Aluminum amorphous materials

Over 50 acidic, basic, and neutral aluminum sulfate hydrates have been reported. Only a few of these are well characterized because the exact compositions depend on conditions of precipitation from solution. Variables such as supersaturation, nucleation and crystal growth rates, occlusion, nonequilihrium conditions, and hydrolysis can each play a role ia the final composition. Commercial dry alum is likely not a single crystalline hydrate, but rather it contains significant amounts of amorphous material. 

This increase in activity was attributed to a lower diffusion resistance of the aluminum-deficient zeolites, which resulted from the removal of amorphous material from the zeolite channels. However, the hydroisomerization of n-pentane... 

Soils found primarily in cool and humid forested regions, Spodosols have subsurface accumulations of amorphous materials, mainly iron and aluminum oxides. These soils are usually strongly leached, blit can be used for crop support with addition of lime and fertilizer,... 

Quasicrystals are solid materials exhibiting diffraction patterns with apparently sharp spots containing symmetry axes such as fivefold or eightfold axes, which are incompatible with the three-dimensional periodicity associated with crystal lattices. Many such materials are aluminum alloys, which exhibit diffraction patterns with fivefold symmetry axes such materials are called icosahedral quasicrystals. " Such quasicrystals " may be defined to have delta functions in their Fourier transforms, but their local point symmetries are incompatible with the periodic order of traditional crystallography. Structures with fivefold symmetry exhibit quasiperiodicity in two dimensions and periodicity in the third. Quasicrystals are thus seen to exhibit a lower order than in true crystals but a higher order than truly amorphous materials. 

As much as 15% of CM matrices may be amorphous silicate, which is associated with comparable volumes of very poorly crystalline phyllosilicates (Barber, 1981). In ALH81002, 5 vol.% of the matrix rims are composed of amorphous regions a few micrometers across that are rich in silicon, aluminum, magnesium, iron, and presumably oxygen, and contain 5-40 nm grains of iron-rich olivines and metallic Fe,Ni (Lauretta et al., 2000). Chizmadia and Brearley (2003) found more abundant amorphous material in the CM2 chondrite, Y 791198. (Origins of matrix components are reviewed in Section 5.7.11.)... 

Analysis of the black material from both sides of the blade yielded similar SEM, XRD, and EDAX data. Micrographs of the two sides show an amorphous material that is more porous on side B and more solid as a fiber replacement on side A. The two have been shown by their XRD patterns to contain aluminum oxide or hydroxide of some form. In addition, the XRD pattern of the black pseudomorphs revealed bands characteristic of malachite, but malachite encrustations on the surface of the pseudomorphs may be the cause, rather than malachite in the internal structure. The EDAX of the interior of the black fiber pseudomorphs, however, reveals the presence of copper as well as aluminum, just as the black material from side B does. 

PHYSICAL PROPERTIES amorphous material consisting of fused sodium potassium aluminum silicate light-gray to glassy-black solid odorless expands when finely grounded and heated expanded (high temperature treated) perlite is a fluffy, white particulate poor solubility in water MP (>1093°C, >2000°F) BP (unknown) DN (2.2-2.4 g/cm (crude), 0.05-0.3 g/cm (expanded)) AVG DN (0.13) SG (2.2-2.4 (crude), 0.05-0.3 (expanded)) VP (0 mmHg approximately). 

Synonyms/Trade Names Expanded perlite [Note An amorphous material consisting effused sodium potassium aluminum silicate.]... 

X-ray and electron diffraction patterns of the cerium-poor as-deposited films exhibit an aluminum ring system and a large halo relative to an amorphous material. By annealing inside the electron microscope a new ring system appears which is characteristic of small crystallites and can be indexed as a hexagonal structure with a = 6.92 A and c = 6.28 A. No compounds of the CeAl system are related to these parameters. Upon further heating this alloy, which is very unstable, disappears and the formation of large aluminum crystals are observed. 

The chemistry of the precipitation of aluminum hydroxides and oxides is very complex (40). When the solubility is exceeded, gelatinous precipitates, which are found to be amorphous by X-ray diffraction, usually form initially. Al MAS NMR shows the predominance of octahedraUy coordinated Al ions in these amorphous hydroxides, as are present in the crystalline trihydroxides and oxyhydroxides. However, in the amorphous materials some pentacoordinated and tetracoordinated Al ions are also found (15). As discussed above, there are many different crystalline hydroxides or oxyhydroxides, and which of them will be formed depends on the conditions (4f). Primary factors are temperature and pH, as well as aging time however, the nature of the anions present and the possible presence of organic components (42,43) also play a role. At low temperature in an excess of water, the hydroxides are preferentially formed, specifically bayerite at pH values between 5.8 and 9 or gibbsite for pH values smaller than 5.8 or larger than 9. 

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