In this article we will discuss about the meaning, purpose and applications of anodising.
Meaning and Purpose of Anodising:
It is the process in which a film of oxide is provided on metal surface is known as anodising.
(i) The give a protective coating on the metal surface like aluminium, zinc, copper and bronze etc.
(ii) To provide a decorative appearance on the surface.
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(iii) To provide a bright and smooth surface on aluminium articles prior to electroplating.
(iv) To provide specific colour base for subsequent painting on the surface.
(v) To improve the corrosion resistance of aluminium and aluminium products.
The anodised is achieved by using different electrolytes varying current and temperature of solution etc.
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Anodising process is neither a purely electrical process nor purely chemical process; it is a combination of both hence called electrochemical process.
The following steps are involved in the completion of electrochemical process:
(i) Cleaning and preparing the surface through different cleaning method.
(ii) It consists of anodising i.e. converting metal surface into an oxidized film.
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(iii) The third stage consists of providing of desired colour.
For anodising aluminium and its alloys products acid solution used are sulphuric acid, chromic acid and oxalic acid. The selection of particular acid solution depends upon the type of colour shade required.
Aluminium anodising is a process in which a film of oxide is formed on the surface of aluminium. The oxide coating is very hard and is highly resistance to corrosion.
The coating is of good appearance. The aluminium article is made the anode and electrolyte is an aqueous solution of sulphuric acid and chromic acid. A dc supply of voltage of 10 to 60 volts is required for the process. It is possible to anodise other metals such as steel galvanised iron, brass, zinc, silver and copper etc.
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This is particularly of special application in aircraft, in which aluminium is used for stressed members. The colour of the film is generally of light grey and gives a decorative finish.
Applications of Anodising:
Some of the applications of anodising:
1. To provide a protective coating on the metal surface.
2. To anodising on steel for producing a black film on various steel parts used a decorative article.
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3. Several galvanized iron and steel articles and machine parts are anodised to improve the resistance of galvanised coating to rusting, abrasion, wear and increase its life.
4. To anodising zinc to give distinct colour coatings.
5. Anodising is done on silver jewellery and show pieces made of silver.