CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
NICKEL CRITICAL POINT PARAMETERS FROM SHOCK
EXPERIMENTS WITH POROUS SAMPLES
Dmitry N.Nikolaev, Vladimir Ya.Ternovoi, and Alexei A.Pyalling
Institute of Problems of Chemical Physics RAS, Chernogolovka, Russia, 142432
Abstract. Results of experiments on expansion of shock-compressed nickel samples into helium
is presented. The brightness temperature of nickel sample and shock velocity in helium were
measured by an optical pyrometer, other parameters (particle velocity, pressure, helium
temperature) were calculated. To increase the shock entropy up to near-critical value, shock
compression of porous (m=1.91) samples were used. Isoentrope with initial pressure 170 GPa
was studied, with final states below 1.4 GPa, determined by initial helium pressures. The
peculiarities of isentrope slope in pressure-particle velocity graph allowed to estimate a point of
it's entrance into two-phase region. The isobaric overheat of expanded nickel by hot shocked
helium allowed to get an additional information about phase diagram and to estimate of critical
temperature and pressure of nickel, using the van-der-Waals model of liquid nickel spinodal.
Registration of light emission snapshot of
unloading specimen gives us the velocity of shock
in helium, and, using helium EOS, we can
calculate particle velocity and final pressure of
expanded metal. Because of it's relative high
ionization potential, helium remains transparent in
shocked state, that makes possible to register
emission from metal surface and to calculate it's
brightness temperature. So the isoentrope can be
traced on both pressure - particle velocity and
pressure - temperature planes.
The results [1-4] were obtained for Pb and Sn metals with quite low values of critical entropies,
that allows to investigate near-critical and even
supercritical isoentropes, using existing explosive
launchers
with
well-defined performance.
Investigation of metals with high critical
parameters requires strikers, accelerated to
velocities more than 10 km/s. Elaboration of such
launchers is serious technical problem, not solved
INTRODUCTION
The method of shock loading and isoentropic
expansion of matter allows one to exceed
limitations of both static methods and common
Hugoniot measurements, and provides the
opportunity to investigate thermodynamics of
liquid - vapor phase transition in near-critical
point region. In particular, this method was used to
investigate location of coexistence curve and
critical point in the P-T phase diagram of lead and
tin [1-4]. In this experiments release isoentropes
were traced for several initial Hugoniot pressures.
A number of final pressures on isoentrope was
defined by variation of shock compressibility of
obstacle medium. Helium was used as obstacle, and
variation of its initial pressure from zero to more
than 100 bar was enough to trace isoentropes in
wide range of parameters.
59
20000
T,K
15000
10000
5000
f
0
200
FIGURE 1. Experimental assembly. 1 - diaphragmed optical
fiber, 2 — pressurized case, 3 — glass window, 4 — helium under
pressure, 5 - porous nickel sample, 6 — steel bottom of assembly,
7 — steel striker
400
600
800
t, ns
1000
FIGURE 2. Typical experimental snapshot. Emission intensity
already recalculated in brightness temperature.
up to now. For achieving the required near-critical
entropy with common launching systems, the use
of porous specimen was proposed. It also solves
another problem: if striker velocity will be very
high, the temperature of shock-compressed helium
would be sufficient to it's noticeable ionization
and, thus, loss of transparency. In this situation
pyrometer would register the emission of shocked
helium.
photoreceivers at several wavelengths. To transmit
emission from assembly, quartz-polymer optical
fiber with diaphragm on assembly end was used.
Light was collected from little area of 2-3 mm
diameter. Before each experiment, pyrometer,
connected with fiber and diaphragm, was
calibrated, using standard tungsten ribbon lamp, so
brightness temperatures on various wavelengths
can be calculated.
Typical experimental snapshot is presented on
Fig.2. For calculating of shock velocity in helium
we needed a precise value of distance between
window and nickel surface. At high initial
pressures of helium the bottom bulge can add
sufficient error in distance measurement, so the
dependence of bulge from initial pressure in
assembly was measured. Parameters of shock wave
in helium were calculated using plasma EOS [5],
although discrepancy between EOS data and basic
expression for monoatomic ideal gas (D = 4/3Up)
wasn't higher than few percents.
EXPERIMENTAL TECHNIQUE
Experimental assembly, used in experiments with
porous nickel samples, was analogous to that, used
in experiments with lead and tin [4].
Porous samples, 20mm diameter, were compacted
from nickel powder in hydraulic press. Thickness
of the samples was chosen about 0.2 - 0.3 mm, to
avoid an overtaking of shock wave by release wave.
Samples with mean density m = p/po = 1.91 (p sample density, p0 - normal density of nickel) is
quite firm, and, glueg to bottom, can follow the
bottom bulge under helium pressure.
Experimental is shown on Fig.l. The sample
was loaded by impact of steel striker, accelerated by
2-stage explosive launching system. Hugoniot
pressure in samples was 1.7 GPa. Thermal
emission from assembly was traced by fast
multichannel pyrometer with p-i-n photodiodes as
RESULTS AND DISCUSSION
Experimental results obtained is presented on
Fig.3 and 4 and in Table 1. As was shown in [6], a
sharp change in slope of isoentrope on pressure particle velocity plane caused by formation of
shock boiling wave in the moment of it's entrance
60
in two-phase region. Thus we can assume, that this
isoentrope crosses with saturation curve at 0.080.09 Gpa.
The process of shock exit on the surface of
sample would be accompanied by various
instabilities, led to intense mixing of Ni and He
and heat-mass exchange. Actually, in experiments
with compact samples we registered the process of
overheating of sample surface by hot shocked
helium and used this data to trace liquid spinodal
of metals.
In case of porous Ni the process of heat-mass
0.20
0.00
4000
6000
8000
10000 12000 14000 16000
T,K
EOS spinodal
—— Van-der-Waals spinodal
+
Cp, Bushman, Lomonosov
D
Cp, our estimation
EOS Isoentrope
Cp, Young, 1971
Cp, Fortov, Yakubov, 1994
Ni temperature
He temperature
FIGURE 4. P-T graph. Experimental points - temperature of
helium and temperatures of Ni overheat.
lead and tin the temperature anomaly was fond. At
pressures, close to critical, process of heat-mass
exchange becomes supereffective, and temperatures
of overheat of metal surface raised close to helium
temperature. On nickel P-T diagram (Fig.4) one
can see this anomaly at pressure about 0.9 GPa. We
suppose, that this is a critical pressure. This value
don't contradicts with existing theoretical
predictions.
For estimation of critical temperature, van-derWaals model of liquid spinodal was applied. If we
know critical pressure and have measured an
experimental spinodal points, it's possible to
construct liquid spinodal, and find a critical
temperature. In our case Tcr.p. = 9100 K. It should
be pointed, that van-der-Waals model is the most
simple model of phase diagram. A lot of other
models exists, and we can use it for this
calculations, for example, spinodal [9].
Another anomaly on experimental spinodal exist
at pressure of isoentrope entrance in two-phase
region. As mentioned above, this is connected with
formation of shock boiling wave. Now we can
estimate parameters of critical point of nickel.
IE-3
FIGURE 3. P-Up graph. Curves - EOS [7] calculation of release
isoentropes with various initial porosity of sample.
transfer become so fast, that it's impossible to
register the initial temperature of metal surface,
moreover, in some experiments we obtained a slow
cooling of initially hot surface. So we accepted, that
in experiments with porous samples measurements
of temperature on isoentrope is impossible, and
only the temperature of overheat (spinodal
temperature) can be measured. Our experience
confirms, that this information is significant for
understanding of phase diagram.
If investigated isoentrope passes considerably
near critical point, it can get into region of low
mechanic and thermodynamic stability [8], where
anomalies in compressibility, heat conductance and
sound speed is predicted. In P-T graphs of both
61
TABLE 1. Experimental data on isoentropic expansion of Ni. Initial Hugoniot pressure l.TGPa.
Po, Bar
D, km/s
Up, km/s
P,GPa
THe,K
T,K
M
AUp, km/s
AT, K
0.056
0.51
0.85
2.005
3.46
10.1
11.6
13.557
22.19
25.33
27.24
34.9
39.14
48.09
30.2
48.09
66.14
67.7
60.02
58.76
67.71
87.33
101.6
117.5
16.96
14.56
14.46
13.25
11.79
11.77
11.16
12
11.26
11.2
11
11.05
11.13
10.84
11.08
11.49
9.86
9.95
10.61
11.04
10.85
9.76
9.91
9.8
13.78
11.12
10.99
9.92
8.78
8.76
8.3
8.94
8.38
8.36
8.17
8.22
8.28
8.07
8.24
8.56
7.31
7.38
7.89
8.21
8.07
7.22
7.31
7.21
0.002185
0.0138
0.0226
0.0441
0.0715
0.174
0.18
0.244
0.351
0.396
0.41
0.531
0.605
0.705
0.741
0.792
0.8
0.836
0.842
0.893
0.994
1.038
1.243
1.402
20140
18342
18310
16000
15110
12750
11500
13680
11700
12400
11150
11260
11430
11960
11330
12170
9000
11330
10410
11260
10890
10800
10900
11300
5400
5730
6680
8900
10300
8750
8200
9400
8150
8390
7850
8100
8380
8740
9070
9700
8500
8400
9000
9900
9100
8100
8100
8000
1.8
2.06
1.63
1.905
2.07
1.9
1.7
1.89
1.9
1.9
1.74
1.969
2.008
1.96
2.008
1.944
1.936
1.935
1.886
1.922
1.84
1.94
1.97
2
0.4
0.5
0.3
0.4
0.45
0.3
0.4
0.28
0.3
0.25
0.33
0.3
0.3
0.29
0.3
0.4
0.4
0.39
0.3
0.3
0.3
0.37
0.29
0.36
400
200
230
280
330
300
290
300
400
240
200
400
300
220
300
350
400
300
300
400
300
300
250
200
Singapore, 1 996, pp. 119-124
3. Pyalling A.A. et al, Int.J.of Thermophysics. 7
1001 (1998)
4. Ternovoi V.Ya., Filimonov A.S. et.al. in: Shock
Compression of Condenced matter - 1997, ed. By
S.C.Schmidt et.al., AIP Conference proceedings 429,
NY, 1998, pp. 87-90.
5. .Ebeling W., Foerster A., Fortov V., Gryaznov V.,
Polischuk A. Thermophysical properties of hot dence
plasmas, Shtuttgart - leipzig: Teubner, 1991,
pp.142-172.
6. Ternovoi V.Ya., Filimonov A.S. et.al. in: Shock
Compression of Condenced matter - 1999, ed. By
M.D.Furnish et.al., AIP Conference proceedings 505,
Melville, NY, 2000, pp. 189-192.
7 V. E. Fortov and I. V. Lomonosov. J. Pure & Appl.
Chem. 69(4), 893-904 (1997).
8 Semenchenko V.K. Selected chapters of theoretical
physics. Moscow: Education, 1966, pp 94.
9. Lienhard J.H., Chemical Engeneering Science 31, pp.
847-849(1976)
= 0.9± O.lGPa . Tcr.p. = 9100 ± 200 K.
cy of Tcr.p. depends on spinodal model
Jnfortunately, in this method it's impossible
to find1 r'ritir'dl HAncitx/ Tr\ ActimatA \7r-r n it'c
necessary to trace isoentrope in wide pressure
range from Hugoniot to critical pressure, and
calculate Riemann's integrals, and accuracy of
such great investigation wouldn't be sufficient.
ACKNOWLEDGEMENTS
The research described in this publication
funded by part from RFBR grants 00-02-17750 and
01-02-06243.
REFERENCES
1. Fortov, V.E., Lebedev M.E., Ternovoi V.Ya.,
Rev.Gen.Therm. Fr. 371, 589-591 (1992)
2. Ternovoi v.Ya., Fortov V.E., et.al. in: Physics of
Strongly Coupled Plasmas, ed.by W.D.Kraeft et.al.,
World Scientific Publishing Co Pte Ltd,
62