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Abstract: The addition of nano-fillers has been widely proposed as a method to enhance the dielectric properties of high voltage polymeric insulation, though there are mixed reports in the literature. Here the potential of silica nano-particles to extend the time to failure specifically through resistance to electrical tree growth in epoxy resin is determined. The benefit of silane treating the nano-particles before compounding is clearly established with regard to slowing tree growth and subsequent time to failure. The growth of trees in needle-plane samples is measured in the laboratory with loadings of 1, 3 and 5 wt% nano-filler. In all cases the average times to failure are extended, but silane treatment of the nano-particles prior to compounding yields much superior results. The emergence of a pronounced inception time before tree growth is also noted for the higher-filled, silane-treated cases. The average time to failure of silane-treated 5 wt% filled material was 28 times that of the unfilled resin. The improvement in performance between the nanocomposites with untreated and treated fillers is attributed to fewer agglomerations and improved dispersion of the filler in the treated cases. Measurements of Partial Discharge (PD) indicated significant differences in PD patterns during the growth of trees in the treated and untreated cases. This distinction may provide a quality control method for monitoring materials. In particular, long periods in which PDs were not measured were observed in the silane-treated cases. Visual imaging of tree growth in the unfilled material allowed the changing nature of the tree from fine to tree to dark tree to be observed as it grew. Corresponding PD measurements suggest the dark tree is gradually becoming conductive, and that growth of maximum PD measured is dependent on the relative rates of the growth of the tree and its carbonization. X-ray computer tomography identified significant differences in average tree channel diameters (a reduction from 2.8 µm to 2.0 µm for 1 wt% and 3 wt% cases). This implies that in addition to tree length changes, evaporated tree volumes also change and may explain the change in partial discharge characteristics observed.

Open Access

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Abstract: We report major advances in the analysis of synchrotron 3D datasets acquired from human healthy and carious dental enamel. Synchrotron tomographic data for three human carious samples and a non-carious reference tooth sample were collected with the voxel size of 325 nm for a total volume of 815.4 × 815.4 × 685.4 μm3. The results were compared with conventional X-ray tomography, optical microscopy, and focused ion beam-scanning electron microscopy. Clear contrast was seen within demineralised enamel due to reduced mineral content using synchrotron tomography in comparison with conventional tomography. The features were found to correspond with the rod and inter-rod structures within prismatic enamel. 2D and 3D image segmentation allowed statistical quantification of important structural characteristics (such as the aspect ratio and the cross-sectional area of voids, as well as the demineralised volume fraction as a function of lesion depth). Whilst overall carious enamel predominantly displayed Type 1 etching pattern (preferential demineralisation of enamel rods), a transition between Type 2 (preferential inter-rod demineralisation) and Type 1 was identified within the same lesion for the first time. This study does not intend to give extensive results on the different lesions studied, but to illustrate a new method and its potential application.

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Abstract: High-resolution synchrotron x-ray radiography with computed tomography is used to observe the evolution of porosity created by thermal exposure in two HMX-based polymer-bonded explosive compositions; LX-04 and BX-63. The measurements were made in situ, over an extended period of time, during which the samples were heated on a slow-rate thermal trajectory. The tests ended with thermal-runaway to ignition after which the samples were consumed by combustion. The primary means of damage appears to be from mechanical debonding of the HMX-binder interface with secondary contribution from chemical decomposition. Confinement and binder properties affect the amount of porosity and permeability that develops. Additionally, observations were made describing the emergence and structure of an internal ignition volume, the formation and transport of a pre-ignition melt layer, and how the early stages of combustion were affected by material morphology, mechanical confinement and melt. The contact angle between molten HMX and the fluoropolymer, Viton A, is also presented. For the first time we have time-resolved x-ray images of ignition in sufficient detail to verify the mechanism of cookoff in polymer-bonded explosive compositions.

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Abstract: Porosity is the term used to describe the voids in a rock. This porosity is made up of many pores which form a pore network. Pore scale displacement in fluid flow is relevant to a number of industrial and environmental applications. The characteristics of the pore network control the way in which fluid flow occurs throughout the network. Carbonate rocks have particularly complex pore networks due a range of post-depositional processes that modify pore size, shape and connectivity. Although the contributions of factors such as pore throat size and pore network connectivity on fluid flow are reasonably well understood, there is a limited understanding of the effect of pore topology. This research aims to provide a pore-scale picture of the dynamics of fluid flow in both single and multiphase immiscible flow through the use of digital image analysis of fluid flow experiments. The dynamics and patterns of interface displacement as well as the size distribution of trapped oil ganglia were visualised using 2D microfluidic experiments. Different pore topologies resulted in different oil recoveries, however the effect of pore topology was not constant across fluid pairs with different viscosity ratios. Pore size was shown to be a key factor in the recovery efficiency of polymer flooding. This demonstrates that microfluidic experiments offer a methodology to quickly assess a number of different pore topologies under different fluid flow conditions. A range of rock types were imaged in 3D using X-Ray micro-computed tomography to visualise and quantify the range of pore topologies which exist in carbonates. These pore systems were used to assess the reliability of using 2D digital image analysis for permeability prediction, and show that 3D digital image analysis is a far superior technique for reliable pore topological characterisation and permeability prediction. A highly correlated multi-linear regression between permeability and pore topological parameters shows the relevance of pore topologies in predicting permeability. In addition to the investigation of single phase flow in a range of different carbonate pore systems, an investigation into multiphase immiscible displacement in a single carbonate pore system has been conducted. Through the use of synchrotron X-Ray tomographic imaging of an experimental core-flood (oil-brine drainage followed by imbibition) insights into the dynamics of multiphase flow have been gained. The pathway followed by the non-wetting fluid during drainage is strongly linked to the pore topological parameters measured during the analysis of the experiment. Oil initially invades simple pores with low elongation, which are aligned with the flow direction, before invading increasingly complex pores, less aligned to the flow direction. A channelization of flow occurs associated with an area of large, elongate pores. This research demonstrates that pore topology, particularly elongation and orientation to flow direction, has a clear influence on flow and warrants further investigation.

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Abstract: Inorganic/organic hybrids have co-networks of inorganic and organic components, with the aim of obtaining synergy of the properties of those components. Here, a silica-gelatin sol-gel hybrid “ink” was directly 3D printed to produce 3D grid-like scaffolds, using a coupling agent, 3-glycidyloxypropyl)trimethoxysilane (GPTMS), to form covalent bonds between the silicate and gelatin co-networks. Scaffolds were printed with 1 mm strut separation, but the drying method affected the final architecture and properties. Freeze drying produced <40 μm struts and large ~700 μm channels. Critical point drying enabled strut consolidation and optimal mechanical properties, with ~160 μm struts and ~200 μm channels, which improved mechanical properties. This architecture was critical to cellular response: when chondrocytes were seeded on the scaffolds with 200 μm wide pore channels in vitro, collagen Type II matrix was preferentially produced (negligible amount of Type I or X were observed), indicative of hyaline-like cartilaginous matrix formation, but when pore channels were 700 μm wide, Type I collagen was prevalent. This was supported by Sox9 and Aggrecan expression. The scaffolds have potential for regeneration of articular cartilage regeneration, particularly in sports medicine cases.