bismuth


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bismuth

(bĭz`məth) [Ger. Weisse Masse=white mass], metallic chemical element; symbol Bi; at. no. 83; at. wt. 208.98040; m.p. 271.3°C;; b.p. about 1,560°C;; sp. gr. 9.75 at 20°C;; valence +3 or +5. Bismuth is a silver-white, reddish-tinged, brittle metallic element with a rhombohedral crystalline structure. It exhibits more metallic properties than the other members of Group 15 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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. It occurs free in nature to a small extent. Bismuth does not tarnish in air, but when heated it burns to form yellow fumes of the trioxide. It reacts with the halogens and with sulfur and is dissolved in nitric acid and hot sulfuric acid. Its soluble compounds are poisonous, but some of its insoluble compounds are used in medicine to treat certain gastric disorders and skin injuries. Bismuth is the poorest heat conductor of all the metals except mercury; it is the most diamagnetic of all metals. The major ores of bismuth, bismuthinite (the sulfide), also called bismuth glance, and bismite (the oxide), are found extensively in South America but are rare in the United States, where bismuth is obtained as a byproduct of lead and copper refining. Bismuth expands upon solidification; this unusual property makes it useful in type-metal alloys and for castings. The most important use of bismuth is in the manufacture of low-melting alloys, such as Wood's metal, used in electrical fuses and in automatic fire alarm and sprinkler systems. Bismuth was recognized as a metal by early observers, including Georg Agricola, in the 16th cent., but was believed to be a kind of lead or tin until Claud J. Geoffroy established it as a separate element in 1753.

Bismuth

 

Bi, a chemical element in Group V of Mendeleev’s periodic system. Atomic number, 83; atomic weight, 208.980. Silvery gray metal with a pinkish tint. Natural bismuth consists of a single stable isotope, 209Bi.

Bismuth was known in the 15th and 16th centuries but was long considered to be a variety of tin, lead, or antimony. It was recognized as an independent metal in the mid-18th century. The French chemist A. Lavoisier included it in a list of simple substances. The origin of the name “bismuth” has not been established.

The bismuth content of the earth’s crust is 2 x 105 percent by mass. Bismuth occurs naturally in the form of many minerals, the most important of which are bismuthinite, Bi2S3; native bismuth, Bi; and bismite, Bi2O3. Bismuth is found in large quantities but low concentrations as an isomorphous impurity in lead-zinc, copper, molybdenum-cobalt, and tintungsten ores. About 90 percent of world bismuth consumption is supplied by bismuth obtained as a by-product in processing complex ores.

Physical and chemical properties. Bismuth has a rhombohedric lattice; lattice constant a = 4.7457 angstroms, and angle α = 57°14’13”. Density, 9.80 g/cm3; melting point, 271.3° C; boiling point, 1560° C; specific heat (at 20° C), 123.5 joules per (kg-0 K), or 0.0294 calories per (g-° C); thermal coefficient of linear expansion at room temperature, 13.3 x 10~6; specific thermal conductivity (at 20° C), 8.37 watts per (m-°K) or 0.020 calorie per (cm-sec-°C); specific electrical resistance (at 20° C), 106.8 x 10~8 ohm-m, or 106.8 x 10-6ohm-cm.

Bismuth is the most diamagnetic metal. The specific magnetic susceptibility is -1.35 x 10~6. Under the action of a magnetic field, the electrical resistance of bismuth increases more than that of other metals; this effect is used to measure the induction of strong magnetic fields. Bismuth has a low thermal neutron capture cross section (34 x 1031 m2, or 0.034 barn). At room temperature bismuth is brittle, splits readily along cleavage planes, and is easily pulverized in a porcelain mortar. It is ductile at 120°-150° C; wire as small as 0.1 mm in diameter, as well as plates 0.2-0.3 mm thick, can be made from it by hot forming (at 240°-250° C). Bismuth’s Brinell hardness is 93 meganewtons per sq m, or 9.3 kilograms-force per sq cm; its scratch hardness is 2.5. The volume contraction of bismuth on melting is 3.27 percent.

Bismuth is stable in dry air, but in moist air it shows surface oxidation. When heated above 1000° C it burns with a bluish flame, forming the Bi2O3. In the displacement series bismuth lies between hydrogen and copper; therefore, it does not dissolve in dilute sulfuric and hydrochloric acids. Solution in concentrated sulfuric and nitric acids takes place with the liberation of SO2 and the corresponding oxides of nitrogen.

The valences of bismuth are 2, 3, and 5. Bismuth compounds of the lowest valence are basic; those of the highest valence are acidic. The most important of the oxygen compounds of bismuth is the trioxide Bi2O3, which on heating changes in color from yellow to reddish brown. It is used to make bismuth salts, which hydrolyze in dilute solutions. The chloride BiCl3 hydrolyzes with the precipitation of the oxychloride BiOCl; and the nitrate Bi(NO3)3, with precipitation of the basic salt BiONO3-BiOOH. The ability of bismuth salts to undergo hydrolysis is utilized in purifying bismuth. Pentavalent bismuth compounds are obtained with difficulty; they are strong oxidizing agents. The salt KBiO3 (corresponding to the anhydride B2O5) is formed as a brownish red precipitate at a platinum anode upon electrolysis of a boiling solution of a mixture of KOH, KC1, and a suspension of Bi2O3. Bismuth combines readily with halogens and sulfur. Bismuthine (BiH3) forms as a result of the action of acids on a bismuth-magnesium alloy; unlike arsine (AsH3), it is unstable and has not been produced in pure form (without excess hydrogen). With some metals (lead, cadmium, and tin) bismuth forms fusible eutectics; with sodium, potassium, magnesium, and calcium it forms intermetallic compounds with melting points considerably above those of the component metals. Bismuth does not react with molten aluminum, chromium, or iron.

Preparation and use. Most bismuth is obtained as a by-product of the flame refining of crude lead. The pyrometallurgical method is based on the capacity of bismuth to form refractory intermetallic compounds with K, Na, Mg, and Ca. Those metals are added to the molten lead, and the resultant solid bismuth compounds (dross) are removed from the melt. A considerable amount of bismuth is extracted from the sludge produced from the electrolytic refining of lead in a fluosilicate solution, as well as from the dust and slime obtained in copper production. The dross and slime containing bismuth are melted under alkaline slags. The resultant crude metal contains admixtures of As, Sb, Cu, Pb, Zn, Se, Te, Ag, and a few other elements. The smelting of bismuth from actual ores is carried out on a small scale. Sulfide ores are processed by precipitation smelting with scrap iron. Bismuth is reduced by coal from oxidized ores under a layer of fusible flux.

Various-methods of purifying crude bismuth, including liquation, oxidation refining under alkaline fluxes, and fusing with sulfur, are used depending on the nature of the impurities. Lead, the impurity that is the most difficult to re-move, is eliminated (to 0.01 percent) by passing chlorine through the molten metal.

Commercial bismuth is 99.9-99.98 percent pure. Very pure bismuth is obtained by zone recrystallization in quartz“boats” in an inert gas atmosphere. A considerable amount of bismuth is used in the manufacture of fusible alloys containing lead, tin, and cadmium (for example, Wood’s alloy), which are used in prosthodontics, for making stereotype blocks from wooden matrices and fusible plugs in fire-fighting installations, and to solder the heads onto armor-piercing projectiles. Molten bismuth can be used as a heat carrier in nuclear reactors.

The use of bismuth in the form of compounds with tellurium for thermal electric generators is growing rapidly. Owing to a favorable combination of thermal and electric conductivity and thermal electromotive force, these compounds make possible the conversion of heat energy to electrical energy with very high efficiency (about 7 percent). The addition of bismuth to stainless steels improves their work-ability by milling.

Bismuth compounds are used in glass manufacturing (to raise the index of refraction) and ceramics (for making fusible enamel). Soluble bismuth salts are poisonous; their action is analogous to that of mercury.

The greatest quantity of bismuth is used in the pharmaceutical industry. Bismuth and its preparations are used in medicine as germicidal and dehydrating agents. Basic bismuth nitrate is used internally in inflammatory intestinal disorders (colitis, enteritis) and ulcerative stomach and duodenal diseases. It is made in powders and tablets—for example, vikalin and vikair. Bismuth preparations in the form of powders and ointments (Xeroform and Dermatol) are used externally for treating burns, dermatitis, and surface pyodermas. Suspensions of some bismuth compounds in vegetable oil(bismoverol, biiokhinol) are used for intramuscular injections in treating syphilis.

REFERENCES

Thomson, J. G. Vismut. Leningrad, 1932. (Translated from English.)
Sazhin, N. P., and R. A. Dul’kina. Poluchenie metallic he sko go vis muta vysokoi chistoty. Moscow, 1955. [Kaganovich, S. la., and G. P. Ivanov.] Proizvodstvo i primenenie vismuta v kapitalisticheskikh stranakh. Moscow, 1963.
Glazkov, E. N. Vismut. Tashkent, 1969.

L. IA. KROL’

bismuth

[′biz·məth]
(chemistry)
A metallic element, symbol Bi, of atomic number 83 and atomic weight 208.980.
(mineralogy)
The brittle, rhombohedral mineral form of the native element bismuth.

bismuth

a brittle pinkish-white crystalline metallic element having low thermal and electrical conductivity, which expands on cooling. It is widely used in alloys, esp low-melting alloys in fire safety devices; its compounds are used in medicines. Symbol: Bi; atomic no.: 83; atomic wt.: 208.98037; valency: 3 or 5; relative density: 9.747; melting pt.: 271.4°C; boiling pt.: 1564±5°C
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