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.

Improving the water-wettability and oxidation resistance of graphite using Al2O3/SiO2 sol-gel coatings

Measures to overcome the main technical di fficulties hindering the development and application of carbon containing castables are discussed The aqueous wettability and dispersion properties of graphite can be improved by coating with materials such as carbides (SiC) and oxides (Al2O3, TiO2, SiO2, MgO, ZrO2) or by forming micropellets / briquettes Thick and dense crack free coatings are needed not only to improve the aqueous wettability and dispersion of graphite, but also its oxidation resistance Small and dense micropellets or briquettes enable a homogeneous distribution of graphite in the matrix to be achieved, along with acceptable mechanical strength and corrosion resistance Coating techniques have also been used to improve the hydration resistance of aluminium based antioxidants, but detailed studies in this area are still needed The main binder systems are currently based on superfine silica fume and hydratable alumina as these do not form low melting phases in castables As well as de

Carbon containing castables: current status and future prospects

Feasible engineering of cathode electrolyte interphase enables the profoundly improved electrochemical properties in dual-ion battery

Improved fast charging capability of graphite anodes via amorphous Al2O3 coating for high power lithium ion batteries

Graphite powders were coated with ZrO2 by the controlled hydrolysis of a zirconium oxychloride aqueous solution. Thehydrolysis process was carried out with temperature control because of the low wettability of ZrO2 to the surface of thegraphite. PVA was added to the solution for the enhancement of Zr ion adsorption. The surface of the graphite particles coatedwith ZrO2 was observed by TEM. There are two types of ZrO2 particles; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 μm size were obtained. The data of oxidation weight loss and surface potentialshow that the graphite surface was successfully modified by the forced hydrolysis of the zirconium chloride aqueous solution.

Preparation of ZrO2 coated graphite powders

Graphite powder was coated with a chelate compound of aluminum and heated at 500°C in air to prepare Al2O3-coated graphite powder. The sedimentation volume and the heat of immersion in water indicated that the wettability of the graphite powder by water was improved by the Al2O3 coating. The oxidation resistance of Al2O3-coated powder was higher than that of the uncoated one. The first and second adsorption isotherms of water vapor indicated that H2O vapor was adsorbed not only physically but also chemically on the Al2O3-coated layer. The specific surface area by N2 and the second adsorption isotherms of water vapor suggest that the layer has micro pores<0.4nm in diameter.

Fujiwara Seiji

Papers

Wettability by Water and Oxidation Resistance of Alumina-Coated Graphite Powder