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A study of the structure change of water by measuring the sound velocity

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Ç N A E M 5 8 Ç N A E M 5 8

T. A. E. C.

ÇEKMECE NUCLEAR RESEARCH ÇENTER

ISTANBUL - TURKEY

A

S T U D Y

O F T H E S T R U C T U R E

C H A N G E

O F W A T E R BY M E A S U R I N G T H E S O U N D V E L O C I T Y

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ÇNAEM 58

A STUDY OF THE STRUCTURE CHANGE OF WATER BY MEASURING THE SOUND VELOCITY

oy

Ertuğrul Yazgan

June, 1968

Çekmece Nuclear Research and Training Center P.O, Box 1, Airport, Istanbul

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ABSTRACT

The sound velocity has been measured in twice distilled water

between 1-40°C with 0.5°C temperature intervals. The differences

between the calculated velocities using a fifth degree polinom which was obtained by a computer and the measured velocities were plotted

as a function temperature. It was noticed that at some temperatures

this curve has not a random distribution character.

The investigations showed that, at same temperatures Qurashi and Ahsanullah observed a series of discrete jumps in the activation energy of viscous flow of water, and Ahsanullah found discontinuities in the thermal expansion of water.

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A STUDY OF THE STRUCTURE CHANGE OF W A T E R BY MEASURING THE SOUND VELOCITY

Several sound velocity measurements in distilled water have been taken over a temperature range 1~39°C at temperature intervals of 1<,5°C using phase change method Barlow and Y a zgan (1966)-,

To minimize the errors arise from the acoustic path and water, these measurements were repeated twice employing two different acoustic paths, and water samples wit h 1«5°C.temperature intervals but shifted

0.5°C relative to the previous temperature values. The difference

b e tween the calculated velocities using the equation,

V = .1400.7873+5.189939T-6.394257x10-2T 2+4.4060241x10“ 4T 3

- 2 . 399801x10 _6T 4 + 6 .214865xlO-9T 5 in. se c " 1

Obtained by Barlow and Yazgan (1966), and the measured velocities at identical temperatures are plotted as a function

of temperature in Fig (l.a). Although the deviation of the velocity

differences are not more than ±0.05 m.sec “ w hich is approximately equal to the experimental error, the averaged velocity difference

curve (dotted line) shows some maximums and minimums. Several

times these measurements were repeated, and each time similar v e l o c i t y .difference curves have been found.

Although the velocity of sound inlliquids is not a fundamental factor regard to the structure of liquids, investigations on some physical properties of w ater encouraged to make a correlation between the observed maximums, minimums, and structure of water.

It is a wel l known phenomenon that the activation energy of an associated liquid decreases smoothly when the temperature increases, but Qurashi and Ahsanullah (1961, 1964) claim to have observed a

series of discrete jumps in the activation energy of viscous flow of water, Fig (l.b) from very accurate differential viscosity measurements, and have concluded that at activation energy step.

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2 s

a 30 to 50% change in the volume of the molecular aggregater or a corresponding change in the entropy of activation for the viscous

flow, or a combination of these takes place. Furthermore it was

shorn that the amount of the change in the activation energy at the steps, corresponds to the necessary energy to break up for a hydrogen

bond between the neighbouring molecules. Qurashi (1963) investigated

the change of the second differential of thermal expansion of water Fig. (l.c) and observed some discontinuities which are in agreement with those found by Qurashi and Ahsanullah (1961), and has suggested that these two phenomena have the same physical basis of intermolecular aggregation, or re-arrangement.

Table (1) shows the9temperatures which corresponds to sharp jumps

in activation energy, , and the minimums of the averaged velocitvş

AT

difference curve. It can be seen that eight of the given nine

temperatures corresponding to three curves are in agreement within

±i.2°C. At the fifth discontinuity point a maximum, and at 24°C a

min.imum, in the averaged velocity difference curve were apparent.

No of Discontinuity 1 2 3 4 5 6 7 8 9 Source Temperature C° Fig. (l.a) 3 7.5 11.5 14.5 - 20 28 35 38 Fig. (l.b) 3 9.5 11.8 15.6 17.5 21.6 27.3 33.9 36.9 Fig. (l.c) 5.3 8.0 11.4 16.0 18.8 22.4 28.9 33.5 36.8

A minimum in the averaged difference velocity curve corresponds

to a maximum in the true velocity of sound. In water, the asspciation-

decreases with temperature and leads to a decrease in adiabatic comp­

ressibility and in density. Considering that the decrease in density

due to a sudden decrease in association is very small (Qurashi, 1963) this sudden decrease in association will decrease the adiabatic comp­

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3,

Consequently although it can not be said that a definite correlation exists between the fluctuations in velocity and any possible structural changes in water there is some evidence to

support this hypothesis. Since eight of the nine discontinuities

of the activation energy, A a 2/Aa2 , and averaged velocity differences are in agreement within 1,2°C, the fluctuations in velocity probably have a physical basis which might be that of inter-molecular aggregation of re-arrangement as proposed by Qurashi and Ahsanullah (1961, 1964). In order to make a definite study the accuracy of the sound velocity measurements must be increased at least twice.

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ACKNOWLEDGMENTS

The author would like to thank to Dr* A* J. Barlow and to Prof* J* Lamb for their invaluable help, encouragements and the provision of facilities, during his stay in the Glasgow University, Scotland.

The experimental measurements were supported by a contract from the National Engineering Laboratory, Ministry of Technology*

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REFERENCES

1. Barlow, A* J, and Yazgan, E, (1966) Brit, J. Appl, Physics, 17, 807 2. Qurashi, M. M. (1963)

Pakis. J, Sci, Ind, Research, 6^, 213

3, Qurashi, M, M. and Ahsanullah, A, K f M. (1961) Brit, J, Appl. Physics, 12, 65

4, Qurashi, M, M, and Ahsanullah, A, K, M, (1964) Pakis, J. Sci, Ind. Research, 15, 480

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. s e c IT tN F IG . 1 DI FF ERENCE V E L O C IT Y ( a ) , A C T IV A T IO N E N E R G Y (b ) , A N D -4 A ~ /A T x 1 0 (c ) A S A FU N C T IO N O F TEMPE RA TUR E

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