Siliceous refractories

Table 20-28 gives the results obtained with Hardinge pebble mills, grinding several siliceous refractory materials. 

Zirconium-silicate refractories have found successful application in certain parts of glass furnaces, in particular those for borosilicate and fluoride glasses (tank, feeder, throat). Refractories based on Cr203 have recently been employed at the critical points of glass tanks. This oxide show s the best resistance to glass-contact corrosion but its application is limited by its colouring effect. 

In siliceous refractories, some of the fireclay grog is replaced with a siliceous raw material, e.g. quartz. Ground, reeycled fireclay ware is sometimes also used as grog. 

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. 

Semi-silica compositions The NazO-95% Si02/5% A1203 vertical section (Fig. 9) shows that as Na20 reacts with a semi-silicate refractory, all Si02 phases should disappear, and tridymite, the only stable form of silica, will form very slowly. Albite will form only at temperatures below 1050°C and liquid is present down to 740°C. Semi-silica refractories are not resistant to alkali attack, and may be even less alkali-resistant than high-silica refractories. 

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... 

Acidic refractories (e.g. silica, fire, clay etc.) These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. Aluminium-silicate refractories These refractories vary widely in their physical, chemical and mineralogical characteristics depending on the nature and proportion of silica and alumina present on them. 

Acid Refractory Material. General term for those types of refractory material that contain a high proportion of silica, e.g. silica refractories (> 92% Si02) and siliceous refractories (78-93% Si02). 

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). 

Continuous Kiln. A kiln in which the full firing temperature is continuously maintained in one or other zone of the kiln. There are two types annular KILN (q.v.) and tunnel kiln (q.v.). Continuous Vertical Retort. A type of gas retort, built of silica or siliceous refractories. Coal is charged into the top of the retort, coke is extracted from the bottom, and town gas is drawn off, the whole operation being continuous (cf. HORIZONTAL retort). Continuous vertical retorts are also used in the zinc industry, in which case they are built of silicon carbide refractories. 

Horizontal Retort. (1) An intermittent unit for the production of town gas from coal it is constructed of segments of silica or siliceous refractory material (cf. CONTINUOUS VERTICAL RETORt). (2) An intermittent unit formerly used for the production of zinc. Horizontal zinc retorts were generally made from a siliceous fireclay, suitably grogged. 

Semi-silica Refractory Semi-siliceous Refractory... 

Semi-silica Refractory Semi-siliceous Refractory. See siliceous REFRACTORY note, however, that ASTM-C27 defines a semi-silica refractory as containing 72% Si02. A tentative ISO recommendation defines a semi-siliceous refractory as containing 85-93% SiOj. 

SESCI Furnace. A rotary furnace, designed to burn low-volatile coal, and used for the melting of cast iron. A rammed siliceous refractory is generally used as lining material. The name derives from the initials of the French makers Societe des Entreprises Speciales de Chauffage Industriel. 

The PRE definition of a siliceous refractory is that the SiOg content shall not exceed 93%, a further... 

Material Porcelain Cordierite Refractory Alumina, Alumina Silicate Refractories Magnesium Silicate... 

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