Diffusion of chromium, manganese, and iron in MnCr 2 O 4 spinel
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Basic and Applied Research: Section I
Diffusion of Chromium, Manganese, and Iron in MnCr2O4 Spinel Jolanta Gilewicz-Wolter, Zbigniew Z˙urek, Joanna Dudała, Jerzy Lis, Marta Homa, and Marcin Wolter
(Submitted July 21, 2005) As a result of the oxidation of chromium (Cr)-manganese (Mn) steels, a multilayer scale is formed. The intermediate layer of this scale is composed of MnCr2O4 spinel, and the outer layer is composed of MnO. The aim of the current study is to examine self-diffusion processes in MnCr2O4 spinel by a tracer method. In experiments, the radioisotopes 54Mn, 51Cr, and 59Fe were used. The serial sectioning method was applied for the simultaneous evaluation of diffusion rates of Cr, Mn, and iron (Fe) in MnCr2O4 spinel at 1173 K under a pressure of 105 Pa in SO2 containing 10 Pa O2. This spinel was obtained by a modified sol-gel method from metal nitrates (R. Gajerski and Z. Zurek, personal communication, 14.04.2004). It was found that the dominant mechanism of Mn transport in the studied samples is a volume diffusion, while Cr and Fe are transported mainly through the high-diffusivity paths.
1. Introduction The full description of the mechanism of the oxidation of Cr-Mn steels requires the knowledge of each partial transport process to find out which of them is the slowest and to determine the corrosion rate. It was found that due to the oxidation of these steels in SO2, the thin innermost, finegrained layer consisting of sulfides and oxides of Mn, Cr, and Fe is formed. The intermediate layer is built mainly of MnCr2O4 spinel, while MnO is the main component of the outer layer.[2] The aim of this article is to establish the transport processes of Cr, Mn, and Fe in MnCr2O4 spinel polycrystals, which is one of the scale components. The application of a multitracer method of diffusion measurements in the material mentioned above is presented.
2. Experimental Procedure The MnCr2O4 spinel was synthesized from Mn and Cr nitrates by a modified sol-gel method. Gel was obtained by the dehydration of molten nitrates at 85 °C, and subsequently the mixture was decomposed at 250 to 300 °C to obtain oxides. The spinel powder was produced by the calThis article is a revised version of the paper printed in the Proceedings of the First International Conference on Diffusion in Solids and Liquids - DSL-2005, Aveiro, Portugal, July 6-8, 2005, Andreas Öchsner, José Grácio and Frédéric Barlat, eds., University of Aveiro, 2005. Jolanta Gilewicz-Wolter and Joanna Dudała, The Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland; Zbigniew Z˙urek and Marta Homa, Institute of Inorganic Chemistry and Technology, Cracow University of Technology Warszawska str. 24, 31-155 Kraków, Poland; Jerzy Lis, The Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland; and Marcin Wolter, Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 30-342 Kraków, Poland. Conta
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