Microcrystalline

BP Microcrystalline cellulose JP Microcrystalline cellulose PhEur Cellulosum microcristallinum USPNF Microcrystalline cellulose 

Avicel PH- Celex-, cellulose gel Celphere Ceolus KG crystalline cellulose E460 Emcocel Ethispheres Pibrocel Pharma-cel Tabulose Vivapur. 

Adsorbent suspending agent tablet and capsule diluent tablet disintegrant. 

Microcrystalline cellulose is widely used in pharmaceuticals, primarily as a binder/diluent in oral tablet and capsule formulations where it is used in both wet-granulation and direct-compression processes.In addition to its use as a binder/diluent, microcrystalline cellulose also has some lubricant and disintegrant properties that make it useful in tableting. 

Microcrystalline cellulose is also used in cosmetics and food 

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Microcrystalline waxes, produced from heavy lubricating oil residues, have a micro-crystalline structure and consist largely of iso-and cycloalkanes with some aromatics. 

Crystalline silicon has the tetrahedral diamond arrangement, but since the mean thermochemical bond strength between the silicon atoms is less than that found between carbon atoms (Si—Si, 226 kJmol , C—C, 356kJmol ), silicon does not possess the great hardness found in diamond. Amorphous silicon (silicon powder) is microcrystalline silicon. 

Polymers are difficult to model due to the large size of microcrystalline domains and the difficulties of simulating nonequilibrium systems. One approach to handling such systems is the use of mesoscale techniques as described in Chapter 35. This has been a successful approach to predicting the formation and structure of microscopic crystalline and amorphous regions. 

AMP-1 4.0 Microcrystalline ammonium molybdo-phosphate with cation exchange capacity of 1.2 mequiv/g. Selectively adsorbs larger alkali metal ions from smaller alkali metal ions, particularly cesium. 

In Section 1.3 it was noted that the energy of adsorption even for a perfect crystal differs from one face to another. An actual specimen of solid will tend to be microcrystalline, and the proportion of the various faces exposed will depend not only on the lattice itself but also on the crystal habit this may well vary amongst the crystallites, since it is highly sensitive to the conditions prevailing during the preparation of the specimen. Thus the overall behaviour of the solid as an adsorbent will be determined not only by its chemical nature but also by the way in which it was prepared. 

The conditioning reagent is used to stabilize the precipitate of BaS04. The high ionic strength and acidity, due to NaCI and HCI, prevent the formation of microcrystalline particles of BaS04, and glycerol and alcohol help stabilize the precipitate s suspension. 

Chiral stationary phases in tic have been primarily limited to phases based on normal or microcrystalline cellulose (44,45), triacetylceUulose sorbents or siHca-based sorbents that have been chemically modified (46) or physically coated to incorporate chiral selectors such as amino acids (47,48) or macrocyclic antibiotics (49) into the stationary phase. 

Microstructurc. Crystal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. As an example, rapidly cooled fused aluminum oxide has a microcrystalline stmcture promoting toughness for heavy-duty grinding appHcations, whereas the same composition cooled slowly has a macrocrystalline stmcture more suitable for medium-duty grinding. 

Crystallization and Purification Solvent. Dimethylacetamide is useful ia the purification by crystallization of aromatic dicarboxyHc acids such as terephthahc acid [100-21-0] and/vcarboxyphenylacetic acid [501-89-3]. These acids are not soluble ia the more common solvents. DMAC and dibasic acids form crystalline complexes containing two moles of the solvent for each mole of acid (16). Microcrystalline hydrocortisone acetate [50-03-3] having low settling rate is prepared by crystallization from an aqueous DMAC solution (17). 

Microcrystalline ceUulose (MCC) is a partiaUy depolymeri2ed from of ceUulose prepared by the hydrolysis of wood pulp with hydrochloric acid. 

To confirm that the matrix is amorphous following primary solidification, isothermal dsc experiments can be performed. The character of the isothermal transformation kinetics makes it possible to distinguish a microcrystalline stmcture from an amorphous stmcture assuming that the rate of heat released, dH/dt in an exothermic transformation is proportional to the transformation rate, dxjdt where H is the enthalpy and x(t) is the transformed volume fraction at time t. If microcrystals do exist in a grain growth process, the isothermal calorimetric signal dUldt s proportional to, where ris... 

In an amorphous material, the aUoy, when heated to a constant isothermal temperature and maintained there, shows a dsc trace as in Figure 10 (74). This trace is not a characteristic of microcrystalline growth, but rather can be well described by an isothermal nucleation and growth process based on the Johnson-Mehl-Avrami (JMA) transformation theory (75). The transformed volume fraction at time /can be written as... 

Applications. Among the P—O- and P—N-substituted polymers, the fluoroalkoxy- and aryloxy-substituted polymers have so far shown the greatest commercial promise (14—16). Both poly[bis(2,2,2-trifluoroethoxy)phosphazene] [27290-40-0] and poly(diphenoxyphosphazene) [28212-48-8] are microcrystalline, thermoplastic polymers. However, when the substituent symmetry is dismpted with a randomly placed second substituent of different length, the polymers become amorphous and serve as good elastomers. Following initial development of the fluorophosphazene elastomers by the Firestone Tire and Rubber Co., both the fluoroalkoxy (EYPEL-F) and aryloxy (EYPEL-A) elastomers were manufactured by the Ethyl Corp. in the United States from the mid-1980s until 1993 (see ELASTOLffiRS,SYNTHETic-PHOSPHAZENEs). 

The lambda type is nongelling, and functions as a thickner. Iota-carrageenan has been recommended (45) for use in formulating low fat ground beef due to its abihty to retain moisture, especially through a freeze—thaw cycle which is typical for ground beef patties. Oat bran and oat fiber can also be used to improve moisture retention and mouth feel. Modified starches can be used as binders to maintain juiciness and tenderness in low fat meat products. Maltodextrins (dextrose equivalent less than 20) may be used as binders up to 3.5% in finished meat products. Other carbohydrates such as konjac flour, alginate, microcrystalline cellulose, methylceUulose, and carboxymethylceUulose have also been used in low fat meat products (see CELLULOSE ETHERs). 

Sodium Peroxoborate. Sodium peroxoborate [10332-33-9] (sodium perborate monohydrate), Na2[82(02)2(011)4], formerly written as NaBO H20, is known only as a microcrystalline powder, made by dehydrating the hexahydrate. The crystal stmcture has not been deterrnined, but the vibrational spectmm (27) indicates the presence of the same cycHc peroxodiborate anion (4) as that in the hexahydrate as well as in the tetrahydrate. 

Microcrystalline grains with latent image centers... 

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

T. Baba, T. Matsuyama, T. Sawada, T. Takahama, K. Wakisaka, and S. Tsuda, Microcrystalline andVanocystalline Semiconductors Materials Kesearch Society Symposium Proceedings, Vol. 358, Materials Research Society, Pittsburgh, Pa., 1995, p. 895. 

SiH plasma with H2, microcrystalline and -materials can be made with conductivities in excess of l(n-cm). ... 

MicrocrystaUine Silicas. Various microcrystalline (cryptocrystalline) materials such as flint, chert, and diatomaceous earth are found ia nature (see Diatomite). These may arise from amorphous silica, often of biogenic origin, which undergoes compaction and microcrysta11i2ation over geologic time. 

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