Abstract
In situ transmission electron microscopy was used to examine the sintering of Pt and Ag on amorphous C, SiO 2, and A1 2O 3 in vacuum. Liquid-like motions were observed for Pt particles on these supports at temperatures of 600–750°C. The Pt particles grew through abrupt surface movement and subsequent coalescence of adjacent pairs. On the other hand, Ag particles on all the supports were stable below 450°C, while at higher temperatures they gradually disappeared from C and A1 2O 3 surfaces due to evaporation but they sintered on SiO 2. The sintering mechanism of Ag/SiO 2 was noted to depend on temperature; atomic migration predominates over Brownian particle migration at higher temperature. This temperature dependence is in accord with that in Ni/C, Ni/SiO 2, and Ni/A1 2O 3 reported previously. The order of the strength of metal—support interaction was estimated to be Pt/A1 2O 3 > Pt/SiO 2 > Pt/C from the temperature dependence of mean particle diameter and the particle morphology, and Ag/SiO 2 > Ag/Al 2O 3 > Ag/C from the relative difficulty of evaporation and the particle shape. The particle migration mechanism is considered to involve liquid-like intermittent movement rather than Brownian type movement when the metal—support interaction is significantly weak.
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