Low-Temperature Synthesis of TiC from Carbon-Infiltrated, Nano-porous TiO 2
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TION
TITANIUM carbide (TiC) has high hardness, high melting temperature, and high chemical and thermal stability.[1–6] Because of these desirable properties, TiC is widely used in many applications including cermets,[7] cutting tools,[8] and corrosion-resistant coatings.[9] TiC is industrially synthesized from titanium oxide and carbon through the following reaction: TiO2 ðsÞ þ 3C ðsÞ ¼ TiC ðsÞ þ 2CO ðgÞ ðDH ¼ 539 kJ/mol;
½1
DG ¼ 0 at 1287 CÞ;
where DH is the standard enthalpy change of the reaction and DG is the standard Gibbs energy change of the reaction.[10–14] Due to the strongly endothermic nature of the reaction, a large supply of heat is required to complete the reaction. Industrially, this
MASAFUMI SANADA is with the Graduate school of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan. KEISUKE ABE, ADE KURNIAWAN, TAKAHIRO NOMURA, and TOMOHIRO AKIYAMA are with the Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan. Contact e-mail: [email protected] Manuscript submitted March 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
reaction requires a heat treatment at 1700 C to 2100 C for 10 to 24 hours.[3,15,16] That is why the synthesis of TiC consumes so much energy and significant energy savings can be achieved if the reaction temperature is lowered. Dewan et al. investigated the effect of different gas atmospheres on carbothermal reduction of TiO2 and ilmenite ore.[17–19] They revealed that the reduction reaction was the fastest under hydrogen. Under an inert atmosphere, reduction degrees of up to 90 pct could be achieved through heating at 1400 C for 4 hours, and similar reduction degrees could be accomplished under hydrogen atmospheres at 1300 C for 2 hours. Hosokai et al. revealed that carbon-infiltrated porous iron ore prepared by tar vapor deposition could be reduced at a much lower temperature than usual.[20] The decrease in reduction temperature is due to the effect of close contact between iron oxide and carbon through the nanopores of the iron ore. Ilmenite (FeTiO3) ore, one of the typical ores of titanium, is usually used as a starting material to synthesize titanium and titanium oxide. It has been reported that ilmenite ore can be turned into nanoporous TiO2 by acid leaching.[21–24] Low-temperature synthesis of TiC may be achieved if the nanopores of porous ilmenite ore are filled with carbon. However, there have been as yet no reports of such a process. The purpose of this study is to prepare carbon-infiltrated TiO2 from porous TiO2 obtained by acid leaching of ilmenite ore and to observe its carbonization behaviors. The carbonization behaviors were investigated at the temperature of 1300 C or lower.
II.
EXPERIMENTAL PROCEDURES
Figure 1 shows a schematic image of the experimental procedures. The experiments were composed of three sections: (a) preparation of porous TiO2, (b) production of carbon-infiltrated TiO2, and (c) synthesis of TiC. A. Preparation of Porous TiO2 Natural i
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