressure of 400MPa. Inverse modelling of the cyclic intrusion curves produces simulated void structures with characteristics which closely match those of experiment. Void size distributions of the structures are presented, together with much Supplementary Information. The simulated void networks provide the bases for future simulations of the radiolytic oxidation process itself. [Copyright &y& Elsevier]

Agricultural soils are a major source of nitric oxide (NO) and nitrous oxide (N 2 O), which are produced and consumed by biotic and abiotic soil processes. The dominant sources of NO and N 2 O are microbial nitrification and denitrification. While N 2 O emissions have been attributed to both processes, depending on the environmental conditions such as substrate availability, pH and water filled pore space (WFPS), NO emissions are thought to predominantly derive from nitrification. Although attributing gaseous emissions to specific processes is still difficult, recent findings challenge the latter of those assumptions. Using the gas-flow-soil-core method, i.e soil cores incubated under a He/O 2 atmosphere at constant surface gas flow, combined with 15 N labelled isotopic techniques, the present study investigated the role of denitrification on NO, N 2 O and N 2 emissions in a UK grassland soil under high soil moisture and an aerobic headspace atmosphere. With the application of KNO3 and glucose to support denitrification, denitrification was the source of N loss of between 0.61 and 0.67% of the added N via NO emissions, 1.60–1.68% via N 2 O and 0.03–0.05% via N 2 emissions. Overall, our study showed that denitrification has been overlooked as a source of NO emissions. [ABSTRACT FROM AUTHOR]

An algorithm has been developed for the a priori calculation of tortuosity in a simulated void network, assuming a Markovian random walk process, with paths identified using the algorithms of Yen and Dijkstra, and path searching extended by successive pruning of the network graph. The void network is derived from the inverse modelling of percolation characteristics derived from mercury intrusion porosimetry. Experimental tortuosities have been determined for two porous limestones and one porous sandstone, by measuring the electric conductivity of inter-pore brine relative to that of the same quantity of bulk brine. A close match between simulation and experiment is obtained ( R 2 =0.95). Tortuosities are also calculated for larger charged particles and for viscous transport. Further validation is provided in the form of a sensitivity analysis of tortuosity with respect to network connectivity. The new approach is particularly useful for the many materials that can be characterised by mercury porosimetry or porometry, but for which tortuosity cannot be measured directly. It has applications in a wide range of areas of current interest, such as oil and gas engineering, nuclear reactor core modelling, filtration, catalysis, ceramics, membranes and soil science. [ABSTRACT FROM AUTHOR]

Although the Park Grass Experiment is an important international reference soil for temperate grasslands, it still lacks the direct extraction of its metaproteome. The identification of these proteins can be crucial to our understanding of soil ecology and major biogeochemical processes. However, the extraction of protein from soil is a technically fraught process due to difficulties with co-extraction of humic material and lack of compatible databases to identify proteins. To address these issues, we combined two protein extraction techniques on Park Grass experiment soil, one based on humic acid removal, namely a modified freeze-dry, heat/thaw/phenol/chloroform (HTPC) method and another which co-extracts humic material, namely an established surfactant method. A broad range of proteins were identified by matching the mass spectra of extracted soil proteins against a tailored Park Grass proteome database. These were mainly in the categories of "protein metabolism", "membrane transport", "carbohydrate metabolism", "respiration" "ribosomal and nitrogen cycle" proteins, enabling reconstitution of specific processes in grassland soil. Protein annotation using NCBI and EBI databases inferred that the Park Grass soil is dominated by Proteobacteria , Actinobacteria , Acidobacteria and Firmicutes at phylum level and Bradyrhizobium , Rhizobium , Acidobacteria , Streptomyces and Pseudolabrys at genus level. Further functional enrichment analysis enabled us to connect protein identities to regulatory and signalling networks of key biogeochemical cycles, notably the nitrogen cycle. The newly identified Park Grass metaproteome thus provides a baseline on which future targeted studies of important soil processes and their control can be built. Identification of the Park Grass Experiment soil metaproteome using Complementary extraction methods. Soil samples processed by surfactant or modified heat thaw phenol chloroform (HTPC) methods, purified and applied to Gel Top. Proteins were then processed and identified using mass spectrometry and a compatible soil protein database. Protein identities were sorted into functional groups and linked to organism data through NCBI and EBI. Data is used to compare extraction processes and present an overall picture of the main processes in the Park Grass microbiome. These processes are linked to the Park Grass metadata repository. [Display omitted] • Complementary protein extraction methods identified 1266 proteins from Park Grass soil • Proteome enriched in ribosomal, respiratory and nitrogen cycle associated proteins • Identification of regulatory and signalling proteins in key biogeochemical cycles • Connects metaproteome to microbiome and biogeochemistry of Park Grass soil • Provides baseline metaproteome for future targeted studies [ABSTRACT FROM AUTHOR]

This work analyses the applicability of the Lucas–Washburn equation to experimental observations of imbibition into real network structures. The experimental pore structures used in this study are constructed from tablets of two finely ground calcium carbonates, with defined differences in particle size distribution. These are compressed under a range of different applied pressures to achieve a controlled series of porosities while maintaining the surface chemical, particulate and morphological pore characteristics constant. The porosities are determined by mercury intrusion porosimetry applying corrections for mercury compression and penetrometer expansion together with a correction for sample skeletal compression (Gane et al., J. Am. Chem. Soc., 35 (1996)). Imbibition studies are made by bringing each porous sample into contact with a supersource of liquid and the dynamic imbibition is recorded gravimetrically. Results follow a long timescale macroscopic absorption rate depending on the square root of time but show a failure to scale according to pore size in the Lucas–Washburn equation even though the constants of surface energy, contact angle and fluid viscosity have been maintained. Furthermore, values of average measured pore radius are shown to be finer than the Lucas–Washburn predicted equivalent hydraulic capillary radius. The predominance of a relevant pore size within a given pore size distribution forming a selective pathway filling based on inertial retardation of larger pores and short-term linear time wetting in finer pores is argued to account for the departure from simple pore size scaling. [Copyright &y& Elsevier]