Oriented crystal fraction

The total crystal fraction, oriented crystal fraction (/oc). and unoriented crystal fraction (/uc) during extension and retraction have been analyzed. Results can be described as follows. At strain zero, the total crystal fraction was the same as the unoriented crystal fraction, which was about 14%, and both values decreased with strain. This indicates that a fraction of the original crystals was destroyed at the initial deformation stages. (This phenomenon was also reported in ethylene-based ethylene-propylene copolymer (34).) At strain 0.7, the total crystal fraction decreased about 4% (from 14% to 10%) at strains above 0.7, both total crystal fraction and oriented crystal fraction increased with strain, indicating the occurrence of strain-induced crystallization, whereas the unoriented crystal fraction decreased continuously with strain. The increase of the total crystal fraction was slower than that of the oriented crystal fraction, suggesting that some unoriented crystals were reoriented by... 

It should be noted that the fraction of ECC in samples obtained by other methods described in Sect. 2 is approximately as small as that of the framework in the orientation-ally crystallized samples. These methods differ in details but depend on the mechanical treatment of the crystallizing system and are therefore given the common name stress-induced crystallization . Although the structure of the samples obtained by these methods has some features in common with that of orientationally crystallized samples, the thermodynamics and kinetics of orientational crystallization are fundamentally different from the mechanism of stress-induced crystallization. 

The total cross-section in any direction is independent of polarisation, but the individual line cross-sections are not. A typical oriented crystal Mossbauer spectrum of FeCOa is shown in Fig. 6.15. One of the consequences of the modified theory is that the theoretical area ratio is comparatively insensitive to the recoil-free fraction and that it is unrealistic to determine it by an area ratio method. The presence of impurities and imperfections in the mineral specimens was held to explain some of the experimental deviations from prediction. No direct evidence for anisotropy of the recoil-free fraction was obtained, a conclusion since verified by Goldanskii [50], who made new polarisation measurements using single crystals of FeCOa as polariser and analyser. 

FIGURE 3.18 Total anisotropic fraction, crystal fraction, and oriented amorphous fraction of sulfur vulcanized NR stretched slowly at ambient temperature. The upper points correspond to extension, and the lower to retraction. For strains >200%, crystallization is induced, resulting in a decrease in the amorphous phase orientation. 

There are two well-known models of GBs that were developed primarily from studies of metals by considering the relative misorientation of the adjoining grains. These are the coincidence-site lattice (CSL) theory and the dis-placement-shift-complete lattice (DSCL). We first define two special quantities E and E Imagine two infinite arrays of lattice points (one array for each crystal) they both run throughout space and have a common origin. For certain orientations, a fraction of the points in each lattice will be common to both lattices. 

All of the fractional amounts of main and sub-crystals, amorphous content, and randomly oriented crystals decrease by irradiation. The reductions of the sub-crystal and randomly orioited crystal are more extensive than the main. The amorphous content was reduced completely in PTOX irradiated over 0.3 MGy. A weight loss took place as a result of irradiation in air as also shown in Table 5.1, indicating the depression of the melting point and the broadening of the endothermic peak by vigorous radiolysis. 

Table 5.1. Reductions of fractional amounte of main crystals, sub-crystals, amorphous contents, and randomly oriented crystals, and weight loss of poly(trioxane) irradiated in air at room temperature...

A very remarkable deconvolution procedure, schematized in Figure 21.3, has been proposed, by which it is possible to extract additional structural information i.e., fractions of oriented crystal, unoriented crystal, oriented amorphous, and unoriented amorphous phases) besides conventional data such as crystal unit cell parameters and crystal size. 

As previously seen, the WAXD pattern of the unstretched sample exhibits an isotropic amorphous halo with no preferred orientation. As deformation is applied, the WAXD pattern becomes the superposition of a diffraction pattern due to oriented crystals and of a residual amorphous halo. The isotropic contribution at the deformed state corresponds to the original amorphous halo that appears in the WAXD pattern before stretching. The anisotropic contribution is composed of oriented crystal reflection peaks and a small amount of oriented amorphous phase. After having separated the two contributions, i.e. isotropic and non-isotropic, ratioing of the crystal diffraction intensity over the total scattered intensity is necessary to measure the mass fraction of the strain-induced crystals. To obtain the total scattered intensity volume, a quite laborious procedure must be carried out, " but afterwards a normal peak fitting procedure can be applied to deconvolute the intensity profile into crystalline peaks and an amorphous halo. On the basis of the data so obtained, it is therefore possible to estimate the amounts of total isotropic and anisotropic... 

Because of the rotation of the N—N bond, X-500 is considerably more flexible than the polyamides discussed above. A higher polymer volume fraction is required for an anisotropic phase to appear. In solution, the X-500 polymer is not anisotropic at rest but becomes so when sheared. The characteristic viscosity anomaly which occurs at the onset of Hquid crystal formation appears only at higher shear rates for X-500. The critical volume fraction ( ) shifts to lower polymer concentrations under conditions of greater shear (32). The mechanical orientation that is necessary for Hquid crystal formation must occur during the spinning process which enhances the alignment of the macromolecules. 

In conclusion, the fundamental features of various methods for obtaining high strength systems from flexible-chain polymers should also be mentioned. Since the presence of ECC leads to an increase in the fraction of tie chains in crystallized samples (their number can be increased by other methods not related to a direct formation of ECC, e.g. by orientational drawing investigated by Marikhin and Myasnikova4)), the main tech-... 

With powdered samples, an image of diffraction lines occurs because a small fraction of the powder particles will be oriented such that, by chance, a certain crystal plane is at the angle 6 to the incident beam for constructive interference (see Fig. 4.4). 

XRD on battery materials can be classified as powder dififaction, a technique developed by Peter Debye and Paul Scherrer. In powder dififaction the material consists of microscopic crystals oriented at random in all directions. If one passes a monochromatic beam of X-rays through a fiat thin powder electrode, a fraction of the particles will be oriented to satisfy the Bragg relation for a given set of planes. Another group will be oriented so that the Bragg relationship is satisfied for another set of planes, and so on. In this method, cones of reflected and transmitted radiation are produced (Fig. 27.2). X-ray diffraction patterns can be recorded by intercepting a... 

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