Microbial corrosion of silicon nitride ceramics by sulphuric acid producing bacteria Acidithiobacillus ferrooxidans

Yttria/alumina doped silicon nitride ceramics were exposed to corrosive Acidithiobacillus ferrooxidans bacteria cultures. These microorganisms produce sulphuric acid as a metabolic product during thiosulfate oxidation. In this study, the effect of microbial corrosion of silicon nitride ceramics is compared with an abiotic-chemical corrosion process in sulphuric acid under similar conditions (e.g. pH, temperature and exposure time). While abiotic corrosion caused only partial lixiviation of the superficial grain boundary phase, microbially induced corrosion lead to an almost total dissolution of the amorphous grain boundary within the corrosion zone. Microbial corrosion is thus more efficient than the abiotic process: it dissolves more silica and causes therefore a higher corrosion rate. This is probably due to the additional microbial release of metal-chelating organic compounds that stimulate the corrosion process.