Molten KF-AIF 3 System: A Study by Raman Spectroscopy

Abstract

Molten AIF₃-KF mixtures have been investigated in a wide composition range by Raman spectroscopy and with the use of a graphite windowless cell. The results of this study clearly show that the most intense spectrum components are made of three distinct bands whose intensities vary when the composition is changed. The most probable interpretation of our data is to consider the existence of an equilibrium between AIF₆^3–, AIF₅^2–, and AIF₄⁻. This explanation is a confirmation of the conclusions of recent papers suggesting the presence of these species in similar AIF₃-NaF mixtures. The presence of only one major polarized band for AIF₅^2– is explained by considering a fast exchange between the axial and equatorial fluoride at the elevated experimental temperature (1300 K). A quantitative analysis of the distribution of the fluoroaluminate species has been performed by decomposition of the Raman-band envelope. The calculated equilibrium constants (expressed in mole fraction units) for AIF₅^2– ⇌ AIF₄⁻ + F⁻ and AIF₆^3– ⇌ AIF₅^2– + F⁻ are K_A = 0.11 ± 0.01 and K_B = 5 ± 1, respectively. Compared with the NaF-AIF, system, these constants correspond to a stabilization of less coordinated fluoroaluminates when the size of the counterion increases.

Keywords

Aluminum fluorides Raman spectrometry Molten salts

Get full access to this article

View all access options for this article.

References

Grjotheim

Krohn

Malinovsky

Matiasovsky

and Thonstad

, Aluminium Electrolysis: Fundamentals of the Hall-Heroult Process (Aluminium-Verlag, Düsseldorf, 1982), 2nd ed.

Gilbert

and Materne

, Appl. Spectrosc. 44, 299 (1990).

Dewing

E. W.

, Proc. Electrochem. Soc. 86-1, 262 (1986).

Xiang

F. N.

and Kvande

, Acta. Chem. Scand. A40, 622 (1986).

Zhou

Hehua

, Ph.D. Thesis, NTH Trondheim, Norway (1991); IUK-rapport 1991:63.

Kolosov

E. N.

Sholts

V. B.

and Siderov

L. N

, Russ. J. Phys.Chem. 48, 1303 (1974).

Stebbins

J. F.

Farnan

Dando

and Tzeng

S. Y

, J. Am. Ceram. Soc. 75, 3001 (1992).

Ratkje

S. K.

Cyvin

S. J.

and Hafskjold

, Appl. Spectrosc. 47, 375 (1993).

Brooker

M. H.

and Papatheodorou

G. N

, in Advances in Molten Salts Chemistry, Mamantov

, Ed. (Elsevier, Amsterdam, 1983), Vol. 5, p. 60.

10.

Gilbert

Mamantov

and Begun

G. M

, Inorg. Nucl. Chem. Lett. 10, 1123 (1974).

11.

Young

J. P.

, Anal. Chem. 36, 390 (1964).

12.

Tixhon

Robert

and Gilbert

, unpublished data.

13.

Irish

D. E.

and Ozeki

, in Analytical Raman Spectroscopy, Grasselli

J. G.

and Bulkin

B. J

, Eds. (Wiley-Interscience, New York, 1991), Vol. 114, Chap. 4.

14.

Gilbert

Mamantov

and Begun

G. M

, Inorg. Nucl. Chem. Lett. 12, 444 (1976).

15.

Harland

, in Coordination Chemistry of Aluminium, Robinson

G. H.

, Ed. (VCH Publishers, New York, 1993), Chap. 1.

16.

Nakamoto

, Infrared Spectra of Inorganic and Coordination Compounds (Wiley-Interscience, New York, 1970), 2nd ed., p. 118.

17.

Hoskins

L. C.

and Lord

R. C

, J. Chem. Phys. 46, 2402 (1967).

18.

Gutowsky

H. S.

McCall

D. W.

and Slichter

C. P

, J. Chem. Phys. 21, 279 (1953).

19.

Muetterties

E. L.

and Phillips

W. D

, J. Am. Chem. Soc. 81, 1084 (1959).

20.

Turner

J. J.

Grevels

F. W.

Howdle

S. M.

Jacke

Haward

M. T.

and Klotbücher

W. E

, J. Am. Chem. Soc. 113, 8347 (1991).

21.

Robert

Materne

Tixhon

and Gilbert

, Vibrational Spectrosc. 6, 71 (1993).

22.

Shanon

R. D.

Chenevas

and Joubert

J. C

, J. Solid. State. Chem. 12, 16 (1975).

23.

Huglen

Cyvin

S. J.

and Oye

H. A

, Z. Naturforsch 34a, 1118 (1979).

24.

Kvande

, Ph.D. Thesis, NTH Trondheim, Norway (1979).

25.

Guzman

Grjotheim

and Ostvold

, Light Metals (Warrendale, Pennsylvania) 425 (1986).

26.

Gilbert

Mamantov

and Begun

G. M

, J. Chem. Phys. 62, 950 (1975).