Fireclay Products

According to their chemical composition, fireclay products belong to the clay ceramic materials. However, their preferred utilization for refractory furnace linings makes it more reasonable to discuss them with the other refractory products. 

The bricks are used in blast furnaces, for the lining of casting ladles and the refractory linings of tank furnaces for the glass industry. 

Fireclay products are cheap refractory construction materials 

In tirecliiy products, mullite and SiOi are bonded together by a glass phase 

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Despite the development of new types of refractories, traditional fireclay products still hold the largest share in the production of refractories. The material is made from refractory clay (fireclay) which is present in the mixture partly as a plastic component, the other part being pre-fired as the coarser grog chamotte . Materials of various grades are obtained according to the type of the raw materials used and their treatment. 

Fireclay product Silica product Magnesite product Chromite product Insulating product 0 00278-0-476 0 0158 -0132 0 0276 -0 265 0147 -1 42 0 00597-0 539... 

Temp. °C. Viscosity ofNg (poises xlO ) Fireclay product Silica product ... 

Refractory bricks in the 50% and 60% AI2O3 classes exhibit improved refractoriness over fireclay products. There are two frmdamental mineral mixtures used in producing these classes of brick, and the physical properties of the products depend, in part, on which mineral mixture was used in the manufacture. 

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

Phosphorus Trisulphide (P2S3).—The calculated quantities of dry amorphous phosphorus and sulphur are carefully melted together in a fireclay crucible. The product is then cooled and broken up. 

Sulphates of the alkali- and alkaline-earth metals are stable at all temperatures lower than that of the electric arc but all other sulphates decompose, the primary product being the oxide of the metal and sulphuric anhydride the latter, however, being unstable at a red-heat, decomposes partly into sulphur dioxide and free oxygen. This decomposition is made use of in the preparation of Nordhausen sulphuric acid, a fuming liquid, consisting chiefly of H2S207 it is made by distilling partially dried ferrous sulphate from fireclay retorts 2 Fe S 04 = Fe2 Oa + S 02 + S 03 the... 

The cast iron muffle was replaced by a fireclay brick muffle. The arch was made of carborundum which conducted heat well and withstood the effect of sulphuric acid. The outer brickwork was circular in shape and not rectangular as in the Mannheim furnace. Consequently, the surface area of the muffle was smaller so that the loss of heat due to radiation was reduced to a minimum. The interchangeable blades on the four arms of the stirring device, which revolved at a velocity of 1 to 2 r. p. m., were made of carborundum which resists to wear and does not pollute the product either with iron or chromium. This is of great importance when manufacturing sulphate for glass works. 

In phosphoric acid production plants, both red shale and fireclay brick have excellent resistance to all concentrations of phosphoric acid at temperatures up to 250°F, provided the acid contains no HF. If HF is present in the phosphoric acid, carbon brick construction must be used. As a rough rule-of-thumb, HF levels above 50 ppm in phosphoric acid require tank linings of carbon brick bonded and jointed with a carbon (or barytes) filled furan mortar over a suitable membrane to match the steel or concrete substrate structure. 

Thermal Expansion and Thermal Shock Resistance In many situations it is difficult to directly substitute silica brick for red shale or fireclay. Changes in design might be needed to avoid subjecting the silica brick to destructive tensile or shear stresses during operation because of expansion differences. The thermal expansion of the specialty type silica product (Type 2) is much less than that of acid brick. The vitreous silica material which contains some crystalline Si02 (Type 1) has a thermal expansion that closely matches that of acid brick at temperatures less than 800°F. Above that temperature, the expansion is much less. 

Ceramics of this type require the presence of a significant amount of clay for their forming and sintering. These ceramics include porcelain, earthenware, stoneware, bricks and related products, and fireclay. The latter is dealt with in a separate chapter on refractories. 

The annual world production of refractories is about 25 million tons. About 60% of this is consumed in metallurgy, the rest in the glass and cement industries, etc. The following shares of the individual types were reported for the late sixties 70% fireclay and high-alumina refractories, 17% basic refractories, 8% silica refractories and 5% other products. 

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