High-Temperature Thermal Insulation

Carbon fibers in felted or woven form are the preferred materials for high-temperature insulation forfurnaces operating above 1500°C in vacuum or inert atmosphere. However, these materials have a tendency to sag and compact with time which eventually results in non-uniform insulation characteristics. This problem is partially solved by the use of rigid insulation which consists of a felt impregnated with a polymer, subsequently pyro-lyzed, and fired and outgassed at 2000°C under vacuum. The material is available in the form of cylinders, boards, disks and specieil shapes to suit furnace demands.  

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Pyrolytic graphite was first produced in the late 1800s for lamp filaments. Today, it is produced in massive shapes, used for missile components, rocket nozzles, and aircraft brakes for advanced high performance aircraft. Pyrolytic graphite coated on surfaces or infiltrated into porous materials is also used in other appHcations, such as nuclear fuel particles, prosthetic devices, and high temperature thermal insulators. 

Brassell, G.W. and Wei, G.C., High temperature thermal insulation, In Proc. Nth Biennial Conf. on Carbon, American Carbon Society, 1979, pp. 247 248. 

Silicon nitride is used in the manufacturing of high-temperature thermal insulation for heat engines and turbines. It is produced by the following reaction. 

High temperature textiles consisting of continuous filaments of amorphous silica in a variety of forms are available conunerdally. These can he used to replace asbestos-based high temperature textiles because of the health hazards associated with asbestos fiber. These high silica fibers are used for a variety of high temperature thermal insulation products for example, welding curtains. 

ASTM C 356-87 Standard Test Method for Linear Shrinkage of Preformed High-Temperature Thermal Insulation Subjected to Soaking Heat, 3 pp (Comm C-16)... 

These fibers are, due to their high thermal stability, particularly suitable for applications in high temperature thermal insulation and for the manufacture of metal matrix and ceramic matrix composites. They arc clearly superior to metal materials due to their lower weight, particularly in the lightweight construction of accelerated structure elements for which the basic material should represent an improve-... 

In the field of high temperature thermal insulation advantage is taken of the special powder properties and the amorphous character of fumed silicas. In principle, mixtures of fumed silicas, an opacifier to reflect the heat radiation and a small quantity of mineral fibers for reinforcing are used for temperatures up to 1000°C. It is necessary to density the mixture to approximately 200 g/1 to obtain the minimum of the superposition of gas and the solid state thermal conduction. Important is also the absence of mineralizing ions, like sodium or potassium, to prevent sintering effects. Commercial thermal insulation systems based on this principle have thermal conductivities of approximately 25 mW/mK at a mean temperature of 200°C and of approximately 30 mW/mK at a mean temperature of 4(X)°C. Therefore, they are... 

Figure 23.14. Tile of a carbon aerogel for high-temperature thermal insulation with carbon-fiber paper covering layers on both sides to enhance mechanical stability [38]...

Wiener, M., Reichenauer, G., Braxmeier, S., Hemberger, F. and Ebert, H.P., Carbon Aerogel-Based High-Temperature Thermal Insulation. International Journal of Thermophysics, 2009. 30(4) p. 1372. 

Paik J-A, Jones S M, Sakamoto J Composite Aerogels for high temperature thermal insulation (In preparation) Worden P, Torii R, Mester J C, Everitt C W F (2000) The STEP Payload and Experiment. Adv Space Res. 25(6) 1205-1208... 

ASTM C-356 Linear shrinkage of preformed high-temperature thermal insulation subjected to soaking heat... 

Carbonization of rayon (and PAN) yams and fabrics was briefly Investigated by Union Carbide Corporation during World War II as a possible substitute material for control grids In vacuum tube power amplifiers [5]. However, the first conmerclal venture Into multifilament carbon fibers was about 1957 by Bamebey-Cheney, a licensee of W. F. Abbott s Carbon Wool Corporation, which briefly manufactured carbon fiber tows, mats, and batting materials from cotton and rayon precursors [6], These materials were developed for use as high temperature thermal Insulation, as particle filters for hot, corrosive gases or liquids and as activated carbon fibers. 

Hlgh>Temperature Thermal Insulation. A potential application of vitreous-carbon foam is high-temperature thermal insulation in vacuum or non-oxidizing atmosphere. Severai factors combine to make this structure an exceiient thermal insulator (a)Vne low volume fraction of the solid phase, which limits conduction (b) the small cell size, which virtually eliminates convection and reduces radiation through repeated absorption/reflection at the cell walls and (c) the poor conductivity of the enclosed gas (or vacuum). An additional advantage is its excellent thermal-shock resistance due to its... 

Other Applications Other applications include foams, low density fillers for plastics and high-temperature thermal insulation. 

Mullite is a catenarian silicate mineral (Al Si2 O5 5 0 5 belonging to the rhombic system and is an excellent refractory material. The biggest advantage of mullite as a metal reinforced material is its chemical inertness. Mullite whiskers can be used as ultra high-temperature thermal insulation material and are used in industrial high-temperature furnaces and reinforcing material of fiber-reinforced metal. The industrial production of mullite whiskers is concentrated mainly in Japan... 

Lin, X. X., Shen, Z. X., Wei, X., Zhang, W. G. (2011). High-temperature thermal Insulation performance of light mass composites. Acta. Materila. Compos. Sinica., 2S( 1), 8-14. 

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