Johtumisyövy

Johtumisyövy, also known as galvanic corrosion or bimetallic corrosion, is an electrochemical process that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. This electrolyte can be anything from saltwater to moisture in the air. The difference in the electrochemical potential between the two metals causes one to act as the anode and the other as the cathode.

The anodic metal, which is more reactive (less noble), will corrode preferentially, losing electrons and dissolving into the electrolyte. The cathodic metal, which is less reactive (more noble), will gain these electrons and be protected from corrosion. This process accelerates the corrosion of the anodic metal compared to if it were in contact with a metal of similar electrochemical potential or no metal at all.

The rate of johtumisyövy depends on several factors, including the difference in the electrochemical potentials of the two metals, the conductivity of the electrolyte, the surface area ratio of the cathodic to anodic metal, and environmental conditions such as temperature and pH.

Common examples of johtumisyövy include the corrosion of steel fasteners in aluminum structures or the corrosion of copper wires in contact with steel. To mitigate johtumisyövy, it is advisable to avoid joining dissimilar metals directly, or to use a sacrificial anode, insulating barriers, or coatings to prevent electrical contact and electrolyte access.