ELECTHON MICKOSCOl'Y 



Fig. 2. Particles from an aerosol containing Ru'''^02 . 

 1. Particles transferred from membrane filter to a Formvar coated screen. 6,375X. 

 The aggregate particles are slightly fused because of exposure to the electron beam in 

 the electron microscope. 2. Three-dimensional chain aggregate particle. 14,450X. This 

 preparation was shadowed with palladium. Negative print. Note the spheroid nature of 

 the particles making up the aggregate. 3. and 4. The same field before and after pro- 

 longed exposure to the electron beam. 6,375X. The arrow in figure 3 points to a large ag- 

 gregate particle. The arrow in figure 4 points to the same particle after it was exposed to 

 the electron beam for 60 seconds. Such behavior is common for ruthenium dioxide par- 

 ticles. The aggregate particle is too large to dissipate the heat evolved liy the impact of 

 the electron beam on the specimen, and the melting point is low enough to cause fusion 

 of the small particles into the resultant sphere. 



74 



