Natural amorphous

Filler Carbon black Natural amorphous silica, precipitated silica, nonblack nanofiller Solvent Organic solvent Aqua-based solvent... 

Schwertmann, U. Fischer, W.R. (1973) Natural amorphous ferric hydroxide. Geoderma 10 237-247... 

Most of the adsorbents used in the adsorption process are also useful to catalysis, because they can act as solid catalysts or their supports. The basic function of catalyst supports, usually porous adsorbents, is to keep the catalytically active phase in a highly dispersed state. It is obvious that the methods of preparation and characterization of adsorbents and catalysts are very similar or identical. The physical structure of catalysts is investigated by means of both adsorption methods and various instrumental techniques derived for estimating their porosity and surface area. Factors such as surface area, distribution of pore volumes, pore sizes, stability, and mechanical properties of materials used are also very important in both processes—adsorption and catalysis. Activated carbons, silica, and alumina species as well as natural amorphous aluminosilicates and zeolites are widely used as either catalyst supports or heterogeneous catalysts. From the above, the following conclusions can be easily drawn (Dabrowski, 2001) ... 

Non-chlorine methods that are based on obtaining basic organic compounds of silicon fr om artificial amorphous silica have many stages and are ineffective, as they use the silica obtained by hydrolysis of tetraalkoxysilane or silicon tetrachloride. So it became necessary to find methods of SOC synthesis based on natural amorphous silica. Such methods are currently being developed by some authors [1-3]. 

So, as we are the first to show, humic acids, being natural polyphenols, actively dissolve the biogenic silica of siliceous rocks, and we used the scheme of obtaining the ammonium salt of the tricatechol ether of monosilicic acid in order to understand the methods of synthesis of biogeochemically active SOC, formed from natural amorphous silica and polyphenols in natural systems. 

Solid amorphous silica (opal) and quartz crystals, as in geodes, are formed on solid sufaces. In a comprehensive investigation of the behavior of silica in hot-spring water. White Brannock, and Murata (45) pointed out that there was no evidence quartz could be formed within any reasonable time under ordinary conditions. In nature, amorphous silica appears to be deposited from the highest concentration of silica, then chalcedony (extremely fine-grained fibrous form of quartz) from a lower concentration, and Hnally macroscopic quartz crystals from lowest concentrations just exceeding the saturation level for quartz. Over millions of years most amorphous silicas in the presence of water are eventually transformed to chalcedony or chert and quartz. 

The activated carbon, owing to its porosity and chemical surface composition, both of which may be appropriately controlled, is also recommended as a suitable catalyst support [179]. On the other hand, both silica and alumina oxides as well as natural amorphous aluminosilicates and zeolites are widely used as heterogeneous catalysts. These adsorbents having acid or (and) base sites are named as solid acid-base catalysts [183]. 

Point of view of the chemistry lignin is a natural amorphous cross-linked resin that has an aromatic three-dimensional polymer structure containing a number of functional groups such as phenolic, hydroxyl, carboxyl, benzyl alcohol, methoxyl, and aldehyde as shown in Figure 5.1, which make lignin potentially useful as an adsorbent material for removal of heavy metal ions from water [52]. 

Pressure-area isotherms for many polymer films lack the well-defined phase regions shown in Fig. IV-16 such films give the appearance of being rather amorphous and plastic in nature. At low pressures, non-ideal-gas behavior is approached as seen in Fig. XV-1 for polyfmethyl acrylate) (PMA). The limiting slope is given by a viiial equation... 

Boron exists naturally as 19.78% lOB isotope and 80.22% IIB isotope. High-purity crystalline boron may be prepared by the vapor phase reduction of boron trichloride or tribromide with hydrogen on electrically heated filaments. The impure or amorphous, boron, a brownish-black powder, can be obtained by heating the trioxide with magnesium powder. 

Carbon is found free in nature in three allotropic forms amorphous, graphite, and diamond. A fourth form, known as "white" carbon, is now thought to exist. Ceraphite is one of the softest known materials while diamond is one of the hardest. 

To a large extent, the properties of acryUc ester polymers depend on the nature of the alcohol radical and the molecular weight of the polymer. As is typical of polymeric systems, the mechanical properties of acryUc polymers improve as molecular weight is increased however, beyond a critical molecular weight, which often is about 100,000 to 200,000 for amorphous polymers, the improvement is slight and levels off asymptotically. 

Principal Adsorbent Types. Commercially useful adsorbents can be classified by the nature of their stmcture (amorphous or crystalline), by the sizes of their pores (micropores, mesopores, and macropores), by the nature of their surfaces (polar, nonpolar, or intermediate), or by their chemical composition. AH of these characteristics are important in the selection of the best adsorbent for any particular appHcation. 

The practical adsorbents used in most gas phase appHcations are limited to the following types, classified by their amorphous or crystalline nature. 

When drawdown is high, the film may be uniaxially oriented and the properties of the final film isotropic. In the manufacture of strapping tape this effect is accentuated. If the cast or quenched film is to be used to feed an orientation tine, additional attention must be given to the amorphous—crystalline nature of the film ia the draw processes so that maximum strength can be achieved and uniform gauge and optical quality maintained. Slot casting is used for the orientation of these resins, polyesters, polyamides, and a variety of others. 

Crystalline nature of the deposit is amorphous unless otherwise noted. 

---