Internal Mobilities in the Molten Binary System (K, Rb) N03
Transcrição
Internal Mobilities in the Molten Binary System (K, Rb) N03
Internal Mobilities in the Molten Binary System (K, R b )N 03 C hao-cheng Yang and Isao Okada Department of Electronic Chemistry, Tokyo Institute o f Technology, Nagatsuta, Midori-ku, Yokohama, Japan Z. Naturforsch. 42a, 1017-1020 (1987); received July 7, 1987 Ratios of internal cation mobilities in the molten binary system (K, R b )N 0 3 have been measured with the Klemm method in a wide range o f concentration (0.0537 < * Rb< 1.00; xRb denotes mole fraction of RbNOj) and tem perature (603 K < 7"<783 K). From these and available data on the densities and conductivities, the internal mobilities of the two cations, b K and b Rb, have been calculated. At high tem perature and high ;cRb, the Chemla effect has been observed, whereas in previous similar experiments * the Chemla effect had not been observed. Except for xRb> 0.9, bK can be expressed by bK = [ A / ( V - Vq)] exp ( - E / R T), where V is the m olar volume; A , E and V0 are constants having almost the same values as in the molten binary system (K, C s)N 0 3. Introduction W e have so far m easured ratios o f internal m obilities o f tw o cations in various binary alkali nitrate melts (see Table 1 in [1]) with K lem m ’s countercurrent electrom igration m ethod [2]. In the system (K, R b ) N 0 3 Ekhed and Lunden [3] m ea sured the internal m obilities o f the tw o cations with the same m ethod. Their m ain aim was to determ ine the isotop e effect o f these cations and they did not cover a w ide range o f concentration and temperature. Thus, they did not clearly observe the C hem la effect [4, 5]. In all binary alkali nitrates except this system the C hem la effect has been observed and no plausible reason could be found that only this system is excep tional. In som e binary alkali nitrate m elts such as (N a, K ) N 0 3 [6 ] and (R b, C s ) N 0 3 [1], in which the relative differences in the radii o f the cations are sm all, the C hem la effect occurs at high concentra tion o f larger cation at high tem perature. There fore, also in (K, R b ) N 0 3 the C hem la effect was supposed to occur under such con d itions. It has been found [6 , 7] that, w hen the C oulom bic attraction is expected to play a dom inant role for the internal m obility, the interal m obility o f cation 1 can be expressed by b\ = [ A / { V - V q)] e x p ( - E / R T ) , (1) * A. Ekhed and A. Lunden, Z. Naturforsch. 34a, 1207 (1979). Reprint requests to Prof. Isao Okada, D epartm ent o f Electronic Chemistry, Tokyo Institute o f Technology at Nagatsuta, Midoriku, Yokohama 227, Japan. 0932-0784 / 87 / 0900-1017 $ 01.30/0. - where A , V0 and E are constants characteristic o f cation 1 and nearly independent o f the co-cation and tem perature. It was another aim to learn w hether ( 1 ) also holds in the present case. Experim ental The chem icals K N 0 3 and R b N 0 3 used were prepared by Soekaw a Chem . C o ., T okyo; the form er was o f reagent grade and the purity o f the latter was better than 99% . The salts were dried at 1 2 0 °C overnight, mixed in a chosen ratio and m elted. The electrom igration cell and experim ental pro cedure were quite similar to the previous ones [5]. In m ost o f the runs the tem perature could be kept w ithin ± 2 ° C with a tem perature controller. At x Rb= 1.00 (x Rb: m ole fraction o f R b N 0 3), radioactive 4 2 K, w hose h alf life is 12.36 hr, was em ployed; this was produced by irradiating ca. 2 0 mg K N 0 3 with thermal neutrons at a Triga II type nuclear reactor at A tom ic Energy Research Laboratory, M usashi Institute o f T ech nology. The irradiated K N 0 3 was poured into ca. 20 g o f R b N 0 3 melt contained in a sm all quartz vessel; the concentration o f K N 0 3, x K, was about 0.0015. A fter electrom igration, the radioactivity in each fraction ( 1 . 5 - 2 . 0 cm long) o f the separation tube w as m easured with a well type N a l(T l) scintillation counter, and then the radioactivity at a fixed time was calculated by extrapolation. The content o f K + and Rb + in each fraction was determ ined with flam e spectrophotom etry; about Please order a reprint rather than making your own copy. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namensnennung-Keine Bearbeitung 3.0 Deutschland Lizenz. This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution-NoDerivs 3.0 Germany License. Zum 01.01.2015 ist eine Anpassung der Lizenzbedingungen (Entfall der Creative Commons Lizenzbedingung „Keine Bearbeitung“) beabsichtigt, um eine Nachnutzung auch im Rahmen zukünftiger wissenschaftlicher Nutzungsformen zu ermöglichen. On 01.01.2015 it is planned to change the License Conditions (the removal of the Creative Commons License condition “no derivative works”). This is to allow reuse in the area of future scientific usage. 1018 C. Yang and I. O kada • Internal Cation M obilities in the System (K, R b )N 0 3 1000 ppm o f C s + were added to each solution in order to depress the easy ionization o f Rb. Results Table 1. Experim ental conditions and results. •*Rb 7VK //h r Q /C 0.054 ±0.003 673 723 783 603 673 783 648 693 723 773 603 643 673 723 733 783 603 643 673 723 783 643 723 753 783 681 715 735 774 653 693 723 773 7.3 8.0 7.0 8.3 8.0 7.6 7.0 7.5 7.3 7.5 8.8 7.0 7.5 7.8 7.7 8.1 8.2 8.2 8.0 8.1 7.8 8.3 8.2 8.2 7.8 7.5 7.3 8.0 7.9 13.8 4.5 6.0 24.0 3668 3911 3961 3681 3603 3616 2476 2827 2550 2983 3140 2913 3302 2957 3649 3176 3635 3616 3566 3420 3350 3816 3869 3927 3467 3215 2874 3912 3265 2222 2250 1974 3302 The relative difference in internal cation m obili ties £( = { b K- b Rh) / b ; b = x Kb K + x Rbb Rh) was cal culated in the usual w ay [ 8 ]. In the case o f x Rb = 1, the equation (2) o f [9] was used to calculate e. From the £ value thus obtained and available data [ 1 0 ] on the densities and the conductivities, the internal m obilities b K and b Rb were calculated. T he m ain experim ental conditions and the re sults are listed in T able 1. In Fig. 1 the isotherm s o f b K and b Rb obtained in the present study are shown together with those obtained by Ekhed and Lunden [3]. 0.257 ±0.002 D iscussion 0.968 ±0.003 Figure 1 show s that the present isotherm s agree w ell w ith those estim ated from the data by Ekhed and Lunden [3]. 0.983 ±0.003 0.496 ±0.001 0.731 ±0.002 0.935 ±0.002 1.00 ^Rb Fig. 1. The isotherms of internal cation mobilities in the system (K, R b )N 0 3. □ : bK [this work], L : bK [3], V : bRb [this work], V : bRb [3], £ 0.0372 ± 0.0062 0.0301 ±0.0053 0.0250 ±0.0056 0.0291 ±0.0088 0.0270 ±0.0087 0.0182±0.0102 0.0030 ± 0.0096 0.0223 ±0.0098 0.0174 ±0.0083 0.0153 ±0.0071 0.0200 ± 0.0063 0.0156 ± 0.0044 0.0117 ±0.0033 0.0124 ±0.0033 0.0109 ±0.0030 0.0104 ±0.0043 0.0123 ± 0.0050 0.0114 ±0.0078 0.0104 + 0.0046 0.0077 ±0.0060 0.0057 ± 0.0040 -0 .0 0 1 0 ±0.0032 -0 .0 0 3 0 ±0.0016 -0 .0 0 4 9 ±0.0070 -0 .0 0 4 7 ±0.0050 -0.0051 ±0.0038 -0 .0 0 9 5 ± 0.0060 -0 .0 1 0 2 ± 0.0062 -0 .0 1 3 0 ± 0.0046 -0 .0 0 3 8 ±0.0018 -0.0051 ±0.0031 -0 .0 0 4 2 ±0.0052 -0 .0 0 3 0 + 0.0038 In the present isotherm s the C hem la effect oc curs and the crossing point shifts toward higher con centration o f the sm aller cation with increasing tem perature. This is a trend observed in all other system s so far studied. Our interpretation has been stated in previous papers [6 , 1 1 ]. In order to see w hether (1) holds, we plotted the reciprocals o f b K and b Rb against the m olar volum e in Figs. 2 and 3, respectively. In Fig. 2, the solid lines are drawn according to (1) w ith the param eters A = 4.21 x 1 0 ~ 11 m 5 V ~ ' • s _ 1 m o r \ E = 16.74 k J m o P 1 and K0 = 1 0 .5 x l 0 ~ 6 m 3 m o l- 1 , w hich were previously calculated from the system (K, C s ) N 0 3 [6 ]. Figure 2 show s that b K in the present system deviates negatively from (1) at high .vRb. A negative deviation has also been observed for &Nain the sys tem (N a , R b ) N 0 3 [12] and was explained as fo l lows: A t high concentration o f R b N O ? free space is expected to be relatively great, and therefore an 1019 C. Yang and I. Okada • Internal Cation M obilities in the System (K, R b )N 0 3 V x \a 6/ m 3 m o l-1 Fig. 3. The reciprocal of bRb vs. molar volume in the molten binary systems (M, R b )N 0 3; A: M = Li [5], O : Na [12], □ : K (this work), V: pure R b N 0 3, <^: Cs [1]. V x to 6/ m 3m o| 1 N a + ion is attracted by the nearest neighbouring N 0 3 ion with less interference from other neigh bouring N O f ions. In other w ords, neighbouring N a + - N 0 3~ ion pairs are m ore structured and therefore their separating m otion is retarded. xVery strong interaction o f a sm all cation with an ions at low density o f the anions has been sub stantiated also in the M D sim ulation o f m olten (L i, K)C1 by Lantelm e and Turq [13], where the L i - C l distance is 212 pm at x K = 0.90 w hile 221 pm in pure LiCl. H ow ever, such a negative deviation has not been observed for b Na in (N a, C s ) N 0 3 [7] nor for b K in (K, C s ) N 0 3 [6 ]. Thus, this might be a p henom enon peculiar to foreign alkali cations at high concentra tion o f R b N 0 3. A lso b u should be m easured under such con d ition . T he reason for the negative devia tion o f £ Na and b K at high concentration o f R b N 0 3 rem ains to be investigated. Figure 3 sh ow s that, even though b Rb in the m olten system s (M , R b ) N 0 3 (M = Li, N a, K and Cs) is well expressed in the form o f (1), the parameters A , V0 and E are som ew hat different from system to system . Figure 3 seem s to indicate also that in the system s where M = Li, N a and K, the agitation effect [6 ] by the M + ions on the inter nal m obilities o f Rb + ions m ight occur. A t a given molar volu m e, i.e. num ber density o f N O f ions, the agitation effect becom es greater in the order L i+ < N a + < K + . This is presum ably because, at a fixed m olar volu m e, the m ole fraction o f these agitator ions is in this order. A t low m olar volum e b Rb deviates negatively from ( 1 ), which is attributable to the free space effect [6 ]. This work was financially supported by the G rant-in-A id for Special Project Research N o. 61134043 from the M inistry o f E ducation, Japan. O ne o f us (C . Y .) gratefully acknow ledges the Ishizaka Scholarship. [1] R. Takagi, K. Kawamura, and I. O kada, Z. Naturforsch. 39a, 759 (1984). [2] A. Klemm, H. Hintenberger, and P. Hoernes, Z. Naturforsch. 2 a , 245 (1947). [3] A. Ekhed and A. Lunden. Z. N aturforsch. 3 4 a , 1207 (1979). [4] J. Perie and M. Chemla, C. R. Acad. Sei. Paris 250, 3986 (1960). [5] I. O kada, R. Takagi, and K. Kawamura, Z. Naturforsch. 3 4a, 498 (1979). [6] C. Yang, R. Takagi, and I. O kada, Z. Naturforsch. 38a, 135 (1983). Fig. 2. The reciprocal of bK vs. molar volume in the molten binary systems (K, M ')N 0 3; A: M' = Li [14], Li [15], o : Na [6], €>: Na [16], <J: Na [17], ffl: pure K N 0 3 , V: Rb [this work], () : Cs [6]. 1020 C. Yang and I. Okada • Internal Cation M obilities in the System (K, R b )N 0 3 [7] C. Yang, R. Takagi, and I. Okada, Z. N aturforsch. 3 5a, 1186 (1980). [8] V. Ljubimov and A. Lunden, Z. N aturforsch. 2 1 a , 1592 (1966). [9] K. Kawamura, I. O kada, and O. Odawara, Z. Naturforsch. 30a, 69 (1975). [10] G. J. Janz, V. Krebs, H. F. Siegenthaler, and R. P. T. Tomkins, Phys. Chem. Ref. D ata 1, 581 (1972). [11] 1. O kada, R. Takagi, and K. Kawamura, Z. N aturforsch. 3 5 a , 493 (1980). [12] I. O kada, R. Takagi, and K. Kawamura, Z. N aturforsch. 36a, 381 (1981). [13] F. Lantelme and P. Turq, J. Chem. Phys. 77, 3177 (1982). [14] A. Lunden, J. H abasaki, and I. Okada, Z. Naturforsch. 42a, 683 (1987). [15] F. Lantelme and M. Chemla, Electrochim. Acta 10, 663 (1965). [16] F. Lantelme and M. Chemla, Bull. Soc. Chim. Fr. 1963, 2200. [17] E. P. Honig and J. A. A. Ketelaar, Trans. Faraday Soc. 62, 190 (1966).