Dispersants precoating

Pretreatment of membranes with dynamically formed polarization layers and enzyme precoats have been effective (12,13,39). Pretreatment with synthetic permeates prevents startup instabiUty with some feed dispersions. 

Other factors that can influence the separability of components of complex natural mixtures, such as adsorbent particle size and layer thickness, are similar to those used in analytical TLC. Mostly, adsorbents of wide dispersion of particle size — 5 to 40 pm and layers of 0.5 to 1 mm thickness — are used. Although the capacities of layers increase with their thickness, the separation efficiency decreases for thickness above 1.5 mm. Commercially available precoated preparative plates (e.g., silica, alumina, and RP2 plates) with fluorescence indicators and plates with preadsorbent zones are more convenient and commonly used. 

Based on the results of these tests, recommended operating conditions for Zr precipitation in the pilot plant system include reaction temperatures of 20 C or 60 C, impeller tip speeds of 320 cm/s during solid dispersal/reaction vising a high efficiency axial flow impeller, addition of 0.83 g NaF/g Zr in solution, and crystallization periods of 24 hours. A filter press will provide acceptable solid/llquid separation even during process upsets without use of a precoat. A diaphragm pump functioned well during these tests. 

For sub-micron metallic powders, precoating with gelatin aids dispersion in aqueous systems. Coating of commercial powders in order to stabilize them is widely used e.g. aluminum oxide coated titanium dioxide. In such cases the interfacial properties will be those of the coating rather than those of the bulk powder. 

FePt nanorods of high quahty have been produced by decomposition of Fe(CO)5 and reduction of Pt(acac)2 in a confined cyUndiical mesophase consisting of surfactants such as oleic acid and oleyl amine at high concentrations and slow heating (61). Self-assembly of FePt nanorods can be carried out on a silicon wafer by evaporating a hexane dispersion. Hydrothermal synthesis has also been used for self-assembly by precoating the substrate with aluminum metal (62). Under hydrothermal conditions, the aluminum metal transforms to a hydrotalcite-like phase which provides a lattice matched substrate for the growth of oxide nanorods such as ZnO (Fig. 7.12). The substrates can be diverse, flat, or curved, such as silicon, polystyrene beads, carbon nanotube array, etc. 

Early adhesive uses of butyl rubber generally consisted of solvent-based dispersions, or tape and rope extrusion of formulated solid rubber. Extensive use was made of butyl rubber s inherent tackiness in highly saturated grades of the polymer to make pressure sensitive tapes and precoated films. The polymers are also extensively used as major components of hot-melt adhesives, solid rubber sealing tapes, and caulking grades of sealants and mastics, of which most were high solids content solvent-based formulations. 

There are several types of powder filter, namely (i) plate and frame, (ii) vertical leaf, (iii) horizontal leaf and (iv) candle or edge filters. The plate and frame filter is more popular in Europe than America [4, 12]. It comprises a succession of vertically dispersed plates each covered with a cellulose sheet folded at the top of the plate. Each plate alternates with a frame which will receive in succession the precoats and the beer plus body feed. The beer passes through the kieselguhr bed, then the sheet and into the plate from which it discharges (Fig. 20.17). Leaf filters have a series of stainless steel leaves disposed either vertically or horizontally inside a filter body. Both surfaces of vertical leaves are used for filtration (Fig. 20.18) but only the upper surfaces in the case of horizontal leaves (Fig. 20.19). The kieselguhr adheres to the septa because of the pressure at which the beer is forced into the filter. At the... 

Such tests will reveal that the manner in which filter aid is removed depends on its properties and the drum speed. In some cases the filter aid will be removed as flakes, while other tests will show that the remaining portion of the cake will acquire a rough surface. High drum speed and filter aid dispersity are known to enhance the quality of the precoat layer. 

Amide-salt derivatives as silica dispersants for precoating diazo materials... 

The acid functional polyolefins are not suited to precoating because they are solids and are therefore predominately used by the in situ process. The polybutadiene types can be used by either precoafing or in situ methods and water dispersible forms are available. 

Mixing can be done under vacuum in order to remove air bubbles. The main experimental parameters are the sequence in which the constituents are added, the energy supplied by the mixer and the residence time as well as the possible precoating of the ceramic powder by the dispersant. 

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