Refractory materials, minerals

Transparent fused silica can be formed at a temperature of 1200°C and a pressure of 13.8 MPa (2000 psi) from silica powder consisting of 15 nm ultimate particles (92) or by electric arc fusion of pure silica sand having low iron and alkali metal contents. The cooled product is ground to the desired particle size. Fused sihca is primarily manufactured by C-E Minerals, Minco, and Precision Electro Minerals in the United States by Chuo Denko, Denki Kagaku Kogyo, NKK, Showa Denko, and Toshiba Ceramics in Japan. Based on 1988 data and projected growth, an estimated 135,000 metric tons of fused siUca were used in 1994 as a sacrificial component or investment casting in the manufacture of metals and as a component in refractory materials (62). 

This is the earliest and the most commonly used casting process. It has the advantages of wide metal suitability, low cost, and simple operation. It uses sand as a refractory material. Many types of sand are utilized by the foundry industry. However, because of its wide availability and relatively low cost, silica sand is the one that makes most metal castings. Silica sand is composed of the mineral quartz (Si02), which has a fusion point of approximately 1670°C (3090°F), which is often lowered by the presence of appreciable quantities of minerals with lower fusion points. 

Aluminum oxide, which has the mineral name corundum, is a solid that has several important uses. Because it will withstand very high temperatures, it is a refractory material, and because of its hardness it is commonly used in abrasives. Corundum often contains traces of other metals that impart a color to the crystals, making them valuable as gemstones. For example, ruby contains a small amount of chromium oxide, which causes the crystal to have a red color. By adding a small amount of a suitable metal oxide, it is possible to produce gemstones having a range of colors. 

Note that these three minerals, which are common in the Earth s crust, are not stable at ambient pressure at high temperatures. At ambient pressure, mullite (3Al203-2Si02), is usually found in refractory materials based on these minerals. 

Bromine trifluoride calorimetry has considerable development potential both with respect to improved accuracy and with respect to the range of materials which can be examined. Thus the more insoluble or refractory materials could be reacted in "acid or "basic solutions in BrF3 or even in molten acids or bases at higher temperatures. (The, 80/180 ratio in rocks can be measured on the oxygen released by dissolving minerals in such melts.)... 

Magnesium occurs in many igneous rocks and in dolomite. It is usually obtained from seawater (1300 mg kg-1) or from the minerals magnesite (MgCC>3) or carnallite (KCl-MgCl2-6H20). The metal is used in lightweight alloys, MgO is employed as a refractory material and as an adsorbent for water treatment, and other Mg compounds find applications in the pharmaceutical and chemical process industries. 

Refractory materials can be damaged by high temperatures and by reactions with gases, liquids and solids. At high temperatures a brick can contain so much melt phase that its strength becomes too small. In addition abrupt expansion can occur which is caused by the conversion of a mineral in the brick into another allotropic form. 

When coal is burned in a combustion unit, mineral matter undergoes major changes that lead to problems of clinker formation, fly ash, slagging, and boiler tube corrosion. The efficiency of a combustion unit is related to the amount of ash produced, since it is a diluent. On the positive side, ash has been utilized as a construction material and is a possible source of refractory materials, as cement additives, or as adsorbents for gas-cleaning processes. However, the composition of the ash must be known before it can be utilized in this way. 

Refractory inclusions are a class of chondritic components that derive their classification in part from the fact that they are composed of some of the most refractory materials found in primitive planetary samples (Grossman 1972 MacPherson et al. 1988 Connolly 2005 Beckett et al. 2006). In meteoritics, refractory refers to the temperature at which materials condense or evaporate within the gaseous environment in the protoplanetary disk. Thus, refractory inclusions are composed of minerals that are among the first predicted to condense from a gas of solar or enhanced solar composition (Ebel 2006). Their abundance in chondrites can potentially range up to 15 vol%, although most appear to be only a few vol% (Grossman et al. 1988 Russell et al. 1998 Ebel et al. 2008 Hezel et al. 2008). 

A newly developed aerosol mass spectrometer (Jayne et ah, 2000 Allan et ai, 2003) deposits size-selected particles on a heated surface so that volatile and semi-volatile materials are vaporized. These are then analyzed quantitatively on line. The instrument is able to provide quantitative, short-time-resolution measurements of the compositions of particles in selected size ranges. However, the instrument has poor sensitivity for refractory materials such as mineral dust and provides no information on particle-to-particle variability in composition. 

Magnesite Refractories.—The mineral magnesite, MgCOa, is the source of bjusic refractories used as furnace linings for various metallurgical processes, in the form of bricks or in the crushed state as a mortar and cement for furnace bottoms. The most prominent uses of these materials are in the basic open-hearth furnace and electric-furnace linings. 

Silicon has been determined as molybdosilicic acid in sewage [48], organic compounds [49], rocks and minerals [19,50,51], bauxites [52], cast iron and steel [53], high purity copper [23], copper alloys [21], various metals [54], refractory materials [55], vanadium pentoxide [22], and semiconductors [56]. The method has been applied also in the differential spectrophotometry [57] and flow injection [58,59] techniques. 

Within industry and commerce, terms other than the mineral classifications are common. Ball clay is a type of kaolin particularly suited to the manufacture of ceramics in 2001, 35% of the ball clay produced in the US was used for tile manufactoe, 22% for sanitary ware, 14% for pottery and various ceramics, 6% for refractory materials, 7% for other uses, and the remainder was exported. Kaolinite (which is white and soft) is of great importance in the paper industry for coatings and as a filler of the 8.1 Mt produced in the US in 2001, 36% was consumed in... 

Radiative Transition Probabilities for X-Ray Lines Radioactive Tracer Diffusion Data for Pure Metals Recommended Daily Dietary Allowances Reduction of Barometer to Sea Level Refractory Materials Resistance of Wires Resistivity of Semiconducting Minerals Solvents for Liquid Chromatography Spark-Gap Voltages... 

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