Notizen 899
Measurement of the Hypersonic Velocity in the Molten Salts NaCl and KCl
Lena M. Torell and H. E. Gunilla Knape
D e p a r t m e n t of P h y s i c s , C h a l m e r s U n i v e r s i t y of T e c h n o l o g y , G ö t e b o r g , S w e d e n
Z. N a t u r f o r s c h . 34 a, 8 9 9 - 9 0 0 (1979);
received M a y 7, 1979
T h e h y p e r s o n i c v e l o c i t y of m o l t e n s o d i u m a n d p o t a s s i u m chlorides h a s b e e n m e a s u r e d o v e r a t e m p e r a t u r e r a n g e of a b o u t 100°C a b o v e t h e m e l t i n g p o i n t s . T h e m e a s u r e m e n t s w e r e carried o u t a t s c a t t e r i n g a n g l e s 90° a n d 140°, cor- r e s p o n d i n g t o a 6 — 1 0 G H z f r e q u e n c y r a n g e . N o d e v i a t i o n f r o m p r e v i o u s u l t r a s o n i c v a l u e s of v e l o c i t y w a s o b s e r v e d a t t h e s e f r e q u e n c i e s , i n d i c a t i n g t h a t t h e m e a s u r e m e n t s w e r e p e r f o r m e d a t f r e q u e n c i e s lower t h a n a n y r e l a x a t i o n f r e - q u e n c y .
As part of a continuing study of the Brillouin spectra of ionic liquids in this laboratory [1], a high temperature thermostat has been constructed [2]
to be used for measurements around 1000 °C in molten chlorides. This work on the molten sodium and potassium chlorides was a natural continuation of our previous study on molten nitrates. Molten alkali halides have a simpler structure t h a n the nitrates, and for comparison w ith theories of liquids it is preferable to study halide melts. The experi- mental difficulties are, however, much larger, due to the higher melting points and the more corrosive nature of halide melts.
The salts used in these experiments were of the highest quality t h a t could be obtained commercially, Merck suprapur quality. To get rid of excess water the salt was kept in a vacuum furnace a t a tem- perature of 240 °C for 24 hours. Then the salt w
Tas loaded into the quartz salt reservoir situated above the scattering cell in the central part of the furnace, where it was kept at a temperature of 300 °C for another 24 hours before melting into the sample cell. The cylindrical scattering cell, diameter 4 cm, was constructed to protect the furnace from halide vapors [2], The exciting source was an Ar-ion laser operating in single mode at a wavelength of 4880 A.
Radiation scattered at 9 0 ° 0 3 ' ± 2 0 ' and 139°56'
± 2 0 ' was collected and analyzed with a pressure- scanned Fabry-Perot interferometer. The free
R e p r i n t r e q u e s t s t o D r s . L . Torell a n d G. K n a p e , F a c k , S-402 20 G ö t e b o r g , S w e d e n .
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spectral range was 29.59 GHz, and during an experiment the interferometer was pressure-scanned over five orders.
Spectra were recorded in the temperature range (800-916) °C for molten NaCl and ( 7 7 6 - 9 0 7 ) °C for molten KCl. From the Brillouin frequency shift the sound velocity, v, was calculated according to the formula
Av c
~ 2 n ro sin dj2 '
where cjvo = Ao = wavelength of the light source, Av = frequency shift of the Brillouin line, n = index of refraction of the scattering medium, 6 = scatter- ing angle.
The index of refraction [3], the measured value of the frequency shift and the calculated hypersonic velocity are listed in Table 1. The velocity as a function of temperature is shown in Fig. 1, where solid lines represent the present results and broken lines the ultrasonic results reported by Cerisier et al. [4]. With an experimental error of 1% t h e hypersonic result is in good agreement with t h e ultrasonic data which can be seen in the figure.
T a b l e 1. E x p e r i m e n t a l d a t a of h y p e r s o n i c v e l o c i t y .
S a l t T e m - R e - F r e - Ve- F r e - Ve-
p e r a - f r a c - q u e n c y locity q u e n c y l o c i t y t u r e t i v e
<°C) i n d e x (GHz) ( r a s- 1) ( G H z ) ( m s- 1)
0 = 90.1
0
0 = 139.9°N a C l 800.4 1.426 7.17 1734 9.57 1743
814.7 1.430 7.14 1722 9.52 1730
829.2 1.423 7.09 1718 9.43 1722
843.4 1.421 7.01 1701 9.35 1710
857.7 1.419 6.98 1695 9.30 1702
872.7 1.417 6.88 1674 9.21 1688
887.0 1.416 6.86 1670 9.10 1669
901.5 1.414 6.80 1658 9.06 1664
916.7 1.412 6.72 1641 8.96 1648
K C l 776.2 1.395 6.40 1582 8.57 1595
790.7 1.393 6.33 1567 8.46 1577
805.2 1.391 6.28 1556 8.37 1563
819.0 1.390 6.20 1540 8.30 1551
833.4 1.388 6.16 1532 8.22 1538
847.5 1.386 6.11 1520 8.14 1525
862.5 1.384 6.03 1504 8.06 1513
876.8 1.382 6.00 1497 7.97 1498
891.6 1.380 5.93 1483 7.93 1493
905.7 1.378 5.89 1475 7.84 1476
900 Notizen
1700
1600
1500
T a b l e 2. V e l o c i t y d a t a a s a f u n c t i o n of t e m p e r a t u r e ( m s- 1) .
600
900Temperature (*C ] F i g . 1. G r a p h of v e l o c i t y v e r s u s t e m p e r a t u r e f o r m o l t e n K C l a n d N a C l . P r e s e n t h y p e r s o n i c m e a s u r e m e n t s a r e l a b e l e d • a t 90° s c a t t e r i n g a n g l e A a t 140°. Solid lines r e p r e s e n t t h e b e s t fit t o t h e p r e s e n t r e s u l t s a t b o t h t h e s c a t t e r i n g a n g l e s ; b r o k e n lines r e p r e s e n t t h e u l t r a s o n i c m e a s u r e m e n t s of [4].
H y p e r s o n i c v e l o c i t y P r e s e n t r e s e a r c h
H y p e r s o n i c v e l o c i t y M a r t i n e t al. [5]
U l t r a s o n i c v e l o c i t y Cerisier e t al. [4]
N a C l S a l t
2 3 6 7 - 0.789 7' 2 4 1 9 (90°)
2 3 8 9 - 0 . 8 0 6 T (140°)
0 . 8 3 4 T 2707.7 - 1.5155 T + 0.39527 • l O -3 T2
K C l S a l t
2 2 2 2 - 0 . 8 2 8 T 3032 - 2.691 T 2477.9 - 1.3760 T
(90°) + 0.10847 • 10-2 T2 + 0.29561 • 10~3 T2
2 2 7 8 - 0 . 8 8 6 T (140°)
The temperature dependence of the velocity from the present and recently reported [5] hypersonic data are summarized in Table 2 together with ultrasonic data [4]. All the tabulated values of the hypersonic velocity and its temperature dependence agree well with the corresponding ultrasonic results;
accordingly no dispersion was found for frequencies lower than 10 GHz. The measurements were thus performed below any relaxation frequency for both liquids.
The authors acknowledge the financial support from Stiftelsen Lars Hiertas Minne.
[1] H . E . G . K n a p e a n d L. Torell, J . C h e m . P h y s . 62, 4111 (1975).
L . M . Torell a n d H . E . G. K n a p e , J . P h y s . D : A p p l . P h y s . 9, 2 6 0 5 (1976).
[2] R . A r o n s s o n , H . E . G. K n a p e , a n d L . M. Torell, J . C h i m . P h y s . 68, 3794 (1978).
[3] J . Z a r z y c k i a n d F . N a n d i n , C. R . A c a d . Sei. P a r i s 256, 1282 (1963).
[4] P . Cerisier, G . Finiels, a n d Y . D o u c e t , J . C h i m . P h y s . 6, 836 (1974).
[5] R . M a r t i n , J . Q u i n a r d , J . C o r d o n n i e r , a n d J . P . P a h i n , R e v . P h y s . A p p l . 13, 99 (1978).
