Mechanical properties of nanocrystalline materials

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Hallmarks of mechanochemistry: From nanoparticles to technology

Magnesium based materials for hydrogen based energy storage: Past, present and future

Mechanochemical synthesis of hydrogen storage materials

Nanocrystalline HfN produced by mechanical milling: Kinetic aspects

Temperature dependence of electron-capture aftereffects in the semiconductor In 2 O 3

Time-differential perturbed-angular-correlation study of pure and Sn-doped In2O3 semiconductors.

The electric field gradient EFG in hafnium pyrovanadate has been measured at Hf sites at different temperatures with the time-differential perturbed angular correlation method. The results obtained show the existence of a phase transition around 110°C.

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Temperature dependence of the electric field gradient at Ta nuclei in hafnium pyrovanadate

Magnesium hydride is a very attractive material for solid state hydrogen storage due to their high mass and volume capacity, but its slow absortion/desortion kinetics does not favours its practical use in mobile applications. Recently it has been observed that the addition of small quantities of transition metals or their oxides has an important catalytic effect on its hydrogen sorption kinetics. Although this effect is well documented very little is known about the precise mechanisms involved in the observed sorption rate improvement. We present here a study of the sorption properties of several samples in the MgH2/Fe system prepared by mechanical alloying in H2 atmosphere and starting from mixtures of Mg or MgH2 with Fe or Fe2O3 of varying composition. The samples were characterized by X-ray diffraction and Mossbauer spectroscopy, before and after milling and after several H2 absorption and desorption cycles in a Sievert-type volumetric apparatus. Some differences were found in the desorption kinetics that can be correlated with the microstucture resulting from the milling process.

L. A. Mendoza-Zélis

Papers

Nanocrystalline HfN produced by mechanical milling: Kinetic aspects

Temperature dependence of electron-capture aftereffects in the semiconductor In 2 O 3

Time-differential perturbed-angular-correlation study of pure and Sn-doped In2O3 semiconductors.

Temperature dependence of the electric field gradient at Ta nuclei in hafnium pyrovanadate

Hydrogen storage properties of the Mg/Fe system