Master of Science By research

Permanent URI for this collectionhttp://192.248.9.226/handle/123/15928

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Now showing 1 - 13 of 13

item: Thesis-Abstract
Synthesis of chitosan/hydroxyapatite nanocomposite scaffolds for tissue engineering applications
(2023) Rajapakse HD; Adikary SU
The objective of this research was to extract chitosan from waste Crustacean shrimp shells of the species Penaeus Monodon, which is a by-product of the shrimp export industry. Then the extracted chitosan was used to synthesize chitosan/nanohydroxyapatite composite by co-precipitation of nanohydroxyapatite onto a chitosan scaffold. A number of characterization techniques were used to analyze the structure and composition of the extracted chitosan and the synthesized composite. The porous structure of chitosan and the Hydroxyapatite nanoparticles embedded in the chitosan matrix could be observed through scanning electron microscopy. Both scanning electron microscopic images and X-ray diffractograms confirmed the size of the nanohydroxyapatite to be in the range of 2-14 nanometers. From the energy dispersive X-ray analysis, a ratio by weight of 2:1 for Ca:P was obtained confirming the presence of hydroxyapatite in the composite. The thermograms obtained from the thermogravimetric analysis revealed that the decomposition temperature drops with increasing hydroxyapatite loading in the composite which can be attributed to the higher crystallinity and better heat transfer in the composite. The degradation studies revealed that the percent degradation increases with time as well as the HAp loading. The biomineralization study done with simulated body fluid depicts that the Ca concentration of the SBF solution decreases over time, this is due to the uptake of Ca2+ ions from the SBF solution to form the apatite layer on the scaffold.
item: Thesis-Abstract
Study the influence of precipitate size distribution on hardness of aluminium 6063 alloy under constant aging temperature
(2021) Dilrukshi LWUR; De Silva GIP
The improvement of mechanical properties of heat-treated (T6) Aluminium 6063 alloy is caused due to hindrance of the dislocation line by the precipitates which is formed during the heat treatment process. The perception of the inter-relation between microstructural variations and mechanical properties with process parameters is essential, as it facilitates the optimization of the processing routes of the industry to be profitable. Several combinations regarding the relationship between properties and process parameters developed in previous studies without considering the precipitate size distributions. The current research focuses on finding the influence of age hardening process parameters on the precipitate size distribution and its effect on the hardness of the final product. Prepared samples were solution treated and quenched in water, followed by aging treatments for different periods. The Scanning Electron Microscope (SEM)/ Energy Dispersive Spectroscopy (EDS) analysis of precipitates was used to identify the FeSi-rich and Fe-Si-Mg-rich precipitates/β phase in the matrix (α phase). Further analysis of precipitates was done through IMAGE J software and MS EXCEL. The change of precipitate size distribution with different soaking times and its effect on the hardness of the Alloy was studied. A significant decrease in hardness was witnessed when the particles coarsen above 1.5 µm, for the aging time beyond 270 min at 190 o C.
item: Thesis-Full-text
Computational study on lead alternative perovskites for perovskite solar cells
(2020) Kumarasinghe KAMM; Galhenage AS
Hybrid organic-inorganic metal halide based perovskite solar cells (PSCs) lie at the heart of the emerging technologies of the solar cells due to their ability to increase the cell efficiencies dramatically over the last decade. CH3NH3PbI3 based PSCs show the highest performances; still, the toxicity of Pb has been the limiting factor for the commercialization of organic lead iodide based solar cells. Thesis discusses about the variations of properties in terms of electronic and dielectric properties due to the substitution of Sn and Bi in place of Pb. A systematic study of ab-initio calculation on the electronic properties of CH3NH3PbI3, CH3NH3SnI3, and CH3NH3BiI3 was performed. The results of the calculated band structures and the density of states of investigated materials reveal that CH3NH3PbI3 exhibits an energy band gap, effective masses of charge carries, and available density of states in favorable values for high performance solar cells than those of CH3NH3SnI3 and CH3NH3BiI3. CH3NH3PbI3 also consist of high dielectric capacity and better energy storage ability than CH3NH3SnI3 and CH3NH3BiI3. Above mentioned facts are the main reasons behind low-performance of Pb-free PSCs and it is paramount important to engineer the band gaps of those perovskites to obtain high performances.
item: Thesis-Full-text
Reinforcement of carboxylated nitrile rubber latex films by surface modified nanosilica
Ramasinghe, RLP; Liyanage, NMVK
Carboxylated acrylonitrile butadiene rubber (XNBR) is synthetic elastomer which inherent number of physical and chemical properties such as comparable barrier protection, good puncture and chemical resistance and high durability under storage. Although that there is a problem associated with synthetic elastomers that they are typically not self-reinforcing elastomers. Therefore, reinforcing fillers are incorporated to improve the properties of the compounds. Silica is extensively used for latex products. Nanofillers can impart more advanced properties to the final nanocomposite than micro fillers. Surface modification has been introduced to avoid the incompatibility between inorganic filler silica and organic XNBR matrix Role of surface modifiers in this study play dual role, as a capping agent: to control the size of nanoparticles & as a coupling agent: to develop compatibility between rubber and filler. Synthetic surface modifiers i.e. Polymethacrylic acid & Polymethacrylic acid ethyl hexyl acrylate and natural surface modifiers i.e. cellulose, collagen, chitosan & gelatin were used in this study. The FTIR analysis confirm that the surface of nanosilica particles has been successfully modified with acrylic polymers, forming ester bonds between carboxylic groups of acrylic polymers and surface silanol groups of nanosilica. TGA confirms the successful surface modification resulting lower weight loss; indicating small number of free surface silanols groups are present on the silica surface. XRD analysis revealed the amorphous nature of unmodified and all modified nanosilica particles. SEM results help to monitor the particle shape, size and agglomerations of synthesized particles. Evaluation of XNBR vulcanizate properties of micro silica, unmodified nanosilica, acrylic polymer modified nanosilica and natural polymer modified nanosilica filled vulcanizates was carried out. The results show that addition of small quantities of nanosilica causes an increase of mechanical properties of XNBR vulcanizates, while high filler loading of nanosilica appear to decrease the mechanical properties due to the aggregation of nanosilica particles. 2% PMAA and 2% cellulose modified nanosilica filled vulcanizates show balance strength with stretch & comfort properties for the glove manufacturing.
item: Thesis-Abstract
Correlation between corrosion rate and ultrasonic attenuation on steel
Dayananda, HGSM; Sivahar, V; Munasinghe, RGNDS
Corrosion is the gradual destruction of material, usually metal, by chemical reaction with its environment. Usually the corrosion rate cannot be measured directly which needs sample preparation, fixing of samples in a particular environment, measuring the weight loss during a given period of time and measuring other parameters (time of wetness, SO2 & NO2 concentration, etc.). This research work was based on measuring the corrosion rate using ultrasound technique, which can be named as a nondestructive testing method. Ultrasound defined as the sound waves, which has a frequency more than 20 kHz. To investigate the behavior of corrosion in accelerated atmospheric conditions mild steel samples was exposed to the concentrated NaCl solution. The assessment mainly conducted by evaluating the loss of mass of specimens against the ultrasonic attenuation. Weight loss is the parameter of corrosion rate and it has a relationship with the surface roughness of the samples. The surface roughness of the samples have an influence on the ultrasonic attenuation. Therefore, corrosion rate has a relationship between ultrasonic attenuation. In this project, efforts were made to find a correlation between surface roughness and ultrasonic attenuation. An equation was derived to calculate the corrosion rate if the ultrasonic attenuation is measured. This method has the advantage of assessing the corrosion rate without sample preparation on a given component.
item: Thesis-Full-text
Reinforcement of carboxylated acrylonitrile-butadiene rubber latex films by surface modified fillers
Liyanaarachchi, LADA; Liyanage, NMVK
Carboxylated acrylonitrile butadiene rubber (XNBR) latex is a widely used synthetic copolymer of acrylonitrile and butadiene with a small amount of a third monomer containing carboxylic groups. Some of the mechanical properties of XNBR latex are not adequate for certain applications and should be enhanced. Incorporation of reinforcing fillers is most widely used technique for that purpose. Silica filler is used in dry rubber industry as a reinforcement agent, but difficult to use in latex applications due to some problems associated with dispersing silica resulted by its surface chemistry. Surface of silica should be modified in order to use as a reinforcing filler in latex applications. In the present investigation, XNBR latex was filled with a series of surface modified precipitated silica. Surface modification of silica was affected by two methods i.e. non aqueous medium modification and aqueous medium modification, with the use of some synthetic polymers (SP). Three types of SPs, containing hydrophillic and hydrophobic groups that are methacrylic acid and 2-ethyl hexyl acrylate, respectively in different ratios were synthesized and used at a concentration of 3 % by weight of silica for the modification. The effectiveness of the SPs in enhancing reinforcing ability of silica in XNBR latex films was evaluated through investigation of mechanical properties of a range of vulcanized films cast from filled XNBR latex compounds containing modified filler in different concentrations in the range of 5 to 20 phr loadings. One of the well known non-sulphur vulcanization systems of XNBR, crosslinking with zinc oxide was used during the study. Latex films were cast from filled latex by several routes with different process sequences in order to investigate the importance of each step of the process to find out the most suitable step for filler addition. Some of the mechanical properties important for rubber latex applications, such as tear strength, of modified silica filled cast films improved over unmodified silica filled cast films. Optimum tear strength of cast films filled with modified fillers was observed at 20 phr filler loading, while films containing 15 phr filler loading gave optimum tensile properties. Morphological studies done by scanning electron microscopy illustrated improved distribution and lower size of modified filler particles within the XNBR matrix indicating surface modification has reduced filler aggregation. SPs used for the modification are capable of enhancing reinforcing action of silica filller in XNBR latex films. The extent of enhancement of physical properties of filled cast films depends on the hydrophillic/hydrophobic ratio of SPs used for surface modification of silica. Highest physical properties were observed for the vulcanizates containing silica modified with the most hydrophobic SP, which is thought to be the result of better rubber filler interactions created by the entanglement of rubber chains with hydrophobic side groups present in this particular SP.
item: Thesis-Full-text
Development of a method to predict the plasticizer evaporation of PVC insulated electrical cables
(2019) Egodage DP; Amarasinghe DAS; Attygalle D; Weragoda VSC
Though insulation is critical to the performance of an electrical cable the assessment of the status of an insulation is still a major challenge. Since the root cause of most electrical cable failures is due to insulation deterioration, if the rate of aging can be predicted, properly scheduled, appropriate maintenance programs can nearly eliminate cable failures. The kinetics of plasticizer evaporation of polyvinyl chloride based locally manufactured electrical cable insulations were investigated. Plasticizer evaporation is a slow process under low temperatures and would take years to study under such conditions. Therefore, accelerated conditions were used to get readings within the limited timeframe. Nevertheless, data obtained under accelerated conditions was mapped to normal conditions through Arrhenius approach. Deconvoluted derivative thermograms were used to identify the initial plasticizer percentages and Arrhenius approach was used to map accelerated condition measurements to ambient temperature evaporation rates. As cables are subjected to time varying temperature profiles a method for finding the equivalent temperature could be developed using kinetics of plasticizer evaporation whereby the operating life of the cable can be determined. The developed method could be applied for an electrical cable under a roof which is subjected to fluctuating thermal stress throughout the day and required time to evaporate critical level of plasticizer was determined.
item: Thesis-Full-text
Development of thermal insulating and light weight roofing materials using fly ash-cement composites
(2019) Ariyadasa GLM; Adikar, SU
This thesis is focused on developing an alternative roofing material for asbestos fibre cement sheets. Coal Fly ash (CFA) was selcted as the main matrix modifier, which was collected from the electrostatic precipitator in Lakvijaya power plant, Norochcholai, Sri Lanka. The study is aimed at extracting low-density particles from CFA, called “cenospheres”. Dry sieving and sink-float methods were adopted to take low-density fractions. Four types of CFA fractions were used in the study which were the unprocessed CFA, the CFA below 75 μm particle size, the CFA below 45μm particle size and the CFA particles extracted from wet separation method. CFA fractions were characterized with respect to morphology, particle size, particle density and chemical composition. The flexural strength and density variations were determined by casting mortar prisms, replacing 10-50% (by weight) of CFA from Ordinary Portland cement (OPC). Glass fibre reinforced fly ash cement (GFFC) roofing tiles were fabricated using size fractionated coal fly ash (CFA) which are the unprocessed CFA, the CFA particle sizes below 75μm and below 45μm. OPC was replaced by 30% (by weight) of each CFA fractions and those matrices were reinforced by Alkali Resistant glass fibres as 1% and 2% by weight. Physical, mechanical, durability and thermal properties were determined and those properties and the costs were compared with Calicut clay tiles, asbestos fibre cement corrugated sheet and non-asbestos fibre cement corrugated sheets. The spherical particle concentration increased with decreasing CFA particle size indicating those spherical particles in the finer fraction could be cenospheres due the relatively bigger spherical particle diameter and the low ratio of Si/Al compared to the unprocessed CFA. Sink-float method yielded the lowest density particles and it could be due to the presence of cenospheres and unburned carbon. The transverse strength was reduced with the decreasing CFA particle size .This could be due to the presence of cenospheres, low Ca content or less amorphous silica amount. All the compositions GFFC roofing tiles complied with the transverse strength requirements (230 N) as specified in the standard SLS 1189 Part 2. Highest value was observed in tile including 2% AR fibres with the unprocessed CFA (1650 N) and the lowest from tile incorporated with the CFA below 45μm (1470 N). The characteristic transverse strengths of GFFC roofing tiles is in comparable with Calicut clay tiles (1000-2000N) in Sri Lanka. The water absorption of GFFC roofing tiles did not comply with the requirement (maximum 10%) whereas the observed maximum value was 20%. Nevertheless, asbestos and non-asbestos roofing sheets have much higher values, which are 23% and 29%, respectively. The dry density of GFFC roofing tiles (1.63-1.68 g/cm3) is comparable with the dry density of asbestos sheet, which is ≈1.65 g/cm3. The long term durability of the GFCC roofing tile is in satisfactory level, it could due to the inclusion of CFA and AR glass fibres. GFFC roofing tiles can be considered as a good thermal insulator due to the high specific heat (1296 J/kg.K), low thermal (0.278 W/m.K) conductivity and diffusivity (1.31×10-7m2/s) compared with the asbestos, non-asbestos roofing sheets and Calicut clay tiles. However, Calicut clay tiles also offer good thermal comfort to dwellings, even though the thermal insulation is not depicted by k.c and α. This is because clay tiles have this natural system to gradually lower the air temperature through the process of evaporation. Hence, GFFC roofing tiles is a promising substitute for asbestos fibre cement roofing sheets using CFA in both unprocessed and sieved form due to the comparable strength, density, water absorption and durability. The cost for GFFC can be reduced by lowering the fibre content and replacing cement by ultrafine crushed rock particles.
item: Thesis-Full-text
Study on heavy metal adsorption by chitosan biopolymer
Unagolla, JM; Adikari, SU
Heavy metal pollution is a serious problem to aquatic ecosystems because some of these metals are potentially toxic even at very low concentrations. Chitosan, a biopolymer produced from crustacean shells, has applications in various areas, particularly in drinking water and wastewater treatment due to its ability to remove metallic ions from solutions. The purpose of this research work was to study the adsorption of cadmium and lead ions into chitosan, produced from shrimp shells at the laboratory level. Shrimp type “penaeus monodon” (giant tiger prawn) was used to synthesis the chitosan. The main characteristic properties such as degree of deacetylation (DD); the amount of amine groups in chitosan, viscosity, crystallinity and thermal analysis were done by using Fourier transform infrared spectroscopy, Brookfield viscometer, X-ray spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). Chitosan, with a degree of deacetylation between 80%- 95% was used in the experimental part and the flake sizes were smaller than 0.25mm. Experimental work involved the determination of the adsorption isotherms and kinetic studies for each metallic ion in a batch system. Effect of Degree of deacetylation (DD) of the chitosan, effect of initial pH of the metal ion solution, effect of particle size, effect of initial heavy metal concentration, and effect of chitosan dosage were studied. The results showed that the adsorption capacity depends strongly on pH of the solution, DD of chitosan and slightly depends on the particle size. According to the results, pH values at 6.5 for cadmium and pH values at 4.5 for lead show higher adsorption capacity. High DD chitosan showed higher adsorption capacity mainly due to the higher number of active amino groups in high DD sample. Simplified kinetic models such as pseudo-first-order, pseudo-second-order, Elovich model and intra-particle diffusion model were used to determine the rate limiting step. Both linear and non-linear According to the kinetic models pseudo second order model best described the adsorption process. Both linear and non-linear models and Elovich model best described the adsorption process. Multilinearity in the intraparticle diffusion model suggested that the adsorption of heavy metal consists of two major steps, due to the different pore sizes of chitosan. Equilibrium experimental data were analyzed by using two different isotherm models namely, Langmuir and Freundlich. According to the results, adsorption process of cadmium and lead heavy metals is heterogeneous and multilayer adsorption as it best fit with the Freundlich isotherm model. According to the thermodynamic experiments, adsorption process is favorable and physical adsorption was predominant in the adsorption process. Desorption of the heavy metals was possible by using different regeneration solutions.
item: Thesis-Abstract
Characterization of locally available montmorillonite clay minerals to be used as nano particles
(2016-01-16) Wanasinghe, DD; Adikary, SU
The research work describes the extraction of nano particles of Montmorillonite clay from local clay deposits located in the dry zone of the country, and its characterization techniques using X-Ray diffraction, Fourier Transform Infrared Spectroscopy, Differential Thermal Analysis and Thermogravimetry analysis, Scanning Electron Microscope, and particle size analysis. Montmorillonite gained an increased attention during the past decade due to the superior properties imparted in polymer-clay nano composite synthesized with nano particles of Montmorillonite. These composites synthesized in this way have superior mechanical and thermal properties compared to their bulk counterparts. At present the local demand for Montmorillonite is fulfilled by imported Montmorillonite which is a purified form of bentonite. It has been found by previous research activities, that in Sri Lankan clay deposits located in the dry region, Montmorillonite is available mixed with other minerals. The main ingredients of these deposits are Montmorillonite and kaolinite. Physically Montmorillonite and Kaolinite are so similar that they are very difficult to be separated from a mixture. However these two minerals have a difference in their specific gravities which can be used to separate the two minerals. This research describes how this separation could be carried out in detail finally leading to the extraction of Montmorillonite from local clay deposits. The clay used in the experiment underwent several purifying processes followed by characterization processes. The characterization of the final extracted clay reveals that it consists of Montmorillonite and the particle size of these falls below 100 nm. This indicates that these extracted Montmorillonite nano particles can be used to synthesize polymer-clay nano composite.
item: Thesis-Abstract
Investigation on sintering behaviour of waste alumina roller material in presence of MgO and ZrO2
(2014-08-07) Rajasingham, S; Jayaratna, M; Adikari, SU
In the present study the feasibility of utilization of high alumina roller waste from fast firing kiln was studied. These roller wastes, which contain important quantities of S i 0 2 and Al203, can be used as cheaply available raw material in ceramic product. The sinterability of alumina waste powder at 1400°C, 1500°C 1600°C and 1700°C was studied by density measurement, XRD analysis, microstructural analysis and determination of mechanical properties of those sintered samples. The study was further done by adding Z r 0 2 to the waste in different wt% (2-8wt %) and modified with 10wt% alumina powder. Temperature required for the sintering waste powder to get theoretical density above 95% decreased with the addition of MgO as sintering aid. It showed the addition of MgO in amount above 0.5% promoted densification at 1500°C. At 1600°C, the higher density (-95%) was achieved with addition of MgO in between 0.5% - 1.5%. At higher temperature at 1700°C densification can be achieved with the MgO addition <0.5%. Densification of modified waste with 10% AI2O3 was increased with addition of MgO at 1500°C. The maximum density with (99.9%) was obtained at 0.5% MgO. The XR.D patterns of the MgO added waste powder compacts sintered at temperatures up to 1700°C for 3h showed the presence of mullite and corundum as the major phases in all samples. But Mg-Al Spinel was formed when the samples sintered at 1400°C for 3h. Optical microstructure was porous for samples with excess MgO (>1%) sintered above 1600°C for 3h. The SEM observation of the microstructure showed the grain morphology as spherical at I500°C for 3h, but with increase in sintering temperature to 1600°C for 3h it was observed as elongated rod like grains. Addition of Z r 0 2 acted as sintering aid and above 97% obtained in the sintering temperature range between 1500°C -1600°C. Z r 0 2 addition significantly improved the fracture toughness of the waste powder compacts also. Better mechanical properties such as hardness and strength were obtained for the densified compacts (above 95%). The maximum hardness was given as 5.35GPaq and 6.13GPa for the compositions 100% waste with lwt% MgO (96.3%) and modified with 10% A1203 with 0.5% MgO (99.9%) respectively which were sintered atl500°C for 3h. Maximum MOR values for the above composition were 169.3MPa and 213.25MPa respectively.
item: Thesis-Abstract
Evaluation of the applicability of natural polymers as coupling agents in imparting reinforcement action of silica fillers in NR latex films
(2014-06-30) Gnanaratna, WDSN; Liyanage, NMVK
The results of an evaluation of the applicability of natural polymers (NPs) as coupling agents in imparting reinforcement action of silica fillers in natural rubber (NR) latex films are described in this research investigation. Three types of NPs namely; chitin, chitosan and cellulose were used for this investigation. Standard extraction processes were used for the extraction of chitin and chitosan. A commercially available grade of cellulose was used for this investigation without purification. Modification of surface of silica particles with NPs was affected by two techniques; in-situ surface modification, and surface modification through a sol-gel process. Coupling action of these NPs was compared with that of the most widely used commercially available coupling agent silane, Si69. A range of stable aqueous colloidal dispersions of precipitated silica were prepared with the use of NPs and Si69. In-situ surface modification performed with NPs and Si69. With NPs, the surface modification was done at four different proportions as 2.5%, 5%, 7.5% and 10% by weight of silica. With Si69, the modification was done at two different proportions as 5% and 10% by weight of silica. Sol-gel surface modification performed with chitosan was done at two different proportions as 5% and 10% by weight of silica. Interactions between polar groups of silica and functional groups of the NP which hinder aggregation of silica particles were confirmed by FTIR spectroscopy. The dispersion stability of the unmodified/modified filler (UMF/MF) dispersions was assessed by observing the phase separation upon standing. Dispersion stability of MF dispersions prepared using both surface modification method is much better than that of UMF dispersions. The particle size distribution of unmodified/ modified filler dispersions was measured by using “Fritsch” particle size analyzer. The particle size of the modified filler with cellulose was found to be lower than that of UMF dispersion. Effectiveness of NPs in enhancing reinforcing action of silica in NR latex was evaluated through investigation of mechanical properties of vulcanized films cast from NR latex compounds containing modified/unmodified fillers in different proportions. Distribution of unmodified/modified fillers within the rubber matrix was investigated through metallurgical microscope and scanning electron microscope by examining micrographs of surfaces of dipped NR latex films and micrographs of cross sections of cast NR latex films containing modified/unmodified fillers respectively. High colloidal stability of modified fillers with NPs indicates that are capable of acting as colloidal stabilizers for silica dispersions. Some of the NPs tested were found to be capable of conferring an appreciable enhancement in reinforcing action of silica in NR latex films. Micrographs graphs of the filled NR latex films revealed that same NPs have conferred uniform distribution of filler particles within the rubber matrix.
item: Thesis-Abstract
The Production of alloyed white cast iron for the use in the crushing and grinding operations in Sri Lanka
(2014-04-10) Ranasinghe, BJM; Jayatilake, ADS
This thesis· describes the work that have been carried out to produce different types of cast iron grinding media and liner plates of good wear resistant quality for the local industry. The types produced ,.,ere lm·r chromium, nickel chromium, martensi tic and high chromium ,.,white cast irons. The castings \·.'ere carried out at the Ceylon Steel Corporation ,.,hile the micro structural examination and mechanical testings were conducted at the University of Moratuwa • At present lm·1 alloyed cast steel grinding balls and Hadfield steel liner plates are produced at the Ceylon Steel Corporation for local use and they are found to contain defects ranging from shrinkage cavities, · sand fusions, blow holes, quench cracks to misruns. It is possible to eliminate most of these defects with certain types of alloyed white cast iron. The grinding balls and liner plates so produced showed greater resistance to wear and the casting yield ,.,as higher when compared with the castings of balls and liners. Although the price of alloyed white cast iron is marginally higher than the. cast steel balls and Hadfield liners, the longer life of the 'former more than compensates the replacement of c-ast steel balls, Lindfield liners with the white cast iron halls and liners.

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