Nanoscale electropolishing of high-purity silver with a deep eutectic solvent

Significance Statement

Ionic liquid mediums are continuously being implemented as replacements for hazardous acid-based electropolishing methods. High grade metals are routinely utilized as components of electrochemical treatments. Pure silver finds a wide range of applications in jewelry and coinage. Owing to its electrical and thermal conductivity as opposed to other metals, silver is ideal for electrochemical applications. Above all, silver is antimicrobial and this makes it a good candidate for myriad biomedical uses and a variety of consumer products.

Dr. Jon Derek Loftis and Professor Tarek Abdel-Fattah from Christopher Newport University in Virginia studied the effects of deep eutectic solvents on silver. Their aim was to generate a clean lustrous surface via electrochemical polishing. They employed a conducive ionic liquid treatment comprised of ethylene glycol mixed with quaternary ammonium salts of choline chloride in a 2:1 ratio for electropolishing treatments of high-purity silver metal, and their work is now published in the journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.

The authors prepared an ionic liquid to polish three silver samples. They adopted small metal samples in order to understand the chemical reactions that occurred within the electrolyte solution. Since the metal sizes varied slightly from one test surface to the next, they set an electropolishing region by restricting electrochemical activity on each piece’s surface using silicone-based tape, and they adopted a platinum anode plate and a silver wire cathode as a reference.

Loftis and Abdel-Fattah observed from voltammetric analysis that setting diffusion at the anode to limit the reaction rate, this gave current potentials necessary for optimizing electropolishing silver metals. After electropolishing, they analyzed the samples’ surfaces to compare the mean surface roughness change. They compared the relative surface roughness and surface morphology of the specimens to industry-produced samples.

The authors recorded a root mean squared surface roughness value of 181.450nm for the as-received silver samples and 31.017nm for the post-treated samples. Comparing the two values, they arrived at 82% smoothing efficiency. Silver possessed the best potential for the optimum electropolishing conditions. Mass loss was also recorded before and after the electropolishing processes. Comparing the samples’ weight before and after the process reveals that silver test pieces experienced the highest surface degradation rate compared to other high-purity metals such as aluminum, nickel, and copper. High electropolishing rates did not translate to a more efficient polish, but were necessary to facilitate a stable low current density for the process to yield the most efficient voltammetric settings.

Drs. Loftis and Abdel-Fattah set up the study with the use of a non-acidic ionic liquid solution to polish pure silver metal samples. The polishing success was validated by an 8× reduction in average roughness of the three silver samples. They noted that low voltage and high current settings coupled with the high electrical and thermal conductivity of silver resulted in pitting and a sub-optimally rough surface. The rate of polishing in pure silver samples was, therefore, linked to electropolishing efficiency. This study demonstrated that the higher the rate of electropolishing, the greater the likelihood of the reduction reaction at the electrode affecting the smoothness of the surface. Therefore, the rate of electropolishing using an ionic liquid definitely has an impact on the resulting surface roughness for silver metal specimens.

Nanoscale electropolishing of high-purity silver with a deep eutectic solvent 1- advancecs in EngineeringComposite 3D graphic of Atomic Force Microscope roughness assessment of a high-purity silver specimen before and after electropolishing with a recyclable deep eutectic solvent over a 10×10µm recording region.

Nanoscale electropolishing of high-purity silver with a deep eutectic solvent 1- advancecs in EngineeringComparison with digital microscopy observations along the transition zone are depicted below, for reference.

About The Author

Dr. Tarek Abdel-Fattah holds a B.S. and M.S. degrees in Chemistry from Alexandria University, Egypt and a Ph.D. degree in Inorganic and Materials Chemistry from Northeastern University, Boston, USA. Currently, Dr. Abdel-Fattah is a Professor of Chemistry at Christopher Newport University (CNU) and the CNU Director of the Applied Research Center (ARC) at Thomas Jefferson National Accelerator Facility (Jefferson National Lab) research complex, Newport News, Virginia. Dr. Abdel-Fattah was the President of Sigma Xi Tidewater Chapter of Virginia 2005-2006 and holds the Program Chair position of the chapter since 2006. Also, Dr. Abdel-Fattah was the chair for the American Chemical Society (ACS) for the Hampton Road section 2009-2010 and in the executive committee since 2000.

Dr. Abdel-Fattah has published over 100 papers, 9 International and US patents, and over 75 presentations in national and international meetings. Dr. Abdel-Fattah has been awarded First Prize from the Physical Sciences Division of the American Association of Advancement of Science (AAAS). Dr. Abdel-Fattah has been awarded twice the American Association for Educational Engineering (NASA-ASEE) award of the summer faculty fellowship program. Dr. Abdel-Fattah was twice the recipient of the NASA Faculty Fellowship. Dr. Abdel-Fattah was awarded three times NASA Certificate of Recognition in different projects concerning nanotechnology for aerospace applications. Dr. Abdel-Fattah was the first recipient of CNU first Annual Faculty Award for Excellence in Scholarship, 2012.

About The Author

Dr. Jon Derek Loftis is an Assistant Research Scientist in the Department of Physical Sciences from the Virginia Institute of Marine Science at the College of William and Mary. Dr. Loftis’ physical electrochemistry research is a continuation of his Master’s thesis research focusing on electropolishing pure metals and frequently used alloys with recyclable ionic liquid solutions. His thesis is published with Christopher Newport University, via research conducted at the Jefferson Lab Applied Research Center, with thesis advisor, Dr. Tarek Abdel-Fattah. Drs. Loftis and Abdel-Fattah have co-authored 9 peer-reviewed publications and several award-winning posters from their collaborative research efforts.

Dr. Loftis’ recent geophysical fluid dynamics research is tasked with building upon the lessons learned from his forecast modeling experiences in the Mid-Atlantic during 2011 Hurricane Irene in the Chesapeake Bay, and from his dissertation research focusing on 2012 Hurricane Sandy in New York City to develop effective methods of predicting tidal and storm surge inundation at the street level. Dr. Loftis continues to research emerging methods of geospatially-validating his street-level inundation model predictions in Hampton Roads, VA.

Reference

Jon Derek Loftis and Tarek M. Abdel-Fattah. Nanoscale electropolishing of high-purity silver with a deep eutectic solvent. Colloids and Surfaces A: Physicochemical and Engineering Aspects, volume 511 (2016), pages 113–119

Applied Research Center at Thomas Jefferson National Accelerator Facility and Department of Molecular Biology and Chemistry at Christopher Newport University, Newport News, VA 23606, USA.

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