Refractories special

EINECS 235-015-3 Holmium oxide Holmium oxide (H02O3), Refractories, special catalyst, Atomergic Chemetats Cerac Noah Chem. Rhdne-Poulenc. 

Properties Lt. yel. solid sol. in inorg. acids Storage SI. hygroscopic Uses Refractories special catalyst Manuf./Distrib. Aldrich http //www.sigma-aldrich.com] Alfa Aesar http //www.alfa.com] Atomergic Chemetals http //www.atomergic.com] Cerac http //www.cerac.com] Fluka http //www.sigma-aldrich.com... 

Casting-pit Refractories. Specially shaped refractories (usually fireclay) for use in the casting of molten steel. The individual items included in the term are LADLE BRICKS, ROD COVERS, STOPPERS,... 

Air-Atmosphere Furnaces. These furnaces are appHed to processes where the workload can tolerate the oxidation that occurs at elevated temperatures in air. In some special appHcations, the oxidation is not only tolerable but is desired. Some furnaces heat the work solely to promote oxidation. Furnaces designed for air operation are not completely gas-tight which results in somewhat lower constmction costs. There are no particular problems encountered in selecting the insulation systems because almost all refractory insulations are made up of oxides. Heating element materials are readily available for the common temperature ranges used with air atmospheres. 

Wall losses through most refractory walls are ca 10% of the heat suppHed by the fuel. Losses increase with rising operating temperature. In special cases, eg, in glass tanks, losses can be as high as 30—35%. In these instances, very high values are requked to maintain the refractory at a temperature below which it does not melt or coUapse. 

C or higher for the kaolin-based products to 1425°C and above for the zirconium-containing materials. At temperatures above 1000°C these ceramic fibers tend to devitrify and partially crystallize. Specially prepared ceramic fibers are used to protect space vehicles on re-entry and can withstand temperatures above 1250°C (see Ablative materials Refractory fibers). 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

Dead-burned dolomite is a specially sintered or double-burned form of dolomitic quicklime which is further stabilized by the addition of iron oxides. Historically, it was used as a refractory for lining steel furnaces, particularly open hearths, but as of this writing is used primarily in making dolomite refractory brick (see Refractories). 

C. W. Hardy and co-workers. Committee on Technology—Special Study Team on Refractories, Refractory Materials for Steelmaking International Iron and Steel Institute, Bmssels, Belgium, 1985. 

A. Egami, Taikabutsu Overseas-Special Topics Refractories for Iron Making, 2(1), 71—77 (1982). 

Strength 2) special high temperature alloys (qv) and (i) vacuum-plasma coating techniques refined in the 1990s (see Plasma technology Refractory COATRJGS). 

The modulus of elasticity (MOE) is related to the strength and can be used as a nondestmctive quaUty control test on high cost special refractory shapes such as sHde gate valves employed in the pouring of steel (qv). The sHde gate type must be selected to ensure chemical compatibiUty and it must be used in a way to reduce thermal shock. The performance of a properly selected and used sHde gate is direcdy related to its strength and therefore predicted by its MOE. 

Oxide and nonoxide refractory fibers have become essential materials for use in modem high temperature industrial processes and advanced commercial appHcations. Future process improvements, cost reductions, and performance enhancements are expected to expand the uses and markets for these specialized fibrous materials. 

B. J. Nemeth, A. T. Santhanam, and G. P. Grab in H. M. Ortner, ed.. Proceedings of the 10th Plansee Seminar on Trends in Refractory Metals and Special Materials and Their Technology, MetaHwerk Plansee, Ruette, Austria, 1981, pp. 613—627. 

Uses. Hot-pressed hBN is useful for high temperature electric or thermal insulation, vessels, etc, especially in inert or reducing atmospheres, and for special materials such as IITV semiconductors (qv). Its low thermal expansion makes it resistant to thermal shock. The powder can be used as a mold release agent or as thermal insulation. Boron nitride is also available in fiber form (19). BN deposited pyrolyticaHy on refractory substrates at 1200—1800°C has a turbostratic stmcture and low porosity it has greater chemical resistance and is impervious to helium. 

In North America, a special, high conductivity, low permeability, "hot-pressed" carbon brick is utilized almost exclusively for hearth walls. Because of their relatively small size and special, heat setting resin cement, and because the brick is installed tightly against the cooled jacket or stave, differential thermal expansion can be accommodated without refractory cracking and effective cooling can be maintained. Additionally, the wall thickness is generally smaller than 1 m, which promotes the easy formation of a protective skull of frozen materials on its hot face. Thus hearth wall problems and breakouts because of carbon wall refractory failure are virtually nonexistent. 

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