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Minima in the strength of MnZn ferrites

Published online by Cambridge University Press:  31 January 2011

M. A. H. Donners ,
L. J. M. G. Dortmans ,
G. de With  and
M. J. M. de Graaf
M. A. H. Donners
Affiliation:
Laboratory for Solid State and Materials Chemistry, Eindhoven University of Technology, POB 513, 5600 MB Eindhoven, The Netherlands
L. J. M. G. Dortmans
Affiliation:
TNO Institute of Applied Physics, POB 595, 5600 AN, Eindhoven, The Netherlands
G. de With*
Affiliation:
Laboratory for Solid State and Materials Chemistry, Eindhoven University of Technology, POB 513, 5600 MB Eindhoven, The Netherlands
M. J. M. de Graaf
Affiliation:
Ferroxcube R&D Center Eindhoven, POB 80058, 500 KA, Eindhoven, The Netherlands
*
b)Address all correspondence to this author.
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Abstract

Like many other oxides, MnZn ferrite shows a considerably decreased strength in a humid environment. Conventionally one explains this behavior by subcritical crack growth, i.e., a kinetic effect affecting the oxygen–metal bond breaking rate at the crack tip via a reaction with water. The dissociation of water in a proton and hydroxyl ion is considered as crucial. However, it appears that also other gases have a detrimental effect on the strength. In this paper the effect of H2O, H2S, NH3, NO, and CO on the strength of MnZn ferrite have been studied experimentally. For water a clear minimum in strength occurs at relative low partial pressure. For the other gases the data also indicate a minimum. An adsorption model taking into account the presence of competitive adsorption mechanisms, involving dissociative and nondissociative adsorption of the adsorbate and the (non)dissociative adsorption of the ever present N2, is presented. This model can explain the experimentally observed features well. Although kinetic effects induce subcritical crack growth in MnZn ferrites, it is concluded that adsorption is an important strength lowering effect for MnZn ferrite when exposed to active gases.

Type
Articles
Information
Journal of Materials Research , Volume 16 , Issue 12 , December 2001 , pp. 3575 - 3582
Copyright
Copyright © Materials Research Society 2001

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References

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