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In this study, the effect of two different filler metals (ERNiCr-3 and ER308) on microstructure and corrosion resistance of gas tungsten arc welded AISI 304 has been investigated. The microstructure of the joints was investigated by optical and scanning electron microscope. The microhardness of samples was investigated to determine the mechanical properties of the welds. Also, the electrochemical corrosion resistance of the samples was studied by Tafel polarization and impedance analysis in 1 M hydrochloric acid. The results showed the niobium-rich carbides in the welded specimen by ERNiCr-3 filler, also this sample exhibited a higher hardness and corrosion resistance. The exchange current density and the polarization radius of the ERNiCr-3 filler metal were 0.069 mA and 244 Ω, and those of ER308 filler metal were 0.121 mA and 66 Ω, respectively. The higher hardness and corrosion resistance is attributed to the formation of hard niobium-rich carbides in the weld zone, which eliminates the formation of chromium carbides.

In the present study, the hydrogen evolution activity of the Ni−Mo/Al2O3 catalyst was investigated. This catalyst was produced by milling of oxide precursors of nickel oxide (NiO) and molybdenum trioxide (MoO3) with aluminum as a reducing agent. So that oxide precursors with 100 % excess aluminum on stoichiometric composition at different times were milled to perform complete reduction operations. Subsequently, X‐ray diffraction (XRD) analysis was performed for phase analysis and scanning electron microscopy (SEM) was used to investigate the microstructure. It was found that oxide precursors with 100 % excess aluminum on stoichiometric composition were reduced after 50 h of milling and nickel molybdenum/alumina composite was produced. On the other hand, to compare the activity of Ni−Mo/Al2O3 two different catalysts (57 NiMo, 80 NiMo) were also produced by the milling method. The specimens were transformed into pills of 10 mm in diameter and 3 mm in height at 900 MPa pressure. A furnace under an argon atmosphere at a temperature of 1400 °C was used to sinter the produced pills. Finally, the hydrogen evolution activity of this sample was investigated by linear polarization tests and impedance spectroscopy in 1 M KOH solution. The sample reduced with 100 % excess aluminum showed higher activity than the stoichiometric combination, with −62 mV cathodic‐Tafel slope, −70 mV over‐potential at a current density of −10 mA cm−2 and a charge transfer resistance of 126.6 ohms.

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