Refractory material

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Furnace lining of blast furnace 6 in the Seraing steelworks

As refractory materials is known in the art in general, ceramic products and materials with an operating temperature of over 600  ° C . According to the definition ( DIN  51 060), however, only materials with a cone drop point greater than SK  17 (= ISO 150) - which corresponds to around 1500 ° C - can be designated as fire-resistant. This limit temperature corresponds approximately to the melting point of iron and is of importance under customs and mining law.

The main components of inorganic non-metallic materials ( ceramics and glass , glass ceramics , glass fibers and mineral fibers ) are the oxides silicon dioxide , aluminum oxide , magnesium oxide , calcium oxide , zirconium oxide and chromium oxide . In addition, carbon (C) and silicon carbide (SiC) are important components. In addition, the so-called refractory metals ( molybdenum , tungsten ) as well as the platinum group metals ( precious metals ) and their alloys must be counted among the refractory materials due to their high melting points and their chemical resistance to many slags and melts.

The following definition would be more precise: Refractory materials are metallic and ceramic materials for use temperatures (from 300 ° C) above 600 ° C (there is no general definition here!) To above 1700 ° C, which are in direct thermal contact with a high-temperature process (e.g. : Melting of metals or glass; burning of ceramics) and related to its thermal subsequent and secondary processes (shaping, heat treatment, ..).

The main application of the refractory materials is therefore furnace linings in the iron and steel , glass , aluminum , cement and ceramic industries as well as shaping tools in the named branches of industry. When selecting the materials that are suitable for a process, not only the temperature plays an important role, but also the atmosphere, the minimum durability or usability, the chemical resistance, the achievable mechanical strength, etc. a. m.

Manufacturing

The production of the high-temperature-resistant materials depends on the material class (ceramic, metal, composite material), but is also largely determined by the material properties required for the planned application. Actually, all production processes for the manufacture of refractory materials are used that are specific to the respective material group. In the case of ceramics, these include a. Pressing, casting, ramming, melt casting and, in the case of metals, for example alloying, rolling or melting.

Physical data

Bricks out Melting point ° C Density g / cm³ Behavior under heat stress Thermal conductivity at 1000 ° C Resistance to chipping
Chamotte 1615-1715 2.65-2.75 Softened at 1350 ° C 16.32 Well
Silica 1705 2.29-2.44 Softens and breaks at 1600–1650 ° C 18.42 bad
Magnesite 2165 3.44-3.60 Breaks at 1410-1550 ° C 33.08 very bad
Silicon carbide decomposes above 2000 ° C 3.12-3.20 No cracking or softening at 1650 ° C 83.74 Well
bauxite 1565-1785 3.15-3.25 Softened at 1350 ° C / Well
Alundum 2050 3.90-4.00 No softening at 1550 ° C 34.75 (650-1020 ° C) Well

Economic data

In 1997, around 17.8 million tons of refractory materials were produced worldwide, while in 2001 it was just over twelve million tons. In Germany, the production of refractory materials fell from over 1.6 million tons in 1980 to just under one million tons in 2004.

The demand for refractory metals and platinum group metals is increasing worldwide, but this increase is not due to applications in the refractory sector, but due to other areas of application. Currently (2005) around 140,000 t of molybdenum are produced worldwide, around 40,000 t of tungsten and around 120 t of platinum (from primary production) and around 100 t of the other platinum group metals.

The price for a ton of refractory material or its main raw material (in 2005) is listed in its order of magnitude for some materials. In the case of platinum group metals, the price is determined by the daily exchange rate, in the case of other materials primarily by the demand for individual raw materials, which are, however, used en masse in other branches of industry:

material Price / (ton ⋅ €)
platinum 25,000,000
Molybdenum oxide 100,000
Fused cast AZS note 20,000
Silica 750
Note AZS: aluminates, zirconates, silicates and also aluminum, zirconium and silicon oxides

Operational behavior

The "problem" of all refractory materials is that, despite their relative insensitivity to the environment and the high temperature, they are subject to more or less severe wear. The lifespan or service life for refractory products is between a few days and many years. This is u. a. depending on the temperature in the application, the chemical resistance to the surrounding media at the high temperatures, the material properties or the operating mode of the units.

Terminology

Many everyday products are not fireproof, but only heat-compatible, heat-resistant, resistant to temperature changes or flame-retardant, but are referred to as "fireproof" in common usage and in advertising. A well-known example is "refractory" glass (formerly known as Jena glass, a borosilicate glass , or today mostly glass ceramics).

The lining of chimney stoves, the building materials of tiled stoves and small biomass combustion systems (e.g. pellet heating systems) are examples of refractory materials in daily use. In addition, high-temperature wool is an important component in catalytic converters (automotive) and household appliances, which, according to their purpose, generate heat.

Industrial use

Different refractory materials are used depending on the application. The use of dense, shaped and unshaped materials (<45% by volume total porosity) aims to effectively withstand process media and, due to their high strength, to give refractory linings the necessary mechanical stability. Heat-insulating, shaped and unshaped, refractory products (> 45% by volume total porosity), on the other hand, should regulate the heat losses from the process and, as a rule, keep them low. Due to their high overall porosity, these products are generally not mechanically stable and are not suitable for use in the direct presence of liquid corrosion media. Dense and heat-insulating products usually complement each other in a typical furnace lining, with the heat-insulating products being installed behind the dense products. Due to their low mechanical resistance, heat-insulating, refractory materials are sensitive to temperature changes, which must be taken into account in particular during the periodic operation of industrial furnaces if these products are to be used directly on the hot side. Here, high-temperature wool is often used , which, due to its high elasticity, is insensitive to thermal shock loads and, due to its low density, also has an extremely low heat capacity.

The specific industrial use usually also dictates which materials are used from a mineral point of view. In addition to the application temperature, the chemical composition of the process media as well as their physical states and the operating mode of the system are decisive for the selection of the material.

Industry Examples Exchange cycle
steel Converters , electric furnaces, steel ladles 2 months
Coking plant Coke oven
Cement / lime Rotary kilns yearly
Non-ferrous metals Copper converter 1-10 years
Glass Glass melting furnaces up to 10 years
(Petro) chemistry Secondary reformer 5–10 years

literature

General

  • Wolfgang Schulle: Refractory materials. Refractory ceramics. Properties, technical testing assessment, material types. German publishing house for basic industry, Leipzig 1991, ISBN 3-342-00306-5 .
  • Gerald Routschka, Hartmut Wuthnow (Hrsg.): Practical handbook refractory materials. 5th edition. Vulkan-Verlag, Essen 2011, ISBN 978-3-8027-3161-7 .
  • German Society for Fireproof and Chimney Construction e. V., Düsseldorf (ed.): Fire-resistant construction. Materials - construction - execution. 3. Edition. Vulkan-Verlag, Essen 2003, ISBN 3-8027-3149-2 .

For glass applications

  • F. Gebhardt, M. Dunkl, K. Wieland, J. Disam, B. Fleischmann: Refractory materials for the glass industry and their testing. Verlag der Deutschen Glastechnische Gesellschaft, Frankfurt am Main 1998, ISBN 3-921089-24-7 .
  • B. Fleischmann, G. Wachter, A. Winkelmann, C. Jatzwauk, B. Schmalenbach: Glass melting furnace construction. Refractory materials and structural features. Verlag der Deutschen Glastechnische Gesellschaft, Offenbach am Main 2005, ISBN 3-921089-44-1 .
  • W. Simader, U. Jantsch, M. Oechsle, D. Lupton, R. Rathke, D. Coupland: Production, properties and applications of refractory and platinum group metals for the contact with glass melts. Publishing house of the German Glass Technology Society, Offenbach / M. 2006, ISBN 3-921089-49-2 .

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