Refractories Concretes

Oxides and mixed catalysts Manufacturing of cement, concrete Refractory ceramics, a brick Faience and porcelain Safe life of medicines Terms and conditions of safe storage Recycling (processing) of products Formation and evolution of breeds (karsts) Evolution of the Solar System and the Universe Development of technologies for the production of materials for optoelectronics (GaN)... 

Stainless steel fibres are added to concrete refractory elements to provide better resistance against cracking and spalling due to thermal cycles and thermal shocks. A considerable increase in service life abundantly covers the additional costs paid for fibres. Strongly reinforced cement-based elements are also applied as part of machinery equipment. 

This cement is very resistant to attack by sulphates, sea water and acid waters. It is also used with crushed firebrick to produce refractory concrete. 

A typical large three-phase ferroalloy furnace using prebaked carbon electrodes is shown in Eigure 4. The hearth and lower walls where molten materials come in contact with refractories are usually composed of carbon blocks backed by safety courses of brick. In the upper section, where the refractories are not exposed to the higher temperatures, superduty or regular firebrick may be used. The walls of the shell also may be water-cooled for extended life. Usually, the furnace shell is elevated and supported on beams or on concrete piers to allow ventilation of the bottom. When normal ventilation is insufficient, blowers are added to remove the heat more rapidly. The shell also may rest on a turntable so that it can be oscillated slightly more than 120° at a speed equivalent to 0.25—1 revolution per day in order to equalize refractory erosion or bottom buildup. 

Refractory Sp, American Concrete Institute, Detroit, Mich., 1988. 

R. L. Wessel, CI Sp-57 Refractory Concrete, American Concrete Institute, Detroit, Mich., 1978, pp. 179—222. 

Furnace Design. Modem carbide furnaces have capacities ranging from 45,000 t/yr (20 MW) to 180,000 t/yr (70 MW). A cross-section of a 40 MW furnace, constmcted in 1981, having a 300 t/d capacity is shown in Figure 2. The shell consists of reinforced steel side walls and bottom. Shell diameter is about 9 m and the height to diameter ratio is shallow at 0.25 1.0. The walls have a refractory lining of 0.7 m and the bottom has a 1-m layer of brick topped by a 1.5-m layer of prebaked carbon blocks. The steel shell is supported on concrete piers and cooling air is blown across the shell bottom. A taphole to withdraw the Hquid carbide is located at the top of the carbon blocks. 

Low-grade ceramics - stone, and certain refractories - are simply mined and shaped. We are concerned here not with these, but with the production and shaping of high-performance engineering ceramics, clay products and glasses. Cement and concrete are discussed separately in Chapter 20. We start with engineering ceramics. 

Ceramics, including concrete, are useful especially in structures, reactors, as refractories in combustion of fuels, and as nuclear fuel. Porcelain insulators on transmission lines are an example of a specialized application of ceramics. 

Brick Construction Brick-lined construction can be used for many severely corrosive conditions under which high alloys would fail. Brick linings can be installed over metal, concrete, and fiberglass structures. Acid-resistant bricks are made from carbon, red shale, or acid-resistant refractory materials. Red-shale brick is not used above 175°C (350°F) because of spalling. Acid-resistant refractories can be used up to 870°C (1600°F). See Table 25-10. 

Silicon is the most important constituent of igneous and many sedimentary rocks, occurring in combination with oxygen in feldspars, micas, quartz, sands and shales. The element is used in electronic devices, while silicon in combination with oxygen as silica and silicates finds application in concrete, bricks, pottery, enamels, glasses, optical fibers for telecommunications, and refractory (high-temperature resistant) materials. 

An alternative to silicate-based Portland cement is the calcium aluminate cement, ciment fondu, which originated with the Lafarge company in France in 1908. Ciment fondu is typically made by heating limestone with bauxite, which is mainly AIO(OH) but contains much iron oxide (see Section 17.2). As noted above, calcium aluminate hydrates and hardens much more rapidly than alite, and so ciment fondu, either as such or mixed with Portland cement, can be used whenever a rapidly setting cement is required, for example, for construction at low temperatures. Concretes made from aluminate cements remain serviceable at higher temperatures than Portland cements and so are used to make cast refractories for pyrometal-lurgical applications. 

Solid State Reaction - Hexaaluminates have been long known as interesting materials for many applications (electrical ceramics, matrices for permanent immobilization of radioactive elements from nuclear wastes and refractory cement and concrete). For many years ceramists prepared hexaaluminates via solid state reaction for both crystallographic and application purposes.6... 

Refractory materials can be divided into three groups, i.e. a) insulation materials, b) refractory concrete and mortar and c) refractory bricks. The last group is not discussed in this paragraph but in a later one. 

Some knowledge of concrete is required to understand that refractory concrete needs to have a different composition from ordinary concrete. The melting point of ordinary concrete is higher than that of several kinds of refractory concrete. However, the fact that the... 

Ordinary concrete also contains sand and gravel, components which melt at high temperatures. They contain a high percentage of free quartz which transfers form a quartz to B quartz at 570 °C this process involves an increase in volume. When the earlier mentioned temperature is exceeded, the concrete will crack and burst. From all of this it is easily concluded that refractory concrete will have to have a different composition from ordinary concrete. A comparison ... 

Minor or trace components derived from raw materials, fuel, refractories or other plant materials, or added deliberately, can affect the reactions of clinker formation, or the properties of the product, or both. Their effects can be beneficial or harmful. Beneficial effects include acceleration of the clinkering reactions or lowering of the temperature at which they occur, or increase in the reactivity of the product leading to more rapid strength development. Harmful effects include decrease in alite content, volatilization in the kiln with consequent formation of kiln rings or other deposits, decrease in the durability of concrete made with the cement, or the introduction of poisonous elements. Some elements have beneficial effects at low concentrations and harmful ones at higher concentrations. Bucchi (B33,B28) reviewed some of the effects on the manufacturing process. 

Technical Observations. Acid orange A is one of the most widely used monoazo dyes because of its low cost and bright color. In large scale preparations, the coupling reaction is done in huge pitchpine vats having a capacity of 15,000 liters or more, or in concrete vats measuring up to 40 meters across and lined with refractory tile. 

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