Electrodeposition of Ni-Fe-Mo-W Alloys - Part 9
Ninth Quarterly Report - AESF Research Project #R-117. This NASF-AESF Foundation research project report covers the ninth quarter of project work (January-March 2015). In this period, Graduate student Avinash Kola has continued work on the influence of deposition conditions on the properties of the Ni-W alloys.
#nasf #surfin #plating
A. Kola and Prof. E.J. Podlaha-Murphy,*
Boston, Massachusetts, USA
Editor’s Note: This NASF-AESF Foundation research project report covers the ninth quarter of project work (January-March 2015). Progress on the previous quarters has been published in summary in the NASF Report in Products Finishing and in full at www.pfonline.com.** A printable PDF version is available by clicking HERE.
The project, initiated in January 2013, addresses the induced codeposition of molybdenum and tungsten alloys with nickel and iron having a focus on developing a toolbox of plating conditions to deposit different combinations of Ni, Fe, Mo and W. Through NASF-AESF Foundation funding, several students, both graduate and undergraduate, have gained experience in surface finishing research. This paper covers progress made during the ninth quarter. In this period, Graduate student Avinash Kola has continued work on the influence of deposition conditions on the properties of the Ni-W alloys.
In our last report interesting electrodeposition behavior was observed with the additive 2-butyne-1,4-diol (BD) in a Ni-W electrolyte at low pH. This additive has been reported in the literature with Ni-W codeposition for the purpose of creating a more corrosion resistant deposit. In the 8th quarter, graduate student Avinash Kola examined parameters that influenced Ni-W deposition, with a notable change of composition reported with the addition of BD. The more BD added to the electrolyte, the higher the nickel content in the resulting deposit. The partial current density evaluation found that it was not the rate of the tungstate reduction that was altered but rather an increase in the nickel rate. It was an unexpected result since it has been documented in the literature that BD should cause nickel to be inhibited.1-3 To examine this behavior further, nickel was electrodeposited under the same conditions as Ni-W in a low pH citrate electrolyte in order to compare with our previous findings. In addition, we have started to examine the behavior at a higher pH in an effort to improve the current efficiency.
In this report all depositions were carried out in the traditional Hull cell with air agitation. The electrolyte used in this study contained 0.1M nickel sulfate, 0.15M sodium tungstate and 0.285M trisodium citrate at a pH of 2 and at room temperature. The BD concentration was varied from 0 to 5 mM. The average applied current density was 50 mA/cm2 on a copper plate in a Hull cell configuration for a duration of 30 min and at an agitation rate of 3 L/min (air). Polarization data was obtained by placing the electrodes parallel to each other, at a scan rate of 10 mV/sec, and with a Ag/AgCl reference electrode. The curves were corrected for ohmic drop with impedance spectroscopy. Composition and thickness were measured using x-ray fluorescence.
Ni electrodeposition in a low pH electrolyte (to compare with Ni-W)
In our previous report, and resulting paper publication in Products Finishing (http://short.pfonline.com/NASF15Jul1), a polarization curve of Ni-W with different amounts of BD showed a depolarizing effect, which was unexpected. In order to evaluate if this unusual trend in BD addition was due to the nature of the low pH electrolyte or the presence of tungstate, a nickel-only electrolyte was examined. Figure 1 shows the polarization behavior when elemental nickel is electrodeposited with different amounts of BD. Consistent with literature reports, there is a small inhibition of the polarization behavior seen at 5 mM BD, and with all BD additions at the low current density region. At higher current densities, there is a smaller difference. However, in this region considerable hydrogen evolution occurs. Figure 2 compares the different polarization curves of the elemental nickel and Ni-W alloy electrolytes at (a) no additive (b) 1 mM BD, (c) 2.5 mM BD and (d) 5 mM BD. The most striking observation is that, without the additive, the nickel-only deposition current density is larger than that of the Ni-W case at a given current density. However, once BD is added to the electrolyte the total current density in Ni-W electrolytes is larger than that for the elemental nickel. The larger the amount of BD, Figure 2 (b,c,d), the larger the difference between the polarization curves of nickel and Ni-W.