Ampoules niobium

A mi dure of about 1-3 g. of solid Nb metal (or, better, Nb filings or powder) and that quantity of vacuum-distilled sulfur which will give the desired product composition Is placed In a quartz tube, which is then evacuated. The mixture is heated slowly and then kept at 700-1000°C for two days. Under these conditions, dpending on the temperature used, either the higher the low-temperature modification of a phase Is obtained. Special conditions are required for some compounds (e.g., hexagonal NbSg 850°C < T < 1050°C, with the niobium placed in the hottest zone of the ampoule rhombohedral Nbx+xSg T > 800°C, niobium in the coldest zone of the ampoule). 

It was a great thrust for reduced rare earth metal chemistry when it was discovered that sealed metal ampoules (mostly produced from niobium and tantalum tubing by He arc welding) were reaction containers inert enough to the corrosive molten salts to allow for pure products. Still, all constituents of air need to be excluded, which is possible, thanks to modem dry box techniques. The unintended incorporation of ubiquitous hydrogen or carbon led to a whole new world of cluster complexes with endohedral atoms, mostly with extended stmctmes, as in H Lu Cl or in CLu2 Cl2 (see Rare Earth Metal Cluster Complexes). 

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