Gentlemen, this is the best compendium I've been able to find on the chemistry of the water; purification, ionization, corrosion and so on.
http://en.wikipedia.org/wiki/Purified_water
Wikipedia – Purified Water
Distilled water is produced by a process of distillation and has an electrical conductivity of not more than 11 μS/cm and total dissolved solids of less than 10 mg/litre. Distillation involves boiling the water and then condensing the vapor into a clean container, leaving solid contaminants behind. Distillation produces very pure water. A white or yellowish mineral scale is left in the distillation apparatus, which requires regular cleaning. Distillation alone does not guarantee the absence of bacteria in drinking water unless containers are also sterilized. For many procedures more economical alternatives are available such as deionized water and, is used in place of distilled water.
Deionization
Deionized water, also known as demineralized water/DM water (DI water, DIW or de-ionized water), is water that has had its mineral ions removed, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate. Deionization is a chemical process that uses specially manufactured ion-exchange resins which exchange hydrogen ion and hydroxide ion for dissolved minerals, which then recombine to form water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup.
Electrical Conductivity
Electrical conductivity of ultra-pure water is 5.5 × 10−6 S·m−1 (18 MΩ cm in the reciprocal terms of Electrical Resistivity) and is due only to H+ and OH- ions produced in the water dissociation equilibrium. This low conductivity is only achieved, however, in the presence of dissolved monatomic gases. Completely de-gassed ultra-pure water has conductivity of 1.2 × 10−4 S·m−1, whereas upon equilibration to the atmosphere it is 7.5 × 10−5 S·m−1 due to dissolved CO2 in it.
http://chemwiki.ucdavis.edu/Physical_Che..._Autoionization
Water Autoionization
Water, even pure water, has an amphiprotic nature. This means that a small amount of ions will form in pure water. Some molecules of H2O will act as acids, each donating a proton to a corresponding H2O molecule that acts as a base. Thus, the proton-donating molecule becomes a hydroxide ion, OH-, while the proton-accepting molecule becomes a hydronium ion, H3O+.
http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Case_Studies/Corrosion
Conditions for Corrosion of Metals
There are three main components necessary for corrosion to occur:
1. Metal (example: iron)
2. Oxygen (usually from the atmosphere)
3. An electrolyte (usually water)
Galvanic Corrosion
Galvanic corrosion involves two metals that are electrochemically dissimilar and an electrolyte to carry an electrical current. The subsequent reactions model a galvanic cell; reduction-oxidation reactions occur in a way similar to those of batteries. Typically, the metal that is lower on the Galvanic Series will act as the anode and corrode faster than without the presence of the second metal, while the second metal gains a stronger resistance to corrosion. These reactions and their directions can change or be altered due to the environment.
http://www.gewater.com/handbook/cooling_water_systems/ch_24_corrosion.jsp
Galvanic Corrosion
Galvanic corrosion occurs when two dissimilar metals are in contact in a solution. The contact must be good enough to conduct electricity, and both metals must be exposed to the solution. The driving force for galvanic corrosion is the electric potential difference that develops between two metals. This difference increases as the distance between the metals in the galvanic series increases. When two metals from the series are in contact in solution, the corrosion rate of the more active (anodic) metal increases and the corrosion rate of the more noble (cathodic) metal decreases.
CONTROL OF CORROSION
Corrosion control requires a change in either the metal or the environment. The first approach, changing the metal, is expensive. Also, highly alloyed materials, which are very resistant to general corrosion, are more prone to failure by localized corrosion mechanisms such as stress corrosion cracking. The second approach, changing the environment, is a widely used, practical method of preventing corrosion. In aqueous systems, there are three ways to effect a change in environment to inhibit corrosion:
- form a protective film of calcium carbonate on the metal surface using the natural calcium and alkalinity in the water
- remove the corrosive oxygen from the water, either by mechanical or chemical deaeration
- add corrosion inhibitors
http://www.gewater.com/handbook/cooling_water_systems/ch_32_closed.jsp
{This article provides a good discussion on closed systems, such as a vehicle cooling system. It also addresses silicates, nitrites, pH control, and the molybdates, which are soon to be the new improvement in coolant/antifreeze technologies.}
