Molybdenum electrical resistivity

Heating and Cooling. Heat must be appHed to form the molten zones, and this heat much be removed from the adjacent sohd material (4,70). In principle, any heat source can be used, including direct flames. However, the most common method is to place electrical resistance heaters around the container. In air, nichrome wine is useflil to ca 1000°C, Kanthal to ca 1300°C, and platinum-rhodium alloys to ca 1700°C. In an inert atmosphere or vacuum, molybdenum, tungsten, and graphite can be used to well over 2000°C. 

Table 4.2 Electrical Resistance of Molybdenum Disulphide at Various Temperatures (Data from Ref.20)...

There is a curious anomaly in the performance of these materials which may be related to the complex effects of purity and temperature reviewed in Chapter 4. Niobium diselenide (Nb 862) is a better conductor than molybdenum disulphide, but apart from one report in which the test conditions were unconventional , compacts containing molybdenum disulphide have generally performed better than those containing niobium diselenide, in terms of wear, electrical resistance and electrical noise. Apart from the compacts listed in Table 12.13, the superiority of molybdenum disulphide was also confirmed in contacts with silver and graphite . 

Tank ovens have been improved further by supplementary electrical heating (electrical boosting) in the melting zone. The glass melt, due to its ionic conductivity, acts as the electrical resistance. Only molybdenum can be used as the... 

The electrical resistance of ductile molybdenum at 25° is 5.6 microhms per cubic centimeter for hard drawn wire and 4.8 microhms for annealed wire. The temperature coefficient of electrical resistance between 0° and 170° C. is 0.005. The specific heat is 0.072. 

The coefficient of linear thermal expansion, the thermal conductivity, the specific heat, and the electrical resistivity as function of temperature are shown in Figs. 3.1-140-3.1-143. The vapor pressure and rate of evaporation are shown in Fig. 3.1-144. In the case of precipitation- and dispersion-strengthened molybdenum alloys, such as TZM, MHC, ML, MY, and K—Si—Mo,... 

Fig. 3.1-1fi3 Specific electrical resistivity versus temperature of molybdenum [1.126], tungsten [1.126], niobium [1.127], and tantalum [1.127]...

A special molybdenum compound, molybdenum disilicide MoSi, has an interesting application. The compound is manufactured by powder metallurgy and, even at very high temperatures (1900°C), is very durable in air. In an oxidizing atmosphere a protective layer of silicon dioxide is formed on the surface. As the electric resistivity of the silicide is suitable it has been used as a resistance material in high-temperature furnaces Kanthal Super ). 

The specimen is initially in thermal equilibrium with the surroundings, which are kept at room temperature. A continuous current is then supplied to the specimen, and measurements of potential difference, current, and temperature are continuously recorded versus time during the heating, giving a heat capacity versus temperature curve for the whole of the range covered. For example, Cezairliyan et measured the heat capacity of molybdenum between 1900 and 2800 K, as well as its electrical resistivity and thermal radiation properties. 

Hak61] Hake, R.R., Leslie, D.H., and Berlin-COURT, T.G., Electrical Resistivity, HaU Effect and Superconductivity of Some b.c.c. Titanium-Molybdenum AUoys, J. Phys. Chem. Solids, Vol 20, 1961, p. 177-186... 

Yos56] Yoshida, S. and Tsuya, Y, The Tfem-perature Dependence of the Electrical Resistivity of the p-Phase Htanium-Molybdenum Alloys, J. Phys. Soc. Jpn.,Vo 11,1956, p. 1206-1207... 

Transpassive dissolution of chromium, molybdenum, and alloys containing these elements has been extensively investigated by Bojinov et al. [151-153] using impedance analysis and steady-state RRDE. Additional in situ information concerning the conductance properties of the films is obtained by CER (contact electric resistance). Many-parameter models were proposed combining reaction steps... 

The high temperature required to sinter the ceramic requires that the conductors be refractory metals. Tungsten or a mixture of molybdenum and manganese, moly-manganese, is used. These metals have an electrical resistance approximately 3 times that of copper, gold. 

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