Refractories carbon

Choosing the filter medium to be used in a pressure filter is a very important consideration. The medium should be selected primarily for its ability to retain the contaminant to be separated, and to have an acceptable life in the filter environment. Filter media are manufactured from cotton, synthetic polymers, glass, cellulose, metal, carbon, refractories, and other porous or perforated solids, and sand and other particulate solids. The filter s effectiveness may be enhanced by the use of filter aids. 

Carbon refractories. Carbon blocks used in the construction of blast-furnace hearths are made from dense coke possibly mixed with anthracite. Suitable grain-size fractions (up to 5—15 mm) are mixed with tar to a plastic mass which is shaped at elevated temperature by pressing or ramming. The products are fired without air at about 1400 °C in saggers covered with fine-grained coke. The carbonized tar produces a firm bond between the grains. Granular mixes arc also used in certain applications. 

Carbon Refractories.—Clay materials containing carbon in some form have been in use for a long time. Carbon itself must be considered a refractory of high grade which can be used wherever the possibility of continuous oxidation is excluded. 

This difference is large with the interstitial nitrides (Ti-N 1.5, V-N 1.4, Zr-N 1.6, Nb-N 1.4, Hf-N 1.7, Ta-N 1.5) but less pronounced with the covalentnitrides(B-N 1.0, Al-N 1.5, Si-N 1.2). Since nitrogen has a higher electronegativity than carbon, refractory nitrides show a greater electronegativity difference than the equivalent carbides. 

Carbon Refractories. These refractories, consisting almost entirely of carbon, are made from a mixture of graded coke, or anthracite, pitch and tar the shaped blocks are fired (packed in coke). The fired product has an apparent porosity of 20-25% crushing strength 50-70 MNm-2 R.u.L. (350 kPa), 1700°C thermal expansion (0-1000 C), 0.65%. The principal use is in the lining of blast furnaces, particularly in the hearth and bosh (cf. plumbago). 

High-alumina refractory 40-300 Carbon refractory 130-160 Magnesite refractory 160-300 Silica refractory 200-300 Morphology. The study of size, shape and texture of particles and particle compacts. B.S. 2455,1958 defines a variety of particle shapes ... 

Run or Run-down. A fault in vitreous enamelling resulting from an excessive amount of cover-coat becoming concentrated in one area of the ware. Runner. (1) The channel in which molten iron or slag flows from a blast furnace when it is tapped. The runner is usually lined with fireclay refractories which are then covered with a layer of refractory ramming material, e.g. a mixture of fireclay, grog and carbon. Refractory concrete has also been used to line runners. 

Some words about carbon materials. Historically, the production of carbon materials has stood apart from the refractory industry, having many commonalities. The producers and researchers of carbon materials introduced several characteristics specific for the refractory industry and do not like the use of term carbon refractories when one refers to carbon cathode materials. Yet we will use the term carbon refractories, taking into account the peculiarities of carbon materials, because it is a material for refractory application, as it can withstand the corrosive interaction of liquid media at high temperatures over a long period. 

In general, the porosity of traditional fireclay refractories (Table 1.2) is 22-25 %, while modern alumina silica materials reach 13-15 %, silicon carbide refractories have porosity 12-18 %, cathode carbon refractories have porosity 15-22 %, while almost all the pores are open and permeable. The porosity of low-cement and ultralow-cement castables is 12-15 %, while the ratio of permeable pores is very low (the permeability is 0.1-0.4 pm ). 

ASTM C767-93(2013). Standard test method for thermal conductivity of carbon refractories. 

One further point about the need to keep the iron oxide content of MgO grains low. In the presence of carbon in magnesia-carbon refractories, iron oxide reacts with carbon therefore, this carbon oxidation-iron oxide reduction reaction contributes to the loss of carbon from the refractory, an undesirable effect that is explored in a later section. 

Carbon, in any form, plays a vital role in minimizing the penetration of steelmaking slags into the microstructure of magnesia-carbon refractories at the same time, MgO becomes incompatible with carbon at these same steel-making temperatures. This incongruity is discussed below. 

Typical carbon refractory material properties are shown in Table 2. 

Table 3 Typical Semigraphite and Semigraphitized Carbon Refractory Material Properties... 

Carbon refractories are used rrrainly in the alurttinum industry to line alrrrttina electrolytic tanks, as blast furnace hearths in the steel industry and in the ferro-alloy and pure sihcon indirstry as furnace lining and electrodes [DUM84]. These materials are used on accoimt of the following trrtique and exceptional properties of carbon ... 

Table 10.6. Characteristics of industrial carbon refractories 10.2.6. Manufacturing principles...

As an example, Figure 10.11 shows a stress-deformation experimental curve of a magnesia carbon refractory. 

ROB 98] ROBIN J.M., BERTHAUD Y., SCHMITT N., POIRIER J., THEMINES D., Thermomechanical behaviour of magnesia-carbon refractories , British Ceramic Transactions, vol. 97, no. 1,1998. 

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