Crystalline-amorphous features

Sensitive observations enable comparative surveys of silicate emission features from disks around low-mass, intermediate-mass, and Sun-like stars. While no strong correlations have been found with disk properties, flatter disks and disks around the coolest stars more often show crystalline silicate features. Cool stars and very low-mass disks display prominent crystalline silicate emission peaks (Apai et al. 2005 Merfn et al. 2001 Pascucci et al 2009). Thus, whatever processes are responsible for the presence of crystals around Sun-like stars must be capable of very efficiently producing crystals around low-mass stars, too. Interferometric measurements suggest that the amorphous/crystalline dust mass fraction is higher in the inner disk than at medium separations (van Boekel et al. 2004 Ratzka et al. 2007). The surveys also show that amorphous silicate grains frequently have similar magnesium and iron abundances in protoplanetary disks. In contrast, those with crystalline silicates are always dominated by Mg-rich grains (e.g. Malfait et al. 1998 Bouwman et al. 2008). 

Solids are classified as crystalline solids or amorphous solids. Crystalline solids, such as an ice cube or a sodium chloride crystal, have a definite melting point. Amorphous solids, such as a chocolate bar or glass, get softer and softer as the temperature is raised. The structures of crystalline solids feature regularly repeating arrangements of the constituent particles. The structure of amorphous solids is not regular, but something like that of liquids sometimes, amorphous solids are called supercooled liquids. ... 

In comparing the shear fracture surfaces of amorphous and semi-crystalline polymers, it appears that the features in both cases are quite similar (Fig. 39a -c ). This indicates that, under comparable conditions, the local stress field rather than details of the crystalline-amorphous microstructure of the polymers tested determines the operating deformation mechanism. Only secondary effects arise from the morphology of the cry stalline material. 

In comparing the different blends, the specific advantages of each type, as well as any potential overlap in performance with other type of blends have also been discussed. The fundamental advantage of polymer blends viz. their ability to combine cost-effectively the unique features of individual resins, is particularly illustrated in the discussion of crystalline/amorphous polymer blends, such as the polyamide and the polyester blends. Key to the success of many commercial blends, however, is in the selection of intrinsically complementing systems or in the development of effective compatibilization method. The use of reactive compatibilization techniques in commercial polymer blends has also been illustrated under the appropriate sections such as the polyamide blends. 

Figure 3.16a shows the storage and loss components of the compliance of crystalline polytetrafluoroethylene at 22.6°C. While not identical to the theoretical curve based on a single Voigt element, the general features are readily recognizable. Note that the range of frequencies over which the feature in Fig. 3.16a develops is much narrower than suggested by the scale in Fig. 3.13. This is because the sample under investigation is crystalline. For amorphous polymers, the observed loss peaks are actually broader than predicted by a...

The ultraphosphates are situated between P O q and the metaphosphates. These comparatively Htde-known, highly cross-linked polymers contain at least some of the phosphoms atoms as triply coimected branching points. This stmctural feature is quite unstable toward hydrolysis. Ultraphosphates undergo rapid decomposition upon dissolution. In amorphous ultraphosphates, the cross-linking is presumably scattered randomly throughout the stmctural matrix in contrast, crystalline ultraphosphates have a regular pattern. 

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