Spinel-Coated Graphite for Carbon Containing Refractory Castables
TL;DR: In this article, a thin sol-gel film of magnesium aluminate spinel (MgAl 2 O 4 ) was applied to graphite flakes to increase their oxidation resistance and water wettability.
Abstract: Oxidation resistance and water wettability of graphite flakes have been improved by a thin sol-gel film of magnesium aluminate spinel (MgAl 2 O 4 ) 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% MgAl 2 O 4 , 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-Al 2 O 3 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.
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TL;DR: In this paper, the effect of replacing the ball pitch with coated graphite (CG) on the microstructure, apparent porosity, physical properties, oxidation resistance, and slag corrosion resistance of Al2O3-SiC-C (ASC) refractory castables was investigated by a scanning electron microscope, an energy-dispersive X-ray spectroscope, a transmission electron microscope and other dedicated equipment.
47 citations
TL;DR: In this article, the authors used the low-temperature molten salt synthesis technique to synthesize TiC-coated graphite flakes, which were mixed with graphite in a mass ratio (Ti/C) between 1/5 and 3/5.
Abstract: Titanium carbide (TiC)-coated graphite flakes were prepared using the low-temperature molten salt synthesis technique. Titanium (Ti) particles were mixed with graphite in a mass ratio (Ti/C) between 1/5 and 3/5, and reacted in alkali chloride salts at 650–950°C for 4–8 h. The TiC formation reaction was complete in KCl or the KCl–LiCl eutectic salt after 8 h at 850°C, but not in LiCl or NaCl, indicating that the former were more effective than the latter in accelerating the TiC coating formation. Although various Ti/C ratios were used, the TiC formation reaction was complete in all samples heated for 4 h at 950°C, indicating that the amounts/thickness of TiC coatings could be readily tailored for future castable applications. TiC coatings prepared in KCl or the KCl–LiCl eutectic salt (after 4 h at 950°C or 8 h at 850°C) were of high quality: crack free, homogeneous, and comprising nanosized TiC particles. The coating synthesis process is believed to be dominated by the “template-growth” mechanism.
36 citations
TL;DR: In this article, a mixture of hybrid precursors having both organic and inorganic origins was used for spinel-coated graphite sols and their performance was compared in terms of oxidation resistance and water-wettability.
36 citations
TL;DR: In this paper, the contributions of nanotechnology in selection of raw materials, the binders and choice of additives to improve the quality of refractory materials, and the future of nanotechnical research in refractories are reviewed.
34 citations
TL;DR: In this article, the performance of alumina-carbon castables containing graphite flakes coated by nanosized Ca-doped γ-Al2O3 phases has been investigated in terms of refractoriness under load (RUL) and oxidation resistance tests.
32 citations
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TL;DR: In this article, the porosity and refractive index of thin films from polymeric precursors are varied as follows: volume percent porosity (0% -56%), pore radius (0-3.1 nm); surface area (1.2-263 m 2 g -1 ); refractive indices (118-1.45).
608 citations
TL;DR: Transparent Al2O3, Al 2O3-SiO2 and SiO2 sols were prepared via hydration of TEOS and Al(OC3H7)3 in distilled water and used to coat natural flake graphite as mentioned in this paper.
Abstract: Transparent Al2O3, Al2O3–SiO2 and SiO2 sols were prepared via hydration of TEOS and Al(OC3H7)3 in distilled water and used to coat natural flake graphite. Graphite coated with these sols was dried at 120 °C for 12 h and heat-treated at 500 °C for 2 h to gel the sols. Water-wettability and oxidation resistance of as-received (uncoated) and coated graphites were examined. Al2O3, Al2O3–SiO2 and SiO2 coatings improved graphites water-wettability and SiO2-coated graphite showed the best water-wettability. All the coatings also improved the graphites oxidation resistance, especially at high temperatures (>1100 °C). Addition of Si greatly improved the oxidation resistance of as-received graphite whereas the oxidation resistance of the coated graphites was only slightly improved, suggesting that it is possible to decrease the level of antioxidant used in commercial castable systems.
108 citations
TL;DR: In this article, microstructural analysis indicates that the corrosion of spinel-alumina castables by a liquid steel ladle slag involves initial reaction of CaO in the slag with alumina fines in the refractory bond.
Abstract: Microstructural analysis indicates that the corrosion of alumina-spinel castables by a liquid steel ladle slag involves initial reaction of CaO in the slag with alumina fines in the refractory bond. The slag becomes saturated in CaO and Al 2 O 3 and CA 2 is precipitated from it along with other calcium aluminates. The spinel fines and grains in the refractory take up the MnO/FeO/Fe 2 O 3 from the slag, which becomes silica-rich as CA 2 is precipitated and highly viscous. The thickness of the remnant slag layer on the corroded samples indicates the viscosity of the liquid slag under the test conditions. Further into the refractory CA 6 is formed, firstly crystallized with a tabular morphology in dense regions and then with a similar morphology in more porous regions. Deeper still in the refractory CA 6 takes a whisker/needle habit suggesting some vapour-phase reaction. MgO-rich spinel-alumina castables undergo less corrosion under these conditions as dissolution of MgO leads to a viscous MgO-rich slag which is less corrosive to the Al 2 O 3 components of the refractory.
92 citations
TL;DR: In this paper, the authors measured the electrical properties of spinel powders made from oxide one pot synthesis (OOPS) using impedance spectroscopy in the frequency range from 10 −2 to 10 5 Hz at different relative humidity (RH) levels in the range 4 −90%.
Abstract: MgAl 2 O 4 spinel powders can be prepared via the oxide one pot synthesis (OOPS) process. Porous ceramic oxide bodies can be produced with these powders and used as humidity-sensing materials. Pellets were characterized by SEM and their electrical properties were measured using impedance spectroscopy in the frequency range from 10 −2 to 10 5 Hz at different relative humidity (RH) levels in the range 4–90%. The spinel pellets made of powder from the OOPS process exhibited good humidity sensitivity with a linear response of the logarithm of resistance with RH in the whole RH range tested.
88 citations
TL;DR: Carboxylate−alumoxanes were synthesized by the reaction of boehmite, [Al(O)x(OH)y(O2CR)z]n, with either hexanoic, octanoic or methacrylic acids as mentioned in this paper.
Abstract: Carboxylate−alumoxanes, [Al(O)x(OH)y(O2CR)z]n, have been uniformly doped with a transition metal or lanthanide. Thermolysis of the doped alumoxanes yields homogeneous mixed-metal oxides. The carboxylate−alumoxanes were synthesized by the reaction of boehmite, [Al(O)(OH)]n, with either hexanoic, octanoic, methacrylic, or [(methoxyethoxy)ethoxy]acetic acids. Reaction of the carboxylate alumoxane with either a metal acetylacetonate complex, M(acac)3 (M = Mn, La, Er), V(O)(acac)2, or a salt, [NH4]2[Ce(NO3)6] and [NH4]4[Ce(SO4)4], results in transmetalation and the formation of a doped-alumoxane. Upon thermolysis these doped-alumoxanes result in homogeneous mixed-metal oxides. The formation of single-phase materials is similar to that of traditional sol−gel methodologies; however, the alumoxane precursors are indefinitely stable, in solid and solution. In addition, these precursors show no propensity to segregation or polymerization and are readily processed in aqueous or hydrocarbon medium. The stability of t...
76 citations