Precipitate particle

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. 

Agglomeration a process where precipitation particles grow by coUision with other particles. Pigment agglomerates can be broken into smaller primary particles with the aid of mechanical shear. 

Several reported chemical systems of gas-liquid precipitation are first reviewed from the viewpoints of both experimental study and industrial application. The characteristic feature of gas-liquid mass transfer in terms of its effects on the crystallization process is then discussed theoretically together with a summary of experimental results. The secondary processes of particle agglomeration and disruption are then modelled and discussed in respect of the effect of reactor fluid dynamics. Finally, different types of gas-liquid contacting reactor and their respective design considerations are overviewed for application to controlled precipitate particle formation. 

The mass transfer effect is relevant when the chemical reaction is far faster than the molecular diffusion, i.e. Ha > 1. The rapid formation of precipitate particles should then occur spatially distributed. The relative rate of particle formation to chemical reaction and/or diffusion can as yet be evaluated only via lengthy calculations. 

A dramatic increase of particle size occurs at around pH = 8. At the higher pH(>8), all precipitated particles were within the size range below 1.9 pm, whereas at lower pH(<8), 60-80%wt of particles were larger than 10 pm. The critical pH value is common to all other stirring conditions. The formation of larger particles was avoided by stopping the chemical reaction before the pH value declined to 8. 

Wachi, S. and Jones, A.G., 1995. Aspects of gas-liquid precipitation systems for precipitate particle formation. Reviews in Chemical Engineering, 11, 1-51. 

Fig. 20.S3 (a) Dislocation shearing a precipitate particle and (b) a dislocation bowing round...

Potassium heptafluorotantalate, K2TaF7, precipitates in the form of transparent needles. The precipitated particles must not be too fine, since fine powder usually promotes co-precipitation and adsorption of some impurities from the solution. Even niobium can be adsorbed by the surface of K2TaF7 developed during precipitation, as shown by Herak et al. [535]. On the other hand, the precipitation of large K-salt crystals should not be strived for either. Laboratory and industrial experience indicates that excessively large crystals usually contain small drops of solution trapped within the crystals. This occluded solution can remain inside of the crystal until drying and will certainly lead the hydrolysis of the material. 

In the second method diphenylcarbazide is employed as an adsorption indicator. The end-point is marked by the pink colour becoming pale violet (almost colourless) on the colloidal precipitate in dilute solution (ca 0.01 M) before the opalescence is visible. In 0.1M solutions, the colour change is observed on the precipitated particles of silver cyanoargentate. 

As mentioned previously, a CVD reaction may occur in the gas phase instead of at the substrate surface if the supersaturation of the reactive gases and the temperature are sufficiently high. This is generally detrimental because gas-phase precipitated particles, in the form of soot, become incorporated in the deposit, causing nonuniformity in the structure, surface roughness, and poor adhesion. In some cases, gas-phase precipitation is used purposely, such as in the production of extremely fine powders (see Ch. 19). 

In the polymer industry, post-reaction product treatment processes such as liquid-solid separation, drying, precipitation, particle size control, and polymer purification are very complex and costly. Future polymer plants should be designed such that process equipment can be easily and quickly converted to making new products at minimal cost and with... 

A retained its compact capsule shape no matter what the initial pH of the dissolution medium. Moreover, the dissolution rate of phenytoin from preparation A was pH-independent. Preparation B, however, broke down into fine particles. When the initial pH was neutral, these particles rapidly dissolved. As the initial pH was lowered, these fine particles precipitated. Since these precipitated particles then dissolved very slowly, it would appear that the precipitate was not the freely soluble sodium phenytoin, but the poorly soluble acid form of phenytoin. Since capsule A did not disintegrate or deaggregate, most of the sodium phenytoin was not exposed to the lower pH media and, as a result, was not converted to its very slowly dissolving acid form. 

Flocculation chamber By slow and gentle mixing, the precipitated particles aided by the flocculating agents, collide, agglomerate, and grow into larger settleable particles. 

In a particular system, the nature of the precipitated particles will be determined by the relative rates of nucleation and particle growth. Where nucleation predominates, small particles are produced and a colloid may... 

To get the precipitate particles to clump together to make them more filterable. 

When a monomer such as acrylonitrile is polymerized in a poor solvent, macroradicals precipitate as they are formed. Since these are living polymers, polymerization continues as more acrylonitrile diffuses into the precipitated particles. This heterogeneous solution polymerization has been called precipitation polymerization. 

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