|
Corrosionist The Website of Corrosion Protection and Corrosion Prevention |
| You are here >>> Corrosion prevention home - - Corrosion Rust FAQ -Oxidation Reduction reactions | ||
What are Oxidation Reduction reactions |
||
| Metal Corrosion |Copper Pipe Corrosion | Galvanic Corrosion | What is Corrosion |Causes of Corrosion | What is Rust | What causes Rust | Definition of Corrosion | Corrosion Prevention | Define Oxidation | Cleaning Oild Copper Pennies | Printable Detailed Periodic Table of Elements | ||
|
|
||
|
What are Oxidation Reduction reactions The corrosion of a metal (that is, the chemical transformation that is recognized as destructive to the metal) is the oxidation step of the overall oxidation-reduction process. Oxidation is the process of losing electrons The metal atoms release electrons (are oxidized) and become positive ions. The site at which this occurs is known as the anode. Typical oxidation half-reactions include the following. (1) Zn ----> Zn2+ + 2e- (2) Al ----> Al3+ + 3e- (3) Fe ----> Fe2+ + 2e- The cations (positive ions) may then go into solution, or they may combine with any available anions (negative ions) or water to form ionic compounds. The exact fate of the cations is important to subsequent processes, but the primary effect is that atoms leave the metallic state, and the metal deteriorates. An oxidation process cannot take place without a simultaneous reduction (gain of electrons) process. The nature of the reduction step in corrosion sometimes varies with the metal and the environment to which it is exposed. For most metals in an aqueous environment, the important reduction half-reaction is the reduction of hydronium ions (a hydronium ion is simply a hydrogen ion attached to a water molecule). (4) H3O+ + e- ----> H + H2O Small concentration variations within a solution in contact with the metal may also affect the rate and nature of corrosion reactions. Therefore, it is often impossible to predict the exact nature of corrosion reactions. It is generally found, however, that for most metals exposed to an aqueous environment the half-reactions involved in corrosion are the reduction reaction of Equation (4) and an oxidation half-reaction of the type shown in Equations (1) through (3). this article is taken from: DOE FUNDAMENTALS HANDBOOK CHEMISTRY Volume 1 of 2 - DOE-HDBK-1015/1-93 JANUARY 1993 | ||