An Interesting Application of Electron Diffraction* 



By L. H. GERMER and K. H. STORKS 



OILICOSIS develops rather quickl}^ in rabbits exposed to air con- 

 ^ taining moderate concentrations of quartz particles finer than about 

 5 X 10~* cm, but is completely prevented if aluminum powder is also 

 present in the air to the extent of about one per cent by weight of the 

 quartz powder. This protective action of aluminum powder was dis- 

 covered at the Mclntyre-Porcupine Mines, and has been studied ex- 

 perimentally by Denny, Robson and Irwin.' 



It has been established that aluminum forms, in the lungs, a pro- 

 tective film upon the surface of silica particles which prevents them 

 from dissolving, and thus prevents toxic effects. From the relative 

 amounts of aluminum and silica, and diameters of silica particles, one 

 can deduce that this protective film need never be so thick, on the 

 average, as 2 X 10~® cm, and is, in general, many times thinner than 

 this. 



The action of the aluminum is sufficiently striking and important 

 to justify a fuller understanding of the nature of the film which it 

 forms upon quartz particles and Dr. Frary, Director of the Aluminum 

 Research Laboratories, suggested to us that the answer might be forth- 

 coming through a study of electron diffraction patterns. 



In our experiments, electron diffraction patterns were obtained from 

 thin films of silica, about 2 X 10~^ cm thick, which had been previously 

 treated with water containing metallic aluminum powder. A beam 

 of high speed electrons was sent through such a treated film and the 

 resulting diffraction pattern recorded upon a photographic plate. 

 From studies of such patterns, and comparisons with X-ray and elec- 

 tron patterns of known substances, materials composing layers upon 

 silica surfaces were identified. 



Silica films for these studies were prepared in the following manner. 

 A glass microscope slide was first covered by gold vaporized in high 

 vacuum from a V-shaped tungsten ribbon; then immediately in the 

 same apparatus silica was vaporized upon the gold from a second tung- 



* Digest of a paper entitled "Identification of Aluminum Hydrate Films of Im- 

 portance in Silicosis Prevention," published in Industrial and Engineering Chemistry, 

 Anal. Edition, 11, 583 (1939). 



^J. J. Denny, W. D. Robson and D. A. Irwin, Canadian Medical Association 

 Journal, 37, 1-11 {\92>'l) ; 40 , 213-228 (1939). 



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