Electroless Ni-based coatings for biodiesel containers Sittha Sukkasi, Ukrit Sahapatsombut, Chamaiporn Sukjamsri, Sawalee Saenapitak, Yuttanant Boonyongmaneerat Ó ACA and OCCA 2010 Abstract Biodiesel commonly experiences oxidative and hydrolytic degradations, leading to problems of low storage stability and corrosion of fuel containers. The present study investigates the fabrication and use of electroless-deposited nickel alloys, containing phos- phorus and tungsten, as potential coating materials that effectively protect steel-based biodiesel containers from corrosion. Through long-term static immersion and high-temperature oxidation tests, coupled with surface analyses of the coatings and assessments of the biodiesel’s acidity and storage stability, it is determined that a nickel coating with 15 wt% of phosphorus is favorably compatible with biodiesel, both in terms of corrosion protection and fuel stability. Keywords Electroless coatings, Biofuel, Oxidation stability, Corrosion Introduction Biodiesel has been considered one of the most viable renewable alternatives to petroleum-derived fuels. 1,2 It is produced from biological sources, such as vegetable oils and animal fats, most commonly by a chemical reaction called transesterification. 3–5 Biodiesel exhibits similar performance to that of petroleum-derived diesel and thus can be used as a substitute to regular diesel directly in most applications, including diesel vehicles, home heating, marine and jet applications, furnaces and boilers, and oil-fueled lighting equip- ment. 3,5,6 In terms of environmental impacts, biodiesel produces cleaner emissions than regular diesel 7,8 and can be carbon-neutral or even carbon-negative over its lifecycle. 9,10 Domestically producible with local feed- stock crops, biodiesel can help raise the national energy security and reduce trade deficits of oil- importing countries, as well as diversify markets for the agricultural sector. Worldwide biodiesel produc- tion and consumption grew strongly at the rate of 32% per year, from 2000 to 2005, and are predicted to grow even more rapidly in the near future. 11 Despite its attractive features and increasing wide- spread global consumption, the use of biodiesel still faces some challenges, including the problems of low storage stability and corrosion of fuel containers. The most dominant storage-instability problem of biodiesel is oxidative instability. It is associated with the oxida- tion of fatty esters that constitute biodiesel. The oxidation of biodiesel is a multi-step reaction that leads to primary products, hydroperoxides, and sec- ondary products, such as aldehydes, alcohols, formic acid, shorter chain carboxylic acids, and polymers. 12–14 Due to the formation of these shorter chain fatty acids, the oxidation of biodiesel always results in increased acidity of the fuel. 14 Furthermore, biodiesel has strong tendency to absorb water 15 which promotes hydrolysis or hydrolytic oxidation. 16 Both oxidative and hydro- lytic degradation in biodiesel can cause corrosion in steel-based fuel containers, which in turn induces a formation of sediments that become deposits on injectors and pump parts, reduce the fuel flow to the engine and cause pressure drop across filters. 14,16 One potential approach to improve the resistance of steel fuel tanks is to apply a protective metal coating on the inner surface. For achieving good compatibility with the fuels, proper coating materials may not con- stitute bronze, brass, copper, lead, tin, and zinc, which have been reported to oxidize diesel or biodiesel. 17–19 S. Sukkasi, U. Sahapatsombut, C. Sukjamsri National Metal and Materials Technology Center, Pathumthani 12120, Thailand S. Saenapitak, Y. Boonyongmaneerat (&) Metallurgy and Materials Science Research Institute, Chulalongkorn University, Bangkok 10330, Thailand e-mail: yuttanant.b@chula.ac.th J. Coat. Technol. Res., 8 (1) 141–147, 2011 DOI 10.1007/s11998-010-9286-x 141