The behavior of silver particles supported on graphite in various gaseous environments

Controlled atmosphere electron microscopy has been used to continuously follow the behaviour of silver particles supported on graphite when heated in the presence of various gases including helium, hydrogen and water vapor. In dry systems, particles were observed to exhibit mobility over the range 3200 to 5150C. When water vapor was introduced, either continuously or as a pulse injection particle, motion was suppressed. At higher temperatures all systems showed similar behaviour irrespective of the nature of the gas. Silver particles tended to collect into large globular islands at 6150C, and in this form showed characteristics of the bulk metal rather than those associated with small discrete particles. When the temperature was raised to 9600C discrete particles re-formed and once again exhibited mobility. This sequence of events and possible reasons for the inhibition of particle movements by water vapor is discussed. (author)