Precipitated silica manufacturing process

Siloxane compounds, in vitreous silica manufacture, 22 414 Siloxane materials, 20 240 Siloxane oligomers, in silicone polymerization, 22 555-556 Siloxanols, silylation and, 22 703 Silsesquioxane hybrids, 13 549 Silsesquioxanes, 15 188, 22 589-590 SilvaGas process, 3 696, 697 Silver (Ag), 22 636-667. See also Silver compounds. See Ag entries Argentothiosulfate complexes Batch desilverizing Lead-silver alloys Palladium-silver alloy membranes analytical methods for, 22 650-651 applications of, 22 636-637, 657-662 as bactericide, 22 656, 657, 660 barium alloys with, 3 344 in bimetallic monetary system, 22 647-648 in cast dental gold alloys, 8 307t coke formation on, 5 266 colloidal precipitation color, 7 343t colloidal suspensions, 7 275 color, 7 334, 335... 

For many decades carbon black has enjoyed a practical monopoly as a filler in the tire industry. It retains this position today, the tire industiy consumes 70% of carbon black production. A major breakthrough for non-black fillers came in the early 1970s when a winter tire containing silica in its treading compound was introduced. This resulted in numerous problems with rubber compound processing. The tire compound had different flow and molding characteristics. The development initiated friendly competition (friendly because the major producers of carbon black are also major manufacturers of precipitated silica) which continues to bring improvements to tire performance. 

Precipitated Silicas. Figure 3 shows a typical manufacturing process for precipitated silicas. Precipitated silicas are formed by the acidification of sodium silicate solution under conditions that form primary particles that coagulate into clusters. In contrast to the conditions in a gel, the entire liquid phase is not enclosed by the solid silica phase. 

Figure 3. Typical manufacturing process for precipitated silicas.

The first manufacturing method is the thermal process (Figure la). Currently, ACEMATT TS 100 is the only matting agent available in this range. Fumed silicas differ from precipitated silicas and silica gels in three major characteristics ... 

Deposition of Additional Silica. If a gel is broken up after it is formed so that particles are in suspension, it can be strengthened by the deposition of more silica from supersaturated solution. Alexander, Her, and Wolter (271) describe a process whereby active silica or silicic acid of low molecular weight can be released into the suspension, which is maintained at pH 9-10.5 and at 95 C, at such a rate that the added silica is deposited uniformly within the gel structure. It is obvious that this is not applicable to macroscopic gels. The process is described further in connection with the manufacture of precipitated silica powders. 

Precipitated silicas are normally made from solutions of sodium silicate (water glass). The sodium silicate solution is usually made by digesting a massive form of silica, such as sand, with sodium hydroxide solution. Precipitation is carried out by adjusting the pH with acid (sulfuric is usually used). Like all precipitations, the process is complex and governed by many variables, including temperature, pH profile, electrolyte concentration, agitation and time. Useful information can be found in Her [38], in Watson [39] and in manufacturer s literature [40]. 

Nanosilica is commercially available under the trademark of AEROSIL (product of Evonik Industries) [27]. Nanosilica powder is industrially produced by both the fuming method and the precipitation method. In the fuming method it is manufactured by a high temperature vapor process in which SiCU is hydrolyzed in a flame of oxygen-hydrogen. Precipitated silica, in turn, is manufactured by a wet... 

In the field of heterogeneous catalysts, silica-alumina ate widely used as acid supports or catalyst matrices. Their preparation involves a large number of unit operations, usualy present in catalyst manufacturing processes, such as precipitation or gelation, tiltration, drying, ion exchange... These unit... 

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