Ceylon Journal of Science (Physical Sciences)

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Effect of As substitution on superconducting properties of the (Bi,Pb)-Sr-Ca-Cu-O System
(University of Peradeniya. Peradeniya, 1995) Dissanyake, M.A.K.L. and others
Superconducting properties of three systems with nominal stoichiometry (Bi0.7Pb0.3)SrCaCu1.5Oy (Sample A), (Bi0.5As0.2Pb0.3)SrCaCu1.5Oy(Sample B) and (Bi0.7As0.2Pb0.1)SrCaCu1.5Oy (Sample C) have been investigated using electrical resistivity, ac magnetic susceptibility and X-ray power diffraction measurements. Results show that, As is incorporated into the structure in sample B, still retaining superconducting properties but with a lower Tc of 80K. Sampel C where As is expected to replace Pb, however, does not show superconductivity and exhibit multiphase behaviour with several impuirty phases.
Ferroelectrics dispersed Li2SO4 composite solid electrolyte
(University of Peradeniya. Peradeniya, 1995) Singh, K.; Bhoga, S.S.
The ferolectric dispersed lithium sulphate composites have been invested using complex impedance analysis. The appearance of two semicircles in the Cole-Cole plots is discussed in the light of brick wall model. The observed breakover in the Arrhenius plots within the monoclinic region is considered to be due to changover mechanism from bulk conduction (within grain) to surface percolation conduction. A considerable enhancement in conductivity due to KNbO3 is observed to be due to its ferroelectric property. The surface charge transfer mechanism at the interface is illustrated to understand the formation of a space charge layer and so the microscopic conduction process.
Chemical and structural studies on natural spinels, MgAl2O4, of Sri Lanka
(University of Peradeniya. Peradeniya, 1995) Udawatte, C.P.; Gunawardena, R.P.; Annersten, H.
Natural Spinels from Sri Lanka (Ratnapura and Bibile) have been found to be mainly in the form, MgAl204 , with minor substitutions of Fe (0.7-3.5 wt% FeO) and Zn (0.07-4.4 wt% ZnO). Concentrations of other elements such as Cr, Co, Ni, V, and Mn were very low and, less than 0.1 wt% oxide. The natural spinels were found to have a complete normal cation distribution, A II[ ,(B III2)O4, suggesting an origin from a slow cooling rock forming process of the igneous and metamorphic rocks. Available experimental data of the Sri Lankan natural spinels indicate that complete ordering occurs at 280 ±175oC. The lattice constants were in the range of 8.087-8.091 A. Heating of the natural spinel results in disordering which may lead to a decreasing cell edge. Disordering of Al at 1000oC, as determined from AI-NMR spectroscopy, shows 13% of the Al occupying the tetrahedral sites. Optical spectra in the visible region are dominated %y spin forbidden transitions in Fe2+ and in some Cr-rich samples by spin allowed transitions in chromium. These are the main features that determine the colour of natural spinels investigated in the present study. The study indicates that the natural spinels have ordered cation distribution and the cation distribution in tetrahedral and octahedral sites depends on the thermal history of the crystal. The presence of transition elements, mainly Fe and Cr upto about 0.01 wt% oxide is sufficient to produce intense colour in spinels.
Pre-test estimation in the linear regression model under stochastic restrictions
(University of Peradeniya. Peradeniya, 1995) Wijekoon, P.; Trenkler, G.
In this paper, a general method to find stochastic properties of various stochastic pre-test estimators and forecasts is developed. This method is applicable if the convariance matrix O of the prior information is nonsingular.
Support points of subordination families
(University of Peradeniya. Peradeniya, 1995) Perera, S.
A general theorem for support points of subordination families is proved. This theorem provides a unified approach to the support points of the families subordinate to starlike functions. Close-to-convex functions of order ß(=1) and functions having boundary rotation at most kπ(K>2). The results for starlike functions and close-to-convex functions were previously known by different methods.
Some geological and geochemical attributes of the phosphate deposit at Ridigama, N.W. Sri Lanka
(University of Peradeniya. Peradeniya, 1995) Hewawasam, A.L.T.; Dahanayake, K.
Ridigama phosphate deposit occurs in the form of apatite rich veins that have intruded into the Precambrian granitic gneisses. Weathering processes active in the tropical Sri Lankan environment have given rise to a residual deposit. This deposit which is a weathering profile contains large primary apatite crystals in a fine matrix composed of ferruginous, siliceous, aluminous secondary phosphate minerals. Chemical studies have revealed that the primary apatite crystals of Ridigama have total P2O5 contents varying from 39% to 41% whereas it is less than 35% in the matrix. The 2% citric acid and water solubilities of primary apatite cystals are around 7% P2O5, and 0.05% P2O5 respectively; for the matrix the values were approximately 4% P2O5 0.04% P2O5 . Neutral ammonium citrate (NAC) solubility exceeds 2.5% P2O5, for crystals and less than 2% P2O5 for the matrix. The primary apatite crystals of this deposit showed higher solubility than those of Eppawala. However, the matrix at Eppawala was more soluble than that of Ridigama. The major components in the primary crystals are hydroxyl chlorapatite and carbonate fluor-apatite. Both these apatite types are associated with crandallite, quartz, feldspar, hematite and magnetite in the fine matrix.
Oxidative dimerisation of Eugenol on Pt electrode in acetonitrile
(University of Peradeniya. Peradeniya, 1995) Perera, J.S.H.Q. and others
Electrochemical investigation of eugenol on a polycrystalline platinum surface in an acetonitrile solution containing tetrabutylammonium tetrafluoroborate is described. The cyclic voltamogramme of the system, measured for an eugenol concentration of 2 mmol dm-3 at scan rate 500 mVs-1, consists of three oxidation peaks centred at 0.425,0.875 and 1.325V, with respect to saturated calomel electrode. The constant potential electrolysis of the system at + 1.325 V resulted in the complete conversion of eugenol to its dimer, which is formed by coupling through the benzene nucleus of eugenol. A plausible mechanism is proposed for this electrochemical conversion.
A new system of Lithium fast ion conductors based on LiTi2P3O12 and Pyrophyllite
(University of Peradeniya. Peradeniya, 1995) Zhao Jingzong, W.W.; Duanyang, L.
Pyrophyllite has been used as a starting material for the synthesis of Lithium fast ion conductors of the Li1+3xAlxTi2-xSi2xP3-2xO12 system by high temperature solid phase reaction. Most of the reactions completed at 1073-1423K. X-ray differaction analysis and an a.c. impedance technique were employed to characterize these fast ion conductors. The results showed that the lattice symmetry of most compositions in the system is R3c and the maximum ionic conductivity reaches upto the order of 10-2Scm -1 at 573K. The highest conductivity corresponds to the initial composition x = 0.15.
Use of minerals in the degradation of organic pollutants from aquatic systems
(University of Peradeniya. Peradeniya, 1995) Weerasooriya, S.V.R.; Senaratne, A.
This paper reports the potential use of mineral surfaces, particularly of iron oxides, as a starting material for the mineralization of chlorinated organic pollutants from aquatic systems. The overall mineralization of rate of CCl4 was optimal at pH 3 when goethite suspensions were utilized in the degradation process. The apparent coverage of the reactive surface sites by various contaminants has been attributed to the reduced reactivities of surface sites when pH exceeds 6.5. In order to enhance the mineralization rate of organic pollutants at environmentally significant acidity conditions, the reactive sites of goethite surfaces were first activated with a coating of Fe(II). The observed rate of mineralization of CCl4 was increased by an order magnitude when the chemical reaction was conducted in the presence of Fe(II)-coated goethite with a pH range of 4 to 7.
Ionic conductivity of the Na2SO4-Na2WO4 system
(University of Peradeniya. Peradeniya, 1995) Sumathipala, H.H.; Dissanayake, M.A.K.L.; Careem, M.A.; Bandaranayake, P.W.S.K.
In this study, the electrical conductivity of the Na2SO4-Na2WO4 system has been measured using complex impedance technique to investigate the effect of anion substitution on the cationic conductivity. In the Na2SO4(I) based solid solubility region the conductivity increases as SO4 ions are substituted by WO4 in the crystal structure. Maximum conductivity of 4x10-4 Scm-1 with an activation energy 0.5 eV at 450oC has been observed around 22 mol% Na2WO4. The secondary conductivity maximum observed at 48 mol % Na2WO4 could be associated with a two-phase mixture consisting of Na2SO4 based and Na2WO4 based solid solutions.
The source of placer gold in the Walawe ganga basin, Sri Lanka
(University of Peradeniya. Peradeniya, 1995) Nawaratne, S.W.; Wijeratne, G.N.
Significant quantities of alluvial gold occur in the zone lying between the gem-bearing gravel layer and the decomposed bed rock of Walawe Ganga, a river draining a Precambrian Highland Complex rock terrain of Sri Lanka. In such zones, the gold content varies from place to place and concentrations up to 9g per tonne of sediment were observed. The gold grains show different morphological features and occur as dust, flakes and nuggets. Some grains contain 100%. Au whereas others have lesser amounts with the balance being constituted of Ag, Cu and Mn. The highest alluvial placer gold concentrations are found in zones of intense shearing and fracturing in the country rock which is commonly intruded by quartz veins and pegmatites. Both shears and fractures show sulphide mineralization. Hydrothermal solutions with high CO2 and S components had been active during or after the deformational phase that formed the shears and the fractures. Such solutions appear to have been responsible for the gold mineralization in the Walawe Ganga basin.
Stereoselectivity in the reaction of Methylmagnesium bromide (CH3MgBr) and Methyllithium (CH3Li) with a Tricarbonyldieneiron diester complex
(University of Peradeniya. Peradeniya, 1995) Bandara, B.M.R.; Birch, A.J.
Tricarbonyl(η4-5α,5β-dimethoxycarbonylcyclohexa-1,3-diene) iron (1) reacted stereoselectively with CH3MgBr to furnish in 65% yield a 2:1 epimeric mixture of -β-endo)- and α-(exo)-(l'- hydroxyisopropyl) complexes, 2 and 3. The reaction of 1 with CH3Li was complex and showed that the ratio of products from the reaction on the β-(endo) and α-(exo) faces was 13:9. An explanation is advanced for metalalkyl reactions of 1 occurring preferentially on the β-(endo) face, whereas alkaline hydrolysis takes place exclusively on the α-(exo) face.
Hydrogen production in photolysis of aqueous manganese(II) bicarbonate
(University of Peradeniya. Peradeniya, 1995) Tennnakoon, K. and others
Photolysis of an aqueous solution of manganese(II) bicarbonate is found to generate hydrogen with precipitation of Manganese (III) hydrous oxide. Manganese(III) hydrous oxide in turn is found to photoreduce water with concomitant oxidation to manganese dioxide. Reaction mechanisms are discussed.
Solid polymer elctrolytes based on natural rubber and poly(ethelene) oxide (PEO) and their application in rechargeable Lithium batteries
(University of Peradeniya. Peradeniya, 1997) Dissanayake, M.A.K.L.; Samantha, W.A.; Bandara, H.M.N.
Hybrid solid electrolyte films have been prepared by incorporating various proportions of natural rubber into (PEO)9-LiCF3SO3 solid polymer electrolyte. Rubbery electrolyte membranes with as much as 50% by weight of natural rubber could be prepared without significantly reducing the ionic conductivity of the polymer electrolyte. The possibility of using these electrolyte membranes in solid state lithium batteries with V6O13 cathode has been demonstrated.
Study of some physical changes in selected foods during ohmic heating
(University of Peradeniya. Peradeniya, 1997) Edirisinghe, E.M.R.K.B.; Bamunuarachchi, A.; De Alwis, A.A.P.
Construction of a keV pulsed ion source and the measurement of damage cross -sections for keV ion induced sputtering from solid targets
(University of Peradeniya. Peradeniya, 1997) Barlodaya, D.D.N.; Ariyaratne, T.R.; Hankansson, P.; Sundqvist, B.U.R.; Ens, W.
Removal of heavy metal ions from textile effluents using burnt brick particles
(University of Peradeniya. Peradeniya, 1997) Priyantha, N.; Keerthiratne, S.
Burnt brick-particle packed columns have a strong ability for removal of heavy metal ions including Cr, Mn, Fe, Co, Cu, Zn, Cd and Pb from aqueous solution. Higher removal efficiencies of Fe, Co, Cu, Cd and Pb from mixtures of metal ions suggest the preferential speciation/adsorption ability of these metals over Cr, Mi and Zn. This methodology can be successfully applied for treatment of textile effluents, and consequently, the amount of heavy metals after treatment falls well below the tolerance limits. Environmental friendliness, readily availability and low cost are other attractive features of these columns.
Uranium - sulfilimine chemistry:the preparation and characterization of Cp*2UCl(NSPh2)
(University of Peradeniya. Peradeniya, 1997) Ariyaratne, K.A.N.S.
A study of grain boundary segregation and determination of thickness of segregate layer of a sialon ceramic using auger spectroscopy
(University of Peradeniya. Peradeniya, 1997) Karunaratne, B.S.B.
This paper presents a method of analysing grain boundary chemical composition and determination of grain boundary thickness of ceramic materials by Auger Electron Spectroscopy (AES). A sialon ceramic hot pressed with Mn3O4 was used as the ceramic sample. The AES analysis of intergranular grain boundary fracture surfaces of the ceramic indicated the presence of Mn, Al, Si, O and impurity Ca at grain boundaries. The chemical profile of segregate atoms normal to the fracture surface was determined using the sputtering technique and AES analysis alternatively. The approximate thickness of the boundary layer phase was estimated from these chemical profiles and it was found to be about 15 - 20 A. This value is somewhat lager than the value (10 A) reported by high resolution electron microscopy. This is because of the presence of lager volumes of residual intergranular glassy phase at triple junctions of the ceramic and also the uncertainty in defining the boundary limits in the AES profiles. However AES may be the most suitable technique available for analyising a thin layer of boundary interface.
Relationship between subsurface geology and ground subsidence of Bangkok metropolis Thailand
(University of Peradeniya. Peradeniya, 1997) Bandara, N.W.A.M.M.K.N.
Bangkok city, the capital of Thailand which has many engineering and environmental problems due to ground subsidence was selected as the main study object in this research study. The study included data collection, bore hole logging and investigations on some important underground geotechnical parameters to prepare thickness maps, static water level maps, ground elevation and subsidence maps of Bangkok subsoil. Thickness of both fine grained compressible clay layers and that of coarse grained non compressible sand layers are highly varying from place to place and they are highly deformed. Area of eastern Bangkok is affected by the highest ground subsidence and this area is underlain by the thickest portion of both first and second compressible clay layers. The lowest static water levels of upper most aquifers is also overlain by this area. The uppermost two compressible clay layers contribute more percentage for ground subsidence.