Deflocculation prevention

Wetting agents —Reduce surface tension Deflocculents —Prevent particle agglomeration... 

Barium carbonate prevents formation of scum and efflorescence in brick, tile, masonry cement, terra cotta, and sewer pipe by insolubilizing the soluble sulfates contained in many of the otherwise unsuitable clays. At the same time, it aids other deflocculants by precipitating calcium and magnesium as the carbonates. This reaction is relatively slow and normally requites several days to mature even when very fine powder is used. Consequentiy, often a barium carbonate emulsion in water is prepared with carbonic acid to further increase the solubiUty and speed the reaction. 

Deflocculants. Deflocculants (34), dispersants (qv), or anticoagulants are added to slurries to improve dispersion and dispersion stabiHty. Dispersants break up floes in a slurry by lowering van der Waals interparticle forces. Deflocculants adsorb on particle surfaces and prevent the approach of particles either by electrostatic or steric stabilization. Deflocculation by electrostatic stabilization is common in clay slurries, as weU as with ceramic particles dispersed in polar Hquids such as water. 

Copolymers or terpolymers of acrylic acid, which contain from 5 to 50 mole-percent of sulfoethyl acrylamide, acrylamide and sulfoethyl acrylamide, ethyl acrylate and sulfoethyl acrylamide, acrylamide and sulfophenyl acrylamide, and acrylamide and sulfomethyl acrylamide, are claimed to be calcium-tolerant deflocculants for drilling fluids [704]. In general, 0.1 to 2 lb of polymer per barrel of drilling fluid is sufficient to prevent flocculation of the additives in the drilling fluid. 

What precautions could be taken to prevent the take up of impurities when reducing the particle size of zirconia from 10 pm to 1 pm Describe the beneficial effects that addition of a deflocculating agent might be expected to have on the ball-milling process. 

Although the production of highly deflocculated suspensions is a primary objective for formulation of suspension concentrates, these systems tend to settle under gravity forming dilatant sediments (clays). The latter must be prevented either by controlled flocculation or by the addition of a second disperse phase to the continuous medium (1). One method which may be applied to sterlcally stabilised dispersions, is to add a free (ie. non-adsorbing) polymer to the continuous medium. 

Properties Miscible with water but insoluble in organic solvents. It possesses sequestering, dispersing, and deflocculating properties and precipitates proteins. In very low concentration, it inhibits corrosion of steel and prevents the precipitation of slightly soluble, scale-forming compounds such as calcium carbonate and calcium sulfate. 

Consider now a deflocculated clay (Figure 22b). Here the ultimate particles are prevented by the high zeta-potential from agglomerating and so remain as separate platelets. When water is removed from such a system, the particles draw closer together, and eventually, being plate-like, they pack one upon the other in an ordered fashion, as in the illustration. In this system the packing is clearly very dense, consequently the system is not easily penetrated by water, with the result that filter-pressing is difficult. 

The shortest distance between the two particles can be larger than the sum of their radii. If the particle surface is covered with polymers there is steric hindrance, which prevents surface contact, so polymers are sometimes used as antiflocculation agents. The sum of the attraction and repulsion potentials is given in Figure 6.6 as a function of the interparticle distance. Once the particles are agglomerated they can only be dispersed again if the attraction between them can be lessened, e.g., with counter ions in the solution. This redispersion is called deflocculation or sometimes repeptization. 

Deflocculant de- fla-ky3- lat. An additive that prevents pigments in suspension from coalescing to form floes. 

Deflocculating agent n. A substance that breaks down agglomerates into primary particles or prevents the latter from combining into agglomerates (ISO). 

Flabby Cast. A fault sometimes encountered in the casting of pottery-ware. The article appears satisfactory as cast but subsequently deforms, either as a result of a thixotropic effect or because the interior of the cast is still fluid if the cause is thixotropy, the amount of Na silicate and Na2C03 used as deflocculant should be increased the second cause is most common in the casting of thick ware and is prevented by increasing the casting rate. 

See CRYSTAL structure fracture. (2) A suspension in water of clay and/or other ceramic materials normally a DEFLOCCULANT (q.v.) is added to disperse the particles and to prevent their settling out. In the whiteware industry, a slip is made either as a means of mixing the constituents of a body (in which case it is subsequently dewatered, e.g. by filter-pressing) or preparatory to CASTING (q.v ). In vitreous enamelling, a slip is used for application of the enamel to the ware by spraying or dipping. 

The pH should usually be kept at 6.8 to 7.8, and acidification to below 6.5 should be avoided as it may cause the activated sludge to deflocculate and make it hard to settle out. A supply of strongly bicarbonate make up water will be advantageous in this connection. If there is none, pH may have to be regulated at the biological purification inlet. Tire possibility of acidifying fermentation (nitrification or oxidation of thiosulfates) must be prevented. 

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