Nanoceria Coatings and Their Role on the High Temperature Stability of 316L Stainless Steels
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Nanoceria Coatings and Their Role on the High Temperature Stability of 316L Stainless Steels. H. Mendoza-Del-Angel and H. F. Lopez. Materials Department, University of Wisconsin-Milwaukee, 3200 N. Cramer St. Milwaukee WI 53211 ABSTRACT In this work, a method is considered to produce uniform nanoceria surface coatings on 316L stainless steel such as dipping. Coated steels using the aforementioned method are exposed to high temperature 800-1000oC and their oxidation behavior is investigated. It is found that the nanoceria particles in the implemented coatings exhibit some growth during high temperature exposure. In addition, thermogravimetric determinations of oxidation resistance in coated and bare samples at 900oC clearly indicates that the nanoceria coated stainless steels exhibits a two fold reduction in mass gain when compared with bare ones. Optical and scanning electron microscopy are employed to characterize the developed oxide scale morphologies. It is found that in areas are nanoceria is not uniformly coated, Fe-rich oxide islands develop, whereas in coated regions the scale is Cr and Ce rich indicating that the scale is probably a Ce doped Cr oxide. INTRODUCTION Structural steels for high temperature applications are prone to undergo oxidation and corrosion in severe environments. The nature of the reaction products is complex and the rate at which the materials corrode vary widely. Therefore, it is highly desirable to improve high temperature alloy properties, as well as the capacity for prediction oxidation/corrosion rates. In particular, corrosion has been a serious problem with significant impact in the operation of conventional power generation plants. The high Temperatures of the process and the complexity of the corrosive environment make it difficult to design for long term operations using conventional steels. Other applications where improved performance is sought are in the field of fuel cells. These cells are units used to generate electricity through an electrochemical process. They do not have any combustion and they produce low emissions, but they operate at high temperatures (659 to 1000oC). These high temperatures are a potential challenge for the metallic alloys (austenitic and ferritic stainless steels) to stand corrosion in the interconnectors and heat exchangers. Stainless steels are the materials of choice for high temperature applications as they can be used in a wide variety of environments. They are fairly inexpensive and posses good oxidation/corrosion resistance. However, it is desirable to enhance the long term oxidation resistance of these steels. A common approach has been the use of surface coatings [1, 2] and it is the approach employed in this work. Accordingly, in the present work nanoceria coatings are employed to protect a 316 stainless steel from high temperature oxidation in dry air. In particular, the work is focused on identifying conditions that will give rise to a uniform nanoceria surface coating and the effect of the coating on improving the oxidation resistance o
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