Papers by Keyword: Graphite

Abstract: In the present study, the experimental results of the mechanical properties of Al6061-Graphite composites presented. The composites containing 6 to 9 wt% of graphite in steps of 3 wt% were prepared using liquid metallurgy route in particular stir casting technique. For each composite, reinforcement particles were preheated to a temperature of 250°C and then dispersed in steps of two into the vortex of molten Al6061 alloy to improve the wettability and distribution. Microstructural characterization was investigated by optical and scanning electron microscopy. Tensile and hardness tests were carried out in order to identify mechanical properties of composites. The results of microstructural study revealed uniform distribution of graphite particles and low porosity in micro composite specimens.The results of this study revealed that as graphite percentage was increased, there was significant increase in ultimate tensile strength, yield strength and ductility, accompanied by a nominal drop in the hardness of the material

Abstract: Porous Sb-doped barium titanate (Sb-BaTiO3) ceramics were fabricated by adding various amounts of graphite powders. The density, structure, microstructure, porosity and electrical resistivity of the porous Sb-BaTiO3 ceramics produced without and with graphite were investigated. All the sintered ceramics showed a tetragonal perovskite structure, irrespective of the amount of graphite added. The porosity of the ceramics increased and the grain size decreased with increasing graphite addition which mainly due to the exothermic reactions of the graphite and oxygen molecules in the ceramics. The prepared porous Sb-BaTiO3 ceramics exhibit PTCR behavior where the PTCR jump of the ceramics with graphite was about 103 which is higher than that of the ceramics without graphite. The increasing in the PTCR jump with increasing graphite addition was attributed mainly due to the increase in the electrical barrier height of grain boundaries and the porosity. It was found that the graphite is an effective pore forming agent for fabricating porous BaTiO3-based ceramics.

Abstract: Nitrogenated ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were prepared in hydrogen and nitrogen mixed-gas atmospheres by pulsed laser deposition using graphite targets. The electrical conductivity in n-type conduction remarkably increase at room temperature with an increase in the nitrogen content. In the nitrogen content range from 7.9 to 10.4 at.%, the electrical conductivity is dramatically decreased and this accompanied by the disappearance of diamond grains in the films. Grain boundaries owing to the existence of diamond grains embedded in UNCD/a-C:H films, which is structural specific to UNCD/a-C:H, should play a significant role in the large electrical conductivity enhancement by nitrogen doping. The X-ray photoemission and near-edge X-ray fine-absorption spectroscopic measurements could not detect an evident difference in the spectra that explain the sudden irregular change in the electrical conductivity

Abstract: Experimental and theoretical studies on the erosion of silica phenolic nozzles with graphite inserts in solid rocket motors were carried out. Two identical segmented nozzles, consisting of graphite inserts and silica phenolic insulation in the convergent and divergent sections, were tested at same operating condition. Due to the different thermal resistance ability, steps are formed at the interface of two materials. The erosion rates, following the distribution of Reynolds number, exhibit an upward trend in the convergent section and decrease in the divergent section for both silicon phenolic and graphite. At high temperature, the graphite erosion rate is limited by the diffusion rate of the oxidizing species,while the erosion rate is limited by the chemical kinetics at low temperature. For the graphite nozzle insert, a switch from kinetics mechanism to diffusion mechanism occurs in the convergent section during the firing test.

Abstract: To figure out the physical and mechanical performance of graphite foam concrete，orthogonal test was applied to ascertain four factors for graphite foamed cement-based material (GFCBM). The influence of water cement ratio, graphite content, hydrogen peroxide content and sodium sulfite content on the dry density, porosity and compressive strength was also discussed. The results show that sodium sulfite has a relatively significant effect on the physical and mechanical performance. The dry density and compressive strength increases first and then decrease with the water cement ratio, adding of hydrogen peroxide and sodium sulfite increasing and increase with adding of the graphite. The trend of porosity is opposite to the dry density and compressive strength. The optimal scheme for this experiment is water cement ratio 0.68, 5% graphite, 8% hydrogen peroxide and 6% sodium sulfate.

Abstract: Graphite-containing plasma electrolytic oxidation (PEO) composite coatings were prepared on Al alloy using periodically constant voltage, with addition of graphite in silicate electrolyte. The surface and cross-sectional morphologies of the coatings were examined using scanning electron microscope (SEM), the composition of the coatings was investigated by X-ray diffraction (XRD) and Raman spectra, the tribological properties of the coatings were evaluated on a tribometer. The results show that friction-reducing PEO composite coatings on Al alloy can be prepared in graphite-dispersed electrolyte using periodically constant voltage, the yielded coatings exhibit relatively lower and more stable friction coefficient.

Abstract: Electromagnetic radiation has become a great threat to human health. In this paper, ferrite and graphite were main absorbing agent, which were prepared to a new type of anti-electromagnetic radiation gypsum board. The results show that the microwave absorbing properties of ferrite/graphite mixed are better than with ferrite or graphite single-agent mixed. The gypsum board with the graphite content of 5wt% and the ferrite content of 25wt% has the best absorbing performance, The effective band width less than-5dB of the samples is 7.1311GHz, and the maximum absorption peak-18.467dB.

Abstract: There were many problems when natural flake graphite was used in gypsum as an absorbing agent, such as absorbing large amount of water, a poor interfacial compatibility and so on. In this paper, polycarboxylate-based water reducer and AES (sodium alcohol ether sulphate) are used to modify graphite-gypsum system. The results show that both agents are effective to improve the properties of gypsum system and the former is best. Compared with the sample without any reagents, polycarboxylate-based water reducer can reduce the water-solid ratio from 1.1 to 0.9, increase the compressive strength from 0.106Mpa to 0.701Mpa and the flexural strength form 0.064Mpa to 0.312Mpa.

Abstract: Over the past decade, rapid progress has been made in the understanding and development of Hybrid Conductive Composite (HCC) to be used as bipolar plate, one of the most important components in Polymer Exchange Membrane Fuel Cell (PEMFC). The formation processes of HCC and loading ratios of composite have significant effects on their properties especially electrical and mechanical properties. Thus, the research focuses on Graphite (Gr) as a filler and Stannum (Sn) as a binder in fabrication of HCC as a bipolar plate. The fabrication process began with Gr and Sn needed to dry mixed used ball mill with several ratios of loading, which are 60/40, 70/30 and 80/20 respectively. The shape of this composite was molded with a diameter of 25 mm through hot compression machine to form discs. The effect of different loadings on the properties such as electrical conductivity, bulk density and microstructure were observed and confirmed to be able to meet the DOE target properties as PEMFC bipolar plates. The result showed that Gr/Sn composite with 20 wt% Sn had the highest electrical conductivity which was 720 S/cm. In the other side, the bulk density showed decrement as Sn contents increased from 1.71 to 1.48 g/cm³. The findings promise an enhanced performance of HCC as a bipolar plate to be used in PEMFC which is beneficial for mobile and portable application industry. A further study on agglomeration and the mechanical properties such as the flexure strength and hardness should be pursued.

Abstract: Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an alternative energy system that has been verified with great potential for high power density, durability and cost effectiveness. Since the bipolar plate is the key component in PEMFC, the component must operate with multifunction and have a balance of properties, essentially well in both electrical and mechanical properties. At present, many different materials have been tested to be applied for bipolar plate in order to fulfill the balance in each property. In this work, the different material is tested and observed. Polypropylene (PP) is used as a binder material, Graphite (Gr) is used as a main filler and Carbon Black (CB), Iron (Fe) and Nickel (Ni) as the second filler. This composite is produced through compression molding and the effect of different filler material loading on the properties such as electrical conductivity, flexural strength, bulk density and shore hardness are observed. The result showed the increasing of electrical conductivity as the increased the CB and Fe loading. But for Ni, the result showed the decreasing of electrical conductivity as the loading of Ni has been increased. The targeted value also achieved for some certain degree of filler loading.