Реферат: Aluminium
Реферат: Aluminium
Review
Aluminium
Content
1. Introduction
2.
Characteristics
3. Isotopes
4. Natural
occurrence
5. Production
and refinement
6. Recycling
7. Chemistry
7.1 Oxidation
state +1
7.2 Oxidation
state +2
7.3 Oxidation
state +3
7.4 Analysis
8.
Applications
8.1 General
use
8.2 Aluminium
compounds
8.3 Aluminium
alloys in structural applications
8.4 Household
wiring
9. History
10. Etymology
10.1
Nomenclature history
10.2
Present-day spelling
11. Health
concerns
12. Effect on
plants
13. Conclusion
14. References
1.
Introduction
Aluminium
is a silvery white and ductile member of the boron group of chemical elements.
It has the symbol Al; its atomic number is 13. It is not soluble in water under
normal circumstances. Aluminium is the most abundant metal in the Earth's
crust, and the third most abundant element therein, after oxygen and silicon.
It makes up about 8% by weight of the Earth’s solid surface. Aluminium is too
reactive chemically to occur in nature as a free metal. Instead, it is found
combined in over 270 different minerals.[4] The chief source of aluminium is
bauxite ore.
Aluminium
is remarkable for its ability to resist corrosion due to the phenomenon of
passivation and for the metal's low density. Structural components made from
aluminium and its alloys are vital to the aerospace industry and very important
in other areas of transportation and building. Its reactive nature makes it
useful as a catalyst or additive in chemical mixtures, including being used in
ammonium nitrate explosives to enhance blast power.
General
properties
Name,
symbol, number aluminium, Al, 13
Element
category other metal
Group,
period, block 13, 3, p
Standard
atomic weight 26.9815386(13) g·mol−1
Electron
configuration [Ne] 3s2 3p1
Electrons
per shell 2, 8, 3 (Image)
Physical
properties
Phase
solid
Density
(near r.t.) 2.70 g·cm−3
Liquid
density at m.p. 2.375 g·cm−3
Melting
point 933.47 K, 660.32 °C, 1220.58 °F
Boiling
point 2792 K, 2519 °C, 4566 °F
Heat
of fusion 10.71 kJ·mol−1
Heat
of vaporization 294.0 kJ·mol−1
Specific
heat capacity (25 °C) 24.200 J·mol−1·K−1
Vapor
pressure
P/Pa
1 10 100 1 k 10 k 100 k
at
T/K 1482 1632 1817 2054 2364 2790
Atomic
properties
Oxidation
states 3, 2[1], 1[2]
(amphoteric
oxide)
Electronegativity
1.61 (Pauling scale)
Ionization
energies
(more)
1st: 577.5 kJ·mol−1
2nd:
1816.7 kJ·mol−1
3rd:
2744.8 kJ·mol−1
Atomic
radius 143 pm
Covalent
radius 121±4 pm
Van
der Waals radius 184 pm
Miscellanea
Crystal
structure face-centered cubic
Magnetic
ordering paramagnetic[3]
Electrical
resistivity (20 °C) 28.2 nΩ·m
Thermal
conductivity (300 K) 237 W·m−1·K−1
Thermal
expansion (25 °C) 23.1 µm·m−1·K−1
Speed
of sound (thin rod) (r.t.) (rolled) 5,000 m·s−1
Young's
modulus 70 GPa
Shear
modulus 26 GPa
Bulk
modulus 76 GPa
Poisson
ratio 0.35
Mohs
hardness 2.75
Vickers
hardness 167 MPa
Brinell
hardness 245 MPa
CAS
registry number 7429-90-5
2.
Characteristics
Aluminium
is a soft, durable, lightweight, malleable metal with appearance ranging from
silvery to dull grey, depending on the surface roughness. Aluminium is nonmagnetic
and nonsparking. It is also insoluble in alcohol, though it can be soluble in
water in certain forms. The yield strength of pure aluminium is 7–11 MPa, while
aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa.[5]
Aluminium has about one-third the density and stiffness of steel. It is
ductile, and easily machined, cast, drawn and extruded.
Corrosion
resistance can be excellent due to a thin surface layer of aluminium oxide that
forms when the metal is exposed to air, effectively preventing further
oxidation. The strongest aluminium alloys are less corrosion resistant due to
galvanic reactions with alloyed copper.[5] This corrosion resistance is also
often greatly reduced when many aqueous salts are present however, particularly
in the presence of dissimilar metals.
Aluminium
atoms are arranged in a face-centred cubic (fcc) structure. Aluminium has a
stacking-fault energy of approximately 200 mJ/m².[6]
Aluminium
is one of the few metals that retain full silvery reflectance in finely
powdered form, making it an important component of silver paints. Aluminium
mirror finish has the highest reflectance of any metal in the 200–400 nm (UV)
and the 3000–10000 nm (far IR) regions, while in the 400–700 nm visible range
it is slightly outdone by tin and silver and in the 700–3000 (near IR) by
silver, gold, and copper.[7]
Aluminium
is a good thermal and electrical conductor, by weight better than copper.
Aluminium is capable of being a superconductor, with a superconducting critical
temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.[8]
3.
Isotopes
Aluminium
has nine isotopes, whose mass numbers range from 23 to 30. Only 27Al (stable
isotope) and 26Al (radioactive isotope, t1/2 = 7.2 × 105 y) occur
naturally; however, 27Al has a natural abundance of 99.9+ %. 26Al is produced
from argon in the atmosphere by spallation caused by cosmic-ray protons.
Aluminium isotopes have found practical application in dating marine sediments,
manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The
ratio of 26Al to 10Be has been used to study the role of transport, deposition,
sediment storage, burial times, and erosion on 105 to 106 year time scales.[9]
Cosmogenic 26Al was first applied in studies of the Moon and meteorites.
Meteoroid fragments, after departure from their parent bodies, are exposed to
intense cosmic-ray bombardment during their travel through space, causing
substantial 26Al production. After falling to Earth, atmospheric shielding
protects the meteorite fragments from further 26Al production, and its decay
can then be used to determine the meteorite's terrestrial age. Meteorite
research has also shown that 26Al was relatively abundant at the time of
formation of our planetary system. Most meteorite scientists believe that the
energy released by the decay of 26Al was responsible for the melting and
differentiation of some asteroids after their formation 4.55 billion years
ago.[10]
4.
Natural occurrence
In
the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic
element and the third most abundant of all elements (after oxygen and
silicon).[11] Because of its strong affinity to oxygen, however, it is almost
never found in the elemental state; instead it is found in oxides or silicates.
Feldspars, the most common group of minerals in the Earth's crust, are
aluminosilicates. Native aluminium metal can be found as a minor phase in low
oxygen fugacity environments, such as the interiors of certain volcanoes.[12]
It also occurs in the minerals beryl, cryolite, garnet, spinel and
turquoise.[11] Impurities in Al2O3, such as chromium or cobalt yield the
gemstones ruby and sapphire, respectively. Pure Al2O3, known as Corundum, is one
of the hardest materials known.[11]
Although
aluminium is an extremely common and widespread element, the common aluminium
minerals are not economic sources of the metal. Almost all metallic aluminium
is produced from the ore bauxite (AlOx(OH)3-2x). Bauxite occurs as a weathering
product of low iron and silica bedrock in tropical climatic conditions.[13]
Large deposits of bauxite occur in Australia, Brazil, Guinea and Jamaica but
the primary mining areas for the ore are in Ghana, Indonesia, Jamaica, Russia
and Surinam.[14] Smelting of the ore mainly occurs in Australia, Brazil,
Canada, Norway, Russia and the United States. Because smelting is an
energy-intensive process, regions with excess natural gas supplies (such as the
United Arab Emirates) are becoming aluminium refiners.
5.
Production and refinement
Although
aluminium is the most abundant metallic element in the Earth's crust, it is
rare in its free form, occurring in oxygen-deficient environments such as
volcanic mud, and it was once considered a precious metal more valuable than
gold. Napoleon III, emperor of France, is reputed to have given a banquet where
the most honoured guests were given aluminium utensils, while the other guests
had to make do with gold.[15][16] The Washington Monument was completed, with
the 100 ounce (2.8 kg) aluminium capstone being put in place on December 6,
1884, in an elaborate dedication ceremony. It was the largest single piece of
aluminium cast at the time. At that time, aluminium was as expensive as
silver.[17] Aluminium has been produced in commercial quantities for just over
100 years.
Aluminium
is a strongly reactive metal that forms a high-energy chemical bond with
oxygen. Compared to most other metals, it is difficult to extract from ore,
such as bauxite, due to the energy required to reduce aluminium oxide (Al2O3).
For example, direct reduction with carbon, as is used to produce iron, is not
chemically possible, since aluminium is a stronger reducing agent than carbon.
However there is an indirect carbothermic reduction possible by using carbon
and Al2O3 which forms an intermediate Al4C3 and this can further yield aluminum
metal at a temperature of 1900-2000°C. This process is still under development.
This process costs less energy and yields less CO2 than the Hall-Héroult
process.[18] Aluminium oxide has a melting point of about 2,000 °C. Therefore,
it must be extracted by electrolysis. In this process, the aluminium oxide is
dissolved in molten cryolite and then reduced to the pure metal. The
operational temperature of the reduction cells is around 950 to 980 °C.
Cryolite is found as a mineral in Greenland, but in industrial use it has been
replaced by a synthetic substance. Cryolite is a chemical compound of
aluminium, sodium, and calcium fluorides: (Na3AlF6). The aluminium oxide (a
white powder) is obtained by refining bauxite in the Bayer process of Karl
Bayer. (Previously, the Deville process was the predominant refining
technology.)
The
electrolytic process replaced the Wöhler process, which involved the reduction
of anhydrous aluminium chloride with potassium. Both of the electrodes used in
the electrolysis of aluminium oxide are carbon. Once the refined alumina is
dissolved in the electrolyte, its ions are free to move around. The reaction at
the cathode is:
Al3+
+ 3 e− → Al
Here
the aluminium ion is being reduced. The aluminium metal then sinks to the
bottom and is tapped off, usually cast into large blocks called aluminium
billets for further processing.
At
the anode, oxygen is formed:
2
O2− → O2 + 4 e−
This
carbon anode is then oxidized by the oxygen, releasing carbon dioxide:
O2
+ C → CO2
The
anodes in a reduction cell must therefore be replaced regularly, since they are
consumed in the process.
Unlike
the anodes, the cathodes are not oxidized because there is no oxygen present,
as the carbon cathodes are protected by the liquid aluminium inside the cells.
Nevertheless, cathodes do erode, mainly due to electrochemical processes and
metal movement. After five to ten years, depending on the current used in the
electrolysis, a cell has to be rebuilt because of cathode wear.
World
production trend of aluminiumAluminium electrolysis with the Hall-Héroult
process consumes a lot of energy, but alternative processes were always found
to be less viable economically and/or ecologically. The worldwide average
specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram
of aluminium produced (52 to 56 MJ/kg). The most modern smelters achieve approximately
12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction, 31 MJ/kg, and
the Gibbs free energy of reaction, 29 MJ/kg.) Reduction line currents for older
technologies are typically 100 to 200 kA; state-of-the-art smelters[19] operate
at about 350 kA. Trials have been reported with 500 kA cells.
Electric
power represents about 20% to 40% of the cost of producing aluminium, depending
on the location of the smelter. Smelters tend to be situated where electric
power is both plentiful and inexpensive, such as South Africa, Ghana, the South
Island of New Zealand, Australia, the People's Republic of China, the Middle
East, Russia, Quebec and British Columbia in Canada, and Iceland.[20]
Aluminium
output in 2005In 2005, the People's Republic of China was the top producer of
aluminium with almost a one-fifth world share, followed by Russia, Canada, and
the USA, reports the British Geological Survey.
Over
the last 50 years, Australia has become a major producer of bauxite ore and a
major producer and exporter of alumina.[21] Australia produced 62 million
tonnes of bauxite in 2005. The Australian deposits have some refining problems,
some being high in silica but have the advantage of being shallow and
relatively easy to mine.[22]
Aluminium
is a strongly reactive metal that forms a high-energy chemical bond with
oxygen. Compared to most other metals, it is difficult to extract from ore,
such as bauxite, due to the energy required to reduce aluminium oxide (Al2O3).
For example, direct reduction with carbon, as is used to produce iron, is not
chemically possible, since aluminium is a stronger reducing agent than carbon.
However there is an indirect carbothermic reduction possible by using carbon
and Al2O3 which forms an intermediate Al4C3 and this can further yield aluminum
metal at a temperature of 1900-2000°C. This process is still under development.
This process costs less energy and yields less CO2 than the Hall-Héroult
process.[18] Aluminium oxide has a melting point of about 2,000 °C. Therefore,
it must be extracted by electrolysis. In this process, the aluminium oxide is
dissolved in molten cryolite and then reduced to the pure metal. The
operational temperature of the reduction cells is around 950 to 980 °C.
Cryolite is found as a mineral in Greenland, but in industrial use it has been
replaced by a synthetic substance. Cryolite is a chemical compound of
aluminium, sodium, and calcium fluorides: (Na3AlF6). The aluminium oxide (a
white powder) is obtained by refining bauxite in the Bayer process of Karl
Bayer. (Previously, the Deville process was the predominant refining
technology.)
The
electrolytic process replaced the Wöhler process, which involved the
reduction of anhydrous aluminium chloride with potassium. Both of the
electrodes used in the electrolysis of aluminium oxide are carbon. Once the
refined alumina is dissolved in the electrolyte, its ions are free to move
around. The reaction at the cathode is:
Al3+
+ 3 e− → Al
Here
the aluminium ion is being reduced. The aluminium metal then sinks to the
bottom and is tapped off, usually cast into large blocks called aluminium
billets for further processing.
At
the anode, oxygen is formed:
2
O2− → O2 + 4 e−
This
carbon anode is then oxidized by the oxygen, releasing carbon dioxide:
O2
+ C → CO2
The
anodes in a reduction cell must therefore be replaced regularly, since they are
consumed in the process.
Unlike
the anodes, the cathodes are not oxidized because there is no oxygen present,
as the carbon cathodes are protected by the liquid aluminium inside the cells.
Nevertheless, cathodes do erode, mainly due to electrochemical processes and
metal movement. After five to ten years, depending on the current used in the
electrolysis, a cell has to be rebuilt because of cathode wear.
World
production trend of aluminiumAluminium electrolysis with the Hall-Héroult
process consumes a lot of energy, but alternative processes were always found
to be less viable economically and/or ecologically. The worldwide average
specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram
of aluminium produced (52 to 56 MJ/kg). The most modern smelters achieve
approximately 12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction,
31 MJ/kg, and the Gibbs free energy of reaction, 29 MJ/kg.) Reduction line
currents for older technologies are typically 100 to 200 kA; state-of-the-art
smelters[19] operate at about 350 kA. Trials have been reported with 500 kA
cells.
Electric
power represents about 20% to 40% of the cost of producing aluminium, depending
on the location of the smelter. Smelters tend to be situated where electric
power is both plentiful and inexpensive, such as South Africa, Ghana, the South
Island of New Zealand, Australia, the People's Republic of China, the Middle
East, Russia, Quebec and British Columbia in Canada, and Iceland.[20]
Aluminium
output in 2005In 2005, the People's Republic of China was the top producer of
aluminium with almost a one-fifth world share, followed by Russia, Canada, and
the USA, reports the British Geological Survey.
Over
the last 50 years, Australia has become a major producer of bauxite ore and a
major producer and exporter of alumina.[21] Australia produced 62 million
tonnes of bauxite in 2005. The Australian deposits have some refining problems,
some being high in silica but have the advantage of being shallow and
relatively easy to mine.[22]
6.
Recycling
Aluminium
is 100% recyclable without any loss of its natural qualities. Recovery of the
metal via recycling has become an important facet of the aluminium industry.
Recycling
involves melting the scrap, a process that requires only five percent of the
energy used to produce aluminium from ore. However, a significant part (up to
15% of the input material) is lost as dross (ash-like oxide).[23]
Recycling
was a low-profile activity until the late 1960s, when the growing use of
aluminium beverage cans brought it to the public awareness.
In
Europe aluminium experiences high rates of recycling, ranging from 42% of
beverage cans, 85% of construction materials and 95% of transport vehicles.[24]
Recycled
aluminium is known as secondary aluminium, but maintains the same physical
properties as primary aluminium. Secondary aluminium is produced in a wide
range of formats and is employed in 80% of the alloy injections. Another
important use is for extrusion.
White
dross from primary aluminium production and from secondary recycling operations
still contains useful quantities of aluminium which can be extracted
industrially.[25] The process produces aluminium billets, together with a
highly complex waste material. This waste is difficult to manage. It reacts
with water, releasing a mixture of gases (including, among others, hydrogen,
acetylene, and ammonia) which spontaneously ignites on contact with air;[26] contact
with damp air results in the release of copious quantities of ammonia gas.
Despite these difficulties, however, the waste has found use as a filler in
asphalt and concrete.[27]
7.
Chemistry
7.1
Oxidation state +1
AlH
is produced when aluminium is heated in an atmosphere of hydrogen. Al2O is made
by heating the normal oxide, Al2O3, with silicon at 1800 °C in a vacuum.[28]
Al2S
can be made by heating Al2S3 with aluminium shavings at 1300 °C in a
vacuum.[28] It quickly disproportionates to the starting materials. The
selenide is made in a parallel manner.
AlF,
AlCl and AlBr exist in the gaseous phase when the tri-halide is heated with
aluminium. Aluminium halides usually exist in the form AlX3, where X is F, Cl,
Br, or I.[28]
7.2
Oxidation state +2
Aluminium
monoxide, AlO, has been detected in the gas phase after explosion[29] and in
stellar absorption spectra.[30]
7.3
Oxidation state +3
Fajans'
rules show that the simple trivalent cation Al3+ is not expected to be found in
anhydrous salts or binary compounds such as Al2O3. The hydroxide is a weak base
and aluminium salts of weak acids, such as carbonate, cannot be prepared. The
salts of strong acids, such as nitrate, are stable and soluble in water,
forming hydrates with at least six molecules of water of crystallization.
Aluminium
hydride, (AlH3)n, can be produced from trimethylaluminium and an excess of
hydrogen. It burns explosively in air. It can also be prepared by the action of
aluminium chloride on lithium hydride in ether solution, but cannot be isolated
free from the solvent. Alumino-hydrides of the most electropositive elements
are known, the most useful being lithium aluminium hydride, Li[AlH4]. It
decomposes into lithium hydride, aluminium and hydrogen when heated, and is
hydrolysed by water. It has many uses in organic chemistry, particularly as a
reducing agent. The aluminohalides have a similar structure.
Aluminium
hydroxide may be prepared as a gelatinous precipitate by adding ammonia to an
aqueous solution of an aluminium salt. It is amphoteric, being both a very weak
acid, and forming aluminates with alkalis. It exists in various crystalline
forms.
Aluminium
carbide, Al4C3 is made by heating a mixture of the elements above 1000 °C. The
pale yellow crystals have a complex lattice structure, and react with water or
dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing
acetylene over heated aluminium.
Aluminium
nitride, AlN, can be made from the elements at 800 °C. It is hydrolysed by
water to form ammonia and aluminium hydroxide. Aluminium phosphide, AlP, is
made similarly, and hydrolyses to give phosphine.
Aluminium
oxide, Al2O3, occurs naturally as corundum, and can be made by burning
aluminium in oxygen or by heating the hydroxide, nitrate or sulfate. As a
gemstone, its hardness is only exceeded by diamond, boron nitride, and
carborundum. It is almost insoluble in water. Aluminium sulfide, Al2S3, may be
prepared by passing hydrogen sulfide over aluminium powder. It is polymorphic.
Aluminium
iodide, AlI3, is a dimer with applications in organic synthesis. Aluminium
fluoride, AlF3, is made by treating the hydroxide with HF, or can be made from
the elements. It consists of a giant molecule which sublimes without melting at
1291 °C. It is very inert. The other trihalides are dimeric, having a
bridge-like structure.
When
aluminium and fluoride are together in aqueous solution, they readily form
complex ions such as [AlF(H2O)5]2+, AlF3(H2O)3, and [AlF6]3−. Of these,
[AlF6]3− is the most stable. This is explained by the fact that aluminium
and fluoride, which are both very compact ions, fit together just right to form
the octahedral aluminium hexafluoride complex. When aluminium and fluoride are
together in water in a 1:6 molar ratio, [AlF6]3− is the most common form,
even in rather low concentrations.
Organometallic
compounds of empirical formula AlR3 exist and, if not also polymers, are at
least dimers or trimers. They have some uses in organic synthesis, for instance
trimethylaluminium.
7.4
Analysis
The
presence of aluminium can be detected in qualitative analysis using aluminon.
8.
Applications
8.1
General use
Aluminium
is the most widely used non-ferrous metal.[31] Global production of aluminium
in 2005 was 31.9 million tonnes. It exceeded that of any other metal except
iron (837.5 million tonnes).[32] Relatively pure aluminium is encountered only
when corrosion resistance and/or workability is more important than strength or
hardness. A thin layer of aluminium can be deposited onto a flat surface by
physical vapour deposition or (very infrequently) chemical vapour deposition or
other chemical means to form optical coatings and mirrors. When so deposited, a
fresh, pure aluminium film serves as a good reflector (approximately 92%) of
visible light and an excellent reflector (as much as 98%) of medium and far
infrared radiation.
Pure
aluminium has a low tensile strength, but when combined with thermo-mechanical
processing, aluminium alloys display a marked improvement in mechanical
properties, especially when tempered. Aluminium alloys form vital components of
aircraft and rockets as a result of their high strength-to-weight ratio.
Aluminium readily forms alloys with many elements such as copper, zinc,
magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk
metal materials that are referred to loosely as "aluminium," are
actually alloys. For example, the common aluminium foils are alloys of 92% to
99% aluminium.[33]
Some
of the many uses for aluminium metal are in:
Transportation
(automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.) as
sheet, tube, castings etc.
Packaging
(cans, foil, etc.)
Construction
(windows, doors, siding, building wire, etc.)
A
wide range of household items, from cooking utensils to baseball bats,
watches.[34]
Street
lighting poles, sailing ship masts, walking poles etc.
Outer
shells of consumer electronics, also cases for equipment e.g. photographic
equipment.
Electrical
transmission lines for power distribution
MKM
steel and Alnico magnets
Super
purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.
Heat
sinks for electronic appliances such as transistors and CPUs.
Substrate
material of metal-core copper clad laminates used in high brightness LED
lighting.
Powdered
aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and
thermite.
8.2
Aluminium compounds
Aluminium
ammonium sulfate ([Al(NH4)](SO4)2), ammonium alum is used as a mordant, in
water purification and sewage treatment, in paper production, as a food
additive, and in leather tanning.
Aluminium
acetate is a salt used in solution as an astringent.
Aluminium
borate (Al2O3 B2O3) is used in the production of glass and ceramic.
Aluminium
borohydride (Al(BH4)3) is used as an additive to jet fuel.
Aluminium
bronze (CuAl5)
Aluminium
chloride (AlCl3) is used: in paint manufacturing, in antiperspirants, in
petroleum refining and in the production of synthetic rubber.
Aluminium
chlorohydrate is used as an antiperspirant and in the treatment of
hyperhidrosis.
Aluminium
fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones,
glass and ceramic.
Aluminium
hydroxide (Al(OH)3) is used: as an antacid, as a mordant, in water
purification, in the manufacture of glass and ceramic and in the waterproofing
of fabrics.
Aluminium
oxide (Al2O3), alumina, is found naturally as corundum (rubies and sapphires),
emery, and is used in glass making. Synthetic ruby and sapphire are used in
lasers for the production of coherent light. Used as a refractory, essential
for the production of high pressure sodium lamps.
Aluminium
phosphate (AlPO4) is used in the manufacture: of glass and ceramic, pulp and
paper products, cosmetics, paints and varnishes and in making dental cement.
Aluminium
sulfate (Al2(SO4)3) is used: in the manufacture of paper, as a mordant, in a
fire extinguisher, in water purification and sewage treatment, as a food
additive, in fireproofing, and in leather tanning.
Aqueous
Aluminium ions (such as found in aqueous Aluminium Sulfate) are used to treat
against fish parasites such as Gyrodactylus salaris.
In
many vaccines, certain aluminium salts serve as an immune adjuvant (immune
response booster) to allow the protein in the vaccine to achieve sufficient
potency as an immune stimulant.
8.3
Aluminium alloys in structural applications
Aluminium
alloys with a wide range of properties are used in engineering structures.
Alloy systems are classified by a number system (ANSI) or by names indicating
their main alloying constituents (DIN and ISO).
The
strength and durability of aluminium alloys vary widely, not only as a result
of the components of the specific alloy, but also as a result of heat
treatments and manufacturing processes. A lack of knowledge of these aspects
has from time to time led to improperly designed structures and gained
aluminium a bad reputation. (See main article)
One
important structural limitation of aluminium alloys is their fatigue strength.
Unlike steels, aluminium alloys have no well-defined fatigue limit, meaning
that fatigue failure will eventually occur under even very small cyclic
loadings. This implies that engineers must assess these loads and design for a
fixed life rather than an infinite life.
Another
important property of aluminium alloys is their sensitivity to heat. Workshop
procedures involving heating are complicated by the fact that aluminium, unlike
steel, will melt without first glowing red. Forming operations where a blow
torch is used therefore requires some expertise, since no visual signs reveal
how close the material is to melting. Aluminium alloys, like all structural
alloys, also are subject to internal stresses following heating operations such
as welding and casting. The problem with aluminium alloys in this regard is
their low melting point, which make them more susceptible to distortions from
thermally induced stress relief. Controlled stress relief can be done during
manufacturing by heat-treating the parts in an oven, followed by gradual
cooling—in effect annealing the stresses.
The
low melting point of aluminium alloys has not precluded their use in rocketry;
even for use in constructing combustion chambers where gases can reach 3500 K.
The Agena upper stage engine used a regeneratively cooled aluminium design for
some parts of the nozzle, including the thermally critical throat region.
8.4
Household wiring
Compared
to copper, aluminium has about 65% of the electrical conductivity by volume,
although 200% by weight. Traditionally copper is used as household wiring
material. In the 1960s aluminium was considerably cheaper than copper, and so
was introduced for household electrical wiring in the United States, even
though many fixtures had not been designed to accept aluminium wire. In some
cases the greater coefficient of thermal expansion of aluminium causes the wire
to expand and contract relative to the dissimilar metal screw connection,
eventually loosening the connection. Also, pure aluminium has a tendency to
creep under steady sustained pressure (to a greater degree as the temperature
rises), again loosening the connection. Finally, Galvanic corrosion from the
dissimilar metals increased the electrical resistance of the connection.
All
of this resulted in overheated and loose connections, and this in turn resulted
in fires. Builders then became wary of using the wire, and many jurisdictions
outlawed its use in very small sizes in new construction. Eventually, newer
fixtures were introduced with connections designed to avoid loosening and
overheating. The first generation fixtures were marked "Al/Cu" and
were ultimately found suitable only for copper-clad aluminium wire, but the
second generation fixtures, which bear a "CO/ALR" coding, are rated for
unclad aluminium wire. To adapt older assemblies, workers forestall the heating
problem using a properly-done crimp of the aluminium wire to a short
"pigtail" of copper wire. Today, new alloys, designs, and methods are
used for aluminium wiring in combination with aluminium termination.
9.
History
Ancient
Greeks and Romans used aluminium salts as dyeing mordants and as astringents
for dressing wounds; alum is still used as a styptic. In 1761 Guyton de Morveau
suggested calling the base alum alumine. In 1808, Humphry Davy identified the
existence of a metal base of alum, which he at first termed alumium and later
aluminum (see Etymology section, below).
The
metal was first produced in 1825 (in an impure form) by Danish physicist and
chemist Hans Christian Ørsted. He reacted anhydrous aluminium chloride
with potassium amalgam and yielded a lump of metal looking similar to tin.[35]
Friedrich Wöhler was aware of these experiments and cited them, but after
redoing the experiments of Ørsted he concluded that this metal was pure
potassium. He conducted a similar experiment in 1827 by mixing anhydrous
aluminium chloride with potassium and yielded aluminium.[35] Wöhler is
generally credited with isolating aluminium (Latin alumen, alum), but also Ørsted
can be listed as its discoverer.[36] Further, Pierre Berthier discovered
aluminium in bauxite ore and successfully extracted it.[37] Frenchman Henri
Etienne Sainte-Claire Deville improved Wöhler's method in 1846, and
described his improvements in a book in 1859, chief among these being the
substitution of sodium for the considerably more expensive potassium.
(Note:
The title of Deville's book is De l'aluminium, ses propriétés, sa
fabrication (Paris, 1859). Deville likely also conceived the idea of the
electrolysis of aluminium oxide dissolved in cryolite; however, Charles Martin
Hall and Paul Héroult might have developed the more practical process
after Deville.)
Before
the Hall-Héroult process was developed, aluminium was exceedingly
difficult to extract from its various ores. This made pure aluminium more
valuable than gold[citation needed]. Bars of aluminium were exhibited alongside
the French crown jewels at the Exposition Universelle of 1855[citation needed],
and Napoleon III was said[citation needed] to have reserved a set of aluminium
dinner plates for his most honoured guests.
Aluminium
was selected as the material to be used for the apex of the Washington Monument
in 1884, a time when one ounce (30 grams) cost the daily wage of a common
worker on the project;[38] aluminium was about the same value as silver.
The
Cowles companies supplied aluminium alloy in quantity in the United States and
England using smelters like the furnace of Carl Wilhelm Siemens by 1886.[39]
Charles Martin Hall of Ohio in the U.S. and Paul Héroult of France
independently developed the Hall-Héroult electrolytic process that made
extracting aluminium from minerals cheaper and is now the principal method used
worldwide. The Hall-Heroult process cannot produce Super Purity Aluminium
directly. Hall's process,[40] in 1888 with the financial backing of Alfred E.
Hunt, started the Pittsburgh Reduction Company today known as Alcoa. Héroult's
process was in production by 1889 in Switzerland at Aluminium Industrie, now
Alcan, and at British Aluminium, now Luxfer Group and Alcoa, by 1896 in
Scotland.[41]
By
1895 the metal was being used as a building material as far away as Sydney,
Australia in the dome of the Chief Secretary's Building.
Many
navies use an aluminium superstructure for their vessels, however, the 1975
fire aboard USS Belknap that gutted her aluminium superstructure, as well as
observation of battle damage to British ships during the Falklands War, led to
many navies switching to all steel superstructures. The Arleigh Burke class was
the first such U.S. ship, being constructed entirely of steel.
In
2008 the price of aluminium peaked at $1.45/lb in July but dropped to $0.7/lb
by December.[42]
10.
Etymology
10.1
Nomenclature history
The
earliest citation given in the Oxford English Dictionary for any word used as a
name for this element is alumium, which British chemist and inventor Humphry
Davy employed in 1808 for the metal he was trying to isolate electrolytically
from the mineral alumina. The citation is from his journal Philosophical
Transactions: "Had I been so fortunate as..to have procured the metallic
substances I was in search of, I should have proposed for them the names of
silicium, alumium, zirconium, and glucium."[43]
By
1812, Davy had settled on aluminum. He wrote in the journal Chemical Philosophy:
"As yet Aluminum has not been obtained in a perfectly free
state."[44] But the same year, an anonymous contributor to the Quarterly
Review, a British political-literary journal, objected to aluminum and proposed
the name aluminium, "for so we shall take the liberty of writing the word,
in preference to aluminum, which has a less classical sound."[45]
The
-ium suffix had the advantage of conforming to the precedent set in other newly
discovered elements of the time: potassium, sodium, magnesium, calcium, and
strontium (all of which Davy had isolated himself). Nevertheless, -um spellings
for elements were not unknown at the time, as for example platinum, known to
Europeans since the sixteenth century, molybdenum, discovered in 1778, and
tantalum, discovered in 1802.
The
-um suffix on the other hand, has the advantage of being more consistent with
the universal spelling alumina for the oxide, as lanthana is the oxide of
lanthanum, and magnesia, ceria, and thoria are the oxides of magnesium, cerium,
and thorium respectively.
The
spelling used throughout the 19th century by most U.S. chemists ended in -ium,
but common usage is less clear.[46] The -um spelling is used in the Webster's
Dictionary of 1828, as it was in 1892 when Charles Martin Hall published an
advertising handbill for his new electrolytic method of producing the metal,
despite his constant use of the -ium spelling in all the patents[40] he filed
between 1886 and 1903.[47] It has consequently been suggested that the spelling
reflects an easier to pronounce word with one fewer syllable, or that the
spelling on the flier was a mistake. Hall's domination of production of the
metal ensured that the spelling aluminum became the standard in North America;
the Webster Unabridged Dictionary of 1913, though, continued to use the -ium
version.
In
1926, the American Chemical Society officially decided to use aluminum in its
publications; American dictionaries typically label the spelling aluminium as a
British variant.
10.2
Present-day spelling
Most
countries spell aluminium with an i before -um. In the United States, the
spelling aluminium is largely unknown, and the spelling aluminum
predominates.[48][49] The Canadian Oxford Dictionary prefers aluminum, whereas
the Australian Macquarie Dictionary prefers aluminium.
The
International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as
the standard international name for the element in 1990, but three years later
recognized aluminum as an acceptable variant. Hence their periodic table
includes both.[50] IUPAC officially prefers the use of aluminium in its
internal publications, although several IUPAC publications use the spelling
aluminum.[51]
11.
Health concerns
Despite
its natural abundance, aluminium has no known function in living cells and
presents some toxic effects in elevated concentrations. Its toxicity can be
traced to deposition in bone and the central nervous system, which is
particularly increased in patients with reduced renal function. Because
aluminium competes with calcium for absorption, increased amounts of dietary
aluminium may contribute to the reduced skeletal mineralization (osteopenia)
observed in preterm infants and infants with growth retardation. In very high
doses, aluminium can cause neurotoxicity, and is associated with altered
function of the blood-brain barrier.[52] A small percentage of people are
allergic to aluminium and experience contact dermatitis, digestive disorders,
vomiting or other symptoms upon contact or ingestion of products containing
aluminium, such as deodorants or antacids. In those without allergies,
aluminium is not as toxic as heavy metals, but there is evidence of some
toxicity if it is consumed in excessive amounts.[53] Although the use of
aluminium cookware has not been shown to lead to aluminium toxicity in general,
excessive consumption of antacids containing aluminium compounds and excessive
use of aluminium-containing antiperspirants provide more significant exposure
levels. Studies have shown that consumption of acidic foods or liquids with
aluminium significantly increases aluminium absorption,[54] and maltol has been
shown to increase the accumulation of aluminium in nervous and osseus
tissue.[55] Furthermore, aluminium increases estrogen-related gene expression
in human breast cancer cells cultured in the laboratory.[56] These salts'
estrogen-like effects have led to their classification as a metalloestrogen.
Because
of its potentially toxic effects, aluminium's use in some antiperspirants, dyes
(such as aluminum lake), and food additives is controversial. Although there is
little evidence that normal exposure to aluminium presents a risk to healthy
adults,[57] several studies point to risks associated with increased exposure
to the metal[citation needed]. Aluminium in food may be absorbed more than
aluminium from water.[58] Some researchers have expressed concerns that the
aluminium in antiperspirants may increase the risk of breast cancer,[59] and
aluminium has controversially been implicated as a factor in Alzheimer's
disease.[60]
According
to The Alzheimer's Society, the overwhelming medical and scientific opinion is
that studies have not convincingly demonstrated a causal relationship between
aluminium and Alzheimer's disease.[61] Nevertheless, some studies[which?] cite
aluminium exposure as a risk factor for Alzheimer's disease, as some brain
plaques have been found to contain increased levels of the metal[citation
needed]. Research in this area has been inconclusive; aluminium accumulation
may be a consequence of the disease rather than a causal agent. In any event,
if there is any toxicity of aluminium, it must be via a very specific
mechanism, since total human exposure to the element in the form of naturally
occurring clay in soil and dust is enormously large over a lifetime.[62][63]
Scientific consensus does not yet exist about whether aluminium exposure could
directly increase the risk of Alzheimer's disease.[61]
12.
Effect on plants
Aluminium
is primary among the factors that reduce plant growth on acid soils. Although
it is generally harmless to plant growth in pH-neutral soils, the concentration
in acid soils of toxic Al3+ cations increases and disturbs root growth and
function.[64][65][66]
Most
acid soils are saturated with aluminium rather than hydrogen ions. The acidity
of the soil is therefore a result of hydrolysis of aluminium compounds.[67]
This concept of "corrected lime potential"[68] to define the degree
of base saturation in soils became the basis for procedures now used in soil
testing laboratories to determine the "lime requirement" of
soils.[69]
Wheat's
adaptation to allow aluminium tolerance is such that the aluminium induces a
release of organic compounds that bind to the harmful aluminium cations.
Sorghum is believed to have the same tolerance mechanism. The first gene for
aluminium tolerance has been identified in wheat. It was shown that sorghum's
aluminium tolerance is controlled by a single gene, as for wheat.[70] This is
not the case in all plants.
13.
Conclusion
As
an individual representative of the periodic table of chemical elements Dmitry
Ivanovich Mendeleyev, the element has unique chemical and physical properties
Element
is of great economic importance and plays a major role in world culture
14.
References
^ Magnetic
susceptibility of the elements and inorganic compounds, in Handbook of
Chemistry and Physics 81th edition, CRC press.
^ Bassam Z.
Shakhashiri. "Chemical of the Week: Aluminum". Science is Fun.
http://scifun.chem.wisc.edu/chemweek/Aluminum/ALUMINUM.html. Retrieved
2007-08-28.
^ a b Polmear,
I. J. (1995). Light Alloys: Metallurgy of the Light Metals. Arnold. ISBN
9780340632079.
^ Dieter G. E.
(1988). Mechanical Metallurgy. McGraw-Hill. ISBN 0070168938.
^ H. A.
Macleod (2001). Thin-film optical filters. CRC Press. pp. 158-159. ISBN
0750306882.
^ John F.
Cochran and D. E. Mapother (July 1958). "Superconducting Transition in
Aluminum". Physical Review 111 (1): 132–142. doi:10.1103/PhysRev.111.132.
^ Applying
lime to soils reduces the Aluminum toxicity to plants. "One Hundred
Harvests Research Branch Agriculture Canada 1886-1986". Historical series
/ Agriculture Canada - Série historique / Agriculture Canada. Government
of Canada.
http://epe.lac-bac.gc.ca/100/205/301/ic/cdc/agrican/pubweb/hs270060.asp.
Retrieved 2008-12-22. Note this link loads slowly
^ J. V.
Magalhaes et al. (2004). "Comparative Mapping of a Major Aluminum
Tolerance Gene in Sorghum and Other Species in the Poaceae". Genetics 167:
1905. doi:10.1534/genetics.103.023580.