One-step mechanosynthesis of nanocrystalline oxides

Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, Ca Fe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD,57Fe Mössbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong c ontrast to the conventio nal solid-state synthes is of the com plex oxides, which req uires prol onged e xposure a t considerably elevated temperatures. It was revealed that the main structural features of the mechanosynthesized oxides a re nonequilibrium cation distribution and distorted oxygen polyhedra

Mechanochemical reactions and syntheses of oxides

Technological and scientific challenges coupled with environmental considerations have prompted a search for simple and energy-efficient syntheses and processing routes of materials. This tutorial review provides an overview of recent research efforts in non-conventional reactions and syntheses of oxides induced by mechanical action. It starts with a brief account of the history of mechanochemistry. Ensuing discussions will review the progress in homogeneous and heterogeneous mechanochemical reactions in oxides of various structures. The review demonstrates that the event of mechanically induced reactions provides novel opportunities for the non-thermal manipulation of materials and for the tailoring of their properties. © 2013 The Royal Society of Chemistry

High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environment of Al nuclei, valuable quantitative insight into the mechanically induced changes in the spinel structure, such as the local cation disorder and the deformation of the polyhedron geometry, is obtained. It is revealed that, independent of the ionic configuration in the initial oxides, the mechanical action tends to randomize cations over the two non-equivalent cation sublattices provided by the spinel structure. The response of the spinels to mechanical treatment is found to be accompanied by the formation of a non-uniform core-shell nanostructure consisting of an ordered crystallite surrounded by a structurally disordered interface/surface shell region. Based on the comparative NMR studies of the non-treated and mechanically treated spinels, an attempt is made to separate the surface effects from the bulk effects in spinel nanoparticles. The non-equilibrium cation distribution and the deformed polyhedra are found to be confined to the near-surface layers of spinel nanoparticles with the thickness extending up to about 0.7 nm. The cation inversion parameter of the mechanically treated spinel is compared with that of the non-treated material at non-ambient conditions. © 2011 The Royal Society of Chemistry

Structural and Mechanical Changes of AlMgSi0.5_{0.5} Alloy during Extrusion by ECAP Method

SPD (several plastic deformations) methods make it possible to obtain an ultrafine-grained structure (UFG) in larger volumes of material and thus improve its mechanical properties. The presented work focuses on the structural and mechanical changes of aluminium alloy AlMgSi$_{0.5}$ (EN AW 6060) during processing by repeated extrusion through the ECAP rectangular channel. After a four-pass extrusion, the samples’ microstructures were observed using an optical microscope, where refinement of the material grains was confirmed. Tensile tests determined the extrusion forces and allowed interpretation of the changes in the mechanical properties of the stressed alloy. The grain size was refined from 28.90 μm to 4.63 μm. A significant improvement in the strength of the material (by 45%) and a significant deterioration in ductility (to 60%) immediately after the first extrusion was confirmed. The third pass through the die appeared to be optimal for the chosen deformation path, while after the fourth pass, micro-cracks appeared, significantly reducing the strength of the material. Based on the measurement results, new analytical equations were formulated to predict the magnitude or intensity of the volumetric and shape deformations of the structural grain size and, in particular, the adequate increase in the strength and yield point of the material