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The screening of coatings shows that the modification by adding individual pigment was not sufficient to protect carbon steel even during a short-term exposure, indicated by the discoloration after only seven days of exposure.
Electrochemical tests indicated that the coating cathodically protects carbon steel or slows down the corrosion reaction.
A long-term exposure test confirmed that the PANI/SiO2 modified coating successfully protects the carbon steel in the Sibayak artificial geothermal water at 150 °C for 6 months.
Colours, nano and surface
(2022)
The basic ideas of colours and pigments are presented. The correlation between nanomaterials and colours are explained. Different methods are presented for investigating nanoparticles and their surface. At the end a case study is presented explaining the importance of coating for the properties of nanoparticles.
Study of Polyaniline/Silicon Dioxide based Coating on Carbon Steel in Artificial Geothermal Brine
(2021)
By using the available resources in Indonesia, such as silicon dioxide and marine coating base, the PANI/SiO2 modified alkyd coating was able to protect carbon steel in a deaerated artificial geothermal water. The screening of coatings shows that the modification by adding individual pigment was not sufficient to protect carbon steel even during a short-term exposure, indicated by the discoloration after only seven days of exposure. Electrochemical tests indicated that there was no significant change in the Ecorr between the coated and uncoated carbon steel at room temperature. At 150 °C, the coated carbon steel has a lower potential than that of carbon steel, indicating that the coating is protecting carbon steel cathodically or slowing down the corrosion reaction. Finally, a long-term exposure test confirmed that the PANI/SiO2 modified coating successfully protects the carbon steel in the Sibayak artificial geothermal water up to 150 °C for 6 months.
A way to increase the application range and the lifetime of metallic substrates is their protection by coatings. Here the effect of alumina coatings on common steel substrates having different Chromium content is examined. The background of the investigations is to expand the application possibilities of mechanically good steels to higher temperatures and corrosive atmospheres in the framework of the European project POEMA (“Production of Coatings for New Efficient and Clean Coal Power Plant Materials”) which was introduced to identify materials that can withstand the aggressive conditions arising during the oxyfuel process in modern coal power plants. This process is one possibility to reduce the CO2 emission by firing the coal in oxygen and recirculated flue gas.
Substrate materials were P92 (9% Cr), K44X (19% Cr), and HR3C (25% Cr). The alumina coatings were deposited by a sol-gel-process using boehmite, this is relatively simple and offers application possibilities for a wide technical range without special surface preparations. All samples were dried for 30 minutes at 650° C to remove the organic components and to start the crystallization process of the alumina. For P92 and HR3C the following conditions simulated the oxyfuel process: 650°C in wet flue gas for 300h for the steel P92, the same conditions for 2000 hours for the steel HR3C. K44X was tested at 900°C in laboratory air for 500 hours. As well after drying as after testing TEM characterizations were performed, where the interfaces between steel and coating are of special interest to characterize the microstructure, detect failure mechanisms, and identify diffusion and crystallization processes and so to understand the mode of action of the alumina coating.
The TEM samples were prepared by the lift-out-technique using a FIB Quanta 3D and were investigated in a STEM JEM2200FS at 200kV.
After the coating and drying process all steels show chromium oxide layers directly at the steel surface, they vary in thickness and are island shaped in the case of the steel K44X. Chromium depletion arose more or less in the superficial zones of all samples. After the long term tests K44X showed breakaway oxidation while P92 and HR3C presented intact interfaces. This reveals: Beside the positive impact of the coating not only the Chromium content of a substrate is essential for the formation and self-healing of protective chromium oxide layers during the service time of steels. One has to consider the possibility of the steel to allow a continuously Cr diffusion to the interface and so e renewal of the Cr-oxide layer.
One of the alternative renewable fuels is biomass but it is a difficult fuel because of its diversity and complexity. It can contain high percentages of K and Cl responsible for corrosion together with sand that have additionally an abrasive effect during combustion. Because of permanently extending the surface reaction due to abrasion the corrosion of the materials increases. In particular in power plants, the superheater tubes are exposed to a corrosive abrasive attack that is one of the main sources of concern. The development of new alloys for multilayer surface, which combines corrosive and abrasive resistance is therefore of high importance. Those new technical approaches must be at the same time cost-effective to be an alternative to conventional materials. The aim of the presented investigation methods is to test and develop suitable alloys for coatings for the super heater tubes of biomass power plants. First results of abrasion investigations show improved abrasion resistance compared to the multi-component reference material Alloy 625.