J. Phys. Chem. 1982, 86, 1013-1015
1013
Homogeneous Nucleation of 1-Pentanol in a Two-Piston Expansion Chamber for Different Carrier Gases R. Strey" and P. E. Wagnert Max-Planck-Instltul fik Biophyslkalische Chemie, 0 3 4 0 0 GlittlnQen, Federal Republlc of Germany (Received: June 24. 198 1; In Flnal Form: October 19, 1981)
The homogeneous nucleation rate in supersaturated 1-pentanol vapor has been investigated as a function of supersaturationand temperature. Various carrier gases (He, Ar, N,) were used. The measured rates were found to be independent of the nature of the carrier gas. While the slope of the experimental curves is in agreement with theory the actual measured values and their temperature dependence considerably deviate from classical nucleation theory.
Introduction In a recent paper1 we described a newly developed two-piston expansion chamber for measurements of homogeneous nucleation rates as functions of supersaturation and temperature. For water vapor we obtained rates over a range from 2 X lo5 to 2 X log s-l and thereby data obtained by Kassner and his associates2were extended by four orders of magnitude. These measurements were performed with argon as the carrier gas. For a correct interpretation of the results obtained and for comparison with data obtained by other authors using different carrier gasesH or pure vapor carriers7it is important to investigate the influence of the carrier gas on the homogeneous nucleation process. The carrier gas serves different purposes: In diffusion chambers light carrier gases (Hz, He)4 are used in order to prevent convection and the correspondingperturbations of heat conduction and mass diffusion. Experiments in expansion chambers,3p6 shock tube^,^^^ and supersonic nozzles7make use of the principle of adiabatic expansion. For the case of ideal gases the temperature (and thereby the supersaturation) of the expanded vapor-carrier gas mixture are readily calculated. In the theory of homogeneous nucleation"1° it is usually assumed that the nature of the carrier gas has no influence on the nucleation process. The few experimental investigations of this question, however, give no clear evidence. The classical expansion cloud chamber work of Wilson3 (using Hz, air, N2, 02), the diffusion cloud chamber experiments of Katz4 (Hz, He, Nz, Ne), and the shock tube experiments of BarschdorfP (He, air, Ar) revealed no carrier gas effects on the respective suitably defined onset of nucleation. On the other hand, Allen and Kassner6 concluded from their measurements of the nucleation rate as a function of supersaturation that "it was definitely established that the nucleation rate of water vapor is higher in an argon atmosphere than in a helium atmosphere. The latter result seems to indicate that the noncondensable gas plays a role in the clustering process...". In the present paper we report measurements of homogeneous nucleation rates in 1-pentanol vapor as functions of supersaturation and temperature for some representative carrier gases (He, Ar, N2). A comparison with the classical nucleation theory is performed. Under the considered operating conditions 1-pentanol has a comparatively low vapor pressure, thus causing only slight deviations from the ideality of the carrier gas-vapor ' P e r m a n e n t address: Institut fur Experimentalphysik, Universit&tWien, Strudlhofgasse 4,A-1090Vienna, Austria. 0022-3654/82/2086-1013$01.25/0
mixture. The droplet growth rate was found to be low enough so that vapor depletion can be neglected during the nucleation time interval.
Experimental Section Measurements were performed by means of a new two-piston expansion chamber which has been introduced recently' and will be described in more detail elsewhere. Here only a brief description of the operation is given. A small volume of filtered carrier gas is allowed to saturate with the considered vapor. After saturation has been achieved the vapor-carrier gas mixture is expanded. Thus, the vapor becomes supersaturated and homogeneous nucleation occurs, the nucleation rate depending on the actually obtained supersaturation. After a short time interval (AtexpZ= 1 me) a small recompression is performed sufficient to reduce the nucleation rate to a negligible value. In the still supersaturated vapor the clusters formed by homogeneous nucleation are developed to macroscopic size. For observation, the growing droplets are illuminated by a He-Ne laser beam. Their number density C is determined from the ratio of the experimental scattered light flux measured under an angle of 15" to the corresponding theoretical scattered light flux calculated from Mie theory for a single particle.ll A typical result from a single run is given in Figure 1 (another can be found in ref 1). It can be seen that even for the higher chamber temperature of 25 "C the growth of the particles (and thereby vapor depletion) occurs clearly after recompression has been performed. Therefore the assumption that steady-state nu(1)P. E. Wagner and R. Strey, "Homogeneous Nucleation Rates Measured in a Two-Piston Expansion Chamber", presented at the Second Chemical Congress of the North American Continent, Las Vegas, NV, Aug, 1980; P. E. Wagner and R. Strey, J.Phys. Chem., 85,2694(1981). (2)R. C. Miller, Ph.D. Thesis, University of Missouri-Rolla, 1976;R. J. Anderson, R. C. Miller, J. L. Kassner, Jr., and D. E. Hagen, J.Atmos. Sci., 37,2509 (1980). (3)C. T. R. Wilson. Phil. Trans.. 189.265 (1897). (4)J. L.Katz and B. J. Ostermier, J. Chem.' Phys., 47,478(1967);J. L. Katz, ibid., 52,4733 (1970). (5)D.Barschdorff, Phys. Fluids, 18,529 (1975). (6)L. B. Allen and J. L. Kassner, Jr., J. Colloid Interface Sei., 30,81 (1968). (7)P. P. Wegener and B. J. C. Wu in "Nucleation Phenomena", A. C. Zettlemoyer, Ed., Elsevier, New York, 1977. (8) R. Becker and W. Doring, Ann. Phys., 24,719 (1935). (9)J. Frenkel, "Kinetic Theory of Liquids", Dover Publications, New York, 1955. (10) A. C. Zettlemoyer, Ed., "Nucleation", Marcel Dekker, New York, 1969;"Nucleation Phenomena", Elsevier, New York, 1977. (11)P. E. Wagner, J. Colloid Interface Sei., 53, 439 (1975);P. E. Wagner and F. G. Pohl, Ges. Aerosolforsch., 5 , 279 (1977).
0 1982 American Chemical Society
The Journal of Physical Chemistty, Vol. 86, No. 6, 1982
1014
1-PENTANOL
-
Strey and Wagner 1 - PENTANOL
ARGON 10'0 r -
I
1
A
lo9
* *A
25OC
.FA .5
A
I
6
' 0 0
10
20 TIME
30
0
A
00"0"
5oc
///
8 .9
1, :; 1
CO
/
[rns]
Flgure 1. Plot of the experimental data obtained during a single measuring run: upper curve, pressure; lower curve, the ratio of the scattered and transmttted llght fluxes -14 bans.
102 c
cleation prevails seems to be justified and the experimental nucleation rate can be calculated by
lo'
,
1
:: A C ~
NITROGEN
I
~-
6
5
The corresponding supersaturation S is calculated according to
by assuming a dry adiabatic expansion (3)
where p&T) denotes the saturation vapor pressure. The indices (i) and (exp) correspond to the total pressure p and temperature T of the initial and expanded state, respectively. The ratio of specific heats K = cP/cv is calculated according to Richarz12 from the respective values K~ and K~ for the carrier gas and vapor:
The classical nucleation rates were calculated according to4
by using literature data for the temperature dependence of the density d,13the vapor pressure and the surface tension c,15 M = 88.15, cp/cv (pentanol) = 1.l,l6 cp/cv (helium) = 1.660, cp/c, (argon) = 1.668, cp/cv (nitrogen) = 1.404.16
The 1-pentanol (>99%, Riedel de Haen) was used as purchased. The carrier gases were specified as 99.99% N2, (12) T. Richarz, Ann. Phys., 19,457 (1908).
(13) Timmermanns, 'Physico-Chemical Constants of Pure Organic Compounds", Elsevier, New York, 1965, p 260. (14) "Handbook of Chemistry and Physics",54th ed,Chemical Rubber Publishing Co., Cleveland, 1973-74, D-168. (15) Timmermanns, "Physico-Chemical Constants of Pure Organic Compounds", Elsevier, New York, 1950, p 326. (16) 'American Institute of Physics Handbook",McGraw-Hill, New York, 1973, p 3-62.
7
8 9 10 SUPERSATURATION
11
13
12
Flgure 2. Homogeneous nucleation rate vs. supersaturation for 1pentanol in hellum (0, e), in argon (0, O ) ,and in nitrogen (A, A)at the initial (chamber) temperatures ( 0 ,) 5 (open symbols) and 25 OC (closed symbols).
TABLE I: The Average Ratio (Jexpt/Jtheoru) of the Experimental and Theoretical Nucleation Rates for Various Carrier Gases and the Corresponding Temperatures of the Initial and Expanded State, 6,and TeXDa
N, N, He He Ai. Ar
5 25 5 25 5 25
250.0 268.3 251.5 270.2 251.0 270.3
9.70 x 9.40 x 2.18 x 4.40 x 1.08 X 5.68 x
1013 10' 1013 10'
lo"
los
110.9 71.1 48.9 20.3 67.6 144.7
8 16 8 7 8 9
a u denotes the relative standard deviation of n single measurements.
99.996% He, and 99.997% Ar (Messer Griessheim).
Results and Discussion In Figure 2 the experimental nucleation rate Jexptl is shown as function of supersaturation for two initial temperatures and for various carrier gases. It can be seen that within experimental scatter the nucleation rate was found to be independent of the carrier gas. Our results thus support the findings of W i l s ~ nKatz,4 ,~ and BarschdorfP and contradict the conclusion of Allen and Kassner.6 It seems furthermore safe to conclude that the expansion is truly adiabatic. Deviations from adiabaticity, due to convective transport and turbulence in the measuring chamber, would be significantly more pronounced in the case of N2 where much larger expansions had to be performed than for the noble gases. The curve in Figure 2 shows the theoretical nucleation rate, calculated by means of the classical nucleation theory for a starting temperature of 25 "C. The discrepancy between experiment and theory is so large that the theoretical curve for the lower starting temperature cannot even be shown in Figure 2. We have calculated the ratios of experimental and theoretical nucleation rates. In view
J. Phys. Chem. 1982, 86, 1015-1018
of the similarity in slope of the experimental and theoretical curves and the magnitude of the ratios obtained we feel that the comparison of experimental and theoretical rates is best characterized by the mean values of the ratios for each initial temperature Ti and carrier gas. These values and the temperatures Texpin the measuring cham= 2 X lo7 cm-3 ber at intermediate nucleation rates (Jexpt s-l) are given in Table I. Further reducing the data it can be stated that the experimental nucleation rates at 250 and 270 K are larger than the theoretical ones by factors of 5(f4) X 1013and 6(f3) X 108,respectively. Accordingly, it is found that the actual experimental nucleation rates in 1-pentanol vapor as well as their temperature dependence considerably deviate from classical nucleation theory. However, the comparatively small relative standard deviation u (see Table I) indicates good agreement between the slopes of experimental and theoretical curves. The
1015
results for other systems will be presented in due course.
Summary We found that homogeneous nucleation in 1-pentanol vapor is unchanged if different carrier gases (He, Ar, and N,) are chosen. These result.9 confirm the corresponding assumption made in the nucleation theories.a10 Furthermore they support experimental evidence given by some author^^-^ and contradict others.6 While the classical nucleation theory succeeds in predicting the slope of the experimental nucleation rate vs. supersaturation curve for 1-pentanol, the actual measured values and their temperature dependence considerably deviate from theory. Acknowledgment. This work was performed in the department of Professor Dr.M. Kahlweit. We thank him for the interest in and support of this work.
Raman Spectroscopic and Chromatographic Study of the Uranium Isotope Effect in Uranyl Acetate Complex Formation Y. Tanaka, Y. FuJIl,and M. Okamoto' Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Ookayama, MegureKu, Tokyo 152, Japan (Received June 24, 198 1; In Final Form: October 20, 198 1)
Raman spectra of aqueous solutions of uranyl acetate complexes were measured. The downward shift of the frequency for the totally symmetrical stretching vibration of the O==U=O bond was brought about by stepwise formation of uranyl acetate complexes. In order to predict the direction of the fractionation of uranium isotopes in complexes,the reduced partition function ratio for each uranyl acetate species was calculated by use of each assigned O=U=O stretching frequency. It was found that the lighter isotope 235Uis accumulated more preferentially in uranyl acetate species than in the hydrated uranyl ion. This trend is consistent with that obtained by cation-exchange chromatography of uranyl acetate solutions.
Introduction Uranium isotope fractionation in complexes formed in solution have been investigated for enrichment of uranium isotopes by chemical exchange methods.l+ In order to predict the magnitude and direction of the isotope fractionation, reduced partition function ratios for uranium isotopes have been theoretically calculated by use of Raman and infrared spectral data of According to these calculations the complexes should incorporate the heavier isotope 238Uin preference to the aquauranium ion (1)H.Kakihana, K. Kurieu, and M. Hosoe, Nippon Kagaku Zasshi, 84, 24 (1963). (2)H.Tomiyasu, H.Fukutomi, and H. Kakihana, J. Inorg. Nucl. Chem., 30 2501 (1968). (3)M.&E, Energ. Nucl. (Paris), 10,376 (1968). (4)H.Kakihana, Nippon Kagaku Zasshi, 89,734(1968). (5)J. Aaltonen and K. G. Heumann, 2.Naturforsch. B , 29,190(1974). (6)H.Kakihana, Sep. Sci. Technol., 15, 567 (1980). (7)Y. Yato and H. Kakihana, Bull. Tokyo Inst. Technol., No. 127.63 (1975). (8) Y. Yato and H. K a k i i a , Bull. Tokyo Inst. Technol., No. 127,71 (1975). (9)H.Kakihana and Y. Yato, Bull. Res. Lab. Nucl. React. (Tokyo Inst. Technol.), 1, 43 (1976). 0022-3854/82/2088-1015$01.25/0
in uranyl systems? This trend is in accord with that observed in cation-exchange chromatography by CiriE3and by Sakuma et al.'O But the results obtained by Okamoto et a1.11J2 using uranyl acetate, tartarate, citrgte, and fluoride are the reverse of the results reported by CiriE and are not consistent with the theoretical calculations. Part of this inconsistency might be due to the fact that the spectral data measured in the solid state13-18 were employed in the calculations for solution systems because of the lack of data for solutions. In the present work, first, (10)Y.Sakuma. M.Okamoto. and H. Kakihana. J. Nucl. Sci. Tech-
no!:, 18, 9 (1981).'
(11)M.Okamoto, R. Goda, A. Nakagawa, Y. Sakuma, and H. Kakihana, Isotopenpraxis, 16, 293 (1980). (12)Y. Tanaka, J. Fukuda, M. Okamoto, and M. Maeda, J. Inorg. Nucl. Chem., in press. (13)J. E.Newberry, Spectrochim. Acta, 25, 1699 (1969). (14)J. I. Bullock, J. Chem. SOC.A, 781 (1969). (15)A. Perrin, J. Inorg. Nucl. Chem., 39, 1169 (1977). (16)A. Perrin and J. Pright, Spectrochirn. Acta, Part A, 33, 781 (1977). (17)W.Scheuermann and A. Van Teta, J. Raman Spectrosc., 6, 100 (1977). (18)C. Caville, J.Raman Spectrosc., 6, 235 (1977).
@ 1982 American Chemical Society
