Grain nanostructures

Figure 10,3. Hardness of WC-Co cermets with nanostructured and conventional grain sizes (after Gleiter 1996, reproduced from a report by Schlump and Willbrandt).

The self-assembly of block polymers, in the bulk, thin film and solution states, produces uniformly sized nanostructured patterns that are very useful for nanofabrication. Optimal utilization of these nanoscopic patterns requires complete spatial and orientational control of the microdomains. However, the microdomains in the bulk state normally have grain sizes in the submicron range and have random orientations. In block copolymer thin films, the natural domain orientations are generally not desirable for nanofabrication. In particular, for composition-asymmetric cylindrical thin films, experimental... 

Fig. 1.16 Particle size and grain size in a nanostructured powder. Black points depict hydrogen molecules ( ) in pores between particles, and hydrogen atoms ( ) diffusing through a grain boundary network and gradually entering the grain interior black triangles point to triple points that are preferential sites for hydrogen atom accumulation...

The coarsest grain size of MgH in the composite containing 10 wt%MgH2 is within 35 0 nm range. Present results confirm our previous findings [179] that the formation of true nanostructure in NaBH is difficult to achieve and hence, clearly demonstrate a high structural stability of the compound under heavy deformation conditions imposed by milling. 

These ordered array materials find interest not only in catalysis, but in several other applications, from optical materials, sensors, low-k materials, ionic conductors, photonic crystals, and bio-mimetic materials.Flowever, with respect to these applications, catalysis requires additional specific characteristics, such as the presence of a thermally stable nanostructure, the minimization of grain boundaries where side reactions may occur, and the presence of a porous structure which guarantees a high surface area coupled to low heat and mass transfer limitations. An ordered assembly of ID nanostructures for oxide materials could, in principle, meet these different requirements. 

So-called nanostructural materials are divided into three main types one-dimensional (or more commonly known as multilayers ) structures made of alternate thin layers of different composition, two-dimensional structures (more commonly known as wire-type elements suspended within a three-dimensional matrix), and three dimensional constructs that may be made of a distribution of fine particles suspended within a matrix (in either periodic or random fashion) or an aggregate of two or more phases with a nanometric grain size (these are illustrated in Fig. 17.1). 

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