What Does Airborne Chlorides Mean?
Airborne chlorides are the suspended salt and gaseous content present in the atmosphere. It is measured through air concentration using the unit µg/m3.
Because salt is corrosive, airborne chloride levels can affect corrosion significantly. Identifying its levels can greatly help in the estimation of corrosivity.
Corrosionpedia Explains Airborne Chlorides
The salinity of the atmosphere increases corrosion rates in a very distinct way, and airborne chlorides have a direct participation in electrochemical corrosion.
For example, iron chloride complexes have the tendency to become unstable in ferrous alloys. This can be true in metals like copper and zinc where chloride salts are lower than compared to iron. The result is lower rates of corrosion induced by chloride.
This phenomenon makes the propagation and initiation of the damage of localized corrosion that is influenced by ions of chloride of utmost importance. For instance, crevice and pitting corrosion that is present in passive alloys like that of titanium, aluminum and stainless steel are instances of that kind of damage.
One method of measuring the degree of contamination of airborne chlorides is the wet candle technique. It is simple, but may be inaccurate as it may also collect dry salt particles that might not go through deposition. This method makes use of a wet wick, which should be kept wet using 40% solution of water and glycol or plain water. The wick traps the retained spray or salt particles. This method shows the level of salinity and the total amount of chloride in the atmosphere.
Airborne chloride levels can also be measured through the dissolved salt concentration in rain water.