High temperature materials

combustion catalysts that can operate up to 900-1000 °C have been developed and studied in both laboratory- and pilot-scales. Still, two catalyst features have not been fully developed. To begin with, a catalyst system that can operate above 1000 °C for one year of operation or more. Secondly, a catalyst system that can ignite natural gas at compressor outlet temperatures of approximately 200-400 °C. However, several combustion chamber designs have been proposed that utilize the features of catalytic combustion, but which operate the catalyst module at approximately 500-1000 °C. Here, a homogeneous zone is used to increase the temperature of the gas to the final maximum temperature. These designs are described in detail in Section 5 of this review. 

In this section, recent development of high temperature stable support materials as well as washcoat and active materials is reviewed. Some of the most promising materials to be used as supports in catalytic combustion for gas turbine applications are summarized in Table 1. These monolithic support materials, such as alumina or zirconia, could also be used as washcoat materials with another preparation method. Typical light-off temperatures and specific surface areas for some of the interesting catalyst compositions are summarized in Table 2. 

1 The Support - To avoid pressure drop and have a large geometric surface, honeycomb-shape monoliths are used in the gas turbine combustion chamber. The desired properties of the support are  

In addition, it is important to find a washcoat that has a thermal expansion of the same order of magnitude as the support, to prevent rupture or cracks between the washcoat and support layers. If the monolithic support has a sufficient activity without applying a washcoat, this problem may be avoided. 

Several different materials have been studied. Metallic monoliths have been used extensively since their first application for automobile converters. They allow very thin walls and have a very high thermal conductivity. However, their thermal expansion gives rise to some problems when looking at the coating and stability of the washcoat on the metallic surface, compared with the ceramic monolith. Furthermore, their maximum operation temperature is limited to 1200-1400 C, cf. Table 1. Probably, the maximum temperature is somewhat lower for long-time exposure. However, several ceramic monoliths that can stand higher thermal conditions have been developed, as reported in Table 1. 

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If a compact film growing at a parabolic rate breaks down in some way, which results in a non-protective oxide layer, then the rate of reaction dramatically increases to one which is linear. This combination of parabolic and linear oxidation can be tenned paralinear oxidation. If a non-protective, e.g. porous oxide, is fonned from the start of oxidation, then the rate of oxidation will again be linear, as rapid transport of oxygen tlirough the porous oxide layer to the metal surface occurs. Figure C2.8.7 shows the various growth laws. Parabolic behaviour is desirable whereas linear or breakaway oxidation is often catastrophic for high-temperature materials. 

Fig. 1. Thermal properties of high temperature materials (a), expansion coefficient (b), thermal conductivity (1). Mar-M-247 has an Ni base Mar-M-509, a...

High temperature materials which exhibit the greatest resistance to high cycle fatigue on a strength basis, ie, fatigue limit/tensile strength vs are... 

Precipitation Hardening. With the exception of ferritic steels, which can be hardened either by the martensitic transformation or by eutectoid decomposition, most heat-treatable alloys are of the precipitation-hardening type. During heat treatment of these alloys, a controlled dispersion of submicroscopic particles is formed in the microstmeture. The final properties depend on the manner in which particles are dispersed, and on particle size and stabiUty. Because precipitation-hardening alloys can retain strength at temperatures above those at which martensitic steels become unstable, these alloys become an important, in fact pre-eminent, class of high temperature materials. 

Computerized High Temperature Materials Properties Data-base Purdue University Purdue University (CINDAS) compiled from Hterature and evaluated reference data for high temperature materials... 

E. Bullock, Research and Development of High Temperature Materials forlndustry Elsevier Applied Science, London, U.K., 1989, pp. 95—106. 

H. H. Hausner, ed.. Coatings of High Temperature Materials Plenum Publishing Corp., New York, 1966. 

Table 11 gives order of magnitude wear rates for high temperature materials sliding against themselves in pia-on-disk tests (30). 

Table 11. Order of Magnitude of the Speeifie Wear Rates for Various High Temperature Materials Sliding Against Themselves at 500°C ...

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

Ceramic matrices are usually chosen on their merits as high temperature materials reinforcements are added to improve their toughness, reUabiUty, and damage tolerance. The matrix imparts protection to the reinforcements from chemical reaction with the high temperature environment. The principal concerns in choosing a matrix material are its high temperature properties, such as strength, oxidation resistance, and microstmctural stabiUty, and chemical compatibihty with the reinforcement. 

High temperature material fed to vessel. Temperature excursion outside the safe operating envelope resulting in a runaway reaction. 

D.R. Gaskell and Y.S. Kim. High Temperature Materials Chemistry. The Institute of Materials, London (1995). 

In the last chapter we said that one of the requirements of a high-temperature material - in a turbine blade, or a super-heater tube, for example - was that it should resist attack by gases at high temperatures and, in particular, that it should resist oxidation. Turbine blades do oxidise in service, and react with H2S, SO2 and other combustion products. Excessive attack of this sort is obviously undesirable in such a highly stressed component. Which materials best resist oxidation, and how can the resistance to gas attack be improved ... 

Recommended materials are outlined in the standards. Some of the recommendations in the standard are carbon steel for base plates, heat-treated forged steel for compressor wheels, heat-treated forged alloy steel for turbine wheels, and forged steel for couplings. The growth of materials technology has been so rapid especially in the area of high temperature materials the standard does not deal with it. Details of some of the materials... 

Neutron diffraction has been used extensively to study a range of ionic liquid systems however, many of these investigations have focussed on high-temperature materials such as NaCl, studied by Enderby and co-workers [3]. A number of liquid systems with relatively low melting points have been reported, and this section summarizes some of the flndings of these studies. Many of the salts studied melt above 100 °C, and so are not room-temperature ionic liquids, but the same principles apply to the study of these materials as to the lower melting point salts. 

This work was supported by JSPS Grant for "Advanced High Temperature Materials - Development of Practicable High Temperature Intermetallics" and Grant-in-Aid for Scientific Research (No.07650818, No.08242216 and No.07405031) from the Ministry of Education, Science, Sports and Culture, Japan, and in part by the NEDO International Research Grant for the Intermetallics Team and the research grant from R D Institute of Metals and Composites for Future Industries. 

Krikorian, O. H., Thermal Expansion of High Temperature Materials, VCRL 6 132, Sept. (I960) ... 

Norton, J. F. (ed). High Temperature Materials Corrosion in Coal Gasification Atmospheres, Applied Science Publishers, London (1984)... 

Perkins, R. A., Proc. Conf. Environmental Degradation of High Temperature Materials , ed. Denner, S. G., The Institution of Metallurgists, London, 5/1-17 (1980)... 

Stringer, J. and Whittle, D. P., Proc. First Petten Colloquium on Advanced High Temperature Materials, 14, 6 (1977)... 

J.P. Docnch, R.A. Huggins in Proc. Symp on High Temperature Materials Chemistry (Eds. ... 

DellaCorte, C., Static Dynamic Friction Behavior of Candidate High Temperature Materials, NASA, 1994. 

High-temperature materials. Uniform, precise coatings for applications like microminiature circuits. 

Experimental high-power and high-temperature material for electronic and optoelectronic devices especially in the UV region of the spectrum. 

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