Silicates oxygen compounds

Silicon w is first isolated and described as an element in 1824 by Jdns Jacob Berzelius, a Swedish chemist. Silicon does not occur uncombined in nature, i.e.- as an element. It is found in practically aU rocks as well as in sand, clays, and soils, combined either with oxygen as silica (Si02= silicon dioxide) or with oxygen plus other elements (e.g., aliuninum, mcignesium, calcium, sodium, potassium, or iron) as silicates. Its compounds also occur in all natural waters, in the atmosphere (as siliceous dust), in many plants, and in the skeletons, tissues, and body fluids of some animals. 

The EDX spectrum (Fig. 11.8) shows the main surface scale impurity peaks of silica, aluminium, sodium, chloride and iron. If this EDX is compared to that of a new, clean membrane surface (Fig. 11.9), the clean surface shows sulphur, carbon and oxygen, which is typical of a porous polysulphone support. It was concluded that the scale is amorphous, composed of aluminosilicate and silicate. These compounds are normally found in trace amounts in brine solutions. Analysis showed that the surface could be cleaned with hydrochloric acid and analysis of the dissolved scale was similar to the EDX spectrum analysis. Review of the plant operation determined that the precipitation was the result of high pH in combination with high silica concentrations in the brine. 

A great many oxides, sulfates, silicates, and similar oxygen compounds may be decomposed in this way and converted into chlorides. Instead of sulfur chloride, it is often of advantage to use carbon tetrachloride, CCI4, or phosgene, COCl2. 

Encompassing the mantle lies the outermost—and thinnest—layer called the crust. It is only about 8 km beneath the oceans (oceanic crust) and an average of about 40 km under the continents (continental crust). Its mass is estimated at 2.4 x 1022 kg, and is constituted primarily of (oxygenated) compounds of Si (approximately 60%) and A1 (approximately 15%) silica, quartz, silicates, silico-aluminates, and others (e.g., metal oxides). As can... 

The chemistry of silicon-oxygen compounds with 1S/O4 skeletons has been studied in great depth. In contrast, compounds with SiOs and SiOe frameworks are significantly less well explored. This article is an account of contributions to the chemistry of molecular silicon compounds with S1O5 and SiOf, skeletons. Studies dealing with higher-coordinate silicon in crystalline silicon dioxide and silicate phases as well as in silicate glasses " will not be discussed. 

Terpeneless and sesquiterpeneless oils have been prepared by adsorption on silicic acid which is followed by eluting the terpenes with hexane and oxygenated compounds with ethanol (21-23). 

Numerous substances throughout nature incorporate silicon or carbon in their structures. Silicon is the staple of the geologist—it combines with oxygen in various ways to produce silica and a family of compounds known as the silicates. These compounds form the chemical foundation of most sand, rocks, and soil. In the living world, carbon combines with hydrogen, oxygen, nitrogen, and sulfur to form millions of compounds. 

Silicon dioxide and other compounds that contain silicon and oxygen comprise over 90% of Earth s crust. Silicates are compounds in which a silicon atom is surrounded in a tetrahedral fashion by four oxygens, as shown in Figure 22.51 . In silicates, silicon is found in its most common oxidation state, +A. The simple Si04 ion, which is known as the orthosilicate ion, is found in very few silicate minerals. We can view the silicate tetrahedra, however, as "building blocks" that are used to build mineral structures. The individual tetrahedra are linked together by a common oxygen atom that serves as a vertex of both tetrahedra. 

If we were to list the materials of technology, sihcon would certainly be prominent on that list. As we mentioned in the previous section, silicon is the basic material in the semiconductor devices that make up CD players, computers, and other electronics gear. (Silicon Valley, an area in Cahfomia that is headquarters for many computer companies, takes its name from the element silicon.) But oxygen compounds of silicon also are important to technology. Quartz crystals, a form of silica (also called silicon dioxide, Si02), for example, are used to control frequencies in radio transmitters and watches. And many practical materials such as cement and bricks are silicate materials. Silicates are compounds of sihcon and oxygen with one or more metallic elements. In this section, we will look at silicon, sUica, and silicates. 

Silicate a compound of silicon and oxygen (with one or more metals) that may be formally regarded as a derivative of silicic acid, H4Si04 or Si(OH)4. (13.6)... 

Silicates (compounds made up of silicon, oxygen and one or more metals with or without hydrogen. Asbestos dust is the most hazardous (page 55). Others, e.g. talc, mica, vermiculite, have caused a silicatosis on prolonged exposure.)... 

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