D. Rodziňák, M. Halama, J. Čerňan and M. Kovalčíková
This article focuses on corrosion of the steel reinforcement in the concrete where the blast or demetalized steelmaking slag as one of the components for fabrication was used. The slag from iron and steel production from U.S. Steel Kosice was used in the experiment. Steel reinforcement type S 235 (STN 11 375) were made by cold drawing. Chemical composition of slag in form of powder and slag leachates was analysed using X-ray fl uorescence spectrometry. Corrosion tests were carried out by measuring the polarization curves based on potentiodynamic polarization of steel samples exposed in leachate and also by polarization resistance method directly on the steel embedded in concrete and exposed in atmospheric precipitation. The results revealed differences in the corrosion rate, depending on chemical composition of the slag, which is closely related to its metallic and sulphur content.
The article summarizes state of the art of the influence of external layer of Fe-Zn intermetallics on corrosion behaviour of galvanized steel in a fresh, hardened and chloride contaminated concrete. Current point of view on formation, composition and crystallography of particular intermetallic Fe-Zn phases, that are present in hot dip galvanized coating. External factors as alloying elements are involved as well. A corrosion resistance of these intermetallic layers (especially ζ-FeZn13) during exposure in concrete is evaluated finally.
A. Faltýnková, M. Hruška, J. Kudláček, M. Valeš and P. Szelag
The study is focused on evaluating hydrogen charging of materials in plating baths approved for aviation and in weak acid plating baths. For the evaluation, ASTM F519, ASTM F326 and a newly patented method of measuring device PCN1 - Pulsator cyclic loading were used. ASTM F519 is time consuming and the results are difficult to compare. ASTM F326 proved to be unsuitable for testing above plating baths because of strong hydrogen embrittlement of probes and thus their destruction. Conversely, the PCN1 method was fast and reproducible. Results showed that the baths approved for aviation caused stronger hydrogen embrittlement than weakly acidic zinc baths.
Accelerated corrosion testing is indispensable for material selection, quality control and both initial and residual life time prediction for bare and painted metallic, polymeric, adhesive and other materials in atmospheric exposure conditions. The best known Neutral Salt Spray (NSS) test provides unrealistic conditions and poor correlation to exposures in atmosphere. Modern cyclic accelerated corrosion tests include intermittent salt spray, wet and dry phases and eventually other technical phases. They are able to predict the material performance in service more correctly as documented on several examples. The use of NSS should thus be restricted for quality control.
Polarization curves measured in a sufficiently aggressive environment (e.g. 0.5 mol dm−3 of H2SO4) may help to assess corrosion resistance of stainless steels. New phases precipitate in steel exposed long-term to high temperatures, which may affect the corrosion resistance. Potentiostatic polarization curves were measured on austenitic steel Super304H in a solution annealed state (from the producer) and in a state aged for 15 000 hours at temperatures of 650, 675 and 700 °C. The higher level of current density in passivity (worse corrosion resistance) was reported after aging at 650 °C.
M. Blahetová, J. Horák, P. Kubesa, S. Lasek and T. Ochodek
The case study of chimney liner corrosion addresses three specific cases of damage of chimney systems from of stainless steels. These systems were used for flue of gas arising from the combustion of brown coal in small automatic boilers, which are used for heating. Detailed analyzes implied that the cause of devastating corrosion of the steel AISI 316 and 304 steel (CSN 17349, 17241) was particularly high content of halides (chlorides and fluorides), which caused a severe pitting corrosion, which led up to the perforation of the liner material. Simultaneous reduction of the thickness of the used sheets was due to by the general corrosion, which was caused by the sulfur in the solid fuel. The condensation then led to acid environment and therefore the corrosion below the dew point of the sulfuric acid has occurred. All is documented by metallographic analysis and microanalysis of the corrosion products.
J. Brezinová, J. Koncz, D. Draganovská and A. Guzanová
The paper presents results of research aimed at determining the corrosive properties of steel with cathode metal coating in selected corrosive environments. The corrosion properties of the tin coated steel were evaluated using electrochemical impedance spectroscopy and potentiodynamic tests. For realised measurements, distilled water, 0.5 mol dm−3 NaCl solution, 0.1 mol dm−3 NaCl solution and SARS, which simulates acid rain were used as corrosive solutions. Both corrosion methods are suitable for diagnosing corrosion properties of steel with metal coatings.
The study summarises current knowledge on microbial corrosion in a deep nuclear-waste repository. The first part evaluates the general impact of microbial activity on corrosion mechanisms. Especially, the impact of microbial metabolism on the environment and the impact of biofilms on the surface of structure materials were evaluated. The next part focuses on microbial corrosion in a deep nuclear-waste repository. The study aims to suggest the development of the repository environment and in that respect the viability of bacteria, depending on the probable conditions of the environment, such as humidity of bentonite, pressure in compact bentonite, the impact of ionizing radiation, etc. The last part is aimed at possible techniques for microbial corrosion mechanism monitoring in the conditions of a deep repository. Namely, electrochemical and microscopic techniques were discussed.
Sarmīte Janceva, Tatjana Dižbite, Gaļina Teliševa, Laima Vēvere, Jeļena Krasiļņikova and Mārcis Dzenis
With the purpose to assess potential of alder tree bark as a renewable source of bioactive polyphenolic compounds, antioxidant properties of hydrophilic extracts and proanthocyanidins (PAC) isolated from bark of two alder species (grey alder and black alder) growing in Latvia have been examined employing two test systems, ABTS●+, DPPH● assays. In the tests the high free radical scavenging capacities of the PAC were demonstrated. The polyphenolic nature of the bark PAC opens the possibility of its application as food additive. The PAC has good potential as an antioxidant for mayonnaise.
The effect of liquid paraffin and diesel oil as nutrient amendments for hydrocarbon-degrading bacteria was compared. Different parameters were analyzed - optical density of bacterial suspension, oxygen consumption by biomass, morphology of bacteria, etc. In some experiments the paraffin was more preferable for microorganisms, but in other tests the results for both substances were similar. The influence of the comparable substances strongly depends on cultivation conditions.