THERMODYNAMIC PROPERTIES OF MANGANESE COMPOUNDS Текст научной статьи по специальности «Техника и технологии»

THERMODYNAMIC PROPERTIES OF MANGANESE COMPOUNDS

NOVRUZLU KHANiM ELCHiN

Master of Baku State University, Baku State University,Academician Z. Khalilov,

Baku Azerbaijan

Annotation. In order to study the ternary Mn-Sb-Te system by EHQ method, the thermodynamic properties of intermediate phases in external binary systems must be known. Values of the standard thermodynamic formation functions of the Sb2Te3 compound present in the Sb-Te system are known from the external Mn-Te(Sb), Sb-Te system. Although the heat capacities of the intermediate phases in the Mn-Te(Sb) systems in a wide temperature range are given in the literature, the values of the standard thermodynamic functions are not known. Considering this, thermodynamic properties of intermediate phases in Mn-Te(Sb) systems were first studied. For this, e.h.g. measurement method was used. 3d metals and intermetallic phases such as MnSb, MnBi, Mn2Sb formed by 5A subgroup elements are interesting technical materials [1]. After the discovery of iron-free ferromagnetic manganese alloys, these phases have been extensively studied by various authors and it has been determined that they have high ferromagnetic and magneto-optical properties.

Keywords. Determination of thermodynamic properties of manganese compounds by e.h.q. method.

Considering that these systems have less electropositive metal manganese, (Mn2+ + 2e ^ Mn; ф0 = -1,180V) density circuits were used for manganese in EHQ method. The scheme of the circuit was as follows:

(-)Mn(b)\qliserin + MnCl2 + KCl\Mn - Sb(Te)(b)(+) (A)

As the right electrode, samples of Mn-Sb(Te) systems homogenized at a temperature of 450K for a long time were taken. Taking into account the temperature dependence of the homogeneity areas of intermediate phases in Mn-Sb(Te) systems, the circuit e.h.q. the values were measured in the temperature range of 290^430K. As a result of measuring the e.h.c. of type (A) solidification circuits, it was found that the e.h.c. values measured at different temperatures are repeatable and the temperature dependence of these values is linear. This indicates that the composition of the intermediate phase remains constant in the given temperature interval and the circuit works in a rotating manner (when the solid state element operates in a rotating manner, equilibrium occurs at the boundary of all phases of the element and there is no diffusion potential in the circuit. To fulfill this requirement during E.h.c. measurements, the measurement must be made in such a way that, as a result, an electric current in the electrochemical circuit For this, the e.h.c. of the circuit must be measured by the compensation method. The measurement of the electromotive force of the electrochemical circuit using modern high-ohm digital voltmeters is practically a measurement by the compensation method [3] . Since the solid state circuit is rotating, the obtained e.h.c. measurements can be used for thermodynamic calculations. To perform thermodynamic calculations, the temperature dependences of e.h.c. using the method of least squares. measurements can be used for thermodynamic calculations. In order to perform thermodynamic calculations, the temperature

dependences of e.h.q. should be brought into the form of equations using the method of least squares.

i

E = a + ЬТ ±t[^ + Si(T -T)2]2 (1)

The results of measuring the e.h.c. of type (A) solidification circuits at different temperatures were brought to the form of equations of type (1) using the least squares method. Those equations are given in table 1.

Table 1. Mn-Sb(Te) systems temperature dependences of the e.h.g.s of (A) type solidification circuits for different phases

System content mol % Mn E,mV = a + bT ±2SE(T)

Mn-Sb 0-50 E = 260,14 + 0,056T 1 \6,4 , ,12 ±2 —+0,4 • 10-4(T - 350.1)2

55 E= 235.58 + 0.047 T ± 2 44 + 0.5 • 10-4(T - 348.3)2 34 y J 1 2

55-66,7 E= 75.7 + 0.012 T ± 2 [ - + 0.4-10-4(T- 348.5)2 34 y J 1 2

Mn-Te 0-33,3 E = 631.7 + 0.077 T ± 2 — + 8-10-4(T- 365.7)2 40 y J 1 2

33-50 E= 474.1 + 0.122T ± 2 — + 7 • 10-4(T - 366.7)2 40 y J 1 2

For MnSb, MmSb, MnTe2 and MnTe phases, the values of standard formation Gibbs energy, enthalpy and entropy were calculated (table 2). Corresponding thermodynamic quantities for Mn0.ssSb0.4s phase

AZ0 = (1-x) С

x2 A %Мп

dx

JX1 (1-x)2

determined by integrating the equation (table 2).

Table 2. intermediate phases in Mn-Sb(Te) systems standard thermodynamic generation functions and standard entropies

System Phase Content, mol%Mn -AfG0(298) -AfH0(298) 5°(298), С mol • К

kC/mol

Mn-Sb MnSb 50 53,47 ± 0,21 50,20 ± 0,87 66,64 ± 4,51

Mni+xSbi- 55 27.82 ± 0.12 26.15 ± 0.45 43.63±3.62

Mn2Sb 66,7 73.70 ± 0.41 69.46 ± 1.67 123.46±9.87

Mn-Te MnTe2 33,3 126.33 ± 0.88 121.90 ± 4.02 146.07±12.53

MnTe 50 112.4 ±0.86 106.70 ±3.90 100.69±11.27

In Table 2, the values of the standard entropies of the phases were calculated based on the equations of the formation reactions of the given phase from elementary substances. During the calculations, the experimentally found standard formation entropies of the phases and the standard entropies of the elemental substances manganese, stibium, and tellurium were used in the literature.

AfS0 (MnSb)= 10,81±1,23

с

mol K

AfS0 ( Mn0_55Sb0A5) = 5.6 ± 1.48 AfS0(Mn2 Sb) = 14.25 ± 4.24 AfS0 ( MnTe2) =14.89 ± 10.92 AfS0 (MnTe) =19.22±10.57

mol К С

mol К С

mol К С

mol K

50(Mn)=31.76; 50(Te)=49.71; S0(Sb)=45.69

с

molK

The MnSb phase is formed by the peritectic reaction liquid +Mn2Sb ^ MnSb at a temperature of 1102K. It has a homogeneity range of 50^54.5 mol% Mn in the temperature range of 300-1000K. NiAs type (f.qr. P63/mmc) forms a crystal lattice. In stoichiometric composition a=4.148(3); c=5.774Q)Â

To determine the thermodynamic properties of the MnSb compound (-)Mn(b)|in the electrolyt |(Mn-Sb)(b)(+)

с

e.h.c. of the solid state circuit values were measured in the temperature range of 295-420K. The temperature dependence of e.h.g. for MnSb was as follows:

E,V = 260,14 + 0,056T ±2

6,4

— + 0,4 • 10-4(T - 350,1)2 34

Values of partial molar thermodynamic properties of manganese were calculated from the temperature dependence of e.h.c. using known thermodynamic relationships and the equation of the potential-forming reaction from the state diagram of the Mn-Sb system and the equation of the potential-forming reaction from the state diagram of the Mn-Sb system (Mn+Sb^MnSb) were

determined. Based on them (as well as the values of S098(Mn) = 31,76; S098(Sb) = 45,69-

the following values were obtained for the MnSb compound:

с

mol-K

AfG0(298) =

kC

53,47 ± 0,21—;

mol kC

AfH0(298) = -50,20 ± 0,87 f^;

S 0(298) = 66,64 ±4,51

mol C

mol-K'

There are two intermediate phases in the Mn-Sb system: MniSb and MnSb. MniSb melts cogruently and the distectic temperature is 1174K. The homogeneity area of the MmSb phase is maximal at the temperature of 1091K and is ~1 at.%. In the temperature range of 300-450K, this phase has practically no homogeneity area.

To determine the thermodynamic properties of the compound MmSb

(-)Mn(b)|in the electrolyt Mn2+I(Mn-Sb)(b)(+) (A)

e.h.c. of the solid state circuit values were measured in the temperature range of 295-420K.

As a result of measuring the e.h.c. of type (A) solidification circuits, it was found that the e.h.c. values measured at different temperatures are repeatable and the temperature dependence of these values is linear. [2] This indicates that the composition of the intermediate phase remains constant in the given temperature range and the circuit operates in a rotating manner. Since the solid state circuit is rotating, the obtained e.h.g. measurements can be used for thermodynamic calculations. Temperature dependence of e.h.g. using the method of least squares to perform thermodynamic calculations the following equation can be obtained

E,V = 75.7 + 0.012T ± 2 [37 + 0-4 • 10-4(T - 348.5)2]

1

212

The values of partial molar thermodynamic properties of manganese were calculated from the

temperature dependence of e.h.g. using known thermodynamic relations. Using these and the

£

corresponding values for the Mn0,55Sb0,45 phase (also S2098(Mn) = 31,76; S0298(Sb) = 45.69^) . Based on the equation of potential formation reaction (Mn + 2.857 Mn0 55Sb0 45 ^ 1.286 MmSb) (Mn + 2.857 Mn0 55Sb0 45 1.286 MmSb) the values of standard formation Gibbs energy, enthalpy and standard entropy for compound MmSb were calculated:

AfG0(298) = -73.70 ± 0.41 —;

mol kC

AfH0(298) = -69.46 ± 1.67 f^; S0(298) =123.46 ±9.87

C

mol

mol-K'

Manganese tellurides are interesting technical materials. After the discovery of iron-free ferromagnetic manganese alloys, these phases were widely studied by various authors and it was determined that they have high ferromagnetic and magneto-optical properties [5]. Manganese tellurides are interesting technical materials. After the discovery of iron-free ferromagnetic

ОФ "Международный научно-исследовательский центр "Endless Light in Science"

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manganese alloys, these phases were widely studied by various authors and it was determined that they have high ferromagnetic and magneto-optical properties.

There are two intermediate phases in the Mn-Te system:MnTe and MnTe2. MnTe phase melts incongruently at 1424 K, MnTe2 phase at 1012 K. The homogeneity areas of these phases are practically independent of temperature in the temperature range of 300-450K and are ~1 at.%. MnTe phase melts incongruently at 1424 K, MnTe2 phase at 1012K [4]. The areas of homogeneity of these phases are practically independent of temperature in the temperature range of 300-450K and are ~1 at.%. In order to determine the thermodynamic properties of MnTe and MnTe2 compounds, the e.h.g. values were measured in the temperature range of 290-430K.

As a result of measuring the e.h.c. of type (A) solidification circuits, it was found that the e.h.c. values measured at different temperatures are repeatable and the temperature dependence of these values is linear. This indicates that the composition of the intermediate phase remains constant in the given temperature range and the circuit operates in a rotating manner. Since the solid state circuit is rotating, the obtained e.h.c. measurements can be used for thermodynamic calculations. In order to perform thermodynamic calculations, the temperature dependences of e.h.q. should be brought into the form of equations using the method of least squares.

S2

— + sl(T-Ty

n

E = a + bT ±t

The temperature dependence of e.h.g. for MnTe2 and MnTe was as follows:

1

V = 631.7 + 0.077 T ± 2 + 10-4(T - 365.7)2]2

i

E,V= 474.1 + 0.122T ± 2 [^ + 7 • 10-4(T - 366.7)2]2

The values of partial molar thermodynamic properties of manganese were calculated from the temperature dependence of e.h.g. using known thermodynamic relations. Equations of potential forming reactions were determined from the state diagram of the Mn-Te system. (Mn + 2Te^ MnTe2, Mn + MnTe2^ 2MnTe) Based on them, S098(Mn) = 31,76; S098(Te) = 49.71^^ the

values of standard formation Gibbs energy, enthalpy and standard entropies for MnTe2 and MnTe compounds were calculated. For the MnTe2 compound:

kC

AfG0(298) = -126.33 ± 0.88- ,

J v J moV

AfH0(298) = -121.90 ± 4.02 —;

J mol

p

S0(298) =146.07±12.53 —

For the MnTe compound:

AfG0(298) = -112.4 ± 0.86—;

J mol

AfH0(298) = -106.70 ± 3.90—;

J mol

S0(298) = 100.69 ± 11.27^—.

y J ~ mol K

REFERENCES

1. 9liyev Z.C., i.M.§ixiyev., Babanli M.B. Sb2Te3-C6bb-Te sisteminda faza tarazliqlari // Kimya problemlari, 2007, №2,s.304-307.

2. Mammadov A.N., Bagirov Z.B., Quliyeva С.Э. Qeyri-molekulyar birla§mali sistemlarin termodinamikasi. Baki: Elm, 2006, 191s. Mammadov A.N., Bagirov Z.B., Quliyeva С.Э. Qeyri-molekulyar birla§mali sistemlarin termodinamikasi. Baki: Elm, 2006, 191s.

3. Бабанлы М.Б., Мусаева С.С.,Алиев З.С.Термодинамическое исследование халькоиодидов сурьмы методом ЭДС. // Елми Ясярляр, Фундаментал елмляр, 2007, №4,Ъилд ВЫ с.85-89.

4. База данных термические константы веществ., Электронная версия под. ред. В.С.Юнгмана, 2006 г.,http://www.chem.msu.su/cgi-bin/tkv.

5. Kanatzidis M.G. The role of solid state chemistry in the discovery of new thermoelectric materials. // Semiconductors and semimetals. / Ed. Terry M. Tritt San Diego; San Francisco; N.Y.; Boston; London; Sydney; Tokyo: Academ. Press, 2001, v.69, pp.51-98