Advanced Materials Research Vols. 55-57

Abstract: Hybrid solar cells based on conjugated polymer poly(2-methoxy,5-(2’-ethylhexyloxy)-p-phenylene vinylene (MEH-PPV) and inorganic n-type zinc oxide (ZnO) nanoparticles were investigated. Polymer solar cells consisting of conducting polymer alone have low minority carrier mobility, for example, MEH-PPV has a high hole mobility but a low electron mobility. The intrinsic carrier mobility imbalance in the MEH-PPV severely limits the performance of pure polymer based solar cells. To overcome this imbalance, another material, i.e. n-type ZnO particles, is incorporated to act as an electron acceptor and a pathway for electron transport. In this experiment, as an active layer, ZnO nanoparticles synthesized in-house were blended with MEH-PPV purchased from Sigma-Aldrich. The front transparent conduction oxide (TCO) electrode used was commercial glass substrate coated with indium tin oxide (ITO) thin film. Blends of MEH-PPV with 0-30 wt% of ZnO in 1,2-dichlorobenzene were prepared and fabricated as active layers of the solar cells. The PEDOT:PSS and active layer were spin-coated onto ITO coated glass substrate. Aluminum was used for the top electrodes. The effects of ZnO solid content and film morphology on the performance of MEH-PPV:ZnO nanoparticle composite solar cells were investigated. Transmission electron microscopy (TEM) revealed that the ZnO nanoparticles consisted of a mixture of spherical and rod-like shapes. An increase in ZnO solid content resulted in an increase in size of the ZnO network. This was found to increase electron transport and, hence, improve solar cell performance.

Abstract: The main purpose of this work is to study the structure of Anadara granosa shell sample and its structural transformation upon heat treatments. The sample was ground and characterized as powder throughout this work. Structural identifications of all samples were characterized, and determined qualitatively by using X-ray diffraction, IR spectroscopy and thermogravimetry measurement (TGA). It was found that the specimen is made of aragonite, a common phase of CaCO3 mineral. The powder sample was annealed at specific temperatures over the range of 200°C - 900°C and the effects of heat treatment on the structure of Anadara granosa shell samples were studied. The results show that aragonite transforms to calcite at the temperatures between 200°C and 400°C and completely becomes calcite between 400-500°C. Then, the calcite transforms to calcium oxide at the temperatures between 500°C - 900°C. The exact structures and quantities of phase at different annealing temperatures were studied by Rietveld refinement. In our study, we also used IR spectroscopy and TGA to study the effect of water absorption of the samples on the phase transformation.

Abstract: The main purpose of this work is to study the structure of Anadara granosa shell sample and its structural transformation upon heat treatments. The sample was ground and characterized as powder throughout this work. Structural identifications of all samples were characterized, and determined qualitatively by using X-ray diffraction, IR spectroscopy and thermogravimetry measurement (TGA). It was found that the specimen is made of aragonite, a common phase of CaCO3 mineral. The powder sample was annealed at specific temperatures over the range of 200°C - 900°C and the effects of heat treatment on the structure of Anadara granosa shell samples were studied. The results show that aragonite transforms to calcite at the temperatures between 200°C and 400°C and completely becomes calcite between 400-500°C. Then, the calcite transforms to calcium oxide at the temperatures between 500°C - 900°C. The exact structures and quantities of phase at different annealing temperatures were studied by Rietveld refinement. In our study, we also used IR spectroscopy and TGA to study the effect of water absorption of the samples on the phase transformation.

Abstract: The Zn0.8Co0.2O ceramics were synthesized by the solid state reaction method with the mixture of ZnO and CoO powders. The mixed powders were sintered at 1200 °C and 1300 °C for 4 hours. It was found that the X-ray diffraction patterns of Zn0.8Co0.2O ceramics were similar to that of the pure ZnO one. The crystal structure of Zn0.8Co0.2O ceramics were then determined using the Rietveld full-profile analysis method to indicate a single phase with a wurtzite-like structure. Their microstructures were examined using the scanning electron microscopy. The results showed that their grain sizes were increased with increasing both the sintering temperatures and the doping effect. Moreover, the optical absorption spectra using UV-Vis spectrometer showed that there were several extra absorption bands appearing in the Zn0.8Co0.2O samples. This confirms that Co2+ is substituted Zn2+ in the wurtzite structure.

Abstract: Montmorillonite is a type of clays that has been used to reinforce polymer including rubber. Therefore this research is aimed to modify mechanical properties of natural rubber (NR) using montmorillonite (MMT) comparing with the organic modified montmorillonite (CTAB-MMT) and organic molecule grafted MMT. The affect of MMT, CTAB-MMT and HTMS-g-CTABMMT on cure characteristics of NR were studied. It was found from the research that the increase of MMT content could prolong the scorch time whereas CTAB-MMT and HTMS-g-CTABMMT could shorten the scorch time. The cure times of the compounds in all cases were not much different. In term of mechanical properties, modulus, tensile strength and tear strength of NR/HTMS-g-CTABMMT vulcanizate were higher than those of NR/MMT and NR/CTAB-MMT vulcanizates. Meanwhile, elongation at break of the NR/ HTMS-g-CTABMMT vulcanizate decreased more than the latter cases

Abstract: There has been a number of works trying to improve thermal stability of PVC as it is one of the most widely used plastics for various applications. The incorporation of heat stabilizer is a general method to stabilize PVC. However, its thermal stability could also be improved by blending with polyethylene. Organoclay, montmorillonite (MMT) in particular, has been found to improve thermal stability of polymers due to its high temperature resistance. This research is aimed to use organic modified MMT (OMMT) to improve thermal property of PVC. It was found from the research that organic grafted MMT (O-g-MMT) could improve thermal stability of PVC better than OMMT. The mechanical properties of O-g-MMT/PVC and OMMT/PVC of the blends were also reported

Abstract: Three ceramic fibres VK-60, ABK and Nextel/VK-80 produced by the steam blowing and nozzle dissemination methods have been investigated for the effect of press load per unit area and temperatures using the advantageous transient plane source (ATPS) method in air. It was noticed that, with the increase of the aluminium content in the composition of the ceramic fibres, the thermal conductivity of the material decreases and the isolation properties improved. The Nextel/VK-80 fibre has the lowest and VK-60 the highest value of thermal conductivity at room temperature. The application of a press load results in an increase in the value of the thermal conductivity for all the fibres analysed. ABK fibres showed the least increase and Nextel/VK-80 registered an increase of about 10% in the value of thermal conductivity within the load increase from 0.6 to 6.6 kN m−2. However, above 6.6 kN m−2 the thermal conductivity of all the samples increased almost linearly. The thermal conductivity measurements as a function of temperature indicated the same trend for an increase in thermal conductivity for all the samples.

Abstract: In this research, titanium carbide-nickel (TiC-Ni) composites, with tungsten carbide addition, were fabricated by using a powder metallurgy technique. The TiC-Ni mixtures containing between 0-15 wt. % tungsten carbide (WC), were compacted and then sintered at 1300°C and 1400°C, respectively. The phase formation and microstructure of the WC-added TiC-Ni composites have been investigated by X-ray diffraction and scanning electron microscopy techniques. Mechanical properties of these composites were assessed by an indentation technique. The X-ray diffraction patterns showed no evidence of tungsten rich phases in the sintered WC-added cermets. This indicates that during the sintering process, tungsten carbide particles were dissolved in metallic binder phase (Ni phase) via dissolution/re-precipitation process during liquid phase sintering. The liquid phase formed during sintering process could improve sinterability of TiC-based cermets i.e., it could lower sintering temperatures. The TiC-Ni composites typically exhibited a core-rim structure. The cores consisted of undissolved TiC particles enveloped by rims of (Ti, W)C solid solution phase. Hardness of TiC-Ni composites increased with WC content. Sintering temperature also had a slight effect on hardness values.

Abstract: Sintered Fe-5 wt. % carbide (SiC or TiC) composites have been prepared via a powder metallurgy (P/M) route. Two carbide particle sizes, < 20 µm and 20-32 µm, were mixed with Fe powder. The powder mixtures were compacted and sintered at 3 different temperatures, 1100, 1150 and 1200 °C. Microstructures of sintered Fe-5 wt. % SiC composites showed evidence of SiC decomposition. The decomposed Si and C atoms diffused into Fe particles resulting in formation of solid solution of Si and C in Fe during sintering. During cooling, the solid solution of C in Fe decomposed to pearlite structure (ferrite and cementite (Fe3C) lamellar structure). Microstructures of sintered Fe-5 wt. % TiC composites showed no evidence of TiC decomposition at the investigated sintering temperatures. Because of the reaction between SiC and Fe, tensile strength and hardness of the sintered Fe-SiC composites were higher than those of the sintered Fe. Experimental results showed that strength and hardness of the sintered Fe-SiC composites increased with increasing sintering temperature and with decreasing SiC particle size. In contrast, mechanical properties of the sintered Fe-TiC composites were inferior to those of the sintered Fe. The reason of poor mechanical properties may be attributed to poor bonding between Fe and TiC particles.

Abstract: Cu powder extrusion developed in this work is aimed to be a pilot processing technique to plausibly replace conventional metal extrusion, which is higher in energy consumption and hence causes negative environment impact. In this study, both spherical- and irregular-shape Cu powders were used. 5 different binder formulae comprising low density polyethylene (LDPE); paraffin wax; and stearic acid of 25:70:5, 30:65:5, 35:60:5, 40:55:5 and 45:50:5 by weight were studied. Wettability between the binders and Cu powder of all formulae observed by naked eye appeared to be satisfactory. The binders were then mixed with 60% by volume of Cu powder. Rheological properties, observed using a capillary rheometer with 2 mm diameter orifice at 95°C, determined that the last 2 formulae gave sufficient green strength in the extrudate. However, only the latter binder formula gave extrudate with smooth surface. Downward extrusion with 45 cm distance from the die gave straight extrudates and no any distortion or warpage was found. Solvent debinding conditions using hexane at 40, 50 and 60°C were studied. The debinding at 50°C was the most effective in dissolving the binder and ensured that the Cu powder remained intact. The 15 cm-long Cu extrudates were sintered in H2 atmosphere at 1030°C for different times. Density and tensile strength of the sintered extrudates were determined.