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Palugolle Ayyana Paththini Dewalaya

(University of Peradeniya, Peradeniya, Sri Lanka, 2001-11-16) Senanayake, P.

pdf attached.

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Farmer perception on cyber extension

(University of Peradeniya , Sri Lanka, 2009-12-03) Dissanayeke, U. I.; Wickramasuriya, H. V. A.; Wijekoon, R.

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Evidence for the presence of Rhinosporidium Seeberi in domestic animals and humans in Sri Lanka

(University of Peradeniya, 2009-12-03) Rajapakse, R. P. V. J.; Arseculeratne, S. N.; Sudasinghe, S. D. T. G.

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Electrical properties of Zircon (ZrSiO4) ceramics doped with different dopants prepared via solid state sintering route

(University of Peradeniya, 2006) Dahanayake, A. D. A. D. J. M. D. S. U.

Zircon (ZrSiO4) is an inexpensive natural mineral which is mined in very large quantities throughout the world including Sri Lanka and is recognized as a potential ceramic material for high temperature applications. It has also been proposed as a waste form for nuclear decommissioning and related applications. Although many studies on the properties of zircon requisite for such applications are reported in literature. electrical properties of zircon have received less attention. The results of a study on electrical properties of doped zircon ceramics prepared via solid state sintering route are reported in the present work. In this study. natural zircon powder was used as the starting material whereas Y2O3. Yb2O3. Eu2O3. Fe2O3, CaO. MgO. Li2CCO3 ; and Na2CO3; were used as dopants. Electrical conductivity of sintered samples was measured using complex impedance Spectroscopy in the temperature range of 100- 500 °C. The electrical conductivity of zircon without any dopants sintered at 1300 °C for 5 hours was 2.53x10ˉ⁷ S cmˉ¹ at 500 °C whereas it was 8.49 x10ˉ⁷ S cmˉ¹ at 500 °C for zircon without any dopants sintered at 1450 °C for 5 hours. It was observed that Y203. Fe2O3. LixCO3 and Na2CO3 doped zircon, with a dopant concentration level of 10 mol %. enhanced the conductivity by one order of magnitude whereas Yb2O3, Eu2O3. CaO and MgO doped zircon did not show any considerable conductivity enhancement. with the same dopant concentration level. The highest conductivity enhancement which was of two orders of magnitude was observed in doubly doped systems: namely (5 mol % Y2O3 + 5 mol % Li2CO3) doped zircon and (5 mol % Y2O3 - 5 mol % Na2CO3) doped zircon. It was also observed that the activation energy values for electrical conduction were quite different from system to system indicating that the rate controlling conduction mechanism is not identical in these systems. The most probable conduction mechanism in each system has been suggested with the aid of subsequent Scanning Electron Microscopic (SEM) analysis. Fe2O3 doped zircon showed some interesting magnetic behaviour and hence magnetic measurements were performed using Vidrating Sample Magnetometry (VSM) for curiosity. It was revealed that the presence of ferromagnetic Fe203 grains in the resulting samples has direct implications with the observed magnetic behaviour. X-ray Fluorescence (XRF) and Inductively Coupled Plasma (ICP) analysis of starting zircon powders confirmed the presence of impurities in different concentration levels. Hence. for a comparative study. zircon was synthesized in the laboratory via solid state sintering of precursor oxides (ZrO2 and SiO2). The zircon yield in the resulting samples. calculated using X-ray diffraction (XRD) data, was dependent on the dopant and the highest zircon vield (100 %) was observed in 10 mol% Fe2O3 doped system whereas doping with Li2CO3, or Na2CO3 completely hindered the zircon formation. Although it was abserved that the most of the laboratory synthesized zircon samples resembled their natural zircon counterparts as far as the electrical conductivity values are concerned the activation energy values were dependent on the synthesis route. The electrical conductivity of natural zircon single crystals along crystallographic axes α and c was also investigated. It was observed that the conductivity values measured along c axis Oc,) were constantly higher than those measured along α axis (Oα,). which is indicative of the conductivity anisotropy of zircon single crystals. However, it was observed that Oc,/Oα, (for a fixed temperature) varies only from 1.50 to 2.77 in the temperature range of interest. The flexural strength of some selected zircon particulate composites was determined in 4- point bending mode and it was revealed that the flexural strength of zircan composites were about twofold higher than that of monolithic zircon. The toughening mechanisms in the composites were identified as crack bridging. crack deflection and microcracking by subsequent microstructural analysis performed on the samples.

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A study of prosody & rhetorics of pali poetry

(University of Peradeniya, 1997) Jayasena, K.L.A.D.

Abstract is attached