Effect of surface‐treated graphites on the properties of carbon‐containing monolithic refractory materials—A comprehensive comparison

Abstract

The performance of alumina‐ and magnesia‐based carbon‐containing refractory castables, suitable for different sectors of steel plants, has been compared. Natural flaky graphites have been modified by their surface treatment via sol‐gel route. The sustainability of graphite in oxidizing atmosphere was noticeably increased by this method with a synergistic possibility of pollution abatement. The hydrophilic nanocoatings of ceramic oxides derived by inorganic precursors reduced the water demand of the composite batch and simultaneously enhanced its oxidation resistance. The oxide coating compositions together with the precursor chemistry have been varied to substantiate their common beneficial features. Scanning electron microscopy (SEM), Raman spectroscopy, Differential thermal analysis (DTA), Thermogravimetry (TG), X‐ray diffraction, thermal conductivity, and zeta‐potential studies have been carried out to compare the influence of heat treatment on as‐received and surface‐modified graphites. The properties of refractory castables, namely, bulk density, apparent porosity, and cold crushing strength have been measured within wide temperature region (110–1500°C), to confirm the positive influence of nanoengineering on graphite surface. The sequence of important phase reactions during sintering of both the composite materials has been discussed. Finally the slag resistance behavior at aggressively fired condition has been investigated to corroborate the improved matrix characteristics due to coated graphites.

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

“…When the three plots are compared the exothermic peak tips in Gr,Gg and Gc occur, respectively, at 1042, 910, and 931°C although Gg shows another sharp peak at 1238°C. As Gg contains the amorphous sol‐gel coating of calcium aluminate precursors, the peak nearby 900°C can be due to crystallization of the gel . As a result the burn out of graphitic carbon has been delayed in Gg and the exothermic peak doublet extends beyond 1200°C.…”

“…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.…”

“…The heat‐treatment step next to sol‐gel reaction and ultrasonication has therefore been identified as a vital step. These findings have not been chronologically explored previously …”

“…The surface of natural flaky graphite containing 97.0% fixed carbon (S.Area 1.8 m 2 /g) has been treated with the precursor of calcium aluminate sol in a definite proportion. The polymeric sol has been synthesized at pH ~ 3.0 using hybrid precursors ie, calcium nitrate and Al‐ sec ‐butoxide along with alcohol‐water mixture, acid peptizers, chelating agent and drying control chemical additive (DCCA) .…”

“…In lieu of uncoated graphites (Gr), the coated graphites (Gc) have been incorporated to a high alumina based castable to prepare the so called alumina‐carbon refractory composite (Table ). The sieve sizes (fineness) and quantity of the common constituents in aggregate and matrix part of the refractory along with their purity have been kept fixed as reported in our previous contributions . The quantity of water required for suitable flow and consistency of the slurry had been determined by ASTM C 860‐00 and C 230 methods.…”