Si O + SiO = Si O + O

Transcription

1 ELEMENS OF SRUCURE IN CHEMICAL HERMODYNAMICS OF OXIDE MELS Michael A. Spiridonov, Vladiir K. Novikov and Irina S. Zinovieva E-ail: Metallurgical Departent, Urals State echnical University -UPI, 622, Ekaterinburg, Russia 1. Introduction he properties of disordered condensed aterials are defined by their short range order. Diffraction investigations of volue [1] and surface [2] layers in the ill-ordered aterials gives the quantitative inforation about the co-ordination nubers and the shortest interatoic distances only for one- and two- coponents systes. Such investigations in the ulticoponents elts cannot practically give the direct connection of the structure paraeters with the physico-cheical properties of the elts, as far as the proble of deterination their partial contributions - the radial or cylindrical distribution functions and structure factors even in the quasibinary glassing systes requires precision neutron data. he received experiental dependencies of short-range order structure are connected with the elts properties by integral equations through the effective interpartical potential of interaction, which deterination presents an independent theoretical proble. In this work we attepted to apply another approach, developed in organic cheistry [3]. 2. herocheical calculations he ain structure eleents in oxide etallurgical elts are silicooxygen anions of the different degree of difficulty, based at the cheical balance between theselves and free oxyanions. he coplex anions present theselves as reiterative chains of silicooxygen tetrahedrons, foring as a result of polyerisation reactions with the participation of tetravalent onoers SiO 4-4. An interaction of coplexes with each other leads to coplication of their structure and is accopanied by separation into the elt of free oxyanions [4] 2( n+ 1) 4 ( n ) Si O + SiO = Si O + O n 3n n+ 1 3n+ 4 he charges of coplex anions and free oxyanions are indenified by the positive charges of etallic cations. For the quantitative evaluation of structures, foring the elt, let's use so called χ - paraeter, based on the graph eleents theory [3] (1) 12 χ = 1/( ν * ν ) / i j (2) In equality (2) ν i and ν j - are accordingly the nubers of outcoing fro the given and nearby tops of a graph relationships and suation leads on all ribs, connecting the tops. In particular, for spatial tetrahedral structure we ll have ν i : (nuber of ribs, leaving fro each top), ν j : (ribs nuber of the central ato). In this case χ - paraeter is equal to two. Let s try to connect this criterion with such property of liquid oxides as the basicity. It is possible to use as a relative easureent of basicity the toughness of cobination the oxides with soe anhydride (SO 3, CO 2, SiO 2, etc.). he collation of the standard change Gibbs foration energy ( G ) of the crystalline sulphates and carbonate shows, that the basicity of oxides decreases abreast BaO > Li 2 O > CaO > MgO > MnO > CdO > FeO > Fe 2 O 3 > BeO Coparison the G of foration the solid ortho- and etasilicates of sodiu, calciu, agnesiu, anganese and iron also witnesses about reducing the basically of oxides in this row. In order to calculate the standard change of Gibes energy ( G ov ) in the reactions of foration the elted silicates, borates, phosphates, titanates, aluinates and ferrates fro the overcooled (ov)

2 fluid oxides at the elting teperatures of cobinations the following equation for G ov, received at the adission of equality the heat capacities of the solid and overcooled oxides [6], has been used o c, c, GOV = G x H1, ( 1 ) H2, ( 1 ) (3) 1, Here G - is the standard change of the Gibbs energy in the reactions with the participation of solid oxides at the elting teperature of cobination ( c, ); 1,, 2, and H 1,, H 2, - are accordingly the teperatures and the heats of elting oxides and x - stoichioetrical coefficient before the base oxide. For exaple in the reaction 2CaO + SiO 2 = Ca 2 SiO 4 (4) the above entioned values will be following: 1, = Ò CaO,, Ò 2, = Ò SiO2,, H 1, = H CaO,, H 2, = H SiO2, and x = 2. he values G were found with the help of standard ethod (ekin-shvartchan) by using the data, widely provided in the references [7,8]. 3. Results he aforesaid approach has been used for a row of oxides, foring silicates, borates, phosphates, titanates, aluinates and ferrates. As an illustration at fig.1 one can clearly see the direct relationship between G ov and the values of structure paraeter Ln (χ c /χ co ). So we can write 2, - G ov = k Ln (χ c /χ co ). (5) Here χ c and χ co - are accordingly Randic s indexes for cheical cobination and coplex foring oxide and k - is an epirical coefficient, depending fro the nature of reagents. Using further the usual equation between G ov and cheical constant of equilibration, expressed through the activities of the coponents in reaction - G ov = R Ln K che (6) we ll receive the equation K che = ( K χ ) k/r, (7) connecting the cheical constant of equilibriu with its structure analogue. Fig.2 shows the reveal single-line dependency between Ln k and electronegativity of the eleents [9]. Here this dependency is presented only for silicates, however for the other systes, the spots lie at direct lines, parallel to the given one. he received regularities allow to build a quantitative scale of therocheical basicity, noralized on CaO. First let s noralize on CaO the oxides Me 2 O and MeO in the following way i o = Ln k Me2O,MeO / Ln k CaO-SiO2 (8) Here i o - is the index of basicity the oxides (Me 2 O, MeO) and Ln k CaO-SiO2 - is a value, found out for silicates (Ln k CaO-SiO2 = 5.33). hen let s noralise the coplex (co) foring oxides: B 2 O 3, P 2 O 5, io 2, Al 2 O 3 and Fe 2 O 3 on SiO 2, using the values Ln k, found out for borates, phosphates, titanates, aluinates and ferrates of calciu (Ln k Cao-co ) = ( Ln k CaO-co / Ln k CaO-SiO2 ) -- 1 (9) hen let s noralise SiO 2 on CaO and use for this the experiental values of optical basicity SiO 2, which in the calcic scale (λ CaO = 1) is equal to λ SiO 2 =.48 [1]. In this case it is possible to write i o =.48 i o. he received indexes of therocheical basicity the oxides in the united scale of CaO (i o,cao = 1) are presented in table. i o

3 Here there are the values of optical basicity of the oxides [1] in sae scale (λ CaO = 1). It can be seen that i o and λ are in coplete agreeent with each other for the different oxides. It is iportant to notice that there is no need to separate the slag coponents at tart and base oxides when using such calcic scale. he value of index basicity ( I o ) for systes, containing several oxides, can be calculated as well as an optical basicity by the equation [1] I o = f n i o, n, (1) where f n - is an equivalent share of cation ( share of the charge of cation in neutralization the negative charge of oxygen), i o,n - index of therocheical basicity of the oxide, containing n-th cation. For exaple, for the elt, having the coposition of CaO-P 2 O 5 (1:1), f 2+ Ca is equal to 2/12 5+ and f P = 1/12. For the elt of coposition CaO-P 2 O 5 (1:1) is was experientally found out the value of optical basicity equal.47 [11]. he index of therocheical basicity agreeable to this coposition is also equal Discussion At the present tie the scale of optical basically is broadly used [11]. It is shown that sulphide, carbonate and phosphate capacities, which are the experiental easures of basically, well correlate with the values λ. In ditto tie, experiental values λ can be received only for the aterials, being transparent in the ultraviolet area of spectru. For the ajority of real slag this ethod is not suitable. he found out possibility of theoretical calculation the optical basicity of oxides, using its correlations with Pauling s electronegativity (x n ) of eleents [11] λ = 1 / 1.36 (x n -.26), (11) cannot be widely spread for the oxides of transitional etals. So, FeO, for instance, has λ FeO = λ SiO2 =.48 and this value disagrees with the experiental data. At the sae tie, fig. 2 witnesses, that the dependency Ln k - x n is linear for all the studied oxides, including MnO and FeO. Within the fraework of the suggested approach there is no nuerical difference between the nature of the cations with alike charge. If the difference between cations with different charges is displayed in the nuber of ribs, coing out fro the tops of a graph, then for the cations with equal charges the values of χ - paraeters will be alike. So, for instance, the elts, containing calciu or bariu oxides with alike coposition will be characterised by equal nuerical paraeters. However, the ultiple experiental data witnesses that the physico-cheical properties distinguish fro each other vastly. he account of different nature of alike charged cations, which don t reveal in the proposed approach, can be ade at the description of physico-cheical properties of real oxide elts on the base of building of ultifactorial equations of the type structure - property. 5. Conclusion Let s notice that the revealed regularities ay be used for estiation of G ov even when the experiental data is absent. here is as well a possibility of estiation the elting teperature of cobinations and heats of elting the oxides. his approach is perspective as for revealing the relationships between the structure and properties in ulticoponent elts and for the developent of the odels of their structure.

4 Fig.1. Connection of the G ov of foration the silicates with the structure paraeter Ln (χ c /χ SiO2 ) - coents in the text. able. herocheical indexes of basicity the oxides (i o ) and their optical basicity ( λ) Oxide K 2 O Na 2 O CaO MgO MnO FeO Fe 2 O 3 Al 2 O 3 io 2 SiO 2 B 2 O 3 i o λ

5 Fig.2. he connection of Ln k for silicates with Pauling electronegativity References [1] Waseda Y.: he Structure of Non-Crystalline Materials. Liquid and Aorphous Solids. McCraw-Hill, New York, 198. [2] Popel S.I., Spiridonov M.A., Lavrov A.V. : Czech. J. Phys. 47 (1997) 455. [3] Randic M.: J. Aer. Che. Soc., 97 (1975) 669. [4] Novikov V.K.: Rasplavy (Melts) 1 (1987) 51. [5] Krebs H.: Grundzuge der Anorganischen Kristallcheie. Ferdinand Enke Verl, AG Stuttgart, [6] Esin O.A.: Physico-cheical bases of the processes in color etallurgy. UPI, Sverdlovsk.1972 ( in Russian). [7] Cubashevskiy O. and Olcocc S.B.: Metallurgical therocheistry. Metallurgy, Moscow, [8] Elliot D.F., Gleyzer M. and Raakrishna V.: herocheistry of steel-elting processes, Metallurgy, Moscow, [9] Pauling L.: Coon cheistry, Mir, Moscow, 1974 [1] Duffy J.A.and Ingra M.D.: J. Che. Soc. Faraday rans. 74 (1978) 141. [11] Masson C.R.: 2 nd Inter. Sypos. Metallurg. Slags and Fluxes Met. Soc. AIME. (1984) 3.