A RIVAL TO PLATINUM
THIS TITLE IS BESTOWED on tantalum, one of the most important rare metals produced on a commercial scale, by a writer in The Engineering and Mining Journal (New York). Says this paper:
“Its unusual resistance to chemical corrosion makes it of much value to the chemical and allied industries as a material for equipment construction. In general appearance tantalum resembles steel, to some extent, and will take a polish. It can be given wonderful iridescent colors by special processes after the article made from it is fabricated. Recent discoveries in this line indicate great possibilities for its use as a semi-precious art metal.
“The working properties of tantalum are such that it can be worked cold, drawn, hammered, machined, polished, hardened, rolled, and punched. The pure metal is rather easily worked. Forms in which the metal can be readily obtained include wire from .001 inch diameter upward to heavy bar; sheet from .002 inch thickness upward; and tubing in special sizes.
“The most characteristic chemical property of tantalum is its unusual resistance to chemical corrosion. It is not attacked by hydrochloric or nitric acids or by aqua regia, either hot or cold. It is not attacked by dilute sulfuric acid at ordinary or more elevated temperatures, but appears to be slowly attacked by boiling, concentrated sulfuric acid. Solutions of caustic alkalies do not attack the metal easily. Hydrofluoric acid seems to be the only chemical agent which will attack it readily, and in the case of pure metal and pure hydrofluoric acid the action is very slow. A mixture of hydrofluoric and nitric acids will attack the metal with avidity, causing it to go into solution as tantalum fluorid.
“If tantalum is heated in the air, the surface becomes blue at a temperature of about 400 degrees C., and at a somewhat higher temperature, nearly black. Above a dull red heat the white oxid is produced and the metal gradually burns. This metal combines with avidity with hydrogen, oxygen, or nitrogen. It will take up 740 times its own volume of hydrogen, producing a very coarse-grained, brittle product.
“Tantalum containing dissolved gases will be harder than the pure metal, and if their quantity is appreciable the metal may even be brittle. All annealing or heating operations with tantalum must therefore be carried out in a vacuum. Solutions of chlorin or the gas itself are without any action on the metal. Tantalum is not affected by any of the chemicals or antiseptics used in dentistry or surgery.”
Source: The Literary Digest for October 1, 1927