ELECTRON MICROSCOPY 



Fig. 2. Modified Al pressing. Fractured, un- 

 poled BaTiOs . 7,000X. (Los Alamos Scientific 

 Laboratory) GMX-1 GT-SITE 



Examples: Fig. 1: A Composite Molding 

 Fig. 2 : Fractured Sm'face of 

 mipoled BaTiOs , 

 14,000 X 



J. H. Bender and E. H. K.\lmus 



Preparation of Aerosols 



Fall-out particles from dust clouds, com- 

 monly called aerosols, may be prepared for 

 observation with the electron microscope. 

 Specimens are collected by means of various 

 types of precipitators on membrane filters 

 made from cellulose esters. During the proc- 

 ess of dissolving this material in acetone, 

 particles adhering to the filter surface are 

 transferred to "Formvar"-coated specimen 

 screens. Losses are negligible, residual filter 

 background is eliminated and particles are 

 clearly visualized for measuring. 



Procedure : 



1. Prepare "Formvar-" or carbon-coated 

 specimen screens. 



2. Cut membrane filters into small squares 

 to fit the screens. 



3. Place three supporting bridges made 

 from coarse and fine brass mesh into a large 

 Petri dish. 



4. Load filter-screen combinations into 

 marked compartments on bridge surfaces. 



5. Fill Petri dish with acetone up to bridge 

 level. Principle of "liquid film" action for 

 dissolution of the filter material. 



6. Make three solvent changes, washing 30 

 minutes each. 



7. Cover dish during and in between steps. 



8. After discarding last solvent change, 

 transfer screens onto filter paper for drying 

 over night under vacuum. 



Examples: Figure 3. Bridge; Figure 4. UO2 

 aerosol after transfer. 



E. H. IVALMUS 



Dispersion of Aerosols 



Ultrasonic dispersion techniciues for car- 

 bon black and graphite particles, with the 

 equipment available (100 KC to 1000 KC 

 output), left much to be desired in effec- 

 tively breaking up large agglomerates. 



A simple method of producing artificially 

 airborne particles was devised, for better 

 over-all particle distribution; it involved 

 using a large cardboard box and spraying 

 the inside with "Krylon" to prevent con- 

 tamination by cellulose fibers, sealing the 



FILTER PAPER 



SPECIMEN 

 SCREEN 



" PETRI DISH 

 DISSECTING NEEDLE 



WATCHMAKERS FORCEPS 



Fig. 3. Bridge. 



272 



