Refractory products

Refractories may be preformed, ie, shaped, or formed and installed on-site, ie, specialties. Iimovations in placement and vessel constmction has led to a greater emphasis on specialty refractory products. Castables, gunning mixes, and plastic and ramming mixes are used either for repair or for complete new constmction of what is known as monolithic linings. The tendency to use monolithics instead of constmctions using shaped products has been steadily increasing. As of the mid-1990s, monolithic installations are as common as conventional shaped product constmction. 

Carbon and Graphite. Carbon (qv) and graphite [7782 2-5] have been used alone to make refractory products for the lower blast furnace linings, and electrodes for steel and aluminum production. They are also commonly used in conjunction with other refractory raw materials. These materials are highly refractory nonwettable materials and are useful refractories in nonoxidizing environments. Carbon blacks are commercially manufactured, whereas graphite for refractory use has to be mined. 

Mechanical Properties. The physical properties of a particular refractory product depend on its constituents and manner in which these were assembled. The physical properties may be varied to suit specific appHcations. For example, for thermal insulations highly porous products are employed, whereas dense products are used for slagging or abrasive conditions. 

Specialty Refractories. Bulk refractory products include gunning, ramming, or plastic mixes, granular materials, and hydrauhc setting castables and mortars. These products are generally made from the same raw materials as their brick counterparts. 

Specifications. Among the many specifications covering refractory products, the best known are those pubUshed by ASTM. In addition, specifications are issued by the U.S. Government and the armed forces. The former are generally preceded by the prefix HH and the later by the prefix MIL. The ASTM refractory specifications always suggest a use, whereas federal and military specifications are iaconsistent ia this respect. 

Inhalation of certain fine dusts may constitute a health hazard. Eor example, exposure to siUca, asbestos, and beryllium oxide dusts over a period of time results ki the potential risk of lung disease. OSHA regulations specify the allowable levels of exposure to kigestible and respkable materials. Material Safety Data Sheets, OSHA form 20, available from manufacturers, provide information about hazards, precautions, and storage pertinent to specific refractory products. 

Refra.ctories, Refractory products are prepared from a wide variety of naturally occurring materials such as chromite [1308-31 -2] and magnesite [546-93-0] or from clays predominandy composed of kaolinite. Increasingly, higher purity synthetic materials are being used to obtain special properties. On the other hand, for many refractory uses, a somewhat lower fusion point than that provided by kaolinite may be adequate, so that clay materials having a moderate amount of other components as, for example, iUite, may be satisfactory. High alumina clays are also used extensively for the manufacture of special types of refractories. 

Dissolved humic substances (DHS) are the main constituents of the dissolved organic carbon (DOC) pool in surface waters (freshwaters and marine waters), groundwaters, and soil porewaters and commonly impart a yellowish-brown color to the water system. Despite the different origins responsible for the main structural characteristics of DHS, they all constitute refractory products of chemical and biological degradation and condensation reactions from plant or animal residues and play a crucial role in many biogeochemical processes. 

Uses. In stainless and alloy steels, refractory products, tanning agents, pigments, electroplating, catalysts, and corrosion-resistant products... 

Carbon pitch is used for carbon electrodes in electrolytic reduction processes, such as aluminum reduction or the production of electro-steels in arc furnaces. Refractory pitch is used in the manufacture of refractory brick, usually burned magnesite or dolomite, the pores of which are filled with pitch by hot impregnation. Upon firing, the pitch in the brick is converted to carbon by carbonization. The remaining pitch coke within the refractory product retards penetration of molten metals and slags, thus prolonging the life of the brick furnace lining. Coke pitch is used in the production of foundry cores. 

Each branch of industry is characterized by specific (production) processes with their corresponding requirements for refractory products. 

In table 11.3.3 some tests are mentioned which can be carried out on refractory products. 

Ceramics are More than Clay Alone Table 11.3.3 Tests on refractory products... 

The UV/ozone process can treat pesticides without little generation of refractory products. One of the most common pesticides found in water supplies is Propoxur. The oxidation kinetics was developed in terms of the reaction orders and apparent kinetic constants (Benitez et al., 1994). The amount of chemical removed (Xp) is inversely proportional to the amount of initial Propoxur concentration (Cp), ozone partial pressure (kPa), temperature, and pH. When Propoxur is degraded by UV /ozone, the reactions can be represented by the following general reactions ... 

Bartha, P., Magnesia spinel bricks - properties, production and use , Proc Int Symp Refractories, in X. Zhong et al., Pergamon, Hangzhou Refractory Raw Materials and High Performance Refractory Products, 1989 661-74. 

Chesters, J.H., Refractories Production and Properties, Iron and Steel Institute, London, 1973. 

National Emission Standards for Hazardous Air Pollutants Taconite Iron Ore Processing National Emission Standards for Hazardous Air Pollutants for Refractory Products Manufacturing National Emission Standards for Hazardous Air Pollutants for Primary Magnesium Refining... 

More specialized ceramics include refractory silicates such as mullite, Al6Si20i3, or binary oxides such as MgO, AI2O3, TiOy, or stabilized zirconia, which are fired and sintered, sometimes under pressure at 1500-2000 °C. A great deal of this refractory production involves the fabrication of low and medium density fire-bricks for ovens and furnaces. 

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