Corrosion and protection of steel structures Corrosion: Flashcards
How much does corrosion cost per year to the US economy?
$ 276 billion
How much of an industrialised country GDP is spent on corrosion?
3.5%
How much of the annual world wide production of iron and steel is used to replace material lost through corrosion?
15%
What is corrosion?
Degradation in properties and appearance and loss of material due to dissolution
Where does it occur?
Surface of material
What are the corrosion costs from Drinking Water and Sewer Systems?
$36 billion
What is the second biggest source for corrosion costs?
Motor vehicles
What are the direct losses from corrosion on the economy?
- Component replacement
- Painting and other preventative measures
- Use of expensive corrosion-resistant materials
What are the indirect losses from corrosion on the economy?
- Plant shutdown
- Loss of product e.g. in pipes
- Loss of efficiency
- Contamination of product
What effect is the corrosion of metals?
Electrochemical effect
What happens in the chemical reaction?
- Electrons are transferred
- REDOX reaction
What occurs at the anode during metal corrosion?
During metal corrosion, metal atoms are oxidized at the anode, meaning they form positive ions and release electrons. This site is where the anodic reaction occurs and where corrosion typically happens.
In the provided examples, what happens to iron (Fe) when it oxidizes?
When iron (Fe) oxidizes, it forms Fe2+ ions and releases 2 electrons (2e-)
How does aluminum (Al) react in an oxidation reaction?
In an oxidation reaction, aluminum (Al) forms Al3+ ions and releases 3 electrons (3e-)
What is the oxidation state and number of electrons released when zinc (Zn) corrodes?
When zinc (Zn) corrodes, it forms Zn2+ ions and releases 2 electrons (2e-)
What happens during the corrosion of Zn in an acidic solution?
During the corrosion of Zn in an acidic solution, Zn corrodes into Zn2+ at the anode, and electrons are transferred to the cathode forming hydrogen gas, with H+ being reduced to hydrogen at the cathode.
What does the nature of the cathodic reaction depend on?
Environment
When electrons formed what are he transferred to?
Electrons formed are transferred to another chemical species
Where is the H+ ions reduced?
Cathode
Where do electrons go to form hydrogen gas?
Cathode
How is iron oxide formed and why is it energetically favorable for iron to form rust?
Iron oxide, or rust, is formed when iron reacts with oxygen in wet conditions. It is energetically favorable for iron to form rust because iron found as iron oxide in iron ore tends to revert to the oxide as part of an electrochemical process.