Corrosion properties of chromia based eco - friendly coatings on mild steel

Ceramic nanocrystalline coatings of chromium oxide (III) on steel S235JRH-1.0038 (EN 10025-1) were prepared using the liquid precursor plasma spraying (LPPS) method from ammonia dichromate (VI). Their structure and anti – corrosion properties were compared to the standard chromium oxide (III) coating prepared by thermal spraying. The newly prepared coatings had very high adhesion and minimal porosity. Anticorrosion properties were characterized by the means of the electrochemical impedance spectroscopy (EIS), measuring the charge transfer resistance Rct and capacitance of electrical double layer CPEdl in the 0,5 mol/l NaCl. Coatings of Cr2 O3 prepared by the LPPS method showed unambiguously improved anti - corrosion properties

Archaeological analogs for verification of container lifetime models for deep radioactive waste repositories : Final report of project TK01010040

More than 200 artefacts from 15 localities were studied within the scope of this project. 4 localities were crucial, because those were pond beds with continual flooding. Soils at all localities were coarser compared to bentonites and lacked swelling ability. Pore solutions of the soils were very similar to bentonite pore solutions. They differ in cation composition, but anion composition was similar, which is more important for corrosion behaviour. The environment was not completely anaerobic, what influenced the composition of corrosion products. The compounds were oxides and oxohydroxides. Very low oxidation-reduction potential (fully anaerobic environment) is necessary for the formation of carbonate-based corrosion products, that were detected as major corrosion products in the previous lab and in situ experiments on another projects. Nevertheless, the oxygen transport was very slow and the contribution of aerobic corrosion was negligible compared to anaerobic corrosion. The evaluation of archaeological artefacts revealed very important factors influencing corrosion mechanism in latter stage of soil burial. Precipitation of corrosion products is a driving phenomenon for transport limitation and decrease of corrosion rate in the early stage of burial, while the ferrous species transport is limited extensively within the latter stage resulting in mechanical stress of inner corrosion products layers to previously formed corrosion products and subsequent cracking. This mechanical damage is repeated in the cycle. The mechanical properties of corrosion products are poor, they are easily deformable and very porous. The project has revealed a very important phenomenon, necessary for the right lifetime estimation, which would not be obvious based on the short-term experiments data

Monitoring of corrosive environment aggressiveness and development of a sensor for monitoring of the water film in exposure chamber

Exposure of copper in corrosive environment is possible way, how to obtain artificial patina. Various solutions based on chloride, ammonia or polysulfide are commonly use in this purpose. Furthermore, it appears that the patina is also formed in an environment with an increased concentration of SO2 in the atmosphere. This procedure was tested in a small (30 l) exposure chamber, where the aggressiveness of the environment was monitored and where the effect of alternating the condensation and drying phases was shown to be positive. Based on this experiment, a 2 m3 pilot chamber was designed for which a water film sensor was developed and tested to ensure drying of the object surface. Monitoring of the aggressiveness of the environment showed that the pH and SO2 concentrations in the atmosphere are stable after approximately 5 hours and the ideal input SO2 concentration is 17.7 g m-3 at which the pH stabilizes at 2.7-3. By recording the voltage variation on the sensor, it was possible to monitor the formation and drying of the water film during the cycling of the condensation and drying phases

Long-term outdoor exposure of artificial copper patina based on brochantite

A typical green layer of patina starts to cover copper in atmosphere condition, which is aesthetically acceptable and also provides protective properties. This work investigates stability of the artificial patina layer based on sulphates prepared from a gaseous phase during two-year exposure in atmosphere condition. XRD and SEM were employed to verify the composition and morphology of artificial patina. Colour and patina coverage were compared before and after exposure also. According to results after 1 and 2 years of exposure, it is possible to see changing of hydroxyl sulphates to more stable brochantite and filling pores in the patina layer. There is almost no colour change, however lower patina coverage is slightly evident due to precipitation and abrasive effect