Properties of Refractory

high alumina (53 wt.% alumina) (20% porosity) Brick, high alumina (83 wt.% alumina) (28% porosity) Brick, high alumina (87 wt.% alumina) (22% porosity) Brick, kaoUn insulating (heavy) 

Diatomaceous earth brick (high burn) 590 1 a2259 795.00 

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The most important properties of refractory fibers are thermal conductivity, resistance to thermal and physical degradation at high temperatures, tensile strength, and elastic modulus. Thermal conductivity is affected by the material s bulk density, its fiber diameter, the amount of unfiberized material in the product, and the mean temperature of the insulation. Products fabricated from fine fibers with few unfiberized additions have the lowest thermal conductivities at high temperatures. A plot of thermal conductivity versus mean temperature for three oxide fibers having equal bulk densities is shown in Figure 2. 

Table 3. Typical Physical and Chemical Properties of Refractory Ceramic Fibers...

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

Thermal expansion characteristics, elasticity (implying thereby the ability to yield to stress without rupture), and strength are among the most important properties of refractories which influence their resistance to spalling. 

A.Yu. Zakharov, V.V. Lebedev. To the theory of reconstruction processes in multi-component condensed systems. // Electron structure and properties of refractory compounds, alloys andmetals. /Proceedings of IAM NAS of Ukraine, 2004, p. 13-21. 

Other physical properties of molybdenum are given under Chemical Elements. See also summary of properties of refractory metals under Niobium. 

T. E. Dietz and J. W. Wilson, Behavior and Properties of Refractory Metals, Stanford University Press, Stanford, Calif., 1965. 

Properties of refractory metal silicides and refractory metals... 

TABLE 8.21. Properties of Refractories and Insulating Ceramics (a) Chemical Composition of Typical Refractories... 

The main property of refractories is their ability to resist high temperatures. This means that the melting points of all the solid phases present in large amounts are higher than their working temperature. At this temperature, the melt must only be present in amounts which cannot result in deformation. 

Despite the disadvantages, the method has found general application with minor adjustments. In another variant, the specimens are heated under load to a certain holding temperature and deformation Is measured after removal from the furnace. Torsion methods are employed for more detailed investigation of the thermomechanical properties of refractories (e.g. Hennicke and Tomsu, 1970 Spicak, 1971 Staron, 1975). 

Thermal conductivity. Thermal conductivity is another practically significant property of refractory ceramics. It is greatly responsible for thermal losses of kilns and furnaces and to a certain degree for thermal shock resistance. A high thermal conductivity is required in some instances to permit as much as possible of the heat to pass into the product (crucibles, muffles, etc.). 

General Properties of Refractories.—It is generally understood by practical men that the virtues and faults of refractories for a given purpose are usually determined by one or two predominating qualities possessed by a material, other considerations being of secondary importance. Not infrequently a refractory, rated low from the heat-resisting standpoint, may be the most desirable material for some special use, say for gas producers, carburetors for l)lue gas, ladles for pouring steel, etc. It is desirable for this reason to consider the principal chemical and physical qualities called into play and to apply their consideration in the... 

Similar to the change in volume the porosities of a material fired to different temperatures may be plotted against the temperature. The curves thus obtained are equally instructive and valuable, for the comparison of the pyro-technical properties of refractories. The lower curve of Fig. 3 gives the results obtained with a fireclay material. Here again the rate of porosity decrease, the temperature at which the structure has become dense, shown by the approach to zero porosity, and the evidence or overfiring offer data of practical importance. The accuracy of the results obtained depends of course upon the accuracy of the temperature measurements. Too much attention cannot be given to the calibration of the pyrometers. 

In the following section we will show that tungsten as the metal gate can possibly solve these issues. A very attractive property of refractory metals, such as Mo, W, Ti and Ta, is that they have mid gap workfunctions which is very beneficial in CMOS technology. 

Timofeeva I.I., Smolin M.D. Effect of high pressures on the structure and properties of refractory compounds, in Physics and Technique of High Pressures. (Kyiv Naukova. Durnka, 1981). 

The effect of rhenium on the properties of refractory metals has been a research topic of discontinuous relevance since its discovery in the 1950 s [1, 2], Several works have been devoted to the mechanical property enhancement seen in VIb group transition metals when solid solution alloyed with rhenium [3-12], In the 1970 s the works of... 

Refractory oxides are an important class of materials that enable processes to exploit extreme environments. A wide variety of unary, binary, and ternary oxides can be considered refractory, based on their melting temperatures. Refractory oxides are generally prepared from powdered precursors using standard ceramic forming techniques such as casting, pressing, or extrusion, and subsequently sintered to achieve final density. In addition to chemical compatibility, the physical properties of refractory oxides such as thermal expansion coefficient, thermal conductivity, modulus of elasticity, and heat capacity must be considered when selecting an oxide for a specific application. 

Table 9-7.4. Characteristics of High-tbmpebaturb Insulation. Classification and Use Properties of Refractory Brick...

Goryachev Yu.M., Siman M.I., Fiyalka L.I. et al. Flydrogen in titanium hydride and GOLKAO method. Book Electronic structure and properties of refractory compounds and alloys and their application in materials science . IPMS NASU, Kyiv, 2000, 85-89. 

TABLE E7.2 Physical Properties of Refractory/lnsulating Materials... 

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