| Fuel cells have attracted considerable attention of domestic and international researchers and governments, due to its unique characteristics, such as high conversion percentage of energy, low volume of emission, simplicity of module structure, convenience for maintenance, etc. Bipolar plate is one of the important parts in fuel cell. Its electrical conductivity, molding, machining properties, and service life have much room for improvement, and the cost remains to be lower. Therefore, the research and development for new material is is currently a subject of extreme importance. In this study, the Ti3SiC2-based composite was synthesized with elemental powders by hot-pressed sintering method. Dependence of the synthesis and properties of the composite on the sintering techniques and the additional C content was investigated. The sintering aid was added to improve the properties of the composite for bipolar plate. In order to expand the selection range of fuel cell bipolar plate and make it cost-effective, the composite is expected to be used as the material for it.According to the performance requirements on fuel cell bipolar plate made by Department of Energy (DOE), some conditions such as the sintering temperature, additional C content were optimized so as to analyze the factors affecting the mechanical property and electrical property of the Ti3SiC2-based composite. The results show that all the properties of the composite which was synthesized using the preparation technology above can meet the requirements of bipolar plate. The optimal sintering conditions are1400℃for the sintering temperature, and5wt%for the content of additional C content. Under such conditions, the composite achieved the bending strength of447.80MPa, the electrical conductivity of28155.68s·cm-1, which reduced by8.43%and5.56%after corrosion process, respectively. The composite also has the residual bending strength of155.71MPa at the thermal shock temperature of900℃, the mean thermal expansion coefficient of12.22×10-6K-1within the range of40℃-900℃, and the electrical conductivity of5287.9s-cm"1at the temperature of900℃Al was used as sintering aid in order to improve the properties of the Ti3SiC2-based composite. The influences of sintering temperature, holding time, and additional C content on the properties of the composite were investigated in details. The results show that with the increase of the sintering temperature and the decrease of the additional C content, the bending strength and the electrical conductivity of the composite increase. With the increase of holding time, the bending strength and the electrical conductivity rise when the holding time is less than60minutes, and decline as the holding time increases further. The whole properties of the composite are improved dramatically, and it is completely applicable in the fuel cell bipolar plate. Compared to the composite without the sintering aid, the optimum one synthesized with the sintering aid achieved the bending strength higher by107MPa, the electrical conductivity higher by10812.26s-cm"’. The composite has the reduction rate of the bending strength and electrical conductivity after corrosion lower by1.1%and0.41%. the residual bending strength higher by18.04MPa at the thermal shock temperature difference of900℃, the mean thermal expansion coefficient lower by0.23K-1within the range of40℃-900℃, electrical conductivity higher by6563.82s-cm-1at the temperature of900℃.Through analyzing the composition of the composite conductive network, it is concluded that with the decrease of Ti3SiC2volume fraction, the electrical conductivity calculated by the estimation formulae decrease. The electrical conductivity errors of the composite with higher Ti3SiC2volume fraction are low. As for the composite with Ti3SiC2volume fraction of73.38, its calculated electrical conductivity which is not revised is higher than that of the experimental values by a huge difference. With the evident decrease of Ti3SiC2volume fraction, the errors caused by the estimation formula which is not revised become lower slightly, while the errors caused by the revised estimation formula increase obviously. Through analyzing the electron movement in the current channel of the composite, it is concluded that more high crystallinity of Ti3SiC2, higher densification of the composite and less other phases are beneficial to the electron movement, which result in higher electrical conductivity of the composite. |
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