Secondary amorphous phase

The higher crystalline, cold compressed sample shows a so-called crystalline phase (a) transition at about 130°C, a (weak) glass-rubber (S) transition at about 50°C and a secondary, amorphous phase (y) transition at -75°C. This weak glass-rubber transition effect is typical for a semicrystalline polymer. It indicated already that it would be difficult to detect this effect by DSC. 

With the emplacement of the cover, the atmospheric oxygen that fuelled the precipitation of secondary As phases was essentially eliminated. Secondary phases such as jarosite, scorodite and amorphous iron sulfo-arsenates became unstable in the present conditions in the ARS (Salzsauler et at. 2005). Reductive dissolution of the secondary phases and residual arsenopyrite gives rise to 100 mg/L As in pore water at the base of the residue pile (Salzsauler et al. 2005). 

High crystallization rates and the possibility to stabilize X-ray amorphous phases, which exhibit ZSM-5 like properties, were among the reasons why we decided to investigate the procedure B in more detail. In order to optimize the particle size, homogeneity, morphology and composition, we have questioned more systematically the influence of secondary synthesis variables such as the pH, solvent viscosity or the nature of the alkali cation, added as chloride. 

Secondary phases predicted by thermochemical models may not form in weathered ash materials due to kinetic constraints or non-equilibrium conditions. It is therefore incorrect to assume that equilibrium concentrations of elements predicted by geochemical models always represent maximum leachate concentrations that will be generated from the wastes, as stated by Rai et al. (1987a, b 1988) and often repeated by other authors. In weathering systems, kinetic constraints commonly prevent the precipitation of the most stable solid phase for many elements, leading to increasing concentrations of these elements in natural solutions and precipitation of metastable amorphous phases. Over time, the metastable phases convert to thermodynamically stable phases by a process explained by the Guy-Lussac-Ostwald (GLO) step rule, also known as Ostwald ripening (Steefel Van Cappellen 1990). The importance of time (i.e., kinetics) is often overlooked due to a lack of kinetic data for mineral dissolution/... 

In conclusion, it can be stated that Si3N4 ceramics are polyphased materials including mainly /fss, ass, secondary phases (mainly oxide nitrides, in ceramic literature generally called oxynitrides) and an amorphous phase, all having characteristic morphologies and can be arranged in a manifold of microstructures (Sect. 6). 

The amount, distribution, size, morphology of the a- and /1-particles, secondary and amorphous phases of Si3N4 ceramics are decisive factors for their quality and reliability. In the following, mainly sintered and gas pressure sintered Si3N4 ceramics will be discussed because of their extraordinary economical interest and because they show all the microstructural features also present in the other Si3N4 ceramics. 

Higher values can be reached for semi-crystalline polymers below Tg the crystalline phase is stiffer than the glassy amorphous phase (e.g. PEEK, E 4 GPa). Semicrystalline polymers above Tg have, however, a much lower E-value, such as PE (0.15 to 1.4 GPa) and PP 1.3 GPa) E is, in these cases, strongly dependent on the degree of crystallinity and on the distance to Tg. Sometimes a low modulus is also found for semi-crystalline polymers below Tg, due to the effect of one or more secondary transitions a strong example is PTFE (E = 0.6 GPa ). 

In addition, one hypothesis for the secondary structure in spidroin suggests that there are amorphous phases, highly oriented crystals, and oriented noncrystalline phases coexisting (Grubb et al., 1997). This structure model has been used to explain the super-contraction of dragline (Liu et al., 2005b). 

Raman spectroscopic measurement was also used to explain the improved thermal stability of nontreated (NoM-C) and silylated cotton fibers (Sil-C).20 In the region 3200-3500 cm-1, peaks become more intense and narrower, demonstrating an apparent increase in the -OH group concentration in the ordered phase and an increase in the crystallinity. This phenomenon was explained by the fact that the silylation reaction cannot take place in the crystalline phase. The increase in crystallinity is the result of easier segmental motion, which is facilitated by the reduction of secondary chemical bonds in the amorphous phase. These structural changes explain the higher thermal stability, since the OH groups in the amorphous phase are more sensitive to thermal dehydration. 

Amorphous iron hydroxide, which precipitates rather spontaneously, is still undersaturated. Maghemite, goethite, and hematite do not usually precipitate spontaneously, but form as secondary mineral phases from hydroxides. That means the trivalent iron mainly remains in solution through complexation reactions. 

The secondary structure, such as a conformation, is studied mainly by solid-state NMR.2 In the solid state, NMR chemical shift is characteristic of specific conformations because the internal rotation around the chemical bonds is restricted. This shows that the NMR chemical shift can be used for elucidating the conformation of polymers in the solid state. In the amorphous phase, the conformation of the polymer chain is not fixed above Tg. Even in such a case, NMR chemical shift and the relaxation parameters can give us useful information such as the averaged conformation or the dynamics of the exchange. Solid-state NMR can also provide information about the crystalline structures, which are classified under the higher order structures through NMR chemical shift, since for most polymers, different crystalline structures accompany conformational changes which affect their NMR chemical shift. 

Nanometer-scale secondary sulfides associated with sulfide-reducing bacteria were reported by Fortin and Beveridge (1997) to have formed within the pyritiferous tailings at Kidd Creek, Timmins, Ontario. The sulfides were identified as mackinawite, amorphous FeS, and pyrite. A bacteriaUy associated secondary AgaS phase, possibly acanthite, was observed by Davis (1997) in the Kidd Creek tailings. 

Oil and amorphous or crystalline materials can be easily distinguished under the microscope. Oil is simply a secondary liquid phase. Amorphous material generally has no definitive shape with no birefringence under polarized light. Crystalline materials typically have a defined shape, showing birefringence under polarized light (Stoiber and Morse 1994). 

In Range II, the nucleation of crystallization takes place and the successive growth by the secondary nucleation follows. In this range, first, the intermediate phase appears and then the crystalline phase appears with a decrement of the amorphous phase. T2 of the amorphous phase is almost constant in this range. Although some kind of orientational order is formed in the amorphous phase which becomes the interfacial phase, the molecular mobility of most parts of the amorphous phase is unchanged. 

In the Range IV, only the T2 for the amorphous phase decreases with time gradually. Other parameters are almost constant. Namely, only in the amorphous phase, the slight change of the structure takes place. This range seems to correspond to the so-called secondary crystallization. Thus, it is possible to investigate the crystallization dynamics by pulse NMR. 

In addition to Tg (amorphous phases) and the melting temperature Tm (crystalline phases), polymers also manifest secondary relaxations at temperatures below those of major relaxations (Tg or Tm, which will collectively be referred to as T. The main secondary relaxation temperature wil be designated generically as Tp, although it may be labeled differently in the literature on specific polymers. For example, it is commonly labeled as Ty for bisphenol-A polycarbonate where Ty is for a relaxation of higher intensity than Tp, and occurring at a lower temperature, which is the main secondary relaxation of this particular polymer. 

Ill) Crystallization of amorphous phase. (IV)-(VI) Growth and faceting of diamond crystal. (VII) Secondary nucleation and growth of diamond.(Reproduced with permission.)... 

It can be seen that the isothermal conversion process became increasingly slower when the form II of PB-1 was crystallized from the melt in the presence of increasing amounts of HOCP. This trend was observed at all aging temperatures except 69°C. It was also noted in the slow phase transformation curves that complete conversion of residual small amount of form II into form I was exceedingly slow. This might have been due to continuous supplies of form II from the amorphous phase by secondary crystallization of the PB-1 (51). 

Based on the strong dilution trends of non-reactive species, such as chloride and sulfate, the extent of interaction of fracture condensate water with matrix pore water must have been very limited. However, reactive species, such as silica, show increasing concentrations owing to reaction with predominantly fracture-lining silica polymorphs and feldspars at higher temperatures. A precipitation zone of secondary mineral phases such as amorphous silica, calcite, and gypsum in... 

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