Temperatures silicon carbides

Brown, D. M., et al., High Temperature Silicon Carbide Planar IC Technology and First Monolithic SiC Operational Amplifier IC, Trans, of 2nd Inti. High-Temp. Elec. Conf. (HiTEC), 1994, pp. XI-17-XI-22. 

At high temperature, silicon carbide exhibits either active or passive oxidation behavior depending on the ambient oxygen potential (65,66). When the partial pressure of oxygen is high, passive oxidation occurs and a protective layer of Si02 is formed on the surface. 

The susceptor materials used in high-temperature processing include zirconia, boron nitride, graphite, carbon black, sodium-beta alumina, zinc oxide, and silicon carbide. While each of these susceptor materials has relatively high dielectric losses at room temperature, silicon carbide is also refractory with a relatively good resistance to oxidation at temperatures up to roughly 1500°C.t ° ... 

Properties of Dense Silicon Carbide. Properties of the SiC stmctural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for appHcations at temperatures over 1400°C and the Hquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

From 760 to 960°C, circulating fans, normally without baffles, are used to improve temperature uniformity and overall heat transfer by adding some convection heat transfer. They create a directional movement of the air or atmosphere but not the positive flow past the heating elements to the work as in a convection furnace. Heating elements ate commonly chrome—nickel alloys in the forms described previously. Sheathed elements are limited to the very low end of the temperature range, whereas at the upper end silicon carbide resistors may be used. In this temperature range the selection of heating element materials, based on the combination of temperature and atmosphere, becomes critical (1). 

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. 

J. R. O Connor and J. Smiltens, eds., Silicon Carbide, A High Temperature Semiconductor, Pergamon Press, Inc., New York, 1960. 

In the Premier Mill the rotor is shaped hke the frustrum of a cone, similar to that in Fig. 20-53. Surfaces are smooth, and adjustment of the clearance can be made from 25 [Lm (0.001 in) upward. A small impeller helps to feed material into the rotor gap. The mill is jacketed for temperature control. Direct-connected hquid-type mills are available with 15- to 38-cm (6- to 15-in) rotors. These mills operate at 3600 r/min at capacities up to 2 mVh (500 gal/h). They are powered with up to 28 kW (40 hp). Working parts are made of Invar alloy, which does not expand enough to change the grinding gap if heating occurs. The rotor is faced with Stellite or silicon carbide tor wear resistance. For pilot-plant operations, the Premier Mill is available with 7.5- and 10-cm (3- and 4-in) rotors. These mills are belt-driven and operate at 7200 to 17,000 r/min with capacities of 0,02 to 2 mVh (5 to 50 gal/h). 

The covalently-bonded silicon carbide, silicon nitride, and sialons (alloys of Si3N4 and AI2O3) seem to be the best bet for high-temperature structural use. Their creep resistance... 

The very hard structural ceramics silicon carbide, SiC, and silicon nitride, Si3N4 (used for load-bearing components such as high-temperature bearings and engine... 

Many ceramic applications are high value and small volume, so energy expenditure is high. Ferroelectric magnets, electronic substrates, electrooptics, abrasives such as silicon carbide and diamond, are examples. Diamond is found naturally, and made synthetically by the General Electric Company at high pressure and temperature. Synthetic diamonds for abrasives require less energy to make than the value in Table 4 nevertheless, the market is carefully divided between natural and synthetic diamonds. 

The main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

Fluidized-bed CVD was developed in the late 1950s for a specific application the coating of nuclear-fuel particles for high temperature gas-cooled reactors. PI The particles are uranium-thorium carbide coated with pyrolytic carbon and silicon carbide for the purpose of containing the products of nuclear fission. The carbon is obtained from the decomposition of propane (C3H8) or propylene... 

Figure 19.3. Tensile strength of CVD silicon-carbide fiber as a function of temperature.

If the composite is left only partially densified, it can be used as a filter for high temperature filtering systems with high collection efficiency as required in direct coal-fired gas and steam turbines. Similar systems are considered for particulate filtering in diesel engines by a carbon foam or felt coated with silicon carbide by CVI. 

FIGURE 26.1 Experimental friction data (left) as function log speed at different temperatures and master curve (right) of an acrylate-butadiene rubber (ABR) gum compound on a clean dry silicon carbide 180 track surface referred to room temperature. (From Grosch, K.A., Sliding Friction and Abbrasion of Rubbers, PhD thesis. University of London, London, 1963.)... 

FIGURE 26.51 Brasion loss per unit energy (abradability) (—) as function of temperature for four different compounds on a silicon carbide track at a speed of 1 cm/s together with energy density measurements (—) at an extension rate of 10 /s. (From Grosch, K.A. and Schallamach, A., Trans IRI, 40, T80, 1961 Rubber Chem. Technol, 39, 267, 1966. 

Temperature measurements, (a) Platinum wire sensor measurements and (b) silicon carbide filaments. 

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