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CORROSION CONTROL AND PREVENTION :red_flag: - Coggle Diagram
CORROSION CONTROL AND PREVENTION
:red_flag:
Corrosion Control
Protective coating
Metallic coating: coating/covering with more noble metal or better corrosion resistant propeties
Coating of Zn in galvanized steel
Coating of Sn on iron for containers
Non-metallic coating (inorganic and organic coatings)
Inorganic coatings - concrete, silica and ceramics
Organic coatings - tar, paint, plastics and etc
Paint coatings are considered the most practical and economical means for the corrosion protection
Paint:
Binder (resin – PV, PU, epoxy, alkyd etc.)
Solvent (organic , water)
Pigment/colouring
Additives (anti-corrosive, anti-fungal etc.)
Modify the environment
Controlling the environment
Controlling the relative humidity
Removal of oxygen
Controlling pH, temperature, pressure, velocity, ionic contaminants
Use of inhibitors
Anodic inhibitor - forms a passivation layer on aluminium and steel surfaces which prevents the oxidation of the metal. e.g. Chromate, nitrit , borate , molybdates, etc.
Cathodic inhibitor - retards the corrosion by inhibiting the reduction of water to hydrogen gas (inhibit the reduction processes). e.g.zinc salts, Magnesium salts, amine etc.
Mixed inhibitor - An inhibitor that acts both in a cathodic and anodic manner.e.g. chromate / polyphosphate
Role of inhibitor:
React with corrosive agents such as Na2SO3 dan N2H4
forms a passivation layer
forms of adsorption film /protection layer on the metal surfaces
Proper Design
Design awareness and the life-cycle: Good control of corrosion requires the awareness and co-operation of the entire design team
Materials selection
Modify the properties of material
Alloying the metal to produce a more corrosion resistant alloy, e.g. stainless steel, in which ordinary steel is alloyed with chromium and nickel.
Passivity: alloying effects
Passive oxide film can inhibit aqueous corrosion as well
Selection of proper material
Metallic:
metal and alloy
Nonmetallic:
rubbers (natural and synthetic), plastics, ceramics,carbon and graphite, and wood
Cathodic and Anodic Protection
Cathodic Protection
: technique to control the corrosion of a metal surface by making that surface become cathodic to the environment or the cathode of the corrosion cell.
Advantage:
can be used for all metals
installation cost is low
corrosion rate can be reduced to zero
Limitation:
can only be used in weak to moderate environment
operating conditions must be determined by empirical testing
Anodic Protection
: Specifically, in metal-environment conditions where active-passive behaviour is demonstrated, anodic protection is usually effective. In practise, the metal-environment potential is held in the passive region by polarizing the structure in the electropositive direction
Advantage:
can be used in extremely aggressive environment
applied current is direct measure of corrosion rate
operating conditions can be easily controlled
operation cost low
Limitation:
only applicable to active-passive metals
installation cost is high
Minimizing or preventing corrosion
Separate the metal from the environment with a barrier layer, e.g. paint
Remove crevices from design
Add chemical to environment that inhibits corrosion
Prevent galvanic corrosion by using compatible materials or electrically insulating dissimilar materials
Remove aggressive species from environment
Reduce T (slow kinetics of oxidation-reduction reactions)
Use more corrosion-resistant material, e.g. metal that passivated
Use cathodic / sacrificial protection or anodic protection
