Techniques for shock loading and recovering mineral samples in simulated lunar condition

De Carli, P. S.

Gates, R. W.

English

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Final Report
PREPARATION OF SIMULATED LUNAR SAMPLES
By: P. S. DeCARLI and R VV. GATES
Prepared for:
MANNED SPACECRAFT CENTER
"^)_OGY AND GEOCHEMISTRY BRANCH
HOUSTON, TEXAS 77058
CONTRACT NAS9-9401 m
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rsE^.I STANFORD RESEARCH INSTITUTEMenlo Park, California 94025 • U.S.A.
Final Report	 January 1, 1970
PREPARATION OF SIMULATED LUNAR SAMPLES
By: P. S. DeCARLI and R. VV. GATES
"M6,1
A
Prepared for:
NASA MANNED SPACECRAFT CENTER
GEOLOGY AND GEOCHEMISTRY BRANCH
HOUSTON, TEXAS 77058
Attention: W. R. GREENWOOD, PROJECT MONITOR
CONTRACT NAS9-9401
SRI Project 7946
Approved:
R. C. CREWDSON, Manager
Physics of Solids Program
G. R. ABRAHAMSON, DIrecror
Physicai Sciences (Poulter Laboratory)
it
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CONTENTS
Page
I . INTRODUCTION AND SUMMARY 1
TI. EXPERIMEN`1'AL STUDIES 2
A.	 Sample Material
B.	 Cylindi, ical Shock Geometry
C.	 Quasi- Plane
 
Wave Geometry
D.	 Plane Wave Geometry
III. DISCUSSION 10
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CONTENTS
1.	 INTRODUCTION AND SUAL1LARA'
II. EXPERIMENTAL STUDIES
A. Sample Material
B. Cylindrical Shock Geometry
C. QuaSi-Platte Wave Geometry
1). Plane !Nave Geometry
II1. DISCUSSION
Page
1
2
10
d
a	
ii
ILLI;STRATIO\S
1. Cylindrical Shock Geometry
2. Quasi-Plalle Wave System
3. Soft Aluminum Container
1.	 Plane Wave Geometry Container and Momentum Trap
Pape
3
4
7
	
N
7
I
iii
I. INTRODucrION AND SUMMARY
This program has been concerned with the development: of techniques
for shock loading; and recovering mineral samples under simulated lunar
condi ti Otis . Program objectives were as follows: The mineral samples
must be sealed in evacuated containers which are then shocked to suffi-
ciently high pressures to lithify the samples. The containers must remain
vacuum tight on release of pressure. 	 In addition, the container must be
designed so that it is possible to conduct the operations of loading; and
sealing the containers and of post-shock opening of the containers with
simple tools in a vacuum glove chamber.
During the course of this program, three basic sample container
systems were designed, tested, modified, and retested. Two of these
systems did not yield satisfactory results. The third system worked very
well, permitting recovery of vacuum-tight sample containers after shock
loading to pressures as high as 300 kbar. The successful system employs
an essentially one-dimensional shock propagat '.on geometry that per,-I.;.ts
reasonably accurate characterization of the pressure histor y of the sample.
Shock-lithified samples prepared in the course of this program have
been sent to Dr. W. R. Greenwood, NASA Manned Spacecraft Center. Some of
these samples were shock lithified in low-pressure atmospheres (— 10 Z Tore•)
of helium and of helium and argon. A further study of these samples should
permit evaluation of the possibility that shock wave gas implantation
occurred within the lunar regolith.
1
II. EXPERIMENTAL STUDIES
A.	 Sample :Material
The sample material used in all of the experimental work is
Vacaville basalt, obtained through the courtesy of the United States
Geological Survey, Menlo Park, California. This rock is approximately
.) ' 0 ^tndesitie (Ati 45-An 53), 31 o augite, an(] 16 o accessory minerals.
	 Tile
rock was comminuted by ball milling until all of the particles would pass
through a -lU mesh sieve.
Aw.	 B.	 Cylindrical Shock Geometry
the cyli tldrical shock geometry used in the initial experiments is
:shown in Fi st. 1. Sample containers were made from 1/2-inch-I.D. soft
copper t 1 tbing with a 0.040-inch-thick wall. A copper plug was silver-
soldered in one end of the tube. The tube was loaded with powdered
Basalt and evacuated. Pumping was continued for several hours to permit;
the sample to outgas and then the tube was --rimped to form a vacuum-tight
seal. It is expected that the residual ga y
 pressure in the sample cube
was sufficiently low that test results would not be affected. Sealed
sample containers were placed in a helium atmosphere for 12 to 16 hours
and t1le:: placed in a vacuum system connected to a helium leak detector.
'}'he failure to detect helium in these tests was considered to he adequate
indication of the vacuum tightness of the sample containers. The sample
containers were centered in lengths of 1-inch-I.D. steel pipe which was
then filled with molten Wood's metal. The pipe was wrapped with explesive
which was detonated at one end, producing a cylindrically converging shock
,, ,,, av,. that traveled down the cylinder.
Three experiments of this general type were performed. In each case,
the sample container and most of the sample were recovered. The fragments
of recovered sample could be described as "shock li thified .
	 However, the
sample containers were ruptured, and it is suspected that the rupt'.'res
were caused by jets originating in t}le sample cavity. These jets could
have been the result of a nonuniform sample density within the tube.
Un the basis of past experience with converging shock recovery experi-
ments we conclude that unbroken sample containers could lie recovered if the
2
TRY
-- DETONATOR
.r
FOAM
I
t- j / WOOD'S METAL
- CRIMP
EL-506D
-_-	 J :
-
_	 ------COPPER TUBE
s
QN
Q
W'.
-- •w:
STEEL PIPE
O -
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sample were packed to uniform density, if the Container• were c}lindricnlly
^vnunetricnl, and i f the container had thicker walls. These requirements
appear to be incompatible  with the requirement that the sample container
be loaded all(] _ilso opened after shock within a vacuum glove chamber.
Furthermor-e , it is virtually impossible to accurately characterize the
shock parameters for a porous sample shock loaded ill the converging
cylindrical shock geometry . We therefore abandoned the cylindrical
gcometrv.
C.	 (quasi-plane Wave Geomct ► •v
A second system, shown in Fig. 2, "as designed and tested. T)Iis
system was intended to combine the advan—iges of crimp sealing a copper
tube with the betlefits of a ►1 apprutiimately Lllal • acterizable shock geometry.
Thr sample was placed in n copper tube which was evacuated and crimp sealed.
The tube was then flattt:ned in a press.
	 It was necessary to reinforce the
crimp seal by silver- soldering; to permit flattening. The container was
leak tested and then placed i ►1 a groove in a ateel block. Type metal was
cast in he groove to fill the gaps between copper container and steel
plate. The surface was then planed and a steel cover plate was bolted on.
The first sample container of this type was shocked to 100 kbar and
recovered. The sample container was cracked and no longer vacuum tight.
However, the damage was not severe, and it was hoped that the damage could
be averted by using a redesigned momentum trapping system.
STEEL PLUG
	
STEEL PLUG
COPPER CAPSULE
	
STEEL BLOCK GA-7946-4
FIGURE 2 QUASI-PLANE WAVE SYSTEM
4
`0
Post-shock examination of the damaE , cd sample container indicated
that the probable cause 01' failure was the interaction of rarefactions
originating at the interfaces between the lo gy-shock- impedance- type metal
,end the high-shock-impedance copper container. A search was made for
alloys with low melting points which more closely matched the shock
impedance of copper. None were found. Howe.cr, it was noted that dental
amalgam is an excellent shock impedance match to copper.
One experimental assembly was made up with the substitution of dental
amalgam for the type metal used in the first experiment. This assemhly
was shock loaded to 100 Icbar and successfully recovered. The recovered
sample container was in excellent conditions, but it was no longer vacuum
tight. The vacuum leak did not appear to be the result of shock wave
damage but rather the result of corrosion cracking attributable to the
presence of mercury in the amalgam. This modified geometry would probable
be satisfactory if a protective coating were used to prevent attack of the
copper sample container by mercury.
The second approach taken to improve the quasi-plane wave geometry
was to fit the sample container very closely to the momentum traps so that
a filler material would not be needed. Cavities that very nearly conformed
to the shape of the sample container were machined in stainless steel
momentum trap halves. The momentum trap halves were pressed into good
contact with the sample container and secured with bolts. Two such
assemblies were built and shock loaded to 100 kbar. Both assemblies were
recovered in good condition, but the momentum trap halves were firmly
boncied together. In the course of splitting the momentum trap halves with
rather vigorous hammer and chisel work, the sample containers were broken.
It was observed that shock wave welding had token place between the copper
sample container and the stainless steel momentum trap halves. It appeared
that it would be rather difficult to split apart the momentum trap halves
in a vac::,:» glove box, but this geometry would be usable if shock «•ave
welding could be prevented. In view of the successful result, obtained
with the plane wave geometry (described below), the quasi-plane geometry
was shelved.
5
1).	 Plane Wave Geometry
The sample container developed for the initial plane wave shoCK
loading experiments is Ehown in Fig. 3. The lock powder %%as placed in
a cup machined from soft a)- ►minum (alloy 1100, 99'- pu ► • c aluminum). The
sample cavity was closed by a soft aluminum piston which was backed up
by a hard aluminum (alloy 2021-'f4) piston. An indium ring was placed
between the aluminum pistons to serve as a seal. Matching steps were
machined in the pistons to minimize the area of indium that must be
compressed to form the seal. The aluminum sample container fit into a
mild steel cup which in turn fit into a mild steel ring. The steel cup,
the steel ring, and a steel anvil (Fig. 4) comprised a iitomentum trap,
which prevented destruction of the sample container by tensile intev-
actions of rarefactions originating at free surfaces. The steel cup
performed an additional ditty in preventing deformatic:, ►
 of the Solt
aluminum cup as the pistons were pressed in to compress the sample and
to form the indium seal.
In the absence of a vacuum glove box, a simple vacuum chamber was
,jury-rigged to permit loading and sealing the sample containers under
vacuum. 'l'he aluminum cup, fitted into the steel cup, was loaded with
:30 grams of basalt and placed in the vacuum chamber. An alignment jig
held the soft aD ►minum piston, the indium ring, and the hard aluminum
piston above and well clear of the mouth Of the cup. The vacuum chamber
, ,as sealed and pumped down overnight to tnorOUghly outgas the basalt. A
plunger, working through a vacuum seal, was used to push the pistons and
seal into ;;he cup. A force of about 20 tons was then applied to the 2-inch-
diameter pistons to compress the sample (to a density of about 1.9 gi"cc)
and to seal the sample cavity. Subsequent helium leak testing indicated
that the indium (and possibly the soft aluminum) had flowed sufficiently
to effect a vacuum tight seal of the sample cavity.
Two sample assemb.lie i of this type were shock loaded to 100 kbar and
successfully recovero:d. After machining off the steel cup to remove a
source of virtual leak, the aluminum capsules were helium leak tested and
fount] tight.
2024 At
PISTON	 '0
s
1100 At
PISTON
POWDERED BASALT
INDIUM RING
1100 At CUP
GA-7946-2A
FIGURE 3
	
SOFT ALUMINUM CONTAINER
STEEL CUP
A] !`11D
UA-7946-3A
FIGURE 4 PLANE WAVE GEOMETRY CONTAINER
AND MOMENTUM TRAP
1
7
Al though some shock wave Hardening of the a 1LIMillllm container had
occurred, it was relatively simple to cut open the container with a
hammer and chisel. We ,judge that this operation could he easily performed
in a vacuum glove box, if it were desirable to do so. However, it would
be awkward to load the containers in a glove box because of the large force
needed to compress the indium seal.
The sample container design was mcxlified by the addition of ,n O-ring
groove to the outer Bare] aluminum piston. The 0--ring serves as a temporary
seal that can be made when it is desirable to load the sample in a vacuum
glove chamber. The container can then be removed from the vacuum chamber
and placed in a Hydraulic press for application of the necessary force to
compact the sample and the indium sealing ring. The indium seal effectively
isolates the sample from the O-ring and from the decomposition products to
be expected as a result of shocking the 0-ring.
Four plane wave geometry assemblies of the 0-ring type were loaded and
tested. One assembly was shocked to 100 mbar and was vacuum tiglit before
and after shock loading. Two assemblies were shocked to `ZOO kbar and were
vacuum tight before and after shock loading. The fourth assembly was
shock loaded to 300 lobar and was vacuum tight before and after shock
loading. The amount; of deformation of the container shocked to 300 kbar
was very large; the diameter increase was nearly 50 	 We therefore consider
that the present sy.item is probably marginal for recovery of samples shocked
to pressures near or above 300 kbar. However, we would expect routine
recovery of vacuum tight containers shocked to pressures in the vicinity
of 200 kbar.	 •
These last four testis of the plane wave geometry were also intended
as gas implantation experiments. After the container and sample had been
outgassed within the vacuum chamber to a residual pressure less than 10-3
Torr, helium was admitted to raise the pressure to approximately 10-2'I'orr.
The container was then closed and removed from the vacuum chamber. The
container was then subjected to a helium leak test, to determine whether
the O-ring seal was effective. The container was next placed in a
hydraulic press for further compaction of the sample and the indium sealing
ring.
8
10 3
10 `
10-2
10-2
2 x 10 `
100
100
(unopened sample
container)
200
200
300
Vacuum
Helium
Helium
I Ie 1 i tim
Helium + Argon
Five shock-lithified samples shock loaded in plane wave geometry
were sent to NASA Manned ' •.pacecraft Center.
	
(See 'fable I).
Table I
SAMPLES SENT TO NASA ;1ISC
(All Shock Loaded in Plane Nave Geometry)
Peal: Pressure
	 Container	 Loading Chamber
	
s
on Container
	 Atmosphere
	
Pressure
(Kl;ar)
	 (Tort.)
9
"tww
III. DISCUSSION
All of the samples shock loaded to pressures of 100 kbar could be
described as shock lithified, although they are rather friable. The
samples shocked to 200 kbar are much stronger, but the sample,
 shocked to
300 kbar is the least well bonded of any of the samples. It is entirely
possil , le that the large permanent deformation of the container shocked
to 300 kbar can account for the poor bonding. This ceformation, which
took place during release of pressure, could have resulted in the
breaking up of bonded material.
For the plane wave geometry experiments the pressure histories of
the samples can be estimated with reasonable accuracy, for the input
pressure pulses were sufficiently long ( > 5 Nsec) to permit the sample
to come to pressure equilibrium with the aluminum sample container. The
actual pressures in the samples are believed to be within 10`< of the
nominal values of 100, 200, and 300 kbar. Since the sample attair_s
pressure equilibrium with the container, via a series of shock reflections,
the pressure estimates do not require knowledge of the Hugoniot equation
Of state of the sample material. 'Ilie pressure uncertainties are due
primarily to uncertainties in the velocities of the axplosivel;•
 accelerated
flyer plates chat impacted the sample containers.
For accurate estimation of shock temperature and residual temperature
(immediately after pressure release) of the samples, one would require
accurat,: knowledge of the 'Hugoniot equation of state and the release
acliabats of the sample material. Unfortunately, the necessary data do
not exist. However, we have made a few rough approximations to permit
crude estimations of the residual temperatures of the shock-lithified
specimens. The flugoniot of the porous sample was approximated on the
basis of the assumptions that the material is compacted to full density
by pressures of 50 kbar or less, and that at higher pressures the
compression curve of the material corresponds to the compression curve
for the solid rock. The release acliabats of the sample were approximated
by the compression curve of the solid rock. Using these data, the path
(in the pressure-volume plane) of the material during a si ► ock compression-
pressure release cycle could be estimated. The area enclosed by the path
10
w
is equated with the internal energy increase of the sample. This energy
increase is assumed to be entirely thermal; phase transitions and other
possible effects are neglected.
For the samples shock,_: to 100 kbar, the estimated temperature
immediately on release of pressure is 400 0C f 150
0
. For the 200 kbar
samples, we estimate 7000C ± 250 0 . For the 300 k bar sample, we estimate
9000C f 3500.
11


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