Thermodynamic Properties of Aluminum and Iron Compounds

Transcription

1 ISSN , Steel in Translation, 27, Vol. 37, No. 2, pp. 5. Allerton Press, Inc., 27. Original Russian Text N.F. Yakushevich, I.V. Chuzhinova, 27, published in Izvestiya VUZ. Chernaya Metallurgiya, 27, No. 2, pp Thermodynamic Properties of Aluminum and Iron Compounds DOI:.33/S N. F. Yakushevich and I. V. Chuzhinova Siberian State Industrial University Progress in metallurgy is associated with the expanded use of methods and concepts from chemical thermodynamics. It is especially important for specialists in ferrous and nonferrous metallurgy to have access to the data necessary for thermodynamic calculations. In the present work, we determine the dependence of thermodynamic functions of complex compounds of aluminum and iron on basic physicochemical parameters. ALUMINUM COMPOUNDS In all, 278 binary and 6 ternary compounds of aluminum are considered, including two nitrides, five fluorides, four sulfides, two borides, four bromides, five iodides, two selenides, two tellurides, and five chlorides [ 5]; the thermodynamic constants are found for 56 binary and 42 ternary compounds. To find the general laws, consider solid compounds of type AlMe n, where n is the ratio of the number of atoms of the other metal in the compound to the number of aluminum atoms. The dependence of the standard enthalpy of compound formation H 298 on n for the systems of solid compounds AlFe n, AlAu n, AlU n, AlTi n, AlNi n, AlCa n (expressed in stoichiometric relation to a single aluminum atom) is found to be linear, and corresponds to the following equations: for the Al Fe system = 2.6n ± kj/mol, k = 2.6; () for the Al Au system =.54n 39.8 ± 5 kj/mol, k =.54; (2) for the Al U system =.43n ± 5 kj/mol, k =.43; (3) for the Al Ti system =.7n ± 4 kj/mol, k =.7; (4) for the Al Ni system =.5n ± 3 kj/mol, k =.5; (5) for the Al Ca system =.49n ± kj/mol, k =.49. (6) The graphs corresponding to Eqs. () (6) intersect at point A, whose abscissa is.25 and ordinate is 4 ± kj/mol (Fig. ). Hence, for all the systems, the function = f(n) may be described by the H 298 H 298, kj/mol 3 B 8 A 23 4 ' 5 2' 3' 6 4' 6' 5' 2 3 n Fig.. Plots of H 298 = f(n) for solid ( 6) and gaseous (' 6') aluminum compounds: () Al Fe; (2) Al Au; (3) Al U; (4) Al Ti; (5) Al Ni; (6) Al Ca; (') Al I; (2') Al Br; (3') Al S; (4') Al Cl; (5') Al F; (6') Al C.

2 2 YAKUSHEVICH, CHUZHINOVA equation of a sheaf of straight lines intersecting at point A = kn (.25) 4 ± kj/mol. (7) Analogously, for systems of gaseous aluminum compounds such as AlI n, AlBr n, AlS n, AlCl n, AlF n, AlC n, linear dependences H 298 = f(n) are obtained; they intersect at the point B, with abscissa.25 and ordinate 265 ± 5 kj/mol (Fig. ). For systems of gaseous compounds, the dependence H 298 = f(n) (expressed in stoichiometric relation to a single aluminum atom) is described by the following linear equations: for the Al I system = 63.n ± 5 kj/mol, (8) k = 63.; for the Al Br system = 239.8n ± 5 kj/mol, (9) k = 239.8; for the Al S system H 298, kj/mol D C ' 2' 4' n Fig. 2. Plots of H 298 = f(n) for solid ( 4) and gaseous (' 4') iron compounds: () Fe Si; (2) Fe P; (3) Fe Cl; (4) FeO; (') Fe I; (2') Fe Br; (3') Fe Cl; (4') Fe F. 3' 2 = 265.n ± 5 kj/mol, k = 265.; 3 () for the Al Cl system = 282.7n ± 5 kj/mol, () k = 282.7; for the Al F system = 53.n ± 5 kj/mol, (2) k = 53.; for the Al C system = 536.4n ± 5 kj/mol, (3) k = In general form, for all the gaseous aluminum compounds considered, the function H 298 = f(n) may be described by the equation of a sheaf of straight lines = kn (.25) ± 5 kj/mol. (4) Note that the difference in the ordinates of points A and B is approximately equal to the heat of sublimation of pure aluminum liberated when solid aluminum enters the gaseous state: = kj/mol. H subl.al IRON COMPOUNDS In all, 63 binary and 35 ternary iron compounds are considered, including 7 carbides, 3 silicides, 3 nitrides, 5 fluorides, sulfides, 2 phosphides, 4 borides, 4 iodides, 2 selenides, and 2 tellurides [ 4, 6, 7]. Thermodynamic constants are found for 52 binary and 3 ternary compounds. For solid and gaseous iron compounds, H 298 = f(n) is determined; n is the ratio of the number of atoms of the other metal (or nonmetal) in the compound and the number of iron atoms. The graphs of H 298 = f(n) for the solid compounds FeSi n, FeP n, FeCl n, and FeO n are also linear and intersect at the point C, with abscissa. and ordinate 25 ± kj/mol. For the gaseous compounds FeI n, FeBr n, FeCl n, FeF n, the linear graphs of H 298 = f(n) intersect at point D, with abscissa. and ordinate 39 ± 5 kj/mol (Fig. 2). The dependences H 298 = f(n) (expressed stoichiometrically for a single iron atom) for the solid iron compounds are described by the equations for the Fe Si system = 75.8n.9 ± 5 kj/mol, k = 75.8; (5) for the Fe P system = 38.9n. ± 7 kj/mol, k = 38.9; (6) STEEL IN TRANSLATION Vol. 37 No. 2 27

3 THERMODYNAMIC PROPERTIES OF ALUMINUM AND IRON COMPOUNDS 3 G FeSn, kj/mol 5 (a) M T = 2 K 5 T = 298 K G Fe/n, kj/mol T = 2 K T = 298 K 5 (b) n n P z = tanα 2 Fig. 3. Plots of G T = f(n, T) for iron sulfides (a) and 4 nitrides (b). α 2 α T, K for the Fe Cl system = 25.n 2.5 ± 8 kj/mol, k = 25.; (7) for the Fe O system = 5.n + 25 ± 2 kj/mol, k = 5.. (8) The corresponding equations for the gaseous iron compounds are as follows: for the Fe I system = 54.8n ± 5 kj/mol, (9) k = 54.8; for the Fe Br system = 95.n ± 5 kj/mol, (2) k = 95.; for the Fe Cl system = 246.8n ± 5 kj/mol, (2) k = 246.8; for the Fe F system = 382.4n ± 5 kj/mol, (22) k = The difference between the ordinates of points C and D in Fig. 2 is approximately equal to the heat of sublimation of pure iron: H subl.fe = kj/mol. The equation of the sheaf of straight lines describing the general functional dependence H 298 = f(n) for systems with solid iron compounds may be written in the form = kn (.) 25 ± kj/mol. (23) Correspondingly, for systems with gaseous compounds = kn (.) + 39 ± 5 kj/mol. (24) Fig. 4. Plots of x = f(t) for iron sulfides () and nitrides (2). GENERALIZED FORMULA For any of the systems considered, the dependence H 298 = f(n) may be expressed by a generalized linear equation of the form = kn ( a) b, (25) where k is the slope of the corresponding line; n is the ratio of the number of atoms of the other metal (nonmetal) in the compound to the number of aluminum or iron atoms; a and b are the abscissa and ordinate of the points of intersection of the H 298 = f(n) lines for the given system of aluminum or iron compounds (solid or gaseous). Analysis of the temperature dependence of the change in Gibbs energy dependence G T = f(n, T) in the formation of iron sulfides and nitrides shows that it may be described, in the first approximation, by equations of a sheaf of straight lines (Fig. 3) =.2Tn + ( ± 2.)n 2 ± 2.; (26) G Fe/n N =.5Tn ( ± 4.2)n (27) +.656T ± 4.2, G FeSn where T is the temperature, K; n is the ratio of the number of sulfur or nitrogen atoms to the number of iron atoms in the compound (for the sake of convenience, we use /n); G is the change in Gibbs energy, kj/mol. The coordinates of the point of intersection M of the sheaf of straight lines for the sulfides are (; 2 ± 2.9); the coordinates of the corresponding point for nitrides are (.4375; 6 ± 4.2). In geometric terms, z = G T /n is the tangent of the angle of inclination α of the G = f(n, T) dependence. For iron sulfides z =.2T + ( ± 2.), (28) STEEL IN TRANSLATION Vol. 37 No. 2 27

4 4 Calculated values of for binary compounds YAKUSHEVICH, CHUZHINOVA Material Coefficients in the formula = k(n a) b, kj/mol, kj/mol k n a b calculated value handbook value, with source AlAu ± [] AlAu ± [] Al 2 Au ± [] Al 4 Ca ± [] Al 3 Ca ± [2] Al 2 Ca ± [] AlFe ± [2] Al 2 Fe ± [2] Al 3 Fe ± [2] Al 3 Ni ± [] AlNi ± [] AlTi ± [2] AlTi ± [] Al 3 Ti ± [2] Al 2 U ± [] Al 3 U ± [] Al 4 U ± [] FeO ± [3] Fe 2 O ± [3] Fe 3 P ± [3] Fe 2 P ± [3] FeP ± [3] FeP ± [3] Fe 3 Si ± [3] Fe 5 Si ± [3] FeSi ± [2] FeSi ± [2] FeCl ± [3] FeCl ± [3] CONCLUSIONS Analytical formulas for the standard enthalpies of formation of solid and gaseous aluminum and iron compounds of type AlMe n and FeMe n as a function of n (expressed stoichimetrically for a single atom of alu- and for iron nitrides z =.5T ( ± 4.2). (29) The corresponding temperature dependences are plotted in Fig. 4. Values of H 298 calculated from the given formulas for binary compounds are presented in the table. minum or iron) have been obtained and described by uniform equations of a sheaf of straight lines. Analytical formulas for the change in Gibbs energy as a function of n and the temperature have also been obtained, for iron sulfides and nitrides. REFERENCES. Kubashevskii, O. and Alcock, K.B., Metallurgicheskaya termokhimiya (Metallurgical Thermochemistry), Moscow: Metallurgiya, Karapet yants, M.Kh. and Karapet yants, M.L., Osnovnye termodinamicheskie konstanty neorganicheskikh i organicheskikh veshchestv (Basic Thermodynamic Con- STEEL IN TRANSLATION Vol. 37 No. 2 27

5 THERMODYNAMIC PROPERTIES OF ALUMINUM AND IRON COMPOUNDS 5 stants of Inorganic and Organic Materials), Moscow: Khimiya, Termodinamicheskie konstanty veshchestv. Vyp. VI. Chast I. Tablitsy prinyatykh znachenii (Thermodynamic Constants of Materials, Issue VI, Part I, Tables of Adopted Values), Moscow: Nauka, Elliot, D.F., Glazer, M., and Ramakrishna, V., Thermochemistry of Steel Smelting (Russian translation), Moscow: Metallurgiya, Diagrammy sostoyaniya dvoinykh metallicheskikh sistem. Spravochnik (Phase Diagrams of Binary Metallic Systems: A Handbook), Lyakishchev, N.P., Ed., Moscow: Mashinostroenie, Kosolapova, T.Ya., Svoistva, poluchenie i primenie tugoplavkikh soedinenii. Sprav. Izd. (Properties, Preparation, and Use of Refractory Compounds: A Handbook), Moscow: Metallurgiya, Diagrammy sostoniya dvoinykh i mnogokomponentnykh sistem na osnove zheleza. Spravochnik (Phase Diagrams of Binary and Multicomponent Systems Based on Iron: A Handbook), Bannykh, O.A. and Drits, M.E., Eds., Moscow: Metallurgiya, 986. STEEL IN TRANSLATION Vol. 37 No. 2 27