Electrodeposition of Ni-Mo Defect-Free Alloy from Ammonium-Citrate Electrolyte in Pulse Current Mode
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Electrodeposition of Ni-Mo Defect-Free Alloy from Ammonium-Citrate Electrolyte in Pulse Current Mode Sergey M. Karabanov, Yulia M. Stryuchkova, Dmitriy V. Suvorov, Gennadiy P. Gololobov, Dmitry Yu. Tarabrin, Nikolay B. Rybin and Evgeniy V. Slivkin Ryazan State Radio Engineering University, 59/1 Gagarina St., Ryazan 390005, Russia ABSTRACT Electrodeposition in pulse current mode of nickel-molybdenum alloy on a nickel substrate was studied. The range of current density variation from 2 to 9 A/dm2 was investigated. The range of pulse and pause step lengths is from tens to hundreds of milliseconds. SEM-images of applied coatings surfaces are obtained. The method of energy dispersive spectroscopy determined that the molybdenum content in the coating is 21-24 wt%. It was found that under transient pulse mode of electrolysis, with the pulse step corresponding to hundreds of milliseconds, the most rigid and smooth coatings of the electrolytic nickel-molybdenum alloy are obtained from ammonium-citrate electrolyte. It is shown that the percentage of nickel in the alloy does not depend on the electrolysis mode. INTRODUCTION Electrolytic nickel-molybdenum alloy is widely used in science and technology due to a number of valuable properties. Because of a highly dispersed structure approaching amorphous one, high erosion resistance, mechanical strength and durability, heat resistance, this alloy is used, e.g., in reed switch contact coatings [1], accelerator-controlled nuclear reactors. Its catalytic properties with respect to the hydrogen evolution reaction in acidic media are known [2]. Currently, the most inexpensive and available way for obtaining coatings with the nickel-molybdenum alloy is the method of electrochemical deposition. This method does not require high energy costs or special complex equipment. The characteristics of the electrolytic alloy depend on the electrolyte composition and the electrolysis mode. There are a number of advantages of coatings electrodeposition in unstable electrolysis mode in comparison with the direct current mode [3]. Coatings deposited in such a mode are of high purity. Besides, the variation of electrical parameters makes it possible to control their structure. There are some works on the deposition of nickel-molybdenum alloy from ammonium-citrate electrolyte in pulse current mode [4]. The quality improvement of the coating under pulse mode is caused by decrease of the diffusion layer width by the substrate surface, which is a cathode; by alignment of the distribution of the ion-ligand concentration along the deposited coating surface; and by more efficient removal of hydrogen microbubbles from the surface. In pulse mode all these factors lead to the formation of fine-grain and dense coatings in comparison with the direct current mode. However, they do not contain comparison with electrodeposition in direct current mode and the advantages of pulse electrodeposition mode are not clearly shown. In this work, nickel-molybdenum alloy deposition from an ammonia-citrate electrolyte, the compo
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