Development of MgO-C Refractory Having High Oxidation Resistance by Metal Coating Process.

Graphite has been modified with a coating reagent, which can form coating layer of a metal on the surface of graphite, to effectively prevent the oxidation of graphite used as a carbon source, compared to common antioxidants. The oxidation of graphite is resisted by the high oxidation reactivity of metal and the oxygen barrier effect of coating layer. Therefore, the metal layer should be homogeneously and continuously coated on the surface of graphite and the coating efficiency of metal should be increased. The metal layer was formed with a metal precursor existed only with a ion phase in an aqueous solution. The unmodified graphite was totally degraded and oxidized after the combustion test at 1000 degrees C in air. However, as graphite was modified by the metal precursor, the color of carbon was not changed after the heat treatment. These results mean that the coating layer is individually and uniformly formed on a surface of graphite, delaying the oxidation of graphite. Consequently, MgO-C refractory with the high oxidation resistance could be successfully fabricated by the modification of graphite with the metal precursor.

Adhesion phenomena between particles according to the content of organic binder in core for thin-wall casting.

The content of organic binder in a core for thin-wall casting has been controlled to investigate the adhesion phenomena of inorganic binder between starting particles, as directly related to the mechanical and thermal properties of the core. The inorganic binder precursor was composed of tetraethyl orthosilicate and sodium methoxide as the silicon dioxide and sodium oxide precursors, respectively. Poly(vinyl alcohol), a hydrophilic polymer, was used as an organic binder. The particles coated with the inorganic precursor were sculpted with the organic binder and then the prepared core samples were heated at 1000 degrees C for 1 h. The core samples prepared with the optimum content of organic binder show the highest fracture strength. This may be due to the enhancement of adhesion by the glass phase formed between starting particles. However, when too much or too little organic binder is employed, the strength values of the core samples are significantly decreased. This is because the network structure of the glass phase is not inadequately created or the glass phase is not uniformly developed between starting particles, resulting in the insufficient contact between starting particles during the convert process.