Silver (Ag)
Silver (Ag) is a metallic element with the atomic number 47, known for its high malleability, ductility, and excellent electrical conductivity. It has a physical appearance characterized by a bright, reflective surface and is commonly found in nature as native silver or in various ore deposits, such as silver sulfides and alloys with gold. Although its average abundance in the Earth's crust is low, silver is recoverable from numerous global sources, with significant production occurring in countries like Mexico, Peru, and the United States.
Historically, silver has been utilized for various purposes, from coinage in ancient cultures to its contemporary applications in jewelry, electronics, and dental amalgams. The decline of silver use in photography, due to the rise of digital technology, has shifted its demand towards industrial uses, including electronics and specialized batteries. Silver also plays a role in the chemical industry and medicine, particularly for its antibacterial properties and use in dental materials.
While mining operations can have local environmental impacts, silver itself is relatively safe, with rare instances of human toxicity. The purity of silver in commercial products is typically expressed in terms of fineness, with sterling silver being a popular alloy for decorative items. As a versatile and historically significant metal, silver continues to hold value across various industries and applications.
Silver (Ag)
Where Found
Silver has an average crustal abundance of 0.07 part per million (0.000007 percent) but is widely distributed and occurs in recoverable amounts in many ore deposits throughout the world. It may occur as native silver, as silver sulfide (acanthite), alloyed with gold as electrum, or as complex copper, lead arsenic, and/or antimony sulfides.
Primary Uses
Previously, the most important uses of silver were in photographic materials; light-sensitive silver salts served to produce negatives and prints. However, beginning in 2000, the use of silver in photography declined significantly because of the emergence of digital technology. Silver is also widely used in electrical and electronic products, jewelry, dental amalgams, and mirrors, and was widely used in the past for coinage.
Technical Definition
Silver (abbreviated Ag), atomic number 47, belongs to Group IB of the periodic table of the elements and is similar in some chemical and physical behavior to copper. It has two naturally occurring stable isotopes, with masses of 107 and 109, and has an average atomic weight of 107.87. Its physical properties are malleability, ductility, reflectivity, and electrical conductivity.
Description, Distribution, and Forms
Pure silver is a malleable, white, highly reflective metal with a density of 10.49 grams per cubic centimeter. It has a melting point of 961.9° Celsius and a boiling point of approximately 2,212° Celsius; it crystallizes in a face-centered cubic structure.
World production of silver was relatively constant at about 15,000 metric tons per year between the mid-1980’s and the late 1990’s; production rose to about 20,000 metric tons by the mid-2000’s. The largest producers have been Mexico, Peru, the United States, Poland, China, Australia, and Chile, but there has been significant production reported in nearly sixty countries. World reserve figures have remained at more than 250,000 metric tons, thus ensuring a stable supply for a number of years. The reserve base, which includes ores that will very likely become economic to mine in future years, was 570,000 metric tons in 2008. Reserve figures are, however, subject not only to changes in the price of silver but also to changes in the prices of the other primary metals in the deposits where silver is recovered only as a by-product.
Silver itself has little or no adverse environmental impact; however, the mines that produce silver may create local problems attributable to the mining and disposal of wastes. The principal impact in older mining districts has been the release of acid generated by the weathering of pyrite that is usually present in the ores. Silver, when released because of acid mine discharge, is rapidly adsorbed onto iron and manganese oxides and hydroxides that precipitate in such situations. Silver poisoning of humans is extremely rare, but prolonged absorption of silver compounds can cause argyria, a grayish-blue discoloration of the skin.
The purity of silver in jewelry, coinage, bullion, and ornamental pieces is usually expressed as fineness or parts per thousand. Pure silver is “1000 fine” (100 percent silver); sterling silver, widely used for decorative items and tableware, is 925 fine (92.5 percent silver and 7.5 percent copper).
History
Silver was one of the earliest known metals because it commonly occurs as a free metal. It was easily shaped by pounding and melting into ornaments, amulets, and utensils. Silver was in use in northern Europe and around the Mediterranean by 4000 b.c.e., but the first known mining sites were in Cappadocia, in eastern Asia Minor. From there silver mining spread throughout the Mediterranean countries and the metal was obtained from many small mines. By about 1000 b.c.e. the most important mines were the silver-lead mines at Laurion, near Athens, Greece. These mines made Athens wealthy and financed the Greek wars; the ultimate production has been estimated to have reached 250 million troy ounces (7,800 metric tons). Because the silver was extracted by open roasting of the lead-rich ores, this mining also resulted in widespread lead pollution.
With the rise of the Roman Empire, silver mining expanded throughout Europe and across the Middle East. Even throughout the Dark Ages, when many of European mineral industries severely declined, silver mining continued to expand. By 1300 c.e. the largest silver mine was at Joachimsthal (now Jáchymov, in the Czech Republic). A large silver coin produced there was called the Joachimsthaler, abbreviated to thaler in German; it became daalder in Dutch and ultimately “dollar” in English.
Colonization of the New World in the early sixteenth century led to the discovery of major silver deposits in Mexico and Peru. In fact, the quantity of silver (16,000 metric tons) shipped back to Spain from the New World between 1520 and 1660 was about ninety times greater than the quantity of gold (181 metric tons) shipped back in the same time span. The abundance of silver led to its use as a primarycoinage metal in the New World. The eight real coin, commonly called the Spanish “piece of eight,” was widely minted and used throughout the Americas and Europe; it remained a viable coin in the United States until the mid-1800’s.
Silver also became one of the principal coinage metals in the early years of the United States; it was used in the first noncirculated test coins in 1792 and then appeared in half-dollars and silver dollars in 1794 and in dimes and quarters in 1796. The minting of silver dollars was terminated in the 1930’s. The other coins remained silver-bearing until 1964, when clad nickel-copper dimes were introduced and when the silver began to be phased out of quarters and half-dollars. The silver was removed because coinage use was outstripping supplies, industrial use was rising, and the cost of silver, long held constant, was allowed to rise. Silver is used today in coinage only in the production of special bullion and commemorative coins.
Obtaining Silver
Silver occurs in many types of ore deposits and in minerals as diverse as the native metal (silver, Ag; electrum, Au, Ag), silver sulfide (acanthite, Ag2S), silver chloride (cerargyrite, AgCl), and sulfosalts (such as polybasite, Ag16Sb2S11, and proustite, Ag3AsS3). Approximately one-third of world silver comes from veins associated with gold as the primary commodity. Two-thirds of modern production is as a by-product from ores mined primarily for copper, lead, zinc, or gold. These ores also exist primarily as hydrothermalvein deposits, but the silver is generally present as sulfosalts, especially tetrahedrite, which is intimately intermixed with sulfides of iron, copper, lead, and zinc. Primary gold ores, both lode and placer types, generally also produce significant amounts of silver that has been held in solid solution in the native gold or electrum.
Uses of Silver
For many years, approximately 50 percent of silver usage in the United States was for photographic materials, especially film and printing paper. These were prepared by depositing thin layers of silver salts along with gelatin and dyes on sheets of plastic or paper. However, beginning in 2000, silver usage in photography was waning because of digital technology.
Silver has the greatest thermal and electrical conductivity of any metal and hence finds broad usage in electrical and electronic products. Because silver is also quite resistant to corrosion and oxidation and is easily welded, it is especially sought for high-quality electronics. Commonly, silver is alloyed with copper, gold, nickel, or platinum group metals to provide working properties that better serve specific applications. Silver has also found considerable use in batteries, where silver compounds are coupled with zinc compounds. Such batteries are expensive and relatively short-lived, but they have a high energy output per unit size and weight. Consequently they find their primary usage in military and space applications where high reliability for a short time is essential. They have also been used in the production of button batteries for calculators, watches, and hearing aids. Silver has found wide use in special “silver solders,” which serve effectively in air-conditioning and refrigeration applications because they bond so well to a wide variety of metals.
Silver has been used in jewelry and other decorative items since prehistoric times. The occurrence of native silver and the relative ease of silver refining allowed for the early use of silver that was quite pure. Modern silver usage for decorative purposes is usually as sterling silver (92.5 percent silver and 7.5 percent copper); sterling silver objects are made entirely of silver-copper alloys. In addition, there is much electroplated silver, which consists of a thin coating of silver, or silver-copper alloy, over a base of some other metal. Because of the high reflectance of silver in the visible spectrum, it has long been used in the making of mirrors.
Silver finds considerable usage in the chemical industry because it catalyzes oxidation reactions and produces organic compounds, such as formaldehyde from methanol, and oxygen and ethylene oxide from ethylene and oxygen. Silver has long served as a primary metal in dental amalgam fillings. The addition of mercury to the silver- and tin-based alloys provides dentists with an amalgam that is malleable at first but soon becomes very hard and corrosion resistant. The amalgam consists of a series of alloy phases that very effectively incorporate and contain the mercury. However, recent studies suggest these types of fillings may not be safe.
Medical applications of silver include the use of soluble silver salts of nitrates and citrates. These have proven very effective in the treatment of bacterially caused medical conditions. Furthermore, silver nitrate reacts rapidly with skin and mucous tissue and thus serves as a low-temperature means of cauterizing where the additional strength of scar tissue is useful.
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