CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
2002 American Institute of Physics 0-7354-0068-7
EXPERIMENT TO CAPTURE GASEOUS PRODUCTS
FROM SHOCK-DECOMPOSED MATERIALS
W. H. Holt, W. Mock, Jr., F. Santiago, and R. M. Gamache
Naval Surface Warfare Center, Dahlgren Division, 17320 Dahlgren Rd., Dahlgren, VA 22448-5100
Abstract. Vacuum-tight steel containers have been designed and impact tested for the purpose of
capturing gaseous products from the shock decomposition of porous polymer materials. This work
extends earlier gas gun experiments in which initially-porous polytetrafluoroethylene (PTFE) powder
specimens were shock compressed inside closed non-vacuum-tight steel containers and soft recovered.
Although a powder decomposition residue was produced in the containers and analyzed in situ, there
was no attempt to recover any gaseous decomposition products for analysis. A series of gas gun impact
experiments has now been performed to develop a gas-tight specimen container that can survive
impact shock loading. The container is evacuated prior to the experiment. The impact of a gas-gunaccelerated metal disk produces a shock wave that passes through the container wall and into the
specimen material. If gaseous products are formed, they can be collected in a sample cylinder for
subsequent chemical analyses. Initial results are presented for PTFE powder specimens.
carbon. Gas recovery experiments have also been
performed on serpentine rock (4).
The purpose of the current experiments is to
extend our earlier work to the include capture of the
gaseous products.
INTRODUCTION
Improved understanding of the response of
materials to mechanical shock loading, and in
particular, the shock-induced decomposition of
materials, can lead to extensions of existing models
for more realistic simulations of material response
to a wide range of shock loading conditions.
In our earlier experiments, initially-porous (4447% porosity) polytetrafluoroethylene (PTFE)
powder specimens were shock compressed at initial
planar stresses of 1.5 and 0.72 GPa, respectively,
inside closed but unsealed steel containers, and soft
recovered (1,2). X-ray photoelectron spectroscopy
analysis of the solid residue indicated significant
unbound carbon and a variety of other chemical
species. No attempt was made to capture gaseous
products, although visual evidence of the expulsion
of solid products from the containers suggested the
presence of gaseous products. Morris, et al, (3) in
experiments at ~50 GPa, have reported evidence of
shock-induced dissociation of initially-solid PTFE,
leading to CF4 gas and a residue of amorphous
EXPERIMENTAL TECHNIQUE
Figure l(a) is a schematic of the experiment
before impact. Figure l(b) shows the experiment at
the time of impact. The Naval Surface Warfare
Center Dahlgren Division Research Gas Gun
Facility (5) was used for this work. The specimen
container is attached to a steel support block,
located 0.8 m from the muzzle of the 40.0 mm
smoothbore barrel. The impactor disk is carried on
the end of a sabot. A thin mica cover on the muzzle
permits evacuation of the barrel prior to firing the
gun. The sabot and impactor disk pass through the
mica cover and through a hole in the support block
to impact the specimen container. A steel cover
disk and momentum trap disks were used to reduce
damage to the container.
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The PTFE specimen material (6) was characterized
with respect to initial particle morphology via
optical and scanning electron microscopy, and was
in the form of nearly spherical white particles
having obvious surface substructures. The average
particle size was 534 microns (7). In all the
experiments, each specimen was pressed to have an
initial porosity in the 44-47% range.
VALVi
RESULTS
A series of experiments was performed with
different specimen container designs to assess
container survivability prior to attempting to capture
product gases. The first container was a pair of
11.5-mm-thick stainless steel vacuum flanges (8)
bolted together with a copper gasket seal and having
a porous PTFE specimen disk (approximately
37mm diameter and 2.3mm thick) sandwiched
between the flanges. A 4.6-mm-thick 6061-T6
aluminum disk impacted this container directly (no
cover disk was used). Figure 2 shows one-half of
the container before and after shock loading, with
visual evidence of shock-induced chemical reaction
(a)
VALVE
CLOSED
VAtVi
(a)
(b)
(b)
FIGURE 2. Specimen disk in one-half of container, (a) Before
impact, (b) After impact. The dark regions indicate shockinduced chemical changes. Impact speed was 986 m/s.
FIGURE 1. (a) Schematic of gas collection experiment before
impact. The impactor disk is accelerated on a sabot in a gas gun.
Impact of the disk produces a shock wave that passes through the
cover disk and container wall and into the specimen material.
The cover disk receives the primary damage of impact. The
system is evacuated prior to impact, and the sample cylinder is
maintained at liquid nitrogen temperature to minimize any
subsequent reactions of collected gaseous products. All the
tubing, fittings, and valves are made of 316 stainless steel, (b)
Schematic of gas collection experiment at time of impact. The
valve connected to the sample cylinder is closed after impact so
that the captured gas sample can be removed for analysis.
in the specimen (dark regions). Because of damage
to the bolts and to the copper gasket, this
configuration did not retain a gas-tight seal.
Figure 3 shows parts for an experiment with an
alternate specimen container design. To fabricate
the container, a 4.6-mm-diameter hole was drilled
radially into the center of a 76.1-mm-diameter,
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the flat end of the 31.9-mm-thick solid cylinder.
The tube is deformed inside the solid cylinder,
compressing the specimen material.
Figure 4 shows this container design mounted
near the gas gun muzzle for impact. The gas
collection system (Figure 1) was attached to this
configuration in an attempt to capture gaseous
products. The pressed porous specimen filled a
28.6-mm-thick solid cylinder of 4130 steel. A
stainless steel tube fitting was welded into the hole
to provide a gas connection. PTFE powder was
pressed into the hole. For this experiment a 3.1mm-thick, 35.6-mm-diameter OFHC copper disk
impacted the 9.53-mm-thick steel cover disk at 976
m/s. This container survived impact and appeared
to be free of cracks affecting the specimen cavity.
A residue of partially-reacted PTFE was found in
the cavity.
Another container design consisted of a 316
stainless steel tube (9.7 mm outside diameter, 7.5
mm inside diameter) that fits through a centered
diametric hole in a solid cylinder of 4130 steel.
A 9.5-mm-thick steel cover disk was placed against
FIGURE 4. Cylinder and tube container mounted on the support
system for connection to the gas collection system and impact.
All the tubing and fittings were made of 316 stainless steel.
25-mm-long region of the gas collection tube and
was centered with respect to the axis of the gas gun
barrel. Connection was made to both ends of the
straight tube to facilitate evacuation of the specimen
region. The container was evacuated by a
turbomolecular pumping system to 1.5 x 10"6 Torr,
measured by an ion gauge near the pump. The gas
collection system was baked at ~125°C, while the
specimen container was kept at -25°C to minimize
thermally-induced changes in the specimen. A 3.1mm-thick OFHC copper disk impacted the
configuration at 977 m/s. As shown in Figure 1,
product gases were collected in a sample cylinder
(9) that was immersed in liquid nitrogen.
Figure 5 shows the container after impact. The
impact side was deformed but had no visible
fractures. The post-impact pressure in the system
was in the 10~4 Torr range. The tube contained a
residue that was partially-reacted PTFE.
Preliminary mass spectrometric analyses of the
captured gas from this experiment have been
(c)
FIGURE 3. (a) Parts for experiment before impact, (b)
Deformed container after impact. This container had one visible
crack near the edge that did not affect the specimen cavity, (c)
Deformed and fractured cover disk for container. Impact speed
was 976 m/s.
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were performed using a residual gas analyzer. One
of the observed strong spectral lines corresponded to
the mass of a gaseous fluorine compound,
trifluoromethane (CHF3).
performed using a residual gas analyzer (RGA). A
background spectrum was first obtained for the
RGA at 10~6 Torr. When small samples of the
captured gas were leaked into the RGA, the
ACKNOWLEDGEMENT
This work was supported by the In-House
Laboratory Independent Research Office of the
Naval Surface Warfare Center, Dahlgren Division.
REFERENCES
1. Mock, W. Jr., Holt, W. H., and Kerley, G. I., "Shock
and Recovery of PTFE Powder," in Shock Compression of
Condensed Matter-1997, edited by S. C. Schmidt et al,
AIP Conference Proceedings 429, New York, 1998, pp.
671-674.
2. Holt, W. H., Mock, W. Jr., and Santiago, F., J. Appl
Phys. 88, 5485-5486 (2000).
3. Morris, C. E., Fritz, J. N., and McQueen, R. G., J.
Chem. Phys. 80, 5203-5217 (1984).
4. Tyburczy, J. A., Krishnamurthy, Epstein, S. and
Ahrens, T. J., Earth Planet. Sci. Lett. 98, 245-260 (1990).
5. W. Mock, Jr. and W. H. Holt, The NSWC Gas Gun
Facility for Shock Effects in Materials, NSWC/DL TR3473, Naval Surface Weapons Center, Dahlgren, VA
22448, July 1976.
6. The material was DuPont Type 8B Teflon PTFE
powder, purchased from E. I. du Pont de Nemours and
Company, Wilmington, DE 19898. Teflon is a registered
trademark of DuPont.
7. Average particle size information provided by Dupont
Certification Office, P.O. Box 1217, Parkersburg, WV
26102-1217.
8. Varian Conflat® Flange, 316 stainless steel, Part No.
F02750000NC6. Varian Vacuum Technologies, 121
Hartwell Avenue, Lexington, MA 02421-3133.
9. Whitey Miniature Sample Cylinder, Single Ended, No.
SS-4CS-TW-25. Whitey Co., Highland Heights, OH
44143.1490.
10. The Condensed Chemical Dictionary, 9th Ed., edited
by G. G. Hawley, Van Nostrand Reinhold Company, New
York, 1977, p.391.
FIGURE 5. Cylinder and tube container after impact. The tube
was deformed but not fractured and remained vacuum-tight.
Impact speed was 977 m/s.
spectra showed a variety of additional peaks, mostly
corresponding to higher masses than were observed
in the background spectrum. These measurements
were repeated eight times with consistent results.
One of the strong peaks in each of the sample
spectra corresponded to the mass for
trifluoromethane (CHF3), which has a boiling point
of-84°C (1 atm) (10). These results are considered
preliminary since the post-impact solid residue
appeared to be only partially reacted. Additional
experiments are planned to include higher impact
stresses and longer stress durations, along with
analyses using a higher resolution mass
spectrometer.
SUMMARY
A series of impact experiments has been performed
using different specimen container designs to
develop a configuration that would permit capture
of product gases from shock-decomposed materials.
For one of the experiments a gas collection system
was connected to the specimen container. Gaseous
products were collected in an evacuated sample
cylinder. Preliminary mass spectrometric analyses
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