Oxygen, reaction with niobium

The reactions of 1,2,5-triphenylphosphole (tpp)(46), 1,2,5-triphenylphosphole oxide (tppO), sulphide (tppS), and selenide (tppSe), with niobium(v) and tan-talum(v) halides in dry, oxygen-free organic solvents have been studied. The complexes formed were characterized by i.r. and X-ray spectroscopy. The... 

Niobium Peroxyfluorides or Fluoroxyperniobates.—Like niobic acid, the alkali niobium oxyfluorides have the property of taking up active oxygen by reaction with hydrogen peroxide. 

Niobium oxytrichloride is also present, as a result of hydrolysis of the pentachloride or reaction with oxygen at any of the previous stages, owing to the presence of traces of moisture or air, i.e. 

Refractory metals and alloys are generally dissolution-resistant in liquid metals and corrosion is often controlled by reactions with impurity/interstitial elements [13,14,27]. In the case of refractory metal alloys based on niobium or tantalum, the concentration of oxygen in the alloy is an important parameter with respect to corrosion in alkali metals, particularly lithium [34-38]. As little as 300 wppm of oxygen in niobium will induce catastrophic penetration of the niobium by lithium. Interstitial oxygen will also cause penetration of niobium tmd tantalum by sodium or potassium, but the threshold of oxygen concentration is higher. 

Once purification of the niobium has been effected, the niobium can be reduced to the metallic form. The double fluoride salt with potassium, K2NbFy, can be reduced using sodium metal. The reaction is carried out in a cylindrical iron vessel filled with alternating layers of K NbF and oxygen-free sodium ... 

For the niobium-copper system different phase diagrams of the simple eutectic type (with the eutectic point very close to Cu) have been proposed, either with an S-shaped near horizontal liquidus line or with a monotectic equilibrium. It was stated that the presence of about 0.3 at.% O can induce the monotectic reaction to occur, whereas if a lesser amount of oxygen is present no immiscibility gap is observed in the liquid. 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

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