ENCAPSUTION OF EXPLOSIVE PARTICLES lac0 b Sando v a t DEVEZOPMENT D I V I S I O N OCTOBER - DEZEMBER 1971 Normal Process Development BY PARVLENE
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4 ~ C A P S U ~ A T I OOF N EXPLOSIVE PARTICLES BY PARYL~NE Jacob Sandowde DEVELOPMENT DIVISION The o b j e c t i v e of t h i s i n v e s t i g a t i o n i s t o e v a l u a t e t h e f e a s i b i l i t y and merit of encapsulating HE p a r t i c l e s and o t h e r materials and components used i n explosive systems. October - December 1 9 7 1 Endeavor No. 213 Acct. NO, 22-2-44-04-213 Section P
C ENCAPSULATION OF EXPLOSIVE PARTICLES BY PARYLENE DISCUSSION Parylene is t h e g e n e r i c name f o r m e m b e r s, e.g. parylene.n,c,d, of a t h e r m o p l a s t i c polymer series developed by Union Carbide ( " R e t a " i s a t r a d e name f o r t h e m a t e r i a l s ~, A l l o f t h e members are l a i d down by a vacuum, vapor deposition process - The properties and uses f o r each m e m b e r of the series d i f f e r from each o t h e r, b u t c o l l e c t i v e l y the Parylenes have a wide range of a p p l i c a t i o n s. The Parylenes are deposited on any substrate maintained i n a deposition chamber, providing the following conditions are m e t : P o The s u b s t r a t e must be able t o withstand vacuum. T h e s u b s t r a t e should not react chemically with t h e polymer. 2. There a r e probably o t h e r c o n d i t i o n s, e.g. having t o do with p a r t i c l e s i z e d i s t r i b u t i o n, The a c t u a l coating process i s promoted a t ambient eemperature. Union Carbide l i s t s many uses for t h e Parylenes. The following a p p l i c a t i o n s a r e l i s t e d i n Union Carbide { b u l l e t i n ), Chemical and P l a s t i c s PhysTcal Prope r t i e s, 1970 E d i t i o n, p. 56: P a r y i e n e is h i g h l y recommended for u s e a s a t r u e c o n f o r m 2 dielectric; c o a t i n g b e c a u s e o f i t s (1) a b i l i t y t o be d e p o s i t e d a s a n u l t r a t h i n, cont i n u o u s, u n i f o r m a d h e r e n t c o a t i n g and 42% i t s o u t s t a n d i n g e l e c t r i c a l and barrier properties. Such c o a t i n g s a s t h i n a s 0,001 m i l or a s thick a s 2 mi1s c a n be d e p o s i t e d on discrete electronic components : resistors, therdstors I s e m i c o n d u c t o r s, i n t e g r a t e d c i r c u i t s, and e 2 e c t r o l u m i n e s c e n t d i s p l a y s O t h e r suggested applications: ParyPene c o a t i n g t o p r o t e c t memory d i s k s, f e r r i t e cores, stator cores and f a s t - r e s p o n d i n g p r o b e s s u c h a s thermistors and t h e r m o c o u p l e s o M i l i t a r y standards : P a r y l e n e m e e t s a l l o f the m i l i t a r y s t a n d a r d s r e q u i r e d f o r conformal coatings f o r circuit boards i n thicknesses o f 0.5 t o 2 m i l s. P a r y l e n e p o l y m e r s are p r o v e n p a s s i v a t i n g a g e n t s f o r semi-conductor devices, and t h e y o f f e r p h o t o r e s i s t c h a r a c t e r i s t i c s when used a s a thin f i l m. Other a p p l i c a t i o n s include: Parylene c o a t i n g t o encapsulate highfy r e a c t i v e p a r t i c u l a t e p r o t e c t i o n f r o m hostile e n v i r o n m e n t s. P-1
Pinhole-free P a r y l e n e pellicles (membranes) can be d e p o s i t e d i n thicknesses f r o m 0.1 t o 2 microns for u s e i n o p t i c a l and r a d i a t i o n a p p l i c a t i o n s and a s a thio f i l m d i e l e c t r i c s u p p o r t. G a s p e r m e a b i l i t y and moisture vapor transmission of Parylene C are v e r y low. These p r o p e r t i e s make Parylene p o t e n t i a l l y very u s e f u l with o r near explosives or components. One of t h e forms, P a r y l m e C-the monomer of dichloro-di-p-xylyl e n e - i s p o t e n t i a l l y a t t r a c t i v e. Its d e n s i t y i s 1.29 g/cc. I n t h i s study t h e i n i t i a l emphasis w i l l be on t h e f e a s i b i l i t y of c o a t i n g HE p a r t i c l e s, Substrates of diminishing p a r t i c l e s i z e w i l l be encapsulated t o e s t a b l i s h t h e p a r t i c l e - s i z e l i m i t a t i o n of t h e process. Any s u b s t r a t e, meeting t h e requirements l i s t e d e a r l i e r, may be encapsulated provided it can be accommodated i n t h e deposition chamber. The equipment can be modified o r scaled-up t o m e e t t h e requirements and c o n f i g u r a t i o n of t h e items t o be embodied. There i s i n t e r e s t i n t h e encapsulation c a p a b i l i t i e s i n s e v e r a l a r e a s. Along w i t h HE particles and shaped charges, encapsulation o r c o a t i n g o f bridgewires, c o a x i a l p i n s, i o n i z a t i o n pins and o t h e r components have been requested. The 2-inch R e t a V a p o r Coating Unit and t h e l a r g e scaled-up Vacuum Deposition U n i t have been d e l i v e r e d and a r e housed i n Building 11-38, Bay 3, where t h e y w i l l be assembled and operated, The 2-inch R e t a V a p o r Coating Unit w a s s t r i p p e d when procured (it had been used by USAF and Union Carbide) ; hqwever, a l l e s s e n t i a l components t o make t h e u n i t operational. a r e on hand. FUTURE WORK; COMMENTS; CONCLUSIONS The i n i t i a t i o n of t h e study on t h e f e a s i b i l i t y of encapsulation of HE p a r t i cles a w a i t s t h e assembly of t h e 2-inch R e t a Vapor Coating Unit. The large Scaled-Up Vacuum Deposition equipment w i l l be p u t i n t o o p e r a t i o n a t a l a t e r date. A s h o r t o r i e n t a t i o n period w i l l be required t o f a m i l i a r i z e t h e personnel with t h e equipment and t h e techniques t o be employed. To preclude any unsafe i n c i d e n t, during t h e f a m i l i a r i z a t i o n p e r i o d, t h e fallow- ing precautions have been e s t a b l i s h e d : 1. Personnel will e n c a p s u l a t e o n l y inert s u b s t r a t e s d u r i n g the orientation period. 2. G l a s s b e a d s (3mm d i a l w i l l be c o a t e d f i r s t. These will +e immersed i n h y d r o f l u o r i c a c i d t o check the f i l m e q q i c i e n c y. Since P a r y l e n e i s u n a f f e c t e d b y a c i d s, no e t c h i n g of the b e a d s s h o u l d r e s u l t. r-2
3. P r i l l e d ammonium n i t r a t e w i l l be coated. The a a t e d p a r t i c l e s w i l l be submerged i n water, and the ph of t h e water recorded f o r a period of time. 4. A s personnel g a i n e x p e r i e n c e and p m f i c i e n c y t h e endeavor w i l l p r o - gress t o t h e encapsulation of e x p l o s i v e particles. P-3