Basic refractories dolomite

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. 

The term basic refractories is used for materials with a high MgO and CaO content they include magnesite, chrome-magnesite, magnesite-chrome and dolomite refractories as the main types. 

Sodium polyphosphates are more suitable than the acid salt for bonding basic refractories such as magnesite, dolomite or chrome magnesite. 

Basic Open-hearth Furnace. An open-hearth FURNACE (q.v.) used in the refining of basic pig-iron. The hearth is built of basic refractory bricks covered with burned dolomite or magnesite. 

Basic Refractory. A general term for those types of refractory material that contain a high proportion of MgO and/or CaO, i.e. oxides that at high temperatures behave chemically as bases. The term includes refractories such as magnesite, chrome-magnesite, dolomite, etc. 

Dead-burned basic refractory material, e.g. stabilized dolomite clinker. 

Cupola. A shaft furnace used in a foundry for the melting of iron. Cupolas are generally lined with fireclay refractories covered with a ganister-clay mixture. For the production of cast iron with a low sulphur content, a basic lining is sometimes used the lining is in this case built of chrome-magnesite or dolomite refractories, or it may be rammed with a monolithic basic refractory composition. 

Hearth. The lower part of a furnace, particularly the part of a metallurgical furnace on which the metal rests during its extraction or refining. In a blast furnace the hearth is constructed of aluminous fireclay or carbon blocks in a basic open-hearth furnace or basic electric-arc steel furnace, the hearth is constructed of basic refractory bricks which are covered with dead-burned magnesite or burned dolomite rammed in place. 

In the class of basic refractories are included bricks manufactured from chrome ore [(MgFe)(AlCr)204], periclase (MgO), calcined dolomite (CaO, MgO), olivine [(MgFe)2SiOJ, and mixtures of these materials. 

Basic refractories react with acidic slags. Therefore, they are not useful in acidic enviroiunents. They are used under basic conditions and are based on MgO. Examples are magnesite, dolomite, chrome-magnesite, magnesite-chrome, alumina, and mullite. 

In Germany and Japan, pulverized quicklime is used in making self-fluxing sinters, partially replacing limestone. Granular dead-burned dolomite is stiU used to protect the refractory lining of open-hearth and electric furnaces, but not the basic oxygen furnace. Refractory time has declined with the... 

In technological practice, refractories are usually classified according to content of SLO2 and divalent oxides, as acid, neutral or basic types. The acid types comprise silica refractories and siliceous fireclay neutral refractories are alumina, mullite and chromite refractories magnesite, chrome-magnesite and dolomite refractories are... 

Dolomite refractories. The basic raw material is dolomite CaMg(C03)2 which is much more abundant in nature than magnesite. Firing of pure dolomite yields a mixture of CaO and MgO which hydrates more readily than MgO but much less so than CaO alone. Protective tar coatings can be used to prevent access of air humidity to the products during storage. 

Industrial applications and uses. Dead burned dolomite exhibits high refractoriness and can withstand temperatures up to 2300 C. It is widely used as a refractory material wherever steel is refined using basic slag. It is used for original hearth installations in open hearth furnaces as well as for hearth maintenance. These hearths are installed using tar-dolomite ramming mixes and rammed dolomite. Dolomite refractories are also used in electrical furnaces and in the cement industry during cHnker manufacture. 

Banks. The sloping parts between the hearth of an open-hearth steel furnace and the back and front walls. They were constructed of refractory bricks covered with fritted sand (Acid O.H. Furnace) or burned-in magnesite or dolomite (Basic O.H. Furnace), cf. breasts. 

Tar-impregnated Refractory. A fired refractory, particularly one subject to hydration, such as dolomite or magnesite, whose pores have been filled with tar by autoclaving at c. 200°C, evacuating and pouring in tar. Tar impregnated refractories are used to line basic oxygen furnaces. 

Phase Diagram Calcium silicates are the most important constituents of hydraulic Portland cements (see Chapter 5), as well as of basic and acidic blast furnace slags and stabilized refractories based on dolomite they also occur as devitrification products of some technical CNS (calcium sodium silicate) glasses. The phase diagram is complicated, as shown in Figure 3.24. 

As for all basic bricks, refractoriness of dolomite is also very high—above 1750°C. The RUL is 1450°C to 1550°C for stabilized dolomite and 1350°C to 1450°C for semi-stable dolomite. The spalling resistance of stabilized dolomite is poor, but the resistance of semi-stable dolomite is moderately good. Semi-stable dolomite can withstand 20 cycles. Slag resistance is poor for both the types of dolomite. In order to increase this resistance, dolomite is doped with magnesia, which combines with silica to form forsterite. Forsterite has better resistance to slag. Semi-stable dolomite has better resistance than stabilized dolomite. 

Carbon, not only classifies by refractory type, but also by MgO content or principal oxides content this classification is shown in Table 10 (52). ISO 1927-1984 covers the ISO classification for dense and insulating monolithic refractories Class IV applies to basic materials, but, like the SIC standards, this standard uses only general types of products with differentiation within the class limited to the principal basic material of the monolithic mixtures—magnesia, chrome ore, spinel, forsterite, dolomite, or other alkaline earth oxides (53). 

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