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Complex Impedance Analysis of Silica Surface Film on Molybdenum Disilicide

Published online by Cambridge University Press:  10 February 2011

Wen-Yi Lin ,
Rosario A. Gerhardt  and
Robert F. Speyer
Wen-Yi Lin
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Rosario A. Gerhardt
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Robert F. Speyer
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
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Abstract

The exposure of molybdenum disilicide to combustion products at 1370° and 1600°C for 1 and 60 hours led to the formation of a silica surface film. The thickness of this protective layer, ranging from 4.4–18.2 μm, increased with temperature and exposure time. However, the dielectric constant (3.16) of the thin film was independent of ac field frequency, exposure time, and temperature, according to complex impedance analysis in the frequency range of 500 Hz to 1 MHz. MoSi2 specimens with a silica coating on one side resembled, in impedance spectroscopy terms, a resistor of low resistivity (MoSi2, 10−4 Ω·cm) in series with a parallel RC circuit of high resistivity (SiO2, 3.0×1010 Ω·cm). From this analysis, a calibration curve was generated for converting measured capacitance to silica film thickness. Relaxation time (on the order of 0.1 sec) and relaxation frequency (on the order of 1–10 Hz) were also derived, with the aid of semicircular regression of the complex impedance curves.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 411: Symposium T – Electricaly-Based Microstructural Characterization , 1995 , 223
Copyright
Copyright © Materials Research Society 1996

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References

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