Electrochemical Process of Anodizing Aluminum – Science Essay

Electrochemical Process of Anodizing Aluminum – Science Essay
In the 1920’s, aluminum quickly became one of the most important metals in the world due to its lightweight, strength, fabrication flexibility and durability. Shortly after, anodizing was developed to provide the alloy with

an extremely hard, durable, corrosion resistant finish that was long lasting. After reading this paper, you will easily understand the anodizing process and why it makes for such a good finish on nearly all alloy metals. Anodizing also has many benefits with very few by-products and is very cost effective.

You may ask yourself, what is anodizing and how is it accomplished? To simplify the process, anodizing is nothing more than an electrochemical process by which aluminum is converted into and aluminum oxide on the surface of a part. The process is fairly simple involving of an anodizing solution usually made of sulfuric acid. A cathode is placed to the negative terminal of a voltage source and placed in the solution, while an aluminum piece is connected to the positive voltage source and placed in the acidic solution. When the circuit is turned on, the oxygen in the acidic solution will be removed from the water molecules and combine with the aluminum on the part to form an aluminum oxide coating. The resultant finish increases corrosion resistance; increases wear resistance, can be colored through dying, and is also an excellent base for primer or other secondary coatings.

Over the last few decades, many different types of anodizing processes have been developed, but there are three main variations used in aluminum anodizing. Chromic anodizing uses a chromic acid electrolyte to yield the thinnest coating out of the three main types of anodizing ranging from .05 to .1 millimeters thick. Chromic anodizing also reduces the fatigue strength of the aluminum less than the other three methods. Sulfuric anodizing produces a coating under 1 millimeter thick that is also more durable than a chromic finish. Sulfuric finishes produce excellent results from dyeing yielding deep and rich colors. The third common process is known as hard coat anodizing. An alloy with a hard coat finish will be the most resistant to wear and usually used in high wear situations.
Anodizing is one of the few finishes that satisfy nearly all of the factors that should be considered when considering an aluminum finish. On of the most important factors is durability. Anodized products have an extremely long life span and require very little maintenance. Scars and wear marks from fabrication and handling are almost non-existent and a simple cleaning with mild soap and water usually returns the finish to its original condition.

Another reason anodizing has become so popular is because of the many different ways and vibrant colors available to coat an alloy with. Coloring is typically obtained through two different methods. The first method is known as electrolytic coloring and is a two step method. After the alloy is anodized, the metal is immersed in a bath containing inorganic metal salt. Current is applied which deposits the metal salt in the base of the pores. The resultant color is dependant on the material used and the processing conditions. Commonly used metals include tin, cobalt, nickel, and copper. This process is the most versatile and the most technically advanced coloring quality. The second method, known as integral coloring, combines anodizing and coloring to simultaneously form and color the oxide cell. Integral coloring is the most expensive process since it requires significantly more electrical power to produce the same finish. Color coatings are very stable to ultraviolet rays and do not chip or peel. Currently, there are many color options and styles available with anodizing. However, anodizing offers the alloy to retain its metallic appearance unlike painting or powder coating.

At first glance, anodizing may appear to be a very dangerous process. However, anodizing is very environmental friendly and relatively safe for human contact. Anodizing uses simple water-based chemicals that can be easily treated and release no harmful by-products. The liquid by-products are recycled and returned to the anodizing process. Solid by-products are separated and extracted for use in the manufacturing of aluminum, baking powder, cosmetics, newsprint, fertilizer, and water purification systems. The main by-product caused from the anodizing process composed primarily of aluminum hydroxide, some aluminum sulfate, and water. However, this by-product is harmless because it contains no significant amounts of heavy metals. Anodizing plants must be well ventilated and workers are carefully trained for acidic material use. Minimal protective equipment is needed and no expensive, heavy, safety equipment is required.

Through many decades of work, anodizing has evolved into one of the best finishes available for alloy metals. It may be the durability of the finish, the unmatched adhesion, the vibrant colors, the extreme resistance to corrosion and wear, or the environmentally safe process used to obtain the finish. All of these qualities make anodizing the premier finish and sets the bar to which all other alloy finishes should be compared to.

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