Ostwald ripening of Pd particles on the (10(1)over-bar(2)over-bar) surfaceof sapphire

Morphological changes of small Pd particles on the (10 (1) over bar (2) ove r bar) surface of alpha-Al2O3 single crystal were investigated by Auger ele ctron spectroscopy in the temperature range 833-923 K. It was shown that pr actically there was no decrease of the effective thickness during heat trea tments under 6 x 10(-9) mbar. Supposing that the observed change in the Aug er intensities is due to the surface Ostwald ripening. it was established t hat the process was controlled by surface diffusion. It a:as shown that in this case, taking into account the dissolution of small particles, the norm alised Auger intensity is inversely proportional to the normalised average radius, The surface mass transport diffusion coefficients were determined a nd they were in the range 10(-15)-10(-17) m(2) s(-1) in the investigated te mperature interval. Their temperature dependence can be given as D-s' = (6( -5.93)(+486)) x 10(-5) exp{[-(203 +/- 30) kJ mol(-1)]/RT} m(2) s(-1). (C) 1 999 Published by Elsevier Science B.V. All rights reserved.