Alumino-silicate refractory

III. Predictions of Alkali Corrosion of Alumino-Silicate Refractories... 

IV. Comparison of Predicted Na20 Corrosion of Alumino-Silicate Refractories with... 

Studies regarding the reactions between sodium carbonate and potassium carbonate vapors and refractories have been limited in scope. (Many studies conducted by industry may not have been reported in the literature.) The majority have involved the examination of the degenerated features of refractories after an average service campaign. Most of the articles published have concerned the reactions between alkalies and alumino-silicate refractories utilized in glass melting and blast furnaces. 

To determine the mechanisms of alkali attack and resulting reaction products, laboratory-prepared powders of alkali and alumino-silicate refractories have been fired at various temperatures. Results obtained from these reaction tests have supported the findings from the field samples. Alkali slag tests are performed by the various manufacturers to determine how their products withstand corrosion by alkalies. 

Similar analyses can be made for the other alumino-silicate refractory compositions, which are summarized below. 

Because of space limitations it is impossible to treat the K20 corrosion of alumino-silicate refractories here. The K20-fireclay vertical section of the K20-Al203-Si02 ternary system is illustrated in Fig. 20. For those... 

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. 

Coke Oven. A large, refractory-lined structure consisting of a series of tall, narrow chambers in which coal is heated out of contact with air to form coke. Silica refractories are used for most of the coke-oven structure. (See BS 4966) (BS 6886 specifies alumino-silicate refractories for coke-ovens). 

The melting points of sodium and potassium reaction products with alumino-silicate refractories are given in Table 4. The melting points of the phases themselves are not indicative of the very low eutectic temperatures found in the system. For example, the lowest eutectic in the system Na20-AljOa-SiOj (Figure 5) is 732°C. 

Alumina and alumino-silicate refractory castables may further be classified or typed in many ways. The American Society for Testing and Materials (ASTM) classifies alumina and alumino-silicate refractory castables in a very simplistic and general classification (3) that is a useful initial guide. In reality, refractory castables are typed or classified by a combination of the attributes listed in Table 1. 

Table 1 Classification of Alumina and Alumino-Silicate Refractory Castables...

Straightforward reaction with the alumino-silicate constituents of the refractory, to produce expansive-type phases such as kalsilite (KzO A1203 2Si02). Considerable volume increases accompany these reactions, thus causing weakening and disintegration of the brick. 

Particulate Fe does not show an eolian influence in the surface layer and its distribution is more constant with depth. 48% of Fe in the surface water (0-100 m) is in the dissolved form and 55% in deep water (500 -4,000 m). Most of the particulate Fe in the intermediate and deep water is in the form of refractory alumino-silicate minerals of eolian origin. The higher concentration of particulate Fe in North Atlantic deep water (1.2 mnol kg ) than in central North Pacific deep water (0.3 nmol kg ) again reflects the higher input of eolian material into the Atlantic compared to the Pacific Ocean. 

Cederqvist studied 17 different tool materials to friction stir weld 50 mm thick copper (Ref 33), and the first material evaluations were for use as the tool pin. Tungsten carbide-cobalt pins provided the initial welding parameter development, but tool life issues (due to large spindle eccentricities) made this tool material impractical for production. Likewise, eccentricity issues caused PCBN, alumino-silicate, and yttria-stabilized zirconium oxide pins to fail within the plunge or dwell sequence of the friction stir welds. A majority of e pins manufactured from refractory metals (four molybdenum-base and three tungsten-base) did not have dimensional... 

Refractory fibers, alumino-silicate typically, are suspended in colloidal silica to form thin slurry. 

High-alumina Refractory. A refractory of the alumino-silicate type. In the UK it is defined in B.S. 3446 as containing over 45% AI2O3. In the USA seven classes of... 

Figure 2 contains images that reveal the microstructural differences between the bonded, vibro-cast, and fused-cast AZS refractories. The microstructure of the fusion-cast AZS material is a mixture of corundum and zirconia co-precipitates, isolated zirconia dendrites, and a sodium alumino silicate... 

Refractories can be classified in two ways. One way is based on chemical composition. The various refractories are silica (Si02), alumina (AI2O3), magnesia (MgO), chromia (Cr203), alumino-silicate, and magnesia-chromia. In the second method, the refractories are classified as acidic, basic, and neutral refractories. This classification is based on the behavior of refractories toward slags. Following is a brief discussion of each of these classes. 

The thermal conductivity trend of dense alumino-silicate and high-alumina refractory castables is similar to that of refractory brick and is easy to predict As alumina content and density increase, so does thermal conductivity. Figure 14 illustrates this for dense conventional castables. As with insulating... 

C401-91 Standard Classification of Alumina and Alumino-Silicate Castable Refractories. Annual Book of ASTM Standards Vol. 15.01. West Conshohocken, PA American Society for Testing and Materials, 2001 75-76. 

Silicate ceramics are generally alumino-silicate based materials obtained from natural raw materials. They exhibit a set of fundamental properties, such as chemical inertia, thermal stability and mechanical strength, which explain why they are widely used in construction products (sanitary articles, floor and wall tiles, bricks, tiles) and domestic articles (crockery, decorative objects, pottery). They are often complex materials, whose usage properties depend at least as much on microstructure and aesthetics as on composition. Silicate products with an exclusively technical application (refractory materials, insulators or certain dental implants) will not be explicitly discussed in this chapter. 

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