High Temperature Corrosion of Spray-Atomized FeAl (40at.%) Based Alloys:Immersed in a Molten Salt Mixture of V 2 O 5 -Na
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Immersed in a Molten Salt Mixture of
V 20 5-Na2SO 4
M. Amaya*, E. J. Lavernia** and L. Martinez* *Centro de Ciencias Fisicas, UNAM, A.P. 48-3, 62251, Cuernavaca, Morelos, Mexico "**Chemical and Biochemical Engineering and Materials Science Department, University of California, Irvine, CA 92697-2575, USA ABSTRACT We studied the high temperature corrosion of spray atomized and deposited FeAl40at% based intermetallic alloys immersed in a molten salt mixture of 80%V 20 5 +20%Na 2SO 4 (wt%) over the temperature range of 600-900'C. Experiments were realized by the weight loss method and the potentiodynamic polarization electrochemical technique in three different samples: FeA140at%, FeA140+0.lat%B and FeA140+0.lat%B+10at%A120 3. Measurements of weight loss and corrosion current density as a function of the molten salts temperature were obtained and discussed in terms of the passive layer morphology and corrosion products formed during the tests. It was found that the iron aluminide doped with boron and reinforced with alumina particulate was more corrosion resistant in the test temperature range. The weight loss experiments revealed that at 700'C all alloys developed maximum corrosion rate. This behavior was related with the dissolution of protective oxide layer on metal base due the formation of vanadate phases which are highly corrosive at this temperature. INTRODUCTION Several studies have reported that FeA1 intermetallic alloys show excellent corrosion resistance at elevated temperatures under oxidizing and sulfidizing environments, and in some molten salts 1-6 Typically molten salt corrosion is present in steam generators burned fossil fuels. Combustion products contain aggressive inorganic impurities such as vanadium, sodium and sulfur rich salts . Sodium sulfate (Na 2SO4), sodium metavanadate (NaVO 3) and vanadium pentoxide (V20 5) are typical ash deposits, that form a stable electrolyte layer on metallic surfaces causing severe corrosion - . In this work we report the high temperature corrosion behavior of the FeA140at% base alloys alloyed with boron and reinforced with alumina particulate obtained by atomization-deposition. The alloys were immersed and tested in a mixture of molten salts of V20 5 +Na 2SO4 in the temperature range of 600-900'C. EXPERIMENTAL Three heats of FeAl base alloys with gaussian shaped cone were produced by atomization and deposition procedure. Initially a master alloy (FeA140at%) was fabricated by cast in an induction furnace under a protective atmosphere, employing iron and aluminum of 99.99% purity. During the synthesis of atomized and deposited alloys, pieces of the master alloy were introduced in the atomization system. In addition 99.99% purity boron in the form of Ni2B was used as microalloying constituent. Commercially pure (99.99%) single crystal a-alumina platelets with an average diameter about of 3 pm was used as reinforcement phase. The synthesis of atomized and deposited FeAl base alloys and experimental variables are described elsewhere 12-3 . The final composition of the
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