RESCON 2021

Permanent URI for this collectionhttps://ir.lib.pdn.ac.lk/handle/20.500.14444/5951

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Simultaneous kinetics and ring-down (SKaR) in a pulsed uniform supersonic laval flow- kinetics of the reaction CN(v=1) + O₂
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Thawoos, S.; Hall, G.; Suits, A.
We report the development of a new apparatus that combines cw-cavity ringdown spectroscopy with a pulsed Laval flow (UF-CRDS). This is related to the CRESU (a French acronym for Reaction Kinetics in Uniform Supersonic Flows) technique, developed in France to study reaction kinetics at low temperatures. Cavity ringdown spectroscopy (CRDS) is a highly sensitive absorption technique relying on the decay of light between two high reflectivity mirrors of a cavity. For time-independent absorbing samples, the enhanced rate of power loss compared to the empty cavity leads to faster exponential decays. When the concentration of the absorbing species changes on the empty cavity ringdown time scale, non-exponential decays result, for which the instantaneous decay rate in excess of the empty cavity reference case provides a time-resolved measure of the sample absorbance. The long hydrodynamic time of the flow provides uniform temperature and pressure conditions well-matched to kinetic ringdown measurements in the time regime from 10 – 300 μs. This simultaneous kinetics and ringdown (SKaR) technique are coupled with a uniform flow for the first time. We will be reporting the design and operation of the newly developed UF-CRDS instrument and the rate constants measured for the reaction of CN(v = 1) with O₂ at 70 K and 24 K obtained with this approach.
Effect of seed layer on morphology enhancement of chemical bath deposited ZnO nanowires for gas sensing applications
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Abeykoon, Y.K.; Munasinghe, M.A.H.M.; Dassanayake, B.S.; Gunawardhana, N.
Metal oxide (MOx) semiconductor has stirred great attention in the gas sensors in the past decades due to the high sensitivity, fast recovery, low working temperature, and low cost. Nanowire-based MO gas sensors which possess a higher surface-to-volume ratio result in higher sensitivity and higher response to the chemical gases. However, it is crucial to synthesise long, thin MOx nanowires with uniform morphology to have superior sensing performance throughout the substrate. The chemical bath deposition (CBD) technique is a widely used technique to synthesise metal oxide nanostructures due to its relatively low-temperature growth conditions (< 100 °C), low cost, and scalability in the deposition. When considering the CBD technique, the seed layer is a significant concern for the well-growth of nanowires. Here, ZnO nanowires were grown on ZnO seeded silicon substrates, using the mixture of Zn(CH3COO)2 and monoethanolamine as the initial solution. The study aims to obtain a uniformly distributed seed layer and understand the effect of seed layer thickness on nanowire formation. ZnO nanowires were synthesised on a seeded glass substrate via CBD. Two different samples were deposited using (a) spin-coated and (b) spray-coated seed layers before carrying out low temperature CBD. An absorption edge at 378 nm, which corresponds to the ZnO nanoparticles, was observed in the UV-visible spectra of both the spin-coated and the spray-coated seed layers. Synthesised NWs showed an absorption edge at 376 nm, confirming the presence of ZnO NWs. The SEM images show that the spray-coated seed layer was uniformly distributed throughout the surface compared to the spin-coated. After the CBD process, the nanowires grown on the spray-coated substrates were well-aligned compared to those grown on the spin-coated seed layer. Nanowires with the spin-coated seed layer were not uniformly distributed, and random clusters were found to have formed on the top of the nanowires. Therefore, the spray-coated seed layer was selected as the better method. Seed layer thickness is a major factor for the formation of vertically aligned nanowires. Thus, the number of layer stacks of the spray-coated seed layer was optimised. The obtained SEM images reveal that nanowires grown on top of 10 layers of spray-coated seed were vertically well oriented throughout the surface compared to the nanowires grown on the surface with five and eight layers of spray-coated seed.
Chemical reduction of Graphene Oxide using L-Ascorbic Acid
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Maddumage, D.C.; Panamaldeniya, S.A.; Kimbulapitiya, K.M.M.D.K.; Munasinghe, M.A.H.M.; Pemasiri, B.M.K.; Gunawardhana, N.; Dassanayake, B.S.
Chemical oxidation-reduction is one of the most promising and cost-effective methods for bulk production of reduced graphene oxide (RGO). The oxidation step causes the exfoliation of graphite to obtain graphene oxide (GO). The reduction process with several washing steps eliminates residual oxygen functional groups and metallic precipitates. The reduction procedure of GO significantly affects the structure as well as the morphology of RGO. In the reporting case, Sri Lankan natural graphite in powder form was used as starting material. The Hummers method with some modifications was used for the oxidation of graphite. During the oxidation process, ultrasonic treatment was carried out to peel off the oxidised outer graphite layers, allowing inner layers to undergo oxidation. The reduction process of GO was carried out at 95 °C for different time durations from 0.5 to 2.0 h using L-Ascorbic acid as the reduction agent. The surface morphology of products was studied using scanning electron microscopy (SEM), and structural analysis was done using powder X-ray diffraction (PXRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS analysis reveals that carbon to oxygen atomic ratio (C/O) decreases after oxidising graphite into GO from 23.4% to 2.3%. PXRD and Raman analysis exhibit the emergence of turbostratic disorder of layers and an increase in the level of disorder in GO compared to graphite. The minimum level of disorder and maximum crystallinity was exhibited by the GO sample reduced for 1.5 h. Compared to the GO sample, the RGO sample reduced for 1.5 h showed an increased C/O ratio (8.5%) and decreased d-spacing (3.62 Å), implying the elimination of some residual oxygen functionalities after the reduction step.
Nano-structured TiO2-B for lithium-ion battery applications
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Panamaldeniya, S.A.; Maddumage, D.C.; Sandaruwan, R.D.L.; Munasinghe Arachchige, H.M.M.; Kumarage, W.G.C.; Dassanayake, B.S.; Gunawardhana, N.
Many researchers have investigated electrode materials for the lithium-ion battery (LIB) industry in the past decade. Among them, titanium dioxide (TiO₂) has attracted a great deal of attention due to its excellent properties, such as high operating potential, chemical and mechanical stability. However, the poor electrical conductivity and low ionic diffusivity are the main obstacles that hinder the production of high-performance LIBs with Titanium anodes. These drawbacks can be minimised by adding (a) conductive additives, (b) controlling the morphology, respectively. This work presents an extensive study of the TiO₂-B nanobelts-based electrode with the reduced graphene oxide (rGO). As a conductive additive, rGO (~5 layers) was synthesised using Modified Hummer’s method. The optimum hydrothermal temperature for growing TiO₂ nanobelt was noted as 176 °C. The length of the synthesised TiO₂-B nanobelt was between 410 nm & 15 µm with an average width of 45 nm. The electrochemical performance of the TiO₂-B/rGO composite anode was tested using constant current charge/discharge studies in the potential range of 1.0 – 3.0 V vs Li/Li⁺ . The first discharging and charging capacities were 177.2 and 138.9 mA h g⁻¹ , respectively. The second discharge and charge capacities were 142.7 and 137 mA h g⁻¹ , respectively. The composite anode material of LIB’s shows low cyclic performance and retained a low discharge capacity of 112 mA h g⁻¹ over 80 cycles, which is a significant capacity loss. A possible capacity fading mechanism will be discussed.
Thermoelectric properties of commercial Zinc Oxide and Aluminium doped Zinc Oxide
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Bandara, Y.M.D.C.Y.; Narangammana, L.K.; Bandara, T.M.W.J.
Most of the available machinery at operation generates excess heat, and hence a significant amount (around 66%) of the input fuel energy is wasted as heat. Therefore, waste heat recovery technologies such as thermoelectric generators are important to increase their overall energy efficiency. Thermoelectric generators are considered reliable technology that directly converts thermal energy into electrical energy. These devices are generally fabricated using alternative arrangements of suitable p-type and n-type semiconductors electrically in series and thermally in parallel. Zinc oxide (ZnO) is an inorganic n-type semiconductor that has received a great deal of attention to realise a high-temperature thermoelectric generator. In the present study, thermoelectric properties of pellets prepared using commercial ZnO and aluminium doped ZnO were observed at relatively lower temperatures. For this purpose, Al-doped ZnO was synthesised using a new chemical method. The successful synthesis of ZnO hexagonal wurtzite phase and doping were confirmed using powder X-ray diffraction pattern (JCPDF-01-079-0205). Pellets of synthesised Al-doped ZnO and commercially available ZnO powder were prepared at an applied uniaxial (non-isostatic) pressure of 295 MPa, which was lower than the pressures used in the literature, and their individual thermoelectric properties were observed at lower temperatures. The findings of this study are the synthesis method, lowpressure palletisation using wet ZnO and the generation of relatively high potential difference at low temperatures. The electrical conductivities of commercial ZnO and Al-doped ZnO were 31.3 S m⁻¹ and 35.6 S m⁻¹ (at 373 K). The thermal conductivities of these materials were 2.38 W m⁻¹ K ⁻¹ and 1.40 W m⁻¹ K ⁻¹ (at 373 K), respectively. Both materials showed negative Seebeck coefficient values of -165 µV K⁻¹ and -225 µV K⁻¹ , respectively, indicating the n-type semi-conductive behaviour. The dimensionless parameter figure of merit (ZT) characterises a material’s ability to convert thermal energy into electricity. The ZT for ZnO and Al-doped ZnO were 1.34 × 10⁻⁴ and 4.80 × 10⁻⁴ (at 373 K), respectively. Commercial ZnO and Al-doped ZnO generated a potential difference of 14.9 mV and 19.9 mV, respectively, at a 90 K temperature difference across the hot and cold ends.
Future onset of deceleration of the expanding Universe
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Karunathilaka, E.L.N.L.; Katugampala, K.D.W.J.
The expansion of the Universe is one of the most important topics of discussion in cosmology. When the Universe is expanding, the expansion rate will change with cosmic time either through acceleration or deceleration. Hence, those changes can be discovered by using experimental data. Otherwise, it can be used as a suitable mathematical model related to the expansion of the Universe. The main purpose of this study is to explain the expansion of the future onset of deceleration with cosmic time. Robertson Walker metric and Einstein’s field equations were used as major equations to obtain the relevant expressions. Non-vanishing Christoffel symbols and Ricci tensor components were obtained by using the Robertson Walker metric. Then, two independent equations with four unknown variables were obtained using modified Einstein’s field equations. Here, the pressure of the Universe is considered to be zero (zero models) as the matter is distributed to space with the big bang. Moreover, the Universe is assumed to continue as a spherical shape throughout the expansion. All the calculations depended on four-dimensional space-time coordinates. Three boundary conditions were used to support calculations. The appropriate model solution of R (radius of the Universe) was used to explain the main objective of this study. The variation of expanding rate of the Universe graph was plotted using the second derivative of the model. Then, cosmic time of future onset of deceleration was obtained when 𝑅̈= 0. According to the calculations, the future deceleration of the expanding Universe will start from 1.85 × 10¹⁶ s (0.58 billion years) after the present epoch. Thus, the deceleration in the present, past and future can be explained using this model. The Supernovae observations are the evidence to verify this graphical explanation.
Impact of temperature on accuracy of dry rubber content measurement affecting the manufacturing process and quality of crepe rubber
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Athukorala, V.H.; Jayasekara, A.G.B.P.; Rathnayake, M.
Sri Lanka is the largest manufacturer and exporter of natural crepe rubber in the world. Dry rubber content (DRC) measurement of natural rubber latex is critical in the crepe rubber manufacturing process. It is used as the guide for standardising the latex and determining the quantity of sodium bisulphite added for the fractionation process. Currently, the DRC is measured through a density calculation using a hydrometer on a sample of diluted field latex. The hydrometer reading is compared with a standard chart published by the Sri Lanka Standards Institute and Rubber Research Institute of Sri Lanka (RRISL). This chart is based on a standard temperature of 29 °C. However, since the temperature has an inverse relationship with density, it affects the DRC value calculated. Incorrect DRC measurement leads to incorrect chemical dosages, improper standardisation, enhancing rubber wastages, and long process times. These result in inferior quality in the final crepe rubber sheets leading to rejections and price drops in the export markets and lower output yield impeding the returns for the manufacturer. This study focuses on the significance of accompanying the temperature with the current measurement method when calculating DRC. The error in measured DRC was calculated for a series of diluted field latex samples of different temperatures based on a temperature-corrected DRC chart by Kudaligama et al. The calculations indicated a significant error component involved in the DRC measurement using the standard chart when temperature variation in the field latex was considered. Due to this error component, DRC is underestimated for temperatures below 29 °C and overestimated for temperatures above 29 °C; with maximum error percentages of approximately 14% at 24 °C and 11% at 32 °C. Hence, this study strongly recommends accompanying a temperature measurement with the hydrometer reading and referring to the temperature-adjusted DRC chart instead of the standard chart. The adverse consequences of erroneous DRC measurements are further discussed, including a quantitative analysis of rubber wastages at different temperatures.
Evaluation of radiation safety programmes in nuclear medicine facilities in Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Karunarathna, N.P.N.; Udugama, J.M.C.; Shantha, T.H.S.
Ionising radiation is vastly used in imaging and therapeutic fields in Nuclear Medicine (NM), where unsealed sources are used. The establishment of radiation protection is of paramount importance in these facilities for the safety of radiation workers, patients, and caretakers. Unintended exposure to ionising radiation and radioactive contamination can be possible if the radiation protection mechanism is not followed correctly. Although NM facilities in Sri Lanka are regulated, incidents occur due to a lack of radiation protection rules and guidelines locally and negligence and carelessness of employees. This study aimed to evaluate the existing radiation safety programmes and practices in NM facilities and then identify the gaps by comparing them with national and international standards to provide recommendations. Occupational exposure, medical exposure, public exposure, radioactive waste management, mitigation and prevention of accidents and safety of transport of radioactive materials are discussed. First, requirements and guidelines in the national and international standards were identified, and a sample radiation protection programme (RPP) was prepared. Secondly, facilities were visited to identify existing RPP. Two questionnaires were launched to collect data from medical practitioners, medical physicists, radiation protection officers (RPO), nurses and technologists in seven NM facilities in government and private hospitals and universities. The data were compared with prepared RPP. All facilities adhered to fundamental requirements. However, in facilities, essential needs such as local written rules, health surveillance, allocation of RPO’s responsibilities, training for radiation staff, and maintenance of logbooks were not according to the guidelines. Accordingly, establishing a proper management system with a written RPP is recommended with special emphasis on the following: assigning responsibilities, preparing local rules written in all three languages, establishing a documented emergency plan, introducing proper radioactive waste management protocols, and developing a safety culture.
Non-destructive ultrasonic method for defect detection in wooden rafters
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Sanjuka, O.W.D.S.; Jayalath, J.A.C.P.
Most ancient buildings in Sri Lanka are wood-framed. The wood components of antique buildings deteriorate with age. Insects and rapid changes in humidity are two of the most common causes of deterioration. Non-destructive testing (NDT) methods are required to preserve the wood components in old buildings. Various NDT methods such as X-ray, drilling resistance test, stress wave, and ultrasound are used to inspect the safety of antique wooden buildings. Among them, ultrasonic testing is simple, accurate, and inexpensive. Rafters are one of the main important components of antique buildings and are severely deteriorated. The main objective of this study was to develop a quantitative ultrasonic test methodology for detecting internal defects in wooden rafters of ancient wooden buildings. In addition, this study aimed to assess and evaluate the wood qualities such as acoustic velocities along longitudinal, radial, and tangential directions of wood and the modulus of elasticity (MoE) of wooden materials. Applying the ultrasonic test directly is challenging because of the connection between wooden parts or the contacted or hidden part by a wall or ceiling or other construction materials. Hence, an indirect ultrasonic testing method was required. Therefore, it was proposed to conduct ultrasonic tests with a newly developed prototype of an ultrasonic system. It is hard to make an artificial defect on the wooden rafter and quantify the amount of deterioration. Hence, a simple artificial slit was considered as an indicator of the deterioration. Regression models were proposed to describe the relationship between the artificial deterioration of the specimen and ultrasonic parameters. Time of flight amplitude (TOF-a), maximum amplitude, time of flight energy (TOF-e), energy value (EV) and pulse length (PL) were considered as the ultrasonic parameters. Ultrasonic parameters of the received ultrasonic signals were analysed using LabVIEW software. Correlation analysis of each ultrasonic parameter and the artificial slit depth showed that TOF-e and PL were proper ultrasonic parameters to predict the size of defects in wooden rafters. Multiple linear regression analysis was performed using TOF-e, PL and the artificial slit depth to establish a prediction equation. The established prediction equation showed a coefficient of determination of 0.77 for the wooden material of Teak. Therefore, the method was found to be effective to evaluate the deterioration in wooden rafters.
Prognostic genetic markers in pre- and postmenopausal breast cancer patient cohort from a tertiary care center in Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Piyawardana, M.D.S.D.; Perera, R.A.C.D.; Sunilrathne, V.S.; Beligala, B.A.D.H.; Siriweera, E.H.; Kodithuwakku, S.P.
Breast cancer is one of the major causes of morbidity among women in Sri Lanka, of which management is challenging due to the limited accuracy of existing classical prognostic markers. Therefore, prognostic molecular biomarkers for precise breast cancer diagnosis are vital. Dysregulated apoptosis plays a critical role in the pathogenesis of breast cancer. The members of the B-cell lymphoma 2 (BCL2) gene family are reported to have a prognostic significance in breast cancer. Epithelial-to-mesenchymal transition (EMT) is important in breast cancer metastasis. Epithelial Cadherin coded by CDH1 is a marker for EMT. This study aimed to assess the expression of BCL2, BAD (BCL-2 associated agonist of cell death) and CDH1 genes in a breast cancer patient cohort in Sri Lanka. Gene expression analysis was carried out using Real-time quantitative PCR (RT-qPCR) in triplicates for 68 breast tumour specimens obtained from patients with histologically confirmed breast carcinoma in Sri Lanka. The gene expressions with the menopausal status and primary clinicopathological parameters were statistically analysed. Our results showed that only CDH1 expression was significantly associated with the menopausal status (p < 0.05) and highly expressed in postmenopausal tumours. The BCL2 expression was significantly associated with estrogen receptor (ER) status and tumour grade, while the BAD expression was associated with the ER status (p < 0.05). Moreover, CDH1 expression was associated with human epidermal growth factor receptor 2 (HER2) status (p < 0.05). Therefore, CDH1 may be suitable for prognosis based on menopausal status and HER2 status in Sri Lanka. BCL2 may be suitable for ER status and tumour sizeassociated prognosis, while BAD may be suited for ER status-associated prognosis. However, analysis of patient survival data and an increased cohort size are required for establishing the suitability of these genes in the prognosis of breast cancer in Sri Lanka.
Mathematical modeling and simulation of acoustic properties of knitted fabrics backed by an air cavity
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Madushika, J.W.A.; Wijerathne, J.K.; Lanarolle, W.D.G.
Noise pollution has become a critical issue in the modern world of ever-increasing industries and machinery. Noise should be controlled due to the physical and psychological health effects associated with noise. Textiles as lightweight and cost-effective porous structures have received increasing interest for acoustic controlling applications. In-room acoustics, knitted fabrics represent a strong source of innovation due to drapability and aesthetic appearance. However, in general, the sound absorption performance of knitted fabrics is relatively low. Therefore, the primary goal of this work is to enhance sound absorption by introducing an air gap between the fabric and a solid wall. The diffuse incident sound absorption coefficient of knitted fabrics was mathematically modeled and simulated using basic equations of fluid dynamics where the fabric is acoustically described by its porosity, thickness, density and airflow resistivity. The air gap varied from 10 to 25 mm in 5 mm increments. Modeling predictions were compared with the experimental data obtained from the literature for sound absorption of knitted fabrics. The modeling predictions were in good agreement with the experimental data for different values of air gap thicknesses. The simulation results indicated that when the air layer thickness increases, the sound absorption coefficient of knitted fabrics increases significantly at low frequencies. The peak value of the sound absorption coefficient moves in the direction of a lower frequency. The sound absorption coefficient reached a maximum value of 0.45 at a resonance frequency equivalent to the quarter wavelength of the air layer thickness.
Scale-up of acid leaching process for vein graphite purification: application for lithium-ion batteries
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Naranpanawa, H.M.H.D.K.; Balasooriya, N.W.B.; Amaraweera, T.H.N.G.; Wijayasinghe, H.W.M.A.C.
With the rapid development of electrochemical energy storage systems, vein graphite has received significant attention as an anode material for Lithium-Ion Batteries (LIBs) due to enhanced power and energy density while maintaining excellent cycling stability in LIBs. The recently patented optimised acid leaching method is one of the well-identified methods for developing natural vein graphite (Sri Lankan Patent: 18729). However, this finding is based on a study conducted using a small sample (< 5.0 g), far less than industrial-scale production of battery anode materials. The present study investigates the feasibility of scaling up the acid leaching method used to purify the vein graphite at the laboratory level before designing an industrial-scale pilot plant. Varying ratios of graphite: acid weight and unit operations parameters were considered to obtain the optimum performance. The Carbon Content (CC) analysis and X-ray diffractogram obtained on the raw and purified scaled-up graphite samples successfully eliminated impurities while improving the CC by more than 99%. The electrochemical characterisation was carried out by assembling purified scaled-up graphite anode/LiPF₆/Li cell configuration with CR 2032-coin cell type. Galvanostatic charge-discharge analysis of the LIB coin cells assembled with the scaled-up upgraded graphite as the anode material revealed a high and stable initial specific discharge capacity of 340 mA h g⁻¹ with high Coulombic efficiency of over 97%. Cyclic voltammetry and electrochemical impedance spectroscopy analysis revealed smooth diffusion and lithiationdelithiation process of Li-ion, an acquiescent formation of solid electrolyte interface and structural stability of scaled-up developed graphite anode materials by acid leaching method. The scale-up process in the laboratory shows similar results, despite the significant volumetric scale-up and slight differences of apparatus. Choosing the correct scale for the scale-up is crucial, and the process should be closely integrated into a multidisciplinary approach before designing the industrial-scale pilot plant.
Construction of ionisation chamber to detect alpha and beta particles
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Amarasinghe, D.P.N.D.; Mendis, D.R.A.
Ionising radiation cannot be observed directly with the naked eye. Therefore, there are various types of detectors available to detect them. An ionisation chamber is the simplest form among the gaseous detectors that can be constructed using inexpensive and readily available materials. The main objective of this research was to build an ionising chamber that can be used in the laboratory to detect alpha and beta particles separately—the design comprised of two components, so-called the detector segment and the measuring segment. The detector segment was constructed using an outer cylinder (anode) and an inner rod (cathode) made of aluminium. Two Teflon insulators were used to separate the electrodes at one end, and the other was kept open. Air at atmospheric pressure was used as the ionisation medium, and an external voltage was applied between the two electrodes. The measuring segment is comprised of a preamplifier and a current/voltage meter. A differential amplifier with four Darlington transistors was used along with an ARDUINO Uno microcontroller board and a voltage sensor to amplify and measure the output voltages from the detector segment. The ARDUINO board was connected to a computer interfaced program to obtain the real-time plot for quantitative analysis. Americium-241 (Am-241), Cesium-137 (Cs-137), and Strontium-90 (Sr-90) radiation sources were used to determine the ionisation region that the ionisation chamber operates and to identify alpha and beta particles by measuring their relevant output voltages over the same period. The ionisation region of the constructed chamber was found to be above the input voltage of 18 V. Background radiation was identified in the form of small fluctuations in the output voltage. The detection of beta particles was done using the radiation sources Cs-137 and Sr-90 where, Cs-137 is both a beta and gamma emitter, while Sr-90 is a pure beta emitter. The obtained output voltage due to the Cs-137 source increased very slightly (~0.05 V), while no significant increase was observed for Sr-90 with respect to the background radiation. This was mainly due to the low activity of Sr-90 compared to Cs-137 sources available at the laboratory. The detection of alpha particles was carried out by using the strong alpha emitter, Am-241. Output voltage due to this source had a significant increase of ~1.00 V compared to the background radiation. This is due to the high ionisation capability of alpha particles compared to beta particles. Hence, the study implies that the output voltage pulses from the constructed ionisation chamber can qualitatively identify alpha and beta particles.
Metal-organic frameworks (MOF) synthesised from monomers derived from post-consumer poly(Ethylene Terephthalate) bottles
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Egodawele, M.G.S.A.M.E.W.D.D.K.; Gunathilake, W.S.S.
Metal-Organic Frameworks (MOFs) are organic-inorganic hybrid crystalline porous materials with a high surface area consisting of a regular array of positively charged metal ions connected by organic linker molecules. This study describes the synthesis of an aluminium-based MOF using bis-(2-hydroxyethyl terephthalate) (BHET), which has not been reported as a linker material to synthesise MOFs before. BHET was obtained by glycolysis of post-consumer polyethylene terephthalate (PET) bottles by reacting with ethylene glycol, followed by recrystallisation. The glycolysed product of PET bottles, BHET, was characterised using melting point, Fourier Transform Infra-red Spectroscopy (FTIR) and Powder X-ray Diffraction (PXRD) techniques. The synthesis of MOF was carried out by solvothermal method using different aluminium salts and BHET. The synthesised MOF was characterised using FTIR and PXRD techniques. The results of FTIR and PXRD analyses confirmed the formation of BHET as the glycolysed product of PET bottles, and synthesised MOF has a similar structure with MIL-53(Al) MOF. Further, it was found that the reaction between the linker BHET and the salt, Al (OH)3, results in the formation of the MIL-53(Al) MOF out of the tested aluminium salts. These results indicate that BHET obtained by recycling the post-consumer PET bottles by glycolysis can be used as a linker material to synthesise the MIL-(53) Al MOF.
Photometric analysis of eclipsing binaries in the region of hydra constellation by using TESS mission data
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Abeykoon, D.A.B.; Pemasiri, B.M.K.; Ranawaka, T.P.
Eclipsing binaries provide more reliable and accurate samples for studying stellar evolution. In this study, we considered four W UMa type eclipsing binaries to determine their stellar parameters and the physical nature of each system. The photometric data of target stars, EG Hya, V0404 Hya, V0452 Hya and V0483 Hya, were obtained from the TESS mission. The Lightkurve python package is used to extract light curves from TESS full-frame images. The stellar parameters were obtained using the PHOEBE 1 program based on Wilson-Devinney code modeling until the minimum values of residuals were obtained. We determined that all the stars had periods between 0.61139 ± 0.00001 to 0.29660 ± 0.00009 days, where EG Hya and V452 Hya have the highest and the lowest values, respectively. V0404 Hya and V0483 Hya recorded 0.3096 ± 0.0003 and 0.4075 ± 0.0003 days for the period of eclipses, respectively. Considering the mass ratio q of each system EG Hya and V0483 Hya had the lowest mass ratios of q = 0.1256 ± 0.0002 and q = 0.1058 ± 0.0004, respectively, while V0404 Hya and V0452 Hya had the highest mass ratios of q = 0.5625 ± 0.0006 and q = 0.566 ± 0.002, respectively. Depending on the value of the fill-out factor (f), a totally eclipsing binary system EG Hya (f = 7.23%) and V0452 (f = 0.18%) were found to be marginal contact binaries, and V0404 Hya (f = 46.49%) and V0483 Hya (f = 14.58%) were identified as over-contacting binary systems. Further, system parameters such as inclination and effective temperatures were derived, and the physical model of each system was discussed.
Numerical study of the effect of Delafossite CuAlO₂ and PEDOT:PSS as hole transport materials in the 3D/2D Perovskite solar cell
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Adihetty, N.L.; Ratnasinghe, D.R.; Attygalle, M.L.C.; Narayan, N.S.; Jha, P.K.
Metal halide perovskite solar cells have shown good performance in photovoltaic. Methylammonium lead iodide (CH₃NH₃PbI₃ or 3D-MAPI) is one of the most popular 3D metal halide perovskite materials. In this study, we numerically modelled metal halide perovskite solar cells having a p-i-n structure with intrinsic layers of 3D-MAPI and 2D monolayers of CH₃NH₃PbI₃ (2D-MAPI). However, the hole transporting material of the p-i-n perovskite solar cell can control the performance of the solar cell due to the recombination in the hole transporting layer (HTL). We simulated and observed how the delafossite CuAlO₂ and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) HTLs affect the solar cell model with the structure of Glass/p-PEDOT:PSS or p-CuAlO₂ (HTL)/i-3D-MAPI/i-2DMAPI/n-PCBM (ETL)/Ag. The fullerene derivative (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) was used as an electron transporting material (ETM). Firstly, the optimised solar cell model was simulated with a p-type PEDOT:PSS layer. Secondly, PEDOT:PSS was replaced with CuAlO₂ to observe its performance. The one-dimensional Solar Cell Capacitance Simulator (SCAPS-1D) has been used to model these solar cells under the AM1.5G solar spectrum. We have first obtained the results, with the power conversion efficiency (PCE) of 20.17%, open-circuit voltage (VOC) of 1.10 V, fill factor (FF) of 76.08%, and short-circuit current density (JSC) of 24.17 mA cm⁻² . After replacing CuAlO₂, the solar cell performance improved, with the PCE of 23.17%, VOC of 1.14 V, FF of 84.07%, and JSC of 24.17 mA cm⁻² since CuAlO₂ has shown high shunt-resistant value than PEDOT:PSS. Consequently, the 3D/2D metal halide perovskite solar cell model with CuAlO₂ has numerically shown better power conversion efficiency than the solar cell model with PEDOT:PSS since the low carrier recombination at the CuAlO₂ layer (HTL).
Poly (Acrylic acid)/sawdust composite for adsorptive removal of selected heavy metal ions from aqueous solutions
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Fiham, M.F.M.; Gunathilake, W.S.S.
The synthesis of a novel adsorbent by grafting poly (acrylic acid) to sawdust to remove heavy metal ions from aqueous solutions is reported here. The ability of sawdust to adsorb heavy metal ions can be enhanced by grafting poly (acrylic acid) which increases the negative charge on the composite, making it a better adsorbent than sawdust. Poly (acrylic acid) was synthesised using potassium persulphate as the initiator by free-radical polymerisation of acrylic acid. Insitu polymerisation of acrylic acid on sawdust yielded the poly (acrylic acid)/sawdust composite (PAA/SD). Fourier Transform Infrared Spectroscopy (FTIR) was used to characterise sawdust, poly (acrylic acid) and PAA/SD. X-ray Fluorescence (XRF) was used to determine the metallic constitution of sawdust. The adsorption percentage of PAA/SD towards Pb²⁺, Ni²⁺, Cd²⁺, Zn²⁺ and Cr³⁺ was determined under conditions of a pH of 6, 60 min of shaking time, 60 min of settling time, (0.100 ± 0.001) g dosage of PAA/SD composite of particle size of 200 µm which was determined using a sieve plate. The procedure was repeated twice. The concentrations of heavy metals were determined using atomic absorption spectroscopy. Results indicate the successful synthesis of poly(acrylic acid) by free radical polymerisation of acrylic acid with a yield of 42%. FTIR characterisation affirms the synthesis of PAA/SD composite. XRF characterisation proves the absence of heavy metals tested in the analysis in sawdust, validating the sawdust sample used for composite preparation. The PAA/SD exhibited adsorption percentages of 51% for Pb²⁺, 40% for Ni²⁺, 60% for Cd²⁺, 57% for Zn²⁺ and 55% for Cr³⁺ under the conditions studied. PAA/SD showed the highest adsorption towards Cd²⁺. The novel PAA/SD composite is very effective in removing all tested heavy metals from aqueous solutions.
Ethylene carbonate and dimethyl carbonate composition dependence: a molecular dynamics study of Li-ions in an electrolyte
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Samarakoon, Y.M.I.B.; Wijayasinghe, H.W.M.A.C.; Amaraweera, T.H.N.G.; Ranatunga, R.J.K.U.
Li-ion rechargeable batteries (LIBs) have excellent durability, long cycling life and high specific density. Computational investigation of the effect of temperature, salt concentration and solid electrolyte interface on the Li-ion behaviour has been reported. However, computational studies on the composition dependence of ethylene carbonate (EC) and dimethyl carbonate (DMC) on the Li-ion behaviour are lacking. Here, we study the effect of the entire range of EC and DMC composition in the electrolyte to determine the optimum composition of EC and DMC in Li-ion rechargeable batteries. All systems were represented using the Generalised Amber Force Field (GAFF) and simulated using the LAMMPS code. The following properties were simulated and analysed; density, self-diffusion coefficient, ionic conductivity, cluster formation and ion pair lifetimes. Results showed that all mean square displacements, diffusivities and ionic conductivities increased with increasing DMC mole fraction (χdmc). Further, irrespective of χdmc, the highest number of F⁻ ions and carbonyl oxygen atoms were found, from1.98 to 2.10 Å from Li⁺ ions. This indicates the competition among PF6⁻ ions and EC and DMC molecules for Li- ions. The system with 0.2 χdmc showed the highest pair correlation of DMC with Li-ions, while 0.7 χdmc showed the lowest. The highest pair correlation for EC with Li-ions was observed for 0.4 χdmc. The incremental increase of χdmc has increased the diffusivity of Li-ions and, hence the ionic conductivity. It has also shown that Li-EC pair correlation has increased with increasing χdmc to 0.4, and a further increase in χdmc has decreased the correlation with Li-ions, indicating that the 0.4 χdmc as the optimum EC/DMC composition.
Potential of banana (Musa sp.) peels as source of electrolytes in voltammetric experiments
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Gunarathne, N.D.W.; Ganehenege, M.Y.U.
Banana (Musa sp.) is an electrolyte-rich fruit due to its high potassium content. Even though banana peel is considered a waste material, many studies have shown that it can be converted into value-added products. The ability of banana peels to function as electrolytes has not been extensively studied. This study aimed to explore the potential of banana peel extract as an alternative for expensive electrolytes utilised in electrochemical experiments. Extractions of three banana varieties: Ambun, Embul, and Seeni were prepared by blending and filtering the fresh peels. The electrical conductivity (EC) and total dissolved solids (TDS) in three extracts were determined using an electrical conductivity meter. Ambun peel extracts showed both the highest EC and highest TDS results. The mineral ion concentrations (Mg⁺², Ca⁺², Na⁺ , K⁺ ) of three types of banana peel extracts were also determined with the flame atomic absorption spectrophotometer using a diluted extract series to confirm the presence of major electrolytes. In cyclic voltammetry (CV) experiments, baseline response of the banana peel extract was first investigated, and then cyclic voltammograms were recorded for 0.001 mol dm⁻³ ferrocene in dimethylformamide using banana peel extract as the supporting electrolyte with glassy carbon electrode as the working electrode; Pt wire as the counter electrode and calomel electrode as the reference electrode under N2 blanket. The results have exhibited the characteristic redox peaks of ferrocene with cathodic peak potential (Epc) at 0.23 V and anodic peak potential (Epa) at 0.38 V for at 0.050 V s⁻¹ scan rate. Anodic and cathodic current ratio (ipa/ipc) , was 2.36 and peak separation (∆Ep) was 0.15, which was higher than the results in a solution of a standard supporting electrolyte. None of these redox peaks of ferrocene was observed in the absence of banana peels extract. The results reveal that banana peels can be used as a source of electrolytes in CV experiments. Attempts were made to convert the extraction of the peel into a solid because solid electrolytes are more appropriate in electrochemical experiments. Further research on the development of solid electrolytes is underway.
Changes in pH of concrete during hydration
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2021-10-29) Natkunarajah, K.; Masilamani, K.; Maheswaran, S.; Amarasinghe, D.A.S.; Attygalle, D.
The pH value plays a major role in the concrete structure and its reinforcement. The corrosion of the concrete structure begins when its pH value falls below a specific level. Many studies have been performed to investigate the environmental factors that affect the pH of concrete. However, limited studies have been carried out on the pH changes in the concrete pore solution for some time. The present study investigates the pH changes of pore solution in the concrete during the hydration reaction up to three months. There is no standard procedure to measure the pH of cementitious structures. In this work, various analytical methods have been used, and the results were compared to find a correct way to measure the pH of concrete. Furthermore, the pH change pattern during the hydration reaction with time was also studied. Ex-situ leaching method with cold water extract methodology was used to extract the concrete pore solution. Various methods, including titration, direct measurement using a pH meter, reverse calculation, and thermodynamic modelling methods, were used to determine the pH of the extracted solutions. Due to the dilution effect of the added water, the methods used for measuring the pH value of the pore solution, such as direct pH measurement with a pH meter and titration method, underestimated the actual pH level. Moreover, both the reverse calculation of ionic activity of H⁺ in the concrete pore solution using titration method and the pH measurement using a pH meter cannot represent the actual ionic activity of H⁺ ion. However, the results obtained by modelling from the measured alkali concentrations showed acceptable results. This research outcome shows that the pH is increased nearly by 5% after a month of hydration of the concrete.

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