Nanocrystalline structures environment

Analysis of these parameters shows that the greatest potential for corrosion and the smallest corrosion current density characterize nickel with the nanociystalline structure. This highlights its highest resistance to corrosion in the test environment. Increased corrosion resistance of electrochemically produced nickel with the nanocrystalline structure in comparison to microcrystalline nickel may indicate a greater tendency to p>assivity of the nanocrystalline nickel. A passive layer that forms on the surface of nanocrystalline nickel... 

ReflEXAES can be used for near-surface structural analysis of a wide variety of samples for which no other technique is appropriate. As with EXAES, ReflEXAES is particularly suited for studying the local atomic structure around particular atomic species in non-crystalline environments. It is, however, also widely used for the analysis of nanocrystalline materials and for studying the initial stages of crystallization at surfaces or interfaces. ReflEXAES was first proposed by Barchewitz [4.135], and after several papers in the early nineteen-eighties [4.136, 4.168-4.170] it became an established (although rather exotic) characterization technique. Most synchrotron radiation sources now have beam-lines dedicated to ReflEXAES experiments. 

The existence of the surface contribution to the effective magnetostriction of nanocrystalline alloys has been confirmed theoretically in terms of the dipolar model (Szumiata et al. 1999). These authors showed that, due to the limited radius of the nanoparticles, additional magnetostrictive stresses are localised at the interfaces. The evaluation of the influence of the dipolar interaction on the magnetostriction in crystalline grains of perfect spherical shape surrounded by a magnetic environment of about 0.S nm with either crystalline or amorphous structure has been calculated. A similar method was previously used to obtain the surface and volume anisotropy (Draaisma and de Jonge 1988) and to... 

The absence of a sharp diffraction pattern characterizing a catalyst is usually an indication of nanocrystalline rather than amorphous structures. Such patterns may change as a result of changes in the environment without a transformation of the material into a crystalline phase. In these cases a change occurs in the molecular motif leading to changes in coordination polyhedra (e.g., tetrahedral to octahedral upon oxidation or hydration) without a growth in crystallite size. 

Once the amorphous gel is heated, 170 NMR shows that both OZr3 and OZr4 environments remain, although there is an increase in line width. There is also an increase in the isotropic chemical shift of the peaks, especially the OZr4 peak, which moves from 303 to 321 ppm as the gel starts to crystallize. At the crystallization temperature (approximately 360°C), EXAFS results show that there is a distinct change in the structure, with the oxygen correlation now better fit by two closely spaced shells and a large increase in the coordination number to 12 associated with the Zr-Zr correlation. This is likely because the particles are nanocrystalline. 

Structure of the band is such that rotational lines in the P branch accumulate near the bandhead, and the -branch rotational lines extend through the tail of the band. Since the bandhead is such a prominent feature of this band but is still optically thin under these conditions, the equivalent width of the bandhead was integrated to give the C2 densities, rather than integrating across the entire band. The bandhead contains rotational lines originating from nearly 30 rotational levels. The C2 densities in these nanocrystalline diamond CVD environments were determined for both hydrocarbon and fiillerene precursors under the variation of several processing parameters. 

Properties of Nanocrystalline Thin-Film Structures Obtained in the Ion Bombardment Environment... 

It is a well-known fact that the hardness of polycrystaUine structures is defined by their microstruc-ture. In order to have an increased hardness, the structure should be able to oppose formation and motion of dislocations and appearance of microcracks. This problem can be solved by several ways, in particular grain refinement, cold strain, alloying, etc. However, these methods are unacceptable for nanocrystalline objects, because alloying atoms leave the grain volume and segregate at its boundaries and dislocations are not formed at all. Therefore, the microhardness of films obtained in the ion bombardment environment is defined by process parameters and by an opportunity to transform grain boundaries of single-phase material by the second phase. This subsection will delve into consideration of the first component. 

In the case of the microcrystalline structure nickel and NiP alloy in corrosive environment of 0.5M NaCl solution, a pickling of their internal structures occurred over the entire surface exposed and even its internal structures was revealed. On the other hand, corrosion of the nanocrystalline nickel in this environment takes the form of uneven local corrosion. 

Chapters 6 and 7 detail two very different applications of nuclear magnetic resonance. Solid-state nuclear magnetic resonance probes the local environment of atoms. As it probes short-range order, it is a powerful technique for studying, for example, the structure of the nanocrystalline calcium-silicate-hydrate phase, which makes up around half of the volume... 

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