Crystalline Fibrous

As must be obvious, we have only touched on the natural occurrences of crystalline fibrous Si02- For example, Si02, usually quartz, often replaces fibrous minerals of another composition as rock masses are altered. Si02 also occurs in fibrous form within some plants (phytoliths) and in the soil. To summarize, in addition to the usual and common occurrences of the mineral quartz and its varieties, several silica polymorphs occur as fibers in a variety of biologic and geologic environments. 

Particle size. The soattering theory described above assumes that the particles are spherical in shape. Although emulsion droplets oan usually be assumed to be spherioal beoause of the effeots of surfaoe tension, they may beoome deformed under shear flow or in oonoentrated systems where they are closely paoked. Many solid particles are non-spherical (granular, crystalline, fibrous). Non-spherioity oan have a substantial effeot on ultrasonio measurements and a number of theories have been derived to consider suoh an effeot [58-60]. 

The magnitude of the two thermally induced contractions is quite uniform among samples of newborn rat corneum, but considerable variation is encountered with human corneum, particularly for the 196 °C contraction. The contraction values for human corneum samples varied from 1 to 5% but were quite consistent for any given subject. The increased magnitude for this contraction in some human specimens could indicate a higher degree of orientation of the crystalline fibrous material 11). 

In raw form silk consists of some 75% fibroin, 20% sericin and 5% of various salts. The former is crystalline fibrous proteins and the latter is amorphous and soluble in hot water or dilute alkali solutions.The degree at... 

Asbestos-cement was the first FRC composite in modern times, and was used extensively as a cladding material, for roofing and wall units as well as pipes. The asbestos fibres are made of natural crystalline fibrous minerals, consisting of bundles of filaments (sometimes known as fibrils), with individual filaments being as thin as 0.1 /tm or less. In the manufacture of the actual composite, the bundles tend to be split up during the processing procedure, though considerable portions of the reinforcement remain in the form of small fibre bundles. 

The asbestos minerals are crystalline fibrous silicates, some of which have been exploited commercially, especially as an insulating material. These minerals comprise sheets, or chains of silicate tetrahedra in which oxygen is either bound to two silicon atoms or to one silicon atom, and possesses a negative charge. There are two major groups of asbestos mineral serpentines and amphiboles. White asbestos or chrysotile is a serpentine mineral, whereas the other forms of asbestos, crocidolite (blue asbestos), amosite (brown asbestos), anthophyllite, tremolite, and aetinolite, are amphiboles. Tremolite can also be found as a contaminant in other minerals, such as chrysotile, talc, and vermiculite. 

CH rCHCH NHCSNH. Colourless crystalline solid with a faint garlic-like odour m.p. 74 C. Manufactured by treating propenyl isothiocyanate with a solution of ammonia in alcohol. It has been given by injection in the treatment of conditions associated with the formation of excessive fibrous tissue. Toxic side reactions may occur. Propenyl thiourea is a chemical sensitizer for photographic silver halide emulsions. 

Refining. The next stage in chocolate processing is a fine grinding in which a coarse paste from the mixer is passed between steel rollers and converted to a drier powdery mass. Refining breaks up crystalline sugar, fibrous cocoa matter, and milk soflds. 

Water-Holding Capacity (WHC). AU polysaccharides are hydrophilic and hydrogen bond to variable amounts of water. HydratabUity is a function of the three-dimensional stmcture of the polymer (11) and is kifluenced by other components ki the solvent. Fibrous polymers and porous fiber preparations also absorb water by entrapment. The more highly crystalline fiber components are more difficult to hydrate and have less tendency to sweU. Stmctural features and other factors, including grinding, that decrease crystallinity or alter stmcture, may iacrease hydratioa capacity and solubUity. 

Granular, crystalline, or fibrous solids Large sohds, special forms and shapes Continuous sheets Discontinuous sheets... 

Finally, a very low-density form of fibrous silica, W-Si02 has been made by the disproportionation of (metastable) crystalline SiO ... 

The interest in the structures of simple R2Si(OH)2 compounds lies in the fact that one of them, Bu 2Si(OH)2, forms a discotic liquid crystalline phase (308,309). Despite many attempts, it has not proved possible to obtain crystals of Bu 2Si(OH)2 suitable for a crystallographic study, the material obtained from various solvents usually being of a fine fibrous nature. The discotic phase of Bu 2Si(OH)2 has been proposed (309) to be due to the formation of dimeric disks of molecules which remain on breaking the interdimer hydrogen bonds in a structure of type 65 at the transition between crystal and mesophase. As has been described, structure type 65 is found for several diols similar to Bu 2Si(OH)2, and it is thus quite likely that Bu 2Si(OH)2 does indeed have the proposed structure. 

Free-flowing powders, granular, crystalline or fibrous solids that can withstand mechanical handling. 

Naturally, very long T,c values are expected for solids as viewed from the expected correlation time at the low temperature side of the T c minimum (0.1-0.2 s) as shown in Figure 1. Indeed, their values turns out to be the order of 10-30 s for carbon sites in the absence of internal fluctuations as in polysaccharides such as (1 — 3)-p-D-glucan and (1 —> 3)-p-D-xylan,46 8 fibrous proteins such as collagen49 and silk fibroin,50 free and metal-complexed ionophores,51 or in some instances up to 1000 s as in crystalline polyethylene.52... 

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