KLKtlTUON >HCKOSCOPY 



Specimen 

 Holder 



Specimen 



Fig. 1. Specimen mounted in plastic block and 

 placed in wedge-shaped specimen holder. 



polished cross section of the coating and 

 tungsten wire. Upon completion of the 

 polishing, the samples were etched in a 10 % 

 nitric + 3 % hydrofluoric acid solution for 

 approximately five minutes. This etch was 

 sufficient to reveal the crystallographic de- 

 tail in the interfacial region. This surface 

 was then replicated by the process pre- 

 viously described. 



The plastic block containing the sample 

 was then mounted in a "Lucite" wedge, as 

 showTi in Fig. 1. The wedge containing the 

 sample and block was placed in the poly- 

 ethylene Buchner funnel, as shown m Fig. 2. 

 With the hosecock closed, etchant was added 

 until the surface of the liquid had crossed the 

 lower edge of the mounting block and was 

 nearly in contact with the lower edge of the 

 shadowed specimen. Distilled water was then 

 added from the buret until the edge of the 

 etchant surface was properly positioned at 

 the bottom edge of the sample. Prior to this 

 step the edges of the sample had been scored 

 so as to break the carbon film and permit the 

 etchant to attack the sample material. 



The progress of the etchant was followed 

 by means of a 15 X microscope which could 

 be swung over the sample on a pivot arm. 

 As the etching progressed, water was added 

 from the buret to raise the level of the liquid 

 and hence help pull the replica from the 

 sample and float it upon the etchant surface. 



When the separation was completed the 

 replica floated freely upon the surface of the 

 etchant. The etchant level was then raised 

 by means of the buret until it was completely 

 free of the mounting block. It was then neces- 

 sary to dilute the etchant to approximately 

 twenty times its volume to raise the pH to 

 a level where the replicas could be picked 

 up on the metal grids. The hosecock shown 

 in Fig. 2 was opened and the stopcock of the 

 buret opened. The flow into and out of the 

 funnel was adjusted so that the liquid 

 level remained essentially constant. The 

 distilled water from the buret was introduced 

 below the surface of the etchant via a poly- 

 ethylene tube. This step greatly reduced the 

 turbulence of the surface and hence reduced 



Buret 



Specimen 

 Specimen Holder 



Buchner Funnel 

 [PolyethylcneJ 



Hosecock 



Fig. 2. Apparatus for separating replica from 

 specimen in solutions of low pH. 



240 



