History of Electroanalytical Chemistry in Molten Salts - American

Chapter 28

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History of Electroanalytical Chemistry in Molten Salts H. A. Laitinen Department of Chemistry, University of Florida, Gainesville, F L 32611 The earliest electroanalytical measurements in molten salts were based on potentiometry using the oxygen electrode to study high temperature acidity and basicity. This electrode is interesting in being applicable only at temperatures above 500°C. At temperatures in the 300-500° range, especially in chloride melts, a large number of metal-metal ion electrodes are useful, including the transition metals and noble metals. Beginning in the 1950's, the scope of electroanalytical measurements has been greatly broadened to include steady state and cyclic voltammetry, coulometry, chronopotentiometry, classical and pulse polarography, and AC impedence measurements. Special problems associated with such measurements include melt purification, metal-glass seals, and porosity effects. Stationary, dropping, and rotating disk electrodes have all been used successfully. While molten salt electrochemistry dates back to the time of Sir Humphry Davy and Michael Faraday, electroanalytical measurements in such systems are of much more recent origin. In such measurements we are primarily interested in solutes in dilute solutions rather than in properties such as activity coefficients or conductivities of major components. Molten salt solvents are almost always mixtures rather than pure compounds and therefore there is literally an infinite array of possible solvents. Because of the experimental difficulties associated with molten salts, it is to be expected that the application of electroanalytical techniques lagged behind the corresponding application to aqueous and even non-aqueous solutions. Potentiometry was the earliest electroanalytical technique applied to molten salts, no doubt because it presented no special problems outside of thermoelectric effects. Interestingly, the scope of potentiometry in high tempera0097-6156/89/0390-0417$06.00/0 © 1989 American Chemical Society

In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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ture systems has turned out to be broader than at ambient temperatures because of the wider variety of reversible electrode reactions at high temperatures. For the various electroanalytical techniques beyond potentiometry, molten salt solvents present several types of special problems depending on the nature of the solvent. First and foremost is the problem of purity. Salts used as solvents are at a much higher concentration than those used as supporting electrolytes in aqueous or non-aqueous solutions and special methods often had to be developed to decrease moisture and trace metal contamination to acceptable levels. In addition, possible reactions such as pyrohydrolytic decomposition or reactions of the melt constituents with containing vessels or components such as insulating materials or salt bridges need to be considered. In general, the simpler the method from the viewpoint of technique the earlier it was applied, but another factor, namely the importance of the solvent system with regard to applications, determined the amount of effort expended. Methods requiring insulation of electrodes and provision for reproducible mass transport to electrodes of known area tended to be developed later than those without such requirements. Thus chronopotentiometry could be applied using a simple flag type electrode suspended from a wire and this method has proven to be relatively much more important in molten salts than in aqueous solutions, especially in exploratory research. Cyclic voltammetry has proven to be the "workhorse" in more detailed mechanistic studies once the solvent purification has been worked out. In contrast, rotating disk electrodes, thin layer electrochemistry chemically modified electrodes, and spectroelectrochemistry have received relatively few applications because of special problems of technique. Each solvent system presents its own problems of purification, insulation, and materials of construction, so it is convenient to consider various types of molten salt solvents in turn. Within each type we shall consider the various electroanalytical techniques with emphasis on the historical development rather than on exhaustive coverage. Oxides, Hydroxides, Carbonates, Silicates, Borates, etc. The earliest electroanalytical measurements were concerned with studies of high temperature acidity in relatively alkaline systems. The oxygen electrode has been used since 1912 (1), and provides an interesting example of an electrode more useful at temperatures of the order of 1000° C than at room temperature. Pioneering work was done by Treadwell (2) in 1916 and Lux (3) in 1939. Flood and Forlund (4) discussed the dependence of potential on oxide ion concentrations. Flood, Forlund and Motsfeld (5) in 1952 and Antipin (6) in 1955 showed that the potential of a platinum electrode surrounded by oxygen and immersed in an alkaline melt gave reproducible potentials corresponding to oxide activities in the melt. At lower temperatures, the oxygen electrode has proven to be of more limited applicability. In 1948 Rose et al. (7) used oxygen electrodes at 400-700° in molten NaOH, and in 1958 Hill et al. (8) measured formation potentials of oxides by using an oxygen electrode



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against a metal coated with its oxide in a eutectic mixture of lithium and potassium sulfates containing dissolved CaO at temperatures of 550-750°C. Attempts to measure reversible oxygenoxide potentials in LiCl-KCl containing lithium oxide were unsuccessful at 400-450° (9). In 1963, an important development was the zirconia membrane electrode showing ionic conductivity due to oxide ion (10). This electrode, initially composed of calcium oxide and zirconia, later has appeared in other forms, notably zirconia-yttria and zirconiathoria. It has proven effective for oxide ion activity measurements over an extremely wide range at temperature of 1000° or higher, but it is of limited use at temperatures below 500° because of excessive resistance. Relatively few electroanalytical measurements beyond oxide ion activity have been made in alkaline melts, although in 1967 Bartlett and Johnson (11) used a Ag(I)/Ag reference electrode to measure the potentials of a few electrodes in lithium carbonate-sodium carbonate melts and for steady state voltammetry. Alkali Metal Chloride Melts Alkali metal chlorides have received a great deal of attention because of their importance in applications such as metallurgy and high temperature batteries. Electrochemically they are interesting because they have moderate melting points, they are excellent solvents for many metal chlorides through the formation of chlorocomplexes, they are reasonably stable towards oxidants and reductants, and can be easily purified. LiCl-KCl eutectic has been widely used because of its moderate melting point, 352°C. Electroanalytical applications were of limited value until a reliable purification method, involving vacuum and fusion in an HC1 atmosphere was worked out (12). If the pyrohydrolysis of moist LiCl is prevented the melts can be used in Pyrex or silica vessels. Osteryoung (13) described a Pt(II)/Pt reference electrode that can be easily generated coulometrically and used at temperatures up to 500°C. Liu used this reference electrode to establish an electromotive force series of 26 entries at 450°C (14), and later entries were added by Pankey (15) and Plambeck (16). It was found that a wide variety of metals, including transition metals and noble metals exhibit reversible potentials against their lowest valence ions, and that a number of redox couples in solution can also be measured.. Halogen/halide ion electrodes, and two types of hydrogen electrode, namely hydrogen/HCl and hydrogen/hydride ion were successfully used (17). These measurements are of analytical significance because at low concentrations (below 0.01 mole fraction) the activity coefficients remain constant, so that the Nernst equation can be used to measure ion concentrations. Laitinen, Tischer, and Roe (18) described a novel application of potentiometry to measure the total concentration of metal ions more noble than cadmium by using molten cadmium to displace these metals and measuring the potential of the cadmium electrode. In a similar way, they estimated the metals more noble than zinc by measuring the potential of the Zn(II)/Zn electrode. Magnesium was used to purify the melt of metals more



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noble than magnesium, but of course at the cost of introducing an equivalent concentration of Mg(II) (of the order of millimolar) into the melt. The ultimate in displacement purification is to use a porous tungsten electrode containing molten lithium to displace less active metals by internal electrolysis (17). Flengas and Ingraham, beginning in 1956, measured the potentials of 14 metals against their ions using a silver/silver chloride reference electrode in a 1:1 mole ratio KCl-NaCl melt at temperatures of 700-900°C, and reported activity coefficient variations at higher concentrations (19). Delimarskii and Markov (20) and Laity (21) have reviewed other potential measurements in melts. As compared with potentiometry, voltammetry presents special experimental problems, because of the necessity for insulation of a microelectrode of a reproducible surface area. The most common metal seals are glasses, which become increasingly conductive at higher temperatures. Lead glass compositions have especially good properties for sealing to metals, but must be avoided due to the cathodic deposition of lead (22). Voltammetry also places stringent demands on solvent purity. In 1954, Black and DeVries (23) used platinum microelectrodes in LiCl-KCl melts to record polarograms (voltammograms) of several metals. From the low decomposition potentials they reported, it is evident that the melts were contaminated with hydroxyl ion and water. Laitinen and coworkers (22) took care to purify the solvent and used simple microelectrodes of platinum sealed glass to record steady state voltammetric curves for a large number of metal ions using a slow polarization rate. During the early 1950's, cyclic voltammetry and linear sweep voltammetry were still in their infancies. While the limiting currents were not highly reproducible for exact work, the results proved to be quite useful in establishing the stable oxidation states of the elements and in estimating the redox potentials of many metal ion systems. Maricle and Hume (24) were able to extend the temperature range of such measurements to 740°C in molten NaCl-KCl by using a tungsten electrode sealed in Vycor. In this way the limitation of excessive conductivity of the glass seal was avoided. They found the limiting currents to be insensitive to scan rate because of the rapid establishment of a diffusion-convection steady state and reported a precision of 5 to 8%. While tungsten is less noble than platinum and therefore not applicable for anodic processes, it is advantageous in the cathodic region, especially for the deposition of several liquid metals that alloy with Pt but not with W. For example, lithium shows an abnormally low reduction potential at Pt because of alloying. Similar difficulties are observed with several other low melting metals, such as Cd, Pb and Zn and Al (18). Some disagreements have arisen as to the shapes of rising portions of voltammetric waves for metal deposition of solid electroes. For example, Panchenko (25) reported S-shaped symmetrical curves usually designated as Heyrovsky-Ilkovic curves for the deposition of Ag, Pb, and Cd on Pt from molten KCl, whereas Laitinen et al. (22) and Maricle and Hume (24) reported the unsymmetrical curves expected for the deposition of a product at constant activity. It appears that the apparent symmetry, which is



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a non-steady state phenomenon, can be caused by impurities in the melt and also by alloying of the plated metal with the electrode material. For example, Gaur and Behl (26) and Delimarskii and Kuz'movich (27) found both types of behavior depending on the metal being deposited. Cyclic voltammetry was introduced relatively late because its extreme sensitivity places severe demands upon melt purity, especially at the high scan rates required to avoid convection effects at stationary electrodes. The 1959 work of Johnson (28) was limited to relatively low scan rates, while recent work in our laboratory (29) and elsewhere has been successful up to scan rates of at least 10 volts/second. Chronopotentiometry is an important molten salt technique because it can be used with electrodes of relatively large areas, such as simple flag electrodes without an insulating seal. By using current-reversal chronopotentiometry, preliminary diagnostic work to determine whether the electrode reaction product is soluble or insoluble, and whether the electrode reaction is reversible or irreversible has proven to be convenient, especially for complex reactions such as the reduction of chromate (30). The important restriction of a short transition time to avoid convective disturbance of the diffusion layer was established in 1957 by Laitinen and Ferguson (31) who evaluated diffusion coefficients of several metal ions in LiCl-KCl at 450°C. In 1963, Stromatt (32) used the same technique in NaCl-KCl melts at 716°C to study the reduction of uranium (VI). Coulometry represents a simple method of quantitative additions to molten salt systems once the electrochemical processes have been established. For example, Laitinen and Liu (14) studied the Nernst equation behavior of a number of metals against their ions by generating the ions coulometrically to form a series of solutions of increasing concentration. Coulometric titrations can be conveniently carried out by electrolytic generation of a reagent and following the course of the titration potentiometrically or amperometrically. In 1958, Laitinen and Bhatia (33) generated iron(III) as an oxidant for Cr(II) or V(II) in LiCl-KCl and followed the titration curves potentiometrically, amperometrically or biamperometrically. Of the three methods, the biamperometric method proved to be most sensitive. It happens that iron (III) chloride is relatively volatile and that the coulometric method therefore has distinct advantages over the use of a standard solution. The rotating disk electrode (RDE) was used in LiCl-KCl melts by Delimarskii et al. (34) as early as 1960. The RDE, although more complex mechanically than stationary electrodes, is an "absolute" method which offers an approach to evaluating diffusion coefficients. In 1955, Laitinen and Osteryoung (35) reported on impedance measurements on platinum electrodes in dilute solutions of metal ions in LiCl-KCl. Platinum(II) showed nearly the behavior expected for a reversible electrode process, while for Co(II) and Ni(II) some anomalous behavior qualitatively attributed to adsorption and underpotential deposition was observed. In 1957, Laitinen and Gaur (36) refined the measurements and used a correction for excessive



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admittance due to adsorption to estimate exchange currents. In 1960, Laitinen, Tischer, and Roe (18) evaluated exchange currents for several metal ions using a voltage step method and a double pulse galvanostatic method. Again, some anomalies attributable to ion adsorption were observed. Zajicek and Hubbard (37) appear to have been the only investigators who have used thin layer electrochemistry techniques in molten salts. They successfully studied the Cr(III)/Cr(II) and Pt(II)/Pt couples in LiCl-KCl melts at 450°C and Ag(I)/Ag in nitrate melts. Evidently because of the experimental difficulties of this technique it has not been pursued by others. Chloroaluminate Melts Quite a variety of electroanalytical techniques have been used in chloroaluminate melts, dating back to 1942, when Yntema et al. (38) determined deposition potentials for a number of metal ions. Polarography with the dropping mercury electrode was described by Saito et al. in 1962 (39), and numerous papers on steady state voltammetry using platinum indicator electrodes have appeared since the work of Delimarskii et al. (40) in 1948. More advanced techniques have included linear sweep and cyclic voltammetry chronopotentiometry, and chronoamperometry. Although mixtures of aluminum chloride and alkali metal chlorides are attractive from the viewpoint of moderate melting points, early work in these solvents was plagued by difficulties due to lack of effective purification procedures and a lack of understanding of the acid-base properties of the solvents. Beginning in the late 1960's, removal of the last traces of water and of nobler metals by means of metallic aluminum yielded melts with low residual currents (41). Acid-base equilibria involving chloride ion donor-acceptor reactions were studied in 1968 by Tremillon and Letisse (42) by means of a potentiometric titration. Later electrochemical studies by Torsi and Mamantov (43) and by Osteryoung et al. (44) elucidated the acid-base equilibria involved in chloroaluminate melts containing an excess or deficiency of aluminum chloride over a wide range of temperatures. In 1974, Gilbert, Brotherton, and Mamantov (45) used chronopotentiometry in chloroaluminate melts to demonstrate the formation of a poorly conducting layer of Al2Cl6 at the surface of an aluminum anode and to demonstrate the reversible behavior of the aluminum electrode. Mamantov et al. (46) studied the oxidation and reduction of sulfur, selenium, and iodine beginning in 1975, and later suggested sulfur (IV) as an oxidant in molten salt batteries. In 1980, Mamantov, Norveil, and Klatt carried out what appear to be the first spectroelectrochemical experiments in chloroaluminate melts using optically transparent electrodes to observe absorption spectra of species formed at the electrode (47). Nitrate Melts Nitrate melts are experimentally convenient because of their low melting points and they were historically among the earliest for



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electroanalytical measurements beyond potentiometry, but they have proved to be of lesser importance than chloride or chloroaluminate melts. The dropping mercury electrode was used in LiNO3-KNO3 and LiNO 3 -NH 4 NO 3 -NH 4 Cl melts at 160°C by Nachtrieb and Steinberg (48) as early as 1948. Its use, of course, is limited to relatively lowmelting systems. Conventional polarograms were observed for several metal ions. In 1962, application of conventional polarography was made by Christie and Osteryoung (49) in LiNO 3 -KNO 3 eutectic at 160°C to study formation constants of chlorocomplexes. Stationary electrode voltammetry was used in nitrate melts as early as 1948 by Lyalikov and Karmazin (50), using a platinum microelectrode in the form of a "dipping" electrode with bubbles of an inert gas to produce a periodically fluctuating current. A similar electrode was used by Flengas (51) and by Bockris, et al. (52) in 1956. In 1960, Hills, Inman and Oxley (53) described an improved version of the dipping electrode, which of course is limited by relatively ill-defined mass transport conditions. Later work has involved linear sweep voltammetry as described by Hills and Johnson (54) in 1961 or steady state voltammetry with stationary electrodes by Swofford and Laitinen (55) in 1963. Jordan and coworkers, beginning in 1959 (56) performed several thermochemical titrations in nitrate melts including precipitation of silver halides and silver chromate, measuring the temperature change in an adiabatic system. Zambonin and Jordan (57) used voltammetry to study oxygen and peroxide species in 1967. The earliest report of the use of AC impedance measurements for measurement of electrode kinetics in melts appears to be that of Randies and White (58), who in 1955 measured charge transfer rate constants for nickel ions in nitrate melts and determined the effects of added moisture. Interest in nitrate melts has diminished in recent years due to the emergence of other low melting systems. Fluoride Melts Although molten fluorides have long been important industrially, electroanalytical measurements have been relatively slow to emerge because of the experimental difficulties of purification and handling these melts. Grjotheim (59) in 1957 reported measurements of the electrode potentials of metal-metal ion couples of NaF-KF at 850°C using Ni(II)/Ni as a reference electrode. This reference electrode has been used in most subsequent work. Beginning in 1963, Manning and Mamantov (60) made several steady state and linear sweep voltammetric studies in LiF-NaF-KF eutectic (mp 454°C). In 1965, Senderoff, Mellors, and Reinhart (61) used the same solvent to study the chronopotentiometry of tantalum (V) at 650-850°C. In 1970 Jenkins, Mamantov and Manning, (62) measured several redox couples against Ni(II)/Ni as a reference electrode in LiF-NaF-KF and LiFBeF 2 -ZrF 4 at 500°C. The latter solvent, with added U(IV)-U(III), was of importance in the molten salt nuclear reactor and was later the subject of a number of electroanalytical studies, using chronopotentiometry and chronoamperametry as well as cyclic voltammetry



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and square wave voltammetry (63). Deserving special mention is the use of a lanthanum fluoride single crystal of the type used for ion selective electrodes as a separator for the Ni(II)/Ni reference electrode for the virtual elimination of liquid junction potentials in fluoride melts, described by Bronstein and Manning in 1972 (64) and used by Clayton, Mamantov, and Manning in several electroanalytical studies in fluoride and fluoroborate melts (65). The use of a rotating disk electrode in LiF-NaF-KF was attempted by Senderoff and Mellors in a study of the electrodeposition of refractory metals (66). The problem of insulation was approached by use of a pressure fitted boron nitride mounting for a tungsten electrode, but the RDE was abandoned in favor of chronopotentiometric measurements with stationary electrodes, which proved to be more practicable because of experimental simplicity. Recently, Tellenbach and Landolt (67) successfully used a similar RDE assembly in molten cryolite at 1020K, plating the tungsten electrode with gold or titanium boride. Ambient Temperature Molten Salts The first electroanalytical studies in molten salts at room temperature appear to have been made by Osteryoung et al. in 1975 (68), although the solvent derived from the early work of Hurley and Wier in 1951 (69), who studied mixtures of various N-substituted pyridinium halides with inorganic halides. In particular, they observed the electrodeposition of aluminum from a mixture of aluminum chloride and ethyl pyridinium bromide, which form a eutectic melting at -40°C. Gale and Osteryoung (70) in 1979 used potentiometry with an aluminum electrode to make acid-base studies of a room temperature melt of butylpyridinium choride-aluminum chloride mixtures. More recent work in this melt by Osteryoung et al. (71) has included rotating disk and ring disk electrodes and cyclic voltammetry with stationary electrodes to study the Fe(III)/Fe(II) system and by Mamantov et al. (72) for cyclic voltammetry and for Raman spectroscopic studies of sulfur species. This work has extended the field to applications in ambient temperature molten salt batteries. A related solvent, containing also antimony chloride, has been used by Mamantov et al. for cyclic voltammetric and spectrophotometric studies of the redox chemistry of hydrocarbons such as anthracene and perylene (73). Another ambient temperature melt system consisting of organic cation tetrachloroborates has recently been described by Mamantov et al. (74). Miscellaneous Melts In 1963, Caton and Freund (75) made preliminary voltammetric studies of a number of redox systems in molten alkali metal metaphosphates, but the work was limited by the lack of a reference electrode. In 1971 Wolfe and Caton (76) devised a silver reference electrode which was applied to potentiometric and chronopotentiometric studies in equimolar mixtures of sodium and potassium metaphosphates at 700°C of several redox couples. Diffusion coefficients and standard potentials were evaluated.



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A limited amount of electroanalytical work has been done in sulfate melts. The oxygen electrode has been mentioned above for alkaline melts. In 1961, Liu (77,78) applied potentiometry, chronopotentiometry and coulometric titrations in lithium sulfatepotassium sulfate melts at 625°C using a silver reference electrode. An electromotive force series of limited scope and voltammetric curves were reported in 1963 by Johnson and Laitinen (79) in a ternary alkali metal sulfate system at 550°C. A complication is the reduction of the sulfate ion at negative potentials. Melts containing magnesium chloride and alkali metal chlorides have received study going back to 1950 (80). An electromotive force series has been described by Gaur and Behl (26). Conclusion Electroanalytical techniques have made significant contributions over the years to our knowledge of the behavior of molten salt systems at temperatures ranging from room temperature to over 1000°C. A wide variety of melts have been investigated both from the viewpoint of fundamental studies of sensors and electrode processes and from the viewpoint of practical applications to battery systems, electroplating, and preparative electrochemistry.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Baur, E.; Ehrenberg, H., Z. Elektrochem., 1912, 18, 1002-1011. Treadwell, W.D. Z. Elektrochem., 1916, 22, 414-421. Lux, H. Z. Elektrochem., 1939, 45, 303-309; 1948, 52, 220-224; 1949, 53, 41-43. Flood H.; Forland, T. Acta Chem. Scand., 1947, 1, 592-604; Discussions Faraday Soc., 1947, 1, 302-307. Flood, H.; Forland, T.; Motzfeldt, K. Acta Chem. Scand., 1952, 6, 257-269. Antipin, L.N. Zh. Fiz. Khim., 1955, 29, 1668-1677. Rose, B.A.; Davis, G.J.; Ellingham, H.J.T. Discussions Faraday Soc., 1948, 4, 154-162. Hill, D.G; Porter, B.; Gillespie, Jr., A.S. J. Electrochem. Soc., 1958, 105, 408-412. Laitinen, H.A.; Bhatia, B.B. J. Electrochem. Soc., 1960, 107, 705-710. Bauerell, J.; Ruka, R. Paper presented at Pittsburgh meeting of the Electrochemical Society, 1963. Bartlett, H.E.; Johnson, K.E.; J. Electrochem. Soc., 1967, 114, 64-67. Laitinen, H.A.; Ferguson, W.S.; Osteryoung, R.A. J. Electrochem. Soc., 1957, 104, 516-520. Osteryoung, R.A. Ph.D. Thesis, University of Illinois, Illinois, 1954. Laitinen, H.A.; Liu, C.H. J. Am. Chem. Soc., 1958, 80, 10151020. Laitinen, H.A.; Plankey, J.W. J. Am. Chem. Soc., 1959, 81 , 1053-1058.


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ELECTROCHEMISTRY, PAST AND PRESENT L a i t i n e n , H.A.; Plambeck, J.A. J . Am. Chem. S o c . , 1965, 8 7 , 1202-1206. Plambeck, J . A . ; E l d e r , J . P . ; L a i t i n e n , H.A. J . E l e c t r o c h e m . S o c . , 1966, 113, 9 3 1 - 9 3 7 . L a i t i n e n , H.A.; T i s c h e r , R . P . ; Roe, D.K. J . E l e c t r o c h e m . S o c . , 1960, 107, 5 4 6 - 5 5 5 . F l e n g a s , S . N . ; Ingraham, T.R. J . E l e c t r o c h e m . S o c . , 1959, 1 0 6 , 714-721. Delimarskii, Y.K.; Markov, B.F. Electrochemistry of Fused S a l t s , t r a n s l a t e d by A. P e i p e r l , Sigma P r e s s , Washington, D . C . , 1961. L a i t y , R. i n R e f e r e n c e E l e c t r o d e s , Janz, G.; I v e s , B . , E d s . ; Academic: New York, 1961, p . 5 2 4 - 6 0 6 . L a i t i n e n , H.A.; Liu, C.H.; Ferguson, W.S. Anal. Chem., 1958, 30, 1 2 6 6 - 1 2 7 0 . B l a c k , E . D . ; D e V r i e s , T. A n a l . Chem., 1955, 2 7 , 9 0 6 - 9 0 9 . M a r i c l e , D . L . ; Hume, D . N . , A n a l . Chem., 1 9 6 1 , 33, 1 1 8 8 - 1 1 9 2 . Panchenko, I . D . Ukr. Khim. Z h . , 1955, 21, 4 6 8 - 4 7 1 ; 1956, 2 2 , 153-155. Gaur, H.C.; B e h l , W.K. J . E l e c t r o a n a l . Chem., 1963, 5, 2 6 1 - 2 6 9 . D e l i m a r s k i i , Y.K.; Kuz'movich, V. Zh. Neorgan. Khim, 1959, 4, 2732-2738. Johnson, K . B . ; Ph.D. T h e s i s , U n i v e r s i t y of London, 1 9 5 9 . Waggoner, J . R . ; u n p u b l i s h e d e x p e r i m e n t s , 1 9 8 2 . Propp, J . H . ; L a i t i n e n , H.A. A n a l . Chem., 1969, 4 1 , 6 4 4 - 6 4 9 . L a i t i n e n , H.A.; Ferguson, W.S. A n a l . Chem., 1957, 29, 4 - 9 . S t r o m a t t , R.W. J . E l e c t r o c h e m . S o c . , 1963, 1 1 0 , 1 2 7 7 - 1 2 8 2 . L a i t i n e n , H.A.; B h a t i a , B . B . A n a l . Chem., 1958, 30, 1 9 9 5 - 1 9 9 7 . Delimarskii, Y.K.; Panchenko, I.D.; Shilina, G.Y. Dopovidi Akad. Nauk. Ukr. R . S . R . , 1961, 2, 2 0 5 - 2 0 8 . L a i t i n e n , H.A.; Osteryoung, R.A. J . E l e c t r o c h e m . S o c . , 1955, 102, 5 9 8 - 6 0 5 . L a i t i n e n , H.A.; Gaur, H.C. J. E l e c t r o c h e m . S o c . , 1957, 1 0 4 , 730-737. Z a j i c e k , L . P . ; Hubbard, A.T. J . E l e c t r o c h e m . S o c . , 1969, 1 1 6 , 80C-82C. V e r d i e c k , R.G.; Yntema, L . F . , J . Phys. Chem., 1942, 4 6 , 3 4 4 352. S a i t o , M.; S u z u k i , S . ; Goto, H. Nippon Kagaku Z a s s h i , 1962, 8 3 , 883-886. D e l i m a r s k i i , Y.K.; S k o b e t s , E.M.; Berenblyum, L . S . Zh. F i z . Khim., 1948, 22, 1 1 0 8 - 1 1 1 5 . Anders, U.; Plambeck, J . A . Can. J . Chem., 1969, 4 7 , 3 0 5 5 - 3 0 6 0 . T r e m i l l o n , B . ; L e t i s s e , G. J. E l e c t r o a n a l . Chem., 1968, 17, 371-386. T o r s i , G.; Mamantov, G. I n o r g . Chem., 1971, 1 0 , 1900 ; 1972, 11, 1439. B o x a l l , L.G.; J o n e s , H.L.; Osteryoung, R.A. J . E l e c t r o c h e m . S o c . , 1973, 120, 2 2 3 - 2 3 1 . Gilbert, B.; B r o t h e r t o n , D . L . ; Mamantov, G. J. E l e c t r o c h e m . S o c . , 1974, 121, 7 7 3 - 7 7 7 . M a r a s s i , R.; Mamantov, G.; Chambers, J . Q . I n o r g . N u c l . Chem. L e t t . , 1975, 1 1 , 2 4 5 - 2 5 2 .


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50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61.

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RECEIVED August 9, 1988


History of Electroanalytical Chemistry in Molten Salts - American

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