Microstructure of amorphous

Kristiak, J., Bartos, J., Fristiakova, K., Sausa, O., Bandzuch, P. (1994) Free-volume microstructure of amorphous polycarbonate at low temperatures determined by positron-annihilation-lifetime spectrospcopy . Phys. Rev.B. 49(10), 6601. 

Oxidative processes are localized in amorphous interlayers, in interfibrillar regions and others. Crystallinity and crystals sizes increase at initial stages of oxidation [303] it also means that oxidation is localized in amorphous part. Destructive decay of passing macromolecules in amorphous interlayers release them and facilitates folding of chains into crystals. Destruction and amorphicity of crystals takes place only at deep stages of oxidation. Solubility of oxygen in polymer depends not only on polymer crystallinity but on microstructure of amorphous or defect sections. 

In summary, laser Raman spectroscopy is useful for investigating the molecular microstructure of amorphous materials especially when reinforced by theoretical calculations. Correlations between spectroscopic data and the results of other physicochemical measurements are established. A detailed evaluation of the implications of these correlations must, however, be omitted to avoid intrusion upon areas of proprietary interest. 

Bartos, J., Free volume microstructure of amorphous polymers at glass transition temperatures from positron aimihilation spectroscopy data. Colloid Polym. ScL, 274, 14—19 (1996). 

Microstructure of amorphous styrene-butadiene block copolymer. 

As has been outlined in Chapt 3, the isomerization reactions in amorphous polymer solids are appreciably influenced by local mobility and heterogeneity of reactive sites, often leading to the deviation of reaction profiles from first-order kinetics. However, this situation allows us to obtain an insist into the microstructure of amorphous polymer solids, e.g. distribution of local free volume, by using photoisomerization reactions as molecular probes. Since the photochromic phenomena in polymer solids were reviewed by Smets in 1983, our discussion below will be limited to more recent advances, putting emphasis on the explanation of non-homo-geneous progress of reactions in terms of the distribution of local free volume in matrix polymers. 

Examples of the unique insights obtained by solid state NMR applications to materials science include the Si/Al distribution in zeolites, the hydrogen microstructure in amorphous films of hydrogenated silicon, and the mechanism for the zeolite-catalyzed oligomerization of olefins. ... 

Characteristic of the microstructure of PET fibers in their final production form is the occurrence of three types of polymer phases crystalline, mesomorphous, and amorphous. The first phase is the result of crystalline aggregation of PET molecules, the second phase—of mesomorphous or, in other words, paracrys-talline aggregation, the third phase—of amorphous aggregation. The mesomorphous and amorphous phases together form a noncrystalline part of the fiber. 

The amorphous orientation is considered a very important parameter of the microstructure of the fiber. It has a quantitative and qualitative effect on the fiber de-formability when mechanical forces are involved. It significantly influences the fatigue strength and sorptive properties (water, dyes), as well as transport phenomena inside the fiber (migration of electric charge carriers, diffusion of liquid). The importance of the amorphous phase makes its quantification essential. Indirect and direct methods currently are used for the quantitative assessment of the amorphous phase. 

Mingwu, Bai, Koji, Kato, Noritsugu, Umehara, Yoshihiko, Miyake, Xu, Junguo, and Hiromitsu, Tokisue, "Dependence of Microstructure and Nanomechanical Properties of Amorphous Carbon Nitride Thin Films on Vacuum Annealing, Thin SoZ/dFz Zms, Vol. 376,2000, pp. 170-178. 

A number of techniques have been employed that are capable of giving information about amorphous phases. These include infrared spectroscopy, especially the use of the attenuated total reflection (ATR) or Fourier transform (FT) techniques. They also include electron probe microanalysis, scanning electron microscopy, and nuclear magnetic resonance (NMR) spectroscopy. Nor are wet chemical methods to be neglected for they, too, form part of the armoury of methods that have been used to elucidate the chemistry and microstructure of these materials. 

The equilibrium, room temperature structure of pure cobalt is hep. The fee structure is stable at high temperatures (422 °C to 1495 °C) and has been retained at room temperature by rapid solidification techniques [101], X-ray diffraction analysis was used to probe the microstructure of bulk Co-Al alloy deposits containing up to 25 a/o Al and prepared from solutions of Co(II) in the 60.0 m/o AlCfi-EtMelmCl melt. Pure Co deposits had the hep structure no fee Co was observed in any of the deposits. The addition of aluminum to the deposit caused a decrease in the deposit grain size and an increase in the hep lattice volume. A further increase in the aluminum content resulted in amorphization of the deposit [44], Because the equilibrium... 

As can be seen from this figure, the heat-resistance was remarkably improved by the drastic changes in the microstructure from amorphous to polycrystalline structure. Another type of SiC-based fiber, SA fiber (2), has a sintered SiC polycrystalline structure and includes very small amounts of aluminum. This fiber exhibits outstanding high temperature strength, coupled with much improved thermal conductivity and thermal stability compared with the Nicalon and Hi-Nicalon fibers. The fabrication cost of the SA fiber is also reduced to near half of that of the Hi-Nicalon Type S [ 17]. The SA fiber makes SiC/SiC composites even more attractive to the many applications [18]. In the next section, the production process, microstructure and physical properties of the SA fiber are explained in detail. 

Only at calcination temperatures above 800°C does the density increase to the literature value of amorphous silica of 2.2 to 2.25 g cm-1. The exact microstructure within the Stober silica particles depends very much on the specific precipitation conditions, which are discussed in more detail in section 2.1.4. 

The time needed for polymer chains of amorphous thermoplastics above Tg and semicrystalline thermoplastics above Tm to diffuse across the interface and randomize is relatively short compared with the time needed for resin flow. It is believed, therefore, that diffusion bonding is completed immediately after the two molten surfaces merge, and that the microstructure of the contact zone is also assumed to be identical to that of the intraply sections [12,13],... 

FIG. 1.13 Spherical and cubic model particles with crystalline or amorphous microstructure (a) spherical zinc sulfide particles (transmission electron microscopy, TEM, see Section 1.6a.2a) x-ray diffraction studies show that the microstructure of these particles is crystalline (b) cubic lead sulfide particles (scanning electron microscopy, SEM, see Section 1.6a.2a) (c) amorphous spherical particles of manganese (II) phosphate (TEM) and (d) crystalline cubic cadmium carbonate particles (SEM). (Reprinted with permission of Matijevic 1993.)... 

Polymerization of propylene oxide-a-d was carried out by the EtZnNBu ZnEt catalyst in benzene solution in the presence of varying amounts of added water at 70° C, and was terminated after 7 days. The microstructure of the crude polymer was determined by the 1H-NMR method and the yields of amorphous and crystalline polymers were determined by a fractionation method (Fig. 16). When the amount of added water was increased up to 0.3 mole per mole of catalyst, the yield of crystalline polymer increased remarkably, whereas that of amorphous one remained nearly constant, and the isotactic dyad content (I) increased remarkably while syndiotactic one (S) remained almost constant. Thus, the striking parallel was observed between the yield of crystalline polymer and the isotactic dyad content, and between the yield of amorphous polymer and the syndiotactic dyad content. It is therefore concluded that water contributes more remarkably to the formation... 

Sodium Poly(4-styrene sulfonate). The sol—gel processing of TMOS in the presence of sodium poly-4-styrene sulfonate (NaPSS) has been used to synthesize inorganic—organic amorphous complexes (61). These sodium silicate materials were then isothermally crystallized. The processing pH, with respect to the isoelectric point of amorphous silica, was shown to influence the morphology of the initial gel structures. Using x-ray diffraction, the crystallization temperatures were monitored and were found to depend on these initial microstructures. This was explained in terms of the electrostatic interaction between the evolving silicate structures and the NaPSS prior to heat treatment at elevated temperatures. 

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