Niobium vapor pressure

The vapor pressures of the monoxides in the niobium-oxygen and tantalum-oxygen systems are much higher as compared to those of the pure metals, even at oxygen concentrations as low as 0.1 at-%. The R values are, therefore, very large. This implies that these metals are very amenable to sacrificial deoxidation. 

V metals, vanadium has the least tendency to deoxidize by carbon monoxide evolution. This means that, at a given temperature and a given value of Pco, the residual carbon and/or oxygen contents in vanadium will be compared more to niobium and tantalum. In other words, the removal of carbon and/or oxygen from vanadium will occur to a much lesser extent than in the cases of niobium or tantalum. The effect of carbon deoxidation can be quite complicated if there is a significant loss of the metal by vaporization. The requirement of a low vapor pressure is also better satisfied by niobium and tantalum than by vanadium. 

Fig.3.1-1iAa,b Vapor pressure (a) and evaporation rate (b) versus temperature of molybdenum, tungsten, niobium, and tantalum [1.129]... 

Few data exist on niobium halides due to the great reactivity of these compounds which makes it extremely difficult to obtain oxychloride-free halides. Also experimental investigations are not easy since they have high vapor pressure and low melting points compared to the alkali halides melts.The data relative to the pure niobium halides reported on thermodynamic tables 77,8/ were mostly obtained by estimation. ... 

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

Other applications of niobium are in electronic and propulsion devices, in electrodes in catalysis and in vacuum tubes and high-pressure sodium vapor lamps. 

Later there was a suggestion to employ sulfur and fhen chalcogenides, primarily sulfides, as active materials for the positive electrode. Sulfur is liquid at the working temperature of the battery. The sulfur elecfrode was manufactured from a mixture of sulfur and carbon or in fhe form of a niobium box wifh niobium filler packed wifh sulfur. The high volafilify of sulfur (af 507°C fhe pressure of sulfur vapor is... 

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