Amorphous scattering profile

Figure 5.6 Wide-angle neutron scattering profiles measured at the various temperatures for (c) DHDPE/LLDPE(2) and (d) DHDPE/LLDPE(3) blend samples in comparison with the profiles of (a) the amorphous state and (b) the crystalline state calculated for the pure DHDPE and the blend of D and H chain components. In (c), the low angle broad scattering is detected at any temperature due to the homogeneous mixing of D and H species in the same crystallite state as well as in the melt state. In (d), the low angle scattering can be seen only in the molten state, while it becomes lower when the sample crystallizes into the separated phases of D and H chains. These observations are consistent with the simulated results of (a) and (b).

The TEM image of the MN-270-Pt nanocomposite after incorporation of pla-tinic acid is presented in Fig. 3.15. One can see that the material contains nanoparticles with a diameter exceeding 0.7 nm (the estimated resolution of the microscope). The mean particle diameter calculated from a particle size histogram is 1.6nm and standard deviation is 0.6 nm. Evidently, since HPS is a very hydrophobic matrix, Pt species do not dissipate within a polymer matrix but form well defined clusters. light colored areas in the TEM image indicate macropores. The XRD profile of this sample confirms the absence of the Pt-containing crystaUine phase, but suggests the presence of Pt amorphous scatterers. 

In fig. 120, the scattering profile of the crystallized sample is compared with the peak positions for several La-Ni and La-Al compounds (Matsubara et al. 1992). All of the compounds except LaaNi explain the experimental data, although a complete match between the compounds and the data is not obtained. Thus, at the present stage, decisive conclusions about the crystalline phase(s) in the crystallized sample cannot be drawn. However, it is plausible that the atomic structure of the crystallized sample may be close to that of these compounds. From a calculation of interatomic distances in La Ni3 and LaNi, it is predicted that the atomic distance is estimated by assuming La-Ni pairs. Identical coordination numbers are obtained for both RDFs in fig. 119, although the difference between the atomic distances in the two RDFs for the crystallized sample is much larger than that for the amorphous samples. This may result from an incorrect assumption concerning the crystalline phase(s) present. 

The results of SAXS (small-angle X-ray scattering) profile analysis yield the size distribution and frequency of particles and are plotted in Fig. 10.4. Particles with radius of about 1 nm were formed in as-MA powder and heat-treated powder below 800°C, even though the results of XRD measurements showed that the oxide complex particles were not detected at those temperatures. This result is quite surprising, but it is supposed that amorphous atomic clusters of 1 nm size were formed at temperatures below 800°C. Therefore, the oxide complex particles in crystalhne stmcture grow in size with broad size distribution with increasing temperature between 960 and 1200°C. 

Four major computational steps are necessary to separate the individual peaks and the different profile-broadening components (i) correction and normalisation of the diffraction data, (ii) resolution of the total peak scattering from the so-called background scatter, and resolution of crystallographic, para-crystalline, and amorphous peaks from each other, (iii) correction of the resolved profiles for instrumental broadening, (iv) separation of the corrected profiles into size and distortion components. In this paper we will discuss these steps in turn, but most attention will be paid to the hitherto largely neglected step of profile resolution. 

It shall be assumed in this chapter that molecular arrangement in the bulk of solid explosives, and all amorphous and liquid explosives, has no preferred orientation direction. The diffraction patterns in this case are isotropic around the primary X-ray beam, and the vector quantity, x, can be replaced by its scalar magnitude. It is customary to speak of diffraction profiles, rather than patterns, when isotropy obtains and the diffraction profiles are derived by integration of the (circularly-symmetric) diffraction pattern over the azimuthal component of the scattering angle. 

The residual difference after a successful DDM refinement or/and decomposition can be considered as a scattering component of the powder pattern free of Bragg diffraction. The separation of this component would facilitate the analysis of the amorphous fraction of the sample, the radial distribution function of the non-crystalline scatterers, the thermal diffuse scattering properties and other non-Bragg features of powder patterns. The background-independent profile treatment can be especially desirable in quantitative phase analysis when amorphous admixtures must be accounted for. Further extensions of DDM may involve Bayesian probability theory, which has been utilized efficiently in background estimation procedures and Rietveld refinement in the presence of impurities.DDM will also be useful at the initial steps of powder diffraction structure determination when the structure model is absent and the background line cannot be determined correctly. The direct space search methods of structure solution, in particular, may efficiently utilize DDM. 

Accordingly, Fig. 4 shows the X-ray diffraction profiles of Nafion 117 and the composite membranes, prepared as described in the experimental section, in the protonic form and dry state. The broad diffraction peaks at 26 = 12-20° result from a convolution of amorphous (20 = 16) and crystalline (20 = 17.50) scattering from the polyfluorocarbon chains of Nafion . 

SAXS profiles, the low angle maximum associated with scattering from well-organised crystal domains was absent in the former, the structure being essentially amorphous. Nafion recast from low-boiling solvents retains a col-... 

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