SPECIMEN PREPARATION 



The technique entails the use of a stand- 

 ard laboratory metallurgical specimen press 

 to produce the necessary pressure to form 

 aluminum foil replicas. The pressure is trans- 

 mitted through a Uquid medium of molten 

 plastic. 



The loading of the mold is accomplished 

 by the following successive steps : 



1. Insert the bottom male die 



2. Place a "Lucite" disc on the die 



3. Several layers of cut-to-fit filter pa- 

 pers 



4. One lead (Pb) foil 



5. One thick aluminum (Al) foil 



6. One thin aluminum (Al) foil 



7. Specimen 



8. Filter papers 



9. "Lucite" disc 



10. Insert upper male die 



For multiple sample replication, the 

 above steps 2 through 8 may be repeated 

 up to full mold capacity. 



For two-sided replication of a specimen 

 the loading is repeated in reverse on the 

 opposite side of the specimen. 



Molding is accomplished by heating the 

 thermoplastic to its melting point, with no 

 pressure applied until this temperature is 

 reached. Pressure is then applied evenly and 

 continuously to maximum, and cooUng 

 commenced at once. The pressure is not re- 

 leased until the mold has cooled to room 

 temperature. 



The separating filter "circles" prevent 

 contact of the plastic with the specimen and 

 foils. There is, however, circumferential flow 

 along the die edges, hence the finished mold- 

 ing must be separated mechanically. 



The aluminum foils are then stripped care- 

 fully from the specimen to prevent the for- 

 mation of strain lines in the foil itself. 



Immediately after removal, the aluminum 

 foils are anodized. The foil side bearing the 

 replica and oxide film is then scribed in 

 squares and stripped as usual by chemical 

 means. 



The mold components were chosen for the 

 following reasons: 



1. Solid discs of thermoplastic instead of 

 molding powders are used in order to form 

 a stable support for the foils and specimens 

 and to alleviate the uneven melting condi- 

 tions inherent in loosely packed porous 

 powders. 



2. The lead (Pb) foil is added only as 

 mechanical backing for the multiple alumi- 

 num (Al) foils. 



This technique as described permits high- 

 speed, high-production rate of specimen 

 replication. 



Fractured surfaces which prevent strip- 

 ping of routinely applied primary plastic 

 coatings can also be successfully treated in 

 this way. 



Recent work has shown this method to be 

 effective in preparing "cool" replicas of plu- 

 tonium and its alloys by washing the Al foil 

 replica several times in 10 % IINO3 before 

 anodizing. 



Fig. 1. Modified Al pressing. Composite mold- 

 ing. (Los Alamos Scientific Laboratory) GMX-1 

 GT-SITE 



271 



