Correct Answer - Option 4 : Flux
Explanation:
Oxides and rust will form on surfaces of most metals when exposed to air. Solder will not adhere if such impurities are present.
Function of flux:
- Fluxes are non-metallic materials which are used at the time of soldering.
- By applying a flux, the oxide is removed and the formation of new oxides during the soldering process is prevented.
- Flux also assists the wetting process by removing oxidized layers from metallic surfaces, and by reducing the surface tensions of solder.
- It decreases the melting point of the solder.
Different types of fluxes
(A) Inorganic fluxes
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Hydrochloric acid: Concentrated hydrochloric acid is a liquid that fumes when it comes into contact with air. It is used as a flux for sheet metals of zinc-iron or galvanized sheets. This is also known as muriatic acid.
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Zinc chlorides: Zinc chlorides are known as killed spirits. It is mainly used for soldering copper, brass, and tin sheets.
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Ammonium chloride or Sal-Ammoniac: It is a solid white crystalline substance used when soldering copper, brass, iron, and steel (cast iron sheets).
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Phosphoric acid: It is mainly used as a flux for stainless steel.
(B) Organic fluxes
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Resin: It is used for soldering copper, brass, bronze, tin plate, cadmium, nickel, silver and some alloys of these metals
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Tallow: It is a form of animal fat. It is used when soldering lead, brass, and electrical joints
