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Scientists Develop Coating for Corrosion Resistance
Scientists from India have recently developed a low-cost iron aluminide coating that can reportedly increase corrosion resistance in harsh environments. According to the Indian Government’s Department of Science and Technology, the coating showed four times increased corrosion resistance than that of mild steel.
Because wear and corrosion can cause damage over a range of surface temperatures, researchers note there is a need to protect the component surface with a suitable material for enhanced economic viability. For example, coating the surface of a turbine blade can increase service life and thus hours of operation.
Currently, thermally sprayed coatings composed of thermally sprayed Chromium Carbide-Nickel Chromium Powder (Cr3C2-NiCr) and Tungsten Carbide-Cobalt (WC-Co) are used for their wear and high-temperature oxidation resistance applications. They reportedly provide hardness, toughness and better corrosion resistance under exposure to up to 550 degrees Celsius (1022 F) in the case of WC-Co coatings and up to 850 C for CrC-NiCr coatings.
However, these powders can be expensive and chromium is toxic in its hexavalent state. Because of this, a team of researchers from the Center for Engineered Coatings (CEC) and International Advanced Research Center for Powder Metallurgy & New Materials (ARCI) state that iron-based coatings are promising.
Iron-based solid phases involving two or more semimetallic elements, or intermetallics, can also provide hardness and better corrosion resistance. Their deployment, however, is reportedly restricted due to low ductility.
To address this, the scientists synthesized the iron-based intermetallic powders and utilized the same for depositing the coatings using detonation spray coating technique. ARCI reportedly developed gas atomized iron aluminide powder and deposited it on mild steel substrates with this method without any cracks or spalling.
Results showed that the coatings exhibited better corrosion resistance when chromium and aluminide are in a solid solution with iron than in the iron-rich phases. They also demonstrated increased wear resistance by 30% to 40% than mild steel.
These results imply that iron-aluminide coatings can be used for high-temperature erosion resistance applications, such as in thermal power plant turbine blades, aerospace engine blades, landing gear shafts or steel rolls in the paper industry.
Researchers report that more studies are currently underway to qualify these coatings for fireside corrosion protection of boiler components in collaboration with NTPC, a power utility in India, to enhance boiler life.
ARCI is an automonomous research and development center of the Department of Science and Technology. The study, authored by D. Vijaya Lakshmi, P. Suresh Babu, L. Rama Krishna, R. Vijay, D. Srinivasa Rao and G. Padmanabham, was published in the journal Advanced Power Technology.
Recent Corrosion Prevention Coating Research
In April, a team of researchers reviewed several plant-based extracts as an environmentally friendly corrosion inhibitor for carbon steel in the oil and gas industry.
According to the study, because of its mechanical properties and low cost, carbon steel is the preferred material for pipeline construction. However, because of higher costs, it is not typically possible to replace carbon steel with corrosion resistant alloys and is highly susceptible to corrosion.
The team notes that the presence of carbon dioxide, hydrogen sulfide and organic acids, such as acetic acid, propionic acid and formic acid, is one of the leading causes of localized or pitting corrosion in oil and gas production.
With an increased focus on creating and using low-cost, biodegradable and environmentally inhibitor formulations, researchers analyzed plant extract-based green corrosion inhibitors that have been investigated to mitigate CO2 corrosion. Additionally, they reviewed extracts’ efficiency to prevent strong acid corrosion by HCl and H2SO4 since both are expected to also prevent weak acid corrosion from CO2.
Researchers looked at phytochemicals, or non-nutritive components that give a plant its smell, taste and color. Additionally, they can be extracted from various parts of a plant, including its fruit, leaves, bark roots, seeds or peels. The molecular structure of some of these phytochemicals resembled those of conventional synthetic organic corrosion inhibitors.
To study the plant extract and its corrosion prevention properties, researchers used various analysis techniques, including weight loss measurements and electrochemical techniques. Concentrated plant extracts were then diluted to prepare inhibitor solutions for tests.
Based on the review, the team states that while a majority of plant-extract-based inhibitors provide adequate levels of protection, there is still a need to optimize the formulations. They suggest conducting phytochemical screening and performing quantum chemical and molecular dynamic simulations to identify the most active ingredient of the various phytochemicals present in a plant extract.
Additionally, the next step would be to study the synergism between active molecules to create an overall “superior” formulation, as most commercial inhibitor formulations are a blend of different chemical compounds.
