A project studied wetting of iron, nickel and platinum by molten MnO-SiO2 (MS) and CaO-Al2O3-SiO2 (CAS) slags of eutectic composition to contribute to understanding of wetting behaviour of solid metal-molten oxide systems relevant to steelmaking. Novel results of dynamic wetting behaviour by the sessile drop method were obtained under strongly reducing atmosphere (oxygen partial pressure 10-20 -- 10-18 atm). Terminal contact angles (after 240 min) for MS slag were: for iron substrates -5??2??(1350??C), 9+-2?? (1390??C), 6+-2 (1450??C); nickel -- 3+-2??(1350 and 1390??C); and platinum --15+-2??(1350 and 1390??C), 12+-2??(1450??C). Contact angles with CAS slag were: iron -- 55+-2??(1350??C), 60+-2?? (1390??C), 44+-2?? (1450??C); nickel -- 59+-2??(1350??C), 60+-2?? (1390??C); and platinum -- 15+-2?? (1350, 1390 and 1450??C). Values for interfacial tension, work of adhesion, spreading parameter (S) and interaction coefficient (Ф) were also determined. Work of adhesion for all three substrates with MS slag changed in a very narrow range 910 - 930 mJ/m2. Interfacial tension with this slag was 1,480 mN/m for Ni at 1350-1390??C, and 1,880-1,890 mN/m for Pt in the temperature range 1,350-1,450??C. For iron, interfacial tension was 1,720 mN/m at 1350??C (γ-Fe); it decreased to 1590-1580 mN/m with increasing temperature to 1390 and 1450??C (-Fe). Lower work of adhesion and higher interfacial tension was found for metals with CAS slag. Wetting properties of Pt substrate with MS slag were close to that with CAS slag, while Fe and Ni substrates showed better wetting by MS slag in comparison with CAS slag. This was attributed to higher reactivity of Fe and Ni with MS slag, particularly reduction of MnO. Although MnO was also reduced in reaction with Pt, oxygen adsorption in contact with both slags was a major factor governing wettability of Pt. Dissolution of manganese in nickel and platinum substrates at elevated temperatures modified the interface chemistry, causing formation of a liquid alloy phase. Degree of silica reduction from MS slag was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS slag. Concentration profiles of Mn and Si across the interface and along the metal surface were used to estimate diffusion coefficients. Diffusion along metal surfaces was generally higher by 1 to 2 orders of magnitude than across the interface. Reduction of oxides and adsorption of oxygen modify the metal-oxide interface, making wetting dynamic. They have a profound on interfacial properties.
| Identifer | oai:union.ndltd.org:ADTP/187596 |
| Date | January 2007 |
| Creators | Parry, Gavin Wayne, Materials Science & Engineering, Faculty of Science, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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