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Synthetic silica properties

Accordingly, work has been done on series of n-paraffins,. isoparaffins, naphthenes, aromatics, and naphthene-aromatics which have been chosen as representative of the major components of petroleum. In addition, olefins, cyclo-olefins, and aromatic olefins have been studied as a means of depicting the important secondary reactions of the copious amounts of unsaturates produced in the majority of catalytic cracking reactions. A silica-zirconia-alumina catalyst was used principally it resembles closely in cracking properties typical commercial synthetic silica-alumina catalysts. [Pg.6]

The inherent variability of the raw mineral, particularly with respect to minor constituents which in certain cases were known to have major effects on the cracking reaction, led to the development by the Houdry Process Corp. of a synthetic silica-alumina catalyst of controlled chemical composition and more stable catalytic properties. Full scale manufacture of synthetic catalyst was started in 1939. [Pg.24]

Acid-treated clay minerals were employed as cracking catalysts in the first commercial process, the Houdry process, widely used in the early petroleum industries to produce high-octane gasoline. The Houdry process catalysts had been discussed extensively by many investigators (2) but were eventually completely replaced by synthetic silica-alumina or zeolite catalysts. Recently, the need for new catalytic materials has revived special interest in the layer lattice silicates because of their ion-exchange properties and their expandable layer structures. [Pg.303]

The silica formed is, like all synthetic silicas, amorphous according to X-ray diffraction spectra. Their most important properties are given in Table 5.8-2. [Pg.539]

Vitreous silica is high purity Si02 glass that can withstand service temperatures above 1,000°C. As a metastable phase of silica, vitreous silica can be readily obtained in nature and synthetically. Silica glass can be produced in a pure and stable form, displaying useful properties, but is rigid and difficult to shape even at 2,000°C. Hence, it is not accessible to mass production plastic-forming methods. However, techniques have been developed to produce vitreous silica in various shapes and sizes [36-39],... [Pg.83]

Silica fibers show some colloidal properties and are often included in the studies of colloidal silica. Figure 6 is an electron micrograph of synthetic silica fibers with a specific surface area of 400 m2/g (9). [Pg.21]

The recent commercial interest in synthetic silica-alumina catalysts containing 25 % alumina prompted a reexamination of the x-ray diffraction properties of such catalysts. By use of more refined x-ray diffraction techniques, the formation of gamma-alumina and mullite (3Al20s-2Si02) in 25 % alumina catalysts has been measured after sintering at temperatures from 700 to 1250°. [Pg.551]

For example, in heat-cured mbber systems a common loading with synthetic silica is around 30%. For economic reasons, precipitated silicas are used in increasing volumes in silicone elastomers such as high-consistency mbber (HCR), liquid silicone mbber (LSR), and two-component room temperature vulcanized elastomers (RTV2). The reinforcement provided by precipitated silicas is only slightly lower than that provided by fumed silicas. However, fumed silicas are necessary in silicone sealants and other high-end applications because of their desirable properties like low moisture content. [Pg.783]

Diatomaceous earth (diatomite) is composed of fossilized silica-based shells of diatoms, single-celled marine organisms. Like synthetic silica, it is used mainly at low percentages for its anti-blocking properties in clear PE films (see Chapter 12). However, also like synthetic silica, diatomaceous earth absorbs water, which limits its shelf life [7-20],... [Pg.107]

Thiophene was found in tar, gas and industrial benzene obtained from coal in the nineteenth century. A large number of thiophene derivatives are described in the literature and their physical properties, nucleophilic substitution and biological activity are still of current interest [ ] As for polymers, thiophene was oxidized by such acidic materials as orthophosphoric acid or a synthetic silica-alumina catalyst to yield liquid oligomer which consisted of its trimer containing a small amount of its pentamer. A report on this was published as early as 1883 [2], However, modem studies on polythiophene, aiming at the preparation of electrically conductive polymers, started at the beginning of the 1980s [3-5]. [Pg.271]

The term Silica represents all materials described by the formula Si02 and can appear in many different modifications (16). Crystalline forms include quartz, tridymite and cristobalite. Quartz is stable at room temperature, while the other two crystalline modifications are high-temperature forms which can exist as metastable forms at room temperature. Synthetic silica particles are usually amorphous, i.e. the silica tetrahedra are connected in a random way. Particles of silica have, in many respects, different properties when compared with colloidal particles made from other materials. In contrast to many other oxides, silica is rather soluble, at... [Pg.9]

Other concerns may be interactions with other additives. For example, antiblocking agents may absorb other additives such as antioxidants, slip agents, and other processing aids. Natural silica shows a low level of interaction whereas synthetic silica types and uncoated talc exhibit a higher absorption of additives. These properties may be affected by surface treatment (2). [Pg.137]

In accordance with the above definitions, a summarized list of solid acids and bases is given in Tables 1.1 and 1.2. The first group of solid acids in Table 1.1 includes naturally occurring clay minerals. The main constituents are silica and alumina. Various types of synthetic zeolites such as zeolites X,Y,A, ZMS-5, ZSM-11, etc. have been reported to show characteristic catalytic activities and selectivities. The well-known solid acid, synthetic silica-alumina, is listed in the seventh group, which also includes the many oxide mixtures which have recently been found to display acidic properties and catalytic activity. In the fifth and sixth groups are included many inorganic chemicals such as metal oxides, sulfides, sulfates, nitrates, phosphates and halides. Many have been found to show characteristic selectivities as catalysts. [Pg.3]

All three antiblocking additives included in Figure 11.12 have a similar influence on haze, but silica is usually used at lower concentrations, which means that some synthetic silicas are most useful in applications which require good optical properties. At the same time, talc manufacturers make extensive efforts to make their products more suitable for such applications. ... [Pg.164]

Natural and S5mthetic silica, and talc, influence haze, clarity, transparency, see-through, and gloss (results of various methods of determination of optical properties) as was documented in various parts of this book. There are many improved additives among diatomaceous earth, synthetic silicas and modified talcs which minimize ehanges in optieal properties. [Pg.265]

A dry, moderately flexible glue, patented by M. Konigsberg, contains 8-20% glycerine but remains free-flowing indefinitely. The method utilizes the absorptive properties of synthetic alkaline earth metal silicates such as hydrous calcium silicates (e.g., Micro-cel, Johns-Man-ville) and other specially prepared synthetic silicas. It has met with considerable success in the bookbinding industry. [Pg.129]

The properties of the synthetic silicas are related to the BET surface area, particle size, and particle shape, as is the case with carbon black, but also to silanol group density. Table 1.8 summarizes the characteristics of synthetic silicas. In rubber processing applications, the degree of reinforcement obtained with silicas is related, like carbon black, to the external surface area. The internal surface area is not conducive to reinforcement it is believed that the internal surface is inaccessible to large polymer molecules and thus excluded from reinforcement. [Pg.35]

Alumina trihydrate (ATH) is made from waste generated by the almninum metal purification process. It has high brightness but low refi active index. At low levels of substitution for Ti02, 25% or less, optical properties can be maintained. Like the synthetic silicas, ATH can be used as a paper brightning pigment when opacity is not as important. ATH is used in NCR (no carbon required) papers where it favorably affects the special dyes used in the paper. ATH is also known for its flame retardant properties. ATH retards bmming by the release of water at rather low temperatures. It is added to impart flame retardance to certain specialty papers. [Pg.183]


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See also in sourсe #XX -- [ Pg.54 ]




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