Clay, compositions refractories

CAS 1332-58-7. A white-burning aluminum silicate that, due to its great purity, has a high fusion point and is the most refractory of all clays. Composition Mainly kaolinite (50% alumina, 55% silica, plus impurities and water). 

Composite Refractory. A refractory brick, different parts of which have different compositions and/or textures, e.g. an insulating refractory having a dense working face, or a metal-cased basic refractory having internal partitions filled alternately with magnesite and chrome-magnesite. Composition Brick. Scottish term for a common building brick made by the stiff-plastic process from clay and colliery waste characteristically, it has a black core. 

Westerwald Clay. A refractory clay occurring in an area east of the Rhine between Coblenz and Marburg. These clays are of Oligocene origin and vary widely in composition from highly siliceous to clays that contain (raw) over 35% AI2O3. 

Vitrified bonds are very widely used in the metalworking industry, especially for machinery manufacture. The basis for this glass type bond is a fusible clay, feldspar. Refractory materials and fluxing agents are added to produce the desired composition. The dried clay and other bond ingredients are pulverized, screened, and blended to form the dry bond. This is added to the water wetted abrasive in a mixer to coat each abrasive particle with the bonding medium. The resulting mix is pressed cold in compression molds to form the basic wheel shape. 

MiscelDneous. Other important properties are resistance to thermal shock, attack by slag, and, in the case of refractories (qv), thermal expansion. For whiteware, translucency, acceptance of glazes, etc, may be extremely important. These properties depend on the clay mineral composition, the method of manufacture and impurity content. 

Fig. 8-3. Curves showing the effect of composition on the intensities of the analytical lines in the silica-alumina system. Marked absorption and enhancement effects "are showm. (Courtesy of K. K. Scott, Determination of Major Elements in Clays by X-ray. Spectroscopy, Fall, 1956 Meeting, Refractories Division, American Ceramic Society.)...

The fusibility of a substance is not solely Influenced by tho elements which enter into its composition, but also by tho manner in which these elements ate arranged and oombined together. The chief constituent of clay—alumina—is a base which, In combination with silica, forms one of the most refractory substances, and this property is possessed by the clays in proportion as they ore unmixed. with other bases, as alkalies, oxide of iron, lime, arid magnesia, in the order here given. In tho purer clays, which for ajl ordinary purposes may be considered fire-proof, the refractory quality is augmented in proportion to the quantity of silica they contain. 

Refractory bricks are divided into two groups according to their chemical composition, based on commercially interesting stones and clays in their natural forms ... 

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. 

Certain refractories like the Marquardt porcelain used for pyrometer tubes consist essentially of sillimanite and sufficient feldspar to bring about a dense structure at about cone 18. Such a mixture would consist of a calcine fired to cone 20 having the composition 71.66 per cent kaolin and 28.34 of anhydrous alumina bonded together by clay. The mixture then would be as follows ... 

Chromite refractories are employed in furnaces as partings between the silica and magnesite bricks and heiice are considered neutral. They consist principally of crushed and ground chromite, and bricks are molded from this material which may be bonded together with a small amount of clay or burnt magnesia by pressing under a heavy pressure. The bricks are then dried and fired to a temperature of about cone 16. The composition of these refractories fluctuates between the following values ... 

In this section, clays are categorized based on how they are used in the ceramics industry. The two major types of ceramic clays are china clay and ball clay. Other materials of note include fire clays, bentonite, and talc. Less refractory materials including those classified as shales and stoneware clays are also of interest. The composition, important properties, and uses for these types of clays are discussed in this section. 

Fireclays of widely varying composition occur, and are concentrated in the Leeds and Halifax districts. Many of them provide high-quality refractory bricks others, which are less refractory, are used for making salt-glazed ware and drain-pipes. Somewhat less refractory fireclays of a more siliceous nature are obtained from the Huddersfield and Sheffield districts. The pot clay seam in the Stannington area of South Yorkshire, a Carboniferous clay mined by opencast methods, is used for casting pit ware and grog production. 

SEM analysis revealed a large mottled area surrounding a soUd center, with laths and needles near the perimeter, as shown in Figure 9(c). EDX analysis revealed the solid center was composed primaiily of sihca and alumina(9(d)) the mottled area was composed of silica, alumina, and soda (9(e)) the elongated lath-Uke crystals which were composed primarily of alumina (9(f)) and the needles were composed primarily of alumina with lesser amounts of silica (9(g)). SEM DX analysis provided the same information as the petrographic techniques. In addition, it provided the elemental composition of the center, laths, needles, and perimeter of the stone. The stone was a clay refractory material with some conversion to corundum, muUite, and nepheline. 

The book has been thoughtfully divided into three parts, viz., the basics, the industrial interface and the environmental impact. The first part titled Understanding the clays Their formation, constituents and properties describes their origin and evolution, chemical composition and structure and finally their chemical and physical properties. The second part under the title Industrial uses of clays and argilloids deals with the applications in glass, ceramic, refractory, cement, medicine, electrical and mining industries as also in agriculture. The third part, Cl s in the environment , illustrates the two poles - the beneficial and hazardous consequences. 

Berlin Porcelain. Porcelain, particularly laboratory porcelain, made at the Berlin State Porcelain Factory. A quoted body composition is 77% purified Halle clay and 23% Norwegian feldspar, all finer than 10mm. The ware is fired at 1000°C and is then glazed and refired at 1400°C. Bemitz Blocks. Perforated refractory blocks designed for the passage of air and steam in water-gas plant. 

Bottger Ware. A dark red stoneware. Bolting Clay. Prepared plastic refractory material for use in the stopping of the tap-holes in cupolas. A typical composition would be 50-75% fireclay, up to 50% black sand, 10% coal dust and up to 5% sawdust. 

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