Electropolishing Valve Metals with Sulfuric Acid-Methanol Electrolyte

Kiev E. Dixon, Boise State University
Pete L. Barnes, Boise State University
Andreas Savva, Boise State University
Hailey Bull, Boise State University
Laura Rill, Boise State University
Devan Karsann
Sterling Croft, Boise State University
Jesse Schimpf, Boise State University
Hui Xiong (Mentor), Boise State University

W29

Abstract

To develop uniform oxide nano-structures on the surface of valve metals, via anodization, it is desirable to start with a polished surface. Electropolishing is a common method to produce highly polished surfaces. However, common procedures utilize toxic, fluoride containing electrolytes. This study reports on a novel method for electropolishing titanium and niobium, in a sulfuric acid/methanol electrolyte, at low temperature (-70 oC). Electropolishing at low temperature has a significant effect on reaction kinetics. Experiments show an expansion of the steady-state current density plateau of anodic polarization curves. Additionally, increasing the sulfuric acid concentration led to broadening of the current density plateau. Optimization of conditions produced a root mean squared roughness of 1.64 nm and 0.49 nm for titanium and niobium, respectively. An improvement over results obtained with fluorine-containing electrolytes. We believe it is possible to apply this method to other valve metals, like zirconium and tantalum. Preliminary experiments with zirconium have shown a brightening and smoothing of the surface. However, there is further work required to optimize results with this metal. Additionally, we show that polished valve metal surfaces produce more uniform nano-structures, formed via anodization.

 

Electropolishing Valve Metals with Sulfuric Acid-Methanol Electrolyte

To develop uniform oxide nano-structures on the surface of valve metals, via anodization, it is desirable to start with a polished surface. Electropolishing is a common method to produce highly polished surfaces. However, common procedures utilize toxic, fluoride containing electrolytes. This study reports on a novel method for electropolishing titanium and niobium, in a sulfuric acid/methanol electrolyte, at low temperature (-70 oC). Electropolishing at low temperature has a significant effect on reaction kinetics. Experiments show an expansion of the steady-state current density plateau of anodic polarization curves. Additionally, increasing the sulfuric acid concentration led to broadening of the current density plateau. Optimization of conditions produced a root mean squared roughness of 1.64 nm and 0.49 nm for titanium and niobium, respectively. An improvement over results obtained with fluorine-containing electrolytes. We believe it is possible to apply this method to other valve metals, like zirconium and tantalum. Preliminary experiments with zirconium have shown a brightening and smoothing of the surface. However, there is further work required to optimize results with this metal. Additionally, we show that polished valve metal surfaces produce more uniform nano-structures, formed via anodization.