Browsing by Author "Wijayasinghe, A."

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    Investigation of Electrical Properties in Different Structural Varieties of Sri Lankan Graphite
    (Uva Wellassa University of Sri Lanka, 2011) Thusyanthy, C.; Amaraweera, G.; Attanayake, N.; Wijayasinghe, A.
    Note: See the PDF Version Graphite is a crystalline polymorphic form of elementary carbon and it consists of parallel sheets of carbon in a hexagonal arrangement. Graphite is a soft mineral with black lead streak having a metallic luster. Sri Lanka is the world's only significant source of crystalline vein graphite. It is very popular all over the world for its high purity and its high carbon content graphite (97-99%) (Herath, 1995). Sri Lankan natural graphite is exported as a cheap raw material and the only local graphite based industry is the pencil industry. Sri Lankan natural vein graphite is found in various morphologies with different structural and physical characteristics (Balasooriya and Bandaranayake, 2010). Four common morphologies of vein graphite have been identified from the Bogala and Kahatagaha-Kolongaha mines. They are coarse flakes of radial graphite, coarse striated-flaky graphite, needle platy graphite and shiny-slippery-fibrous graphite. Natural graphite is a host material for lithium intercalation and there is a potential of using it as an active anode material for the rechargeable lithium cells. Among the requirements to be such an active anode material, electrical conductivity is a main factor and the candidate material should possess sufficient conductivity in the order of around 102 Scnil at operating temperature to support the anode function (Pushpaka et al, 2008). Further, there is only very limited work reported on morphology and structural characteristics of Sri Lankan natural graphite. Any information on the electrical behavior of them, specially the electrical conductivity, has not yet been reported elsewhere. By considering these factors, this study was performed to identify suitable verities of Sri Lankan graphite based on their electrical conductivity.
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    Purification of Low Grade Quartz Bearing River Sand
    (Uva Wellassa University of Sri Lanka, 2018) Kalubowila, C.N.; Garthiga, Y.; Amaraweera, T.H.N.G.; Wijayasinghe, A.
    The demand for the high-grade quartz is increasing rapidly with the advancement of semiconductor and photovoltaic industries. Therefore, it is essential to enhance the purity of low grade quartz. Quartz bearing gravel, quartzite and, river and beach sand are the major low-grade silica sand deposits in Sri Lanka. In this study, a method was investigated to remove impurities in quartz bearing river sand depending on its mode of occurrence. Microscopic analysis implies that the impurities in the silica sand are present as mineral grains, coatings, interlocking grains and inclusions. In the physical purification process, sieving was carried out to separate river sand according to the grain size. The highest weight percentage of river sand is in the size range between 0.5 and 0.15 mm. This portion consists of more than 90% of quartz. Therefore, physical separation, depending on the grain sizes, can effectively use to remove the mineral grains present as impurities in quartz grains. Panning together with scrubbing and washing was carried out to remove the clay particles, heavy minerals and other undesirable materials present in the river sand. A chemical purification of physically separated river sand was carried out by acid leaching with 5 - 30 vol. % of HCl solutions in the temperature range between 27 and 100 °C. The mineralogical analysis and X-ray diffraction analysis imply the possibilities to remove iron oxide coating from the surface of quartz grains with low concentration of HC1, at low temperature. Accordingly, this physical separation and chemical treatment process is a more effective method to purify the low-grade river sand suitable for the advanced technological applications.
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    Synthesis of Expanded Graphite using Sri Lankan Vein Graphite via Ultrasonication
    (Uva Wellassa University of Sri Lanka, 2018) Senavirathne, M.M.K.R.N.D.; Kanagaratnam, J.N.; Amaraweera, T.H.N.G.; Wijayasinghe, A.
    Sri Lankan vein graphite, which is found in highly crystallized form with high purity (95 - 99 % carbon), have already been successfully developed for the anode of the lithium ion rechargeable battery. However, for their use in future energy storage applications, such as in sodium ion batteries, modification of the vein graphite structure is essential. Hence, this study focuses on structural modification of purified vein graphite by converting into expanded graphite via solvent assistant ultrasonication. Graphite oxide was synthesized from purified vein graphite by employing improved Hummer's method and then sonicated with propylene carbonate. The dried product was heated and again subjected to sonication with the same solvent. Then the solution was centrifuged to remove any non exfolliated graphite. Finally, the solution containing Graphite Oxide (GO) particles in PC were thermally reduced to produce reduced graphite oxide (rGO-PC). X-ray diffraction of crystal phase of the resulted graphite oxide shows the existence of a broad peak at 23.19 ° (20) corresponding to an interlayer spacing of 0.38 nm. The Fourier transform infrared spectrum obtained on the synthesized GO confirm the presence of O -H, C=O, COOH and C-0 oxygen functionalities, which are then, confirm to be partly removed by the successive thermal treatment. Scanning electron microscopic images are evidence for the expanded structure with wrinkles and folded nature in contrast to the opaque and smooth structure observed in the pristine graphite. Altogether, these results confirm the successful formation of expanded graphite by the solvent assisted ultrasonication technique.