W.A. Kaczmarek

Preparation of Fe/sub 3/O/sub 4/ and /spl gamma/-Fe/sub 2/O/sub 3/ powders by magnetomechanical activation of hematite

Total phase transformation of hematite to magnetite was accomplished at room temperature by wet magnetomechanical activation of hematite. Low energy mechanical activation of the oxide surface is sufficient to effect the transformation. Oxygen bonds on /spl alpha/-Fe/sub 2/O/sub 3/ oxide surface are apparently broken during the mechanical activation process and oxygen is released (removed) to the dispersing polar liquid. The oxygen pressure during the process as well the nature of the dispersing liquid have a critical influence on successful and fast phase transformation. Thus, all preparations performed in air, dry conditions or with nonpolar hydrocarbons (benzene, anthracene) show that the process of hematite reduction is non existent or very slow. Normal air pressure and/or application of hydrocarbons suppress the transformation. >

Synthesis and structural evolution of tungsten carbide prepared by ball milling

Tungsten carbide has been synthesized directly by ball-milling tungsten powder and activated carbon in vacuum. The structural development of the WC phase with milling times up to 310 h has been followed using X-ray, neutron diffraction and scanning electron microscopy. Subsequent annealing (at 1000 °C for 1 and 20 h) of material milled for 90 h or longer, results in samples comprising almost entirely crystalline WC. The production of WC itself during milling results in enhanced iron contamination from the steel mill and balls on extended milling which were monitored by energy-dispersive X-ray and Mossbauer spectroscopies.

Mechanochemical transformation of haematite to magnetite

Abstract The transformation of α-Fe 2 O 3 to Fe 3 O 4 on wet-milling α-Fe 2 O 3 under low energy conditions in vacuum has been investigated by Mossbauer effect spectroscopy. The structural transformation is discrete with no evidence of interdissolution of the 2 phases. The resultant ∼ 30 nm scale crystal blocks of magnetite exhibit hyperfine features characteristic of bulk Fe 3 O 4 although evidence for structural distortion of the octahedral (particularly) and tetrahedral iron sites is obtained. The results are consistent with a primarily physical origin for the transformation in which oxygen bonds on the cleaved α-Fe 2 O 3 surface are broken and oxygen released to the milling environment.

Ball milling of Fe75-C25 : formation of Fe3C and Fe7C3

Abstract Powder mixtures of Fe 75 -C 25 (both graphite and activated carbon) have been ball-milled in vacuum for periods of up to 285 h. X-ray diffraction, Mossbauer spectroscopy and thermal analysis measurements indicate that an amorphous Fe 3 C-type phase is produced on short-term milling (less than 70 h), with a crystalline Fe 3 C being obtained on further milling to 140 h. This Fe 3 C-type phase was found to undergo partial carbon oxidation between 500 and 1000 °C during thermogravimetric measurement, indicating the metastable state of this phase. The carbon-rich Fe 7 C 3 phase was observed on extended milling of Fe 75 C 25 (graphite) to 285 h, in agreement with earlier findings.

Extended solid solubility in ball-milled Al-Mg alloys

Mixtures of elemental aluminium and magnesium powders corresponding to Al70Mg30 and Al50Mg50 compositions have been mechanically alloyed. After milling, an extended solid solubility of magnesium in aluminium upto 18 at% in the case of Al70Mg30 and 45 at% for Al50Mg50 was observed. These materials typically nanostructural (grain size 2–10 nm) transform into equilibrium structure upon heating. The stability of these materials was investigated using thermal analysis.

Ball-milling of Fe-C (20–75% Fe)

Abstract Powder mixtures of Fe and activated C containing 20, 50 and 75 at % Fe have been milled in vacuum for periods of up to 210 h. X-ray diffraction and Mossbauer effect measurements of the as-milled and annealed materials (500°C, 15 min) show the presence of γ-phase austenite (typically ∼10%) and the Fe3C phase at different stages of the milling process in all samples, with the Fe7C3 phase also present in the milled Fe50C50 material. The behaviour of Fe-C (activated) milled in vacuum is found to be similar to that of Fe-C (graphite) milled in a gaseous atmosphere.

Formation of titanium nitrides via wet reaction ball milling

A new mechanochemical route to synthesize TiN has been developed by ball milling elemental titanium powders with the organic compound pyrazine in a benzene solution for periods of up to 336 h. The structures of the milled powders were examined by means of X-ray diffractometry. Titanium nitrides were formed directly during the milling. Unlike the dry ball-milling process, the present wet milling resulted in the formation of an intermediate titanium nitride Ti2N which has never been found in previous studies using dry milling. With increasing milling time, Ti2N was observed to gradually transform into the stoichiometric compound TiN. Upon heating, the Ti2N formed during milling was completely transformed to TiN. The intrinsic mechanisms of the solid–liquid reactions are discussed.

Preparation of high‐coercivity fine barium ferrite powder

The structural and magnetic properties of the thermally activated transformation from nanostructural material, mechanically disordered and decomposed BaFe12O19 ferrite powder to pure crystalline phase, have been studied by x‐ray diffraction, scanning electron microscopy, and vibrating sample magnetometry analysis techniques. All experiments were performed on as‐milled (1000 h) in air, and in vacuum and annealed Ba‐ferrite samples (4 h at 773 and 1273 K). In parallel with the structure and particle morphology changes, we investigate the influence of heat treatment on the powder M‐H hysteresis parameters in relation to the preparation routes, i.e., powder obtained by ball milling in air and vacuum, and annealed in air or vacuum.

The effect of milling condition on the formation of nanostructures; Synthesis of vanadium carbides

The mechanical alloying process (MA), has been successfully used to synthesize a number of commercially important alloys and composites. High-energy ball-milling is generally used to mechanically alloy metallic powder and develop microstructural changes to enhance structure dependent properties. Mechanical alloying is usually carried on in commercially available milling devices as: vibratory ball mills or planetary mills. These ball mills, designed mainly for pulverization of ceramics, have very limited control of the milling process. It can be noticed that in commercial ball mills the maximum milling condition has been selected to reduce the milling time. Available adjustment of the milling energies is limited to a narrow range. There are certain disadvantages to that near fixed characteristic in studying of the effect of milling condition on the formation of nanostructures. None of the commercially available devices was designed with the specific needs of the MA process in mind. In this work ball milling was performed using a locally designed ball mill with precise control of milling parameters. The effect of milling intensity on the formation of nanostructures and, in consequence, of V{sub 2}C and VC intermetallics, is described in this paper.

Application of surface active substances in mechanical alloying

Abstract Solid state reactions during mechanical alloying of metal-metal and metal-metalloid mixtures can be dramatically affected by small amounts of organic surfactants. We discuss the extended solid solubility of magnesium in aluminium, the formation of highly reactive nanostructures of TiC and AlTi, and the particle shape and size modifications in (CoFe)75Si15B10 soft magnetics. A decreased level of contamination with the milling cell materials is also observed.