Silver

Occurrence and extraction

Main article: Silver mining

  Silver is found in native form; combined with pyrargyrite (Ag₃SbS₃). The principal sources of silver are the ores of copper, copper-nickel, gold, lead, and lead-zinc obtained from Peru, Mexico, China, and Australia. Peru and Mexico have been mining silver since 1546 and are still major world producers.

The metal can also be produced during the Parkes process on lead metal obtained from lead ores that contain small amounts of silver. Commercial-grade fine silver is at least 99.9% pure silver, and purities greater than 99.999% are available. In 2005, Peru was the top producer of silver with almost one-seventh world share, closely followed by Mexico, according to the British Geological Survey.

Notable characteristics

Silver is a very uranium during World War II (mainly because of the wartime shortage of copper). Another notable exception is in high-end audio cables, although the actual benefits of its use in this application are questionable.

Among metals, pure silver has the highest silver(II) fluoride: AgF₂) and +3 compounds (for example, potassium tetrafluoroargentate: K[AgF₄]) are also known.

Isotopes

Main article: isotopes of silver

Naturally occurring silver is composed of the two stable isotopes, ¹⁰⁷Ag and ¹⁰⁹Ag, with ¹⁰⁷Ag being the more abundant (51.839% natural abundance). Silver's standard atomic mass is 107.8682(2) u. Twenty-eight half-life of 41.29 days, ¹¹¹Ag with a half-life of 7.45 days, and ¹¹²Ag with a half-life of 3.13 hours.

All of the remaining radioactive isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 3 minutes. This element has numerous meta states, the most stable being ^108mAg (t_* 418 years), ^110mAg (t_* 249.79 days) and ^106mAg (t_* 8.28 days).

Isotopes of silver range in cadmium (element 48) isotopes.

The palladium Radiogenic ¹⁰⁷Ag was first discovered in the Santa Clara meteorite in 1978. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. ¹⁰⁷Pd–¹⁰⁷Ag correlations observed in bodies that have clearly been melted since the accretion of the solar system must reflect the presence of live short-lived nuclides in the early solar system.

Silver compounds

• Silver carbonate is used to remove carbon dioxide from the air.
• cement for glass.
• pH testing and potentiometric measurement.
• Silver fulminate is a powerful explosive.
• Silver iodide has been used in attempts to seed clouds to produce rain.
• antiseptic and in some chemical reactions.
• Silver sulfide, also known as silver whiskers, is formed when silver electrical contacts are used in an atmosphere rich in hydrogen sulfide.
• cathode) in watch batteries.

Applications

As a precious metal

A major use of silver is as a Argentium Sterling Silver is formed, with improved properties including resistance to firescale.

Silver is used in medals, denoting second place. Some high-end musical instruments are made from sterling silver, such as the flute.

In dentistry

The malleability and non-toxicity of silver make it useful in amalgams for dental fittings and fillings.

In photography and electronics

Photography used 24% of the silver consumed in 2001 in the form of halides, while 33% was used in jewellery, 40% for industrial uses, and only 3% for coins and medals.^[1]

Some electrical and electronic products use silver for its superior conductivity, even when tarnished. For example, printed circuits are made using silver paints,^[2] and computer keyboards use silver electrical contacts. Some high-end audio hardware (DACs, preamplifiers, etc.) are fully silver-wired, which is believed to cause the least loss of quality in the signal. Silver cadmium oxide is used in high voltage contacts because it can withstand arcing.

In solder and brazing

Silver is also used to make batteries. Silver in a thin layer on top of a bearing material can provide a significant increase in galling resistance and reduce wear under heavy load, particularly against steel.

In mirrors and optics

Mirrors which need superior reflectivity for visible light are made with silver as the reflecting material in a process called sputtering, silver (and sometimes gold) can be applied to glass at various thicknesses, allowing different amounts of light to penetrate. This is most often seen in architectural glass and tinted windows on vehicles.

As a catalyst

Silver's catalytic properties make it ideal for use as a polyesters)—a very important industrial reaction.

monolayers thickness. Such a membrane could be used to filter pure oxygen from air.

As money

Silver, in the form of bullion has the ISO currency code XAG.

The name of the United Kingdom monetary unit "pound" reflects the fact that it originally represented the value of one troy pound of sterling silver.

In the 1800s, many nations, such as the United States and Great Britain, switched from silver to a gold standard of monetary value, then in the 20th century to fiat currency.

In medicine

Silver ions and silver compounds show a toxic effect on some bacteria, viruses, algae and fungi, typical for heavy metals like mercury, but without the high toxicity to humans that is normally associated with them. Its germicidal effects kill many microbial organisms in vitro.

Hippocrates, the father of modern medicine, wrote that silver had beneficial healing and anti-disease properties, and the Phoenicians used to store water, wine, and vinegar in silver bottles to prevent spoiling. In the early 1900s people would put silver dollars in milk bottles to prolong the milk's freshness. Its germicidal effects increase its value in utensils and as jewellery. The exact process of silver's germicidal effect is still not well understood, although theories exist. One of these is the oligodynamic effect, which explains the effect on microbial lifeforms but does not explain certain antiviral effects.

Silver compounds were used successfully to prevent infection in World War I before the advent of silver sulfadiazine cream (SSD Cream)^[3] which was generally the "standard of care" for the antibacterial and antibiotic treatment of serious burns until the late 1990s. Now, other options, such as silver-coated dressings (activated silver dressings), are used in addition to SSD cream and may present advantages such as pain reduction and capacity for treatment at home.

The widespread use of silver went out of fashion with the development of modern antibiotics. However, recently there has been renewed interest in silver as a broad-spectrum antimicrobial. In particular, it is being used with alginate, a naturally occurring FDA has recently approved an endotracheal breathing tube with a fine coat of silver for use in mechanical ventilation, after studies found it reduced the risk of ventilator-associated pneumonia.^[7]

As a medication

Today, various kinds of silver compounds, or devices to make solutions or argyria over a period of months or years, and several cases have been documented in the last few years in the medical literature, including one possible case of coma associated with a high intake of silver (see medical references). It is strongly advised to notify a doctor when taking silver as a form of self-medication.

Silver is widely used in topical gels and is impregnated into bandages for wounds because of its wide-spectrum antimicrobial activity. Medical devices containing silver can be prescribed by a physician.

The anti-microbial properties of silver stem from the chemical properties of its ionized form, Ag+. This ion forms strong molecular bonds with other substances used by bacteria to respire, such as molecules containing oxygen.^[8] Once the Ag+ ion complexes with these molecules, they are rendered unusable by the bacteria, depriving it of necessary compounds and eventually leading to the bacteria's death.

In food

In India, foods, especially sweets, can be found decorated with a thin layer of silver known as vark. Silver as a food additive is given the food coloring. It is used solely for external decoration, such as on chocolate confectionery, in the covering of dragées and the decoration of sugar-coated flour confectionery. In Australia, it is banned as a food additive.

In clothing

  Silver inhibits the growth of bacteria and fungi. It keeps odour to a minimum and reduces the risk of bacterial and fungal infection. In clothing, the combination of silver and moisture movement (wicking) is the best combination to reduce the harmful effects of prolonged use in active and humid conditions.

Silver is used in clothing in two main forms:

• A form in which silver nanotechnology)
• A form in which the silver is physically coated onto the yarns.

In both cases the silver prevents the growth of a broad spectrum of bacteria and fungi. At the same time, silver is a very skin-friendly and highly compatible agent to which – unlike many antibiotics – bacteria rarely build up resistance.

Recorded use of silver to prevent infection dates to ancient Greece and Rome. It was rediscovered in the Middle Ages, where it was used for several purposes, such as to disinfect water and food during storage, and also for the treatment of burns and wounds as wound dressing. In the 19th century, sailors on long ocean voyages would put silver coins in barrels of water and wine to keep the liquid pure. Pioneers in America used the same idea as they made their journey from coast to coast. Silver solutions were approved in the 1920s by the US Food and Drug Administration for use as antibacterial agents. Today, wound dressings containing silver are well established for clinical wound care and have recently been introduced in consumer products such as sticking plasters.^{[citation needed]}

History

The word "silver" appears in Anglo-Saxon in various spellings such as seolfor and siolfor. A similar form is seen throughout the Teutonic languages (compare Old High German silabar and silbir). The symbol "Ag" is from the Latin for "silver", argentum (compare Greek αργυρος (argyros)), from the Indo-European root arg- meaning "white" or "shining".

Silver has been known since ancient times. It is mentioned in the book of Genesis, and slag heaps found in Asia Minor and on the islands of the Aegean Sea indicate that silver was being separated from lead as early as the 4th millennium BC.

Price

Main articles: Silver standard

Silver is currently about 1/50th the price of Free Silver to benefit the agricultural sector, which was among the most prolonged and difficult in that country's history and dominated public discourse during the latter decades of the nineteenth century.

Over the last 100 years the price of silver and the gold/silver price ratio have fluctuated greatly due to competing industrial and store-of-value demands. In 1980 the silver price rose to an all-time high of US$49.45 per troy ounce. By December 2001 the price had dropped to US$4.15 per ounce, and in May 2006 it had risen back as high as US$15.21 per ounce. As of 2006, silver prices (and most other metal prices) have been rather volatile, for example, quickly dropping from the May high of US$15.21 per ounce to a June low of US$9.60 per ounce before rising back above US$12.00 per ounce by August.^[9]

It is of note that in Judaic Law the price of silver is important. The lowest fiscal amount that a Jewish court, or Beth Din, can convene to adjudicate a case over is a shova pruta (value of a Babylonian prutra coin). This is fixed at 1/8 of a gram of pure, unrefined silver, at market price.

Folklore and popular culture

Because of the mysticism surrounding silver's lunar associations, as well as the aesthetic qualities of the white, reflective metal that cause it to be associated with purity, silver in European folklore has long been traditionally believed to be an antidote to various maladies and mythical monsters. Notably, silver was believed to be a repellent against vampires (this primarily originates from its holy connotations; also, mirrors were originally polished silver, and as such, vampires allegedly cannot be seen in them because they have no soul) and it was also believed that a werewolf, in his bestial form, could only be killed by a weapon or bullet made of silver. This has given rise to the term "silver bullet", which is used to describe things that very effectively deal with one specific problem.

In the Gospels, Jesus' disciple Judas Iscariot is infamous for having taken a bribe of silver from religious leaders in Jerusalem to turn Jesus Christ over to the Romans.

In heraldry, the tincture argent, in addition to being shown as silver (this has been shown at times with real silver in official representations), can also be shown as white. Occasionally, the word "silver" is used rather than argent; sometimes this is done across-the-board, sometimes to avoid repetition of the word "argent" in blazon.

Precautions

Silver plays no known natural biological role in humans, and possible health effects of silver are a subject of dispute. Silver itself is not toxic but most carcinogenic.

Silver and compounds containing silver (like argyria which results in a blue-grayish pigmentation of the skin, eyes, and mucous membranes. Although this condition does not harm a person's health, it is disfiguring and usually permanent. Argyria is rare, and mild forms are sometimes mistaken for cyanosis.

See also

• Precious metal
• Silver as an investment
• Silver coin
• Silver standard
• Silver mining
• Silver compounds

References

1. ^ Butterman, WC & Hilliard, HE (2005) Silver. Open file report 2004-1251. US Geological Survey mineral commodity profiles, Reston, Virginia.
2. ^ Los Alamos National Laboratory, Silver, accessed 12 Feb 2007.
3. ^ Te-Wen Chang and Louis Weinstein, "Prevention of Herpes Keratoconjunctivitis in Rabbits By Silver Sulfadiazine" Antimicrob Agents Chemother. 1975 December; 8(6): 677–678. PMID 429446
4. ^ AGC Flat Glass Europe launches world’s first antibacterial glass (2007-09-04).
5. ^ Samsung laundry featuring SilverCare Technology. Samsung. Retrieved on 2007-08-06.
6. ^ "Ultra-Fresh technology is based on the power of silver to fight bacteria". Express Textile.
7. ^ FDA Clears Silver-Coated Breathing Tube For Marketing (2007-11-08). Retrieved on 2007-11-11.
8. ^ Slawson, R. Van Dyke, M. Lee, H. Trevors "Germanium and Silver Resistance, Accumulation and Toxicity in Microorganisms" Plasmid 27, 72-79 (1992)
9. ^ Silver Cash daily plot. Barchart.com.