Surface Finishing Tutorial
#053 Corrosion Resistance of Metals
Category : Corrosion - Corrosion Protection
August27, 2010
Corrosion resistance of various metals in corrosive environments are shown in [Table 1]. Whether any metal would be dissolved in corrosive environment or not will be up to the metal's corrosive reaction would advance thermodynamically or not. And the speed of the reaction dictates the speed of the corrosion.
The reaction of steel dissolving in hydrochloric acid is...
and corrosion due to dissolved oxygen is...
These reactions occur from left to right because the free energy of the systems decrease. Unless energy is given artificially, reaction will never occur where free energy increases.
However, in some actual cases, corrosions do not occur in accordance with this theory. The column headings in [Table 1] is explained as follows. Concentrated Sulfuric Acid is approx. 98% or higher, Concentrated Nitric Acid is 75% or higher. Acidic Solution and Alkaline Solution are at levels which can be measured with pH levels.
[Table 1] Corrosion Resistance of Metals
Metal | Concent- rated Sulfuric & Nitric Acid | Hydro- chloric Acid, Dilute Sulfuric Acid1) | Acidic Solution | Neutral Solution2) | Sea Water | Alkaline Solution3) |
Aluminum | Passive | Corrodes | Corrodes | Passive | Passive (Pitting) | Corrodes |
Titanium | Passive | Corrodes | Passive | Passive | Passive | Passive |
Zinc | | Corrodes | Corrodes | Protective Film | Protective Film | Corrodes |
Iron | Passive | Corrodes | Corrodes | Corrodes | Corrodes | Passive |
Chromium | Passive | Corrodes | Passive | Passive | Passive | Passive |
Nickel | Corrodes | (Resistant) | (Resistant) | Passive | Passive (Pitting) | Passive |
Lead | Corrodes | Corrodes | Protective Film | Protective Film | Protective Film | Corrodes |
Stainless Steel | Passive | Corrodes | Passive | Passive | Passive (Pitting) | Passive |
Copper | Corrodes | Stable | Protective Film | Protective Film | Protective Film | Protective Film |
Gold | Stable | Stable | Stable | Stable | Stable | Stable |
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* | 1) Dissolved oxygen and chlorine degassed, 2) No chlorine ions, 3) Excluding strong alkali such as 40% caustic soda and ammonia (ammonia will form complex salt and dissolve). |