Refractories dolomite

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). 

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... 

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. 

Products containing periclase and more than 15% of another phase which may be CaO (dolomite refractories), chromic spinel (chrome-magnesite refractories), or forsterite and calcium silicates. In the first case (CaO), the lowest eutectic temperature of the system is 2370 °C, in the others about 1800 °C. 

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. 

Dolomite Refractories.— The scarcity of magnesite during the war has brought... 

Calcia-magnesia (from dolomite) Refractoriness Refrtictory bricks... 

Dolomite refractories Produced by calcining natural dolomite which is mainly a mixture of lime and magnesia. ... 

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. 

Coade Stone. A vitreous ware, used for architectural ornament, made in London by Mrs Coade from 1771 until her death in 1796 manufacture finally discontinued in about 1840. The body consisted of a kaolinitic clay, finely ground quartz and flint, and a flux (possibly ground glass). Coated Dolomite Grain. Also known as unfired semi-stable dolomite refractory, this comprises calcined dolomite bonded with tar or oil. 

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. 

Diopside. Mg0.Ca0.2Si02 m.p. 1392°C sp. gr. 3.3 thermal expansion (0-1200 C) 8.8 X10-6. There is a deposit in New York State. Trials have been made with synthetic diopside as a high-frequency electro-ceramic. It is formed as a devitrification product of sodalime glass if the CaO is partially replaced by MgO it is also formed when siliceous slags attack dolomite refractories. 

Kaki. An opaque stoneware glaze, in which a surface layer of iron oxide crystal produces a reddish brown colour. Kaldo Process. A process for the production of steel by the oxygenblowing of molten iron in a rotating, slightly inclined vessel the latter is usually lined with tarred-dolomite refractories. The name is derived from the first letters of the name of the inventor, Professor Railing, and of the Domnarvet Steelworks, Sweden, where the process was first used. 

L-D Process. A process for the production of steel by the oxygenblowing of molten iron held in a static vertical vessel. The latter is lined with tarred or fired dolomite refractories dead-burned magnesite is also sometimes added to the batch. The process was first used in 1952, at Linz, Austria, and L-D stands for Linzer Diisenverfahren, i.e. Linz Nozzle Process (not Linz-Donawitz, as is commonly believed). 

Merriman Test or Sugar Test. A quality test (now discarded) for hydraulic cement. The sample is shaken with a solution of cane sugar and the amount of cement dissolved is determined by titration with HCl (T. Merriman, 7. Boston Soc. Civil Eng., 26, (1), 1939, p.l). Merwinite. 3CaO. MgO. Si02 melts incongruently at 1575C thermal expansion (0-1200°C) 13.4 x 10-. It may occur in, or be formed during service in, dolomite refractories. 

Rotor Process. A process for the production of steel by the oxygenblowing of molten iron held in a horizontal, rotating vessel. This is usually lined with tarred dolomite refractories, but tarred magnesite refractories have also been used. 

White s Test. A method for the detection of free lime, for example in Portland cement or dolomite refractories. A few mg of the powdered sample is placed on a glass microscope-slide and wetted with a solution of 5g phenol dissolved in 5 ml nitrobenzene with the addition of two drops of water. Micro-examination (x 80) will reveal the formation of long birefringent needles if free CaO is present. (A. H. White, Industr. Engng. Chem. 1, 5, 1909.) Whiteware. A general term for all those varieties of pottery that usually have a white body, e.g. tableware, sanitary ware and wall tiles. See also ceramic WHITEWARE, which has an ASTM definition. 

Figure 4.9 Areas of stability, and eutectic and peritectic temperatures, respectively, of calcium silicate and calcium magnesium silicate associations, depending on the Ca0/Si02 ratio of the raw materials used as precursor for magnesia and dolomite refractories.

Dolomite refractories were used in AOD service in the early stages of development of the AOD process. Dolomite brick contain islands of MgO crystals in a continuum of CaO. The hot face region of a used dolomite brick after AOD service is shown in Figure 29. In this photomicrograph, the immediate hot face is to the right of the photomicrograph. The central area of the photomicrograph is the affected zone where corrosion has resulted in reaction of... 

In the early 1960s, fired dolomite bricks had been developed for use in the burning zone of rotary cement kilns. Dolomite is chemically compatible with the cement-making process and readily acquires a protective coating with the clinker in the burning zone. The need for chrome-free linings in the cement-making process added impetus to penetration of dolomite refractories in this application. 

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