An article presents results of a study of wetting of iron, nickel, and platinum substrates by molten MnO-SiO 2 slag of near-eutectic composition by the sessile-drop method in reducing atmosphere (oxygen partial pressure of 10 -20 to 10 -18 atm). Significant MnO reduction and manganese dissolution into substrate was observed in reactions with all three substrates. Silica also was reduced in reaction with Fe and Ni, although the extent of reduction was much smaller in comparison with MnO and was not observed in reaction with Pt. The dissolution of manganese led to modification of the interface with formation of molten phase for nickel and platinum substrates. Terminal contact angles (after 240 minutes) for MnO-SiO 2 slag were as follows: for iron substrates-5 ± 2 deg at 1350°C, 9 ± 2 deg at 1390°C, and 6 ± 2 deg at 1450°C; and for platinum-15 ± 2 deg at 1350°C and 1390°C, and 12 ± 2 deg at 1450°C. The contact angle for the Ni-(MnO-SiO 2 ) system was close to zero-3 ± 2 deg at 1350°C and 1390°C. Modification of the metal-oxide interface as a result of reduction of oxides and adsorption of oxygen made wetting dynamic and affected interfacial properties.
Wetting of solid metals-iron, nickel and platinum, by molten MnO-SiO 2 (MS) and CaO-Al 2 O 3 -SiO 2 (CAS) oxide systems was studied by the sessile drop method at 1 350-1 450°C in reducing atmosphere. Terminal contact angles (after 240 min) for MS system were: for iron substrates-5Ϯ2 deg at 1 350°C, 9Ϯ2 deg at 1 390°C, 6Ϯ2 deg at 1 450°C; platinum-15Ϯ2 deg at 1 350°C and 1 390°C, and 12Ϯ2 deg at 1 450°C. Contact angle for the Ni-MS system was close to zero-3Ϯ2 deg at 1 350°C and 1 390°C. Contact angles with CAS system were: iron-55Ϯ2 deg (1 350°C), 60Ϯ2 deg (1 390°C), 44Ϯ2 deg (1 450°C); nickel-59Ϯ2 deg (1 350°C), 60Ϯ2 deg (1 390°C); and platinum-15Ϯ2 deg (1 350°C, 1 390°C and 1 450°C). Work of adhesion for all substrates with MS system was 910 to 930 mJ/m 2 . Interfacial tension with MS system was 1 480 mN/m for Ni at 1 350 to 1 390°C, and 1 880 to 1 890 mN/m for Pt in the temperature range 1 350 to 1 450°C. For iron, interfacial tension was 1 720 mN/m at 1 350°C; 1 580 mN/m at 1 390°C and 1 450°C. Lower work of adhesion and higher interfacial tension were found for metals with CAS system. Reduction of MnO from MS system was observed, leading to Mn dissolution in metal substrates. Degree of silica reduction from MS system was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS system. Reduction of oxides and adsorption of oxygen modify the metal-oxide interface, making wetting dynamic and profoundly affecting interfacial properties.KEY WORDS: interface wetting; interface dynamics; oxides. ExperimentalThe study is based upon in-situ observation of high-temperature wettability of a solid metal by molten oxides using the sessile drop method. In these experiments, the change in behavior with time and temperature of a liquid drop of oxide upon a solid metal substrate was recorded. The experiments were conducted in a graphite furnace described elsewhere. 6)A digital video camera with a resolution of 720ϫ576 pixels was used to record image sequences during the wettability experiments. Zoom lenses (one 4ϫ, one 1ϫ) were added to the camera lens to provide the correct focal length. Welding lenses were placed in between the camera and the furnace window to reduce glare from the sample at high temperatures.Iron was obtained in the form of chips (2 mm diameter). Approximately 1 g of iron chips were melted in an alumina crucible under a Varigon (5 vol% hydrogen, 95 vol% argon) atmosphere at 1 600°C. Nickel was obtained as ϳ1 g pellets. The iron or nickel was placed inside an envelope of titanium foil for rolling to a thickness close to 1 mm, giving a diameter of ϳ15 mm. After rolling, the metal disc was polished down to a roughness of 0.05 mm.Platinum was supplied in the form of foil of 0.5 mm thickness then polished to the same finish as iron and nickel. Chemical analysis of iron, nickel and platinum by Inductively-Coupled Plasma spectroscopy and LECO analyzers (CS-244 Carbon/Sulfur and TC-436DR Oxygen/ Nitrogen) is given in Table 1.The MnO-SiO 2 (MS) system was prepared from MnO (99...
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