Understanding hydrophobicity variations in dense medium ferrosilicon from different production routes

Dense medium ferrosilicon (FeSi) powders produced via submerged arc furnace smelting, granulation, and milling route show varying hydrophobicity, sometimes totally nonwetting, amounting to production losses. This does not occur in powders produced via induction furnace smelting and atomization. Although wetting is fundamentally a surface phenomenon, bulk property can dictate surface behavior. Hence, for detailed insight into the cause of the variation, particles of powders from different production routes were studied from surface to the core. Particle shapes differ clearly for the two production routes, but this was found inconsequential to the wetting behavior. Rather, size distribution, proportion of ultra-fine particles in the powder, was seen to have effect, being more in the nonwetting sample. From the optical microscopy: in the granular particles (that is, before milling), it is visible that different phases formed from the Fe-Si-C system, and this will impact milling differently; particles from nonwetting milled powders show a notable surface layer, and in contrast, the atomized particles show more homogeneous equiaxed grains. From X-ray photoelectron spectroscopy, argon ions sputtering, and depth composition profiling, graphitic carbon (C1s at 284.5 eV binding energy) was found on the surface for all samples at levels above bulk alloy composition but highest (65%) for the totally nonwetting sample. From these pointers, graphite coating on particles is responsible for varying hydrophobicity. Carbon affects solid FeSi microstructure, milling, and powder properties. Controlling carbon content from the smelting stands out for avoiding milled FeSi hydrophobicity. This is however not a straight forward minimization problem.