EXPLOSIVE PARTICLES PARVLENE ENCAPSUTION. lac0 b Sando v a t. Normal Process Development OCTOBER DEVEZOPMENT D I V I S I O N DEZEMBER 1971

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1 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

2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its usc would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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4 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 Endeavor No. 213 Acct. NO, Section P

5 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

6 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

7 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