Tantalum lamps zirconium

Hollow Cathode Lamps. Hollow cathode lamps are the most widely used radiation sources in the AA technique. A hollow cathode lamp consists of a glass cylinder, and an anode and a cathode (Figure 18). The cylindrical cathode is either made of the analyte element or filled with it. The diameter of the cathode is 3 to 5 mm. The anode is in the form of a thick wire and usually made of tungsten, nickel, tantalum, or zirconium. The glass tube is first evacuated and then filled with an inert gas (argon or neon). The pressure of the inert gas is about 0.5 to 1.3 kPa. 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

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