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Research Activities in the
Physical Sciences

- Photonic Crystal Fibres

- Structured Wood Composites

- Membrane Fouling and Cleaning
- Glazes on Ceramics
- Fibre Reinforced Composites
- Polyvinyl Acetate Composites
- Lead/Acid Batteries
- Hydroxyapatite Coating Methods
- Rare Earth Glasses
- Vapour Deposition of Films

Photonic Crystal Fibre
Researchers are investigating the behaviour of photonic crystal fibre produced in the form of a long thread of silica glass with a periodic array of air holes running down its length. They are interested in the theory of light propagation in the fibre and are experimenting with changes to its structure and fabrication. Possible uses are as a low loss waveguide with novel properties for communications and for sensing applications. Scanning Electron Microscopy provides high resolution imaging of the fibre cross-sections enabling fabrication quality to be assessed and microfeatures analysed.
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Mechanical Properties of Structured Wood Composites The main thrust of work on wood mechanics is centred on the mechanical properties of structural wood composites , including laminated wood veneer lumber (LVL), glulam and particle, flake and fibreboards. There is special emphasis on the joining of timber structures, the fatigue and creep response of wood composites, and the environmental credentials of wood. Scanning Electron Microscopy is fundamental to gaining an understanding of the microstructure of these materials, which closely links to macroscopic properties.
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Membrane Fouling and Cleaning Scanning Electron Microscopy and Atomic Force Microscopy techniques have been used in the characterisation of the effects of multiple fouling and cleaning cycles upon the performance of filtering membranes in the food industry. Work is ongoing to determine whether steady state filtration performance of yeast and whey protein solutions used in the brewing industry are affected by the prior fouling and cleaning regimes that are used.
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Glazes on Ceramic Bodies
Concerns about the possible dangers to health of the presence of lead in conventional ceramic glazes have given urgency to the search for leadless alternatives. In the development of suitable replacement material polished sections of the glaze-ceramic interface can be examined in the Scanning Electron Microscope using both primary (backscattered) and secondary electron imaging. Backscattered electrons highlight small changes in atomic number between microscopic components which can be analysed using Energy Dispersive X-ray Analysis. During firing the glaze becomes fluid and attacks the underlying ceramic body. As a result an interaction layer is developed in the glaze body interface. X-ray Microanalysis enables the complex chemistry to be understood. The reactions at the glaze layer play a major role in determining the properties of the ceramic article such as strength, hardening and thermal expansion.
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Densified Natural Fibre Reinforced Composites The aim of the research is to develop highly densified natural fibre-reinforced composites with maximum fibre and minimum resin content. Natural resins , formulated from cashew nut shell oil and rosin, produced in Tanzania, are to replace synthetic resins as the matrix phase. Scanning Electron Microscopy will be used to monitor the composite composition. Unique densified structures will be developed and useful engineering applications proposed
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Polyvinyl Acetate Composites and Adhesion
This collaborative work with the University of Zagreb is concerned with the properties of polymer films produced from polyvinyl acetate emulsions into which calcite fillers have been incorporated. Scanning Electron Microscopy is able to highlight the differences in loading level, surface area and shape of filler particles and the effect of surface treatment of the filler by different levels of stearic acid. It should then be possible to have a range of emulsions from which filled polymer films can be produced with a range of properties. Procedures for producing PVAc-metal bonds and for measuring the adhesion obtained have been established, and it is hoped that these will be further developed in the future.
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Valve Regulated Lead/Acid Battery Electron Microscopy and Analysis has played an important role in research carried out on the failure mechanisms of valve regulated lead acid batteries. Scanning Electron Microscopy has been used to study the morphological changes that occur in the lead dioxide positive material and lead active negative material during cycling by examining fracture surfaces of samples removed from the electrode grids. During battery operation a corrosion layer consisting of PbOn (2>n>1) forms on the surface of the positive electrode grid. The stoichiometry of the oxide determines the conductivity and will therefore influence battery operation. Cross sections of the corrosion layer have been produced using metalographic techniques and electron probe microanalysis used to quantitatively determine changes in oxide stoichiometry across the interface.
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Comparison of Hydroxyapatite Coating Methods for Orthopaedic Applications Hydroxyapatite has been reported to encourage direct apposition with bone, hence its use as a coating material to aid early fixation of orthopaedic prostheses. Several techniques can be used to apply such coatings but commercially the most commonly used are thermal spray processes. In this work hydroxyapatite coatings on titanium substrates have been produced using two thermal spray techniques—vacuum plasma spraying and detonation gun spraying. X-ray diffraction and optical microscopy were used to compare crystallinity, residual stresses and porosity. Scanning Electron Microscopy was used to characterise the surface morphologies of the coatings. The vacuum plasma sprayed coatings were found to have a lower residual stress, a higher crystallinity and a higher level of porosity than the detonation gun coatings. It was concluded that consideration needed to be given to the significance of such variations within the clinical context
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Rare Earth Metaphosphate Glasses
The properties and structure of various glasses doped with rare–earth elements such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er are being investigated. X-ray adsorption fine structure and thermal expansion studies have been undertaken in addition to the study of elastic and nonlinear acoustic properties. Electron probe microanalysis has been carried out by the CEOS to determine the precise quantitative composition of each glass and determine any deviations from the R(PO3)3 , metaphosphate composition ,where R is the rare-earth element.
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Synthesis of Volatile Precursors for the Chemical Vapour Deposition (MOCVD) of Doped Films
Work is being carried out to synthesise a number of novel precursor complexes in order to deposit thin films of gas-sensing materials by metal-organic chemical vapour deposition (MOCVD) either at low pressure or by using a carrier gas at atmospheric pressure . Currently films of doped tin oxide and other p-block metal oxides are being produced. Their suitability is being assessed for the development of gas-sensing devices. Some of the factors that may be important in this include the degree of crystallinity, the magnitude of the grain boundaries and other physical characteristics. Wavelength Dispersive X-ray Analysis is able to assess the stoichiometry of the materials deposited on the substrates and Scanning Electron Microscopy used to examine the crystallinity of the films, the shape of the crystals , and the thickness of the crystalline films.
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