MICROBIAL DETERIORATION OF MATERIALS - FUNDAMENTALS - BASIC CORROSION PROCESSES

Microbial growth on metal surfaces induces a number of corrosion reactions which are due to changes in the conditions on the boundary layer. The corrosion systems in question are numerous and damage mechanisms correspondingly manifold. Metallic materials corrode according to known electrochemical mechanisms, whereby microorganisms act indirectly. They produce biofilms which are the cause of concentration cells (oxygen, pH, metal salts) and finally lead to local corrosion effects. Another widespread mechanism is based on the formation of sulphide by sulphide-reducing bacteria which stimulate electrochemical partial reactions. A third large group is attributed to the acid producing microorganisms which attack both metallic and inorganic materials. There is no indication that microorganisms are directly involved in the basic reactions of metal corrosion. The corrosion mechanism of inorganic materials, such as the concrete/sulphuric acid system, is of a purely chemical nature and involves processes, such as binding rupture by ion exchange, solvation, hydrolytic cleavage and chemical conversion. Contrary to this, microorganisms participate directly in the deterioration process of organic materials. For each natural polymer a microorganism exists which is capable of complete or partial decomposition of the polymer, whereby it, or additives (e.g. plasticizers), act as C and/or N sources. Explanations of mechanism are, therefore, transferred to the field of microbiology and phyico-chemical interpretation is only partially possible.