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Name: Abhishek
Status: student
Grade: 9-12
Country: India
Date: Summer 2012


Question:
What is the effect of temperature or pressure or both on the rate of corrosion?



Replies:
Abhishek,

Since we are talking about the *rate* of corrosion, and anytime we talk about rates we have to be concerned about the effects of multiple factors, we have to be careful and keep everything else, all other factors, constant. In general, as temperature goes up, reaction rates go up. So we can expect that corrosion also goes up. However, there are obvious exceptions. Steel in tap water at room temperature will eventually form a brown corrosion product that tends to be soluble in the water. Steel in boiling tap water will form a black corrosion product that adheres to the metal and actually provides a coating against further corrosion. So eventually the corrosion rate slows down. ... Again, the idea of everything else being constant rule has been violated.

Likewise, if the corroding agent is a gas, then a higher partial pressure of that gas will mean more reactants and in general the reaction will proceed faster. However, if the pressure were to be increased by adding an inert gas (keeping the partial pressure of the corroding gas constant), then there may be no effect on the rate, or the mechanism of corrosion may change as a result of the higher over-all pressure.

We really have to be careful in defining the conditions when we talk about rates.

Greg (Roberto Gregorius) Canisius College


Hi Abhishek,

Much depends on the exact type of corrosion and the metals and environment involved, but generally speaking, the rate of corrosion increases with increasing temperature. Pressure has a very minor effect.

Regards, Bob Wilson


Increase in temperature will accelerate the rate of corrosion similar to that observed in rates of many chemical reactions. The effect of pressure arises from the changes in concentration of gases consumed or produced as part of the corrosion process. For example the corrosion of iron in water ( neutral pH) required oxygen as a reactant. Thus, increase of pressure will increase the concentration of oxygen and therefore accelerate the reaction. In acidic media, the corrosion of iron produces hydrogen. The increase of overall pressure will decrease the partial pressure of hydrogen and increase the driving force for corrosion.

Sri R Narayan Professor Loker Hydrocarbon Research Institute,


Corrosion is a chemical reaction, and you can frequently find a chemical reaction that increases or decreases with temperature and with pressure.

It depends on what is being corroded, what is the corrosive reagent, and various reaction parameters such as pH, ionic strength, etc.

If you wanted to make a generalization, you could invoke the principle that the rates of chemical reactions tend to increase with increasing temperature. But that would just be a guess in the face of no data. In the case of pressure (in general) the rates of chemical reactions involving only solids and liquids, pressure has little effect for pressures between 1 and 10 atm. So that could be your guess in the face of no data.

I would not be surprised however if you could find exceptions to those “rules”.

Vince Calder


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