Серебра

Описание

Silver is one of the earliest known metals. Silver has no known physiologic or biologic function, though colloidal silver is widely sold in health food stores. Silver has high thermal and electrical conductivity and resists oxidation in air that is devoid of hydrogen sulfide.

Химические свойства

Silver is a white lustrous metal that is extremely ductile and malleable. Silver does not oxidize in O2 by heating. It becomes Ag2O3 in O3 and black Ag2S3 in S2 and H2S. It is soluble in HNO3 and concentrated H2SO4 . It is not soluble in alkali.

Физические свойства

Silver is located in group 11 (IB) of period 5, between copper (Cu) above it in period 4 andgold (Au) below it in period 6. Thus, silver’s chemical and physical properties are somewhatsimilar to these two group 11 partners.Silver is a soft, while, lustrous metal that can be worked by pounding, drawing througha die, rolling, and so forth. It is only slightly harder than gold. It is insoluble in water, but it will dissolve in hot concentrated acids. Freshly exposed silver has a mirror-like shine thatslowly darkens as a thin coat of tarnish forms on its surface (from the small amount ofnatural hydrogen sulfide in the air to form silver sulfide, AgS). Of all the metals, silver isthe best conductor of heat and electricity. This property determines much of its commercialusefulness. Its melting point is 961.93°C, its boiling point is 2,212°C, and its density is10.50 g/cm³.

Изотопы

There are 59 isotopes of silver, ranging from Ag-93 to Ag-130 with half-livesfrom a few milliseconds to a few days to 418 years. All but two of these 59 isotopes areradioactive and are produced synthetically. The two stable isotopes found in nature areAg-107 and Ag-109. These two make up 100% of the element’s existence in the Earth’scrust.

Происхождение имени

Silver’s modern chemical symbol (Ag) is derived from its Latin word argentum, which means silver. The word “silver” is from the Anglo-Saxon world “siolfor.” Ancients who first refined and worked with silver used the symbol of a crescent moon to represent the metal.

Вхождение

Silver is the 66th most abundant element on the Earth, which means it is found at about0.05 ppm in the Earth’s crust. Mining silver requires the movement of many tons of ore torecover small amounts of the metal. Nevertheless, silver is 10 times more abundant than gold.And though silver is sometimes found as a free metal in nature, mostly it is mixed with theores of other metals. When found pure, it is referred to as “native silver.” Silver’s major ores areargentite (silver sulfide, Ag₂S) and horn silver (silver chloride, AgCl). However, most silver isrecovered as a by-product of the refining of copper, lead, gold, and zinc ores. Although silveris mined in many countries, including the United States, Mexico, and Canada, most silver isrecovered from the electrolytic processing of copper ores. Silver can also be recovered throughthe chemical treatment of a variety of ores.

Характеристики

Silver is somewhat rare and is considered a commercially precious metal with many uses.Pure silver is too soft and usually too expensive for many commercial uses, and thus it isalloyed with other metals, usually copper, making it not only stronger but also less expensive.The purity of silver is expressed in the term “fitness,” which describes the amount of silverin the item. Fitness is just a multiple of 10 times the silver content in an item. For instance,sterling silver should be 93% (or at least 92.5%) pure silver and 7% copper or some othermetal. The fitness rating for pure silver is 1000. Therefore, the rating for sterling silver is 930,and most sliver jewelry is rated at about 800. This is another way of saying that most silverjewelry is about 20% copper or other less valuable metal.
Many people are fooled when they buy Mexican or German silver jewelry, thinking theyare purchasing a semiprecious metal. These forms of “silver” jewelry go under many names,including Mexican silver, German silver, Afghan silver, Austrian silver, Brazilian silver, Nevadasilver, Sonara silver, Tyrol silver, Venetian silver, or just the name “silver” with quotes aroundit. None of these jewelry items, under these names or under any other names, contain anysilver. These metals are alloys of copper, nickel, and zinc.

Использование

This malleable white metal is found as argentite (Ag2S) and horn silver (AgCl) or in lead and copper ore. Copper plates coated with a thin layer of elemental silver and fumed with iodine were used by Niépce and Daguerre. Aside from the heliograph and physautotype, silver halide compounds were the basis of all photographic processes used in the camera and most of the printing processes during the 19th century.

Определение

A transition metal that occurs native and as the sulfide (Ag₂S) and chloride (AgCl). It is extracted as a by-product in refining copper and lead ores. Silver darkens in air due to the formation of silver sulfide. It is used in coinage alloys, tableware, and jewelry. Silver compounds are used in photography. Symbol: Ag; m.p. 961.93°C; b.p. 2212°C; r.d. 10.5 (20°C); p.n. 47; r.a.m. 107.8682.

Общее описание

Silver is a noble metal, extensively used in SERS, photocatalysis and solar cells. The surface of silver can be functionalized to attain specific properties such as biocompatibility and vapor selectivity of sensors.3 Iodized silver foils and thin films find potential use as SERS-active metal substrates.1 Cu substrates laminated with Ag foils, have compatible coefficient of thermal expansion (CTE), to be used for electronic packaging. Porous ZnO nanoplates deposited on silver foil with tunable hydrophobicity may be fabricated.3

Профиль реактивности

Silver reacts violently with chlorine trifluoride (in the presence of carbon) [Mellor 2 Supp. 1 1956]. Bromoazide explodes on contact with Silver foil. Acetylene forms an insoluble acetylide with Silver [Von Schwartz 1918 p. 142 ]. When Silver is treated with nitric acid in the presence of ethyl alcohol, Silver fulminate, which can detonated may be formed. Ethyleneimine forms explosive compounds with Silver, hence Silver solder should not be used to fabricate equipment for handling ethyleneimine. Finely divided Silver and strong solutions of hydrogen peroxide may explode [Mellor 1:936 1946-47)]. Incompatible with oxalic acid and tartaric acid [Nav Aer. 09-01-505 1956]. Silver can form explosive salts with azidrine. ("Ethyleneimine" Brocure 125-521-65, Midland (Mich.), Dow Chemical Co., 1965). Ammonia forms explosive compounds with gold, mercury, or Silver. (Eggeman, Tim. "Ammonia" Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. 2001.). Acetylene and ammonia can form explosive Silver salts in contact with Ag. (Renner, Hermann, Gunther Schlamp. “Silver, Silver Compounds, and Silver Alloys." Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA. 2001.)

Опасность

Toxic material.

Угроза здоровью

The acute toxicity of silver metal is low. The acute toxicity of soluble silver compounds depends on the counterion and must be evaluated case by case. For example, silver nitrate is strongly corrosive and can cause burns and permanent damage to the eyes and skin.
Chronic exposure to silver or silver salts can cause a local or generalized darkening of the mucous membranes, skin, and eyes known as argyria. The other chronic effects of silver compounds must be evaluated individually.

Пожароопасность

Dust is flammable.

Воспламеняемость и взрывоопасность

Silver and most soluble silver compounds are not combustible. However, silver nitrate and certain other silver compounds are oxidizers and can increase the flammability of combustible materials.
Silver acetylide, azide, fulminate, oxalate mixtures, styphnate, tartarate mixtures, and tetrazene are all explosives and must be handled as such.

Профиль безопасности

Human systemic effects by inhalation: skin effects. Inhalation of dusts can cause argyrosis. Questionable carcinogen with experimental tumorigenic data. Flammable in the form of dust when exposed to flame or by chemical reaction with C2H2, NH3, bromoazide, ClF3 ethyleneimine, H2O2, oxalic acid, H2SO4, tartaric acid. Incompatible with acetylene, acetylene compounds, aziridine, bromine azide, 3-bromopropyne, carboxylic acids, copper + ethylene glycol, electrolytes + zinc, ethanol + nitric acid, ethylene oxide, ethyl hydroperoxide, ethyleneimine, iodoform, nitric acid, ozonides, peroxomonosulfuric acid, peroxyformic acid. See also POWDERED METALS and SILVER COMPOUNDS.

Возможный контакт

Silver may be alloyed with copper, aluminum, cadmium, lead, or antimony. The alloys are used in the manufacture of silverware, jewelry, coins, ornaments, plates, commutators, scientific instruments; automobile bearing; and grids in storage batteries. Silver is used in chromenickel steels, in solders and brazing alloys; in the application of metallic films on glass and ceramics, to increase corrosion resistance to sulfuric acid, in photographic films, plates and paper; as an electroplated undercoating for nickel and chrome; as a bactericide for sterilizing water; fruit juices; vinegar, etc.; in bus bars and windings in electrical plants; in dental amalgams; and as a chemical catalyst in the synthesis of aldehydes. Because of its resistance to acetic and other food acids, it is utilized in the manufacture of pipes, valves, vats, pasteurizing coils and nozzles for the milk, vinegar, cider, brewing, and acetate rayon silk industries.

Канцерогенность

The U.S. Department of Health and Human Resources has extensively monitored published studies on the occupational therapeutic and domestic exposures to metals over many years, but has failed so far to identify unequivocal clinical evidence that silver is carcinogenic to humans under any circumstances. On the basis of human experience and supportive studies in experimental animals, silver is currently classified as a noncarcinogen (62, 94, 141). On occasions patients exposed to silver in antibiotic prostheses and other devices have died from cancer, but in each case the role of silver in the etiology of the malignancies was not proven.
It is expected that human contact with any of the radioactive isotopes of silver may lead to local or other carcinogenic changes in humans through the action of the radioactive emissions as have been reported with gold in jewelry. No cases have been seen to date.

Экологическая судьба

Silver is a rare element, which occurs naturally in its pure form. It is a white, lustrous, relatively soft, and very malleable metal. Silver has an average abundance of about 0.1 ppm in the Earth’s crust and about 0.3 ppm in soils. It exists in four oxidation states (0,+1,+2,and +3). Silver occurs primarily as sulfides with iron, lead, tellurides, and with gold. Silver is found in surface waters as sulfide, bicarbonate, or sulfate salts, as part of complex ions with chlorides and sulfates and adsorbed onto particulate matter. Silver is released through natural processes, for example, erosion of soils. Sources of atmospheric contamination arise from processing of ores, steel refining, cement manufacture, fossil fuel combustion, and municipal waste incineration. Of anthropomorphic release, over 75% was estimated to be from disposal of solid waste. Ore smelting and fossil fuel combustion can emit fine particulates that may be transported long distances and deposited with precipitation. The major source of release to surface waters is effluent from photographic processing. Releases from the photographic industry and from disposal of sewage sludge and refuse are the major sources of soil contamination with silver. Silver can leach into groundwater, which can be extenuated in acidic conditions. Silver can bioconcentrate in fish and invertebrates.

хранилище

Most silver compounds should be protected from light during storage or while in use.

Методы очистки

For purification by electrolysis, see Craig et al. [J Res Nat Bur Stand 64A 381 1960]. For purification of crude, or silver residues to pure silver see Glemser & Sauer in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 1028-1030 1963, and for the preparation of colloidal silver see ibid (Ed. Brauer) p 1034.

Несовместимости

Dust may form explosive mixture with air. Powders are incompatible with strong oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides May react and/or form dangerous or explosive compounds, with acetylene, ammonia, halogens, hydrogen peroxide; bromoazide, concentrated or strong acids, oxalic acid, tartaric acid, chlorine trifluoride, ethyleneimine.

Утилизация отходов

Recovery, wherever possible, in view of economic value of silver. Techniques for silver recovery from photoprocessing and electroplating wastewaters have been developed and patented.