Electroplating
The deposition of superior or noble metal on an inferior or a lease metal by means of electrolysis of an aqueous solution of suitable electrolyte is called electroplating.
Electroplating is essential on metals like iron which can easily corrected by atmospheric it, moisture and carbon dioxide are coated by deposits of nickel or chromium. Electroplating is also used on metals to protect them from chemical attack and the same time to give them a good polish.
Sometimes it is just alone for ornamentation and decoration purpose. Example may articles which are made of copper such as table vase, decoration pieces are coated with her or gold.
The electrolytic processes are crystalline in nature. The deposition must be very fine in under to get firm and uniform deposits. To achieve this suitable electrolytes and current density sed should have an appropriate value. The temperature should also be maintained at a proper level
Before electroplating the object some operations are to be done on the object. The persons are as follows:
1.Removal of the oil, grease or any other organic material. This can be done by using soaps, hot alkali solutions or organic solvents such as gasoline, or carbon tetrachloride.
2. Removal of rust, scale, oxides, or other inorganic coatings adhering to the material. They can be removed with the help of various acids, alkalies and salt solutions.
3.Mechanical preparation of the surface of the metal to receive the deposited metal by polishing buffing etc. For this electrolytic cleaning, mechanical abrasion and polishing are used.
The object to be electroplated is cleaned using different cleaning methods. If the object to be electroplated is not cleaned, polished and degreased the deposit formed may well adherent to the base metal and may peel off in due course of time.
For smooth, bright and hard deposit, the surface of the object to be electroplated should be thoroughly cleaned first mechanically by grinding or scratching against the rough surface or sand blasting and then chemically by treating them with hot alkalies if the surface is greasy or with dilute acids if the surface has oxide films.
The electrolyte used in the electrolytic bath depends on the nature of the metal to be
deposited.
For copper plating:
For copper plating two types of electrolytic baths are used, the acidic bath and the
cyanide bath.
In acidic bath solution is made up of 150-200 gm of copper sulphate and 25-35 gm of sulphuric acid per 1000 cc of solution. Current density used is 150-400 A/m temperature is 25 to 50°C and the deposit obtained is thick, rough and requires polishing.
In cyanide bath solution is made of 28 gm of copper cyanide, 6 gm of sodium carbonate
and 6 gm of sodium bisulphate per 1000 cc of solution. Current density is 50-150 A/m² and
temperature is 25-40°C. It gives thin and smooth deposit. Copper electrodes are used in both baths.
For silver plating
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| silver- platting |
For Gold plating
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| Gold plating |
For gold plating the solution consists of 18 gm of potassium gold cyanide, 12 gm of potassium cyanide, 6 gm of potassium sulphate and 12 gm of caustic potash per 1000 cc. The electrodes are of stainless steel. The current density required is 50-150 A/m and temperature used is of 50°-70°C.
For chromium plating :
For chromium plating the most commonly used solution is of 180-300 gm of chromic acid and 2-3 gm of sulphuric acid per 1h000 ce of solution. The current density required is 1500-2500 A/m and the temperature is of 35-50°C. Anode are made of antimonial lead vats used for chromium plating are of steel with lead lining. Chromic acid is added to the solution at regular intervals.
For nickel plating:
For nickel plating the solution consists of 180-240 gm of nickel sulphate, 36 gm of nickel chloride and 24 gm of boric acid per 1000 cc. The current density used is 100-200 A/m² and working temperature is of 25-40°C. Anode is made of pure nickel.
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