Adsorption and Kinetic Effects on Crack Growth in MnZn Ferrites

Abstract

The variation of the fracture toughness of MnZn ferrite ceramics with varying loading rate and humidity was determined with the aid of the single edge notched beam (SENB) test. A strong decrease with increasing humidity and decreasing loading rate was observed. A model for subcritical crack growth incorporating kinetic and adsorption effects was formulated to analyze the data. The value of the adsorptioncontrolled fracture toughness was determined independently by double torsion experiments and agreed favorably with the values as determined from the SENB data using the model. The strength of the material was determined, and analysis showed a strength behavior similar to the fracture toughness behavior, as predicted by the model. The analysis presented can be used to assess the subcritical crack growth behavior using a limited number of SENB specimens. a) Present address:

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

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Computer Simulation of Dissociative Adsorption of Water on the Surfaces of Spinel MgAl2O4

“…16 In this paper, we present a comprehensive study of atomistic simulations about hydration on low-index surfaces. Knowledge of hydration on the surfaces of spinel MgAl 2 O 4 is useful to understand the fracture of spinel in a humid environment and its possible extension to other spinels, 17 as well as the stability of compounds with the spinel structure. 16 -18 …”

Adsorption of H2O, H2S, and N2 on MnZn ferrite

“…The fits of the Langmuir adsorption isotherm are shown in Fig. 6 For the Langmuir isotherm the amount of water vapor absorbed per gram is translated to the surface excess in moles per square meter, ⌫ M,H 2 O , using the specific surface areas as determined by BET analysis. For reference the fit parameters are given in Tables IV and V. Although the Langmuir isotherm results in a fit of lower quality for the overall p H 2 O range, for p H 2 O ഛ 0.90, the fit quality is good and the relative simplicity of the equation will facilitate its use in other analyses.…”

“…6 With regard to oxidation state, these materials compare to powders I and II respectively, explaining their different reactivity toward water vapor. Also, the differences between the adsorption behavior of the three powders is still different.…”

“…This stimulates the interest in the mechanical reliability of ferrites. 6 Finally, since most fracture experiments are done in air, the adsorption of N 2 is investigated as well. [1][2][3][4][5] On the one hand, some authors have explained this effect for cubic ferrites by subcritical crack growth.…”