Linear shrinkage (S L ) is utilized as a criterion to modify the size of the sintered ceramic tiles, and the sintering cycle affects the shrinkage variation. The exact sintering cycle associated with the S L of ceramic tiles is difficult to verify experimentally, and it affects the quality of the final ceramic tiles. Production costs also increased due to the large amount of experimental work. This study investigated a powerful numeric model of the sintering process within ceramic tile, using computational fluid dynamics (CFD) to evaluate the variation of the S L in ceramic tiles during the sintering process. The sintering process was simultaneous and integrated with energy and mass transport phenomena. Numerical formulas were developed for the sintering operation, and the S L behavior of ceramic tiles during sintering was examined using a kinetic model. An unsteady 3D model was established, and simulation was performed using the CFD tool by varying the temperature profile. The results of CFD simulation can ascertain the temporal and spatial changes in the S L of ceramic tiles through sintering. To validate the model, the green body mixture of ceramic tile was prepared and analyzed. Ceramic tiles were shaped by a powder pressing technique on a laboratory scale. Dried tiles were sintered in a laboratory furnace by adjusting the maximum sintering temperatures. The structure of sintered ceramic tiles was analyzed. The S L variation of each sintered tile was determined and compared with the results of CFD simulations. The results of the CFD simulation were validated and concurred with experimental outcomes, and the R 2 value of the results was 0.9. The developed CFD model is capable of predicting the temporal and spatial changes in S L of ceramic tiles through sintering, and it is a great help to find the exact sintering cycle associated with S L . Finally, the quality of the tile is increased, and production costs are also reduced.

Bone defects with critical-size fractures require clinical intervention for fracture healing. Commonly used treatments have limitations like donor morbidity, limited donors, and mechanical mismatches. Bone scaffolds are developed to address these limitations and improve bone formation, vascularized ingrowth, and biodegradability as bone remodels. In this study, bone healing scaffolds have been fabricated using a coprecipitated chitosan-nanohydroxyapatite composite. Fourier-transformed infrared spectroscopy, scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction spectroscopy and thermogravimetric analysis were used to analyze the extracted chitosan and composite. Cylinder-shaped bone scaffolds were obtained by freeze-drying the composite with gelatin. Scaffold fabrication experiments were conducted by varying the composite: gelatin ratio for better shape retention and mechanical properties. Bone scaffolds were analyzed for porosity, pore size distribution, compressive strength and in-vitro bio-activity. An optimum composition in terms of shape retention and other required properties was obtained by the scaffold fabricated using $70 \%$ composite (Chitosan: nanohydroxyapatite 70:30) and $30 \%$ gelatin. This sample had $85 \%$ porosity exhibiting a compressive strength of 0.2 MPa that mimics the compressive strength of cancellous bone. The bioactivity of the scaffolds was successfully analyzed by conducting an in vitro biomineralization test for the composite and an in vitro biodegradation test for the scaffold.

Recent developments in nano-level energy harvesting are mainly focused on using piezoelectric power generators from compression and vibration modes. In this work, a vertically integrated zinc oxide piezoelectric nanowire array was modeled to scavenge energy from a low-frequency compression force. COMSOL Multiphysics $\mathbf{5. 4}$ software was used to simulate and model nanowire array structures to ensure the potential distribution and overall electric energy generator of the piezoelectric structure under compression displacement. Piezoelectric constitutive equations were used to develop mathematical equations in terms of comparing and confirming induced piezoelectric outputs. Theoretical and mathematical results confirmed that the voltage output of the nanowire array does not depend on the number of nanowires. Total electric energy harvested by the array depends on the number of nanowires and nanowire density.

In this study, we investigate the influence of supersaturation on the particle size and crystallite size of Hydroxyapatite nanoparticles, $[\mathrm{Ca}_{10}(\mathrm{PO}_{4})_{6}(\mathrm{OH})_{2}]$ synthesized using the wet chemical precipitation technique. For the synthesis process, different concentrations of calcium hydroxide and orthophosphoric acid were used to achieve different supersaturations. The $\mathrm{Ca}/\mathrm{P}$ molar ratio was kept at 1.67 while changing the supersaturation. The synthesized nanoparticles were characterized using a laser particle analyzer, Scanning Electron Microscope (SEM), X-ray diffractometer (XRD), Energy Dispersive X-Ray Analysis (EDAX), and FourierTransform infrared (FT-IR) spectroscopy to study their size, morphology, structure, and composition. The results showed that the particle size and crystallite size of Hydroxyapatite nanoparticles can be controlled by varying the precursor concentrations to initiate different supersaturations.

In this research, design, and simulation of solidstate insulin micropump based on piezoelectric actuator for wearable insulin pump device to human body was introduced. The objectives of the design are reducing frequent dosing, oral therapy, and painful injections for diabetes conditions. We presented key concepts, operation principle, design of the pump, material selection, theoretical study, optimization of the pump using finite element analysis and simulation of the pump. All the simulations are done using COMSOL Multiphysics 5.3 a software.

The drying process of the green ceramic body is concurrent and coupled with heat and mass transfer phenomena. Dimensional variations and mechanical stresses occur within the body during the drying process. In this research, the drying behavior of ceramic tile was investigated, and a ceramic tile body mix was developed using M2 kaolin clay as the main clay mineral. Initially, the composition and structure of the M2 kaolin clay were analyzed using X-ray diffraction and wet chemical analysis, and it consists of 56.78 % silica. The body mix of the green ceramic tile was prepared, and the particle size distribution was analyzed. The powder pressing method was used to obtain the shape of the tiles. Samples were dried in an oven at 80 °C and the moisture variation of the green ceramic tile was determined with time. A mathematical relationship was formulated to determine the drying behavior of green ceramic tiles. An unsteady three-dimensional model was formulated and simulated in the computational fluid dynamics (CFD) framework. Results developed by the simulated model were compared with data obtained by experiments conducted using green ceramic tiles. The model results were validated and complied with the experiment results, and the R 2 value was 0.9

Due to recent developments in energy harvesting, there has been a subsequent rise in MEMS (Micro electromechanical systems) powered by low-frequency vibrations in the environment through effective transduction procedures like piezoelectricity. In this paper, a vertically integrated single piezoelectric Zinc Oxide nanowire-based system is modelled for energy harvesting applications. To reinforce this development, different structures of nanogenerators were modelled and simulated using COMSOL Multiphysics 5.3 software for their performance upgrades. It was developed to analyse the compression and bending effect of the nanowire. To compare and validate the induced piezoelectric output, mathematical equations were derived using piezoelectric constitutive equations. Moreover, the voltage output of the nanowire under a constant lateral force was analysed varying with the nanowire dimensions in terms of aspect ratio. The analysis results have shown that the compression of ZnO nanowire gives more output voltage compared to the bending of the nanowire for the same nanogenerator. The theoretical and simulation results also prove that the length of the nanowire does not influence the piezoelectric potential in a lateral bent nanowire.

In general, Quartz, Feldspar, Ball Clay, and Dolomite are the main raw materials used in the tile industry. The availability of quality Ball Clay for the tile manufacturing industry has decreased over the years in Sri Lanka and the tile industry intends to substitute ball clay with another suitable clay. In this study, the New Kaolin source was investigated for the tile industry as the main clay mineral with Feldspar, Dolomite, and Bentonite Clay. Initially, new Kaolin clay was characterized using X-ray diffraction, wet chemical analysis, and differential thermal analysis. It consists of 56.78% of Silica. The body mix of the tiles was prepared and the Particle size distribution of the body mix was determined. The shape of the tiles was obtained using a powder pressing method. Samples were dried in an oven and fired in a muffle furnace at 1100°C, 1150°C, 1180°C, and 1200°C. Relationships between the physical properties of the fired tiles have been established. The improved physical properties of tiles at the firing temperature of 1200 0C complied with ISO 13006 standard. Based on this study, M2 Kaolin can be strongly recommended as a highly appropriate clay material for the ceramic tiles manufacturing industry in Sri Lanka.

The wet chemical synthesis of Nano-Hydroxyapatite HAP [Ca10(PO 4 ) 6 (OH) 2 ] derived from precursors Ca(OH) 2 and H 3 PO 4 was experimented using a kinetic model derived based on the classical nucleation theory. The model gives a mathematical formulation for the nucleation rate in terms of the process variables of the wet chemical synthesis namely supersaturation, temperature, and interfacial tension. Only the effect of supersaturation for nano formation was studied in the experimental work of this study. The different supersaturations for five different samples were initiated by changing the precursor concentrations keeping the Ca/P molar ratio at 1.6 to 1.7 in the solution being mixed. Finally, the model was statistically and experimentally validated using Fourier Transform Infrared Spectroscopy (FTIR) analysis, and data obtained by laser particle analyzer. This model can be potentially used to synthesize Nano-Hydroxyapatite particles in a quantitative manner changing the supersaturation of the wet medium by precursor concentrations.

This study was focused on modeling and simulation of micro size ultrasonic generator and receiver of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) using finite element analysis (FEA). When PZT-5 H was selected as both ultrasonic generator and receiver, the resonance frequency of the generator and receiver were determined as 15 MHz and 13 MHz respectively and the simulation was performed at 13 MHz frequency to generate ultrasonic wave. In addition to that, when PVDF was utilized as the receiver material its resonance frequency was determined as 10 MHz and therefore simulation was performed at 10 MHz. The resonance frequency remains the same (5 MHz) When PVDF was selected as an ultrasonic generator with whatever receiver materials (PVDF and PZT-5H) used. Then the generated ultrasonic wave was directed to hit the ultrasonic receiver to generate electric potential. To compare and validate the induced voltage across the receiver mathematical equation was derived using piezoelectric constitutive equations. When PVDF worked as receiver it generated higher voltage value than PZT-5H. On the other hand, when PZT-5H worked as an ultrasonic generator, it induced higher voltage across the receiver.

Chitosan/nanohydroxyapatite composite was synthesized by co-precipitation of nanohydroxyapatite onto a chitosan scaffold. The aim of this research was to extract chitosan from locally sourced shrimp shells species Penaeus Monodon and to synthesize chitosan/nanohydroxyapatite composite. The morphology, crystalline structure and composition of the composites were investigated using Scanning electron microscopic analysis, X-ray diffractometry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Hydroxyapatite nanoparticles dispersed in the chitosan matrix were observed in the scanning electron microscope (SEM). The size of the nanohydroxyapatite particles was estimated to be 13 nm by the X-ray diffractometer pattern using the Halder-Wagner method and this value was confirmed by the SEM images. From the energy dispersive X-ray analysis, the Ca/P weight ratio obtained was around 2 which equivalents to that of hydroxyapatite. The thermogravimetric analysis measurements of the composites concluded that the decomposition temperature decreases with increasing Hydroxyapatite content.

Drying process of green ceramic bodies are complicated due to simultaneous and coupled heat and mass transfers. Dimensional variations and mechanical stresses occur within the ceramic body during drying may create defects in the final product if drying conditions are not carefully controlled. In this study, the drying behavior of Sri Lankan Kaolin was investigated. Initially, Kaolin was characterized using wet chemical analysis and X-ray diffraction to investigate structure and composition. Two batches of Kaolin with different particle size distributions were prepared using wet ball mill grinding with average particles size (D50) of $4.07\ \mu\mathrm{m}$ and $3.57\ \mu\mathrm{m}$ respectively. Green ceramic samples were obtained using extrusion process. Samples were dried in oven at 60°C and moisture variation of the green product was measured with time. Critical moisture content of the Sri Lankan Kaolin was 1.50%. Mathematical relationship was formulated to determine drying behavior of Sri Lankan Kaolin. An unsteady three-dimensional (3D) model was developed and simulated in Computational Fluid Dynamics (CFD) framework. Simulation results developed by the model were compared with data obtained by experiments conducted using Sri Lankan Kaolin. The model results were validated and comply with experiments results and R2 value was 0.9.

In this research, a low cost piezoelectric ultrasonic wave generator was developed using mathematical calculation and finite element analysis. Then a prototype was fabricated to compare the performance. Resonance frequency, dimensions of design and acoustic impedance of matching layer and backing layer were determined by mathematical calculation. To optimize the parameters of the design, finite element analysis was used. The layer parameters were calculated using 3D model of Finite Element Analysis. Finally, transmitting wave frequencies in water and air were calculated from acoustic pressure variation, which derived as a result of simulation using 2D axisymmetric model. Arduino software was used to feed controlled electric signal to piezoelectric material. Based on Finite Element Analysis, the prototype device was fabricated using Lead Zirconate Titanate as the piezoelectric ceramic, Aluminum as the matching layer and Low Carbon Steel as the backing layer. Terminal wires were soldered and all three were merged together using glue gun with polymer based binders. Testing of the prototype was performed using the Oscilloscope. The resonance was observed at 75 kHz, 182 kHz, and 231 kHz. It was also confirmed by Impedance vs. Frequency analysis using Inductance Capacitance Resistance meter.

When buildings are exposed to vibration or shock, those buildings can be damaged partially or fully depending on the vibration energy. Therefore, quantitative analysis of building vibration has become popular among researchers. In this research, vibration sensor was developed using piezoelectric ceramic cantilever beam and tip mass to confirm the vibration frequency of the building does not exceed the cosmetic damage range. As the first step, mathematical model was derived to calculate the resonance frequency of cantilever beam with a tip mass. At the resonance frequency, maximum amplitude could be achieved resulting a higher output voltage of piezoelectric sensor. The derived mathematical model and finite element analysis were used to determine the accurate dimensions of the cantilever beam based piezoelectric sensor. 31 coupling mode was used to measure the voltage difference in piezoelectric material. Faster Fourier Transformation function was used to analyze the signal. Output voltage of piezoelectric sensor was calculated using finite element analysis at vibration frequency range that corresponds to cosmetic damage. According to the calculations, threshold voltage level and frequency of sensor are 4.35mv and 9.5Hz respectively to activate the alarm. Finally, by using a vibration source, comparatively high accuracy of 92% voltage value was obtained from the prototype device compare to the software modelling. The developed sensor module is capable of indicating harmful vibrations on building structures.

Many toys for children are partly or totally made of plastic. In these plastics, additives such as lead (Pb), cadmium (Cd), arsenic (As), chromium (Cr) and mercury (Hg) are added as pigments, fillers, UV stabilisers and plasticisers which are used to alter the properties of the material or to improve the production process. These additives, unreacted starting substances and impurities, can migrate from the plastic. As young children chew, lick and suck frequently on their toys, they can ingest certain amount of these compounds. The aim of this study was to identify the presence of heavy metals in plastic toy samples collected from market. Total of 145 plastic toys were screened on-site using handheld X-ray Fluorescence spectrometer (Skyray instrument-Genius 3000XRF) in Colombo Fort and Pettah area. The XRF device equipped with beryllium-window Silicon Drift Detector and 139 eV resolution was held on to the surface of the product and measurement was triggered for 45s in Plastics Mode. To eliminate the possibility of contamination, dust was removed prior to the XRF measurement. The built-in intensity correction method of the device corrects all deviations from samples of irregular geometric shape and uneven structure and density. The imported plastic toys were randomly selected from wholesale shops, retail shops and road side stalls considering accessibility to middle and low-income families. Results of the study revealed that the plastic toys contain heavy metals; Pb from 30.34 to 4,469.09 mg/kg, Cd from 15.09 to 1,140.73 mg/kg, As from 15.53 to 46.02 mg/kg, Cr from 15.21 to 247.78 mg/kg and Hg from 28.12 to 94.92 mg/kg respectively. Out of these 8.97% show high level of Cd and 1.38% show high level of Pb. However, the concentrations of Cr, As and Hg are under the permissible limits as per the testing standards by Restriction of Hazardous Substances (RoHS) directive. The permissible limits as per the testing standards by RoHS directive are 100 mg/kg for Cd and 1,000 mg/kg for Pb, Hg, and Cr and As. These results of the present study revealed that some toys are potential sources of heavy metals. Keywords: Plastic toys, Heavy metals, XRF, Chemical screening

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.

In this study Glass fibre reinforced fly ash -cement roofing tiles were fabricated using three different forms of coal fly ash (CFA) such as CFA as it is, CFA particle sizes below 75μm and below 45μm.The separated CFA was used to replace cement 30% by the weight and those matrices were reinforced by Alkali Resistant (AR) glass fibres adding 1% and 2% by weight.The corrugated roof tiles have dimensions of 490×250×8mm and they were hand cast using ordinary vibration. Physical and mechanical tests were performed after 28 days of aging. The tiles were tested in accordance with SLS 1189. Transverse strength increased with increasing fibre percentage. Further, the transverse strength decreased with decreasing CFA particle size. Highest characteristic transverse strength was observed in the CFA as it is sample which is 1650N and the lowest from CFA below 45µm particle size sample which is 1240N. However, all the samples satisfy the strength requirement which is 230N. High water absorption was observed in all the samples which is around 20%.The dry density was ranged in between 1.62-1.68g/cm3 .The lowest average dry density was observed in CFA as it is samples whereas CFA below 75μm particle size and CFA below 45μm particle size samples showed similar density values. The dry density of tile samples is in comparable with the dry density of asbestos cement sheets (≈1.63g/cm3) and the characteristic transverse strength is in comparable with Calicut clay tiles (1000-2000N) in Sri Lanka. Therefore, glass fibre reinforced fly ash-cement roofing tiles are promising substitute for asbestos roofing sheets.

Clay has been a predominant industrial raw material from ancient periods in Sri Lanka. Abundant availability and quality of available clay has been few of the many reasons why clay products have been very popular in the country. Not much has been changed in the technology used in the fabrication of clay products mined from various sources, since ancient time. But with the development of the technology more research has been focused on using the existing minerals of the country for advanced applications. In many recent developments in polymer-clay nano composites, it has been discovered that usage of Montmorillonite clay in a polymer composite can greatly enhance many of its properties. Hence more focus has been given on the isolating of Montmorillonite nano particles which are suited for these composites applications. This research has been focused on extracting Montmorillonite nano particles from already existing clay deposits of the country, which in turn can be used in the synthetization of polymer-clay nano composite. Preliminary analyses were conducted on selected clay deposits to confirm the presence of Montmorillonite and then they were subjected to various processed to increase the clay constituents while removing the impurity contents. Afterward selected specimens were subjected to the Montmorillonite extraction which involved mainly the isolation of this clay mineral from other types. Resultants were then analyzed by using various techniques to confirm the presence of required properties.

Since heavy metal pollution is a significant aspect to aquatic ecosystems, the objective of this research work was to investigate adsorption characteristics of chitosan as an alternative adsorbent material. In this study, chitosan, synthesized from locally available shrimp type “penaeus monodon” was used to observe adsorption characteristics of cadmium (Cd) and lead (Pb) heavy metals from aqueous solution. Batch kinetic experiment studies were conducted for changing initial pH, initial concentration of metal ions, particle size and degree of deacetylation (DD) of chitosan. Simplified models such as, pseudo first order, pseudo second order and intra-particle diffusion models were used to analyze the experimental data. The result showed that the adsorption capacity strongly depends on pH and DD. It was clearly seen that higher adsorption of heavy metals occur at comparatively high pH and high DD. Equilibrium experimental data were analyzed by using two different isotherm models namely, Langmuir and Freundlich. The characteristic parameters for each isotherm and related correlation coefficients were determined by using mathematical modeling software. Isotherms show that adsorption process of Cd and Pb is a heterogeneous process.

Chitosan, a natural biopolymer synthesized from crustaceans shell, plays an influential role in accumulation of heavy metals from wastewater effluents because of its active functional groups. In this study, adsorption characteristics of cadmium and lead were studied using chitosan which was synthesized from locally available shrimps. Kinetic studies were conducted for batch systems using different pH values of initial metal ion solution and two different degree of deacetylation (DD) values of chitosan. Simplified models such as pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations were used to determine the rate controlling step. A strong dependence of the adsorption capacity on pH and DD was observed, the capacity increases as pH and DD values increase.Tropical Agricultural Research Vol. 26 (2): 395 – 401 (2015)