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Included here are ceramics, metals, and metal oxide nanoparticles. In the last two decades a class of materials with a nanometer-sized microstructure have been synthesized and studied. These materials are assembled from nanometer-sized building blocks, mostly crystallites. The building blocks may differ in their atomic structure, crystallographic orientation, or chemical composition. In cases where the building blocks are crystallites, incoherent or coherent interfaces may be formed between them, depending on the atomic structure, the crystallographic orientation, and the chemical composition of adjacent crystallites.
Materials Made from Nanometer-Sized Crystallites are Microstructurally Heterogeneous
In other words, materials assembled of nanometer-sized building blocks are microstructurally heterogeneous, consisting of the building blocks (e.g. crystallites) and the regions between adjacent building blocks (e.g. grain boundaries). It is this inherently heterogeneous structure on a nanometer scale that is crucial for many of their properties and distinguishes them from glasses, gels, etc, that are microstructurally homogeneous.
Grain Boundaries and Deviation of Nanostructured Materials
Grain boundaries make up a major portion of the material at nanoscales, and strongly affect properties and processing. The properties of NsM (Nanostructured Materials) deviate from those of single crystals (or coarse grained polycrystals) and glasses with the same average chemical composition. This deviation results from the reduced size and dimensionality of the nanometer-sized crystallites, as well as from the numerous interfaces between adjacent crystallites. An attempt is made below to summarize the basic physical concepts and the microstructural features of equilibrium and non-equilibrium NsM.
Properties and Benefits of Nanocrystallites Made from Bulk Inorganic Solids
Nanocrystallites of bulk inorganic solids have been shown to exhibit size-dependent properties, such as lower melting points, higher energy gaps, and non-thermodynamic structures. In comparison to macro-scale powders, increased ductility has been observed in nanopowders of metal alloys. In addition, quantum effects from boundary values become significant, leading to such phenomena as quantum dot lasers.
Using Nanometals and Oxides as Catalysts, Starting Materials for Reactions, and in Nanocomposites
One of the primary applications of metals in chemistry is their use as heterogeneous catalysts in a variety of reactions. In general, heterogeneous catalyst activity is surface dependent. Due to their vastly increased surface area over macro-scale materials, nanometals and oxides are ultra-high activity catalysts. They are also used as desirable starting materials for a variety of reactions, especially solid-state routes. Nanometals and oxides are also widely used in the formation of nanocomposites. Aside from their synthetic utility, they have many useful and unique magnetic, electrical, and optical properties.
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