3. Rise in temperature increases the rate of corrosion
due to increase in the rate of diffusion of ions.
Humidit
y
The rate of corrosion will be more when the
relative humidity of the environment is high.
The moisture acts as a solvent for oxygen,
CO2, SO2 etc in the air to produce the
electrolyte which is required for setting up of
an electrochemical cell.
4. Chemicals
-Acid Rain: Acid rain contains weak acids, such as sulfuric
acid and nitric acid, which can react with the car body and
cause corrosion.
-Road Salt: Road salt is used on roads during winter to
prevent freezing, but it can react with the car body and
cause corrosion.
-Car Wash Chemicals: Some car wash chemicals contain
harsh chemicals that can react with the car body and cause
corrosion.
-Gasoline and Fuel: Spills or leaks of gasoline or fuel from the
fuel tank or fuel lines can react with the car body and cause
corrosion.
-Glass Cleaners: Some glass cleaners contain harsh chemicals
that can react with the car body and cause corrosion.
5. Mechanism
1️⃣Galvanic corrosion
1. Car body (steel) and copper mounting screws:
-Visual: You might see rust forming around the
screw holes on the car body, with the area closest
to the screw showing the most significant
deterioration.
-Explanation: Steel (anode) is less noble than
copper (cathode), so the steel corrodes faster
where it touches the copper screw in the presence
of moisture (electrolyte).
2. Aluminum car paint and exposed steel:
-Visual: You might see bubbles or cracks in the paint near exposed steel areas, with the
steel underneath showing rust.
-Explanation: Aluminum (cathode) is more noble than steel (anode), so the exposed
steel corrodes faster where it touches the aluminum paint in the presence of moisture.
6.
7. Prevention and Control
1️⃣Material Advances
-Protective Coatings: Applying waxes, sealants, or specialized anti-corrosion coatings
provides a physical barrier between the metal and corrosive elements in the environment.
-Cathodic Protection: In some cases, applying electrical currents can suppress corrosion on
specific structures like car frames. However, this method is typically used for large-scale
applications.
-Design Considerations: Designing cars with improved drainage and minimizing areas where
water can accumulate helps prevent moisture-induced corrosion.
-Galvanic Compatibility: Selecting materials with similar corrosion potential when they
come in contact (e.g., using aluminum screws with aluminum body panels) minimizes the
risk of galvanic corrosion, which occurs when dissimilar metals are in close contact.
8. -Powder Coatings: These dry coatings are electrostatically applied and then cured
with heat. They offer excellent corrosion resistance, durability, and chip
resistance. Powder coatings are often used for car frames and undercarriage
components.
-Zinc Coatings (Galvanization): A common and effective method, galvanization
involves coating steel with zinc, which acts as a sacrificial anode. When exposed,
the zinc corrodes first, protecting the underlying steel. This is why you see a
white, flaky substance on older cars – it’s the zinc sacrificing itself.
-Conversion Coatings: These chemical treatments convert the metal surface into a
corrosion-resistant phosphate layer. Conversion coatings often serve as a pre-
treatment for other coatings, enhancing their adhesion and effectiveness.
Coating Applications
