Growing particle size

Boudart [4] TOFs can either be independent of particle size (structure-insensitive reactions), increase (antipathetic structure sensitivity) or decrease (sympathetic structure sensitivity) with growing particle size, or cross a maximum (Figure 2). 

Experiment B—Growing Particle Size of Seed Latex No. 2. Water (90 kg.), vinyl chloride (13.27 kg.), and seed latex No. 2 (7.85 kg.) (2.73 kg. solids) were placed in the kettle. About one hour after the start of the reaction, 64 kg. of the remaining VC was fed continuously, while simultaneously a solution of 0.336 kg. Empicol Ser in 2.0 kg. water was introduced, continuously, dropwise. Vinyl chloride (64 kg.) and soap (0.336 kg.) were introduced by the following procedure. In the... 

Experiment C—Growing Particle Size of Seed Latex No. 1. The... 

Experiment D—Growing Particle Size of Seed Latex No. 3. Quantities of H20, VC, and seed (see Table I) are given in Table II. A total of 720 grams of soap was introduced dropwise during the reaction. Empicol Ser was dissolved in water. Conversion was about 90% for all runs. 

Growing Particle Size. According to Vandegaers (10) procedure, the total surface (TS) of all the particles during the growth can be calculated, so that the emulsifier addition can be adjusted not to exceed the 100% surface saturation, thus preventing formation of new particles. The following equations were used ... 

Precipitate particles grow in size because of the electrostatic attraction between charged ions on the surface of the precipitate and oppositely charged ions in solution. Ions common to the precipitate are chemically adsorbed, extending the crystal lattice. Other ions may be physically adsorbed and, unless displaced, are incorporated into the crystal lattice as a coprecipitated impurity. Physically adsorbed ions are less strongly attracted to the surface and can be displaced by chemically adsorbed ions. 

During Stage II the growing particles maintain a nearly constant monomer concentration. The concentration of monomer is particle-size dependent, with smaller particles having lower concentrations (28). 

Fig. 10. Polymerization behavior of silica. In basic solution (B), particles grow in size and decrease in number in acidic solution or in the presence of flocculating salts (A), particles aggregate into three-dimensional networks and form gels (1).

In the absence of a suitable soHd phase for deposition and in supersaturated solutions of pH values from 7 to 10, monosilicic acid polymerizes to form discrete particles. Electrostatic repulsion of the particles prevents aggregation if the concentration of electrolyte is below ca 0.2 N. The particle size that can be attained is dependent on the temperature. Particle size increases significantly with increasing temperature. For example, particles of 4—8 nm in diameter are obtained at 50—100°C, whereas particles of up to 150 nm in diameter are formed at 350°C in an autoclave. However, the size of the particles obtained in an autoclave is limited by the conversion of amorphous siUca to quartz at high temperatures. Particle size influences the stabiUty of the sol because particles <7 nm in diameter tend to grow spontaneously in storage, which may affect the sol properties. However, sols can be stabilized by the addition of sufficient alkaU (1,33). 

The determination of particle size and stmctural iaformation for fibers and polymers, and the study of stress, texture, and thin films are appHcations that are growing ia importance and can be examined with x-ray iastmments. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

In the total particle size distribution, some particles of small diameter decrease in radius, and those in the larger diameter range increase in radius during Ostwald ripening. There will therefore be a radius at which particles neither decrease nor grow in size and if [Pg.210]

---