Silver
Silver is a chemical element with atomic number 47 located in group 11 of the periodic table of elements. Its symbol is Ag (it comes from the Latin argentum, 'white', 'white' or 'brilliant'). It is a noble metal, transition, bright white, soft, ductile and malleable.
In nature it is found as part of different minerals (generally in the form of sulfide) or as free silver. It is rare in nature, representing one part in a thousand of the earth's crust. Most of its production is obtained as a by-product of the treatment of copper, zinc, lead and gold mines.
Etymology
Its name is an evolution of the Latin word *platus (cf. flat), which originally meant 'flat' and later 'metal sheet'. In the Romance languages of the Iberian Peninsula, the specific term refers to metal: in Catalan, Aragonese and Spanish silver and in Galician and Portuguese prata.
The symbol for silver, Ag, comes from the Latin argentum and the Greek ἄργυρος, names for the metal in those languages, derived from an Indo-European root meaning & 'brilliant'. From the Latin word derive the names of silver in most Neo-Latin languages, such as French argent, Italian argento and Romanian argint.
In Spanish there is also the adjective argentino, for exclusively literary use, from which the name Argentina arose.
General properties
Silver is a very ductile and malleable metal, somewhat harder than gold, and has a metallic white luster that is amenable to polishing. It maintains itself in water and air, although its surface tarnishes in the presence of ozone, hydrogen sulfide, or sulfur-containing air.
It has the highest electrical conductivity and thermal conductivity of all metals, but its higher price has prevented its widespread use in electrical applications. Pure silver also has the whitest color and the highest reflective index.
Applications
Approximately 70% of the world's silver production is used for industrial purposes, and 30% for monetary purposes; Much of this metal is used in goldsmithing, but its most important uses are in the photographic industry and chemistry.
Some uses of silver are described below.
Photography
- Photography. Because of its sensitivity to light (especially bromide and iodide, as well as phosphate). The silver iodide has also been used to produce artificial rain.
Medicine
Silver ions and compounds have a toxic effect on some bacteria, viruses, algae and fungi, a typical property of heavy metals such as lead or mercury, but without the high toxicity to humans normally associated with these other metals. Its germicidal effects kill many microbes in vitro, but testing and standardization of silver products is difficult.
Hippocrates, the "father of medicine," wrote that silver had beneficial healing and disease-fighting properties, and the Phoenicians used to store water, wine and vinegar in glass bottles. silver to prevent it from spoiling. In the early 19th century, people put silver coins in milk bottles to prolong their freshness.
Silver compounds were used to prevent infection in World War II before the discovery of antibiotics. Silver nitrate solutions were a standard treatment, but were superseded by silver sulfadiazine creams, which was generally the standard treatment for antibacterial and antibiotic treatment of severe burns until the turn of the century XX. Today, other options are used, such as silver-coated dressings (activated silver dressings), in conjunction with silver sulfadiazine. Still, studies of the efficacy of these silver-treated dressings have given mixed results. A systematic review by the Cochrane Collaboration found insufficient evidence to recommend the use of silver-treated dressings to treat infected wounds.
It has long been known that the antibacterial action of silver is enhanced by the presence of an electric field. The application of a few volts of electricity through silver electrodes significantly improves the rate at which bacteria in the solution are killed. The antibacterial action of silver electrodes was found to be greatly enhanced if the electrodes are covered with silver nanorods.
Medications
Various types of silver compounds, or devices for making solutions or colloids containing silver, are sold today as remedies for a wide variety of ailments. Although most colloidal silver preparations are safe, some people who overused these homemade solutions have developed argyria after months or years. High doses of colloidal silver can result in coma, pleural edema, and hemolysis.
Silver is widely used in topical ices and impregnated in bandages because of its broad-spectrum antimicrobial activity. The antimicrobial properties of silver are due to the chemical properties of its ionized form, Ag+. This ion forms strong molecular bonds with other substances that bacteria use to breathe, such as molecules containing sulfur, nitrogen, and oxygen. When the Ag+ ion forms a complex with these molecules, they remain unusable by the bacteria, depriving them of necessary compounds and ultimately causing death.
- Silver is also used in alloys for dental parts.
Electricity
- Electricity. The contacts of electric generators of diesel-electric locomotives carry contacts (approximately 1 in. thick) of pure silver; and these machines have an electric motor on each wheel or shaft. The diesel engine moves the electricity generator, and it is also necessary to add the contacts of the best quality home keys or pushers that do not use only copper (more economical).
Electronics
- In electronics, its high conductivity is increasingly used, for example, in integrated circuit contacts and computer keyboards.
- Manufacture of mirrors of great reflectivity of visible light (the common ones are made with aluminum).
Coinage
- The silver has been used to make coins from 700 to. C., initially with electrum, natural alloy of gold and silver, and later of pure silver.
Jewelry and silverware
- In jewellery and silverware to manufacture a variety of ornamental and everyday household items, and with a lesser degree of purity, in jewellery articles. To identify the authentic Silver of Law or sterling silver that is used for the manufacture of jewellery, a stamp with the inscription "925" and some other symbol that identifies the jeweler comes from the Middle Ages and still today this method is used to identify it. The jewellery and standard silverware are a alloy of 92.5% silver with 7.5% copper. In the United States you can only sell as a "silver" an alloy that has at least 92.5% of fine silver. The silver is tougher than pure silver, and has a melting point of 893 °C, lower than pure silver or pure copper. Britannia Silver is an alternative contrast quality standard that contains 95.8% silver, and is often used to produce silverware and other objects that require special work. The addition of germanium forms the patented modified alloy called "Argentium Law Plate", which has improved properties such as resistance to fire stains.
Chemical industry
- Catalyst in oxidation reactions. For example, in the production of formaldehyde from methanel and oxygen.
- In computer assembly, compounds formed mainly of pure silver are used to attach the microprocessor plate to the base of the dissipator, and thus refrigerate the processor, due to its heat conductor properties.
- Alloys for welding, electrical contacts and electrical batteries of silver-zinc and high capacity silver-chadmium.
History
Silver is one of the seven metals known since ancient times. It is mentioned in the book of Genesis; and slag heaps found in Asia Minor and islands in the Aegean Sea indicate that the metal began to separate from lead at least four millennia before our era.
It is not difficult to imagine the effect that it would have had on those settlers (who had carved and polished stone, who found and used copper and later tin, even going so far as to alloy both by means of fire to obtain bronze) discovery of a rare and infrequent metal, white in color, imperishable shine and insensitive to the fire that melted other metals. Such astonishment meant the attribution to the metal of singular properties, of which the other metals lacked, except gold of course; for both were nothing but gifts of nature, one formed by the influence of the Moon, and the other by that of the Sun. The rest, vile metals, were subject to changes and transformations, which by the rudimentary means then available could be produced; far, far away, from the perfection of silver and gold. It is not surprising that for this reason the idea of the transmutation of metals arose in a vain attempt to perfect those vile metals and giving rise to the appearance of the first doctrines of Alchemy. Mercury seemed particularly suitable for this purpose, in which the appearance and color of silver was observed, to such an extent that it was given the name hydrargyrum (liquid silver) from which its chemical symbol comes. (Hg).
Silver, like the rest of the metals, was used to make weapons of war and was later used in the manufacture of utensils and ornaments, from where it spread to commerce when the first silver coins were minted and came to constitute the basis of the monetary system of many countries. In 1516 Juan Díaz de Solís discovered the Sweet Sea in South America, which Sebastián Caboto later called Río de la Plata, believing that the precious metal abounded there, and from which Argentina would take its name. Years later, the discovery of large silver reserves in the New World in Zacatecas and Taxco in Mexico; Potosí, in Bolivia; as well as Paramillos de Uspallata, in Argentina: and its importation through Europe, caused a long period of inflation, which, far from being limited to Spain, spread throughout Europe; The phenomenon was studied by Earl Jefferson Hamilton, who in 1934 published the book The American Treasure and the Price Revolution in Spain, 1501-1650.
Dalton's chemical symbol for silver was a circle with the letter "S" in its center
Abundance and obtaining
Silver is found native, combined with sulfur (argentite, Ag2S), arsenic (proustite, Ag3AsS3), antimony (pyrargyrite, Ag3SbS3) or chlorine (horny silver, AgCl), forming a large group of silver minerals. The metal is obtained primarily from copper, copper-nickel, gold, lead and lead-zinc mines in Mexico, Canada, Peru and the US.
Metallurgy from its ores is carried out fundamentally by cyanidation:
- Ag2S + 4 KCN → K2S + 2 KAg(CN)2
Mining production
World silver production during 2011 reached a total of 23,800 metric tons. The main silver-producing countries are Mexico and Peru, which alone account for 1/3 of world silver production.
ReservationsAccording to information provided in the annual report of the United States Geological Survey (USGS), estimates indicate that known silver reserves worldwide in 2011 would reach 530,000 metric tons of fine silver. According to USGS estimates, in Peru there would be an order of 120,000 metric tons economically exploitable, equivalent to 23% of total world mineral reserves; followed by Poland with 85,000 metric tons economically exploitable, equivalent to 16% of total world mineral reserves.
Alloys and compoundsSilver is easily tied to almost all metals, although with nickel it does it with difficulty. With iron and cobalt it cannot be tolerated. Even at regular temperature, silver forms amalgams with mercury. Alloy metal par excellence is copper, which hardens silver if added to it up to 5% content (which is known as sterling silver), although silvers have been used with higher content of copper. Copper additions do not alter the color of the silver even if it reaches up to 50% content, although in this case the color is preserved in a superficial layer that when worn out will show a reddish alloy, both more accused the greater the amount of copper. Alloys have also been used with cadmium in jewelry, as this element gives alloy a suitable ductility and malleability for metal work. Among the silver compounds of industrial importance are:
IsotopesNatural silver consists of two stable isotopes Ag-107 and Ag-109, being the first slightly more abundant (51.839%) than the second. Twenty-eight radioisotopes have been characterised of which the most stable are Ag-105, Ag-111 and Ag-112, with semi-disintegration periods of 41,29 days, 7.45 days and 3.13 hours respectively. The other isotopes have shorter half-disintegration periods than an hour, and most of them less than three minutes. Numerous metastatic states have been identified among which the most stable are Agm-108 (418 years), Agm-110 (249,79 days) and Agm-107 (8,28 days). Silver isotopes have atomic weights that vary between 93,943 uma of the Ag-94 and 123,929 uma of the Ag-124. The main disintegration mode of the lightest isotopes than the most abundant stable is electronic capture resulting in isotope of palate, while the heaviest isotopes than the most abundant stable are disintegrated mainly by beta emission leading to cadmium isotopes. The Pd-107 isotope is disintegrated by beta emission producing Ag-107 and with a semi-disintegration period of 6.5 million years. The ferrous meteorites are the only known objects with a Pd/Ag reason sufficiently high to produce measurable variations in the natural abundance of the isotope Ag-107. The Radiogenetic Ag-107 was discovered in the meteorite of Santa Clara (California) in 1978. Incidence on living organismsSilver is not toxic but most of its salts are poisonous and can be carcinogens. Silver-containing compounds can be absorbed by the circulatory system and deposited into various tissues causing argiria, a condition consisting of grayish skin coloring and mucous membranes, which is not harmful. Since Hippocrates the germid effect of silver is known and have been marketed, and today they market various remedies for a variety of ailments. In June 2013, a study has been published that has shown in mice its therapeutic usefulness as an antibiotic. "Our work is the first to decipher the mechanisms by which silver kills microorganisms. Silver is like a Trojan horse that opens cellular doors to antibiotics," says Dr. José Rubén Morones-Ramírez, researcher at the Autonomous University of Nuevo León (Mexico) and co-author of the study. Dr. Morones-Ramírez is currently at the Howard Hughes Medical Institute at the University of Boston in the United States. It is recognized that soluble silver salts, especially silver nitrate (AgNO3), are lethal in concentrations of up to 2 grams. Silver compounds can be slowly absorbed by body tissues, with the consequent blue or black pigmentation of the skin, an effect known as argiria. In addition:
Chronic overexposure to a component or several components of silver has the following effects on laboratory animals:
Chronic overexposition to a component or several components of silver is supposed to have the following human effects; effects that should still be corroborated by further research:
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