Spinel‐Coated Graphite for Carbon Containing Refractory Castables

Abstract

Oxidation resistance and water wettability of graphite flakes have been improved by a thin sol–gel film of magnesium aluminate spinel (MgAl2O4) over its surface. The hydrosol has been synthesized by less expensive precursors and the spinel formation has been studied by scanning electron microscopy (SEM), supplemented with energy dispersive spectral analysis. After an easy‐to‐use mixing procedure, drying (110°C), and subsequent calcination (550°C), coated graphites were sieved to below 75 μm. The coating over the powder contained 1.5 wt% MgAl2O4, which enormously increased the oxidation resistance (performed at 600°, 900°, and 1200°C) and water wettability, as revealed by hydrophilic functional groups from infrared spectra. Defective, intermediate spinel structure of fine, lamellar Mg‐doped γ‐Al2O3 has been considered to be significant for this improvement. An approximate (1:2) stoichiometry of (Mg:Al) in the coating composition was confirmed by an X‐ray photoelectron spectroscopy test. Castables prepared by this graphite remarkably improved their bulk density and apparent porosity compared with those prepared by the as‐received graphite. Casting water was reduced along with the amount of antioxidants. This also enhanced the resistance toward the basic slag by retaining the graphite in the refractory.

In depth studies on cementitious nanocoatings on graphite for its contribution in corrosion resistance of alumina based refractory composite

“…5a(i)) represents the overall /average composition of graphite surface. Ca, Al, Si all are observed due to both calcium aluminate coating and alumino silicate ash/clayey impurities inherently present on to graphite flakes [15]. The second adjacent plot (Fig.…”

“…The refractory castables preparation has also been elaborately discussed in our previous contributions [15][16][17]. It was a low cement (4.0 mass%) batch containing white fused alumina(WFA) aggregates (72.0%) in several size fractions, e.g.…”

“…When assisted with ultrasonication and heat treatment, partly exfoliated graphite platelets with intermittent graphite oxide formation are quite likely. In our maiden effort it has been reported that surface treatment of graphite by inorganic sol-gel routed precursors was found to be quite promising for application in refractory castables [15][16][17][18][19][20][21][22][23]. However our persistent research on this area recently revealed that some special facets of this material are yet to be unfolded.…”

Significant improvement of refractoriness of Al2O3–C castables containing calcium aluminate nano-coatings on graphite

“…A secondary problem of atmospheric pollution arises due to emission of carbon monoxide (CO) and/or carbon dioxide (CO 2 ) gases because of prevailing oxidizing atmosphere at the application site. Surface modification of graphite has thus been adopted by many researchers with a desire to reduce water content of batch and minimize rate of emission of carbonaceous products by environmentally benign manner [5,6,7]. The use of novel forms of carbon materials e.g.…”

Extended studies on surface‐treated graphite vis‐à‐vis its application in high alumina refractory castable

“…In this pursuit of achieving high‐tech and heavy‐duty ceramic‐carbon monoliths for steel plants, our ideal choice was to develop coated graphite by sol‐gel route. Taking the clue that hydrophilic thin film on graphite can assist fabrication and carbon protection, a cost‐competent nanostructured ceramic oxide coated graphite for monolithic refractories has already been reported . Our preliminary observations revealed that this coating behaved as an intermediate bridging link between the castable and graphite that upgraded the performance of alumina based refractory.…”