Using organic dispersing agents

These products are used to maintain the particles in suspension so as to prevent the formation of deposits in areas of low circulation rates and on the heat exchange surfaces. They can also regulate the formation of protective layers by corrosion inhibitors. They are, in fact, often included in inhibitor formulation. 

Among the products that are used, the following can be listed  

These products are very often anionic and this must be taken into account if they are to be used in the presence of opposing ions. 

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Polymerization of vinylidene fluoride by emulsion or suspension polymerization in water is conducted at conditions of 10-130 °C and 10-200 bar. In the emulsion polymerization, either water-soluble peroxides or monomer-soluble peroxy or organic peroxides are used as initiators [ 17]. Fluorinated surfactants, such as ammonium perfluorooctanoate, are used as dispersing agents. Chain transfer agents, such as acetone, chloroform, or trichlorofluoromethane, may be... 

N,N -Dinitrosopentamethylenetetramine (DNPA) is the cheapest (except for urea oxalate) and most widely used organic blowing agent accounting for 50% of all blowing agents used. It however disperses poorly in mixtures and is sensitive to shock and friction (explosive). 

Inorganic blowing agents are difficult to disperse in polymers thus, in spite of their low cost, they are seldom used. Organic blowing agents offer more application possibilities. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Evaporators require the continuous low level (1-3 ppm) application of a suitable antisealant chemical treatment. Traditionally, polyphosphate has been used (sometimes in conjunction with an antifoam and/or a dispersant agent), but it generally performs poorly because of a lack of thermal stability. Treatments based on polymaleic acid (PMA) and other modem organic polymers tend to perform much better. 

Complexes of tetravalent zirconium with organic acids, such as citric, tartaric, malic, and lactic acids, and a complex of aluminum and citric acid have been claimed to be active as dispersants. The dispersant is especially useful in dispersing bentonite suspensions [288]. Polymers with amine sulfide terminal moieties are synthesized by using aminethiols as chain transfer agents in aqueous addition polymerizations. The polymers are useful as mineral dispersants [1182]. 

When formulating a deflocculated system, a number of materials may be used as dispersion aids. De-flocculating agents include polymerized organic salts of... 

So far, we have prepared and tested many kinds of colloids, mainly in nonaqueous suspensions with combinations of metals or alloys as a dispersed phase and organic liquids as the dispersion media, without the use of any dispersing agents these are listed in Table 9.4.1. We next give some examples of transmission electron micrographs of nanoparticles produced by an aerosol method. A sample for TEM measurement was obtained by dropping colloidal suspension onto a Cu mesh coated with an evaporated carbon film of 10 nm thickness. Many colloids were so unstable... 

Figure 3.7—Preparation of spherical particles of silica gel via a sol-gel. The dispersive medium, called sol, is made of particles that are only a few nanometres in diameter. The small spheres are then agglutinated together with the aid of an organic binding agent (urea/methanol) to yield spheres with the requisite size (3-6 pm). Pyrolysis is then used in the final treatment.

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