SOME THERMODYNAMIC ASPECTS OF WO3 REDUCTION BY ALUMINUM

Technology of arc surfacing using flux cored wire, in which tungsten oxide (WO₃) and aluminum are used as fillers, is of interest for practical application in order to save tungsten. Thermodynamic estimation of probability of 14 reactions between them under standard conditions was carried out using tabular thermodynamic data of reagents in temperature range 1500  –  3500  K. This interval includes temperature at the drop surface on the electrode at time of separation, so are temperatures at the arc periphery and in the upper layers of surfacing bath. The following states were considered as standard states for reagents: WO₃(solid), WO₃(liquid), WO₃(gas); Al(ref), Al(liquid), Al(gas), Al₂(gas), and as possible reaction products and standard states for them: W(ref), W(liquid), W(gas), Al₂O₃(solid), W; Al₂O₃(liquid), AlO(gas), AlO₂(gas), Al₂O(gas), Al₂O₂(gas). Reduction reactions of the oxide were recorded at 1 mole O₂ . Probability of reactions was evaluated using standard Gibbs energy of reactions. Calculations were carried out in four stages. Aggregate states of oxide, metal and structure of aluminum vapor, in which oxide and metal have the greatest chemical affinity for each other were established on the first and second stages. At the third and fourth stages, the most probable state was determined for metallic tungsten and the most probable composition, and aggregate state of aluminum oxide formed as a result of alumothermy of Al₂O₃(solid, liquid); Al₂O₃(liquid); AlO(gas); AlO₂(gas); Al₂O(gas); Al₂O₂(gas). According to Al – W system state diagram, there are a number of intermediates between tungsten and aluminum: W₂Al, WAl₃ , WAl₄ , WAl₅ , WAl₇ , WAl₁₂ ; however, a search for thermodynamic properties for them shows that data are available only on melting pattern (congruent or in-congruent) and temperature of transformation. No other thermodynamic data. At the same time, based on results of our previous work on restoration of tungsten oxide by carbon and silicon, it can be predicted that aluminides of a free-frame will necessarily be formed. Performed thermodynamic analysis shows that presence in flux-cored wire used for surfacing, along with tungsten oxide WO₃ as an aluminum reducing agent, will necessarily lead to occurrence of reduction reactions with formation of tungsten aluminides, and possibly tungsten itself. Tungsten oxide has the highest reactivity, being in state of WO₃(gas). Aluminum itself has the highest chemical affinity for WO₃(gas) in form of Al₂(gas) and Al(gas). Al₂O(gas) appears most likely as an oxidation product of aluminum.

1. Metlitskii V.A. Flux-cored wires for arc welding and surfacing of cast iron. Welding International. 2008, vol. 22, pp. 796–800.

2. Filippov M.A., Shumyakov V.I., Balin S.A., Zhilin A.S., Lehchilo V.V., Rimer G.A. Structure and wear resistance of deposited alloys based on metastable chromium-carbon austenite. Welding International. 2015, vol. 29, pp. 819–822.

3. Liu D.S., Liu R.P., Wei Y.H. Influence of tungsten on microstructure and wear resistance of iron base hardfacing alloy. Materials Science and Technology. 2013, vol. 30, pp. 316–322.

4. Kejžar R., Grum J. Hardfacing of wear-resistant deposits by MAG welding with a flux-cored wire having graphite in its filling. Welding International. 2005, vol. 20, pp. 961–976.

5. Li. R., He D.Y., Zhou Z., Wang Z.J., Song X.Y. Wear and high temperature oxidation behavior of wire arc sprayed iron based coatings. Surface Engineering. 2014, vol. 30, pp. 784–790.

6. Ma H.R., Chen X.Y., Li J.W., Chang C.T., Wang G., Li H., Wang X.M., Li R.W. Fe-based amorphous coating with high corrosion and wear resistance. Surface Engineering. 2016, vol. 46, pp. 1–7.

7. Lim S.C., Gupta M., Goh Y.S., Seow K.C. Wear resistant WC-Co composite hard coatings. Surface Engineering. 1997, vol. 13, pp. 247–250.

8. Zhuk Yu. Super-hard wear-resistant coating systems. Materials Technology. 1999, vol. 14, pp. 126–129.

9. Hardell J., Yousfi A., Lund M., Pelcastre L., Prakash B. Abrasive wear behaviour of hardened high strength boron steel. Tribology-Materials, Surfaces & Interfaces. 2014, vol. 8, pp. 90–97.

10. Deng X.T., Fu T.L., Wang Z.D., Misra R.D.K., Wang G.D. Epsilon carbide precipitation and wear behavior of low alloy wear resistant steels. Materials Science and Technology. 2016, vol. 32, pp. 320–327.

11. Osetkovskiy I.V., Kozyrev N.A., Kryukov R.E. Studying the influence of tungsten and chromium additives in flux cored wire system Fe-C-Si-Mn-Mo-Ni-V-Co on surfaced metal properties. Materials Science Forum. 2017, vol. 906, pp. 107–113.

12. Kozyrev N.А., Galevsky G.V., Kryukov R.Е., Titov D.А., Shurupov V.М. New materials for welding and surfacing. IOP Conf. Series: Materials Science and Engineering. 2016, vol. 150, pp. 1–8 (012031).

13. Gusev A.I., Kozyrev N.A., Usoltsev A.A., Kryukov R.E., Osetkovsky I.V. Study of the properties of flux cored wire of Fe-C-Si-Mn-Cr-Mo-Ni-V-Co system for the strengthening of nodes and parts of equipment used in the mineral mining. IOP Conference Series: Earth and Environmental Science. 2017, vol. 84, pp. 1–8(012018).

14. Samsonov G.V., Vinnitskii I.M. Tugoplavkie soedineniya [Refractory compounds]. Moscow: Metallurgiya, 1976, 560 p. (In Russ.).

15. Patsekin V.P., Rakhimov K.Z. Proizvodstvo poroshkovoi provoloki [Cored wire production]. Moscow: Metallurgiya, 1979, 80 p. (In Russ.).

16. Tekhnologiya elektricheskoi svarki metallov i splavov plavleniem [Technology of electric welding of metals and alloys by melting]. Paton B.E. ed. Moscow: Metallurgiya, 1974, 768 p. (In Russ.).

17. Choi J.H., Lee J., Yoo C.D. Dynamic force balance model for metal transfer analysis in arc welding. J. Phys. D: Appl. Phys. 2001, vol. 34, pp. 2658–2664.

18. Lu F., Wang H.P., Murphy A.B., Carlson B.E. Analysis of energy flow in gas metal arc welding processes through self-consistent three-dimensional process simulation. International Journal of Heat and Mass Transfer. 2014, vol. 68, pp. 215–223.

19. Tashiro S., Zeniya T., Murphy A.B., Tanaka M. Visualization of fume formation process in arc welding with numerical simulation. Surface & Coatings Technology. 2013, vol. 228, pp. 301–305.

20. Kozyrev N.A., Bendre Yu.V., Goryushkin V.F., Shurupov V.M., Kozyreva O.E. Thermodynamics of reactions of WO3 reduction by carbon. Vestnik Sibirskogo gosudarstvennogo industrial’nogo universiteta. 2016, no. 2, pp. 15–17. (In Russ.).

21. Bendre Yu.V., Goryushkin V.F., Kryukov R.E., Kozyrev N.A., Shurupov V.M. Some thermodynamic aspects of WO3 recovery by silicon. Izvestiya. Ferrous Metallurgy. 2017, vol. 60, no. 6, pp. 481–485. (In Russ.).

22. Termodinamicheskie svoistva individual’nykh veshchestv. Spravochnik. T. 1. Kn. 1 [Thermodynamic properties of individual substances. Reference book. Vol. 1. Book 1]. Glushko V.P., Gurvich L.V. etc. eds. Moscow: Nauka, 1978, pp. 22. (In Russ.).

23. NIST-JANAF Thermochemical Tables 1985. Version 1.0 [Electronic resource]: data compiled and evaluated by M.W. Chase, Jr., C.A. Davies, J.R. Dawney, Jr., D.J. Frurip, R.A. Mc Donald, and A.N. Syvernd. Available at URL: http://kinetics.nist.gov/janaf. (Accessed 20.11.2018).

24. Hansen M., Anderko K. Constitution of binary alloys. 2nd ed. New York: McGraw Hill, 1958, 1287 p.