Synthesis of disordered Fe3C alloy by mechanical alloying of iron powder with liquid hydrocarbon (toluene)

Abstract

Recently a large number of amorphous alloys based on transition metals have been obtained by mechanical alloying [1-5]. Heinike [6] was the first to report the formation of Fe3C by milling iron and carbon powders. Nasu et al. [7] reported about amorphous alloys of Fe3C powders obtained by the mechanical alloying of iron and carbon powders. The aim of this work was to study the possibility of synthesis of amorphous Fe3C alloys by the mechanical treatment of iron powder in liquid hydrocarbon (toluene). The iron powder treatment was performed with a centrifugal planetary mill of Pulverizette type with 25 milling balls (the diameter of the balls, made of tungsten carbide, was 10 ram). 2 g initial powder (the size of the powder particles was ~<300/zm) together with toluene was placed in the closed tungsten carbide container (volume 80 cm 3) of the mill and treated for different times in the range from i to 8 h for each loading. X-ray investigation was carried out with a diffractometer using CoKo~ radiation. The MOssbauer spectra were recorded using a constant-acceleration spectrometer with a 57Co(Cr) source and a resonance scintillation detector. The X-ray and M0ssbauer investigations were carried out at room temperature. Thermomagnetic measurements were performed in the temperature range 77-1100 K with a vibration sample magnetometer and a device for research into magnetic susceptibility. The treatment of powder in toluene leads to essential changes in the MOssbauer spectra and X-ray diffraction patterns in comparison with those of pure 0~-Fe. In the sample spectrum after 4 h grinding the second sextet with a smaller value of hyperfine magnetic field H~ff appears (parameters of H~ff = 20.5 T and isomer shift 6 = 0.1 mms -t in relation to o~-Fe). In the corresponding diffraction pattern of the structural line (110) of the b cc structure of oL-Fe broadening and the appearance of new wide lines of weak intensity at diffraction angles of 20 = 44 and 47 ° were observed. The increase of the treatment time up to 8 h resulted in only a new sextet in the MOssbauer spectrum and a few overlapping broadened lines in the diffraction pattern (Fig. lc). According to the magnetic measurements the specific saturation magnetization at 300 K decreased from 215 A m 2 kg -z for pure oc-Fe to 116 A m e kg -t for powder after 8 h milling. From the analysis of the data obtained, the new state of powders can be concluded to be Fe3C. The formation of Fe3C was confirmed by the diffraction pattern of the powder after 8 h treatment followed by heating for 1 h at 770 K (Fig. ld) [8]. Also, the formation of Fe3C was confirmed by the MOssbauer parameters of the new sextet obtained (as above), which agreed well with the known data for Fe3C [9]. The Curie temperature of this sample was 477 K, which is in accordance with the value known for Fe3C [10]. Thus, after the mechanical treatment of the iron powder in toluene for 8 h, the formation of 100% Fe3C takes place, being confirmed by quantitative analysis of the MOssbauer spectra (Fig. 2). It should be noted that although the lines of the sample spectrum after 8 h milling were broadened,