This reaction occurs spontaneously in 2 steps. The first reaction is
2 Fe(s) + O2(g) + 2 H2O(l) ® 2 Fe(OH)2(s)
The second reaction is:
4 Fe(OH)2(s) + O2(g) ® 2 H2O(l) + 2 Fe2O3 · H2O(s)
Non-spontaneous redox reactions also occur but require a voltage potential to drive the reaction. These non-spontaneous redox reactions are known as the process of electrolysis. Water can be broken into its elements through electrolysis. This reaction requires 1.229 vdc of potential.
2 H2O(l) ® O2(g) + 4 H+ (aq) + 4e- -1.229 vdc
Corrosion On Electrical Components
As discussed previously, non-spontaneous redox reactions can occur if a voltage potential is applied between two or more elements. For electrical components, we will study the effects of salt water (NaCI (aq)) on copper wire. For this reaction, there are several chemical elements involved. Salt water is a solution of sodium ions (Na+) and chloride ions (Cl-) in water (H2O). For simplicity, the sodium ions (Na+) will not be used in the calculation. The other elements involved are oxygen (O2) and copper (Cu). For all of these chemical elements, they can be written as 3 half reactions.
2Cl-(aq) ® Cl2(g) + 2e- -1.36 vdc
Cu(s) ® Cu+2(aq) + 2e- -0.34 vdc
O2(g) + 2 H2O(l) + 4e- ® 4 OH-(aq) +0.40 vdc
When you add up all of the reactions, you get
2 Cl-(aq) + 8 Cu(s) + O2(g) + 2 H2O(l) ® 4 Cu2OH(s) + Cl2(g) -1.30 vdc
This equation states that when copper is in the presence of chlorine, water, oxygen and 1.30 vdc of electrical potential, the copper becomes oxidized into copper hydroxide. The solid copper wire is eaten away (reduced) and copper hydroxide is produced (oxidized). A reaction will also occur without the presence of chlorine; but chlorine, a small atom and an excellent oxidizer, greatly accelerates the corrosion process.
Solutions in Environmental Protection
Comair Rotron, the leader in innovative cooling ideas, has pioneered the way in environmentally protected fans. With the continuous advancements in conformal coating materials, Comair Rotron has researched various chemicals, materials, and processes that provide the greatest degree of protection to our customers. The results have produced our latest value-added product, "Enviro-Shield". The Enviro-Shield products are rates 3 levels of protection; which are described later in this paper as Type 1,2, & 3. Each material fully encompasses all electrical components, wires, circuit paths, motor windings, and stator assemblies; ensuring the optimum protection for any condition. These materials can be sprayed, dipped, or injected into the motor assemblies, creating a protective barrier between the delicate electrical components and the outside environments. Comair Rotron's environmentally protected fans are designed and tested to withstand mild environmental conditions such as light water mists to the harshest environments including long term salt exposure. There are several standard specifications written with various degrees of protection and methods for testing to these standards. The most common standards are NEMA, IP, BELCOR,MIL,UL, and ASTM. These standards and the testing methods can be made available to you upon request. To test a fan's ability to maintain such reliable protection, Comair uses a variety of testing apparatus. The most commonly refer to test is the salt fog test. This test demands that the fan be subjected to as many as 14 days of continuous exposure to salt fog environment. Types 2 and 3 materials have gone as high as 80+ days before encountering a failure. This says a lot considering 14 days is estimated as the equivalent to 10 years of normal operations. other tests include direct water spraying on the fan, humidity, and dust.