Niobio - Rondella
Discovered in 1801 by C. Hatchett in London, England. Niobium is a silver coloured metal which is generally found in conjunction with tantalum, the two elements being separated by fractional crystallisation of their respective fluoro-complexes. It has an abundance of 20 ppm in the earth's crust. As a pure metal, is very reactive and forms an extremely stable oxide when exposed to air which enhances its corrosion resistance. Niobium will react with a variety of non-metals at elevated temperatures. Niobium and its alloys have high melting points and are, therefore, used in high temperature engineering products (for use at temperatures in excess of 1200C). It is also used as an alloying agent for certain steels where it greatly improves the strength of the resulting material. Niobium also finds applications in atomic reactors due to its corrosion resistance and, when combined with either tin (Nb₃Sn) or zirconium, it has a high degree of superconductivity. Un sottile, piatto pezzo di materiale con un foro nel mezzo, utilizzato in combinazione con bulloni e dadi per distribuire il carico di un dispositivo di fissaggio filettato.