الفهرس 
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Abstract
Electrodeposition involves metal deposition from an electrolyte into a conductive electrode by application of electromotive force; electrodeposition is the process of producing a coating, usually metallic, on a surface by action of electric current. The deposition of a metallic coating onto an object achieved by putting a negative charge on the object to be coated and immersing it into a solution containing a salt of the metal to be deposited. The metal ions are driven through the electrolyte by a combination of electrostatics, diffusion and convection, and finally cross the solution/electrode interface (the electric double layer).
Electrochemical deposition involves the reduction of metallic ions from aqueous, inorganic, and fused salt electrolytes. The reaction in aqueous medium at the cathode in its simplest form follows the equation:
Mn+ (solution) + ne- (metallic) M (1.1)
The reduction process can be accomplished by processes in which electrons are supplied by an external power supply or by electroless (autocatalytic) deposition processes in which a reducing agent in the solution is electron source (with no external power supplied).
Many metals deposited are in a very rough or powdery form when electroplating carried is out at the limiting current density. The possibility of preventing powder formation at the limiting current by means of suitable additive is of great interest and represents a significant activity in electroplating, electrowinning, electrorefining.
1.1. Deposition :
Electrodeposition or electroplating is defined as the process in which” the ”deposit of a (usually) thin layer (of metal) is formed ”electrolytic” upon a substrate. The purpose of such process may be to enhance or change the substrate’s appearance and/ or attributes (such as corrosion resistance). Examples are the deposition of gold or silver on jewelry and utensils, and the deposition of chrome on automobile parts. Electroplating is performed in a liquid solution called an electrolyte, otherwise referred to as the ”plating bath”. The bath is a specially designed chemical solution that contains the desired metal (such as gold, copper, or nickel).
In addition, various substances (additives) introduced in the bath to obtain smooth and bright deposits. The object to be plated is submerged into the electrolyte (plating bath). Placed usually at the center of the bath, the object that is to be plated acts as a negatively charged cathode. The positively charged anode(s) completes the electric circuit; those may be at opposite edges of the plating tank, thus causing film deposit on both sides of the cathode. A power source in the form of a battery or rectifier (which converts ac electricity to regulated low voltage dc current) is providing the necessary current.
This type of circuit arrangement directs electrons (negative charge carriers) into a path from the power supply (rectifier) to the cathode (the object to be plated).
Now, in the bath the electric current carried largely by the positively charged ions from the anode (s) toward the negatively charged cathode.
This movement makes the metal ions in the bath to migrate toward extra electrons that are located at or near the cathode’s surface outer layer.
Finally, by way of electrolysis the metal ions are removed from the solution and are deposited on the surface of the object as a thin layer, we refer this as ”electrodeposition”, process.
1.2. Mechanism and kinetics of the Deposition Process:
Electrodeposition or electrochemical deposition (of metal or alloys) involves the reduction of metal ions from aqueous, organic, or fused salt electrolytes. The reaction in aqueous medium at the cathode in its simplest form follows the equation:
M n+ + ne- M (1.1)
With a corresponding anodic reaction .The anode material can either be the metal to be deposited (in this case the electrode reaction is electro-dissolution that continuously supplies the metal ions) or the anode can be an inert material and the anodic reaction is oxygen evolution (in this case the plating solution is eventually depleted of metal ions).
The deposition may, in principle, be accomplished via two different paths:
1) An electrodeposition process in which electrons are provided by an external power supply.
2) An electroless (autocatalytic) deposition process in which a reducing agent in solution is the electron source.
The deposition reaction presented in equation (1.1) is a reaction of charged particles at the interface between a solid (metal) electrode and a liquid solution. The two types of charged particles that can cross the interface are metal ions″ M n+″ and electrons ″e -″.
The deposition reaction involves four issues:
1)Metal – solution interface as the locus of the deposition process.