Nickel-cobalt alloy coatings prepared by electrodeposition Part I: Cathodic current efficiency, alloy composition, polar
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Nickel-cobalt alloy coatings prepared by electrodeposition Part I: Cathodic current efficiency, alloy composition, polarization behavior and throwing power Rasha Muneer Al Radadi* and Magdy Ahmed Mahmoud Ibrahim**,† *Chemistry Department, Faculty of Science, Taibah University, Al Madinah Al Mounwara, 30002 Saudi Arabia **Chemistry Department, Faculty of Science, Ain Shams University, Abbassia, Cairo, 11566 Egypt (Received 17 January 2020 • Revised 29 March 2020 • Accepted 1 April 2020) AbstractA systematic study was carried out to electrodeposit Ni-Co alloy coatings from a complexing acidic glycine bath on copper substrates. The effects of [Co2+]/[Ni2+] ratio, gly concentration, pH, current density and temperature on the current efficiency, Co content in the coatings and on polarization behavior were investigated. It was found that the CCE of these baths has a wide range starting from 55% up to a maximum value of 99.3%, relying on the operating parameters and the bath constituent. However, the CCE decreased from 96.2% to 84.8% when the gly content was enhanced from 25 to 150 g/L. On the other hand, the Co content in the deposit reached 97% (wt%) at [Co2+]/ [Ni2+]=0.43, i=16 mA cm2, t=10 min, T=20 oC. The codeposition of Co and Ni from acidic gly baths obeys the anomalous type of codeposition. The kinetic results indicate that the Tafel slope increased in the case of alloy deposition, while both the transfer coefficient c and the exchange current io decreased. Moreover, the obtained results indicated that increasing the Co2+ content in the electrolytic solution has an inhibiting impact on the kinetics of the nickel-cobalt alloy plating. The throwing power is enhanced with enhancing [Co2+]/[Ni2+] ratios, while the addition of gly decreases it. However, the outcomes of macrothrowing power, throwing index and Wagner numbers are in excellent accord. Keywords: Ni-Co Alloy Coatings, Cathodic Efficiency, Tafel Lines, Throwing Power, Polarization Behavior
to its good action as a buffer and its ability to preserve the pH constant adjacent to the electrode surface [46,47,49-54]. Electrolytic plating solutions involving gly are characterized by good current efficiency and producing amorphous coatings [53]. Besides, electrolytic gly baths are more environment-favorable than classical cyanide solutions. Continuous to our successful electrodeposition of Co and Ni individually from acidic gly baths [53,54], it was ecxiting to investigate the codeposition of Ni-Co alloy coatings from these baths. Therefore, our aim was to examine the codeposition of Ni-Co coatings from acidic gly bath and to study the influence of some working circumstances, such as gly concentration, pH and temperature on the CCE%, Co percentage in the alloy, the polarization behavior and on the throwing power.
INTRODUCTION Nickel, cobalt and their alloy coatings are economically important in a variety of industrial applications, such as electronics, computers, automotive and devic
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