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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: “Stickies” are tacky species, present in recycled paper and coated broke, derived from coating formulations, adhesives etc. They impact negatively on paper quality and cause web runnability problems by deposit build-up. To sustain recycling, stickies are controlled by adsorbing them onto minerals added to the recycled stock. We report isotherms for a fatty acid ester defoamer and an acrylic acid ester copolymer adsorbing from colloidal suspension onto various talcs and modified calcium carbonates. We used commercial preparations of the fatty acid ester defoamer and acrylic acid ester copolymer to provide a simple analogue to the industrial process. The modified calcium carbonates are hydrophilic with anionic and cationic sites present. Adsorption isotherms for low surface area modified calcium carbonate conform to the Langmuir model, while those for high surface area modified calcium carbonate reflect a two stage process involving the formation of a monolayer over the mineral surface and subsequent partial aggregation. Talc platelets display hydrophilic edges and hydrophobic surfaces. Adsorption onto them appears to involve three stages; specifically, a hydrophilic interaction between hydrophilic groups on the molecules and the talc edges, followed by hydrophobic interactions between the molecules and the talc surfaces, and finally by formation of multilayers. [ABSTRACT FROM AUTHOR]

Abstract: Re-packed soil columns of the Crediton series were sown with white clover or perennial ryegrass, with nitrate managed according to organic and conventional farming regimes respectively. Visual observations revealed a rapid enhancement in soil structure beneath white clover compared to ryegrass and unplanted soil. Enhanced structural differentiation beneath white clover was supported by greater permeability to air and freer drainage to water. Differences in soil structure were verified by water retention measurements over a range of tensions between the wilting and gravity drainage points. The void structure was simulated with the Pore-Cor network model, which verified larger pores beneath clover, a difference in local structuring and a saturated hydraulic conductivity which was four times greater than ryegrass. The study highlighted inadequacies in current approaches to the measurement and interpretation of water retention. [Copyright &y& Elsevier]

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]

Abstract: A void network model, named Pore-Cor, has been used to study the permeation of an ink solvent into paper coating formulations coated onto a synthetic substrate. The network model generated anisotropic void networks of rectangular cross-sectional pores connected by elliptical cross-sectional throats. These structures had porosities and mercury intrusion properties which closely matched those of the experimental samples. The permeation of hexadecane, used as an analogue for the experimental test oil, was then simulated through these void structures. The simulations were compared to measurements of the permeation of mineral oil into four types of paper coating formulation. The simulations showed that the inertia of the fluid as it enters void features causes a considerable change in wetting over a few milliseconds, a timescale relevant to printing in a modern press. They also showed that in the more anisotropic samples, fast advance wetting occurred through narrow void features. It was found that the match between experimental and simulated wetting could be improved by correcting the simulation for the number of surface throats. The simulations showed a more realistic experimental trend, and much greater preferential flow, than the traditional Lucas–Washburn and effective hydraulic radius approaches. [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]

Presents the Molecular Dynamics Simulator, a computer software package that provides a display of molecular motion in a solid, liquid or gas. Calculation processing; Molecular motion displays as tracks or as spheres.

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]

Abstract: Mineral particles are used in many industrial applications as fillers, in coatings, as ad- and absorbers or in catalysis. In these manifold fields the particle size and shape control the final performance and properties of the minerals. Much has been published using different techniques to describe the aspect ratio of platy particles. This study describes a simple method to calculate aspect ratios for platy particles based on particle size data and specific surface area determined by nitrogen adsorption, exemplified with three different talc grades which vary in their amount of specific surface area and geological origin, as well as with one nano-sized synthetic Laponite (Laponite® RD) to illustrate the sensitivity to input parameters and their physical interpretation. The contrast between mass/volume and number probability distribution of particle size is discussed and illustrated. [Copyright &y& Elsevier]

Abstract: Mineral particles are used in many industrial applications as fillers, in coatings, as ad- and absorbers or in catalysis. In these fields the particle size and shape may control the final performance and properties of the minerals. This work aims to develop a size distribution and surface area defined particle aspect ratio for rod-like particles, using a previously discussed improvement of the input parameters to the Hohenberger model. The tested aragonite particles were shown to have an aspect ratio of ~2 determined using laser scattering particle size data and surface area data, proven by image analysis. Palygorskite showed the limitation of the current model with respect to the surface area input parameter as measured by nitrogen adsorption due to its internal porosity. An aspect ratio of 21 of the fibrous material was calculated in contrast to the value of 7 found by image analysis. The calculation procedure can thus be recommended to approximate the aspect ratio of non-porous fibrous and rod-like particles in a fast, easy and reproducible way. [Copyright &y& Elsevier]

• Heterotrophic nitrification is an important source of N 2 O at low WFPS. • Similar contributions of nitrification, heterotrophic nitrification and denitrification occurred at medium WFPS level. • High N 2 O emissions result via nitrification coupled denitrification at medium & high WFPS. • Abiotic factors need to be considered as well as biotic factors to understand the cause of emissions. To identify the production and consumption pathways and temporal dynamics of N 2 O emitted from soil, this study uses 15N-labelled substrate-N to quantify the underlying gross N transformation rates using the Ntrace analysis tool and link them to N-emissions. In three experiments twelve soil cores each were incubated in a lab incubation system to measure gaseous emissions, while parallel incubations under the same conditions were set up for destructive soil sampling at 7 time points. Using the triple labelling technique (applying NH 4 NO 3 with either the NH 4 +-N or the NO 3 −-N, or both being 15N labelled), this study investigated the effects of 55, 70 and 85% water filled pore space (deemed to promote nitrification, both nitrification and denitrification, and denitrification, respectively) in a clay soil on gaseous N emissions and investigates the source and processes leading to N 2 O emissions. To assess the utilisation of applied NO 3 − vs. nitrified NO 3 − from applied NH 4 +, the 15N tracing tool Ntrace was used to quantify the rates of immobilisation of NO 3 − and NH 4 +, oxidation of NH 4 +, mineralisation of organic N and subsequent nitrification by the analysis of the 15N in the soil. Gross transformation rates were calculated, indicating the relative importance of added NO 3 − and NO 3 − derived from nitrified added NH 4 +. Results show an important contribution of heterotrophic nitrification (organic N oxidation to NO 3 −) which was highest at the 55% water filled pore space (WFPS), decreasing in its contribution to N-transformation processes with increasing WFPS, while nitrification (NH 4 + oxidation to NO 3 −) was contributing the most at 70% WFPS. The contribution of denitrification increased with increasing WFPS, but only became dominant at 85% WFPS. While denitrification still showed to be most important at high and nitrification at lower WFPS, the actual % WFPS values were not as expected and highlight the fact that WFPS is a contributor, but not the sole/most important parameter determining the type of N-transformation processes taking place. [ABSTRACT FROM AUTHOR]

Rationale: Isotopic signatures of N2O can help distinguish between two sources (fertiliser N or endogenous soil N) of N2O emissions. The contribution of each source to N2O emissions after N‐application is difficult to determine. Here, isotopologue signatures of emitted N2O are used in an improved isotopic model based on Rayleigh‐type equations. Methods: The effects of a partial (33% of surface area, treatment 1c) or total (100% of surface area, treatment 3c) dispersal of N and C on gaseous emissions from denitrification were measured in a laboratory incubation system (DENIS) allowing simultaneous measurements of NO, N2O, N2 and CO2 over a 12‐day incubation period. To determine the source of N2O emissions those results were combined with both the isotope ratio mass spectrometry analysis of the isotopocules of emitted N2O and those from the 15N‐tracing technique. Results: The spatial dispersal of N and C significantly affected the quantity, but not the timing, of gas fluxes. Cumulative emissions are larger for treatment 3c than treatment 1c. The 15N‐enrichment analysis shows that initially ~70% of the emitted N2O derived from the applied amendment followed by a constant decrease. The decrease in contribution of the fertiliser N‐pool after an initial increase is sooner and larger for treatment 1c. The Rayleigh‐type model applied to N2O isotopocules data (δ15Nbulk‐N2O values) shows poor agreement with the measurements for the original one‐pool model for treatment 1c; the two‐pool models gives better results when using a third‐order polynomial equation. In contrast, in treatment 3c little difference is observed between the two modelling approaches. Conclusions: The importance of N2O emissions from different N‐pools in soil for the interpretation of N2O isotopocules data was demonstrated using a Rayleigh‐type model. Earlier statements concerning exponential increase in native soil nitrate pool activity highlighted in previous studies should be replaced with a polynomial increase with dependency on both N‐pool sizes. [ABSTRACT FROM AUTHOR]

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]

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]

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]

RATIONALE This study aimed (i) to determine the isotopic fractionation factors associated with N2O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N2O production and reduction occurred simultaneously. METHODS Soil incubations were performed under a He/O2 atmosphere and the denitrification product ratio [N2O/(N2 + N2O)] was determined by direct measurement of N2 and N2O fluxes. N2O isotopocules were analyzed by mass spectrometry to determine δ18O, δ15N and 15 N site preference within the linear N2O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N2O production and reduction, taking into account emissions from two distinct soil pools. RESULTS A clear relationship was observed between 15 N and 18O isotope effects during N2O production and denitrification rates. For N2O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller. CONCLUSIONS The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η18O/η15N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The soil water release characteristic is controlled by the soil pores and so alteration of the pore system will have an effect. We sought to examine the effects of various pore deformations in a range of arabic and grassland soils from the UK. Sieved topsoil materials were compressed to 50 or 200 kPa, or remolded to simulate shear deformation at the plastic limit. They were then subjected to matric potentials from 0 to -1500 kPa using conventional tension and pressure plate apparatus. Volume changes were monitored to assess shrinkage. Further samples in the compressed state were subjected to x-ray computed tomography scanning to nondestructively characterize the soil pore system. Increasing the compression from 50 to 200 kPa mainly affected the >30μm pores, changing a dual porous system of inter and ineraaggregate pores to one mainly dominated by intraaggregate pores, as confirmed by gravimetric water release characteristic data and the scans. Shear-deformed soils retained more water than the compressed soil and shrank more, such that they remained tension saturated at low (negative) matric potentials. We developed a function to predict the soil saturation state as a function of matric potential and porosity. This explained 28 to 63% of the variance, irrespective of the initial structural state, but up to 94% of the variation when one of the fitted parameters was allowed to vary for the different initial states. This was sufficiently systematic to suggest that a general model of the effects of soil deformation and shrinkage on the water release characteristic may be possible. [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]