MEASUREMENTS OF THE THERMAL BOUNDARY
RESISTANCE BETWEEN 3He AND SILVER FROM
0,4 TO 10 mK.
A. Ahonen, O. V . Lounasmaa, M. Veuro
To cite this version:
A. Ahonen, O. V . Lounasmaa, M. Veuro. MEASUREMENTS OF THE THERMAL BOUNDARY RESISTANCE BETWEEN 3He AND SILVER FROM 0,4 TO 10 mK.. Journal de
Physique Colloques, 1978, 39 (C6), pp.C6-265-C6-266. <10.1051/jphyscol:19786117>. <jpa00217521>
HAL Id: jpa-00217521
https://hal.archives-ouvertes.fr/jpa-00217521
Submitted on 1 Jan 1978
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Colloque C6, supplement au n" 8, Tome 39, aout 1978, page
JOURNAL DE PHYSIQUE
C6-265
MEASUREMENTS OF THE THERMAL BOUNDARY RESISTANCE BETWEEN 3He AND SILVER FROM 0.4 TO 10 mK.
A.I. Ahonen , O.V. Lounasmaa, and M.C. Veuro
Low Temperature Laboratory,
Helsinki
University of Technology,
SF-02150, Espoo IS,
Finland
Résumé.- Nous avons mesuré de 0.4 à 10 mK la résistance de contact thermique entre l'3He à
pression nulle et une poudre d'argent frittée. Nous trouvons une loi de variation en 1/T.
Abstract.- The thermal boundary resistance between silver sinter and 3 He at zero pressure
has been found to have a 1/T temperature dependence from 0.4 to 10 mK.
As a by-product of tests on our nuclear re-
10 nW, to 3!Ie by means of a Speer carbon resistor
frigerator /1/ we have measured the thermal boundary
ground to a thin slab of less than 1 mm thickness.
resistance between silver sinter and liquid 3He at
R = AT/Q, where AT is the temperature increment due
zero pressure in the temperature range from 0.4 to
to the heat flux, is the total thermal resistance
10 mK. The work thus extends to both the normal and
between*3He and the nuclear stage. In order to ex-
the superfluid regions of the liquid, with the tran-
tract the Kapitza boundary resistance R^, the ther-
sition temperature T
mal resistance of the long cell support was separa-
=1.1 mK. Our data are of
interest in theoretical investigations of the Kapit-
tely measured and subtracted. R^ was found to be
za resistance and in the construction of refrigera-
responsible for 75 % of the total heat barrier
tors for cooling superfluid 3He below 1 mK.
between the 3He
3
The experiments were performed in the He
and the rest of the cryostat.
Figure 1 shows our results. The best data
cell of our nuclear demagnetization refrigerator.
are below 1 mK, where the heat capacity of the nu-
The silver sinter inside the silver cell body was
clear stage was largest and consequently the tempe-
made of 0.07 um diameter powder /2/ of 99.6 %
rature drift, due to external heat leaks, was smal-
purity. The total surface area was found with the
lest.
BET method to be A = 12.9 m 2 , corresponding to a
characteristic surface area of 1.3 m 2 per gram of
50i
'
|
' ' 'i |
1
1
>
1
) I . , , ,
sinter. The silver powder was first presintered at
200°C for 20 min. The resulting material, ground to
a rough powder, was then packed into the 8 mm deep
and 2 mm wide grooves in the cell body by exerting
a pressure of 200 bar. The final sintering was done
by heating the cell to 220°C in about 15 min. and
then cooling quickly back to room temperature.
The temperature of the 3He sample was determined by measuring the nuclear magnetic susceptibility of
195
Pt by pulsed NMR techniques. The tempe-
rature scale was calibrated by the spin-lattice
relaxation time of the platinum powder at 2 mK and
it was also checked against the superfluid transition temperature T . The applied magnetic field was
rfmK)
28 mT during all our experiments.
The thermal resistance was measured by applying a heat current <3, typically between 0.1 and
Present address : Department of Physics, Cornell
University, Ithaca, New York 14853, USA
Fig. 1 : The thermal boundary resistance L
function of temperature.
as a
At the high temperature end of our measurements the
rapid temperature drift made precise determinations
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19786117
of AT difficult, leading to scatter of the data.
superfluid B phase, a revision of current theories
The Kapitza resistance is observed to have
a 1/T dependence over the whole temperature region
investigated; the line drawn into figure 1 fits
on the heat transfer mechanism at a liquid 3 ~ e metal interface is needed.
the equation
=
86/T K~/w.Above 1 mK this beha-
viour is expected /3/
, but
same temperature dependence below the superfluid
transition at 1.1 mK is somewhat surprising.
The absolute magnitude of the boundary
resistance, R
@
T
= 1100 ~ 2 m * / ~is
, four times larger than that found by Andres and Sprenger 131.
The probable reason for this discrepancy is that
our sinter is made of much smaller particles than
the 5 5 pm powder employed in Reference 131. The
heat conductivity of our sinter is presumably poorer than that of a sinter made of larger particles.
The thermal conductivity of bulk liquid 3 ~ e
is good in the low millikelvin region but inside
the sinter, with the voids much smaller than the
e
the heat
mean free path of the 3 ~ quasiparticles,
conductivity is greatly reduced 141. A temperature
gradient can thus develop across liquid 3 ~ confie
ned inside the relatively deep sintered regions.
Therefore, the effective surface area in our cell
may be smaller than the measured A = 12.9 m2.
The lack of any sign of change in the temperature dependence of RK in the superfluid B phase
is astonishing because the nuclear spin of the 3 ~ e
atom is assumed to be involved in the energy transfer process across the liquid 3He-metal interface.
e
drastiThe nuclear spin properties of 3 ~ change
cally in the superfluid; in the B phase the thermal
boundary conductance is expected to decrease faster
than in the normal phase 151.
A'simple explanation for the observed behaviour of
Reference
the observation of the
$ is that the liquid inside the sinter
may not undergo the superfluid transition at all.
The pare size of our sinter, a 0
:
l pm, is of the
same order of magnitude as the coherence length of
the superfluid and, therefore, the transition may
be suppressed. If this is the case, the use of
sinter made of very fine particles is advantageous
for cooling liquid 3 ~ below
e
1 mK. In this way one
could benefit from the smaller boundary resistance
of the'normal liquid inside the sinter while investigating the superfluid in the open areas of the
experimental cell.
On the other hand, if the thermal boundary
resistance between 3 ~ and
e a metal has the same
temperature dependence in the normal and in the
/l/
Veuro, M.C., Ph.D.Thesis, Acta Polytechnica
Scandinavica (to be published in April 1978).
See also paper XXX at this Conference.
Purchased from Vacuum Metallurgical Co.,Shonanbuilding 1-12-10 Ginza, Chuo-ku, Tokyo, Japan.
/3/ Andres, K. and Sprenger, W.O., Proc. 14th Int.
Conf. on Low Temp.Phys. 1 (1975) 123.
/4/ Befts, D.S., Brewer, D.F., and Hamilton,R.S.,
J. Low Temp. Phys. 16 (1974) 331.
/ 5 / Maki, K., Beal-Monod, M.T., and Mills, D.L.,
Phys. Rev.
(1976) 2900.
/2/