Fibrous fine structure

The physical or petrographic components of coal are defined or described in various ways. In one system, which depends on microscopic observation, the principal components are called exinite, vitrinite, micrinite, and fusinite. Transparency of these in a thin section decreases in that order, whereas reflectance from polished surface increases in the same order. Vitrinite, the major component of most coals, occurs in bands or strands and is usually uniform in appearance, though sometimes shows cell structure exinite consists of the remains of plant spores, pollen, and cuticles with characteristic shape micrinite occurs in very fine granular form or massive structureless, irregular form fusinite shows characteristic fibrous, cellular structure. Semifusinite is transitional between vitrinite and fusinite. On a macroscopic scale, vitrain and... 

Fig. 13. Schematic view of the periodic fine structure (phosphotungstic acid-stained) of the repeating elements of various reconstituted collagens native pattern, fibrous long spacing (FLS) collagen and segment long spacing (SLS) collagen. (From Schmitt et al., 1955.)...

Melting point, °C 1000-1500 Relative density (water -1) 2.5 Solubility in water none WHITE, BROWN OR BLUE SOLID WITH FIBROUS CRYSTALLINE STRUCTURE Unable to react with virtually any other substance. Becomes powdery (amorphous) and loses Its hazardous properties when heated above approx. 1200°C. Processes entailing the release of fine fibers Into the air should be avoided wherever possible. ... 

Silk is derived from the cocoon of the silkworm (JSombyx mort). It is defined as protein fibre. Fibroin chains are believed to be nearly fiill-extended, highly crystalline, and almost perfectly aligned in the fibre direction, all of which contribute to the fibre s considerable stiffiiess and strei th. Fibrous proteins, such as silk, are characterised by a highly repetitive primary sequence that leads to significant homogeneity in fine structure. Because of these structural properties it ows impressive mechanical properties and provides important material options in the field of controlled release, biomaterials and scaffolds for tissue engineering (5). 

The external shape of a natural mineral is a manifestation of its crystal structure, which will be briefly discussed in Chapter 2. It is also dependent on the environmental conditions in which the mineral was formed. If allowed to grow without constraint, then the particles are bounded by crystal faces, which are disposed in a regular way such that there is a particular relationship between them in any one mineral species, which is derived from regular atomic arrangement. However, under pressure, temperature or the effects of impurities, the crystal may adopt different shapes or habits. These include cubic, fibrous (fine, long, needles), acicular (needle-like), lamellar (plate-like) and prismatic. It is very unusual for perfect crystals to be found, but even poorly formed ones will always show evidence of their intrinsic symmetry. 

It is reasonable to inquire at this point whether the principles that have been set forth above have any applicability to natural functioning contractile systems. Muscles are very intricately constructed fibrous structures developed by nature to convert chemical energy into mechanical work. Detailed and sophisticated electron microscopic and x-ray diffraction studies have established the fine structure of muscle. The chemical processes and enzymatic activity that are intimately involved... 

The model extends the structural hierarchy proposed by Dobb, Johnson and Saville [374] for the aramids. Three distinct fibrillar elements have been noted microfibrils, on the order of 50 nm in size fibrils, on the order of 500 nm in size and macrofibrils, about 5 pm (5000 nm) across. The importance of this structural model is that it not only describes the structure of uniaxially oriented fibrous materials, but it also shows the fine structure of the thicker LCP forms of moldings and extrudates. In these thicker materials, process history and temperature affects macrostructures, such as skin-core, bands and layering (Fig. 5.85). The fiber structural model shows the arrangement of the fine structure within those macro units. This structural model improves the understanding of relationships between processes, structure and properties in LCPs. 

Since fibrous proteins generally have periodical amino acid sequences and higher-order structure, the clarification of their fine structure in the solid state becomes very important not only when discussing... 

Surface evaporation can be a limiting factor in the manufacture of many types of products. In the drying of paper, chrome leather, certain types of synthetic rubbers and similar materials, the sheets possess a finely fibrous structure which distributes the moisture through them by capillary action, thus securing very rapid diffusion of moisture from one point of the sheet to another. This means that it is almost impossible to remove moisture from the surface of the sheet without having it immediately replaced by capillary diffusion from the interior. The drying of sheetlike materials is essentially a process of surface evaporation. Note that with porous materials, evaporation may occur within the solid. In a porous material that is characterized by pores of diverse sizes, the movement of water may be controlled by capillarity, and not by concentration gradients. 

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. 

Techniques commonly used to produce fibrous webs include the wet laid, dry laid carded, and meltblown processes. The wet laid or paper making process is the predominant method for several reasons. The wet laid process, configured properly, allows for the blending of cellulosic and polymeric components. Also, the ability to use short cut length and fine denier fiber provides for consistent blending, uniform formation, and controlled pore structure. 

All deposits of metals are made of grains whose structural-physical nature (1) can be divided into four types (1) columnar, (2) fine-grained, (3) fibrous, and (4) banded. In terms of their practical macroscopic physical properties, their main characteristics may be summarized as follows ... 

As might be anticipated for minerals with chain structures, pyroxenes commonly occur in columnar, prismatic, rodlike, and acicular forms. Enstatite has been found in the form of rosettes of fine-fibrous crystals. Special names such as victorite, chladnite, and shepardite were assigned to different occurrences in this distinctive morphology, possibly because the fibrous aggregates were located in iron meteorites. However, the composition and crystal... 

Clays are silicate minerals that may be platy or fibrous and are usually of exceedingly fine grain size, ranging from colloidal, a few nanometers in diameter, to a maximum of about a tenth of a micrometer. Similarly to other aluminosilicates, clays show considerable range in chemical composition with concomitant structural modifications (Fig. 2.13). A few of the clay minerals described as fibrous are briefly mentioned here. 

---