Nanocrystalline CaF{sub 2} particles obtained by high-energy ball milling
- Institut fuer Chemie, Humboldt-Universitaet zu Berlin, Brook-Taylor-Street 2, D-12489 Berlin (Germany)
- Bundesanstalt fuer Materialforschung und -pruefung, 12200 Berlin (Germany)
Structural changes in mechanically treated CaF{sub 2} powders have been studied by X-ray diffraction, transmission electron microscopy, thermal analysis, {sup 19}F and {sup 1}H MAS Nuclear Magnetic Resonance and Electron Paramagnetic Resonance methods. Applying the same methods, the results could be compared with those of mechanochemically synthesized CaF{sub 2} samples, prepared for the first time in this study by high-energy ball milling. The applied methods indicate that the mechanically treated samples become, under the applied conditions, nanocrystalline. Unexpectedly, the mechanochemically synthesized samples show the same effects, i.e., nanocrystalline samples were formed. In contrast to many oxide compounds, a weak amorphization takes place only after a strong mechanical impact, and essentially in grain boundaries of spherical particles. Observed effects after the application of mechanical impact like broadening of XRD reflections, broadening of {sup 19}F resonances, or the decreasing ability for H {sup {center_dot}} trapping at ambient temperature, are mainly due to decreasing particle sizes as well as very small structural changes in the bulk of the particles. Surprisingly, the spin relaxation of both nuclear spins ({sup 19}F) and electron spins (H {sup {center_dot}}) appears to be the most sensitive tool for the investigation of mechanically and chemically induced changes indicating the increasing surface to bulk ratio with increasing mechanical impact.
- OSTI ID:
- 20784964
- Journal Information:
- Journal of Solid State Chemistry, Vol. 179, Issue 4; Other Information: DOI: 10.1016/j.jssc.2005.12.035; PII: S0022-4596(05)00644-4; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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