- 1.GROUP NO 6Group Members Name Waqas Ahmad Umair Aslam Tayyab
Naveed Muhammad Umair Muhammad Mudeser khalid Mujahid Ali
2. Definition of CorrosionCorrosion is the slow process of decay
of the metal, due to the attack of the atmosphere gases on the
surface of the metal, resulting in the formation of metallic
compounds such oxides, hydroxides, carbonates, sulphides etc. 3.
FORMS OF CORROSION CORROSIONWET CORROSIONDRY CORROSIONCORROSIONROOM
TEMPERATURE CORROSIONHIGH TEMPERATURE CORROSION 4. 1. Dry or
Chemical Corrosion: It is due to the direct chemical action of
environmental atmosphere gases such as O2. H2S, SO2, N2, halogens
or anhydrous inorganic liquids with metal surfaces. 2. Wet or
Electrochemical Corrosion: It is due to the existence of separate
anodic and cathodic areas in the system between which current flows
through the conducting liquid and the anode gets oxidized and
wasted. 5. WET / AQUEOUS CORROSION Based on the appearance of the
corroded metal, wet corrosion may be classified as Uniform or
General Galvanic or Two-metal Crevice Pitting 6. UNIFORM CORROSION
Corrosion over theentire exposed surface at a uniform rate. e.g..
Atmospheric corrosion. Maximum metal loss by this form. Not
dangerous. Rate can be measured in the laboratory 7. GALVANIC
CORROSION When two dissimilarmetals are joined together and
exposed, the more active of the two metals corrode faster and the
nobler metal is protected. This excess corrosion is due to the
galvanic current generated at the junction a) Steel plates with
copper rivets in seawater 15 months. b) ) Copper plates with steel
rivets, same environmental conditions 8. CREVICE CORROSION
Intensive localizedcorrosion within crevices & shielded areas
on metal surfaces Small volumes of stagnant corrosive caused by
holes, gaskets, surface deposits, lap joints 9. PITTING A form of
extremely localized attack causing holes in the metal Most
destructive form Autocatalytic nature Difficult to detect and
measure 10. Electrochemical Theory of Corrosion (Mechanism Of
Corrosion) Corrosion is an electrochemical process.Galvanic cells
are setup between dissimilar metals in contact with each other or
between dissimilar parts of he same metal when surrounded by moist
air or liquid. Anodic area oxidation takes place Cathodic area
reduction takes place. Metallic ions formed at the anodic part and
ions formed at the cathodic part diffuses towards each other
through conducting medium and the corrosion product is formed
somewhere between the anodic and cathodic areas. 11. Anodic iron
gets oxidised to Fe2+ MMn+ + ne-The oxygen at the cathode changes
to OH- by reduction. O2 + H2O +2e2 OH- 12. Factors Affecting
Corrosion Rate & Extent of corrosion 13. 1. The position of
metals in the electrochemical SeriesMore oxidationDecreasing
tendency to loose electronsMetal SRP, Eo Lithium Potassium Calcium
Sodium Magnesium Aluminum Zinc Nickel Tin Hydrogen---------------
0.00 Copper Silver Platinum Gold---------------------- +1.15 VLess
ReductionIncreasing order of std reduction potential 14. 2. Purity
of the metalA pure metal is more corrosion resistant than an impure
metal. The rate and extent of corrosion increases with the amount
of impurities present. 15. 3.Physical state of the metalSmaller the
size of the metal, more the area under stress and greater is the
corrosion. 16. 4. Solubility and volatility of corrosion productIf
the product of corrosion is soluble in the corroding medium and
also is volatile, corrosion occurs faster. 17. 6. Nature of the
corroding environmentA.Temperature: Corrosion generally increases
with rise in temperature of environment. B.Humidity of the air:
Rate of corrosion increases with presence of moisture in the
atmosphere. C.Impurities: Presence of impurities like CO2, H2S,
SO2, acid fumes etc increases corrosion rate. D.Influence of pH: In
acid medium corrosion is more and in alkaline medium it is less.
18. Prevention of Corrosion 19. 1. Maintaining the purity of the
metal Pure metals are generally corrosion resistant. 20. 2.
Alloying with other elements It to found that alloying with
suitable elements increases corrosion resistance of most metals.
21. 3. Modification of environment Deaeration of aqueous
environment and dehumidification decreases the rate of corrosion.
22. 4 . Protective coatings1.Metallic Coating 2.Non-metallic
coatings 3.Organic coatings 23. i. Metallic Coating a) Using less
active metal b) Using a more active metal 24. ii. Non-Metallic
Coatinga) Phosphate coating by Alkaline solution of phosphate. b)
Chromate coating using chromate solutions. 25. iii. Organic Coating
Plastics, polythene, rubber etc, are used for coating to prevent
corrosion. Mainly on articles like, ship, submarines. Etc. 26.
ELECTRICAL PROTECTION 27. Zn2+ + 2e-Zn O2 + H2O +
2e-Anode2OH-CathodeCathod e ZnAnode 28. THANK YOU FOR ATTENTI
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