抄録
Thin iron films formed by evaporation were carburized in CO gas stream. The carbides ε, χ and θ were found to be formed in the temperature ranges (i) below 250°C, (ii) from 250° to 350°C and (iii) above 350°C, respectively. The ε-carbide is hexagonal with lattice constants a=4.767Å and c=4.354Å, and its structure belongs to the space group P6322, iron atoms occupying 6g positions with the parameter x=1⁄3 and carbon atoms 2d positions. Irreversible phase transitions from ε to χ and from χ to θ take place at 380°∼400°C and at about 550°C, respectively. By the transitions changes in the chemical compositions may be very small. Observation on the crystal growth suggests that a mechanism of the ε-carbide formation is different from that of the χ- and θ- carbide formations.
