جستجوی مقالات مرتبط با کلیدواژه « پیل سوختی » در نشریات گروه « مواد و متالورژی »

Bipolar plates are one of the most important components in a PEM fuel cell. In this study, a bipolar plate made of stamping method is developed to increase electrical conductivity and mechanical behavior and manufacturing productivity of the fuel cell and to decrease electrical resistance according to DOE. For fabrication these plates, phenolic resins were used as matrix and expanded graphite to increase electrical conductivity and graphite to filler and carbon fiber to increase flexural strength and optimize electrical conductivity. The electrical conductivity increased up to 40 percent respect to the DOE. The flexural strength and impact strength of the measured specimens were improved respect to the DOE about 11 and 170 percent, respectively. The experimental results are in accordance with DOE. According to SEM images and test curves, electric conductivity increases with expanded graphite filler. Finally, the results showed that expanded graphite weight gain did not affect the mechanical behavior of the composite and increased the electrical conductivity.

Ni-Cr-Al-Hf alloys containing 0, 0.1, 0.2 and 0.4 wt.% Hf were produced and their isothermal oxidation behavior and electrical resistance has been investigated in air for 75 h at the temperature of 1000 °C. Microstructures of the oxidized samples were examined using scanning electron microscopy (SEM) and electrical resistance was measured. The samples showed different microstructures, and oxidation behavior depending on their chemical composition. The results indicated that the sample containing 0.4 wt.% Hf had the lowest weight gain, while the weight gain of the sample without Hf was the highest. An external scale of spinel overlying a region of internal oxides precipitates formed on Ni-12Cr-4.5Al. Conversely, an external Al2O3 formed on the samples containing Hf additions. In absence of Hf, Cr2O3 was the major scale that formed on surface. The improvement in the oxidation resistance is believed to be due to the transition between the internal and external oxidation of aluminum, adherent and protective Al2O3 oxide layer on the surface of the Ni-12Cr-4.5Al-0.4Hf alloy. It was found that the scale adhesion can be affected by mechanical keying at the alloy/scale interface resulting from the pegs’ formation during oxidation. Higher electrical resistance of Alloy without Hf is due to higher thickness of oxide scale formation on surface and sample with 0.4 wt.% Hf showed lowest electrical resistance due to thinner scale of Al2O3.

In the present study, the optimization of pulsed Nd:YAG laser welding parameters was done on a lap-joint of a 316L stainless steel foil in order to predict the weld geometry through response surface methodology. For this purpose, the effects of laser power, pulse duration, and frequency were investigated. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to evaluate the effect of welding parameters on weld width. The results showed that the weld width at the upper, middle and lower surfaces of weld cross section increases by increasing pulse durationand laser power; however, the effects of these parameters on the mentioned levels are different. The effect of pulse duration in the models of weld upper, middle and lower widths was calculated as 76, 73 and 68%, respectively. Moreover, the effect of power on theses widths was determined as 18, 24 and 28%, respectively. Finally, by superimposing these models, optimum conditions were obtained to attain a full penetration weld and the weld with no defects.

Chromium containing alloys are among the best candidates for solid oxide fuel cell interconnects. However, the problem of reduction of electrical conductivity during high temperature oxidation should be solved. The aim of this research was to investigate the electrical behavior of AISI 430 ferritic stainless steel which was coated in a Mn-base pack mixture by pack cementation method. Electrical conductivity was tested as a function of oxidation time at 750 ºC and as a function of temperature by annealing the samples from 400 to 900 ºC. Results showed that the coating layer was converted to Mn3O4 and MnFe2O4 spinels during oxidation. These spinels caused to the improvement of the electrical conductivity of coated substrates compared to uncoated substrates.