Ceramic service temperature

Service temperature limitations must be considered in the use of composites, not only in the selection of polymer and process, but sometimes in the selection of the reinforcement as weU. Composites cannot generally perform as weU as metals or ceramics in very high temperature appHcations, but they can be made fire resistant to meet most constmction and transportation codes. 

Ni brazes are attractive when components must endure high service temperatures and evaluation of the potential of Ni eutectic brazes containing additions of Cr, such as BNi-5 and BNi-7 (Ni-19Cr-1 OSi and Ni-14Cr-10P), as the active metal for joining Si3N4 and SiC ceramics has been vigorous, (McDermid et al. 1989,... 

Polyester and Vinyl Ester Mortars These two mortars, of which there are many types, are suitable for a pH range of about 0-11 and a continuous service temperature of 225°-230°F. The two related resins, which complement the epoxy resins, resist dilute and concentrated acids and weak alkalies. Their resistance to acid bleaches such as chlorine dioxide and to oxidizing acids such as nitric and chromic is superior to that of other resinous mortars, and they are excellent in acetic acid and related esters. However, polyester and vinyl ester mortars are the poorest resin mortars in other organic chemical exposures including solvents in general. Such mortars are widely used in paper mills and are suitable with acid brick or ceramic tile in the lower temperature zones of mildly acidic utility FGD systems. 

Moreover, the service temperature of CVI materials can be much higher than CVI processing temperatures. The reason for this advantageous feature is that the ceramic matrix produced by CVI is much purer than that obtained with the hot-pressing method, in which sintering additives are generally needed. 

Table 8.5 Maximum service temperatures for glass aud ceramic fibres iu thermally protective textiles...

Epoxies are used for structural bonding of metals, glass, ceramics, wood, concrete and plastics, including thermosetting reinforced plastics. Typical service temperatures for epoxies range from -55° to -i-120°C and for epoxy novolacs up to -i-250°C. 

Advanced heat engines require a strong ceramic matrix to offer reliable performance, especially high impact, oxidation and creep resistance, at service temperatures exceeding... 

Ceramic aluminate and zirconate fibers have higher melting temperatures, moduli, service temperatures, corrosion resistance, and iower dieiectric constants and strength than amorphous siiica and silicate giass fibers as discussed in Chapters 5,6 and 7. 

This chapter is an overview of the applications for cart>on and ceramic fibers. These applications mainiy involve composite materiais where the fibers are embedded in a polymer or a metallic or ceramic matrix, depending on the service temperature or the specific properties which are required. 

Ceramic matrix composites (CMCs), in which carbon or ceramic fibers are embedded in a ceramic matrix, have been designed to overcome the intrinsic brittleness of monolithic ceramics with a view toward structural uses at extremely high service temperatures. The most commonly used are carbon (C/C) and SiC matrix composites (C/SiC and SiC/SiC). Ceramic matrix composites with a silica based glass or glass-ceramic matrices have also been studied [12] [53-56]. 

Structural materials can be classified as metals, ceramics or polymers, each with its own advantages and disadvantages. For example, metals are strong, tough, inexpensive, but are heavy, chemically reactive and limited to service temperatures below 1,000 °C. Ceramics are hard, chemically stable and useful at high temperatures, but they are brittle and difficult to fabricate. Polymers are light, easy to process, but are relatively... 

The very low coefficient of linear thermal expansion, the extremely high maximum service temperature, and excellent thermal shock resistance are outstanding characteristics of Robax glass ceramic. 

The low density and the inherent stability, as well as the maximum service temperature are characteristics that make this glass ceramic an interesting design material. In many ambients, the material is chemically resistant. Since - because of the extremely low thermal expansion - mechanical stresses occur-ing in the material and attributable to changes of temperatures are negligible, the material does not fatigue due to these stresses. 

Ceramics can often be bonded with epoxy or acrylic adhesives, but there are limitations in their use at high temperatures. Few organic adhesives can perform >250 °C, and inorganic adhesives have been developed for ceramics that offer a service temperature of >2000 °C. These are based on inorganic binding compounds such as sodium silicates and various metal phosphates, with carbon, alumina, silica, magnesia or zirconia powder fillers. Ceramic adhesives can be... 

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