Niobium Electrical resistance

Titanium alloyed with niobium exhibits superconductivity, and a lack of electrical resistance below 10 K. Composition ranges from 25 to 50 wt % Ti. These alloys are P-phase alloys having superconducting transitional temperatures at ca 10 K. Thek use is of interest for power generation, propulsion devices, fusion research, and electronic devices (52). 

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 . 

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

Figure 8-9. Variation of electrical resistance in niobium nitride fibers with temperature.

Source J.L. Wyatt, Electrical Resistance ofTitanium Metal, J. Met, Vol 5,1953, p 903-905 S.L. Ames and A.D. McQuillan, The Resistivity-Temperature Concentration Relationships in the System Niobium-Titanium, ActaMetall., Vol 2,1954, p 831... 

The balance of the plates were then tested ultrason-ically for bond integrity and tested for uniformity of clad thickness by resistivity measurements. Because the electrical resistivity of the l-l/2% niobium-5% zirconium alloys has nearly the same magnitude as the resistivity of the Zircaloy 2 cladding, the measurement and the variation in clad thickness could not be determined as accurately as that obtained with the 3% and 6% niobium binary alloys. 

A Nigro, G Nobile, MG Rubino, R Vaglio. Electrical resistivity of polycrystalline niobium nitride films. Phys Rev B37 3970, 1988. 

It is somewhat less corrosion resistant than tantalum, and like tantalum suffers from hydrogen embrittlement if it is made cathodic by a galvanic couple or an external e.m.f., or is exposed to hot hydrogen gas. The metal anodises in acid electrolytes to form an anodic oxide film which has a high dielectric constant, and a high anodic breakdown potential. This latter property coupled with good electrical conductivity has led to the use of niobium as a substrate for platinum-group metals in impressed-current cathodic-protection anodes. 

Niobium is a very important metal in both ferrous and nonferrous metallurgy. As an additive to alloys or when alloyed with other metals niobium imparts high mechanical strength, high electrical conductivity, and ductihty to alloys. It enhances corrosion resistance of most alloys. The metal and several of its alloys exhibit superconductivity. Nobium is used as an additive in... 

The other major difference between the various synthetic dichalcogenides lies in their electrical conductivities, as shown in Table 14.1. These figures should be considered relative rather than absolute, since values quoted by different investigators have differed by factors of over two hundred . Overall the lowest resistivity is that of niobium diselenide, and this has led to many investigations of its potential for use in situations, such as high vacuum, where graphite cannot be used. In brush compositions, however, molybdenum disulphide has generally been more successful, and this subject has been considered in more detail in Chapter 12. 

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