Silicon sand

The manufacture of Portland concrete consists of three basic steps—crushing, burning, and finish grinding. As noted earlier, Portland cement contains about 60% lime, 25% silicates, and 5% alumina with the remainder being iron oxides and gypsum. Most cement plants are located near limestone (CaCOs) quarries since this is the major source of lime. Lime may also come from oyster shells, chalk, and a type of clay called marl. The silicates and alumina are derived from clay, silicon sand, shale, and blast-furnace slag. 

That is 82.5% as abundant as the element silicon, making 5 Fe one of the hugely abundant nuclear species. In the universe itis the lothmostabundantnucleus. On the crust of the Earth, however, iron is nowhere near as abundant as silicon. Sand (silica) is much more abundant than the metal iron and its ores because much of the iron setded to the center of the Earth during its early molten phase. 

The silicon employed for microelectronic and photovoltaic applications must first go through extensive processing to ensure that the material is of utmost purity. This section will describe these steps, with a discussion of perhaps the most intriguing conversion in the realm of materials science the synthesis of high-purity polished silicon wafers from a naturally occurring form of silicon - sand. 

Silicon sand is used in moulding, the grains of sand being held together in different ways. 

After oxygen, silicon is the most abundant element in the earth s crust, It occurs extensively as the oxide, silica, in various forms, for example, flint, quartz, sand, and as silicates in rocks and clays, but not as the free element, silicon. Silicon is prepared by reduction of silica, Si02- Powdered amorphous silicon can be obtained by heating dry powdered silica with either powdered magnesium or a... 

Silicon makes up 25.7% of the earth s crust, by weight, and is the second most abundant element, being exceeded only by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, hornblende, asbestos, feldspar, clay, mica, etc. are but a few of the numerous silicate minerals. 

Silicon Carbide. Sihcon carbide is made by the electrofusion of siUca sand and carbon. SiUcon carbide is hard, abrasion resistant, and has a high thermal conductivity. It is relatively stable but has a tendency to oxidize above 1400°C. The siUca thus formed affords some protection against further oxidation (see Carbides). 

P. deLinde, Silicon Metal Mn Era of Growth and Prosperity SiHcon for SiHcones Conference III, Sande ord, Norway, June 1996, p. 337. 

Silicon (96-99% pure) is now invariably made by the reduction of quartzite or sand with high purity coke in an electric arc furnace the Si02 is kept in excess to prevent the accumulation of SiC (p. 334) ... 

This is the most important and most widely used mechanical method of surface preparation. Originally, sand was used as an abrasive but now, because of the hazard to health, it has already been replaced in the UK by metal or non-silicon materials. There are two main types of process. 

Sand consists mainly of silicon dioxide. When sand is heated with an excess of coke (carbon), pure silicon and carbon monoxide are produced. 

To produce silicon, used in semiconductors, from sand (Si02), a reaction is used that can be broken down into three steps ... 

Silicon is the second most abundant element in the earth s crust. It occurs in sand as the dioxide Si02 and as complex silicate derivatives arising from combinations of the acidic oxide Si02 with various basic oxides such as CaO, MgO, and K20. The clays, micas, and granite, which make up most soils and rocks, are silicates. All have low solubility in water and they are difficult to dissolve, even in strong acids. Silicon is not found in the elemental state in nature. 

Silicon Dioxide (Quartz, Lechatelierite, Tri-dymite, Silica, Silicic Anhydride, Rock Crystal, Cristobalite, Sand). Si02, mw 60.08,... 

Silicon is the second most abundant element in the Earth s crust. It occurs widely in rocks as silicates, compounds containing the silicate ion, Si032, and as the silica, Si02, of sand (Fig. 14.33). Pure silicon is obtained from quartzite, a granular form of quartz (another solid phase of SiOz), bv reduction with high-purity carbon in an electric arc furnace ... 

Some metals that are chemically combined with oxygen (metal oxides) also dissolve in sodium hydroxide. For example, aluminum ore (known as bauxite) is treated with sodium hydroxide to isolate pure aluminum oxide, from which pure aluminum is obtained. Sand (silicon dioxide) will also dissolve in sodium hydroxide to form a chemical known as sodium silicate or water glass. 

Compounds of silicon with oxygen are prevalent in the Earth s crust. About 95% of crastal rock and its various decomposition products (sand, clay, soil) are composed of silicon oxides. In fact, oxygen is the most abundant element in the Earth s crast (45% by mass) and silicon is second (27%). In the Earth s surface layer, four of every five atoms are silicon or oxygen. 

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 "conventional" methods for the preparation of SiC and Si3N4, the high temperature reaction of fine grade sand and coke (with additions of sawdust and NaCl) in an electric furnace (the Acheson process) for the former and usually the direct nitridation of elemental silicon or the reaction of silicon tetrachloride with ammonia (in the gas phase or in solution) for the latter, do not involve soluble or fusible intermediates. For many applications of these materials this is not necessarily a disadvantage (e.g., for the application of SiC as an abrasive), but for some of the more recent desired applications soluble or fusible (i.e., proces-sable) intermediates are required. 

Silicon is one of the most abundant elements in the earth s crust. We find silicon in sand and quartz, and in our NMR tubes. Of course we also find it in the computers which run our NMR spectrometers. 

Oxides Metal ion(s) + oxygen ion Haematite (composed of iron oxide), a red pigment and an iron ore Corundum (composed of aluminum oxide), an abrasive silica (composed of silicon dioxide), common sand... 

---