الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
Metallic materials are still the most widely used groups of materials, particularly in both mechanical engineering and the transportation industry. In addition, metals are commonly used in electronics and increasingly also in the construction industry.
1.1. Corrosion
Corrosion is a naturally occurring phenomenon commonly defined as deterioration of metal surfaces caused by the reaction with the surrounding environmental conditions. Corrosion can cause disastrous damage to metal and alloy structures causing economic consequences in terms of repair, replacement, product losses, safety and environmental pollution. It is necessary to devote more attention to metallic corrosion nowadays than earlier due to:
1- A more corrosive environment due to the increasing pollution of air and water.
2- An increased use of metals within all field of technology.
3- The use for special applications as in the atomic energy field of rare and expensive metals. [1]
The corrosion costs in most of the countries are in the range of 2-4 % of the gross national product. So it is imperative that economically, useful measures should be taken to minimize corrosion. [2] The total annual cost of corrosion in the U.S. is approximately 276 billion dollars and is increasing every year. [3] Due to these harmful effects, corrosion is an undesirable phenomenon that ought to be prevented. There are several ways of preventing corrosion and the rates at which it can propagate with a view of improving the lifetime of metallic and alloy materials. The use of inhibitors for the control of corrosion of metals and alloys which are in contact with aggressive environment is one among the acceptable practices used to reduce and/or prevent corrosion.
Corrosion inhibitors
Corrosion inhibitors are substances which when added in small concentrations to corrosive media decrease or prevent the reaction of the metal with the media. Inhibitors are added to many systems such as, cooling systems, refinery units, chemicals, oil and gas production units, boiler etc. Corrosion inhibitors can be divided into two broad categories:
•Enhance the formation of a protective oxide film through an oxidizing effect
•Inhibit corrosion by selectively adsorbing on the metal surface and creating a barrier that prevents access of corrosive agents to the metal surface.
Inhibitors function by adsorption of ions or molecules onto metal surface. They reduce the corrosion rate by,
•Increasing or decreasing the anodic and/or cathodic reaction
•Decreasing the diffusion rate for reactants to the surface of the metal
•Decreasing the electrical resistance of the metal surface
Inhibitors are often easy to apply and offer the advantage of in-situ application without causing any significant disruption to the process.
However, there are several considerations when choosing an inhibitor:
•The cost of the inhibitor can be sometimes very high when the material involved is expensive or when the amount needed is huge.
•Toxicity of the inhibitor can cause jeopardizing effects on human beings, and other living species.
•Availability of the inhibitor will determine the selection of it and if the availability is low, the inhibitor becomes often expensive.
•Environment friendliness.]
1.3. Amino acids inhibitors
Amino acids are biologically important organic compounds composed of amine
(-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid. The key elements of an amino acid are carbon,hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. About 500 amino acids are known and can be classified in many ways. They can be classified according to the core structural functional groups’ locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side-chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acids comprise the second-largest component (water is the largest) of human muscles, cells and other tissues. Outside proteins, amino acids perform critical roles in processes such as neurotransmitter transport and biosynthesis.
Amino acids form a class of non-toxic organic compounds which are completely soluble in aqueous media and produced with high purity at low coast.
Amino acids have the ability to control corrosion of various metals such as carbon steel, zinc, tin and copper. It behaves as an inhibitor in acid medium, neutral medium and in desecrated carbonate solution.
Generally amino acids have two polar groups, namely, one amino group and one carboxyl group. It can coordinate with metals through the nitrogen atom and oxygen atom of the carboxyl group. So it has been widely used as corrosion inhibitor. It has the ability to control the corrosion of a wide variety of metals such pure iron, carbon steel, zinc aluminum and tin. It behaves as corrosion inhibitor in acid medium, neutral medium and in deaerated carbonate solution.
Amino acids and derivatives of amino acids have been used to prevent the corrosion of a wide variety of metals. Amino acids and its derivatives have the ability to prevent the corrosion of carbon steel (mild steel) , Cu-Ni alloys, aluminum, aluminum alloy, aluminum silicon carbide composite, pure iron, stainless steel, copper, aluminum and zinc pigments, nickel, tin, NST-carbon steel, Pb-Ca-Sn alloy, Pb-Sb-Se-As alloy, reinforcing steel, sulfur on the corrosion of mild steel, aluminum and magnesium alloys, Armco iron, copper electrode, cobalt, brass, and bronze. [5]
Electropolishing
Electropolishing is as a surface finishing process based on anodic dissolution of metal or alloy in an appropriate chosen electrolyte. Applications of the technique are numerous and range from the polishing of steel cutlery to the preparation of samples for transmission electron microscopy. The polishing phenomenon is characterized by the elimination of micro-roughness (leveling) and the absence of crystallographic and grain-boundary attack (brightenting) and the results in the production of smooth bright surfaces. A complete summary and discussion of the scientific literature concerning electropolishing from its patented publication by Jacquet in 1930 [6-8] up to and including research results from the mid 1980s can be found in the review by Landolt. [9]
Mass-transport limitations for anodic are generally believed to be responsible for electropolishing, and this view is supported by the observation in numerous experimental systems of polishing for anodic dissolution along a limiting-current plateau. Leveling behavior for anodic dissolution for anodic dissolution at the limiting-current can be interrelated as the preferential dissolution of protrusions, on the order of the diffusive layer due to their greater accessibility for diffusive transport. Brightening can also be interpreted as a result of mass -transport control, but on a smaller scale where diffusion is essentiall