Tungsten, also known as wolfram, enjoys a unique position among metals. It has the highest melting point, 3410 C. (6170 F.), of any metal. Its corrosion resistance is also one of the highest. When properly worked it is elastic and ductile, and tensils of up to 600,000 pounds per square inch can be obtained.
The word tungsten is derived from the Swedish words tung and sten, which mean “heavy stone.” It was first used about 1758 by A. F. Cronstedt, who applied the term to the mineral scheelite because of its high density.
The origin of the word wolfram is more obscure. Lazarus Ercker described “wolfram” as early as 1574, but undoubtedly it was known long before that time. Georgius Agricola suggested that it stems from the early German word wolf and ram or rahm (froth), which mean literally “the foam of the wolf” and suggest that in some manner the ore has wolfike qualities. These qualities were connected by tin miners in England with the tendency of wolframite–frequently associated with tin ore but originally believed to be a mineral of tin–to “eat up” tin during the process of the smelting. It was not realized at the time that this detrimental impurity contained a new element.
In 1781 a Swedish chemist, C-irl Scheele, pointed out that in tungsten ore (scheelite) there existed a peculiar acid, which he called tungstic acid, combined with lime. In recognition of his discovery the mineral now bears his name: scheelite. Torbern Bergman thought the base of the acid was a metal but was not able to isolate it. However, he as well as Scheele, suggested the possibility of extracting the element in a manner similar to that used in the recovery of arsenic from its oxide ores known centuries before, that is, with carbonaceous material.
J. J. & F. de Elhuyar found the same acid in wolframite and gave the first published account of isolating the metal in 1783. Their experimental procedure consisted merely of mixing tungstic acid and charcoal in a crucible and heating to bring about inter action between the two. The residue was a crumbly metallic button which upon close examination revealed small globules of elemental metal which they called wolfram. The English called it tungsten. ( Scheele probably had already prepared the metal but made no accounting of it.) Thede Elhuy,u brothers had further shown that in wolfram the metallic element was associated with iron and manganese instead of lime.
The first important use of tungsten commercially was in a tungsten-manganese steel which hardened upon air cooling from proper heat-treating temperatures. This steel was devised by Mushet in the middle of the 19th century. Several other European investigators experimented with steels containing tungsten.
The most notable achievement in the field of tungsten steels was made by Taylor and White, who developed the composition known today as high-speed steel. Their work was received with great enthusiasm when the first high-speed steel was exhibited by the Bethlehem Steel Company at the Paris Exposition in 1900. Its ability to hold a cutting edge at dull red heat promised to revolutionize the tool-steel industry. Many investigations were subsequently carried out with other compositions and the possibility of substituted elements was later considered when tungsten became a critical alloying element. At present, standard grades of high-speed steels include the use of tungsten, molybdenum, chromium, vanadium, and cobalt.
One of the more important applications of tungsten, because it contributes to man’s comfort, is in the field of electric lamp filaments for lighting and for electronic tubes. Tonnage wise, the actual amount thus used is small–1 ton is enough to make over 10 million electric lamps. Progress in this field was slow for the first few years because of the difficulty of producing from tungsten metal powder a solid material posses sing good ductility. Just and Hanaman in 1904-06 had some success in making filaments with a process of “squirting” into thread a mixture of fine tungsten powder and organic binder through appropriate-sized dies, and then volatilizing the binder in hydrogen to prevent oxidation. Tungsten particles were thus sintered to form a conducting filament suitable for lamps. However. its lack of flexibility was a serious drawback.
The difficulty was overcome by Coolidge (General Electric Company) who. after several years of research. produced fine flexible wire by the application of high initial temperatures and judicious use of mechanical deformation in the initial stages of fabrication. Once deformation had occurred. subsequent mechanical working below the re-crystallization temperature permitted the material to be drawn into very fine wire even at room temperature. Coolidge’s efforts had produced fine wire of commercial importance by 1906 and by 1911 incandescent lamps using coiled filaments were on the market. Filaments as fine as .0004 inches in diameter are now commercially available.
Tungsten carbide. recognized. Mois san in 1896, was first made by reducing tungstic oxide with carbon. About 1919. tools and die materials were made from the carbides. 1n the twenties tungsten car bide was bonded with cobalt at the Krupp Laboratory at Essen. Germany. and used for tools, etc. Cobalt is almost invariably the bonding material used for cementing carbides for use as cut ting tools and dies. The carbides of titanium and tantalum are often mixed to produce cemented tungsten carbide for use in cutting operations. These products of powder metallurgy involve the pressing of various metallic powders into desired shapes and sintering at high temperatures.
Tungsten carbide is also cast into desired shapes for other applications. It is being used as a substitute for diamonds in drills for drilling oil wells. For this application it is necessary that the drill be extremely abrasion resistant in order to maintain the gage of the drill hole.
The use of tungsten carbide products is rapidly expanding, and new uses are constantly developing. There are wide applications in the field of mining. such as for rock drill bits and oil-well drilling tool; in metal cutting tools; in dies for wire drawing; and in metal forming such as for facing rolls for producing certain sheet metals. Tungsten carbide is also used for hard facing materials where it may be deposited by means of arc welding. During World War II. the Germans introduced armor-piercing projectiles made from tungsten carbide for use in tank warfare. This innovation has consequently placed greater demands upon the ballistic performance of armor plate,
Tungsten pigments. lakes. and mordants are used in the manufacture of printing inks, paints. enamels. waxes, rubber. and paper. Tungsten finds other uses in corrosion resistant alloys. targets in X-ray tubes, electrodes in atomic hydrogen or gas – shielded electric arc welding. electrodes for spark plugs. cross hairs for optical instruments. in glass-blowing equipment. and. in some instances, as electrodes for arc melting titanium metal, it is used in certain chemical applications such as discs and vessels. Tungstates are used in fluorescent lamps and optical glass. especially in aerial camera lenses to raise the refractive index.
The chief sources of tungsten are the ores. wolframite. Ferberite, huebnerite, and scheelite. The first three form a continuous series of naturally occurring iron-manganese tungstates with ferberite on the iron end and huebnerite on the manganese end. (See table VIII-5 for limiting compositions.) Compositions in between are the wolframites. Scheelite is a calcium tungstate. At the present time wolframite is the greatest world source of tungsten but domestically scheelite predominates. Scheelite is used principally in the manufacture of ferrotungsten and directly in tungsten steels, while the wolframite group is mostly used in the production of tungsten powder, However, in certain cases they can be interchanged. The. products made from tungsten ores can be grouped as: (1) Tungsten compounds. (Z) tungsten metal powder, including tungsten carbide, (3) metallic tungsten, and ( 4) ferrotungsten.
The total world reserves are estimated at 175 million units of tungstic oxide, W0 3 (equivalent to nearly 3 billion pounds of tungsten). Ash has the largest deposits, principally in Burma, Malaya, China, Japan, and Korea. China has the largest and richest deposits in the world. Lesser or poorer grade deposits are found in North America., South America. Europe. and Australia. With the recent closing of the door to Chinese tungsten. United States needs for tungsten have greatly stimulated domestic and other sources of production. Domestic tungsten ore production in this emergency period accounted for about one-third of the total U1lited States supply. 86 percent of which in 1952 came from California, Nevada and North Carolina.
Numerous methods of dressing and concentrating tungsten ores are used. depending upon the nature of the ores and the complexity of the auociated minerals. Some are primitive while others use the most modern flotation, magnetic-, or electrostatic separation techniques. Domestic scheelite, which is often fine grained, presents the problem of sliming as a result of too fine crushing. Chemical treatment is, therefore, often used in order to produce synthetic scheelite which is used in steel production or further processed into metal powder.
The military demands for tungsten in armor-piercing projectiles, its expanded use in tooling in war economy-, and its use in jet aircraft clarify it as a “war element.” Its price has strongly reflected war and preparedness programs since 1914. To conserve this strategic element during emergency, it has been necessary for the Government to institute controls over prices, distribution, and uses
Guaranteed prices for Government purchases of domestic ore have been incorporated into the control program. Almost the entire commercial development and growth of the tungsten industry has taken place since 1900. Variations in demand have made production and prices vary erratically, with conspicuous peaks in 1918, 19Z9, 1937, 1943, and 1953. Since World War I, China (except for World War II years 1943-45, when transportation routes were blocked) has maintained the lead as the world’s greatest ore producer followed by the United States and Burma. Bolivia and Portugal have contributed lesser amounts. For convenience, development and growth of the industry can be grouped into four periods: Early development through World War I; post-World War 1–the twenties and thirties; World War II; and the post-World War II period.