LYCOS RETRIEVER 
Corrosion: Rates
built 280 days ago
Corrosion rates are usually expressed in terms of loss of thickness per unit time. General corrosion rates may vary from on the order of centimeters per year to micrometers per year. Relatively large corrosion rates may be tolerated for some large structures, whereas for other structures small amounts of corrosion may result in catastrophic failure. For example, with the advent of technology for making extremely small devices, future generations of integrated circuits will contain components that are on the order of nanometers (10รขˆ’9 m) in size, and even small amounts of corrosion could cause a device failure.
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![[corrosion diagram]](http://retrieverimages.lycos.com/images/c/o/r/corrosion/i/058.gif)
Both oxygen and moisture must be present in order for corrosion to occur. Non-uniformities in moisture, oxygen, and chloride levels can create electrical potentials that drive the corrosion reaction. Other factors that influence the rate of corrosion include concrete resistance and permeability, temperature, and depth of cover over the reinforcement.
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The corrosion of silicate glasses in aqueous solutions is governed by two mechanisms: diffusion-controlled leaching (ion exchange) and glass network hydrolytic dissolution[1]. Both corrosion mechanisms strongly depend on the pH of contacting solution: the rate of ion exchange decreases with pH as 10-0.5pH whereas the rate of hydrolytic dissolution increases with pH as 100.5pH [2]
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