2922
J. Pbys. Cbem. 1980, 8 4 , 2922-2927
conditions within collapsing cavities, oxygen gas may directly attack Fez+to form a complex, similar to the Na-Ar exciplex formed during the sonolysis of argon-saturated solutions of sodium chloride.26 Complex formation between iron and oxygen has been observed during the radiationZ6tz7and photochemically28induced oxidation of Fe2+,but such a species would not be detected as either Fez+or Fe3+ and so the number of Fe3+ions formed will not be equal to the number of Fez+ions oxidized, as observed by Elpiner and S o k o l ~ k a y a As . ~ ~these complexes have covalent character, it may be conjectured that they have relatively higher vapor pressures than their parent ionic species. This would enable species with low pressure to get into cavities as has been observed experimentally.26 In conclusion the present studies indicate that alcohols when added to Fricke solution participate chemically to enhance oxidation of iron(I1). The net effect produced is similar to that observed during the oxidation of Fez+by radiation; Le., the analogy between sonochemistry and radiation chemistry holds true in this case. In view of the complexity of the phenomenon of cavitation, a detailed quantitative consideration is not possible a t this time. However, salient features can be accounted for qualitatively by the suggested mechanism. Acknowledgment. Financial support from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged. References and Notes (1) Sehgai, C.; Steer, R. P.; Sutheriand, R. 0.; Verraii, R. E. J. Pbys. Cbem. 1977, 81, 2618. (2) Negishi, K. J . Pbys. SOC.Jpn. 1961, 76, 1450. (3) Griffina. V. J . Cbem. Pbvs. 1950, 18. 997. (4) Jarmaii, P. Proc. Pbys..Soc. London, Sect. B 1959, 73, 628.
(5) Weissier, A. J. Am. Cbem. Soc. 1959, 81, 1077. (6) Jennings, B. H.; Townsend, S. N. J. Pbys. Cbem. 1961, 65, 1574. (7) Eipiner, I. E. “Ultrasound: physical, Chemical and Biological Effects”; Consultant Bureau: New York, 1964; Chapter 3. (8) Sehgai, C.; Sutheriand, R. G.; Verrail, R. E. J. Pbys. Cbem. 1980,
84 - . , 388 - - -. (9) Haissinky, M.; Mangeot, A. Nuovo Cimento 1956, 4 , 1086. (IO) Miller, N. Trans. Faraday SOC. 1950, 46, 546. (11) Miller, N. J . Cbem. Pbys. 1951, 48, 242. (12) Spinks, J. W. T.; Woods, R. J. “An Introduction to Radiation Chemistry”, 2nd ed.; Wiiey: New York, 1976. (13) Mead, E. L.; Sutherland, R. G.; Verraii, R. E. Can. J . Cbem. 1975, 53, 2394. (14) Mead, E. L.; Sutherland, R. G.; Verrali, R. E. Can. J . Cbem. 1976, 54, 1114. (15) Todd, J. T. Ultrasonics 1970, 8 , 234. (16) Dewhurst, A. H. J . Cbem. Pbys. 1951, 19, 1329; Trans. Faraday Soc. 1952, 48, 905. (17) Cottin, M.; Haissinky, M.; Vermeil, C. C . R . Hebd. Seances Acad. Sci. 1952, 235, 542. Rosinger, S.; Giocker, R.; Ooubeau, J. Z,Pbys. 1957, 73,1. Prudhomme, R.; Grabar, P. J. Cbem. Pbys. 1949, 46, 323. Margulis, M. A.; Maltsev, A. N. Russ. J. phys. Chem. (Engl. Trans/.) 1972, 46, 1697. Parke, A. V. M.; Taylor, D. J. Cbem. Soc. 1956, Part IV, 4442. Loiseieur, J.; Letrajet, R.; Crovisier, C. C . R . SOC.Bbl. 1942, 736, 56. Benson, S. W. “Thermochemicai Kinetics”, 2nd 4.;Wiley: New Yolk, 1976. Knapp, R. J.; Daily, J. W.; Hamitt, R. G. “Cavitation”; McGraw-HIii: New York, 1970. Sehgal, C.; Steer, R. P.; Sutheriand, R. G.; Verrail, R. E. J. Cbem. Pbys. 1979, 70, 2242. Proskurnin, M. A.; Orekov, V. S.; Bareiko, E. V.; Chernova, A. I. “Radiobiology, Transactions of Ail-Union Scientific Technical Conference on the Use of Radioactive and Stable Isotopes and Radiation in the National Economy and in Science, 1957”, Kurin, A. M. et ai., Eds.; 1958; p 113. Proskurin, L. A. “Transactions of All-Union Conference on Radiation Chemistry, 1980”, Polack, L. S., Ed.; 1962; p 207. Orekov, V. D.; Chernova, A. I.; Proskurnin, M. A. Zb. Flz. Kbim. 1957, 37, 873. Elpiner, I. E.; Sokolskaya, A. V. B k l . Akad. Nauk. SSSR 1959, 129, 202.
Ultrasonic and Dielectric Relaxation of LiC104 in 1,2-Dimethoxyethane and 1,3-Dioxolane at 25 OC S. Onishi, H. Farber, and S. Petrucci” Departments of Electrlcal Engineering and Chemisty, Brooklyn and Farmingdale Campuses, Polytechnic Institute of New York, Brooklyn New York (Received: March 31, 1980; In Final Form: July 3, 1980)
Ultrasonic absorption data in the frequency range 10-900 MHz for LiC104in 1,3-dimethoxyethane(DME) and 1,3-dioxolane(DXL) are reported. The data above 300.MHz have been obtained by pulse techniques exciting thin piezoelectric films of ZnO, deposited over quartz delay lines. LiC104 showed an ultrasonic relaxation dependent on concentration in DME, but no relaxation in DXL. However, the latter pure solvent showed a relaxation at f 1 300 MHz at 25 “C. The relaxation of LiC104 in DME was interpreted as due to ion-pair quadrupole equilibria. Electrical conductance of LiC104in both solvents indicates that the electrolyte is mainly M, the maximum associated in the form of ion pairs. A small amount of triple ions was also detected at c < concentrationwhere the data have been analyzed. Dielectric complex permittivities for LiC104in both solvents in the frequency range 0.45-70 GHz were analyzed as the sum of two Debye relaxations,one for the solute and one for the solvent. On the contrary,in dimethoxymethane, where extensive concentration for the species exists, the dielectric spectrum is more complex. This reinforces our view that dielectric spectrometry reflects mainly the rotational relaxation of the polar species present. The dielectric strength eo - tmlfor the solute, LiC104, correlates to the concentration for the pairs through the Bottcher equation in both DME and DXL solvents. Introduction In our continuing effort to investigate the structure a d dynamics of Li+ salts in media of low permittivity as ethers, we have extended OW previous work1 to the solvents 1,2-dimethoxyethane and 1,3-dioxolane. DME has a permittivity of -7, almost isodielectric with DXL. U1trasonic studies were extended to these solvents to in0022-3654/80/2064-2922$01.OO/O
vestigate the dynamics of species transformation and to give estimates of the formation constants related to the equilibria investigated. Electrical conductance measurements were’performed to obtain 811 overall picture of the structure of the systems investigated. A comparison of the dielectric spectra of LiC104in DME (e 7) in contrast to the previously investigated DMM
-
0 1980 American Chemical Society
The Journal o f Physical Chemistry, Vol. 84, No. 22,
Ultrasonic and Dielectric Relaxation of LiC104
IO1
(002) cZno up
h
70-
u
i58
Y
t z
5
50-
N \
40-
0
= 7
B
Au/ZnO/Au/QUARTZ
-
E
U
a 6
-B*
30-
2ob
2 5
z
LiVO4 0.049M IN DME t 25*C
-'E 6 0 N
5
1980 2923
2
5
IO
20 50 IO0 200 f(MHz)
500 (a)
4
-
E 3
LiVO4 0.23M IN DME
t=25'C
100-
N*
-i 80-
2
E
Y
I
30
32
313 42 46 50 54 58 DlFFlPACTlON ANGLES (DEGREES)
62 (a
11
6040-
\
J
f.9113.5 MHz
/
a
f.606.8 MHz
201
1'
/
2
5
IO
50 f (MHz)
20
IO0 200
500 (b)
Figure 2. Representative plots of alf, vs. the frequency ffor LiCIO, 0.049 M (a) and 0.23 M (b) in dimethoxyethane at 25 OC., Solid lines are the calculated Debye functions.
:j 4
L I 2 3 4
00
5 6 7 8 1 x 1 0 3 , INCH
9 101'1
1'2
(b)
Flgure 1. (a) Plot of an X-ray diffractometer scan of (002) oriented ZnO on Au-Cr/fused quaitz substrate. Ordinate: normalized intenslties. Abscissa: angles (degreles). (b) Attenuation (dB) vs. distance (In.) for
La$S04)30.015 M in water at 25 O C at the frequencies Indicated: Pulse technique; ZnO thin-film transducer.
(e = 2.76) could show the disappearance of a considerable amount of larger aggregates than ion pairs. In this case the complexities in the dielectric spectra shown to be present for the DMM solutions should disappear. Notice, in fact, that the alternate explanation of the appearance of a distribution of relaxation times as due to collision of ion pairs2$should not depend strongly on the permittivity of the solvent (unless one invokes the stability of the products of collision as the source of the deviation from a single Debye process).
Experimental Section The ultrasonic anti dielectric equipment and the procedure in the respective frequency ranges 10-300 MHz and 0.45-70 GHz have been described e1sewhere.l For the frequencies of -455, -607, and -910 MHz, thin piezoelectric films of ZnO deposited over quartz delay lines have been used to generate and receive the longitudinal elastic waves. The films were sputtered from a ceramic zinc oxide cake by using a conventional rf sputtering system; the substrate temperatures were -420 "C, and the atmosphere was 50% oxygen and 50% argon. Given the films had strong c-axis normal orientation as shown in Figure la, tiransducer quality longitudinal mode ZnO films have been produced having k, coupling constank4approaching those of single-crystal ZnO. In our rf diode sputtering system, the rod substrates, on which the
ZnO was deposited, were suspended on one side of the target.s In this way, the surface of the deposited film was kept out of the plasma column,6 thus avoiding electron bombardment during the sputtering process. Gold film deposited below and above the ZnO f i i provided electrical contacts. Samples of the performance of the ultrasonic cell mounted with the ZnO piezoelectric film are shown in Figure l b for La2(S04)30.015 M at the three fundamental frequencies. ?'he correlation coefficients of the straight lines are good. The values of a / f "are in agreement, within experimental error, with the data collected7 for the same system studied at the University of Gottingen by one of us by surface excitation of crystals8 at the end of resonant cavities. The purifications of DME and DXL have been reported previou~ly.~ Preparation and handling of the solutions have been de5cribed.l Results Figure 2 shows the representative plots of the ultrasonic absorptions expressed as a/fL (cm-' S2)vs. the frequency f (MHz) for LiC104in DME. The concentrations shown are c = 0.049 M and c = 0.23 M. The solid lines are the fittedlO Debye function for a single relaxation process: (a/fL) = A / P
+ (f/fRYI + B
(1)
where a is the absorption coefficient (Np cm-l) and A , B, and f R are relaxation parameters. The results for these quantities are reported in Table I. For LiC104 in DXL, no relaxation is visible with the exception of the onset of a relaxation at f > 200 MHz which is due to the presence of an ultrasonic relaxation in the pure solvent. Figure 3a shows the equivalent conductance vs. the concentration (expressed as log A vs. log c ) for LiC104in both DME and DXL at 25.00 "C. A minimum is clearly visible.
The Journal of Physical Chemistry, Vol. 84, No. 22, 1880
2924
Onishi et al.
TABLE I: Ultrasonic Relaxation Parameters A, B, and Sound Velocity u, Ion-Pair Concentrations e,, Experimental and Calculated Values of the Maximum Excess Sound Absorption per Wavelength g~ for LICIO, in 1,2-Dimethoxyethaneat 26 C, and Electrolyte Concentration c (MI Investigated
fR,
71
1 0 1 7 ~ ,1 0 1 7 ~ ,
cm-I
cm-'
a
1O5&Mb
~ O - ~ U ,
s2 MHz cm/s cp,(lM exptl calcd 35.5 17 1.175 0.0288 27 26 62 64 35 36 1.174 0.0486 35 90 1.182 0.103 197 218 35 130 1.186 0.142 347 351 32 200 1.187 0.226 681 653
c, M
sz 0.029 27 0.049 30 0.104 37 0.144 50 0.230 57., a C -c(1Kpl'$l'z.
fR,
4 5 :
3 1 0.1
f (GHz)
~~~T);OI=~/(K~"'C~'~);~~T=(KT/ g~ = (Oih)max= ( A l 2 ) U f ~ .
01-
30
COLE-COLEPLOT LIC.404 O.IOM IN 1-2 DME
A
LO,
LICOO~IN ETHERS I:25"C
0 1st RUN 0 2nd RUN 0 3rd RUN
0.51
2 DIMETHOXYETHANE 0*5'0
60
70' ct
I
-4
'1 st
-2
-3
LOG,O c
-I
0
90
'
160
Flgure 4. (a) Representation plot of the real and Imaginary coefficients e' and (e" - e l f x ) of the complex permittivity plotted vs. the frequency ffor LICIO, 0.10 M In DME and at 25 OC. ex is the conductance contribution to the loss. (b) Cole-cole plot for the same system. Arrows indicate the position of the relaxation frequencies.
I
g(c) contains the interionic effect upon the conductance, and the activity coefficient f* of Debye and Hiickel. Equation I1 results from the combination of the latter expression for fi, the two mass equilibrium constants for Kp and KT in the expression for A
LiCPOaINETHERS 1=25': FUOSS-KRAUS THEORY FOR TRIPLE IONS #-2
8'0
DIMETHOXYETHANE
i4
.r! I?
1-3 soDIOXOLANE 100
0
20
40
where S is the coefficient of the Onsager tangent. Neglect of A/&, of ( S / A O ~ / ~ ) ( C Aand ) ~ / ~the , assumption of fi = 1leads to g(c) = 1and
120
60
c
-
(I %)xi04
Flgure 3. (a) Plot of log of equivalent conductance vs. log of concentration for LiCiO, in the solvents 1,Bdimethoxyethane and 1,3dioxolane at 25 OC. (b) Fuoss-Kraus function A g(c)c"* vs. c(l - Aliio) for LiCIO, in DME and DXL at 25 OC.
Figure 3b reports the quantity A g(c)c1l2vs. c(1- A f &) for the two solvents according to the Fuoss-Kraus relation:ll
For the present data it was found that eq V is inadequate, the data showing a downward curvature when plotted as A ( C ) ~ vs. / ~ c. On the contrary eq IV gives reasonably straight lines (Figure 3b), the curvature having almost disappeared. In order to apply eq IV, it is necessary to have estimates of A. and assume a value of boT.Assuming A$ = 2/3Ao (ref 12) and using the Walden rule value Aoq = 0.614 (ref 1)for DME (q = 0.004 129Igand for DXL (q = 0.005 888): one calculates the following for LiC104: For DME A0 = 149 E' cm2equiv-l; Kp = 4.1 X 10s M-l; KT = 20.3 M-l. For DXL A. = 104 i2-l cm2 equiv-l; 2.36 X lo7 M-l; KT = 33.6 M-1. Figure 4a shows a representative plot of the coefficients of the real and imaginary parts of the complex permittivity vs. the frequency f for LiC104 in DME. Figure 4b shows the Cole-Cole plot of (e" vs. e' for the same system. is the conductance contribution to the loss: e''x = 1.8 X 1012X/fwith x the specific con-
Ultrasonic and Dielectric Relaxation of LiCIO,
The Journal of Physical Chemistv, Vol. 84, No. 22, 1980 2925
a
k
2AB
2 AzB2 kr
(VII)
one has1
v
where AVs is the isoentropic volume change for the observed process. Introducing the formation constant Kq = [AzBz]/[AB]2,one can rewrite the above as
01 0 2
10
05
20 50 f (GHz)
2.5
1
50
20
100
COLE -COLE PLOT L 1 0 0 40.14M IN 1-3 DIOXOLANE t :25'C
3.0 h
IO
t
'v" 2 0 -
.-
IO-
09
O 30
L 40
, 50
I
60
70
80
06
\,
90
I
100
c'
Flgure 5. (a) Representrition plot of the real and Imaginary coefficients e' and (e" 6'' ) of the complex permlttlvity plotted vs. the frequency f for LiCIO, 0. M in 1,3-dloxolane at 25 OC. (b) Cole-Cole plot for the same system. Arrows Indicate the position of the relaxation fre-
-
where cp = [AB] N (1- a - 3aT)c is calculable in a first approximation from the conductance results above. In the above a = (1/Kp1/2c1/2)and aT = (KT/K2/2c1/2). In particular for Kqc >> 1and Kqcp
