Anaerobic microbial corrosion of carbon steel under conditions relevant for deep geological repository of nuclear waste.

We examined microbial corrosion of carbon steel in synthetic bentonite pore water inoculated with natural underground water containing microorganisms over a period of 780-days under sterile and anaerobic conditions. Corrosion behaviour was determined using the mass loss method, SEM-EDS analysis and Raman spectroscopy, while qualitative and quantitative changes in the microbial community were analysed using molecular-biological tools (16S rDNA amplicon sequencing and qPCR analysis, respectively). Corrosion rates were significantly higher in the biotic environment (compared with an abiotic environment), with significant localisation of corrosion attacks of up to 1 mm arising within 12-months. Nitrate reducing bacteria, such as Pseudomonas, Brevundimonas and Methyloversatilis, dominated the microbial consortium, the high abundance of Methyloversatilis correlating with periods of highest localised corrosion penetrations, suggesting that this bacterium plays an important role in microbially influenced corrosion. Our results indicate that nitrate-reducing bacteria could represent a potential threat to waste canisters under nuclear repository conditions.

Structure and Properties of Fe-Al-Si Alloy Prepared by Mechanical Alloying.

Fe-Al-Si alloys have been previously reported as an interesting alternative to common high-temperature materials. This work aimed to improve the properties of FeAl20Si20 alloy (in wt.%) by the application of powder metallurgy process consisting of ultrahigh-energy mechanical alloying and spark plasma sintering. The material consisted of Fe3Si, FeSi, and Fe3Al2Si3 phases. It was found that the alloy exhibits an anomalous behaviour of yield strength and ultimate compressive strength around 500 °C, reaching approximately 1100 and 1500 MPa, respectively. The results also demonstrated exceptional wear resistance, oxidation resistance, and corrosion resistance in water-based electrolytes. The tested manufacturing process enabled the fracture toughness to be increased ca. 10 times compared to the cast alloy of the same composition. Due to its unique properties, the material could be applicable in the automotive industry for the manufacture of exhaust valves, for wear parts, and probably as a material for selected aggressive chemical environments.