974

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 6, pp. 974–979. © Pleiades Publishing, Inc., 2009.Original Russian Text © T.V. Gubanova, E.I. Frolov, E.G. Danilushkina, I.K. Garkushin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 1037–1042.

METHODS AND REAGENTS

The title quaternary system was investigated by thedifferential thermal analysis (DTA). A Pt–Pt/Rh (10%Rh) thermocouple served as a temperature sensor, anda KSP-4 potentiometer was as a recording device.Freshly calcined

Al

2

O

3

was used as an indifferent sub-stance. Cooling rates were 12–15 K/min. The systemwas investigated in the temperature range

350–900°ë

.All compositions are expressed in molar percent, andtemperatures are expressed in degrees Celsius. Thebatch weight was 0.2 g.

The starting reagents (high purity grade

Li

2

SO

4

,chemically pure grade LiBr and

Li

2

MoO

4

, and pure foranalysis LiF) were preliminary calcined or fused(LiBr).

The specific enthalpy of melting was determined byquantitative DTA. A DTA setup with the thermocoupleattached to the crucible bottom was used for the mea-surements. Three cooling and heating curves wererecorded for the eutectic composition under study anda reference (

Na

2

MoO

4

, polymorphic transformation at

451°ë, 113

kJ/kg). The areas of DTA peaks wererestricted according to the recommendations of theInternational Confederation of Thermal Analysis andCalorimentry [1]. The specific enthalpy of melting wascalculated from [2]:

kJ/kg

, (1)

where is the specific enthalpy of the reference

whose phase transition temperature is close to the stud-ied composition, kJ/kg;

S

E

,

and

S

ref

are the areas of the

∆mHE ∆tHref

SE

Sref-------

TE

T ref--------⋅ ⋅= ,

∆tHref

DTA peaks corresponding to melting of the eutecticcomposition and reference, respectively; and

T

E

,

and

T

ref

are the melting point of the eutectic compositionand the phase-transition temperature of the reference,respectively, K. The final value of enthalpy was foundas the average of three measurements. The specificenthalpies of melting were determined accurate to

±

5%

.

EXPERIMENTAL

The experiment in the Li

||

F, Br,

SO

4

, MoO

4

systemwas designed according to the rules of the projectionthermographic method [3]. The data on the phase trans-formations of individual substances were taken from[4]. All binary subsystems of the

LiF–LiBr–Li

2

SO

4

–Li

2

MoO

4

quaternary system, were investigated in [5–7].All ternary systems were investigated in [8–11]. Allsystems are eutectic, and complex formation reactionsare absent in them. The systems containing lithium sul-fate are characterized by the presence of its

α

-

(high-temperature) and

β

-

(low-temperature) polymorphs.The data for the binary and ternary systems are presentedin the table and are plotted on the development of the facesof the concentration tetrahedron (Figs. 1, 2).

Proceeding from the arrangement of the invariantequilibrium points in the systems of lower dimension,we chose, in the crystallization volume of lithium bro-mide (where the liquid solubility of components is eas-ier), the two-dimensional polytherm

a

=

[80.0% LiBr +20.0% Li

2

SO

4

],

b

= [80.0% LiBr + 20.0% LiF],

c

=[80.0% LiBr + 20.0%

Li

2

MoO

4

] (Figs. 2, 3). Further, inthis section, we chose the one-dimensional polythermaljoin

CD

where

C

= 80% LiBr + 14.0% LiF + 6.0%

Investigation of the LiF–LiBr–Li

2

SO

4

–Li

2

MoO

4

Quaternary System

T. V. Gubanova, E. I. Frolov, E. G. Danilushkina, and I. K. Garkushin

State General Institution of Higher Professional Education Samara State Technical University, ul. Galaktionovskaya 41, Samara, 443010 Russia

Received February 4, 2008

Abstract

—Phase equilibria in the

LiF–LiBr–Li

2

SO

4

–Li

2

MoO

4

system have been investigated by differentialthermal analysis. The eutectic composition has been determined (mol %): LiF, 13.3; LiBr, 62.0;

Li

2

SO

4

, 15.4;and

Li

2

MoO

4

, 9.3. The melting point is

415°ë

, and the ehthalpy of melting is 200 kJ/kg.

DOI:

10.1134/S0036023609060229

PHYSICOCHEMICAL ANALYSIS OF INORGANIC SYSTEMS

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

Vol. 54

No. 6

2009

INVESTIGATION OF THE LiF–LiBr–LiSO

4

–LiMoO

4

975

Characteristics of invariant points in binary and ternary subsystems in the LiF–LiBr–Li

2

SO

4

–Li

2

MoO

4

system

System Point

Content of components, mol %

Melting point,

°

C

1 2 3

LiF–LiBr [5] Eutectic 23.0 77.0 467

LiF–Li

2

SO

4

[6] EutecticPeritectic

41.0 26.0

59.074.0

530575

LiF–Li

2

MoO

4

[6] Eutectic 38.0 62.0 609

LiBr–Li

2

SO

4

[7] EutecticPeritectic

75.030.5

25.069.5

480575

LiBr–Li

2

MoO

4

[8] Eutectic 73.0 27.0 450

Li

2

SO

4

–Li

2

MoO

4

[6] Eutectic 62.0 38.0 581

LiBr–Li

2

SO

4

–Li

2

MoO

4

[8] EutecticPeritectic

65.02.0

14.062.0

21.036.0

421575

LiF–Li

2

SO

4

–Li

2

MoO

4

[9] EutecticPeritectic

30.11.5

43.461.0

26.537.5

501575

LiF–LiBr–Li

2

MoO

4

[10] Eutectic 18.0 72.0 10.0 444

LiF–LiBr–Li

2

SO

4

[11] Eutectic 21.45 61.0 17.55 423

* Figures 1, 2, and 3 denote the ordinal number of the salt in the system.

976

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

Vol. 54

No. 6

2009

GUBANOVA

et al.

Li

2

SO4; D = 80% LiBr + 14% LiF + 6.0% Li2MoO4

(Figs. 3, 4).

From the phase diagram for the CD join, we deter-

mined the projection of the quaternary eutecticpoint, and from the composition of the projection, wecalculated the concentration ratio for the lithium sulfateand molybdate components in the quaternary eutectic.

Consecutive investigation of the joins

(Figs. 3, 5) and LiBr– (Fig. 6), gave us the con-stant component ratio LiF : Li2MoO4 : Li2SO4 in thequaternary eutectic in the abc section and the composi-tion of the quaternary invariant point: 13.3% LiF,62.0% LiBr, 15.4% Li2SO4, and 9.3% Li2MoO4. Thephase reaction corresponding to the eutectic is L LiF + LiBr + Li2SO4 + Li2MoO4.

E

b –– EE

–EE

The concentration polyhedron of the LiF–LiBr–Li2SO4–Li2MoO4 system consists of the crystallizationvolumes of fluoride, bromide, and α- (high-tempera-ture) and β- (low-temperature) polymorphs of lithiumsulfate, and lithium molybdate (Fig. 1).

The specific enthalpy of the eutectic compositioncalculated from the results of three measurements was200 kJ/kg.

We investigated the phase complex of the LiF–LiBr–Li2SO4–Li2MoO4 system and experimentally deter-mined the composition, melting point, and enthalpy ofmelting of the alloy corresponding to the eutectic in theLiF–LiBr–Li2SO4–Li2MoO4 system. The compositioncan be used as a working body of heat storages and amolten electrolyte of chemical current sources.

LiBr

a b480° 467°

c

421° 415°

575°

575°

530°

501°

575°

609°

LiFLi2SO4858°

Li2MoO4702°

849°

581°

550°

Fig. 1. Schematic crystallization volumes for the LiF–LiBr–Li2SO4–Li2MoO4 system.

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 6 2009

INVESTIGATION OF THE LiF–LiBr–LiSO4–LiMoO4 977

LiBr

a b480° 467°

575°

575°

LiFLi2SO4858° 849°

550°

E2

p

P1

P2

E4

E1

E3

a

c c

b

LiBr550°

LiBr550°

467°

450°450°

480°

581°575°

575°

530°

501°

609°

p575°

p

421°

Li2MoO4702°

423°

444°

Fig. 2. Development of the faces of the concentration tetrahedron for the LiF–LiBr–Li2SO4–Li2MoO4 system.

20% LiF

20% Li2SO4

80% LiBr

421°

20% Li2MoO480% LiBr

80% LiBr

E4E

E2

E3

a

C

c bD

423°

E

444°

Fig. 3. Phase diagram for the polytherm ‡bÒ of the LiF–LiBr–Li2SO4–Li2MoO4 system.

978

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 6 2009

GUBANOVA et al.

L

L + LiF

L + LiF + LiBr

L + LiF +LiBr + β-Li2SO4

L + LiF + LiBr + Li2MoO4

LiF + LiBr + β-Li2SO4 + β-Li2MoO4

T, °C500

450

400C

0 1 2 3 4 5 6D

444°

Composition, mol % Li2MoO4 6% Li2MoO4

E4

6% Li2SO414% LiF80% LiBr

14% LiF80% LiBr

E3

E

421°

Fig. 4. Phase diagram for the CD of the LiF–LiBr–Li2SO4–Li2MoO4 system.

L

L + LiF

L + LiF + β-LiBr

LiF + LiBr + β-Li2SO4 + Li2MoO4

T, °C500

450

400

Composition, mol % LiF20% LiF80% LiBr

E

b 16 12 8 4

E

Fig. 5. Phase diagram for the polytherm of the LiF–LiBr–Li2SO4–Li2MoO4 system.b –– EE

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 6 2009

INVESTIGATION OF THE LiF–LiBr–LiSO4–LiMoO4 979

L

L + LiF

LiF + LiBr + β-Li2SO4 + Li2MoO4

T, °C

415°

Composition, mol % LiBr

LiBr

E

550

500

450

400

100 95 90 85 80 75 70 65 60

E

55

Fig. 6. Phase diagram for the invariant LiBr– of the LiF–LiBr–Li2SO4–Li2MoO4 system.E E–

ACKNOWLEDGMENTS

This work was supported by the Project for Analyt-ical Departmental Target Program on the Developmentof the Scientific Potential of the Higher School (years2006–2008).

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