"The Sulfur-Iodine thermochemical cycle has been proposed as a method for producing large quantities of hydrogen gas from water. However, the extreme operating environments involved limit the possible materials for construction.
Through proper heat treatment and composition control, the modified patented Ni₃(Si,Nb) alloy keeps high temperature strength to greater than 750⁰C and can be deformed by cold rolling more than 50% using multiple passes and intermediate anneals. The corrosion resistance is reproducible and maintains less than 5 mpy for a broad range of boiling sulfuric acid concentrations, including 70 wt%.
In the boiling 70 wt% sulfuric acid corrosion tests, kinetic analyses using log-log plot of these results were carried out for each alloy and condition. For all alloys, the data fell into three different regions indicative of multi-stages corrosion mechanism. At State I, an oxide film is formed on the surface. At State II, the greatest oxide spallation and weight loss of samples was observed. At State III, the passivation state, the amounts of oxide spallation and weight loss are extremely low. The oxide film initially formed during corrosion consists predominantly of SiO₂ and NiSO₄·(H₂O). Although the amount of NiSO₄·(H₂O) is small, it may have a critical influence on oxide spallation and the large weight loss at State II. A Si-rich area forms locally at the metal-oxide interface, after Ni ions diffused through the oxide film and dissolved into the solution. After passivation, the oxide film is composed of almost on SiO₂ and the significant Si-rich area at the interface was observed. It seems that once the Si concentration is enriched to the critical level, the formation of NiSO₄·(H₂O) ends. After this, there is almost no NiSO₄·(H₂O) in the oxide film and the sample is passivated"--Abstract, leaf iii.
Newkirk, Joseph William
Van Aken, David C.
Schlesinger, Mark E.
Brow, Richard K.
Kohser, Ronald A.
Materials Science and Engineering
Ph. D. in Metallurgical Engineering
Nuclear Energy Research Initiative (U.S.)
United States. Department of Energy
Missouri University of Science and Technology
xiv, 116 pages
© 2010 JenHsien Hsu, All rights reserved.
Dissertation - Restricted Access
Library of Congress Subject Headings
Nickel alloys -- Mechanical properties
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://laurel.lso.missouri.edu/record=b8262453~S5
Hsu, Jen-Hsien, "Understanding corrosion of Ni₃(Si,Nb) alloys in hot sulfuric acid" (2010). Doctoral Dissertations. 1786.
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