Paolo Matteazzi

Mechanically driven syntheses of carbides and silcides

Most metal carbides or slicides may be synthesized at room temperature, by ball milling mixtures of elemental powders for some tens of hours with a vibratory mill. Both stable and metastable compounds containing a high density of defects can be obtained. In general, phases stable at low temperatures are synthesized. This observation allows us to confirm recent estimations for the maximum temperature (∼600 K) attained in these powders during mechanical alloying. Exceptions are found for some MSi2 suicides with M = titanium, iron or molybdenum for which both low- and high-temperature phases are formed.

Reduction of haematite with carbon by room temperature ball milling

Abstract The solid state reduction of haematite (α-Fe2O3) to mainly nanocrystalline wustite by room temperature dry ball milling of haematite and carbon, in an inert atmosphere, is described. In addition to wustite, a smaller amount of nanocrystalline magnetite is also formed, possibly by a disproportionation reaction of wustite. The reaction is completed in about 70 h in a Spex vibratory ball mill. Haematite alone is converted by dry milling for 70 h into nanocrystalline magnetite with an average crystallite size of 10 nm as shown by X-ray diffraction and Mossbauer spectroscopy.

Designing a high energy ball-mill for synthesis of nanophase materials in large quantities

Abstract Nanophase materials can be synthesized by high energy milling. However, processing of large quantities finds a limitation in the devices available commercially, which are usually designed mainly for comminution and for laboratory-scale operations. We propose the design of a high energy, high capacity ball-mill which can be easily scaled up. An experimental device capable of processing up to about 250 g of powders with about 5 kg of balls has been realized. Impact velocities of about 3.5 m s −1 has been measured with operating frequencies of 17 Hz. The synthesis of nanophase iron carbides (assumed as a test system) is shown to be feasible with the new mill, with kinetics comparable with the best obtained in a Spex mill.

Synthesis of nanostructured materials by mechanical alloying

Materials can be processed by grinding not only for comminution, but also to obtain a variety of structures (amorphous, nanophased), fine mixing of phases, alloys and to directly synthesize compounds such as carbides. Nanocomposites can also be synthesized by reduction, exchange and mixing reactions driven by grinding, as well as by combining the above processes. Large scale economical production of such materials is feasible by grinding in mills designed for that purpose. The mechanical properties of materials are enhanced by the nanophase structure.

Mechanosynthesis of nanophase materials

Abstract Among the synthesis methods of nanocrystalline materials, high energy milling is promising at production scale. The mechanochemical synthesis (Mechanosynthesis) of nanophase materials can be realized by direct synthesis of compounds from the elemental powders or by several exchange, transfer and mixing reactions such as for: 1) most metal carbides; 2) intermetallic compounds (silicides, aluminides); 3) semiconducting III-V compounds (GaAs and AlAs); 4) metal-oxide M-RO composites by reduction of a metal M oxide with a suitable reductant R; 5) metal-sulhide M-RS composites by reduction of a metal M sulphide with R; 6) fluorides and nitrides by exchange reactions. Reactions are driven in a ball mill at almost room temperature.

Mechanical alloying of Fe and V powders: Intermixing and amorphous phase formation

Moessbauer spectrometry and x-ray diffractometry were used to characterize the microstructural changes that occurred during the mechanical alloying of Fe and V powders. After 3 hrs of essentially no interatomic intermixing, an Fe-V alloy began to form. At first the chemical composition of this alloy was highly inhomogeneous, having large variations over distance scales of less than 100 A. After about 24 hrs of ball milling, the alloy homogenized and then became at least partly amorphous.

A study of formation of nanometric W by room temperature mechanosynthesis

Abstract Nanometric particles of elemental tungsten can be produced by solid state room temperature reduction of tungsten (VI) oxide with magnesium metal. The reaction is driven by high-energy ball milling powder mixtures of WO 3 and Mg and involves a thermite route that allows for very short reaction times (as small as 8 min) under the proper milling conditions. The evolution of the reaction was followed as a function of time by X-ray diffraction, showing a gradual decrease in crystallite size of the reactant WO 3 , with formation of intermediate reaction products, until a near-instantaneous reaction takes place leaving only MgO and elemental W as final products. MgO was removed by leaching in diluted HCl and high purity tungsten (purity >99%) was obtained with a typical molar yield of 84%. The W powders are formed of impact welded aggregates of small particles of homogeneous dimension of about 70–100 nm, the typical crystallite size is 19 nm.

Mechanically activated room temperature reduction of sulphides

Abstract Solid state room temperature reduction and exchange reactions of metal (M) sulphides are described. Reactions are driven by ball mining powder mixtures of the sulphide and the reductant (R) or exchange compound (CaO). Reduction reactions show a complete reduction of the metal sulphide with formation of M-R sulphide nanocomposites. Exchange reactions with CaO show the formation of M oxide -CaS nanocomposites. Reactions having positive enthalpy or even positive free-energy changes in a wide temperature range are shown to occur. The effect of milling iron sulphide alone is also reported. Milling was performed for 24 h to assess the feasibility of the various reactions involved. X-ray diffraction and Mossbauer spectroscopy for iron-containing systems were used to characterize the powders before and after processing.

Mössbauer study of mechanosynthesized iron carbides

Syntheses of Fe1−xCx alloys (forx≲0.15) and carbides (for 0.15≲x≲0.50) can be obtained by room temperature grinding of the elemental Fe and C powders. The formation of cementite is completed after about 20 h, whereas the alloys are synthesized in critical processing conditions. Synthesized cementite has a high density of defects and particle size down to 10 nm.

Mechanomaking of Fe/Al2O3 and FeCr/Al2O3 nanocomposites powders fabrication

Abstract Nanocomposite powders (Fe or Fe-Cr alloy)/α-Al2O3 (75 and 85 vol.%) were obtained by room-temperature high-energy milling powder mixtures of hematite (and chromium oxide) with aluminum and alumina in a high-capacity mill for 8-10 h. The composition of iron and iron alloys was followed by Mossbauer spectroscopy, while the appearance of other phases was revealed by X-ray diffraction. The powder particles produced are assemblies of grains (10–20 nm in size) with a wide size distribution (from well below 1 μm up to several hundreds) and low porosity (fully dense particles). Both the metallic and ceramic phases have crystallite sizes below 15 nm for all the compositions investigated. Nano-nano type ceramic nanocomposites were, therefore, obtained.