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 critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

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Mechanochemistry: opportunities for new and cleaner synthesis

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

A review of about 300 published and unpublished rock friction experiments that reproduce seismic slip conditions suggests that a significant decrease in friction occurs at high slip rate. Extrapolating the experimental data to conditions that are typical of earthquake nucleation depths, the authors conclude that faults are lubricated during earthquakes, irrespective of the fault rock composition or specific weakening mechanism involved. This study reviews a large set of fault friction experiments and finds that a significant decrease in friction occurs at high slip rate. Extrapolating the experimental data to conditions typical of earthquake nucleation depths, it is concluded that faults are lubricated during earthquakes, irrespective of the fault rock composition or specific weakening mechanism involved. The determination of rock friction at seismic slip rates (about 1 m s−1) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip1. Given the difficulty in determining friction by seismological methods1, elucidating constraints are derived from experimental studies2,3,4,5,6,7,8,9. Here we review a large set of published and unpublished experiments (∼300) performed in rotary shear apparatus at slip rates of 0.1–2.6 m s−1. The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built4,5,6, quartz-built3 and carbonate-built7,8) rocks and non-cohesive rocks (clay-rich9, anhydrite, gypsum and dolomite10 gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger11,12 a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates13,14 suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7–15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.

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Fault lubrication during earthquakes

Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

Mechanochemistry and Nanoscience.- High-Energy Milling.- Selected Identification Methods.- From Minerals to Nanoparticles.- Mechanochemistry in Minerals Engineering.- Applied Mechanochemistry.

Mechanochemistry in Nanoscience and Minerals Engineering

https://digital.csic.es/bitstream/10261/110775/1/Influence%20of%20the%20milling%20parameters.pdf

Influence of the milling parameters on the mechanical work intensity in planetary mills

Various types of nanocrystalline materials have been prepared using high-energy milling. Bismuth–ceramic (Bi/MgO, Bi/Al2O3, Bi/SiO2) and copper–iron sulphide (Cu/FeS) composites as well as lead sulphide (PbS) nanocrystalline particles have been synthesized with this technique. X-ray powder diffraction was used to characterize the composition and particle size of as-prepared nanopowders. PbS particles as nanophase may be prepared in the laboratory planetary mill as well as in an industrial vibratory mill. High-energy milling thus has considerable possibility for easily scaling up the production of advanced materials under ambient conditions in reasonable time without the use of any solvent.

Preparation of nanocrystalline materials by high-energy milling

The role of multi-elements and interlayer on the oxidation behaviour of (Hf-Ta-Zr-Nb)C high entropy ceramics

Au-Ag noble metal wastes represent a wide range of waste types and forms with various ballast elements and components. The thiourea process of gold and silver extraction from ores, concentrates or secondary raw materials con- sists of gold and silver leaching into the thiourea solution and the consequent precipitation of these metals from the solu- tion. Due to the non-toxic character of thiourea it is the perspective alternative to the up to now most frequently used cya- nide method. The thiourea leaching of gold and silver from electronic waste, goldsmith's waste and ceramic waste using crushing as the pretreatment step was investigated. For electronic waste, it was possible to achieve 97 % gold and 94 % silver recovery within 120 minutes of thiourea leaching. Up to 98 % of gold and 96 % of silver were recovered from gold- smith's waste after 60 minutes of leaching. In the case of ceramic waste, we achieved up to 98 % gold and 97 % silver ex- traction efficiency after only 45 minutes of leaching. In comparison with the classical cyanide leaching, thiourea leaching acts faster and without a harmful environmental impact.

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Peter Balaz

Papers

Mechanochemistry in Nanoscience and Minerals Engineering

Influence of the milling parameters on the mechanical work intensity in planetary mills

Preparation of nanocrystalline materials by high-energy milling

The role of multi-elements and interlayer on the oxidation behaviour of (Hf-Ta-Zr-Nb)C high entropy ceramics

Leaching of Gold and Silver from Crushed Au-Ag Wastes