Tantalum lamps

Tantal, n. tantalum, -erz, n. tantalum ore, specif, tantalite. tantalig, a. tantalous, tantalisch, a. of tantalum, tantalic. Tantal-lampe, /. tantalum lamp, -ozyd, n. 

Niobium and tantalum suddenly received considerable attention about the year 1905 as possible materials for the filaments of incandescent electric lamps in place of the carbon filament then in use The metals were then prepared in the pure state for the first time by Dr Werner von Bolton,6 and their properties were examined. Niobium was found to be unsuitable for the purpose in view, but tantalum proved to be satisfactory. Tantalum lamps were manufactured in large quantities between the years 1905 and 1911, when the metal was displaced by the electrically more efficient tungsten. 

Electric Lamp Association of the U.S.A. used 5 million feet of tantalum wire weighing less than 100 lb. Each 1 lb. of wire yielded some 20,000 lamps. After some 100 million lamps had been made and used, tantalum was largely superseded by the more efficient tungsten, melting only at 3382° C. Tantalum lamps are still. used, however, when required to resist more than ordinary vibration, as on railways. But only D.C. lamps are possible, for with A.C. tantalum undergoes progressive crystallisation. 

Tungsten with the addition of as much as 5% thoria is used for thermionic emission cathode wires and as filaments for vibration-resistant incandescent lamps. Tungsten—rhenium alloys are employed as heating elements and thermocouples. Tantalum and niobium form continuous soHd solutions with tungsten. Iron and nickel are used as ahoy agents for specialized appHcations. 

The first commercial use of tantalum was as filaments ia iacandescent lamps but it was soon displaced by tungsten. Tantalum is used ia chemical iadustry equipment for reaction vessels and heat exchangers ia corrosive environments. It is usually the metal of choice for heating elements and shields ia high temperature vacuum sintering furnaces. In 1994, over 72% of the tantalum produced ia the world went iato the manufacturiag of over 10 x 10 soHd tantalum capacitors for use ia the most demanding electronic appHcations. 

The industrial practice for the production of tantalum consists of two steps. In the first, the carbide is made by charging a graphite crucible with an intimate, pelletized mixture of lamp black and tantalum pentoxide and heating it in a high-frequency furnace under a dynamic vacuum (10 torr). In the next step, the ground carbide and the requisite amount of tantalum pentoxide are mixed, palletized, and fed to a reduction furnace where the reduction to the metal occurs. The formation of tantalum carbide as well as the reduction to the metal occur at about 2000 °C. The product leaving the reduction furnace is in the form of pellets or roundels (small cylinders) of porous metal, usually sintered together. 

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 ). 

Because of its hardness and noncorrosiveness, tantalum is used to make dental and surgical tools and implants and artificial joints, pins, and screws. The metal does not interact with human tissues and fluids. Since tantalum can be drawn into thin wires, it is used in the electronics industry, to make smoke detectors, as a getter in vacuum tubes to absorb residual gases, and as filaments in incandescent lamps. It has many other uses in the electronics industry. 

In 1905 niobium and tantalum received commercial attention, as possible material for electric lamps filaments to replace the fragile carbon then in use. Niobium was soon found to be useless, but tantalum with a melting point of 2850° C proved valuable, and was extensively used during 1905 to 1911. In 1910 the National... 

Owing to its high electrical efficiency tungsten has since 1911 almost completely ousted tantalum for ordinary lamp filaments, except when lamps are required to resist unusual vibration (p. 241). Usually the wire is mechanically drawn through a die at 2000° C. A rod the thickness and length (7 inches) of an ordinary pencil will give 100 miles of filament fewer than two tons of metal are required to supply filaments for 100 million electric bulbs. 

In the boat technique, the liquid sample is deposited in a narrow, boat-shaped container and carefully dried. The container is made of tantalum or other high-melting-point metal. The boat is placed under the light path of the hollow cathode lamp and the dried sample is vaporized by electrical heating or with a conventional acetylene-oxygen flame. This technique, although simple, is not free from interferences and offers better sensitivity for a few elements only. 

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 first ductile tantalum was manufactured by W. von Bolton at Siemens Halske in Germany in 1903 and was used for metal wire in electric light bulbs. Many milHons of tantalum wire lamps were produced until the metal tungsten replaced it Tungsten is less volatile at the high working temperature and is thus more suitable. 

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