Functional Coatings on Carbon‐Bonded Ceramic Foam Filters for Steel Melt Filtration

Abstract

Ceramic foam filters (CFFs) have been used by steel foundries for several years as an effective physical refining solution after the ladle treatment. Recently, new approaches involving "active" and "reactive" coatings applied on the filters have been proposed, in order to improve their efficiency during operation. In this work, two different coating methods are presented. The first exploits the reaction of carbon-bonded alumina-magnesia filters when immersed in a steel melt at about 1650 8C. In this case, the coating is formed directly during operation: due to the carbothermal reduction of magnesia and dissolution of alumina, in situ spinel formation is observed. This also results in a volume expansion that counteracts the shrinkage of the filter material related to sintering and pyrolysis phenomena. Next, multi-walled carbon nanotubes (MWCNTs) are applied on carbon-bonded alumina filters by means of spray coating to increase the reactivity of the surface. The performance of the coated filters is assessed in comparison to uncoated ones, using a special steel casting simulator under controlled atmosphere. The microscope investigations after 10 and 30 s of immersion indicate a better performance of the MWCNTs-coated filters.

Numerical Assessment of a Filtration Experiment Influenced by Microscale Carbon Monoxide Bubbles Arising in Steel Melt

“…The numerical model used in that work has been coupled with a pore-scale simulation to determine the efficiency of two CFFs (10 and 20 ppi), produced in CRC 920. 22 The filtration efficiency was relatively low compared with that measured experimentally by Storti et al 23,24 or Schmidt et al, 25 even though the duration of the filtration process was longer in the simulation. The considerable difference between the efficiency values determined experimentally and by simulations was attributed by Storti et al 23,24 to the fact that reaction between carbon (C) and oxygen (O) takes place to create CO bubbles in the melt.…”

Characterization of the In Situ‐Formed Oxide Layer at the Steel Melt/Carbon‐Bonded Alumina Interface

“…The formation of an in situ-formed oxide layer or oxide whiskers was observed for ceramic filters based on MgO-C, [4] Al 2 O 3 -MgO-C, [12] and Al 2 O 3 -C [13][14][15] after immersion in liquid steel. The in situ formation of oxide structures was described qualitatively and by thermodynamic calculations, but the influences on the morphology development of the formed oxide crystals were not studied before.…”

Reactive ceramic pellets incorporated iron for removing As(III), As(V), and Cr(VI) from aqueous solutions

“…Ceramic filters can remove contaminants (e.g., suspended solids) from wastewater through a membrane process via the fine pores in a filter, and they are effective for use in precision filtration processes under extreme conditions such as at high temperatures and/or in acidic conditions, due to their high thermal and chemical stability and high mechanical strength [18]. There is currently a demand for the development of reactive ceramic filters with enhanced wastewater treatment capacities that can be used in heavy metal contaminated wastewater treatment under extreme conditions [18][19][20].…”

“…Reactive ceramic filters have recently been the focus of wastewater treatment studies, as they exhibit a heightened heavy metal treatment capacity in relation to their enhanced reactivity, which is achieved by coating the filters with reactive substances [19,20,28]. However, these filters currently have a limitation for use: when the reactive material is applied as a coating on the ceramic filter, the reactive material can be peeled from the filter's surface.…”