How Corrosion Relates To Cleaning

How Corrosion Relates To Cleaning

The Effect of Chloride ions from Bleach-based Cleaning Products 

Of interest to cleaning directly and to the affect of cleaning operations, is the corrosion-initiating potential of chloride and other aggressive ions common in cleaning products. There are a number of aggressive cleaning products which are known to cause or accelerate corrosion, but there is one that is particularly damaging to metals including stainless steel – Hypochlorites.  Hypochlorites in the form of sodium hypochlorite is bleach, a common household and industrial disinfectant, although safer alternatives are now in use for industrial applications, it is sadly still very common in the home. Bleach is a good source of chloride ions and the common practice is to wipe the surface with a bleach solution and leave it to dry; this has the effect of concentrating and allowing the chloride ions time to penetrate the surface as the solution dries. Once the chloride ions have penetrated, corrosion starts to take place and if the metal is under stress, then cracking could occur, leading to failure.

Another source of aggressive ions is through the use of sodium hydroxide (caustic soda) in solution, the hydroxide ion dissolves the protective surface film on metals like aluminium and exposes the underlining metal to water and dissolved oxygen.

Hydrogen Embrittlement Caused by Acid Cleaning

It is quite common to use acid solutions to clean metal surfaces, either as paint or coating preparation, water scale removal or cleaning protein-based soiling. In these circumstances these acids work exceptionally well, nevertheless, acids in solution dissociated releasing hydrogen ions (H+) which are particularly aggressive. Incidentally the common measure of the acidity (or alkalinity) of a solution is the concentration of the hydrogen ions. The hydrogen ions can penetrate the protective surface film and are even small enough to absorb into the metal lattice, where they are reduced to hydrogen. The absorbed hydrogen starts to exert an influence to the metal lattice, although the mechanism is not fully understood, it is likely that hydrogen creates pressure leading to microscopic deformation of the metal lattice. If the metal is under stress, these deformation can lead to the propagation of cracks, eventually leading to complete failure.

Rafael Cobos