Fabrication and investigation of polymer-based carbon composite as gas diffusion layer of proton exchange membrane of fuel cells

Carbon paper is one of the most important component in polymer electrolyte PEM fuel cells. In this research, we report two methods of manufacturing carbon papers that do not need the steps of carbonization and graphitization are common steps in carbon paper. At first method (mixing method), the short carbon fibers have a random distribution in the composite and in the second method (fabric method), the long carbon fibers are oriented in planar configuration .In order to investigate on the properties, the effect of paper thickness and expanded graphite value have been considered and compared with Toray carbon paper. The characterization is performed by scanning electron microscope, maximum pore size, mean pore size, permeability, electrical conductivity, flexibility, and performance (I-V) curve. The results show that mixing method resulting in a higher electrical conductivity, pore size, and permeability, as well as I-V curve similar to Toray paper. In addition, the cost estimates and flexibility test show that both fabric and mixing methods results in a much lower cost, due to removing the graphitization and carbonization steps, and more flexible samples in comparison to Toray paper

Новый численный метод для определения эффективных упругих констант ортогонально армированных композитов

In this paper a composite material with similar cross-ply fibers is considered. Assuming orthotropic structure, theory of elasticity is used for investigating the stress concentration. The effective characteristicsof this composite are studied numerically by using ANSYS software. In this research a volume element of fibers in square array in the coordinate x, y, z and the generalized stress state is considered. In order to investigate the numerical finite element modeling, the modeling of a quarter unit cell is considered. For determining the elasticity coefficients, stress analysis is performed for considered volume with noting to boundary conditions. Effective elasticity and mechanical properties of composite which polymer epoxy is considered as its matrix, are determined theoretically and also by the proposed method in this paper with finite element method. Numerical experiments modeled four cases of uniaxial tension in the directions x, z and shear in the planes xy, yz. Finally, the variations of mechanical properties with respect to fiber-volume fraction are studied. Numerical results are compared with approximate estimates method proposed.Статья посвящена исследованию эффективных характеристик ортогонально армированных композитов. Результаты получены при помощи ПК ANSYS. В результате численного исследования напряженного состояния представительской ячейки были определены эффективные упругие свойства ортогонально армированного композита. Для нахождения эквивалентных упругих постоянных композитов выполнен анализ напряженного состояния представительской ячейки в координатах x, y, z и обобщенного напряженного состояния в программном комплексе ANSYS. Численными экспериментами смоделированы четыре случая одноосного растяжения в направлениях x, z и сдвиг в плоскости xy, yz

Electrochemical Evaluation of Hydroxyapatite/ZrN Coated Magnesium Biodegradable Alloy in Ringer Solution as a Simulated Body Fluid

Magnesium alloys as biodegradable materials can be used in body as an implant materials but since they have poor corrosion resistance, it is required to decrease their corrosion rate by biocompatible coatings. In this study, hydroxyapatite (HA) coatings in the presence of an intermediate layer of ZrN as a biocompatible material, deposited on AZ91 magnesium alloy by ion beam sputtering method at 300 °C temperature and at different times 180, 240, 300, 360 and 420 min. Then changes in corrosion resistance of samples in Ringer's solution as a solution similar to the human body was evaluated in two ways, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). To investigate the causes of the destruction of the samples, the surface of samples was studied by scanning electron microscopy (SEM). The results showed that because of porous coatings created, the corrosion potential of the samples was about +55mV higher than the uncoated substrate that by changing the deposition time, was not observed the significant change But with increasing deposition time to 360 min, corrosion current decreased which represents an increase of corrosion resistance of magnesium alloy in body solution. However, a further increase in deposition time to 420 min, due to increase thickness and stress in the layer, the corrosion resistance of the samples was reduced. The results of the EIS confirm the corrosion behavior of the polarization method, too.   </div