ABSTRACT
Silicon carbide elements, usually in the form of tubes or bayonets, have a maximum temperature of about 1550°C and are cheaper than platinum windings. However, since the crosssectional area of these elements is so large, their resistance is low. Thus a transformer (see section 2.4.2) and/or a currentlimiting device may be needed to avoid blowing fuses. The electrical resistivity of silicon carbide elements decreases with increasing temperature (semiconductor) to about 650°C [7] and then increases again at higher temperatures. SiC elements are used in models of the Netzsch and Orton Dilatometers, as examples. One of the highest temperature oxidizing atmosphere heating elements ( rv 1700°C) is molybdenum disilicide (trade
name "Kanthal Super 33"[8]), which also requires a step down transformer (discussed in the next section). Stabilized zirconia [9] used after pre-heating to 1200°C with another heating element, can heat to 2100°C in air. Under reducing atmospheres, temperatures up to 2900°C can be obtained with graphite or tungsten heating elements. Considerable engineering is involved in the design of these furnaces.
