Corrosion-
coreosion is a natural process that converts metal into more chemically stable from such as oxide,hydroxide or destruction of metal by chemical reaction.
*Open air corrosion -
It is a electrochemical process , whereby thin film of water aredeposited and leading to wet corrosion.
1] It is degradation of material caused by air and pollutants in air. It is defined as , he electrochemical process wich depend on presence of electrolyte wich may be due to rain dew or melting snow. When the critical certain corrosion humidity reach. For Fe is around 60% in unpoluted atmospheres.
2]Atmospheric corrosion has not only its own share of engineering catasporous such as collapse of concrete, bridges and public utilities.
*Rusting of iron-
1]Rust is an iron oxide usually red oxide form by redox reaction of iron and oxygenin presence of oxygen water or air moisture.
2]Givenn sufficient oxygen and water any iron mass convert to rust.
*Electroplating process-
It is the process of coating an object with metal
Process-
1]The metal bar is dissolved in solutions and plates out an object.
2]Forming a thin but durable coatingof metal on object. A process that uses to reduced the metal cation. So that the form thin concerant metal coating on electrodes.
Ex- Electroplating of copper in wich metal to plated [copper ] is use as anode and electrolyte solution contains ion of metal to be plated.
Cu2+, cu goes into solution at anode and it plated at cathode.
*Galvanizing -
1] Galvanizing is a process in wich zinc coating prevent oxidation of protected metal by forming barrier and by coating as sacrificial anode if barrier is damaged.
2]zinc oxide is fine white dust that does not cause breakdown of substrate surface.
3]The protection accorded to aluminium and stainless steel by their oxide layers.
4] The majority of hardware part are zinc plated rather than cadmium plated.
Zn + Fe2+ -> zn+ + fe
* Factor affecting corrosion The nature and extent of corrosion depend upon metal and environment. The imp factor wich influences corrosion are -
1] Nature of metal
2] Environment
3] Concentration of electrolyte
4] Solubility of corrosion products.
* How nickel plating prevent corrosion? [ Nov 18]-
1] In the plating Nigel and cadmium are coated on metal surface. Before process there is the process of pre treatment.
2] The material to be plated clean by series of chemical and known as pre-treatment method.
3] Unwanted soil from surface is removed by water rinsing . Decreasing removes oil from surface.
4] Activation done by weak acid or nickel strike. he nickel is plated on metal , after plating process, plated material must finished with anti-oxidant chemical, trisodium-phosphate.
5] It does not use any electrical power there is flexibility in plating volume wich prevent metal from corrosion.
At cathode- Ni2+ [Ni2+]+2e-
At Anode- H2po2 + H2o ----> H2po+2H+
*Underwater corrosion -
1] It occurs when the steel piles are used in seawater , it react chemically to form anode and cathode resulting in flow of electricity.
2 Result in corrosion of [Anodic] ea of piles.
3] chemically active surface area of underwater steel piles act as anode and less chemically active and surface cat as cathode.
* Explain manufacturing of varnishes and its applications.
1]The manufacturing of varnishes involve mixing and blending of various ingredientto produced wide range of products
2] Chemical reaction are inhibited by heating temperature to 93-340 degree Celsius
3] varnishes depending on cooking temperature and time , solvent used degree of tank enclosed and type of product used
4] Emulsions from varnish range from 1-6% of raw material. In the process raw material are collected and put in pre-mixing wich goes through dispersion.
5] After process material to be cooled and granulated collected , after this screening and packing is done.
Diagram-
Application --
1] varnishes are transparent and hard material use for shining furniture.
2]wood finishing .
3] visible to highlight pore of wood .
4] To visible grain in wood.
*Manufacturing of oil paints -
The process involve dispersion of coloured oil or Ghent in vehicle, usually an oil or resins followed by addition of organic solvents . Only physical process is done such as mixing , grinding, packaging etc.
*Manufacturing --
1] The first step in making paints involve mixing pigment with resin, solvents and addictive to form a paste.
2] if paint is to be for industrial usally then routed into sand mill .
3] Larger cylinders that agitate tiny particle of send or silica to grind pigment particles, making them smaller and disappearing them throughout mixture.
4] In contrast, most commercial used paint is process in high-speed dispersion tank , in wich a circular blade attached to rotating shaft agitated mixture and blend pigment into solvents.
Diagram-
*Applications --
1]Interiour or exterior housepainting.
2] Boats , atomobile, industry.
3]Mashinary, planes .
4]Electrical appliances and other.
5] Toys , furniture etc.
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