9 research outputs found
Characterisation of the porous structure of Gilsocarbon graphite using pycnometry, cyclic porosimetry and void-network modeling
file: :C:/pdf/1-s2.0-S000862231400164X-main.pdf:pdfThe 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
Improved Interpretation of Mercury Intrusion and Soil Water Retention Percolation Characteristics by Inverse Modelling and Void Cluster Analysis
This work addresses two continuing fallacies in the interpretation of percolation characteristics of porous solids. The first is that the first derivative (slope) of the intrusion characteristic of the non-wetting fluid or drainage characteristic of the wetting fluid corresponds to the void size distribution, and the second is that the sizes of all voids can be measured. The fallacies are illustrated with the aid of the PoreXpertÂŽ inversemodelling package.Anewvoid
analysis method is then described, which is an add-on to the inverse modelling package and addresses the second fallacy. It is applied to three widely contrasting and challenging porous media. The first comprises two fine-grain graphites for use in the next-generation nuclear reactors. Their larger void sizes were measured by mercury intrusion, and the smallest by
using a grand canonical Monte Carlo interpretation of surface area measurement down to nanometre scale. The second application is to the mercury intrusion of a series of mixtures of ground calcium carbonate with powdered microporous calcium carbonate known as functionalised calcium carbonate (FCC). The third is the water retention/drainage characteristic of a soil sample which undergoes naturally occurring hydrophilic/hydrophobic transitions. The first-derivative approximation is shown to be reasonable in the interpretation of the mercury intrusion porosimetry of the two graphites, which differ only at low mercury intrusion pressures, but false for FCC and the transiently hydrophobic soil. The findings are supported
by other experimental characterisations, in particular electron and atomic force microscopy
Mechanism of adsorption of actives onto microporous functionalised calcium carbonate (FCC)
Microporous âfunctionalisedâ calcium carbonate (FCC) has potential for use as a carrier for the controlled release of âactivesâ, by permeation and diffusion. We have investigated the nature of the FCC surface and the mechanism of adsorption of two typical actives, namely the anti-inflammatory drug aspirin and the flavour compound vanillin, from chloroform and aqueous ethanolic solutions. There is indirect evidence from the quantitative perturbation of TĂłth isotherms that their adsorption is hindered by a stagnant diffusion layer of water trapped in the micro-porosity of the FCC. To complement previous studies of the surface of FCC, it was also tested with the cationic probe benzyltrimethylammonium bromide and the anionic probe sodium 2-naphthalenesulphonate. Experimental procedures were validated by comparison with adsorption onto ground calcium carbonate and high surface area talc
Biochar improves fertility in waste derived manufactured soils, but not resilience to climate change
We present a soil manufactured from waste materials, which could replace the use of peat and topsoil in plant production and reduce the pressure on natural soil resources. We tested the effect of the manufactured soil on ecosystem functions and microbial communities with and without plants present, and with and without biochar addition (Experiment 1). The resilience of the soil in response to drought and flooding, and also the effect of biochar was also tested (Experiment 2). Biochar increased soil C and N regardless of plant presence and negated the effect of the plant on soil peroxidase enzyme activity. The manufactured soil was largely resilient to drought, but not flooding, with negative impacts on microbial communities. Results indicate that biochar could improve soil properties, but not resilience to climatic perturbations. Results suggest that manufactured soils amended with biochar could offer a useful alternative to natural soil in many contexts
Biochar improves fertility in waste derived manufactured soils, but not resilience to climate change
We present a soil manufactured from waste materials, which could replace the use of peat and topsoil in plant production and reduce the pressure on natural soil resources. We tested the effect of the manufactured soil on ecosystem functions and microbial communities with and without plants present, and with and without biochar addition (Experiment 1). The resilience of the soil in response to drought and flooding, and also the effect of biochar was also tested (Experiment 2). Biochar increased soil C and N regardless of plant presence and negated the effect of the plant on soil peroxidase enzyme activity. The manufactured soil was largely resilient to drought, but not
flooding, with negative impacts on microbial communities. Results indicate that biochar could improve soil properties, but not resilience to climatic perturbations. Results
suggest that manufactured soils amended with biochar could offer a useful alternative to natural soil in many contexts
Diffusion and Tortuosity in Porous Functionalized Calcium Carbonate
Calcium carbonate can be âfunctionalizedâ
by use
of etching agents such as phosphoric acid to create inter- and intraparticle
porosity with a range of morphologies. Functionalized calcium carbonate
has potential for use as a carrier for the delayed release of actives,
such as drugs, plant protection chemicals, and food additives such
as flavors. The drug or flavor is released slowly by permeation and
diffusion. In order to measure the effective rate of diffusion within
a range of morphologies, and hence gain insights into the optimum
mode of functionalization, the diffusion of vanillin in ethanol is
reported. Effective diffusion coefficients <i>D</i>â˛
were measured in a flow cell connected to a high performance liquid
chromatograph (HPLC). Samples were also subjected to mercury intrusion
porosimetry. The resulting percolation characteristics were inverse
modeled using the PoreXpert package to generate representative void
structures with estimated tortuosities. It is shown that the primary
particle size of a sample was a better predictor of <i>D</i>Ⲡcalculated from the experimental diffusion curves, and also
of the porosity-scaled tortuosity values, than the porosity or surface
area. There was also a correlation between intraparticle tortuosity,
scaled by porosity, and diffusion coefficient. The approach is validated
by experimental evidence from this and related studies