Shigeki Sasahara1, Kazuo Araki2, Shigekatsu Mori2 and Akira Moriyama2
1Graduate School, Nagoya Institute of Technology, Nagoya. Present address: Kobe Steel, Ltd., Kobe
Kinetics of the reaction between iron and zinc in the solid state has been studied at temperatures from 220 to 360°C. Iron-zinc-coupled specimens prepared with the electrodeposition of zinc on the polished iron surface were heated in argon atmosphere at nine different temperature levels between 220 and 360°C.
Depending on the temperature range, three kinds of the growth pattern of the alloy layers were observed as follows. Within a range of 320 to 360°C, both ζ and δ 1 phases grew up with the equilibrium boundary concentrations. From 280 to 310°C, a quasi-stable phase pseudo- ζ , having the concentration from stable phase ζ to δ 1, was produced after some latent time and grew up as a single phase. Then this phase was separated into the stable ζ and δ 1. Under the heating condition between 220 and 260°C, the pseudo- ζ phase was only observed after some latent time.
Except the ζ phase separated from the pseudo- ζ , the growth rates of the product phases of the reaction could be described by the parabolic rate law.
Based on the Al2O3 marker test, it was found that the reaction was controlled by the zinc diffusion in the product layers.
An analytical model of the reaction rate process was developed. All kinds of the growth patterns of the alloy layers observed could be explained by the model developed here and the diffusion coefficients along with other rate constants were determined.
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