Mossbauer studies on self-diffusion in pure iron

Abstract

The line broadening of the Mossbauer resonance due to diffusion in pure iron was studied for the first time from 1200 degrees C to near the melting point (1536 degrees C). The investigation became possible through the development of a furnace and an encapsulation technique preventing evaporation of the sample. The diffusion study includes the upper region of the FCC gamma phase (1200 to 1390 degrees C) and nearly the full region of the BCC delta phase. At the gamma - delta phase transition (1390 degrees C) drastic line broadening appears. For a pure element-as in this study-the 'microscopic' diffusion coefficient can be determined from the line broadening without making any assumptions as to various vacancy-impurity jump frequencies as had been necessary in former Mossbauer studies on alloy systems. The diffusion coefficient in the gamma phase is D=1.5*10-4 m2 s-1*exp ((-3.1+or-0.2) eV/kBT), within the error bars, in agreement with results from ('macroscopic') tracer diffusion. This proves that the often claimed discrepancy between diffusion data determined from Mossbauer spectroscopy and tracer diffusion does not exist in well defined systems. In the delta phase the Mossbauer data scatter is large, therefore no analysis of the preceding type was attempted.