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Aluminum (Aluminium in British English) is a silver-white ( with a face-centered
cubic crystalline structure), ductile and light metal element in the member of
group IIIa of the periodic table. Symbol Al; Atomic number 13; atomic mass
26.98154; melting point ca 660°C; boiling point ca 2,467°C; specific gravity
2.6989 at 20°C; valence +3; electronic config. [Ne]3s23p1. Aluminium crystallizes in a face-centered cubic lattice that is stable
from 4 K to melting point. It is an excellent
conductor of heat and electricity (60% of copper's). The coordination number is 12, it is light,
malleable soft. Though pure aluminium is soft and lacks strength,
it imparts a variety of useful properties including strong hardness when
alloyed with small amounts of Cu, Mg, Si, Mn and other elements. Aluminum is very reactive chemically but it resists corrosion
by the self-protecting continuous thin layer of oxidation which forms quickly
on the nascent aluminium surface when exposed to oxygen, water or other oxidants and prevents further corrosion. The chemical properties of aluminium resemble those of beryllium and silicon.
Due to its amphoteric character, it is rapidly attacked by
alkalis (such as lye) and by mineral acids. Aluminium begins to polymerize when the pH of an acidic solution
increases notably over pH 4.5. Polymerization implies two hydroxyls shared by two aluminium atoms
in the
first step, e.g.,
2 Al(OH)(H2O)52+ -> Al2(OH)2(H2O)84+ + 2 H2O.
Polymerization gradually proceeds to larger structures, eventually
leading to the formation of the Al13 (polycation). As polymers coalesce, they increase
in relative molecular mass, eventually becoming large enough to
precipitate aluminium hydroxide from solution. Aluminum is one of the most
abundant metals in the earth. It is not found in nature as the free element but
in combination in clay, bauxite, mica, feldspar, alum, cryolite, and in the
several forms of alumina such as emery, corundum, sapphire, and ruby (forms of
aluminum oxides). Aluminum is very important in world economy. Aluminium is allied
to
form many hard, durable, light, corrosion-resistant and readily worked into a variety of
shapes which are vital to
the building, transportation, aerospace and consumer durable goods industries.
The development of aluminum coating that reflects both visible light and radiant
heat is useful in the industry of telescope mirrors, jewelry and colored wall
covering. Aluminum powder is used in paints and in welding with iron oxide. The
mixture (called thermite) gives off large amounts of heat when ignited. Finely divided aluminium dust can ignite and cause explosions.
It is used in making explosives. Aluminum
is used in packing industry as cans and foil. Owing to the high ratio of Al3+ in aqueous solutions,
the ion proteolyses part of the water envelope and forms hydroxo complexes. It
can also complex with electron-rich species, such as fluoride and chloride. Commercial aluminum compounds in
chemical industry are:
- Alum:
Various isomorphous solid sulfates composed of trivalent metals and
univalent metals, especially aluminum potassium sulfate, AlK(SO4)2·12H2O, a
white, crystalline compound. Alums have the general formula
M2SO4·MIII2(SO4)3·24H2O, where M is one of alkali metals (potassium, sodium,
rubidium, caesium, silver. thallium or ammonium), and MIII denotes one of the
trivalent cation (e.g., aluminum, chromium, iron, manganese, cobalt, or
titanium). In aqueous solution, alums show all the chemical properties that their
components show separately. These salts are used in water purification, leather tanning, coagulation agent for rubber latex,
mordant
dyeing, fireproofing textiles, modifying concrete,
baking powder,
preparation of lakes, clarifying of turbid liquids and as astringents.
- Potassium aluminum sulfate (KAl(SO4)2·12H2O, CAS RN: 7784-24-9 (Dodecahydrate), 10043-67-1
(Anhydrous))
- Sodium aluminum sulfate (NaAl(SO4)2·12H2O, CAS RN: 10102-71-3)
- Ammonium aluminum sulfate (NH4Al(SO4)2·12H2O, CASR RN:
7784-25-0 (Anhydrous), 7784-26-1 (Dodecahydrate))
- Chromium potassium sulfate (KCr(SO4)2·12H2O, CAS RN: 10141-00-1 (Anhydrous), 7788-99-0
(Dodecahydrate))
- Aluminum fluorosulfate
(FAl(SO4)2·12H2O, CAS RN: 73680-58-7)
- Alumina (Al2O3,
CAS RN: 1344-28-1, 11092-32-3): White crystalline
powder that is found as balls or
lump of various mesh sizes. Aluminium oxide is
found in different modifications. The natural form
occurs as corundum (alpha-Al2O3)
or in hydrated forms. The hexagonally closest-packed
alpha-modification (corundum) is the most stable
oxide. Emery is an abrasive composed of pulverized, impure corundum, and ruby and sapphire
are the gem varieties of the mineral corundum occurs as masses in limestone and as segregations in igneous rock.
All
transitional aluminas produced at low temperatures converts to alpha-alumina
at high temperature (1400°C)
since a series of alumina formation by dehydration of the hydroxides contain a small proportion of
hydroxyl groups and retaining some chemical reactivity. Example are gamma-aluminas (or activated aluminas)
formed by dehydration at below 600°C and rho-aluminas
formed by
dehydration at higher temperatures (900-1000°C) which are
nearly anhydrous Al2O3.
The structural and compositional differences among various forms of
alumina are associated with differing particulate size, particulate
surface area, surface reactivity and catalytic activity.
Alumina is used in abrasive and as a adsorbent as well as in manufacturing other
aluminum compounds, paper, spark plugs (Alumina porcelain),
fluxes, heat resistance fiber and chromatographic
analysis. The form of balls to inch (6.4 to 19 millimeters) in diameter
are used
in reactor and catalytic beds. Alumina bricks containing 50, 60, or 70% alumina
are used
in high temperature applications. Alumina bubble
bricks which are manufactured by passing an air jet over molten alumina to produce small hollow
bubbles are used to line kiln walls. Alumina fibers (also known as sapphire whiskers), linear
crystals of alumina which have a strength of up to 200,000 lb/in2
are used in plastics as a filler to improve heat resistance
and dielectric properties. aluminous cements containing high percentage of alumina
sets to a high strength in
24 hours and are used for constructing bank walls and laying roads. Various
forms of aluminum oxides;
- Bayerite (CAS
RN: 20257-20-9, alpha-aluminium
trihydroxide, alpha-Al(OH)3 or
alpha-Al2O33H2O)
- Boehmite (CAS
RN:1318-23-6, gamma-AlO(OH) or
gamma-Al2O3H2O)
- Corundum (CAS
RN:1302-74-5, alpha-Alumina , Al2O3)
- Diaspore (CAS
RN:14457-84-2, alpha-AlO(OH) or
alpha-Al2O3H2O)
- Gibbsite (CAS
RN: 14762-49-3, ,
gamma-aluminium, gamma-Al(OH)3 or
gamma-Al2O33H2O)
- Nordstrandite (CAS
RN: 13840-05-6, beta-aluminium
trihydroxide, beta-Al(OH)3 or
beta-Al2O33H2O)
- Aluminate:
A negative ion usually assigned the formula AlO2- and derived from
aluminum hydroxide.
- Aluminide: An
intermetallic alloy containing aluminum plus another element, such as nickel,
iron, or titanium.
- Aluminite (Al2(SO4)(OH)4·7H2O,
also known as websterite) Native monoclinic hydrous aluminum sulfate; used in tanning,
papermaking, and water purification.
- Aluminize
:To apply a film of aluminum to a material, such as glass.
To form a protective surface alloy on a metal by treatment at
elevated temperature with aluminum or an aluminum compound.
- Aluminized explosive:
An explosive to which aluminum has been
added.
- Aluminized Steel:
A steel
coated with an aluminum-iron alloy coating; prepared by dip-coating and
diffusing aluminum into steel at 870°C; resists scaling and oxidation
up to 900°C. Also known as alumetized steel; calorized steel.
- Aluminum
Alkoxides: used in varnishes, for textile impregnation, in cosmetics and
as an intermediate in pharmaceutical production
- Aluminum Antimonide
(AlSb); employed in the semiconductor
technology industry
- Aluminum
Borate: used in the production of glass and ceramics
- Aluminum
Butylate
(Al(OC4H9)3,
CAS RN: 2269-22-9)
- Aluminum Chloride (AlCl3, CAS
RN: 7446-70-0): Used as a catalyst in the process of Friedel Crafts.
(It
has an electron deficient molecule forming only
3 bonds, and has
no lone pairs. The catalyst acts as an electron acceptor for a lone pair on the halide atom). It is widely used in the manufacturing of
petrochemicals such as alkylbenzene, ethylbenzene,
alkyl aryl ketone, ethyl chloride. It is also
used in the manufacturing pharmaceuticals, dyes
intermediates and other organics chemicals such
as anthraquinone, phthalocyanines, acetophenone, butyl rubber, phenylethyl alcohols.
It is used as a nucleu inhibitor in the production of titanium dioxide.
Aluminum Chloride is also used in the production of aluminum, in the metallurgical industry and as a
flux in aluminum smelting; in the production of rubber; lubricants and wood preservatives,
and in cosmetics as an astringent; active ingredient
in antiperspirants.
- Aluminum Chlorohydrate (AlCl(OH)5, CAS
RN: 1327-41-9, 11097-68-0, 84861-98-3)
- Aluminum Fluoride (AlF3, 7784-18-1):
used in aluminum
production and ceramics and glass
manufacturing, as a catalyst for organic
synthesis, inhibitor of
fermentation.
- Aluminum Halogenides, hydrides and lower aluminium alkyls react
violently with molecular oxygen, and are spontaneously inflammable in
air and explosive with water. Industrially these compounds are used as
co-catalysts for organometallic and organic synthesis, and as
intermediates in various production processes.
- Aluminum Hydroxide
(Al2O3·3H2O, or Al(OH)3,CAS
RN: 21645-51-2
) Hydrated
alumina, or simply hydrate, is more accurately chemically
designated as aluminum trihydroxide, Al(OH)3. The aluminium hydroxides found abundantly in nature are
gibbsite, diaspore, and boehmite. They all convert to aluminium oxide when heated.
Aluminum Hydroxide
is a non-abrasive powder with a Mohs' hardness index
of 2.5 - 3.5 and a specific gravity of 2.42. Alumina
trihydrate is the largest volume flame retardant
used in the world. On heating to 200°C, hydrated
alumina decomposes into 66% alumina and 34% water.
This irreversible process is, in part, what makes
ATH an effective flame retardant. Aluminium
hydroxide is also used as an adsorbent, emulsifier,
ion exchanger, mordant, antacid, and filtering medium.
It is also used in the manufacture of paper, ceramics,
printing inks, detergents, for waterproofing fabrics
and in dentrifrices and antiperspirants
- Aluminum
Isopropylate
(Al(OCH(CH3)2)3,
CAS RN: 555-31-7): used in the soap and paint industries; waterproofing
textiles
- Aluminum Lactate (Al(C3H5O3)3, CAS
RN: 18917-91-4)
- Aluminum Magnesium Silicate
(MgAl2(SiO4)2,
)
- Aluminum Nitrate
(Al(NO3)3,
CAS RN: 13473-90-0)
- Aluminum Orthophosphate
(AlPO4, CAS
RN: 7784-30-7): Flux for the production of glass, mixture
of ceramic, waterproofing concrete and dental
cements, in cosmetics as a emollient, flame retardant,
catalyst in organic synthesis, fireproofing
textile, pharmaceuticals, dyes.
- Aluminum Phosphide (AlP):
used as a rodenticide and pesticide.
- Aluminum
Selenide (AlSe): employed in the semiconductor
technology industry
- Aluminum Silicates
(Clay); They have cation-exchange capacity
and the amounts and types of clay minerals in a soil largely determine
its physical properties and suitability for agriculture. Used in component of dental cement; antacid, food additives
- Aluminum Sulfate:
can exist with varying proportions of water,
the common form being Al2(SO4)3•18H2O. It is almost insoluble
in anhydrous alcohol, but readily soluble in water. Above 770°C
decomposition to aluminium oxide is observed. Aluminium sulfate is
mainly used in water treatment, dyeing, leather tanning and in the
production of other aluminium compounds.
Aluminum Sulfate (Alum) is a white
crystalline product which is almost insoluble
in anhydrous alcohol, but readily soluble in water. It decomposes to aluminium oxide
on heating or on
burning (above 770°C)
producing toxic and corrosive fumes including sulfur oxides.
Its can exist with a variable number of
water molecules (n close to 18),
the form being Al2(SO4)3•nH2O.
It dissolves with clear water at the concentration of 1 - 5%. The solution in water
is a medium strong acid reacts with alkalis and attacks many metals in presence
of water. It
is widely applied as a coagulant for clarification of water
treatment for industrial and drinking and in dyeing, leather tanning,
in paper
production, as a mordant in dyeing, and as a starting
material for the production of other aluminium compounds.
Another
application for hydrated alumina is for the manufacture of
zeolites.
- aluminum Trisulfate
(Al2(SO4)3,
CAS RN: 10043-01-3)
- Ammonium Alum
(NH4Al(SO4)212H2O,
CAS RN: 7784-26-1)
- Anorthosite
(Na2OAl2O36SiO2):
Sodium calcium silicoaluminate
- Bauxite
(CAS RN: 1318-16-7)
- Cryolite
(Na3AlF6,
CAS
RN: 15096-52-3) Sodium calcium
- Kaolinite
(Aluminium silicate, hydrate -Al2Si2O5(OH)4
)
- Potash Alum
(K(AlO)3(SO4)212H2O,
CAS RN: 7784-24-9)
- Sodium Alum
(NaAl(SO4)212H2O,
CAS RN: 7784-28-3)
- Sodium Aluminate
(NaAlO2, Na2OAl2O3 or
Na2Al2O4,,
CAS RN: 1302-42-7)
- Sodium Aluminium Phosphate:
used in food additives
- Topaz
(Aluminium Silicofluoride, 2Al2O32Al(F,OH)33SiO2
)
- Trimethylaluminium
(Al(CH3)3, CAS
RN: 75-24-1)
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