Polycrystalline materials with nanometer-sized grains, termed nanocrystalline materials, can be formed by crystallizing completely amorphous solids under proper heat treatment conditions. The crystallized nanocrystalline materials exhibit some unique structural characteristics and novel properties which are fundamentally different from those of the conventional coarse-grained polycrystalline materials. This article reviews the present state of the art in this field. The current status of research and developments on the nanocrystallization, microstructure and properties of the materials will be summarized. Comparisons of structural characteristics and properties are made between the crystallized nanocrystalline materials and those prepared by other methods. Further considerations of the development and applications of this new class of materials will also be presented.

Nanocrystalline metals crystallized from amorphous solids: nanocrystallization, structure, and properties

Nanoparticles are discrete nanometer (10−9 m)-scale assemblies of atoms. Thus, they have dimensions between those characteristic of ions (10−10 m) and those of macroscopic materials. They are interesting because the number of atoms in the particles is small enough, and a large enough fraction of them are at, or near surfaces, to significantly modify the particle’s atomic, electronic, and magnetic structures, physical and chemical properties, and reactivity relative to the bulk material. Nanoparticle surfaces themselves may be distinctive. Particles may be terminated by atomic planes or clusters that are not common, or not found, at surfaces of the bulk mineral. These, and other size-related effects will lead to modified phase stability and changes in reaction kinetics.

What makes a nanoparticle a nanoparticle? Definitions of the size ranges for molecules, nanoparticles, and macroscopic solids must be compound specific. However, a useful upper limit for nanoparticles is the size at which one of its properties deviates from the value for the equivalent bulk material by an amount that is significantly larger than the error of the method used to make the measurement (a few percent). In practice, some characteristic will probably be different enough to warrant description as a “nanoparticle” if it is less than a few tens of nanometers in diameter, and perhaps less than a fraction of a micron in diameter.

Because of the importance of size-dependent property changes to the materials sciences, size-property relationships have been studied in detail for some systems. For example, for semiconductors, size effects become important when the particle diameter is close to the Bohr diameter of excitons in the bulk phase. Generally, semiconductor size quantization effects (relevant for naturally occurring metal sulfides, for example) appear when particles are less than 10 nm in diameter (Vogel and Urban 1997).

Definition of the …

Nanoparticles in the Environment

Calorimetric measurements of the glass transition are presented for metallic glasses, ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$, and organic polymers with cooling and heating rates ranging over more than three orders of magnitude. Fits of the onset temperatures of the glass transition to a Vogel-Fulcher-type equation give divergence temperatures significantly above the values obtained for Vogel-Fulcher fits to the viscosity. The width of the glass transition extrapolates to a sharp step transition at a finite heating and cooling rate, which is close to the range where the data were taken. The results suggest that the glass transition becomes independent of the experimental time scale in a regime that may be accessible to measurements.

Glass transition on long time scales

Microstructure, fabrication and properties of quasicrystalline Al–Cu–Fe alloys: a review

Aluminum 5083 powder was mechanically milled under liquid nitrogen to achieve a nanocrystalline grain size in the range of 20 to 30 nm. The powder was subsequently sprayed using a nozzle designed with a validated numerical model for cold spray technology. The resulting coatings were evaluated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro- and nanoindentation. The TEM analysis shows that the nanocrystalline grain structure of the cryomilled feedstock powder was retained after the cold spray process. A significant increase in hardness from 104 to 261±8 (HV300g) was observed when comparing the nanocrystalline coating with cast, cold-worked, Al 5083. The ability to use cold spray to produce nanocrystalline large deposits was also demonstrated in this work.

https://link.springer.com/content/pdf/10.1007%2Fs11661-005-0099-y.pdf

Cold spray deposition of nanocrystalline aluminum alloys

The utilisation of labels in description of ternary systems is summarized. Different types of nonvariant three-phase equilibria including critical tie lines are described regarding the Cu-In-Se system. Explaining labels are proposed which are based upon examples found in the literature.

Comments on the labelling of nonvariant three-phase equilibria in ternary systems

A physical displacement across a slip plane or a domain boundary may be resolved into a sequence of phason flips which restore the nearest neighbour configurations and the tile forms of the original quasicrystal. The number or density of required new vertices is correlated with the square of the implied internal space component of the physical shift. Examples are shown which are relevant to domain boundary widths and the ease of progress of physical slip in the relevant quasicrystal.

A tiling approach to the recovery of a slip plane and the interfaces between domains in ico-related quasicrystals

Highly faceted microholes (voids) in icosahedral Al-Mn-Pd quasicrystals form during annealing at temperatures between 750 and 830°C via classical Ostwald ripening. The specimens were single-phase icosahedral with a composition of Al 71 Mn 9 Pd 20 . If such a specimen containing voids is cooled to room temperature with a constant cooling rate of typically 0.6 to 5 K/min, the facets of the voids are frequently found to be decorated by a different material. The decorations have typically a morphology similar to fractals. Specimens rapidly quenched after isothermal heat treatments around 830°C never showed similar decorations. By X-ray microanalysis in a scanning electron microscope it has been found that this decoration material is considerably poorer in Al-content that the icosahedral phase, namely: Al 60 Mn 10 Pd 30 . Accordingly, these decorations are precipitations at the surfaces of voids inside a single-phase icosahedral matrix. This implies that these decorations are formed at the void surfaces bya diffusion induced local equilibrium. The local equilibrium can be understood on the basis of the equilbrium results in a single icosahedral phase.

Phase Equilibria at Internal Interfaces of Icosahedral Al-Mn-Pd

Kalorimetrische Bestimmung der Mischungsenthalpien flüssiger Eisen-Zirkonium-Legierungen / Calorimetric Determination of the Enthalpy of Mixing of Liquid Iron-Zirconium Alloys

Thermodynamic calculations in quaternary transition metal systems

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