Ultrafine

Y. H. Chia and P. Somasundaran, in Ultrafine Grinding and Separation of Industrial Minerals, S. G. Malghan, ed AIME, New York, 1983. 

Kondo A, Oku S and FllgashItanI K 1991 Structural changes In protein molecules adsorbed on ultrafine silica particles J. Colloid Interfaoe Sc/. 143 214-21... 

Kofman R ef al 1991 Melting of non-spherical ultrafine particles Z. Phys. D 20 267... 

H. Aranha-Creado, K. Oshima, S. Jafari, G. Howard, Jr., and H. Brandweia, Scientific and TechnicalEeport STR-PUF-24, Pall Ultrafine Filtration Co., East HiUs,N.Y., 1995. 

A special use for meltblown olefin fiber is in filtration media such as surgical masks and industrial filters (78). The high surface area of these ultrafine filament fibers permits preparation of nonwoven filters with effective pore sizes as small as 0.5 p.m. 

Ultrafine CeUulose Fibre from Weyerhauser Co.," Medical Textiles, (Nov. 1990). 

The type of floe requited depends on the separation process which foUows, eg, rotary vacuum filtration requites evenly sized, smaU, strong floes that capture ultrafines to prevent cloth blinding and cloudy filtrates. The floes should not be subject to sedimentation in the vat or breakage by the agitator. 

The precursor glass powders may be produced by various methods, the simplest being the milling of quenched glass to an average particle size of 3—15 p.m. Sol gel processes, in which highly uniform, ultrafine amorphous particles are grown in a chemical solution, may be preferable for certain apphcations. 

Fig. 2. Ultrafine fibers are produced by spinning bicomponent or biconstituent polymer mixtures, highly stretching such products to ultrafine deniers, and extracting or otherwise removing the undesked matrix carrier to release the desked ultrafine fibers (30). For example, spinning polyester islands in a matrix of polystyrene and then, after stretching, dissolving the polystyrene to leave the polyester fibers cospinning polyester with polyamides, then stretching,...

Industrial Fillers. Whiting is widely used ia paints as a filler and pigment extender. A high refiective white color is a requisite for paint. Both ultrafine and relatively coarse carbonate fillers ate iacorporated ia mbber products. The latter type of a nominal 0.074 mm (200 mesh) size is for iaexpensive mbber products. 

Property Technical grade Controlled particle size (CPS) " CPS-ultrafine (UF) usp"... 

The TEM is one of the most generally useful microscopes many thousands of them ate in daily use throughout the world. They ate appHcable to the study of ultrafine particles (eg, pigments abrasives and carbon blacks) as well as microtomed thin sections of plant and animal tissue, paper, polymers, composites of all kinds, foods, industrial materials, etc. Even metals can be thinned to sections thin enough for detailed examination. 

Gas purification processes fall into three categories the removal of gaseous impurities, the removal of particulate impurities, and ultrafine cleaning. The extra expense of the last process is only justified by the nature of the subsequent operations or the need to produce a pure gas stream. Because there are many variables in gas treating, several factors must be considered (/) the types and concentrations of contaminants in the gas (2) the degree of contaminant removal desired (J) the selectivity of acid gas removal required (4) the temperature, pressure, volume, and composition of the gas to be processed (5) the carbon dioxide-to-hydrogen sulfide ratio in the gas and (6) the desirabiUty of sulfur recovery on account of process economics or environmental issues. 

Fig. 11. Cross-sectional schematic of a Matsu2aka Elbow-Jet classifier where Fj = ultrafine particles, F2 = fine particles, M = medium particles, and...

A most useful feature of the agglomeration technique is its ability to work with extreme fines. Even particles of less than nanometer size (ca 10 ° m) can be treated, if appropriate, so that ultrafine grinding can be appHed to materials with extreme impurity dissernination to allow recovery of agglomerates of higher purity. A number of appHcations of Hquid-phase agglomeration have reached either the commercial or semicommercial pilot scale of operation. 

Specific Surface. If a defined specific surface area is required, this can affect the choice of equipment. Machines that apply stress by cmshing generally create more ultrafines, and hence higher surface area, than impact mills. 

As only a small proportion of the material is in contact with the roUs and friction on the rollers is low, hard materials can be processed with tittle wear. The high pressure action creates a slab of ultrafine particles which usually requires a low speed impact milting system to disagglomerate. Used in closed circuit with such a disagglomerator and an air classifier, such machines can reduce the energy requirement for fine grinding many minerals. 

The value of crude ore produced ia the United States was estimated to average 32.50/t in 1994. Product pricing was reported to vary from 99/t for New York State 200-mesh paint grade to 220/t for ultrafine Montana paint grade. Cosmetic grades were quoted at 263/t. 

Titanium carbide may also be made by the reaction at high temperature of titanium with carbon titanium tetrachloride with organic compounds such as methane, chloroform, or poly(vinyl chloride) titanium disulfide [12039-13-3] with carbon organotitanates with carbon precursor polymers (31) and titanium tetrachloride with hydrogen and carbon monoxide. Much of this work is directed toward the production of ultrafine (<1 jim) powders. The reaction of titanium tetrachloride with a hydrocarbon-hydrogen mixture at ca 1000°C is used for the chemical vapor deposition (CVD) of thin carbide films used in wear-resistant coatings. 

The calcium carbonate industry is one of the most competitive of the industrial minerals industry. The market for fine products (97% <45 fim) is estimated to be between 5—9 million tons annually in the United States. The pricing is dependent on the grade which is determined by fineness, purity, and brightness it ranges from 30/kg for coarse materials to over 440/kg for some ultrafine coated or food grades (4). 

The ultrafine siUcon carbide produced in an electric arc is used as an insulation in cryogenic appHcations (152) (see Cryogenics). It generally increases the wear resistance of the paint film when added to paint formulations. 

Finely ground cements often called ultrafine cements, having particles less than 10 p.m and an average size of 4 pm are used to grout soils with fine pore spaces, such as fine sand with a permeabiUty of lO " cm/s. These cements can be made with a wide combination of Pordand cement, slag, or siUca fume (72). 

Chemically Synthesized Powders. Chemical synthesis provides a means of produciag powders for manufacturiag advanced ceramics. Disadvantages of chemically synthesized raw materials are expense and difficulties ia scale-up and availabihty. Additionally, ultrafine particle-size powders produced by chemical synthesis pose some unresolved processiag problems ia the areas of handling and mixing. 

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

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