Materials refractory

Oil cracking catalysts contain identical concentrations of the following components a silica-alumina refractory material, and inert substance and sodium zeolite doped with La, Nd and Pr. The presence of REE in the zeolite increases the cracking capacity of the catalyst and its thermal stability at high temperatures [4]. 

In smaller amounts, REE are included in catalysts used to line automobile exhaust pipes. Their presence favors the oxidation of toxic fumes and reduces the release of CO, nitrogen oxides and unburnt fuel components. 

The glass industry has traditionally been one of the greatest consumers of REE. In glass making, the rare earths are used individually or in mixtures, but always as oxides. 

in proportions of up to 40%, is used in main optical glass (lanthanum heavy crown and heavy flint). The presence of this oxide endows the glass with a high transparency and improves its structural properties [5]. 

Ce203 is used for decolorizing glasses [6]. At a high temperature, it dissociates with release of oxygen this increases the partial pressure of the gas in the vitrifiable mass and converts the metal to its tetravalent form, which is particularly stable. The conversion facilitates the oxidation of ferrous to ferric ion (colorless) and hence glass refining. 

Whatever binder applied, the physical and chemical properties of the refractory material used to make the moulds or cores affects their characteristics and their behaviour during pouring. This is not surprising as these materials make up 95 to 99 % of the products used. 

The different types of refiactory sands used for foundry purposes are described in the following sections. 

Apart from crystallisation conditions, the materials that are used in ribbon growth equipment and the atmospheric environment are important factors that influence the wafer characteristics. In most of the ribbon technologies, the solidification area is in close proximity to refractory materials, such as the shaping die in EFG or the casting frame and substrate in RGS. In contrast to 

Typical annual wafer 0.5 mill, wafer per 20 mill, wafer per 

Crystal size Extended crystals in pulling directions, mm up to cm dimensions perpendicular to pulling direction 100 pm up to 1 mm range 

Thermal stress High (tolerable thermal stress limits growth velocity) Low 

The behaviour of quartz crucibles and the interaction with liquid silicon was examined thoroughly to control the oxygen content in Cz wafers [42]. Important factors are the dissolution of quartz in liquid silicon and the evaporation of SiO from the melt. This results in a transport process of Si02 via the silicon melt into the gas phase and respectively to crucible dissolution and silicon melt contamination. 

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Acid refractory materials include fireclays, flint clays, china clays (kaolins), silica, flint, chalcedony, ganister and titanium dioxide. 

Neutral refractory materials include graphite, charcoal, coke, chromite and various carbides. 

Basic refractory materials include lime, magnesia, various materials composed chiefly of alumina (bauxite, diaspore, laterite, gibb-site, etc.), dolomite and most of the rarer refractory oxides, particularly zirconia. 

Refractory linings Refractory materials Refractory metals... 

High Carbon Yield. Furfuryl alcohol and furfural are reactive solvents (monomers) and are effective in producing high carbon yield (heat induced carbonization in a reducing atmosphere). They function as binders for refractory materials or carbon bodies. Furfuryl alcohol usually requires acidic catalysis and furfural basic catalysis. Mixtures of furfuryl alcohol and furfural are generally catalyzed with acid although some systems may be catalyzed with base. 

The performance of SCWO for waste treatment has been demonstrated (15,16). In these studies, a broad number of refractory materials such as chlorinated solvents, polychlorinated biphenyls (PCBs), and pesticides were studied as a function of process parameters (17). The success of these early studies led to pilot studies which showed that chlorinated hydrocarbons, including 1,1,1-trichloroethane /7/-T5-6y,(9-chlorotoluene [95-49-8] and hexachlorocyclohexane, could be destroyed to greater than 99.99997, 99.998, and 99.9993%, respectively. In addition, no traces of organic material could be detected in the gaseous phase, which consisted of carbon dioxide and unreacted oxygen. The pilot unit had a capacity of 3 L/min of Hquid effluent and was operated for a maximum of 24 h. 

Two types of magnesia, caustic-calcined and periclase (a refractory material), are derived from dolomitic lime. Lime is required in refining food-grade salt, citric acid, propjiene and ethylene oxides, and ethylene glycol, precipitated calcium carbonate, and organic salts, such as calcium stearate, lactate, caseinate. 

Fig. 4. The Norsk Hydro cell. Refractory material, A graphic anode, B steel cathode, C refractory cover, D metal oudet, E metal, F partition wall, G ...

Very reactive metals, eg, titanium or 2irconium, which in the Hquid state react with all the refractory materials available to contain them, also require reduction to soHd metal. Titanium is produced by metallothermic reduction of its chloride using Hquid magnesium at 750°C (KroU process). 

Refractory Materials. Extremely high melting metals and those that are more resistant to deformation when hot are considered refractory... 

Plasmas are used extensively to melt materials for a variety of purposes. In many cases, the materials are introduced as a powder into the gas stream in a plasma torch. The molten droplets can be used to grow crystals of refractory materials such as niobium (166). 

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. 

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