Master of Science By research
http://dl.lib.uom.lk/handle/123/15928
2024-03-28T22:19:43ZComputational study on lead alternative perovskites for perovskite solar cells
http://dl.lib.uom.lk/handle/123/16939
Computational study on lead alternative perovskites for perovskite solar cells
Kumarasinghe KAMM
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.
2020-01-01T00:00:00ZReinforcement of carboxylated nitrile rubber latex films by surface modified nanosilica
http://dl.lib.uom.lk/handle/123/14587
Reinforcement of carboxylated nitrile rubber latex films by surface modified nanosilica
Ramasinghe, RLP
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.
Correlation between corrosion rate and ultrasonic attenuation on steel
http://dl.lib.uom.lk/handle/123/13839
Correlation between corrosion rate and ultrasonic attenuation on steel
Dayananda, HGSM
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.
Reinforcement of carboxylated acrylonitrile-butadiene rubber latex films by surface modified fillers
http://dl.lib.uom.lk/handle/123/13824
Reinforcement of carboxylated acrylonitrile-butadiene rubber latex films by surface modified fillers
Liyanaarachchi, LADA
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.