638 



UNITED STATES MINERAL RESOURCES 



inert toward weak acids, bases, air, and other cor- 

 rosive agents by the formation of a thin film of tin 

 oxide. Probably the most important property of tin 

 is its extreme fluidity in the molten state and thus 

 its ability to wet many other metals and alloys. 

 The fluidity and excellent wetting characteristics 

 lead to its most important use as tinplate, which 

 accounts for nearly 50 percent of the tin used in 

 the United States. 



USES 



The six principal use categories of tin, in decreas- 

 ing order of importance, are tinplate, solders, bear- 

 ing alloys, bronze, chemicals, and coatings other 

 than tinplate. In the highly developed countries, the 

 principal use of tin is as a coating on steel plate for 

 use in the manufacture of tin cans. Although alu- 

 minum, plastics, and tin-free steel (steel with a very 

 thin coating of chromium) are capturing a large 

 share yearly of established can production in these 

 nations, tin is normally used in cans produced in the 

 newly developing nations. These two factors roughly 

 balance each other; as a result, the total yearly 

 world consumption of tin in tinplate increases only 

 slightly. 



Because of a strong and sustained research pro- 

 gram funded by contributions of the tin-producing 

 nations to the Tin Research Institute (Fraser Road, 

 Greenford, Middlesex, England), new uses of tin 

 are established almost yearly, ofi'setting active 

 trends toward the substitution of aluminum and 

 plastics for tin. Only a few of the new uses are 

 mentioned here; the interested reader is referred 

 to the "Quarterly Review" of the Tin Research Insti- 

 tute and to the various minerals yearbooks of the 

 U.S. Bureau of Mines. 



One of the fastest growing new uses of tin is in 

 the production of organotin chemicals. These are 

 chemicals in which quadrivalent tin is linked to three 

 hydrogen atoms and to an "X Group," which includes 

 OH, Br, CI, I, acetate, alkenyl, alkanoyloxy, or more 

 complex derivatives. These organotin chemicals 

 have proved to be very efl'ective pesticides, fungi- 

 cides, and wood preservatives and have relatively 

 low toxicity. Between 1950 and 1968, production of 

 organotin compounds rose from 50 tons to more than 

 10,000 tons, largely because of research initiated 

 worldwide by the Tin Research Institute. A very 

 rapid rise in use of organotin compounds has re- 

 sulted from their use as a stabilizing agent in poly- 

 vinylchlorides (PVC). Organotins have proved eff'ec- 

 tive in preventing discoloration and embrittlement 

 of clear PVC. Because of its low toxicity, PVC sta- 



bilized with organotins may be legally used in pack- 

 aging of foodstuffs. 



Within the automotive industry, tin continues its 

 long-established uses in bearings, bronzes, solders, 

 body fillings (to smooth joins and contours), terne- 

 plate for gasoline tanks, and pewter parts. In addi- 

 tion, tin is being added to cast-iron or cast-steel 

 parts to improve their machinability and is being 

 used as an additive in sintering of iron powders. 

 Much of the safety glass now used is made by the 

 new technique of floating liquid glass on a molten 

 bath of tin metal. 



In keeping with the space- and nuclear-age tech- 

 nology, an alloy of tin and niobium has been found 

 to be a highly superior superconductor. Such a 

 superconductor, consisting of more than 20 km of 

 niobium-tin ribbon wound on a wheel of 5-foot diam- 

 eter, when activated in liquid helium will produce a 

 magnetic field so strong that the entire assembly 

 will float in space in its own magnetic field. This 

 extreme magnetic field will be used to trap a high- 

 energy plasma of electrons and ions produced by 

 thermonuclear fusion. This energy source and trap- 

 ping arrangement ultimately may supply unlimited 

 quantities of cheap electric power. 



Finally, mention should be made of the irreplace- 

 able lov/-fusing-point eutectic alloys of tin with 

 elements such as bismuth or antimony. These are 

 bright, silvery, nontamishing alloys which can be 

 melted and remelted with negligible loss to oxide 

 films. One such alloy, consisting of tin, bismuth, 

 cadmium, lead, and indium, melts at 47°C. Such 

 alloys are indispensable in automatic fire-control 

 systems; in machining of fragile parts, which are 

 cast in low-melting temperature alloys and ma- 

 chined to shape, after which the alloy is melted 

 away; and in engineering research. 



In spite of loss of some established markets, such 

 as tin foil, new uses of tin are likely to more than 

 offset these losses, and tin consumption is not likely 

 to decrease in the foreseeable future. 



SUPPLY 



U.S. consumption of primary tin — about 57,000 

 tons in 1968 — is about 30 percent of the free world's 

 mine output, which in 1968 amounted to about 

 182,000 tons. About 90 percent of the world's tin is 

 produced by seven countries. In 1970, Malaysia fur- 

 nished 63 percent of tin imported into the United 

 States ; Thailand furnished 30 percent, and five other 

 nations — Australia, Brazil, Indonesia, Nigeria, and 

 the United Kingdom — combined to furnish the re- 

 maining 7 percent. 



Because the United States consumes almost 30 



