Final Report: Aluminum Plating With Ambient Temperature Ionic LiquidsEPA Contract Number: 68D03019
Title: Aluminum Plating With Ambient Temperature Ionic Liquids
Investigators: Carter, Michael T.
Small Business: Eltron Research & Development Inc.
EPA Contact: Manager, SBIR Program
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $69,996
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , SBIR - Nanotechnology , Small Business Innovation Research (SBIR)
This Phase I research project demonstrated the feasibility of using an ambient temperature ionic liquid as an aluminum (Al) plating medium. The goals of the project included demonstration of effective Al plating from an Al-containing ionic liquid plating bath and determination of the minimum amount of various cosolvents that could be added to the melt to improve the quality of the plated Al. Electrochemical methods (cyclic voltammetry, chronoamperometry, alternating current impedance spectroscopy) and scanning electron microscopy (SEM) were used to characterize the ternary organic solvent-melt mixtures and the Al plated onto platinum and stainless steel substrates from this medium. Dependence of plating quality on the addition of several organic cosolvents to the melt was systematically investigated. Plating bath throwing power (T) was characterized and demonstrated experimentally for plating on threaded bolts. Eltron Research, Inc., demonstrated that the ionic liquid has the potential for the development of a competitive, alternative Al plating process that significantly reduces the used of volatile organic solvents.
Eltron Research, Inc., found that Al plating was most effectively performed using at least 35 percent toluene in the Al-containing ionic liquid plating medium. Constant current plating was performed at low current density and low cell voltage for between 30 and 60 minutes to yield 5-20 µm thick Al on planar platinum and steel substrates. SEM was used to determine the grain size and packing in the plated Al layer. Using 35 percent toluene in the melt, densely packed Al grains of less than 5 µm diameter could be formed. These films were adherent and completely and evenly covered the substrate material. Current efficiencies generally were greater than 85 percent and were dependent on the current density and amount of organic cosolvent added to the melt. Plating conditions could be adjusted to alter the appearance of the aluminum surface from matte to lustrous. T measurements indicated that the toluene-ionic liquid mixture was a very effective medium for achieving even Al coverage (T = 91). T was confirmed by demonstration of plating on threaded surface of stainless steel bolts, a typical, practical, irregular surface. Continuous, even Al layers between 7 and 14 µm thick were produced over the threaded surface, with somewhat thicker Al deposited at the peaks of threads and relatively thinner coatings deposited in the thread valleys. X-ray diffraction spectrometry (XRD) and energy-dispersive x-ray spectrometry showed that face-centered cubic Al was plated on both platinum and stainless steel substrates with no detectable inclusion of melt constituents. Anodization was performed in 5 percent boric acid and formation of passive oxide film was confirmed by XRD.
The ambient temperature ionic liquid provides an efficient, high T means for Al plating that produces high-quality layers while using 65 percent less organic solvent than conventional Al plating processes. These results showed that the ionic liquid has the potential for the development of a competitive, alternative Al plating process that significantly reduces the used of volatile organic solvents.