Specific surface area, water absorption

The crospovidone grades are obtained with different specific surface areas, depending on the polymerization conditions, and their particle size. The micronization process has less influence on the specific surface than small modifications of the polymerization conditions. When a normal crospovidone was micronized the specific surface only increased from l m2/g to i.8 m2/g (N2-BET method). The micronized crospovidone of the lowest bulk density available in the market has the highest specific surface of 2.5 to 6 m2/g (Table 118). 

Crospovidone is almost as hygroscopic as povidone. It has not been possible to find any significant difference in water adsorption between the different grades of crospovidone, so that Fig. 67 applies for all grades. 

If water is added to crospovidone instead of merely exposing it to atmospheric humidity, it binds significantly more. Its hydration capacity is best determined by the following method [3]  

0 g of crospovidone to 40 ml of water in a 100-ml centrifuge tube and shake vigorously until a suspension is obtained. Shake up again after 5 and after 10 minutes. Then centrifuge for 15 minutes at 2000 rpm. Decant off the supernatant liquid. Then reweigh. 

The hydration capacity is calculated as the quotient of the weight after hydration and the initial weight. For normal crospovidone, usually it lies in the range 3-6. 

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Carbon blacks are synthetic materials which essentially contain carbon as the main element. The structure of carbon black is similar to graphite (hexagonal rings of carbon forming large sheets), but its structure is tridimensional and less ordered. The layers of carbon blacks are parallel to each other but not arranged in order, usually forming concentric inner layers (turbostratic structure). Some typical properties are density 1.7-1.9 g/cm pH of water suspension 2-8 primary particle size 14-250 nm oil absorption 50-300 g/100 g specific surface area 7-560 m /g. 

Reduction of particle size increases the total specific surface area exposed to the solvent, allowing a greater number of particles to dissolve more rapidly. Furthermore, smaller particles have a small diffusion boundary layer, allowing faster transport of dissolved material from the particle surface [58]. These effects become extremely important when dealing with poorly water-soluble drugs, where dissolution is the rate-limiting step in absorption. There are numerous examples where reduction of particle size in such drugs leads to a faster dissolution rate [59-61], In some cases, these in vitro results have been shown to correlate with improved absorption in vivo [62-64]. 

C. The Meaning of Specific Surface Areas Calculated from Water Absorption Studies... 

Absorption of harmful organic compounds by activated carbons from gas and liquid media is of interest and importance for human and environmental protection purposes.1"21 The influence of the texture of carbon granules (size and volume of pores, specific surface area, granule size d, and carbon bed depth V), gas stream humidity and velocity, and amounts of pre-adsorbed water are investigated on adsorption of organics in different media.1 21... 

In these calculations the total volume of monomer was constant (300 cm /dm water) and the specific surface area of SDS on the monomer was set to 50 A per molecule. The other parameters arc given in the table footnote. It appears that absorption of emulsifier on the monomer droplets surface starts to become significant at droplet radii S/rm. With S — 2 g/dm HjO one passes the CMC for the emulsifier at a droplet diameter of about 1.5 foa, with 5 g S the corresponding value is 0.2/im. With droplets below that size one should expect that the droplets may become the important loci for particle nudeation. 

The water-absorption rate of superabsorbent polymers is affected by 1) the specific surface area of the polymers 2) the capillary action and 3) the formation of fish-eyes in the polymer hydrogels. 

Liquid or amorphous materials may (also) show absorption. Here, the absorbate can dissolve in the absorbent, or it can be seen as adsorbing onto the surface of a great number of fine pores in the absorbent. Anyway, the amount absorbed would be proportional to the mass of absorbent, other things being equal. In most dry foods, it is unclear whether the mechanism is adsorption or absorption in liquid foods, it is always the latter. It is rarely observed in a dry food that the equilibrium amount of water taken up depends on the specific surface area of the food. Generally, the term sorption is used, leaving the mechanism involved out of consideration. 

Energy of break, effect on, 137 Flexural modulus, effect on, 137 Flexural strength, effect on, 137 Impact restance, effect on, 137, 138 Mohs hardness, 137 Moisture content Mold shrinkage, effect on, 137 Particle size, 137, 139 Plastic softening point, effect on, 137 Specific gravity, 137 Specific surface area, 137 Warpage, effect on, 139 Water absorption, effect on, 137, 139 Tannins, 75, 84, 94, 105, 106 Stains on a deck, 105, 106 TBBPA (tetrabromobisphenol-A), 471... 

Although the maximum pore radius distribution in conventional gypsum microstructures usually lies within the range of capillary suction action (100 nm to 1 mm) [44, 52], the roughly 50% water absorption that occurs in untreated gypsum is often reduced to less than 5 wt% [44, 45] at standard market application rates of just 0.3 - 0.5 wt% H-siloxane. The optimum amount to use depends upon the gypsum raw material, the fineness of the grain in the plaster of Paris, its specific surface area, and the reaction temperature. 

One such possibility consists in the acceleration of contaminant hydrolysis. Hydrolytic detoxification in an alkaline medium is known to be several orders of magnitude faster than that in a neutral medium. Therefore, one can cover underwater places of contaminant burial with any solid alkaline reagent, which will create an alkaline medium in the zone of the contaminant s location. Requirements for such a reagent are rather simple. It should be very poorly soluble in sea water, have a considerable specific surface area (no less than 50 m /g), display clearly defined alkaline properties and be a nontoxic, low-priced, and easily available substance. I believe that chemists-technologists working in the fields of silicate industry, metallurgy, and absorption processes already understand that a wide variety of well-known materials, including some industrial wastes, comply with the above requirements. 

This has obvious disadvantages. The water removed in this way would, if kept, have helped to reduce flammability as well as increase the specific surface area, thus increasing the hygroscopic character and the oil absorption, and it would also have moderated the adverse effect on polymer viscosity. The practical significance is that ATH can be used in environmentally-friendly, halogen-free printed circuit boards, achieving a UL-94 V-0 fire rating. 

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