Silica fines

Hydrophobic silica Finely divided silica in polydimethyl siloxane Aqueous foaming systems... 

In our previous paper [6], the authors have demonstrated that production of fine silica powder is possible by phase hydrolpis of tetramethoxysilane fTEMS). In this communication, we report the effect of the shape of reactor and operational condition, especially mixing condition on conversion of the reaction and properties especially diameter of produced silica fines. 

Hydrofluoric acid may be prepared by dilution of a concentrated aqueous solution or by reaction of enough ammonium bifluoride with aqueous 15% HC1 to prepare a 12% HCl/3% HF solution. Hydrochloric - hydrofluoric acid blends have the major advantage of dissolving silicaceous mineral including clays and silica fine particles. HCl/HF blends are quite corrosive. 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

Copolymers of MDTHD and DMAPMA appeared to be the most effective silica, calcite, and hematite mineral fines stabilizers. Increasing the copolymer MDTHD content had little effect on polymer performance. Similar results were observed for a series of MDTHD -DMAEMA copolymers and a series of DMAEMA CH-C1 salt - DMAEMA copolymers (Table VI). In contrast, increasing the MDTHD content of MDTHD - NNDMAm copolymers from 67% to 90% improved copolymer performance as a silica fines and hematite fines stabilizer. 

The observation that the quaternary ammonium monomer content of MDTHD.-DMAEMA and DMAEMA CH3C1 DMAEMA copolymers had little effect on their silica fines stabilization properties of prompted an investigation of nonionic polymers as mineral fines stabilizers (17,18). A series of N-vinylpyrrolidinone (NVP) copolymers with DMAEMA have been studied. Results are summarized in Table VII. 

Limited silica fines stabilization data indicated that increasing copolymer molecular weight from 100,000 to 1,000,000 daltons had, if anything, a negative effect on silica fines stabilization. At a molecular weight of 1,000,000 daltons, this copolymer appeared to be more effective in stabilizing silica fines than silica/kaolinite, calcite, or hematite fines. However, the results may be due in part to the larger particle size and lower surface area of the silica fines (see Table II). 

When the DMAEMA content of NVP - DMAEMA copolymers was reduced from 20% to 8%, the silica fines stabilization effectiveness appeared to improve slightly. When the 80/20 NVP - DMAEMA copolymer was converted to a terpolymer containing 8% DMAEMA (CH SO, silica fines stabilization was substantially unaffected. However, stabilization of silica/kaolinite fines was greatly improved. This suggested that the interaction of polymer quaternary nitrogen atoms with anionic sites on mineral surfaces was important for the stabilization of migrating clays but a different interaction was important for the stabilization of silica fines. Calcite fines stabilization improved while hematite fines stabilization effectiveness decreased. This also indicated the nature of the adsorbed polymer - fine particle complex varied for different minerals. 

The results summarized in Table IX indicated that another copolymer which does not contain quaternary nitrogen atoms, poly (DMAEMA - co - methyl acrylate) was also an effective silica fines stabilizer. 

Increasing the molecular weight of a copolymer containing 5% methyl acrylate (MA) from 100,000 to 1,000,000 daltons had little effect on silica stabilization effectiveness (see Table IX). Increasing the methyl acrylate content from 5% to 30% had also little effect on silica fines stabilization effectiveness. Acidizing substantially reduced the effectiveness of this class of copolymer. Results for the injection of 10,000 pore volumes of water indicated that silica fines elution from the test column was substantially reduced on a long-term basis. 

Relaxation dispersion data for water on Cab-O-Sil, which is a monodis-perse silica fine particulate, are shown in Fig. 2 (45). The data are analyzed in terms of the model summarized schematically in Fig. 3. The y process characterizes the high frequency local motions of the liquid in the surface phase and defines the high field relaxation dispersion. There is little field dependence because the local motions are rapid. The p process defines the power-law region of the relaxation dispersion in this model and characterizes the molecular reorientations mediated by translational displacements on the length scale of the order of the monomer size, or the particle size. The a process represents averaging of molecular orientations by translational displacements on the order of the particle cluster size, which is limited to the long time or low frequency end by exchange with bulk or free water. This model has been discussed in a number of contexts and extended studies have been conducted (34,41,43). 

Fig. 3. Schematic representation of the topological space of hydration water in silica fine-particle cluster (45). The processes responsible for the water spin-lattice relaxation behavior are restricted rotational diffusion about an axis normal to the local surface (y process), reorientations mediated by translational displacements on the length scale of a monomer (P process), reorientations mediated by translational displacements in the length scale of the clusters (a process), and exchange with free water as a cutoff limit.

On the other hand, wet process metal coating method was applied to the surface-modified nylon 12 particles (24). Nylon 12 particles modified by alumina or silica fine particles were given metallic coating by an electroless plating method. 

Hyodo, T., Kakimoto, M., Chang, T.B., Deng, J., Akahane, T., Chiba, T., McKee, B.T.A. and Stewart, A.T. (1989). Relaxation of the momentum distribution of free positronium atoms interacting with silica fine particles. In Positron Annihilation, eds. L. Dorikens-Vanpraet, M. Dorikens and D. Segers (World Scientific) pp. 878-880. 

Specialty Chemicals Coatings Additives Plastics Acetate Cable Rare Earths Silicas Fine Chemicals Sulfuric Acid Services... 

Pebble mills are frequently fined with nonmetaUic materials when iron contamination would harm a product such as a white pigment or cement. Belgian silex (silica) or porcelain block are popular finings. Silica finings and ball media have proved to wear better than other nonmetaUic materials. The higher density of sflica media increases the production capacity and power draft of a given miU. 

Thus, it can be assumed that in the presence of small amounts of water, the interaction between magnesium hydroxide and silica, finely ground and thoroughly mixed, proceeds via the dissolution of silica in the presence of magnesium hydroxide. This followed by the interaction of silica with magnesium hydroxide resulting in the formation of insoluble magnesium silicate. 

FIG. 20.6 Variation in mineral volumes over a kinetic reaction path designed to illustrate Ostwald s step sequence. The calculation traces the reaction at 25°C among the minerals amorphous silica (fine line), cristobalite (medium line), and quartz (bold line). The top diagram shows results plotted against time on a linear scale the time scale on the bottom diagram is logarithmic. The decrease in total volume with time reflects the differing molar volumes of the three minerals. 

Synthetic PVC Plastic Made from mixture of PVC, silica fine powder, and a solvent, and then extruded, calendared, and extracted Small to medium average pore size and relatively low electrical resistance... 

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