Browsing by Author "Adikari, SU"

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Development of a high thermal shock resistant ceramic body suitable for cookware applications
(2015-07-22) Pussepitiya, PPSS; Adikari, SU
Development of a ceramic based cookware body with adequate thermal shock resistance was successfully developed using low cost raw materials. The objective of this work was to develop a ceramic body composition suitable for cookware to be used in direct flame cooking. To achieve this objective, cookware body should have low thermal expansion coefficient, high strength, low water absorption and high thermal shock resistance. In this study, ball clay, talc, alumina and zirconium silicate were used as starting raw materials and twenty five samples were investigated with different compositions. All samples were wet-mixed, shaped by slip casting, dried and fired to a temperature of 12500C in an electric furnace. Modulus of Rupture was tested by the three point bending method, the thermal nductivity of each body was measured with Lee’s disk method and the coefficient of thermal expansion was measured by thermo mechanical analyzer. The thermal shock resistance of each sample was calculated with Kingery’s formula. Optimum thermal shock resistance of 0.74 kJm-1s -1 was achieved for a body composition of 45% of clay, 15% of talc, 15% of alumina and 25% of zirconium silicate which was fired to 12500C. Further, modulus of rupture and coefficient of thermal expansion of the ceramic body were 74 MPa and 30.2×10-7 K-1, respectively. These results suggest that the ceramic body is suitable to be used in cookware applications.
item: Conference-Full-text
Development of a vibration energy harvesting device using piezoelectric sensors
(IEEE, 2018-05) Jayarathne, WM; Nimansala, WAT; Adikari, SU; Chathuranga, D
Piezoelectric energy harvesting has become popular among researchers because of the ease of converting mechanical energy into electrical energy using piezoelectric materials. In this context, a vibration energy harvesting device was developed to harvest vibration energy from vehicles. Lead zirconate titanate (PZT) was selected as the piezoelectric material. First the vibration sources were analyzed to identify the resonant frequency. Piezoelectric energy harvester was developed using the cantilever type configuration. Euler–Bernoulli beam theory was used to analyze the cantilever beam under free vibration. Finite element analysis (FEA) was used to identify the design parameters of the prototype which includes the metal beam, tip mass and the PZT plate. The maximum theoretical voltage was obtained as 5.99V according to the FEA modeling. The prototype was developed and voltage was measured fixing the prototype to the motor bike. The average voltage output was 3.65V.
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: Conference-Abstract
Modelling and validation of nano hydroxyapatite formation for medical applications
(Department of Materials Science and Engineering, University of Moratuwa., 2021-12) Dhananjaya, GS; Madushanka, D; Adikari, SU; Abeygunawardana, AAGA
In this study, a wet chemical synthesis of Nano-hydroxyapatite HAP [Ca10(PO4)6(OH)2] was investigated through a kinetic model derived based on the classical nucleation theory. The model mapped the nucleation rate from synthesis variables, supersaturation, temperature, and interfacial tension. During the study, the effect of supersaturation for nano formation of hydroxyapatite particles was experimentally studied keeping the other two variables constant. Since a direct measurement is not possible to measure the nucleation rate, the induction time, which is inversely proportional to the nucleation rate, was introduced to the model. The model simply suggests that the induction time will decrease with increased supersaturation. Also, it indirectly predicted the finer particles for lower induction times caused by higher supersaturations. Then the model was subjected to the validated process with a proper experimental design. During the experiment, the nano-hydroxyapatite powder was synthesized using Ca(OH)2 and H3PO4 as precursors at five different supersaturations while the temperature for the whole study remained the same as 300C. The supersaturation for hydroxyapatite was caused by changing the concentration of precursors maintaining the constrained Ca/P molar ratio near 1.6-1.7 between Calcium and Phosphorus. The H3PO4 was added to the Ca(OH)2 suspension at a constant acid addition rate of 4 ml/min using a burette under vigorous stirring having maintained the final pH at 10. During the synthesis reaction, the variation of pH of the mixed precursor suspension was measured and analyzed. The main parameter obtained from the experiment was the induction time. This induction time was marked by the onset of the first and more significant pH drop in the final mixture. After 48 hrs. of aging, the precipitate was separated by centrifuging at room temperature. Then the resulting wet powder samples were dried and characterized. First, the predicted model validity was investigated through a linear regression model and the regression/ kinetic constants were determined. In statistical validation, 95.84% variability could be described by the predicted model according to R2-test. In addition, the validated model could be applied to describe the nucleation process with the critical radius approach for each sample. With laser particle analyzer results, it was obvious that there was a significant reduction in the particle size when the supersaturation was higher. The model predicted this was caused by the higher nucleation density with increased supersaturation. In that scenario, the nucleation mechanism would be dominant compared to the growth of hydroxyapatite. The morphological and chemical analysis with SEM revealed that the formation of hydroxyapatite in solution is not a single-step process and it takes place via some amorphous intermediates with a time-dependent Ca/P molar ratio. In nano-sized form, hydroxyapatite is extensively used for a variety of extended medical applications. Finally, this model was experimentally validated by Laser Particle Analyzer and SEM studies. FTIR studies showed the characteristic peaks in hydroxyapatite and a trace amount of carbonate incorporation was observed in the lattice due to the synthesis in atmospheric conditions.
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.