Precipitated silica synthetic, types

The inorganic thickening agents are of two types [59]. The first t3rpe is produced from clay minerals such as hectorite, montmorillonite, saponite, attapulgjte, and sepiolite, and the second type includes the synthetic pyrogenic (fumed) silicas, precipitated silicas, synthetic clays (hectorite), and synthetic alumina. 

Of the various synthetic processes that are available, two are of most relevance in the present context - precipitation from aqueous solution and melt forming. These methods are used where it is not possible to produce adequate products directly from natural sources. This will be because there is no suitable mineral, due to the chemical nature of the product, of particle size and shape requirements, or to purity considerations. The other principal synthetic method in use for filler production is pyrolysis/combustion. This type of process in which the particles are formed in the gas phase is used where very small particles are required, such as with carbon blacks and some silicas. This type of filler is not widely used in thermoplastics and so these processes are not discussed in any detail here, although some information specific to the production of antimony oxide will be found later. 

There are at least five types of synthetic silicas that can be considered for use in polymers. These are generally known as fumed, arc, fused, gel and precipitated. A detailed review of their production and uses has been given by Watson [96]. The types most often encountered in thermoplastics are the gel and precipitated silicas which are frequently used as antiblocking agents in polymer films and as gloss reducing agents in polymer sheets. 

Hydrophobic silicas are aftertreated products. Aftertreatment processes can be carried out with the various Aerosll types as well as with the different precipitated silicas. Aerosil R 972 has been offered on the market since 1962. It is the oldest chemically aftertreated synthetic silica, i.e. the first hydrophobic product. In contrast to the silicas which are hydrophilic by nature, the hydrophobic variants are not wetted by water. Despite the higher density of these hydrophobic silicas in comparison with water, they float on the water surface. 

Synthetic silica types are used in coatings less as filler than as thixotropic, antisettling and matting additives. The different types include pyrogenic silica, precipitated silica and silica aerogels and hydrogels. They consist of coagulated amorphous spherical particles of very fine... 

Three types of synthetic silica are used as antiblocking agents, including micronized gel, fume, and precipitated silicas. Silica gels are the most common... 

Anhydrous, fumed, silicas have a higher li than hydrated, precipitated silicas and, moreover, the lower the specific surface area, the lower the dispersive component, irrespective of the production process. According to Wang et al., the difference in the dispersive component between both types of synthetic silica might depend on the surface topology of their particles, and less on the concentration of hydroxyl groups. 

Section 1 considers the methods of synthesis and physico-chemical properties of new types of inorganic sorbents (complex carbon-mineral sorbents, co-precipitated hydroxides, functional polysiloxane sorbents, porous glasses with controlled porosity, colloidal silicas, aluminium oxyhydroxide colloids, apatites). These sorbents are widely used in scientific investigations, in chemical practice and are important from a technological point of view. The presented results provide additional possibilities for the preparation of inorganic sorbents possessing unique adsorption and catalytic properties. Moreover, Section 1 presents the possibilities of the computational studies on the design of synthetic materials for selective adsorption of different substances. 

Acid-resisting Cement. The principal types are as follows 1. Silicate an inert filler bonded with silica gel that has been precipitated in situ from Na- or K- silicate in the presence of Na2SiFg, or from silicon ester. 2. Rubber Latex essentially cement sand mixes impregnated with rubber. 3. Synthetic Resin with an inert filler. 4. Sulphur Cements usually with sand as filler. 5. Bituminous Cements. ASTM specifications for these materials are listed in Vol 4-05 of the Annual Book of ASTM Standards, and number some 25, including specifications for mortars and grouts. 

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