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A N D

THIN FILM PENETRATION BY HYPERVELOCITY MICROPARTICLES

Electr~nics Research Center

https://ntrs.nasa.gov/search.jsp?R=19710010457 2019-08-08T08:45:24+00:00Z

-- eport No.

XGA m X-2065 -- ----- 4. T ~ t l e end Subtbtie

Thin F i l m P e n e t r a t i o n by ~ypervelscit Microparticles

9. Performing Organization Name and Address

Electronics Research Center

Technical Memorandum National Aeronautics and Space Administration

I S . Supplementary Notes

16. Abstract

Carbonyl iron microparticles were accelerated electro- statically to velocities up to 25 km/s. Particles with selected velocities were impacted on thin parylene films mounted on 100-mesh electron microscope grids. The ratio of average hole-diameter to average particle-diameter increases from 1 to 7 as the velocity increases from 2 to 20 km/s. Particles whose diameters are greater than the film thickness punch a hole through the film whereas particles whose diameters are less than the film thicknes! break up during the impact interaction and thus enlarge the hole diameter beyond the particle diameter.

Unclassified

th or sale b~ the National Technical Information Service, Springfield, Virginia 22161

-- . ~4~~ - . l!ith-kkiony k t rre~qi,s ant1 Robert A. " Wa.7.ter E].ec*i-.:conics Research C e n t e r

Carbonyl iron microparticles were accelerated electro- statically to velocities up to 25 km/s. Particles with selected velocities were impacted on thin parylene films mounted on 160- mesh electron microscope grids. The ratio of average hole- diameter to average particle-diameter increases from I to 7 as the velocity increases from 2 to 20 km/s. Particles whose dia- meters are greater than the film thickness punch a hole through the film whereas particles whose diameters are less than the film thickness break up during the impact interaction and thus enlarge $he hole diameter beyond the particle diameter.

INTRODUCTION

A number of micrometeoroid detectors depend upon the inter- action sf the impacting micrometeoroid with a thin film, For example, Coddard Space Flight Center has developed a thin film telescope* detector which has been successfully flown on a num- ber sf probes and satellites (ref. 1). This unit determines particle velocity by time-of-flight measurements between two thin-film arrays (Figure 1). The ionization produced by a particle penetrating the thin films is measured and also serves to initiate the "start" and "stop" pulses for the time-of-flight determination, The amount af ionization is indicative of the particle energy and composikion but the quantitative relationship is, as yet, not fully known.

To gain a better quantitative understanding of the inter- action we have impacted thin films (0.2 pm thick) of parylene with carbonyl iron spherules of known masses and velocities.

*The telescope detector consists essentially of a velocity measuring component and a momentum (or energy) sensitive compo- nent. These are usually mounted in a tube such that the direc- tion of the impacting micrometeoroid can be determined and that the micrometeersid penetrates the velocity-measuring component prior to impact on the momentum (or energy) sensor. Time- coincident ou tpu t pulses are generally required from both sensors for an event to be considered a true impact as opposed to accidental or noise output pulses. The term 9tePscope detector"

used sn analogy to two-component nuclear par t i c l e detectors - - - - 3 Y - + = i P I @ S * which ~ e r f ~ r m simiPar measuring functions f o r n u c a e a ~ pUL.-----

GLASS PLATE

CC mu

LEAD ZIRCONATE Figure 1.- Micrometeroid detector developed by Goddard Space Flight Center

- 7 v

Although these initial data do not yield definitive results, they are interesting nonetheless in that they demonstrate some quan- titative relationships and indicate the directions in which future work should proceed.

EXPERIMENT

Carbonyl iron spherules (Figure 2 ) , with velocities up to 25 km/s, were impacted on thin plastic films. Acceleration to hypervelocities was accomplished electrostatically, using a 150-kv ion accelerator converted to microparticle acceleration (ref. 2). The performance of the accelerator is shown in Figure 3 where particle velocity is plotted as a function of particle size. Particle masses and velocities were selected and measured using the system described in reference 2.

Discs of parylene (TM - Union Carbide), 3 mm diameter, were punched from a 3-inch diameter, 0.2 pm thick sheet of material. The discs were glued to a 100-mesh electron microscope grid, which was placed in a standard Hitachi electron microscope grid holder. The film was then examined with a transmission electron microscope for holes, cracks, and excessive glue. Grids with acceptable films were removed from the electron microscope still attached to the holder and mounted in the accelerator target chamber. This procedure assured that the parylene films were never touched after being inspected in the electron microscope. Double thin films of parylene were made by gluing discs to both sides of the electron microscope grid.

The films were impacted by microparticles in a selected velocity range. During bodardment, the velocities and masses of the impacting particles were measured. After bo&ardment, the film and holder were removed from the target cbamlaer and re- examined, us ing the transmissian electren microscope, The num- ber of holes in the film and their s i z e s were recorded,

Figu re 3 . - M i c r o p a r t i c l e v e l o c i t y a s a f u n c t i o n o f p a r t i c l e s i z e

F igu re 2 . - E l e c t r o n photo- micrograph of ca rbonyl i r o n powder

IRON SPHERULES

150 k V ACCELERATING POTENTIAL

PARTICLE RADIUS ( f iml

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Figure 5 , - Bole s i z e - p a r t i c l e s i z e r a t i o a s a func t ion of p a r t i c l e s i z e

4 - * 6 - w _J

0 - -

- W (3 - - a IIC

MICROCRATER S l Z E - TO PARTICLE S l Z E DATA FROM REF 3

w - - t-

-

NOTES I IMPACTS ON PARYLENE - FILM 2 0 0 0 8 THICK

2 NUMBERS AT DATA POINTS - ARE THE NUMBER OF PARTICLES USED TO OBTAIN AVERAGE FOR THAT POINT -

P A R T I C L E VELOCITY ( K M I S )

LT W

> a I -

Another p r e s e n t a t i o n of t h e puncture d a t a i s given i n F igu re 6 where t h e r a t i o of average hole-diameter t o average p a r t i c l e - d i a m e t e r i s p l o t t e d a g a i n s t t h e average p a r t i c l e - d iameter . The number of p a r t i c l e s and t h e minimum, median, and maximum v e l o c i t i e s of t h e s e p a r t i c l e s a r e shown f o r each d a t a p o i n t . Bars a r e n o t used t o avoid c l u t t e r i n g t h e p r e s e n t a t i o n .

-& - 27 - -

A t lower v e l o c i t i e s t h e p a r t i c l e d iameters exceed t h e f i l m t h i c k n e s s , whereas a t t h e h igh v e l o c i t i e s t h e p a r t i c l e d iameters are l e s s t h a n t h e f i l m th i ckness . F igure 9 shows punc tures of a double f i l m , mounted a t a s l i g h t ang le t o t h e beam, made by one l a r g e ( 0 . 5 ym d iameter ) and s e v e r a l s m a l l ( 0 . 2 5 ym and $0.1 urn d iameter ) hyperve loc i ty p a r t i c l e s . The l a r g e p r o j e c t i l e (upper r ight-hand co rne r ) passed c l e a n l y through bo th f i l m s g i v i n g up l i t t l e k i n e t i c energy on doing s o ; an i n d i c a t i o n of t h i s i s t h e s i m i l a r i t y i n s i z e of t h e two ho le s . The sma l l e r p a r t i c l e s broke up i n t h e f i r s t f i l m expending a l l t h e i r k i n e t i c energy doing s o . Debris of t h i s break up can be seen on t h e second f i l m . This mechanism e x p l a i n s q u a l i t a t i v e l y why t h e ho le -d i ame te r /pa r t i c l e - diameter ratio increases so r a p i d l y when t h e p a r t i c l e s i z e approaches the f i l m thickness. T h i s disintegration has also been reported by Auer , et ale (ref. 3 ) using 0.8 urn Fe projectiles on 0,8 ym A$ f o i l ,

0 0 2 / / l l / l l l l l l l 4 6 8 10 12 14 16 18 2 0 2 2 24

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0 0.1 0 . 2 0.3 0.4 0.5 0.6 0.7

AVERAGE PARTICLE D IAMETER ( p M 1

Figure 6 . - Hole s i z e - p a r t i c l e s i z e r a t i o a s a func t ion of p a r t i c l e s i z e

F igure 7 . - Double t h i n f i l m showing p e n e t r a t i o n by l a r g e and smal l p a r t i c l e s

! 2 3 y M E T E R S

REFERENCES

1. Nilsson, C . S . ; and Wilson, D: The Micrometeoroid Experiment on the 060-2 Satellite. NASA C R - 1 0 0 6 8 3 , 1 9 6 9 ,

2. Lewis, A.R.; and Walter, R.A.: Electrostatic Acceleration System for Hypervelocity Microparticles with Selected Kinematic Properties. NASA TN D-5780, 1970.

3. Auer, S.; Grun, E; Rauer, P.; Rudolph, V.; and Sitte, K.: Studies in Simulated Micrometeoroid Impact. Space Research VIII. North-Holland Publishing Co., Amsterdam, 1968, pp. 606-616.

'The uero?uivticsk avPs spuce &tipities of the U ~ i t e d Ststes SW he codacted so ar to con~rib#!e , . . to ibe expaprsim of binlw~ kneoaul- edge of phenomena dn the utvrosphtre a~ed spucg. Tbe ~ n z ~ ~ s t r u t ~ o ? 8 shull prop& for tbe ~uideJt prdctiubie and uppro@iute d i s s m i w t i m of infor~)zutioa conceraJng its uctitlitjes apzB the rejnlts thereof!'

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