Amorphous structural environment

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. 

An acid papermaking environment is corrosive. In the same manner that acidity can affect the reasonable life expectancy of paper by breaking down the amorphous structure of cellulose, acidity can affect the reasonable life expectancy of the working parts of a paper machine by corroding the exposed metal surfaces. An alkaline papermaking environment is noncorrosive, extends life, and reduces maintenance costs. Paper machine systems get dirty, and dirt affects the quality of the paper. 

As with other active-passive-type metals and alloys, the pitting corrosion of aluminum and its alloys results from the local penetration of a passive oxide film in the presence of environments containing specific anions, particularly chloride ions. The oxide film is y-Al203 with a partially crystalline to amorphous structure (Ref 13, 59). The film forms rapidly on exposure to air and, therefore, is always present on initial contact with an aqueous environment. Continued contact with water causes the film to become partially hydrated with an increase in thickness, and it may become partially colloidal in character. It is uncertain as to whether the initial air-formed film essentially remains and the hydrated part of the film is a consequence of precipitated hydroxide or that the initial film is also altered. Since the oxide film has a high ohmic resistance, the rate of reduction of dissolved oxygen or hydrogen ions on the passive film is very small (Ref 60). 

Amorphous silica has also been studied recently using first principle molecular dynamics (Samthein et al., 1995). Such simulations are currently restricted to rather small unit cells (24 Si02 units) and short time spans ( 10 ps), unlike the simulations using interatomic potentials described in Chapter 9. Nevertheless, the direct simulation of the liquid phase followed by a rapid quench produces an amorphous state with structural and electronic properties in reasonable agreement with neutron diffraction and spectroscopic studies. QM simulations are able to treat a wide range of structural environments on an equal footing while providing information on both structural and electronic properties. 

Yoo ES, Im SS (1999) Effect of crystalline and amorphous structures on biodegradability of poly(tetra methylene succinate). J Environ Polym Degrad 7 19-26... 

Poly(lactic acid) (PLA)-based products have been largely considered for both biomedical and environment-friendly applications [1-9]. Processing conditions and final properties of PLAs are strongly determined/influenced by the crystalline or amorphous structure of the polymer [10-12]. 

The atomic sizes of the constituent elements in the ternary R-Al-M amorphous alloys differ significantly. Therefore, the interpretation of the total radial distribution function (RDf) obtained by the ordinary X-ray diffraction method is complicated, and it is extremely hard to obtain structural parameters for each independent pair of elements. By using the anomalous X-ray scattering (AXS) method with which the structural environment around a particular constituent element can be determined, it is expected that this difference is observed and the structural environment around Ni in the amorphous La55Al25Ni2o alloy is estimated in as-quenched, annealed (in the supercooled liquid region) and crystallized states. From these systematic AXS measurements, the structural changes due to crystallization were discussed. 

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