Refractory fireclays

The largest group of fireclay refractories is based on mixtures of plastic fireclay, flint clay, and fireclay grog. All these materials tend to form mullite on heating. In addition, quartz is often present as an impurity in plastic fireclay, and is sometimes added to reduce firing and drying shrinkage. 

Alkali, alkaline earth, iron, and similar impurities that are present largely combine with the siliceous material to form a low-melting-point glass and decrease the refractoriness of the brick. 

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A few fireclay refractories are produced by the stiff-mud process using an auger machine that pugs, de-aks, and continuously extmdes a clay column. A wke cutter cuts the clay into blanks which are then sized, shaped, and branded by a repress machine. 

Fireclay Refractories. These products are made from clay minerals containing ca 17—45% AI2O2. Pure kaolin has the highest alumina content. 

Fireclay refractories are used in kilns, ladles, and heat regenerators, acid—slag-resistant apphcations, boilers, blast furnaces, and rotary kilns. They are generally inexpensive. 

High Alumina Refractories. The desired alumina content, from 100% to just above 45%, is obtained by adding bauxites, synthetic aluminosihcates, and synthetic aluminas to clay and other bonding agents. These refractories are used in kilns, ladles, and furnaces that operate at temperatures or under conditions for which fireclay refractories are not suited. Phosphate-bonded alumina bricks have exceptionally high strength at low to intermediate temperatures and are employed in aluminum furnaces. High alumina and mullite are used in furnace roofs and petrochemical apphcations. 

The content of AI2O3 in fireclay refractories varies in the range 15—46 %. The... 

Fast firing, 295 Fayalite, 307, 387 Feldspars, 42—45 Ferric oxide, 32 Ferrite ceramics, 328—333 Ferrites, 328—331,379—380 synthesis of, 331 — 332 Ferroelectric ceramics, 322—327 Ferroelectric glass-ceramics, 236 Ferromagneticceramics, 328—333 Fibre optics, 216 Fibreous insulations, 394 Fibres, 215-217 Fictive temperature, 58 Fireclay, 34, 370-371 Fireclay brick, deformation of, 356—358 Fireclay refractories, 370—373 Firing, 273—297 fast, 295... 

Fireclay refractories are divided into several groups according to their properties and quality. The main criteria are refractoriness, AI2O3 content, porosity and strength. The complex of properties then determines the field of application. In addition to shaped ware, granular fireclay mixes are also manufactured for the preparation of mortars in furnace construction, for repairs or for monolithic linings. 

In the second phase of his study, Yamaguchi [28] investigated the corrosion of certain burned refractories by sodium carbonate vapor. He suspended the test piece with a platinum wire from the bottom of an alumina crucible placed upside down. The entire assembly was heated at 1200°C for various times. Included in this part of the study was a fireclay refractory composed of mullite and silica minerals. Mullite reacted with NazO to form nepheline and alumina. The nepheline increased in amount as the remaining soda vapor reacted with the newly formed alumina and the preexistent silica. For refractories composed of mullite and corundum, carnegieite solid solution was the major reaction product. The formation Yamaguchi described resulted when Na2C03 vapor reacted with the alumina liberated from mullite and preexistent as corundum, forming... 

Now that the phase diagram has told us what will form during NazO reaction with a fireclay refractory, we must evaluate whether or not these phases create a serious problem. This information can be obtained from various sources, especially any text on high-temperature silicate chemistry. The important information follows ... 

The crystalline phases—corundum, albite, nepheline, and carnegieite —all possess a high thermal expansion coefficient. (This is typical of most alkali compounds.) As these phases form in increasingly higher amounts, the thermal shock resistance of the reacted portion of the fireclay refractory will decrease significantly. 

In summary, we can conclude that very small amounts of NazO will cause liquid to form in a fireclay refractory above 1063°C. If the liquid is confined to the surface of the refractory, a glazing effect will prevent serious damage to the refractory. If Na20 concentrations are significant, even a fraction of 1 wt %, a fireclay refractory will be prone to erosion at high temperatures and serious thermal shock at low temperatures. Fireclay refractories would seem to have poor-to-moderate resistance to Na20. 

Fig. 16. Photograph of fireclay refractory before and after reaction with soda vapor at 1350°C/12 h.

Fire clay Refractories 0.3 Fireclay refractories contain 25-45% alumina... 

There are four major categories of corrosion resistant brick red shale, fireclay, refractory, and carbon. Each type has somewhat different properties and compositions. However, all resist attack by most acids and are fired at 2000°F/1093°C therefore, they are capable of handling process temperature at least that high. Their application temperatures, however, are determined by their resistance to thermal shock. In general, red shale is for ambient temperatures, fireclay for temperatures up to 1000°F/538°C, and refractory brick up to 3000 F/1649 C. 

After Contraction. The permanent contraction (usually expressed as a linear percentage) that may occur if a fired or chemically-bonded refractory product is re-fired under specified conditions of test. Fireclay refractories are liable to show after contraction if exposed to a temperature above that at which they were originally fired (cf. firing shrinkage). 

Alumino-silicate Refractory. A general term that includes all refractories of the fireclay, sillimanite, mullite, diaspore and bauxite types. BS 1902 Pt 2 defines it as a refractory containing 8 to 45% AI2O3, the balance being predominantly silica. Aluminous Cement. See ciment fondu. Aluminous Fireclay Refractory. This type of refractory material is defined in B.S. 1902 Pt 2 as a refractory containing in the fired state, > 45% AI2O3, the balance being predominantly silica. Alundum. Trade-name Fused alumina made by Norton Co. 

Bosh. (1) The part of a blast furnace between the tuyere belt and the lintel it is usually lined with high-grade fireclay refractory and is water-cooled. 

Carnegieite. Na20.Al20,.2Si02, m.p. 1526°C. It is formed when nepheline (same composition) is heated above 1248°C and is sometimes found in fireclay refractories that have been attacked by Na20 vapour. 

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. 

Fireclay Fireclay Refractory. A clay, commonly associated with the Coal Measures, that is resistant to high temperatures it normally consists of kaolinite together with some free silica, other impurities rarely exceeding a total of 5%. The most important deposits in the UK are in the Central Valley of Scotland and Ayrshire,... 

Building bricks dost firing of pottery Engineering bricks Earthenware biscuit Salt-glazed pipes China biscuit Fireclay refractories Hard porcelain Silica refractories Basic refractories... 

Flatting. A process for trueing-up handmade fireclay refractories while they are still only partially dried. Handmaking is now little used except for some special shapes. 

Hot-metal Ladle. A ladle for the transfer of molten iron from a blast furnace to a mixer furnace and from there to a steel furnace alternatively, the ladle may transfer molten pig-iron direct from blast furnace to steel furnace. Such ladles are generally lined with fireclay refractories but for severe conditions high-alumina and basic refractories have been tried with some success. 

Kalsilite. K20.Al203.2Si02 together with a small amount of Na20. This mineral is sometimes formed when alkali vapour attacks fireclay refractories. Kandife. Group name for the kaolinite minerals, i.e. kaolinite, nacrite, dickite and halloysite. (Clay Minerals Bull., 2, 294, 1955.)... 

PIN, PIP, POST (or prop), printer s bit, RING, SADDLE, SAGGAR, SETTER, SPUR, STILT, thimble see also Fig. 4. As well as fireclay refractory, recrystallized silicon carbide and nickel metal have been used. 

Lessing Rings. A particular shape for chemical stoneware tower fillings. Leucite. K20.Al203.4Si02 there are two forms stable above and below 620°C respectively sometimes formed when alkali attacks fireclay refractories, as in a blast furnace stack. 

Matrix. That part of a ceramic raw material or product in which the larger crystals or aggregates are embedded. A fired silica refractory, for example, consists of crystalline silica (quartz, cristobalite and tridymite) set in a glassy matrix a fireclay refractory may consist of quartz and mullitic grog (q.v.) set in a largely amorphous matrix. (Also sometimes known as the ground-mass.)... 

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