Katya Ignatova, Iskra Piroeva, Stela Vladimitova-Atanasova 99 Journal of Chemical Technology and Metallurgy, 51, 1, 2016, 99-105 EFFECT OF THE ELECTRODEPOSITION CONDITIONS ON THE MORPHOLOGY AND CORROSION BEHAVIOR OF Ni-Co ALLOYS PART 1: CHEMICAL COMPOSITION, CATHODIC CURRENT EFFICIENCY, AND MORPHOLOGY OF Ni-Co ALLOYS ELECTRODEPOSITED FROM CITRATE ELECTROLYTE Katya Ignatova 1 , Iskra Piroeva 2 , Stela Vladimitova-Atanasova 2 1 University of Chemical Technology and Metallurgy Department of Inorganic and Electrochemical Technologies 8 Kl. Ohridski, 1756 Sofa, Bulgaria E-mail: katya59ignatova@gmail.com 2 Bulgarian Academy of Sciences Institute of Physiсal Chemistry “Rostislav Kaishev” Laboratory of Scanning Electron Microscopy ABSTRACT Ni-Co alloys with varying cobalt content are electrodeposited in stationary potentiostatic mode employing citrate electrolyte, either with or without addition of saccharin (SHR) at different Ni/Co ratios and variable content of sodium citrate (Na 3 citrate) in the electrolyte. The changes in the microstructure, chemical composition and cathodic current ef- fciency of deposition (CCE) of Ni-Co alloys are studied. Scanning electron microscope, energy dispersive X-Ray and atomic absorbtion analysis are used to characterize the alloy coating.The alloy deposition is proved to be of an anomalous type. It is found that with the increase of the value of ratio Ni/Со in the solution from 1 to 5, the percentage of Ni in the Ni-Co alloy grows to 48 mass %, and the CCE decreases to about 70 %, whereas more fne-crystalline Ni-Co coatings (size of crystallites less than 100 nm) are deposited. The addition of SHR results in a strong decrease of CCE (up to 50 %), but also in formation of smooth and shimmering coatings with average size of crystallites much less than 50 nm. The coatings obtained from electrolyte with higher content of sodium citrate contain more Ni but are more coarse-crystalline, as the effect of the complexing agent is generally less pronounced in comparison with the case with SHR addition. Keywords: Ni-Co alloys, anomalous deposition, polarization studies, morphology, stationary potentiostatic mode. Received 23 April 2015 Accepted 01 October 2015 INTRODUCTION The nanostructured alloys and multilayer coatings, based on Ni and Co, have been highly topical recently in such areas as magnetoelectronics and medicine but also in oil, automotive and nuclear power industry [3] mainly due to the fact that the crystallites reach size of less than 100 nm, the microhardness, wear resistance, and corrosion resistance unevenly increase, unlike the conventional polycrystalline coatings [1 - 4]. The Ni-Co alloys are employed because of their specifc magnetic and catalytic properties behavior combined with excel- lent mechanical and corrosion behavior [2, 3] inmagnetic sensors, actuators and inductors, and in fuel elements [3, 5, 6]. The deposition of Ni and Со is of “anomalous” type in almost all studied electrolytes, i.e. such with predomi- nant deposition of the more negative metal, which is Co in the current case [2, 3, 7 - 9]. This type of deposition is typical for the metals of iron group [2, 3] and shall be considered in the development of electrolytes and the selection of deposition methods. The Ni-Co alloys are deposited from sulphateelec- trolyte [8, 10 - 13] or typical Watts electrolyte [6, 10], chloride 10, 14], chloride-sulphate [15, 16], sulphamate [5, 7, 17, 18], glycinate [19], gluconate [20] and citrate