Chockstone Forum

      Sponsored By
      ROCK
   HARDWARE

Chockstone Photography

Australian Landscape Prints

Chockstone Forum - General Discussion

General Climbing Discussion

Topic Date User

Grid bolting at Windjammer Pt Perp 10-Dec-2014 At 11:07:56 AM uwhp510

Message

On 10/12/2014 egosan wrote:
>Please elaborate.
>
>Cheers, Sol
>

Crevice corrosion.

According to the internet;

>2.2.1 Mechanism of Crevice Corrosion
>The crevice corrosion mechanism is dependent on several parameters and it may
>change accordingly with a change in the parameters[14]. The attack happens in a
>restricted area, often a narrow fissure with a width of normally only a few micrometers.

>These fissures can occur where there are external agents such as paint remnants,
>tape or insulation, that forms a crevice against the pipe surface. The chemistry within
>the fissure develops differently from the rest of the bulk solution. In a review[15],
>several mechanisms were proposed for crevice corrosion, since any single mechanism
>fails to explain all aspects of crevice corrosion. Here, only deoxygenation-acidification,
>also called the passive dissolution mechanism, of crevice corrosion proposed by
>Oldfield and Sutton[16] is briefly explained to give an introduction to
>crevice corrosion. In fissures the most common reduction reaction, which is a
>requirement in order to introduce crevice corrosion, is the oxygen reduction reaction.
>Other reduction reactions may also occur, for example, reduction by chloride ion. The
>only reduction reaction at the cathode, is the proton (H+ ) or water reduction reaction;
>in the case where no oxidising agent is left in the pit, or depletion of oxygen is called
>deoxygenation. This is caused by too slow oxygen diffusion into the crevice and
>therefore a concentration gradient builds up between the crevice and the outer passive
>surface of the material. Hydroxide forms in the crevice in alkaline seawater, causing a
>rise in the pH. (etc)