Moessbauer studies of Fe-based direct coal liquefaction catalysts
- Univ. of Kentucky, Lexington, KY (United States)
{sup 57}Fe Moessbauer spectroscopy has been used to investigate a variety of ultrafine iron-based direct coal liquefaction catalysts having either Fe{sub 2}O{sub 3} or FeOOH structure. The Moessbauer spectra of these catalysts showed pronounced superparamagnetic effects. The superparamagnetic relaxation spectra were analyzed as a function of temperature using a novel fitting model to determine the particle size distribution for these catalysts. The resulting size distributions are in the nanometer range and agree reasonably well with size information obtained by Scanning Transmission Electron Microscopy (STEM), SQUID magnetometry, and X-ray Diffraction (XRD). Investigation of a 30{angstrom} iron oxyhydroxide catalyst by Moessbauer spectroscopy revealed that the recoilless fraction decreased dramatically with increasing temperature, becoming effectively zero at 50K. This effect is explained on the basis of a combined effect of the recoil of the particle and the particle motion due to thermal agitation. The mean square amplitude of particle motion is derived as a function of temperature.
- OSTI ID:
- 143134
- Report Number(s):
- CONF-930304--
- Country of Publication:
- United States
- Language:
- English
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