Fine composites Composite particles

Finely-ground composition, particles preferably of laminar shape to prevent settling when the enamel is molten. 

Clay particles are so finely divided that clay properties are often controlled by the surface properties of the minerals rather than by bulk chemical composition. Particle size, size distribution, and shape the nature and amount of both mineral and organic impurities soluble materials, nature, and amount of exchangeable ions and degree of crystal perfection are all known to affect the properties of clays profoundly. 

The synthesis effort was initiated by the Horie group on mechanically blended powder mixtures of 3 parts nickel with 1 part aluminum in molar proportions and a similar sample composed of a composite particle of nickel plated on aluminum in similar proportions. The powders were a 44 74 m nickel powder and a 5-15- m micron aluminum powder, a coarse fine mixture. The powder mixtures were shock loaded to peak pressures of 7.5 and 22 GPa with starting powder densities of 60% of solid density. 

Primary clay is also known as residual clay, indicating that they are either the in situ residue of one type of weathered rock or the transported residue of many types of rocks most primary clay deposits occur, however, in situ, at the location where the clay particles were formed. The clay is usually quite pure and colorless or white, but very small relative amounts of minerals mixed with the clay, such as quartz and/or iron oxides, may impart to it a yellow, brown, or green color. Primary clay is also characterized by the extreme fineness of its particles, which usually measure below 2 micrometers (0.002 mm) in diameter. The more than 20 different types of primary clay minerals can be distinguished by their chemical composition, which varies widely, and by their physical properties. Primary clays that have been used for making ceramic objects are listed in Table 55. 

The most important characteristic of cement is its pore structure and aqueous phase hence, the microstructure of the hardened cement paste via the pore system. It is highly alkaline (pH >13) due to rapid and almost quantitative dissolution of Na and K salts from the cement clinker. The porosity of the paste comprises interconnected and isolated pores, the pore sizes of which are important to the strength and dimensional stability of cement products. Different types of cement are used to meet different performance criteria. Properties can be estimated from compositions and fineness (i.e., particle size and size distribution). In the past, additives... 

This result may be deceptive, however, as we had to eliminate the many studies from Cols. 2 and 3 that contained no size Information, so the two sets of averages are not for the same populations of plants. A further problem with these data may also be the Inclusion of particles up to 2.5-pm dlam, whereas, recent studies (44, 46) indicate that the large changes of composition occur below about 0.5-pm dlam. Thus, our "fine" particles In Table IV Include particulate mass between 0.5 and 2.5 ym that Is chemically similar to larger particles, which reduces the Rvalues. We made the cut at 2.5 ym to develop components for separate CEBs of fine and coarse particles In ambient air, which are commonly divided at about that point. 

One particular type of source that should be studied carefully Is entrained soil. As shown above, this Is often the greatest contributor of TSP In urban areas. As there Is so much of It present, we need to know concentrations of all measured elements quite well to make an accurate determination of the residual amounts left to be accounted for by other sources. The composition of selved soil Is often used for the soil component, but there may be considerable fractionation Imposed by entrainment, e.g., preferential selection of very fine clay mineral particles. Such fractionation has been demonstrated In the very limited studies of entrainment of particles from soil of known composition (e.g.. Refs. 21, 49). These studies can probably best be done In controlled environments such as wind tunnels. One cannot simply collect ambient particles In the countryside and consider it to be soil, as there are anthropogenic contributions even at great distances from cities ( ). There Is further confusion betwen clean, "continental" dust and "urban" dust. The latter, which Is usually collected near city streets (21, 50), typically has a composition of soil contaminated by anthropogenic emissions, especially from motor vehicles. 

Coal also may contribute to the fine modes of Zn, Mn, Fe, and other metals in the polluted atmosphere. However, the relative elemental compositions of fine mode aerosol particles in polluted and clean atmospheric samples from the Beijing region are quite similar, so that the pollution and natural components are not readily distinguished by composition alone ( ). 

The chemical composition of particles collected in the museums was also compared to that outdoors using a mass balance model. The results indicated that there were significant indoor sources of fine particle organics and that this source(s) was a significant fraction of the total indoor fine particle organic concentration (Ligocki et al., 1993). A similar conclusion was reached by Naik et al. (1991) in measurements made in a telephone... 

St and divinylbenzene (DVB) were polymerized in a dispersion of acryl-amide-methacrylic acid-methylenebisacrylamide terpolymer particles (25). Fine polystyrene particles were formed in/on each seed terpolymer particle. The former was smaller by about one-twentieth than the latter. The distribution of polystyrene particles depended on the cross-link density. Different amounts of St and DVB were charged in the seeded polymerization, and the resulting composite particles were used for protein adsorption measurement to assess the hydrophobicity of the particle surface. The adsorbed amount was almost proportional to the amount of St and DVB charged. In contrast, cells were less stimulated by the 5% St-containing particle than by the 0% St-containing one, that is, the seed particle. This phenomenon is attributed to selective protein adsorption on the 5% St-containing particle (26). 

The so-called dry mixing or dry blending method has been used for the modification of" particles in the powder technology (59). In this method, surface modification of coarse particles is carried out by mixing fine particles and coarse particles with an auto ceramic mortar or with a centrifugal rotating mixer. This procedure can be applicable for the production of variety of composite magnetic particles. 

Figure 13.3.7 shows scanning electron microscopy (SEM) photographs of the surface of the polyethylene particle after the silica particles were peeled off. The specimen was prepared in the following way. After the composite particles were potted in epoxy resin, the dried resin block was cut using a microtome to produce fine sections. The fracture surface appearance of the polyethylene was then observed under a microscope. The mean depth penetration into the surface of the core particles could be measured using the SEM photographs. Silica 0.3 pan in diameter was embedded in the surface of the polyethylene particles at a depth of 0.03 xm. In... 

Table I. Average Aerosol Composition for Fine and Coarse Particles at a Rural, Forested Location (Great Smoky Mountains, Tennessee) and an Urban Location (Houston, Texas) ...

CLAYS. The terms chy or cloys commonly refer to cither rocks that are consolidated or unconsolidated sediments, nr a group of minerals having unique properties. Traditionally, clays (rocks) are distinctive in al least two properties that render them technologically useful plasticity and composition. Clays are predominantly composed of hydrous phyllosilicates. referred to as clay minerals. These are hydrous silicates of Al. Mg. K, anti He. and other less ahundanl elements. Clay minerals arc extremely fine crystals or particles, often colloidal in size and usually plate-like in shape. The nonclay mineral portion of clays (rocks) may consist of other minerals, portions of rocks, and organic compounds. 

Pigments. These arc finely divided powders (particles between 0.1 and 50 micrometers in diameter) which are dispersed throughout llie binder. In addition to reinforcing the final film, much as they do in composite plastics, they influence a coating s resistance to abrasion and corrosion, and they also are the major factor in the gloss, color, and opacity of a coating. 

A comparison of fine and coarse particle compositions supports this hypothesis. Figure 4 shows EFcrust values for fine and coarse particles from six eastern-coal-burning plants equipped with ESPs. (We wanted to emphasize size-fraction differences without the additional effects of coal type and pollution control device.) For... 

If the compositions comprise particles as large as 0.2 micrometers, it is preferred to use a digestion procedure. The digestion procedure is not necessarily ideal for silver compositions that may have been manufactured or stored in contact with halides or other anionic species that may react with finely divided silver, or combined with protein or other gelatinous material. An embodiment of the digestion procedure is as follows ... 

---