Browsing by Author "Wewegedara, W.G.C.N."

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    Preliminary Investigation on the Occurrence of Reddish Brown Colour in Zircon from Kolonna, Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2020) Rifkhan, M.N.M.; Wewegedara, W.G.C.N.; Jayasinghe, R.M.N.P.K.; Dharmaratne, T.S.; Malaviarachchi, M.A.S.P.K.; Rohana, C.
    Sri Lanka is famous for various types of gem minerals. From among these minerals, gemquality zircon is found in both primary and secondary deposits. Kolonna is a location where zircon is found in primary deposits with a reddish-brown colour. The main objective of this study was to investigate the occurrence of reddish-brown colour in zircon from Kolonna area. Although many factors could cause the colour of gem minerals, the colour of zircons is known to be produced by trace elements (transition metals, lanthanides, actinides, and REEs), radiation damage (radiation-induced color centers) and charge transfer. Five randomly selected reddish-brown zircon samples were selected for this study. All samples were translucent, highly fractured, sub-adamantine, and with euhedral to subhedral crystal form. Samples were analyzed with EDXRF, UV-Vis Spectrophotometer, and FTIR methods. The UV-Vis spectrum of these samples showed an increase in absorption towards the UV region and declines towards the NIR region with a shoulder at around 500 nm. This can be identified as a structurally defected colour center that may occur due to the radiation damage caused by radioactive elements such as U and Th. This was further confirmed by the U4+ peak at 654 and 690 nm. The U5+ peak at 6663 cm-1 in the FTIR spectrum further confirmed the presence of U in samples. This was confirmed by the EDXRF analyses that showed a trace amount of radioactive elements. The average weight percentage of U and Th were 0.06 and 0.02, respectively. It was also noted an occurrence of an OH- group indicated at 3196 cm-1 on FTIR spectra. This may be probably due to slight radiation damage caused by radioactive elements in zircon samples. This study revealed the presence of U which accounts for structural defects that form colour centers in reddish-brown zircon from the Kolonna region. Keywords: Absorption, Colour center, Cause of color, Zircon, Radiation
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    Purification of Vein Graphite by Alkali Roasting for Anode Material for Lithium ion Batteries
    (Uva Wellassa University of Sri Lanka, 2013) Wewegedara, W.G.C.N.
    Lithium Ion Battery (LIB) has been an attractive energy source since its birth because of its advantages over other power sources. Researches are carried out search alternative anode materials as the high cost of production of commercially used synthetic carbonaceous materials. Recent researches have focused to use low cost natural graphite as an anode. However Morphology, surface chemistry and mechanically attached and intercalated impurities in natural graphite govern the electrochemical performance of the natural graphite as an anode martial. Even though Sri Lanka is known for high purity and highly crystalline vein graphite further enhancement of purity is necessary before it is used as anode material. Therefore this study is focused to study the effectiveness of alkali roasting process, which consists of roasting with NaOH at low temperatures, water washing and sulphuric acid leaching to remove the impurity in natural vein graphite. Purity level of graphite varieties with initial purity above 98% could be upgraded above 99.9% and varieties with initial purity around 95% could be upgraded up to 99.3%. Fe removal shows a direct relationship to the purity enhancement. D.C. electrical conductivity data of treated graphite shows that the vein graphite possesses electrical conductivity sufficient for the anode of LIB. It can be concluded that the alkali roasting purification method is an effective method for purification of Sri Lankan vein graphite and treated graphite is a promising material for the anode application of lithium-ion rechargeable batteries. Key words: Alkali roasting, Purification, Impurities
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    Purification of Vein Graphite by Alkali Roasting for Anode Material in Lithium Ion Batteries
    (Uva Wellassa University of Sri Lanka, 2013) Wewegedara, W.G.C.N.; Amaraweera, T.H.N.G.; Wijayasinghe, H.W.M.A.C.
    Unique vein graphite deposits with highly crystallized and high purity graphite are present in the mineralization zone of the central highlands of Sri Lanka This graphite has been identified as a potential candidate for the lithium ion rechargeable batteries (Balasooriyaet al., 2007). Recent attention has been made towards the purification of vein graphite in order to prevent the anode ageing and decomposition of the electrolyte in lithium ion batteries (Amaraweera et al., 2013). Alkali roasting for purification of graphite has found to be a very effective method to remove sulfide and silicate impurities at low temperatures (Lu et al., 2002). Therefore, this study focused on studying the effectiveness of alkali roasting for the purification of vein graphite in Sri Lanka Methodology Graphite powder (<53 µm) from Needle Platy Graphite (NPG) and Shiny Slippery Fibrous (SSF) morphological types from Bogala and Kahatagaha mines were used for this study. The graphite was treated in aqueous solutions containing 5, 10, 15, 20, 25, 30 and 35 vol. % NaOH (Solid: liquid, 1:2) separately and roasted at 250 C under air for one hour. Then, the roasted sample was acid leached in 10 vol. % H2SO4. After that, the solid was filtered, washed to neutral and vacuum dried at 100 C for 15 hours. Minimum concentrations of NaOH for the purity enhancement were identified for each graphite type. Roasting treatments were repeated at 150 C, 200 C, and 300 C, using the data obtained previously to identify the effect of roasting temperature on purity enhancement. Carbon percentages of the treated graphite samples and untreated graphite samples were determined by heat treating at 950 C for 3 hours in Muffle Furnace, according to ASTM – C 561 and weighing the residues. Pellets of treated and untreated graphite powder (D =12 mm and L = 5 mm) prepared by cold uniaxial pressing at 100 Mpa were used to measure D.C conductivity by four-probe method at room temperature.