טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYitzhack Neta
SubjectElectrodeposition of Aluminum from Non-Aqueous Organic
Solutions Containing Aluminum Bromide Salt
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Yair Ein-Eli
Full Thesis textFull thesis text - English Version


Abstract

Aluminum (Al) is one of the most abundant elements on earth. It is light, inexpensive, has excellent thermal and electrical conductivities, and exceptional corrosion resistance thanks to its native oxide layer, which can be further anodized. Al can be processed and recycled quite readily, thus it is an indispensable engineering material in many industries, including electronics, vehicles and transportation, packaging, etc.

The common methods used in the industry for preparation of Al coatings suffer from some drawbacks, including: expensive high-vacuum equipment; elevated temperatures that are inadequate for all the materials and may also increase the process costs; limited chemical purity; and failure to coat complex or large structures. Electrochemical deposition solves many of these problems, and in addition, it carries with it many other advantages. Electrochemical deposition is a relatively rapid and low-cost process, and at the same time it produces high purity coatings even on intricate parts and it is most applicable for industrial processes.

The electrochemical deposition of Al from aqueous solutions is problematic due to its highly negative reduction potential, and therefore it is necessary to use aprotic non-aqueous solvents for this purpose. One type of such electrolytes is those based on aromatic solvents, which have been considered as candidates for Al electroplating for many years. This research is aimed at investigating the deposition of Al from an aromatic electrolytic bath composed of aluminum bromide (AlBr3) and potassium bromide (KBr) in ethylbenzene.

The electrolytic bath presented here enables the reversible reduction of Al. The reduction of Al species from this electrolyte begins at negative potentials, (ca. -50 mV vs. Al), and leads to deposition of pure and crystalline Al at room temperature.

The work studies the behavior of distinct substrates in this electrolyte. The most noteworthy effect of the substrate over the morphology of the Al deposits originates from its impact during the electrocrystallization of Al. For instance, it is found that the oxide layer present on an Al substrate, hinders the nucleation of Al from this electrolyte, particularly at lower potentials, and promotes growth of larger Al crystals than those obtained on copper or nickel (Cu and Ni, respectively). The study also concludes that a carbon nanotube (CNT) tissue facilitates the deposition of individual Al microcrystals from this electrolyte and suggests a propitious two-step method for the deposition of thick Al layers on CNT.

As evidenced, this electrolyte has a corrosive effect on Cu and Ni that undergo general dissolution under applied anodic potentials. Al also dissolves in this electrolyte under applied anodic potentials, though by a different mechanism; in the presence of its oxide layer, the anodic potentials induce local dissolution at the surface, followed by a general dissolution of the bulk.