Amorphous noncrystallinity

Diffraction of x-rays from many atoms with many electrons results in a two-dimensional continuous pattern of peaks and valleys. Diffraction from a hquid or an amorphous (noncrystalline) soHd results in a continuous pattern with few features, mainly broad peaks and valleys. 

Deposition involves the formation and precipitation of both crystalline and amorphous (noncrystalline) scales and the ultimate adherence of these mineral salt scales onto a heat transfer surface. Problems of deposition have the deleterious effect of reducing the rate of heat transfer, thus increasing the heat input requirements and raising the costs of operation. In addition, deposition reduces the efficiency of cooling the fabric of the boiler (especially the heat transfer metals), which leads to long-term problems of fatigue failure. 

The properties of the polycarbonate of bisphenol A are directly related to the structure of the polymer. The molecular stiffness associated with this polycarbonate arises from the presence of the rigid phenyl groups on the molecular chain or backbone of the polymer and the additional presence of two methyl side groups. The transparency of the material arises from the amorphous (noncrystalline) nature of the polymer. A significant crystalline structure is not observed in the polycarbonate of bisphenol A because intermolecular attractions between phenyl groups of neighboring polymer chains in the melt lead to a lack of flexibility of the chains that deters the development of a crystalline structure. 

Although rapid solidification may not produce a truly amorphous (noncrystalline) material for some alloy compositions, crystallite sizes of rapidly solidified crystalline... 

Anhydrous Lactose Glass (Amorphous Noncrystalline Glass)... 

When a lactose solution is dried rapidly, its viscosity increases so quickly that crystallization cannot take place. The dry lactose is essentially in the same condition as it was in solution, except for removal of the water. This is spoken of as a concentrated syrup or an amorphous (noncrystalline) glass. Various workers have shown conclusively that lactose in milk powder (spray, roller, or freeze-dried) is noncrystalline and exists in the same equilibrium mixture of a- and /3-lactose as existed in the milk prior to drying (Zadow 1984). 

For a batch size of 5 L, 587.5 g (3.2 moles) of mannitol is dissolved in 3.5 L of water. Pamidronic acid (31.6 g, 0.133 moles) is mixed with a 1.0 L aliquot of the mannitol solution to form a slurry. The slurry is then transferred into the remainder of the mannitol solution, and stirred for at least 15 min. Aqueous 1 N sodium hydroxide (270 ml) is then added and the mixture is stirred until a clear, colorless solution results. The pH is then adjusted to 6.50.1 using either 1 M aqueous phosphoric acid or 1 N aqueous sodium hydroxide, as needed. The solution is then filtered through a 0.22 micron filter, and filled at 20°C into vials at 4.0 ml (4.172 g)/vial, under sterile conditions. The aqueous solution is frozen at -37°C and lyophilized (20 mbar, 20°-40°C) to yield 1,250 vials, each containing 30 mg of amorphous disodium pamidronate. The vials are sealed under positive nitrogen pressure. The disodium pamidronate is amorphous (noncrystalline) by X-ray diffraction and contains 0.7 wt-% water. 

Figure 7.3. (a) In the Kronnig-Penney model, the potential at each lattice site in a monatomic crystalline solid is of the same depth, (b) The random introduction of impurity atoms in the crystalline lattice produces variation in the well depths, known as diagonal, or Anderson, disorder, (c) Amorphous (noncrystalline) substances have unevenly spaced potential wells, or off-diagonal disorder. 

Carbohydrates and proteins are typical hydrophilic components of concentrated food systems. These components tend to form amorphous, noncrystalline structures at low water contents (White et al. 1966 Slade et al. 1991 Roos 1995). Well-known food processes resulting in glass formation by amorphous or partially amorphous food components include baking, extrusion, dehydration and freezing (Roos 1995). In these processes, removal of water as part of the manufacturing process results in the formation of a noncrystalline, amorphous state, which is extremely sensitive to water and may show various time-dependent changes causing loss of quality and reduced shelf life. 

LPCAT polymerization or coating could be considered more or less the same as the plasma polymerization or coating by other conventional plasma processes, except that the kinetic pathlength of growth is short. The ultrathin layers prepared by LPCAT polymerization have the general characteristics of plasma polymers, i.e., amorphous (noncrystalline), high concentration of the dangling bonds (free radicals... 

Water appears in various condensed forms 15 different crystalline ice structures are reported, as well as at least three amorphous (noncrystalline) ices and a similar number of metastable liquid water forms (14). This structural diversity has its origin in the elementary building blocks of water the hydrogen bonds and the tetrahedral arrangement of H-bonded neighbors [which is often called the Walrafen pentagon (15)]. Both building... 

Because of their orderly arrangements, the chains of the tactic polymers (syndiotactic and isotactic) can lie closer together and the polymers are partially crystalline, whereas atactic polymers are amorphous and soft indicating the absence of all crystalline order. Isotactic pol q)ropy-lene is highly crystalline with a melting point of 160°C, whereas the atactic isomer is an amorphous (noncrystalline) soft polymer with a melting... 

Crystalline silica includes the silica minerals quartz and its polymorphs such as cristobalite and tridymite, which have the same chemical formula but different crystal structures. Amorphous, noncrystalline silica can also occur in a wide variety of geologic environments (Ross, 1999). 

Since the X-ray diffraction pattern of every crystalline form of a compound is imique, the technique is widely used for the identification and characterization of solid phases. XRD is the technique of choice to identify different polymorphic forms of a compound (Fig. 1). It can also be used to identify the solvated and unsolvated (anhydrous) forms of a compound, provided their lattice structures are different. The technique can also reveal differences in the crystallinity of compounds. The XRD pattern of an amorphous (noncrystalline) compound will consist of one or more broad diffuse halos (Fig. 2A). ... 

Knowledge of the existence of the various stereoregular forms and a comprehension of their respective structures adds both to the scientific interest and an appreciation of the physical properties and the potential utility of these materials. In general terms, atactic (heterotactic) polymers tend to be amorphous (noncrystalline) in the solid state. They will have a lower melting... 

For the lOMD model, the primary assumption is that sorbent organic matter is a polymeric-type substance within which sorbate can diffuse. The organic matter associated with natural sorbents has been reported to be a flexible, cross-linked, branched, amorphous (noncrystalline), polyelectrolytic polymeric substance (Choudhry, 1983 Hamaker and Thompson, 1972 Hayes and Swift, 1978 Schnitzer, 1978 Stevenson, 1982 Wershaw, 1986). Direct confirmation of the porous nature of organic matter has been reported (Degens and Mopper, 1976 Schnitzer, 1978). 

The individual chains of a polymer such as polyethylene are held together by van der Waals forces. Because these forces operate only at small distances, they are strongest if the polymer chains can line up in an ordered, closely packed array. The regions of the polymer in which the chains are highly ordered with respect to one another are called crystallites (Figure 28.4). Between the crystallites are amorphous, noncrystalline regions in which the chains are randomly oriented. The more crystalline—the more... 

Plastics can be classified according to the physical properties imparted to them by the way in which their individual chains are arranged. Thermoplastic polymers have both ordered crystalline regions and amorphous noncrystalline regions. Thermoplastic polymers are hard at room temperature, but soft enough to be molded when heated, because the individual chains can slip past one another at elevated temperatures. Thermoplastic polymers are the plastics we encounter most often in our daily lives—in combs, toys, switch plates, and telephone casings, for example. They are the plastics that are easily cracked. 

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