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1.INTRODUCTION
Silver (Ag) is a shining white metal which occurs in nature as in ores and as a free metal. It is
an element in group 11 of transition metals in the periodic table with a mass number of 108
and atomic number of 47.
Silver is a rare but naturally occurring metal, often found deposited as a mineral ore in
association with other elements. The ores are smelted to extract silver and use for different
applications. Silver found to be the metal with highest electrical conductivity. This led the
use of silver in high-tech electric equipment. And its tensile strength can be improved with byforming alloys to suit for different application such as dental fillings and replacement for
some internal parts of our body.
With the developments in science and technology, more uses of silver has been discovered
which are around as. Pure silver is converted to other compounds and used to make
photographic film. It is utilized in electrical and electronic equipment including specialized
batteries. It is also practiced as a medicine for some diseases. For making control rods in
nuclear reactors silver rods are applied as it absorbs neutrons. In some chemical reaction it is
being used as catalyst. And its endless uses continue.
Silver forms both soluble and insoluble salts by reacting with other non-metals. Ions of silver
are formed by dissolving in water or leach from the soil. The global biogeochemical
movements of silver are characterized by releases to the atmosphere, water, and land by
natural and manmade sources, long-range transport of fine particles in the atmosphere, wet
and dry deposition, and sorption to soils and sediments. It is a mildly toxic element to our
health.
As silver has played an important role in the past, it has become a significantly material in
todays life and will continue to be a vital element for future generation.
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2.DISCOVERY OF SILVER.No one actually knows exactly who discovered the chemical element silver or when and
where it was discovered, but there is evidence that it was known to the ancients. Silver was
probably first discovered after gold and copper. Archaeologists have found silver objects
dating to about 3400 B.C. in Egypt. The earliest known large-size mines were those of
Cappadocia in eastern Anatolia. The best-known of the ancient mines were located at the
Laurium silver-lead deposit in Greece and were actively mined from 500 BC to AD 100.
About 2500 B.C. the Chaldeans used a mining process called "cupellation" to extract silver
from lead-silver ores. Today the most common silver ores found are argentite (Ag2S);cerargyrite, or "horn silver" (AgCl); proustite (3Ag2S As2S3); and pyrargyrite (Ag2S
Sb2S3).
A significant discovery of silver ore occurred in 1492, and from 1500 to 1800 Bolivia, Peru
and Mexico supplied 85% of the world's silver. Rapidly developing technology from 1876 to
1920 contributed to exploitation of new worldwide silver supplies from Australia, Central
America and Europe to Canada, the U.S. and Africa.
Today, Peru is the worlds biggest silver mining country. In 2008, global silver mine
production reached a record high value of 680.9 Moz due to the increase in production in
Bolivia, Russia and Peru. Other leading countries in silver mining are Mexico, China,
Australia and Chile. Due to its unique properties, demand of silver is increasing.
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3.PHYSICAL PROPERTIES SILVER3.1. Introduction
Silver is a soft white, lustrous metal that is extremely malleable, ductile, and has the
highest electrical and thermal conductivities of all metals. It is relatively a stable
element which does not react with moist air or dry oxygen and does not react readily
with organic acids and bases.
3.2. ConductivitySilver has the highest electrical conductivity of all the other metals. As a result it is
considered as futures interconnect material for ultra large scale integrated (ULSI)
circuit technology.
In integrated circuit technologies, with the increase in multilayer metallization the
performance limiting resistive and capacitive signal delays increase accordingly. To
solve this problem, a low resistive metal has to be used. Since silver has the lowest
resistivity of all the metal, it suit for the job.
Fig.3.1. Resistivity of pure metals
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The electrical resistivity of metal films usually decreases during an annealing
treatment. This is because surface morphology of thin film metal affects the electrical
resistivity and surface morphology changes during annealing.
In the thin metal film, rough surfaces occur at the initial stage of agglomeration
process which begins at the grain boundary. During the initial stage of agglomeration
more source of conducting electrons are provided through the thin films thus
decreasing electrical resistivity. Void and island formation occurs in the final stage
which cause the reduction of conducting area thus prevent further decrease ofresistivity of silver.
Electron migration another fear identified as a primary failure mode of interconnects
lines used in semiconductor-integrated circuits. Silver as the most conductive metal,
has a better electromigration resistance when compare with aluminum but need to be
further improved since copper has a better electronmigration resistance.
Fig.3.2. Resistivity () of a 50-nm-thick silver film independence on the annealing
temperature T.
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3.3. StrengthMost commercially used silver has a tensile strength of 170 MPa in annealed
condition and when it is 50% cold worked, tensile strength increases to 296 MPa.
Commercially pure silver has 74 GPa of modulus of elasticity.
3.3.1. Silver in AmalgamsAn important application of silvers strength is alloying with tin to form silver-tin
amalgams used for dental filling. When amalgam is used for dental filling, it is
subjected to compression. Therefore to choose the appropriate different
composition of amalgams is subjected to compression strength at different
temperature.
Composition and Homogenization of Silver-Tin Alloys
AlloyTin
Composition(%)
HomogenizationPhaseTemperature
(C)Time
(Days)A 4.00 852 1(hr) B 8.00 765 4
C 12.00 550 7 +D 16.00 672 3 E 20.00 624 4 +F 24.00 392 14 +G 26.85 392 14 H 30.85 204 10 +Sn
The most successful amalgam alloys are formed at 25-27 percent range of silver-tinsystem. Ag3Sn intermetallic compound occurs within this range containing silver,
73.15 weight percent, and tin, 26.83 weight percent.
Table 3.1: Different composition of silver-tin alloy and its homogenization with
phase.
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The results show that compressive strength increased with increase in trituration
time, until a maximum strength is obtained that was not changed by further
trituration. From this it can be considered that increased trituration increases bond
strength in amalgamation.
When the composite has and phases, it shows less strength than others. And if
and phases were combined in same alloy, the strength increased with the addition
of . The phase alloy resulted in the strongest amalgam, probably due to less
volume of matrix and greater bond strength.
Fig.3.3. Relationship of amalgam compressive strength to alloy composition.
=0.5 minute; =1.0 minute; =2.0 minutes; =3.0 minutes.
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3.4. Phase diagram (copper-silver system)In copper-silver system, three phase regions are found: , and liquid. The phase
is a solid solution rich in copper with silver as the absolute component and an FCC
crystal structure. The phase solid also has an FCC structure, but copper is thesolute. Pure copper and pure silver are also considered to be and phases,
respectively.
In this phase diagram, the solubility of each of these solid phases is limited. Any
temperature below lineBEG, only a limited concentration of silver will dissolve in
copper (for the phase), and similarly for copper in silver (for the phase). The
solubility for phase in the region labeled as CBA, increase with increase in
temperature up to a maximum point atB (8.0 wt% Ag at 779C) and decrease back
to zero at meting temperature of pure copper, pointA (1085C).
The line separating the region and + is termed as solvus line and the line
between and +L is termed as solidus line. Both these lines also exist for
Fig.3.4. coppersilver binary phases diagram.
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phase,HG and GF, respectively as shown in the figure and the maximum solubility
ofcopper occur at point G (8.8 wt% Cu at 779 C).
As silver is added to copper, the temperature at which the alloys become totally
liquid decreases along the liquidus lineAE; decreasing the melting temperature ofcopper with addition of silver. Introduction of copper also reduces the melting
temperature of silver at line the liquidus line FE. The point at these liquidus lines
meet is known as invariant point (E).
Upon cooling a liquid phase is transformed into the two solid and phases at the
temperature TE and the opposite reaction occurs upon heating. This is called
eutectic reaction.
Important properties of silver
Description Value Units
Melting point 962 C
Thermal conductivity 4.29 W/cm CCoefficient of thermal expansion 18.6 x 10-6 cm/cm C
Specific heat 0.237 J/g mol
Specific gravity 10.5
Elastic modulus 71 GPa
Tensile strength (annealed) 152 Mpa
Electrical resistivity (commercially pure) 1.59 -m
Density 10.5 g/cc
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4.CHEMICAL PROPERTIES OF CLOUD ANDSILVER
4.1. IntroductionClouds are condensed water vapor in air. But clouds are not an inert mixture.
Particles that facilitate cloud formation have various chemical compositions and
the atmospheric gases around the droplet also can modify its chemical
composition.
Silver is a transition metal. It has 47 protons and the electron configuration is
[Kr]4d105s1. The number of neutrons varies with different isotopes of silver. The
two isotopes of silver that exist are 107Ag and 109Ag. It exhibit three oxidation
states, Ag (I), Ag (II) and Ag (III) and most common ions found are Ag+ and
Ag2+.
It does not react with air or pure water in normal condition. Silver reacts with
halides and acids to form its salts. It also acts as a catalyst in some chemical
reactions.
4.2. Cloud FormationCloud is formed from the water vapor that evaporates from sea, river lakes and
other sources. These vapors condense and form droplets or ice crystals. Particles
that allow the clouds formation are called Cloud Condensation Nuclei (CCN),
which have various chemical compositions according to their origin (from
human or natural source). Since clouds are surrounded by atmospheric gases, it
can also affect the chemical composition of cloud.
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4.2.1. The particle inside the dropletThe water soluble fraction of an aerosol governs its capacity to grow into a
droplet. The chemical composition of the particles that act as CCN determines the
initial composition of the cloud droplet, as its soluble content dissolves in the
condense water.
4.2.2. The atmospheric gases around the dropletWhether a chemical species stay in the gas phase or is absorbed in the water
droplet is estimated by considering the Henrys law equilibrium: A (aq) = HA PA,
where A (aq) is the aqueous phase concentration (mol/L), PA is the partial pressure
of A in the gas phase (atm), and HA is the Henrys law coefficient of the gas
considered. Some species go back to the gas phase and migrate away from the
drop; others, once captured, remain associated with the aqueous phase unless total
evaporation occurs.
Fig. 4.1. Four main processes occur within the cloud droplet: the CCN
composition and size can change after the droplet has evaporated (1); dissolution
of soluble content of the particle (2) and aqueous reactions inside the water
droplet (3); transfers between atmospheric gases and liquid phase (4).
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4.2.3. Reactions inside the droplet.Hundreds of chemical reactions take place in the droplet. They are effective in
changing the acidity of the precipitation, which may lead to acid rain. The main
chemical species that are involved in acid rain are sulfuric and nitric acids
All this complex chemistry in which a cloud is involved modifies the cloud itself
and the atmosphere around the cloud.
4.3. Reactions of SilverSilver does not react with clean air or water under normal condition.
4.3.1. Reaction with halides.Aqueous silver reacts with elements of group VII to form its salt.
Ag+(aq) + X-(aq) = AgX(s)
By reacting with silver and halides, various precipitate will be formed.
Ion present Observation
Cl White precipitate
Br Very pale cream precipitate
I Very pale yellow precipitate
4.3.2. Reaction with acids.Silver does not react with dilute sulphuric acid. But it dissolves in hot
concentrated sulphuric acid and produces its sulphate and hydrogen gas.
H2SO4 (aq) + Ag(s) = AgSO4(s) + H2 (g)
Silver metal also dissolves in dilute or concentrated nitric acid to give silver
nitrate and nitrogen dioxide. This method is use in manufacture of silver nitrate.
Ag(s) + 2HNO3 (aq) AgNO3 (aq) + NO2 (g) + H2O (l)
Table. 4.1. Different colors silver halogens.
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4.3.3. Reactions of Silver NitrateSilver nitrate reacts with hydroxide of group 1 metals to from solid silver
hydroxide and aqueous metal nitrate.
AgNO3 (aq) + NaOH (aq) = AgOH (s) + NaNO3 (aq)
When copper metal is dipped into a solution of silver nitrate, AgNO3, silver
crystals and a blue-green solution of copper nitrate is formed.
Cu(s) + 2 AgNO3(aq) Cu (NO3)2(aq) + 2 Ag (s)
Similar reaction takes place when metals of lead or zinc are used.
4.3.4.
Reaction with water.
Silver sulphides present in soil reacts with water and produce silver metal.
3 Ag2S + 2 H2O = 6 Ag + 2 H2S + SO2
4.3.5. Decomposing of silver nitrateOn heating, silver nitrate decomposes to give silver metal.
2AgNO32Ag +2NO2 +O2
4.3.6. Reaction with organic materials.Disilver Acetylide
Silver ions react with acetylene in solution to yield the acetylide compound,
Ag2C2.
2Ag(NH3)2NO3(aq) + C2H2(aq) = Ag2C2(cr) + 2NH4NO3(aq) + 2NH3(aq)
Silver Phenylacetylide
Phenylacetylide reacts with disilver acetylide to from silver phenylacetylide.
PhCCPh(s) + Ag2C2(s) = 2PhCCAg(s)
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Silver cyanide
Potassium cyanide reacts with silver nitrate to give a white precipitate of silvercyanide.
KCN + AgNO3 = AgCN + KNO3
Solid silver fulminate reacts with nitrogen gas to give solid silver cyanide anddinitrogen oxide.
AgCNO(s) + N2(g) = AgCN(s) + N2O(g)
Solid silver cyanide reacts with ammonia gas to produce complex of ammoniumsilver cyanide.
AgCN(s) + NH3(g) = AgCNNH3(s)
Alkylsilver complex
Alkylsilver complexes can be formed by the reaction of silver nitrate with
tetraalkyllead in alcoholic solution at a low temperature.
AgNO3 + R4Pb = AgR + R3PbNO3
The yellow precipitates of the formula RAg (R = methyl, ethyl, propyl ...) werestable at -80 C for several hours, but decompose to metallic silver and gaseous
hydrocarbons upon warming to room temperature.
4AgCnH2n+1 = 4Ag0 + CnH2n+2 + (CnH2n+1)2 + CnH2n
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Properties of silver atom
Description Value Units
Density 10.5 g/cc
Atomic radius 144 pmAtomic Volume 10.3 cc/mol
Covalent Radius 134 pm
Ionic Radius 89 (+2e) 126 (+1e)
Specific Heat (@20C) 0.237 J/g mol
Fusion Heat 11.95 kJ/mol
Evaporation Heat 254.1 kJ/mol
First Ionizing Energy 730.5 kJ/molOxidation States: 2, 1
Lattice Structure: Face-Centered Cubic
Lattice Constant ( ) 4.090
Table 4.2. Properties of silver atom and silver compound.
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5. PRODUCTION OF SILVER5.1. Introduction
Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that humanslearned to separate silver from lead by about 2000 BC and ever since used it for
jewelry and medium of exchange. Silver is produced from different ores and other
silver bearing compounds. Few ore bodies contain sufficient silver to justify
extraction for the silver alone. Three-fourths of all silver is produced as a by-
product of Pb, Zn, Cu, and Au mining. The most common silver-bearing
compounds are sulfides and chlorides.
5.2. Extraction of silver from lead ore using thiourea leaching solutionSilver can be extracted from silver lead ore by using thiourea [SC(NH2)2] leaching
from a pretreated Ag-Pb ore in an ammonia carbonate solution. The process of
pretreatment is carried out in a covered reactor under pure oxygen pressure.
During leaching with thiourea, silver is leached in to its solution. Silver is then
refined from this solution.
During leaching with thiourea, still some silver is not leached. This solid is treated
with Fluorosilicate solution which leaches the lead into solution, leaving silver in
it.
Fig.5.1. Principle flowsheet for processingof AgPb ore.
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5.3. Extraction from silver sulfate by electrolysisThe silver ore content subjected to leaching with HNO3. The nitric acid nitric
oxide formed is removed and solution is heated until dryness. This perocedure is
repeated with distilled water to obtain a neutral pH. NH3 is added to form silverion complexes.
Then the solution is treated with Na2SO3 and NaH2PO4. The pH of solution is then
decrease to 4.0 by adding H3PO4 solution followed by Na2S2O3 powder and
stirred. Temperature of solution is increased to 5060 C and keeps it to leach for
46 hours.
The solution is then transferred to electrolytic cell. Electrolysis is carried out usingplatinum electrode and silver that deposit on the anode is collected.
Overall reactions
During leaching
Ag2S + 4S2O2-
3 + 2SO2-
3 + 6H+ 2Ag(S2O3)
3-2 + 3S + 3H2O
During electrolysis
2Ag(S2O3)3-
2(aq) + e- Ag(s) + S2O3
2-(aq)
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6. APPLICATION OF SILVER AND SILVERCOMPOUNDS
6.1. IntroductionSilver is best known as precious metal used as jewelry and decoration in important
places. This is because of it is a rare metal which is chemically stable in normal
condition and shiny color. Other than as jewelry, there are many more uses of
silver.
6.2. Silver coinsSilver has been used as a medium of exchange since earliest recorded history, but
silver coinsthose minted by an authority either public or privatecame on the
scene in the eastern Mediterranean during 550 BC. By 269 BC, the Roman
Empire adopted silver as part of its standard coinage and it was used throughout
the trading world.
Today, other than collector's silver coins, silver bullion coins are popular among
people who desire to be cautious against currency inflation or store of value.Bullion coins are coins struck from precious metal and kept as a store of value or
an investment, rather than used in day-to-day commerce.
Description Year of introduction % purity
Canadian Silver Maple Leaf 1988 99.99%
Mexican Silver Libertad 1982 99.90%
Chinese Silver Panda 1983 99.90%
American Silver Eagle 1986 99.90%
Australian Silver Kookaburra 1990 99.90%
Australian Silver Kangaroo 1993 99.90%
British Silver Britannia 1997 95.80%
Austrian Silver Vienna Philharmonic 2008 99.90%
Russian George the Victorious 2009 99.90%
Table 6.1. Worlds most common silver bullions
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6.3. PhotographySilver-based photography is based on light striking sensitive silver-halide crystals
suspended on a film. Through use of chemical developers the differences in light
intensity form negative images which can then be processed into paper pictures byusing silver-imbedded paper. Approximately 5,000 color photographs can be
taken using one ounce of silver.
6.4. BatteryRechargeable and disposable batteries are manufactured with silver alloys as the
cathode or negative side. Silver is an expensive material to use in this application,
but it has higher efficiency when compare to batteries with other metals. The mostcommon of these batteries is the small button-shaped silver-oxide cell (used in
cameras, toys, hearing aids, watches and calculators) which is approximately 35
percent silver by weight.
In a silver-oxide cell, silver-oxide is used as the positive electrode and zinc as the
negative electrode with an alkaline electrolyte (usually sodium hydroxide or
potassium hydroxide). Inside the cell, silver ions in silver oxide reduce to solid
silver at the cathode and zinc oxidizes from metal to its ion at the anode. Thefollowing reaction takes place in the cell.
Zn + Ag2OKOH/NaOH ZnO + 2Ag
6.1. A typical silver oxide round cell.
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Due to environmental and safety concerns, silver-oxide batteries are beginning to
replace lithium-ion batteries in mobile phones and laptop computers. Silver-zinc
batteries feature a water-based chemistry and contain no lithium or flammable
liquids.
6.5. BearingSteel ball bearings electroplated with silver have greater fatigue strength and load
carrying capacity than any other type. These bearings are used in continuous,
heavy-duty applications such as in jet engines. Because steel has a poor
coefficient of friction, placing a layer of silver between the steel ball bearing and
the housing reduces friction between the two, increasing the performance andlongevity of the engine. Despite high internal temperatures, silver-coated bearings
provide superior performance and a critical margin of safety for engines. Even in
the event of an oil pump failure, silver-plated bearings provide enough lubrication
to allow a safe engine shut-down before more serious damage can occur.
6.6. Brazing and SolderingThe joining of two parts facilitated by introducing a second, low melting metal
between them is called brazing, when done at temperature above 600 C and
soldering when done at a lower temperature. During this process the parts do not
melt and produce strong, leak-tight, corrosion-resistant joint with high tensile
strength, ductility and thermal conductivity. Silver brazing alloys are used widely
in applications ranging from air-conditioning and refrigeration to electric power
distribution. It is also used in the automobile and aerospace industries.
Silver-tin solders are used for bonding copper pipe, where they not only eliminate
the use of harmful lead-based solders, but also provide the piping with silvers
natural antibacterial action. In refrigerator, silver-based bonding materials are
used to provide the ductility required for constant changes in temperature of the
cooling tubes.
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6.7. CatalystA catalyst is a substance that allows or facilitates a chemical process chemically
without involve in the reaction. Silver, because of its unique chemical properties,
has become an increasingly important catalyst for many industrial processes.
Every year over 700,000 kg of silver is being used in catalytic reactions and
approximately 90% of these are used in the production of ethylene oxide from
ethylene. Ethylene oxide is the foundation for flexible plastics such as polyester
textiles, used to make all types of clothing and a variety of specialty fabrics. It is
also used for molded items such as insulating handles for stoves, key tops for
computers, electrical control knobs, domestic appliance components, andelectrical connector housings. About 25% of ethylene oxide production is used to
manufacture antifreeze coolant for automobiles and other vehicles.
Formaldehyde, a chemical produced from methanol, is the building block of solid
plastics including adhesives, laminating resins for construction plywood and
particle board. Formaldehyde also helps to produce finishes for paper and
electronic equipment, textiles, surface coatings that resist heat and scratches,
dinnerware and buttons, casings for appliances, handles and knobs, packaging
materials, automotive parts, thermal and electrical insulating materials, toys and
many other products
Silver is a recognized powerful oxidizer. Metallurgists have long known the
unique affinity of silver with oxygen. Molten silver will hold ten times its volume
in oxygen. On freezing, the contraction of silver vigorously ejects the oxygen; a
dangerous activity known as spitting. Not all oxygen is ejected; much is retainedin the silver lattice as well as adhered to its surface.
6.8. ElectronicsBecause of silvers excellent electrical conductivity, it finds many applications in
electronics from printed circuit boards to switches and TV screens.
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Silver membrane switches, which require only a light touch, are used in buttons
on televisions, telephones, microwave ovens, childrens toys and computer
keyboards. These switches are highly reliable and last for millions of on/off
cycles. Silver is also used in conventional switches likes those used for controlling
room lights.
For printed circuit boards, used in consumer items from mobile phones to
computers, silver-based inks and films are applied to composite boards to
create electrical pathways. In similar fashion, silver-based inks produce so-called
RFID tags (radio frequency identification) antennas used in hundreds of millions
of products to prevent theft and allow easy inventory control.
Silver is also used to coat Compact Disks (CDs) and Digital Video Disks (DVDs).
In addition, silver is employed in Plasma Display Panels used in television sets
and monitors.
6.9. Medical ApplicationsSilvers anti-bacterial powers have been known for centuries and have been tested
and proven scientifically. For example, the ancient knew that water, wine orvinegar kept in silver vessels stayed fresh during long sea voyages.
Scientists have discovered that silver interrupts a bacteria cells ability to form
chemical bonds essential to its survival. These bonds produce the cells physical
structure so bacteria in the presence of silver literally fall apart. Cells in humans
and other animals have thick walls and are not disturbed by silver. Therefore,
silver prevents bacteria growth but is harmless to humans.
One of the most important uses of silver as a biocide is in hospitals and other
health care facilities because they grapple with MRSA (Methicillin-resistant
Staphylococcus aureus), a type of life-threatening Staph germ. MRSA is resistant
to almost all chemical antibiotics; therefore many hospitals are employing silver-
imbedded equipment including surgical tools, catheters, needles, stethoscopes,
furniture, door handles and even paper files.
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One of the most promising applications is in silver-imbedded bandages for burn
and wound victims. The silver ions help prevent infection but also speed healing
because the body doesnt have to focus its energy on fighting infection.
Currently were seeing a surge of applications for silver-based biocides in all
areas: industrial, commercial and consumer. New products are being introduced
almost daily. The newest trend is the use of nano-silver particles to deliver silver
ions.
6.10.Mirror and CoatingsWhen polished, silver offers nearly a perfect reflectivity which makes it ideal for
energy-efficient windows. An extremely thin, transparent coating of silver on
window panes reflects the hot, summer sun and deflects inward the rooms own
internal heat. So-called low E squared double pane windows reflect away almost
95 percent of the hot rays of the sun, offering household energy savings.
Silver halide crystals melted into the glass can change light transmission from 96
percent to 22 percent in less than 60 seconds and block at least 97 percent of the
sun's ultraviolet rays.
Another increasing use of silver is in paints. Silver ions offer an anti-bacterial
shield that keeps the coating germ and fungus free. This is particularly important
in health care facilities, jails, schools, food and beverage factories and other places
in which bacteria growth can be dangerous to health.
6.11.Solar EnergyAs the price of fossil fuels rises, scientists and engineers are more interested in
solar cells to produce electricity.
Silver paste is used in 90% of all crystalline silicon photovoltaic cells, which are
the most common types of solar cell. Photovoltaic systems are simple and provide
immediately useful power with no pollution.
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Silver is used in another way to generate electricity by reflecting and
concentrating solar energy onto collectors containing salts which are used to run
generators. In California, for example, 1,926 silver-coated mirrors reflect solar
heat onto black-coated stainless steel tubes at 300-foot tower. This heats the tubes
and the nitrate salt inside them to over 1050 F. The scalding hot salt is then
piped to boilers, turning water to steam which drives steam turbines that run
electric generators. They generate electricity to power 10,000 homes.
6.12.Water PurificationAs silver ions prevent bacteria and algae growth, silver is employing in
purification systems in hospitals, small community water systems pools etc. byusing silver in purification process, it has replaces the traditional methods of
germ-killing methods that employ harsh and dangerous chemicals.
In building water supply systems, silver ions can destroy Legionnaires disease,
which is caused by bacteria building up in pipes, connections and water tanks. In
pools and spas, silver ions, usually held in canisters within filters, are activated by
water to spread a biocide blanket to all components, keeping the water pure and
disease free.
With several different methods of water purification in the tube, often including a
charcoal filter, silvers role is to prevent the growth of bacteria and fungi that
could overwhelm the system and render it useless.
6.13.Making RainSometimes in cloudy days, it does rain. This happen because the droplets are two
small and light to fall under gravity and they are stable, that is to say they do not
become large enough to fall. Rain falls when the droplets freeze to ice so that it
will be a stable nucleus which grows by attracting water vapors from surrounding
droplets. The ice particle then grows to a size which gravity can pull it down, and
it falls as rain.
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The difficult stage in rain formation is getting the ice to nucleate it. If the water
droplets are clean, then the any nucleation catalysts. In this situation the only
nucleation agent is ice which can be formed at a very low temperature (about -40
C). Industrial dusts and smokes also do the nucleation.
Crystal of ice and crystal of silver has hexagonal structure with similar lattice
constants (H20; a = 0.452 nm, AgI; a = 0.458 nm). If silver iodide is put into super
cooled water, it can act as nucleation agent. More ice can grow on it easily, at a
low under cooling. This makes silver iodide a perfect material for artificial rain
maker.
In artificial rainmaking silver iodide, in the form of a very fine powder of crystals,
is either dusted into the cloud from a plane flying above it, or is shot into it with a
rocket from below. The powder seeds ice crystals which grow and start to fall,taking the silver iodide with them. But when it starts to fall, it leaves tiny
fragments of ice to seed next lot of crystals, thus self-catalyzing.
Fig. 6.2. Rain falls when the water droplets in clouds turn to ice. When dust
particles are present they can catalyze nucleation at temperatures quite close to
0C. This is why there is often heavy rainfall downwind of factory chimneys.
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7.SILVER IN ENVIRONMENT
7.1. IntroductionSilver and its ions are considered mildly toxic. Higher concentration of silver in
may cause danger to life in the environment.
Seawater contains approximately 2-100 ppt of silver, and the surface
concentration may be even lower. River water generally contains approximately
0.3-1 ppb of silver. The phytoplankton concentration is 0.1-1 ppm (dry mass),leading to a 104-105 bio concentration factor in seawater. In oyster tissue
concentrations of approximately 890 ppm (dry mass) were found. Dissolved in
water silver mainly occurs as Ag+ (aq), and in seawater as AgCl2 (aq).
Under normal conditions silver is water insoluble. This also applies to a number of
silver compounds, such as silver sulphide. For example, silver chloride has a
water solubility of 0.1 mg/L, maximum. Silver nitrate has a water solubility of
2450 g/L. Silver fluorides are generally water soluble, but other silver halogens
are not.
7.2. Source of SilverThe main source of silver contamination of water is silver thiosulfate complexes
in photographic developing solutions that photofinishers discard directly to
sewers. During waste treatment, most of the silver thiosulfate complexes are
converted to insoluble silver sulfide and forms some metallic silver. Silver on
suspended matter and in colloidal forms and insoluble salts ultimately settles out
in the sediments. At the water treatment plant, most of the silver is precipitated
after treatment with lime or adsorbed after treatment with alum flocculant.
Chlorination converts some silver to silver chloride or to a soluble silver chloride
complex. Aerobic biodegradation of a photoprocessing wastewater containing
1.85 mg total silver/liter did not adversely affect the activated sludge process.
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When fresh sludge and aerobically digested sludge solids is subjected to leaching
procedures, the silver concentration increases in water.
Forms of silver in atmospheric emissions are mostly silver sulfide, silver sulfate
(Ag2SO4), silver carbonate (Ag2CO3), silver halides, and metallic silver. About
50% of the silver released into the atmosphere from industrial operations is
transported more than 100 km and is eventually deposited in precipitation.
Emissions of silver from coal-fired power plants may lead to accumulations in
nearby soils. Silver in soils is largely immobilized by precipitation to insoluble
salts and by complexation or adsorption to organic matter, clays, and manganese
and iron oxides.
7.3. Effects to EnvironmentSensitive marine algae accumulates silver from water containing as little as 2 g
silver/liter (as silver nitrate) to whole-cell burdens as high as 58 mg silver/kg dry
weight. Uptake of silver by phytoplankton is rapid but proportional to silver
concentration, and inversely proportional to water salinity. Silver once integrated
with phytoplankton does not lose even if the salinity increases since it is tightlybound to the cell membrane. The ability to accumulate dissolved silver varies
widely between species. Silver accumulation is higher in marine species through
dissolved silver ions. At concentrations normally encountered in the environment,
food-chain biomagnifications of silver in aquatic systems is unlikely.
Silver inhibits enzymes for the phosphorus, sulfur, and nitrogen cycles of
nitrifying bacteria in soil thus effecting the plant growth. The concentration of
silver also can affect the germination process of the seeds. In some birds,
increasing silver concentration reduce their growth rate. In wild mammal, silver
accumulates in liver and kidneys which result in damaging the kidney.
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7.4. Health Effects of SilverSilver is not a dietary requirement for humans. The body of an adult contains
approximately 2 mg of silver. From a daily intake of 20-80 g silver,
approximately 10% is absorbed which are not health threatening. However, a
higher concentration of silver ions may be toxic due to its high affinity for sulhur
hydryl and amino groups thus the process of complexation occurs with amino
acids, nucleic acid and other compounds in the body.
Silver that ends up in the body is generally deposited in connective tissue, skin
and eyes and causes a gray to black colouring. Within 50 years, one is able to
accumulate approximately 9 mg of silver. Silver oxide is harmful uponswallowing, because it irritates the eyes, respiratory tract and skin. Silver nitrate is
much more harmful, because it is a strong oxidant. It causes corrosion and at oral
uptake it leads to vomiting, dizziness and diarrhoea.
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8.SILVER AND ISLAM8.1. Introduction
Silver as precious metal can be used in different application. It is used as
jewellery, sanitary applications and some fixtures. In Islam, these applications are
given different judgments. Therefore being a Muslim one have to follow the path
shown in Islam. In this section, I try to explain those ruling in light of Quran and
sunnah of Messenger of Allaah (peace and blessings of Allaah be upon him).
8.2.
Silver Jewellery
Silver and other kinds of jewelleries are allowed to Muslim women as adornment.
But for men there are limitations in using jewelleries. Wearing gold is haraam for
men. Men are permissible to wear rings of silver and there is nothing wrong with
it.
Anas (may Allaah be pleased with him) said: When the Prophet (peace and
blessings of Allaah be upon him) wanted to send a letter to the Romans, he wastold that they would not read any letter unless it had a seal on it, so he took a ring
of silver. It is as if I can see it shining on his hand, and engraved on it were the
words Muhammad the Messenger of Allaah. (Narrated by al-Bukhaari, 5537;
Muslim 2092).
Shaykh al-Islam (Ibn Taymiyah) was asked about men wearing silver, and he said:
As for rings of silver, this is permissible according to the consensus of the
imaams, for it was reported that the Prophet (peace and blessings of Allaah be
upon him) had a ring of silver and that his companions wore rings. This is unlike
gold rings, which are forbidden according to the consensus of the four imaams. It
was reported that the Prophet (peace and blessings of Allaah be upon him) forbade
that. As for wearing silver, there is no general statement that it is forbidden, and
no one has the right to say that it is forbidden if there is no shari evidence (daleel)
to that effect. As the Sunnah permits wearing silver rings, this is evidence thatwearing silver is permissible
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Wearing chains and adornments on the wrist and neck, and on the ears, is an
imitation of women, as this is something that is only for women and there is no
report which says that it is permissible for men to wear chains made of silver. So
it is not allowable for men to wear bracelets, earrings, anklets, or chains.
Ibn Abbaas (may Allaah be pleased with him) reported that The Messenger of
Allaah (peace and blessings of Allaah be upon him) cursed men who make
themselves look like women and women who make themselves look like men.
(Reported by al-Bukhaari, 5435).
8.3. Silver as a ValuableSilver has been mentioned in Quran as a valuable and medium of exchange. Our
Prophet Muhammad (sallalahu alaihi wa sallam) also explains the status of silver
while establishing the basics of Islamic economic system.
Ab Sad al-Khudri reported Allahs Messenger as saying: Gold for gold, silver
for silver, wheat for wheat, barley for barley, dates for dates, and salt for salt.
(When a transaction is) like for like, payment being made on the spot, then if
anyone gives more or asks for more, he has dealt in Rib, the receiver and thegiver being equally guilty. (Sahh, Muslim)
The above Hadth of Prophet Muhammad (sallalahu alaihi wa sallam) has very
clearly established money in Islam to be either precious metals such as gold and
silver, or other commodities such as wheat, barley, dates and salt which are
commodities of regular consumption as food but which have a shelf-life.
In Quran, silver was referred as Dirham and gold as Dinar.
And they sold him for a few measly Dirhams and they did so because they
considered him to be of little worth. (Ysuf, 12:20)
In this verse of the Qurn Allah Most High has referred to money as silver
coins (Dirhams).
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There are other verses of the Quran that also refer to gold and silver as wealth.
Beautified for mankind is love of the joys (that come) from women and
offspring; and stored-up heaps of gold and silver (i.e., heaps of Dinars and
Dirhams), and horses branded (with their mark), and cattle and land. That is
comfort of the life of the world. Allah! With Him is a more excellent abode.
(le Imrn, 3:14)
O ye who believe! Lo! Many of the (Jewish) rabbis and the (Christian) monks
devour the wealth of mankind wantonly and debar (men) from the way of Allah.
They who hoard up gold and silver and spend it not (this would obviously be in
the context of use of gold and silver as money) in the way of Allah, unto them
give tidings (O Muhammad) of a painful doom. (Al-Tauba, 9:34)
"And if you wish to have (one) wife in place of another and you have given one of
them a Qintr (i.e., a treasure of gold and silver coins), then take not from it
anything; would you take it by slandering (her) and (doing her) manifest wrong?
(Al-Nis, 4:20)
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The Quran had revealed the amazing news that gold and silver would keep up
their status as objects of great value in the next world as well.
Their raiment will be fine green silk embroidered in gold. Bracelets of silver will
they wear. Their Lord will quench their thirst with a drink (sparkling) with
purity. [This verse, as well as others that follow, reveal that gold and silver will
remain precious and valuable in the hereafter as well.] (Al -Insn, 76:21)
8.4. Silver VesselsVessels of gold and silver are forbidden according to the texts of Islam and
according to scholarly consensus. It was proven that the Messenger of Allaah
(peace and blessings of Allaah be upon him) said: Do not drink from vessels of
gold and silver; do not eat from plates of gold and silver, because they are forthem in this world and for you in the Hereafter. (Saheeh, agreed upon; from the
hadeeth of Hudhayfah may Allaah be pleased with him). And it was proven that
he (peace and blessings of Allaah be upon him) said: Whoever eats and drinks
from vessels of gold and silver, is taking fire from Hell into his belly. (Saheeh,
agreed upon; from the hadeeth of Umm Salamah, may Allaah be pleased with
him; this version was narrated by Muslim).
It is not permissible to use gold and silver as vessels, whether for eating or
drinking. All of that is prohibited according to the hadeeth of the Messenger of
Allaah (peace and blessings of Allaah be upon him). It is not permissible to use
them in spoons, coffee cups or teacups; all of that is forbidden, because these are
kinds of vessels.
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8.5. Zakaah on SilverThe scholars are agreed that zakaah is obligatory on gold and silver jewellery if it
is a kind of adornment that it is haraam forbidden to use, or if it is prepared for
trading etc. But if it is a permissible kind of jewellery that is intended to be usedor loaned, such as a silver ring or womens jewellery, or things that it is permitted
to use to adorn weapons, then there is a difference of scholarly opinion as to
whether zakaah is obligatory on these things.
And those who hoard up gold and silver (Al-Kanz: the money, the Zakaah of
which has not been paid) and spend them not in the way of Allaah, announce unto
them a painful torment (al-Tawbah 9:34)
Al-Qurtubi said, in his tafseer of this aayah: Ibn Umar explained the meaning ofthis in Saheeh al-Bukhaari, when a Bedouin said to him, Tell me about the aayah
(interpretation of the meaning), And those who hoard up gold and silver. Ibn
Umar said: (It means) the one who stockpiles them and does not pay zakaah on
them woe to him. This was before (the order to pay) zakaah on them was
revealed, and when it was revealed, Allaah made it a means of purification of
wealth. (Narrated by al-Bukhaari, 2/111, taleeqan; 5/204, also taleeqan. Ibn
Maajah, 1/569-570, no. 1787. Al-Bayhaqi, 4/82).
Zakat is obligatory on
The free, adult sane Muslim, When he possesses the nisab with complete possession, and A [lunar] year has passed over it.
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Zakat Nisab
1. There is no charity [obligatory] on any [silver] less than 200 dirhams.2. Then, if it is 200 dirhams, and a [lunar] years passes over it, 5 dirhams are due
for it.
3. There is nothing due on the excess until it reaches 40 dirhams, and then 1dirham is due for it. [Similarly] for every 40 dirhams, there is 1 dirham . Abu
Yusuf and Muhammad said: Whatever exceeds 200 [dirhams] its zakat is in
proportion.
4. If the silver is dominant in silver coins, then their ruling is that of silver. But,if alloy is dominant then their ruling is that of trade goods, and its reaching
nisab is taken into account.
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9. CONCLUSION
Silver is precious metal with long history. With its discovery unknown, silver had
been used by ancient Egyptians during the time Pharaoh for decorations and
jewelries.
Silver is an important metal not because of its price or its brightness. It is important
to us due to different application its can be used and the achievement we have
made in science and technology with the help of silver. It made our life easy and
comfortable.
Because of its unique properties, silver is most preferred metal for high-tech
industries. Due to high conductivity, it is preferred to use in electronics and heat
transmitting appliance. Due to the unique chemical and biological properties, it is
perfect for medical functions. With these properties, scientists and researchers are
still trying to find more about silver.
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10. REFERENCE
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