High-Temperature Metals

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

Table 1. Physical Properties of High Temperature Metals...

D. L. Hildenbrand andD. D. Cubicciotti, eds.. High Temperature Metal Halide Chemistry, 1977. 

J. B. Rosenbaum, Vanadium Ore Processing, Meeting of High Temperature Metal Committee, preprint A71-52, AIME, New York, 1971,14 pp. 

Hoyt, W. B., and Caughey, R. H., High Temperature Metal Deterioration in Atmospheres Containing Carbon Monoxide and Hydrogen, Corrosion, 15 (12) 627t-30t (1959). 

J. R. C. Petten, in The role of active elements in the oxidation behaviour of high-temperature metals and alloys. The Netherlands, 12-13 Dec. 1988, ed. Lang, E., Elsevier Applied Science Publishers (1989)... 

Splash condenser dross residue. The treatment of steel production pollution control sludge generates a zinc-laden residue, called dross. This material, generated from a splash condenser in a high-temperature metal recovery process, is known as a splash condenser dross residue. Because this material contains 50 to 60% zinc, it is often reclaimed, reused, or processed as a valuable recyclable material. Facilities commonly handle this material as a valuable commodity by managing it in a way that is protective of human health and the environment, so U.S. EPA excluded this residue from the definition of solid waste. 

At high temperature, metals will react in an atmosphere of nitrogen to produce metal nitrides. An example of this behavior is... 

Figure 20. Electronic structure and transport in mixed conducting perovskites. (a) Band picture of electronic structure in the high-temperature metallic phase of Lai- r tCo03-(5. (Reprinted with permission from ref 109. Copyright 1995 Elsevier.) (b) Localized picture of electron/ hole transport in semimetallic Lai- 3r Fe03-(5, involving hopping of electrons and/or electron holes (depending on the oxidation state of iron).

Milal, S.K., Murthy, P.L.N. and Chamis, C.C. (1993). Interfacial microfracture in high temperature metal matrix composite. J. Composite Mater. 27, 1678-1694. 

The phase transition consists of a cooperative mechanism with charge-ordering, anion order-disorder, Peierls-like lattice distortion, which induces a doubled lattice periodicity giving rise to 2 p nesting, and molecular deformation (Fig. 11c). The high temperature metallic phase is composed of flat EDO molecules with +0.5 charge, while the low temperature insulating phase is composed of both flat monocations... 

Palmour, J. W., H. S. Kong, and R. F. Davis, Characterization of Device Parameters in High-Temperature Metal-Oxide-Semiconductor Field-Effect Transistors in fi-SiC Thin Films, J. of Applied Physics, Vol. 64, No. 4, August 15, 1988, pp. 2168-2177. 

Ti by V up to 10% makes the system metallic, the c/a ratio of the solid solution corresponding to that of the high-temperature metallic phase of Ti203-... 

Before the theory of metal oxidation had been formulated, a large number of experiments showed that, at sufficiently high temperatures, metals and alloys react with oxidizing gases and liquids by forming more or less adherent (protective) product lay-... 

TABLE I PHYSICAL PROPERTIES OF HIGH TEMPERATURE METALS... 

Containerless processing is also of interest in physical metallurgy, as it provides opportunities to study thermophysical properties of high temperature metals and alloys, avoid sample contamination due to contact with container walls, and observe the solidification of materials that have been rapidly cooled from the melt. 

Investigation of the H0CI3-AICI3 Vapor Complex as a Potential High Power Laser, H.R. Hoekstra, J.P. Hessler, C.W. Williams, and W.T. Camall. In Proceedings of the Symposium on High Temperature Metal Halide Chemistry, D.L. Hildenbrand and D.D. Cubicciotti (Eds.), The Electrochem. Soc., Princeton, NJ, 1978, pp. 123-132. 

For both nuclear and solar systems, appropriate material selection will be essential. A qualification programme for high temperature metallic materials must demonstrate their good long-term performance. In the nuclear case, candidate materials will be exposed to helium of 1 000°C with impurities such as CO, C02, H2, H20, CH4 and to neutron irradiation. The experience gained so far has disclosed that the technical solution of material problems requires further efforts in the future. 

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