Chemical Decomposition of Crystals of Explosive Materials 



343 



microscope. Type I diamonds show a conchoidal 

 type of cleavage surface with local changes in height 

 of several microns: type II diamonds show much 

 smoother cleavage surfaces which do, however, have 

 a considerable amount of tine structure ranging up 

 to perhaps 1500 A in depth, with a few larger steps 

 of a micron or more crossing the surface. Regions 

 similar in appearance to type II cleavage surfaces 

 have been found on a type I diamond. It is believed 

 that this is due to real inhomogeneity in the diamond. 

 The results are in agreement with those obtained 

 by other workers and, in particular, with those 

 obtained by Wilks (II) in a recent interferometric 

 study of diamond surfaces.' 



' The above results are in agreement with some observa- 

 tions made by Custers (unpublished) on the inhomogeneity 

 in the optical properties of diamonds. He observed that, 

 under ultra violet irradiation, some diamonds fluoresced 

 strongis in parts and were non-fiuorescent in others. These 

 diamonds showed local ditVerences in transparency below 

 3000 A. One diamond in particular showed inhomogeneity 

 in the visible part of the spectrum, being partly blue and partly 

 white with a clear boundary between the two regions. 



The author thanks Dr. F. P. Bowden, C.B.E., F.R.S., 



for his advice and encouragement, and Messrs. Industrial 

 Distributors (1946) Ltd. for a research grant and for the 

 loan of the diamonds. 



RtFERENCES 



9. 

 10. 



AiitAKN, A. J., Phys. Rev. 96, 828 (1954). 

 Champion, F. C, Proc. Roy. Sue. A 220, 485 (1953). 



— ibid. 234, 541 (1956). 



CottRiNE ^-Pkai r, J. S., Mfntfr, J. W., and Sial, M., 



Proc. 3rd Intern. Conf. Elect. Microsc. London 



1954. 

 CusTFRS, J. F. H., Re.secirch 4, 131 (1951). 

 Ramachandran, G. N., Proc. Iiulian Acad. Sci. A 



24, 65 (1946). 

 Robertson, R., Fox, J. J., and Marmn, A. L., P/iil. 



Trans. A 12,1, 463 (1934). 

 SuTHFRLAND, G. B. B. M., BiA( KvvrLi, D. E., and 



Simeral, W. G., Nature, Loud. 174, 901 (1954). 

 ToLANSKY, S., Microstructures of Diamond Surfaces. 



N.A.G. Press. London, 1955. 

 Wilks, E. M., Dissertation, University of London. 



1952. 



— Private communication (1956). 



The Direct Observation in the Scanning Microscope of 



Chemical Reactions 



J. H. L. McAusLAN and K. C. A. Smith 



P.C.S. Laboratory, Depart iiient of Physical Cheniistry, and Engineering; Laboratories. University of Cambridge 



This paper contains an account of the application 

 of the scanning electron microscope (2) to an explo- 

 ratory study of the slow chemical decomposition of 

 single crystals of explosive materials. 



The materials so far investigated in this way have 

 been the metallic azides and lead styphnate. Although 

 normally considered explosive these materials will 

 decompose slowly if the temperature is kept below 

 about 200 C. Their explosive properties have been 

 extensively studied and it is known that reaction 

 starts from small centres of I0~-'-10"^ cm, termed 

 hot-spots, and grows to burning and detonation by 

 a self-heating mechanism. 



It was considered that an electron-microscopical 

 study of the slow thermal decomposition would give 

 information on reaction mechanisms possible in the 

 hot-spot size range. Study in the light microscope 

 had already shown large scale break-up effects but 

 until Bowden and Singh (1), with a standard replica 

 method, and Sawkill (3). with direct viewing of very 

 thin crystals, there was little work done in this field. 



The problem of specimen heating in an electron 

 beam is a well known one to electron microscopists 

 and Sawkill in fact used this effect to decompose 

 crystals during direct observation. This was not 

 entirely satisfactory as he suspected from his results 



that the primary action of bombardment by high- 

 energy electrons was responsible for some of the 

 change. Attempts have been made to observe explo- 

 sive crystals in the conventional reflexion instrument 

 without success, the high intensity of bombardment 

 resulting in premature and uncontrolled decomposi- 

 tion. 



Because of the low intensity obtaining in the 

 scanning instrument the above difficulties may be 

 largely overcome and it has been found possible to 

 observe the genuine effects of thermal treatment 



SILVER 

 PLATE. 



NICHROME 

 ELEMENT. 



MICA 



5INDANY0, 



Fig. I. Hotplate for scanning electron microscope. 



