Dynamic Wetting of CaO-Al2O3-SiO2-MgO Liquid Oxide on MgAl2O4 Spinel

Inclusion type and content in steel is critical in steelmaking, affecting both productivity through clogging, and downstream physical properties of the steel. They are normally removed from steel by reacting with a slag (liquid oxide) phase. For efficient inclusion removal, the inclusions must attach/bond with this liquid phase. The strength of the attachment can be in part characterized by the wettability of the liquid oxide on the inclusions. In this study, the dynamic wetting of liquid oxides of the CaO-Al2O3-SiO2-MgO system on a solid spinel (MgAl2O4) substrate with low porosity of 1.9 pct was measured at 1773 K (1500 °C) using a modified sessile drop technique. The dynamic contact angle between the liquid and solid spinel was determined for different CaO/Al2O3 mass percent ratios ranging from 0.98 to 1.55. Characteristic curves of wettability (θ) vs time showed a rapid decrease in wetting in the first 10 seconds tending to a plateau value at extended times. A mathematical model for spreading behavior of liquid oxides by Choi and Lee was adopted and shown to provide a reasonable representation of the spreading behavior with time. The chemical interaction at the interface between spinel (MgAl2O4) and slag was analyzed by carrying out detailed thermodynamic evaluation and characterization using scanning electron microscopy/energy dispersive spectroscopy. There is evidence of liquid penetrating the substrate via pores and along grain boundaries, forming a penetration layer in the substrate. The depth of the penetration layer was found to be a function of substrate porosity and sample cooling rate. It decreased from ~350 µm for 6.7 pct-porous substrate to ~190 µm for substrate with porosity of 1.9 pct and from ~190 µm to ~50 µm for a slow-cooled liquid oxide-spinel substrate sample in the furnace to a rapidly cooled liquid cooled-spinel substrate sample, respectively

Kinetics of spinel formation and growth during dissolution of MgO in CaO-Al2O3-SiO2 slag

The formation and growth of MgAl2O4 spinel crystals on a single crystal MgO substrate submerged in a 40% CaO, 40% SiO2 and 20% Al2O3 slag was directly observed using high temperature microscopy. This showed that the crystals initially form on the MgO surface, but may break off and be carried out into the liquid slag. Still pictures extracted from digitally recorded images were used to measure the size of these crystals at 1420, 1440 and 1460oC as a function of time. Growth of the crystals was found to follow the parabolic rate law, with rates increasing with temperature. An estimate of the activation energy made from the data (564 kJ mol-1) was found to be comparable with previously published results from different types of experiments on spinel formation

A study of parameters that influence growth and stability of the (Bi sub 1 minus x Pb sub x ) sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub y phase

The growth and stability of the (Bi{sub 1-x}Pb{sub x}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) phase contained in silver-sheathed wires has been investigated by a combination of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and transmission electron microscopy. Silver tubes loaded with Bi-2223 precursor powders were processed into filaments using established metallurgical techniques. The filaments were then heat-treated at selected temperatures (800 to 845{degrees}C) for a range of times (10 to 6000 min) in a 7.5% oxygen atmosphere. From these studies it has been possible to investigate the time-temperature-oxygen pressure domains wherein Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi-2212) + second phases transform to Bi-2223. Fractional conversion (Bi-2212) {yields} (Bi-2223) versus time data show good conformance to the kinetic model for a diffusion-controlled reaction at the interface between thin sheets and a fine powder or a fluid. Quenching experiments also reveal that the Bi-2223 phase is stable in a limited temperature interval between 810 and 830{degrees}C