Refractory oxides

By far the most common iadustrial refractories are those composed of single or mixed oxides of Al, Ca, Cr, Mg, Si, and Zr (see Tables 1, 4, and 6). These oxides exhibit relatively high degrees of stabiHty under both reduciag and oxidizing conditions. Carbon, graphite, and siHcon carbide have been used both alone and ia combination with the oxides. Refractories made from these materials are used ia toa-lot quantities, whereas siHcides are used ia relatively small quantities for specialty appHcation ia the auclear, electronic, and aerospace iadustries. 

Siilfuric acid from iron pyrites Paint pigments roasting of metallic oxides Refractory clays calcination of refractory clay to reduce shrinkage Foundry sand removal of carbon from used foundry sand Fullers earth calcination of fuller s-earth material... 

In the more common wet process the frit is milled with water, colloidal clay, opacifier, colouring oxide, refractory and various electrolytes in a bail mill to a closely controlled fineness or coarseness. 

Chemical Composition of Three Classes of High Chrome Oxide Refractories Used in Air-Cooled Slagging Gasifiers (wt%)... 

The development of non-chrome oxide refractories (because of real/ perceived concerns with the formation of hexavalent chrome and the associated enviromnental risks. Note that except with the potential formation of hexavalent chrome with biomass feedstock, this is not a known issue. 

TABLE 30, Properties of some non-oxidic refractory compounds... 

Metallurgical industry uses the gases 02 (e.g. for welding, and for oxidation of impurities such as P and S in steel production) and N2 and Ar (as an inert blanket to prevent oxidation), refractory materials such as MgO and CaO for furnace linings, and acids such as HC1 and H3P04 for pickling or removing oxide films. 

The specific application defines the type of refractory material that can be utilized not only by property requirements but also by cost requirements. Each of the industries mentioned balances refractory performance with refractory cost. At times higher quality oxide refractories are abandoned in favor of less costly, but also less affective alternatives. As these industries continue to evolve to higher and higher production temperatures, acceptable lower cost alternatives will become increasingly less available. 

Alloying elements, electrode mass, minerals, ores, oxidizers, refractories, fluxes. 

Stable compound formation will always cause a depressive effect. Typical examples are the lowering of alkaline earth metal absorbances in the presence of phosphate, aluminate, silicate and some other oxo anions, the low sensitivity of metals which form thermally stable oxides (refractory oxide elements), and the depression of the calcium signal in the presence of proteins. In addition, some refractory oxide elements may also form stable carbides, especially in rich hydrocarbon flames. 

Exolon Aluminum Oxide Refractory Grain t[Exol on-Esk http //www. exoionesk. com] Exolon Fastblast [Exolon-Esk http //www.exoionesk.com] Fujimi A t[Fujimi... 

Exolon WP White, Exolon WW White, Exoion Aiuminum Oxide Refractory Grain, Exoion Fastbiast . See Alumina Exotex iB. See lllipe butter (Bassia latifolia) Exotex LSB. See Shea butter (Butyrospermum parkii) extract... 

Exolon Aluminum Oxide Refractory Grain Exolon Fastblast ... 

The reaction between titanium chlorides and oxide refractory materials with the formation of lower titanium oxides is mentioned in [5]. The following schemes of the processes are proposed ... 

Because of the high temperature corrosion resistance and thermal stability exhibited by magnesium-chromium oxide refractories in copper smelting, converting and fire refining furnaces, little research has been conducted on other refractory families. However, the concern for hexavalent chromium (Cr ) as a potentially hazardous waste in spent refractories from copper production furnaces has prompted the recognition that a more environmentally acceptable material is needed for the copper industry. 

Synthesis of ammonia. The synthesis reaction is dependent on the conditions of equilibrium and the kinetics of the reaction. The latter is dictated by the efficacy of the catalyst, which in turn is chosen because of its cheapness and activity. Iron is the only realistic catalyst, but its activity can be greatly increased by the use of suitable promoters. It is prepared by melting iron oxide, refractory oxides such as potassium and aluminium oxides. A solid sheet forms on cooling, and is broken down into 5-10 mm lumps. The whole is then reduced in the ammonia synthesizer, where the oxide is converted to iron crystallites separated by the refractory oxides and covered in part by KOH as a promoter. The KOH can enhance the reactivity twofold. This catalyst must be used within the temperature range 400°-540 °C. Below this the catalyst becomes uneconomically inactive above, it sinters and loses surface area. An improved iron catalyst of higher activity and longer life is a feature of the AMV process. It is important to note that much of the reason for improved and continued activity is due to the careful removal of poisons such as CO, CO2, and H2S. 

The application of equilibrium constant in predicting the stability of a specified oxide refractory under a designated atmosphere has been illustrated in Example 5.A. Example 5.B illustrates how the value of the equilibrium... 

Types of oxide refractories used in glass melters are ... 

Tables 1.8 and 1.9 and Fig. 1.21 give some reference data on the values of the thermal coefficient of linear expansion for oxides, refractory, and ceramic materials [100-102]. Crystals with a cubic lattice (CaO, MgO) have equal values of linear coefficients of expansion along aU axes. The typical linear coefficients of thermal expansion for such materials are 6-8 x 10 and increase with the temperature up to 10-15 X 10 K . Anisotropic crystals with low symmetry have different values of linear coefficients of thermal expansion along different axes, but with a temperature increase, this difference becomes smaller. Materials with strong chemical bonds (silicon carbide, titanium diboride, diamond) have low values of linear coefficients of thermal expansion. However, these materials have high values of Debye characteristic temperature (values of the linear coefficients of thermal expansion grow below the Debye temperature and are almost constant above it).

These working conditions led to the selection of non-oxide refractory ceramics as fuel coating. Thus, carbides turn out to be great candidates thanks to their remarkable mechanical and thermal properties. However, their behaviour under irradiation has to be studied in more details. 

Corrosion resistance of the refractory metals is second only to that of the noble metals. Unlike the noble metals, however, refractory metals are inherently reactive. It is this very reactivity that can provide corrosion resistance. On contact with air or any other oxidant, refractory metals immediately form an extremely dense, adherent oxide film. This passivating layer prevents access of the oxidant to the underlying metal and renders it resistant to further attack. Unfortunately, these oxides can spall or volatize at elevated temperatures, leaving the metals susceptible to oxidation at a temperature as... 

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