Aluminium is a chemical element in the boron group with symbol Al and atomic number 13. It is silvery white, and it is not soluble in water under normal circumstances.Pure aluminium is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is easily formed, machined, and cast. Pure aluminium is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminium is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminium from bauxite, an aluminium ore.
Basic information about and classifications of aluminium:
*Name: Aluminium
*Symbol: Al
*Atomic number: 13
*Atomic weight: 26.9815386 (8)
*Standard state: solid at 298 K
*CAS Registry ID: 7429-90-5 Group in periodic table: 13
*Group name: (none)
*Period in periodic table: 3
*Block in periodic table: p-block
*Colour: silvery
*Classification: Metallic
History & Production:
From Latin alumen, meaning bitter salt. It derives its name from alum, KAl(SO4)2.12H2O, where the ancient Greek and Roman used it in medicine as an astringent and as a mordant in dyeing. In 1807, H. Davy, who was not able to isolate the metal, proposed the name alumium and later changed to aluminum.It was then modified again to the name aluminium. The impure metal was first isolated by H.C. Oersted using the reaction of dilute potassium amalgam on aluminium(III) chloride, in 1825. Nowadays, it can be obtained by electrolysis of alumina (Al2O3) dissolved in cryolite. The former can be obtained from bauxite mineral via the Bayer process, while cryolite has been largely synthesized since the natural mineral is rather rare. Aluminium is used for kitchen utensils, and a variety industrial and building materials. When alloyed with small amount of other metals such as magnesium, copper, manganese etc, it is used for construction of aircrafts and rockets. It is also used in coating applications in telescope mirrors, packages, etc.
Biological Role:
Aluminium has no known biological role. It can be accumulated in the body from daily intake, and at one time was suggested as a potential causative factor in Alzheimer’s disease (senile dementia), although some studies have disproved this theory. Only a small amount of what we take in with our food is absorbed by our bodies. Foods with above average amounts of aluminium are tea, processed cheese, lentils and sponge cakes (where it comes from the rising agent). Cooking in aluminium pans does not greatly increase the amount in our diet except when cooking acid foods such as rhubarb. Some indigestion tablets are pure aluminium hydroxide.
Natural Abudance:
Aluminium is not found uncombined in nature, but is the most abundant metal in the Earth’s crust (8.1%) in the form of minerals such as bauxite and cryolite. Most commercially produced aluminium is obtained by the Bayer process of refining bauxite. In this process the bauxite is refined to pure aluminium oxide, which is mixed with cryolite and then electrolytically reduced to pure aluminium. A lot of energy is needed to extract it from its ores: however, this is worthwhile because it does not rust and is fairly easy to recycle.
Aluminium Properties:
After iron, aluminium is now the second most widely used metal in the world. This is because aluminium has a unique combination of attractive properties. Low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity are amongst aluminium’s most important properties. Aluminium is also very easy to recycle.
Weight:Aluminium is light with a density one third that of steel, 2.700 kg/m3.
Strength:Aluminium alloys commonly have tensile strengths of between 70 and 700 MPa. The range for alloys used in extrusion is 150 – 300 MPa. Unlike most steel grades, aluminium does not become brittle at low temperatures. Instead, its strength increases. At high temperatures, aluminium’s strength decreases. At temperatures continuously above 100°C, strength is affected to the extent that the weakening must be taken into account.
Linear expansion:Compared with other metals, aluminium has a relatively large coefficient of linear expansion. This has to be taken into account in some designs.
Machining:Aluminium is easily worked using most machining methods – milling, drilling, cutting, punching, bending, etc. Furthermore, the energy input during machining is low.
Formability:Aluminium’s superior malleability is essential for extrusion. With the metal either hot or cold, this property is also exploited in the rolling of strips and foils, as well as in bending and other forming operations.
Conductivity:Aluminium is an excellent conductor of heat and electricity. An aluminium conductor weighs approximately half as much as a copper conductor having the same conductivity.
Joining:Features facilitating easy jointing are often incorporated into profile design. Fusion welding, Friction Stir Welding, bonding and taping are also used for joining.
Reflectivity:Aluminium is a good reflector of both visible light and radiated heat.
Screening EMC:Tight aluminium boxes can effectively exclude or screen off electromagnetic radiation. The better the conductivity of a material, the better the shielding qualities.
Corrosion resistance:
Aluminium reacts with the oxygen in the air to form an extremely thin layer of oxide. Though it is only some hundredths of a (my)m thick (1 (my)m is one thousandth of a millimetre), this layer is dense and provides excellent corrosion protection. The layer is self-repairing if damaged.
Anodising increases the thickness of the oxide layer and thus improves the strength of the natural c orrosion protection. Where aluminium is used outdoors, thicknesses of between 15 and 25 ¥ìm (depending on wear and risk of corrosion) are common.
Aluminium is extremely durable in neutral and slightly acid environments.
In environments characterised by high acidity or high basicity, corrosion is rapid.
Further details are given in Corrosion Resistance.
Non-magnetic material:Aluminium is a non-magnetic (actually paramagnetic) material. To avoid interference of magnetic fields aluminium is often used in magnet X-ray devices.
Zero toxicity:After oxygen and silicon, aluminium is the most common element in the Earth’s crust. Aluminium compounds also occur naturally in our food.
Applications:
*Low density and strength make aluminium ideal forconstruction of aircraft, lightweight vehicles, and
ladders.An alloy of aluminium called duralumin is often usedinstead of pure aluminium because of its improved properties.
*Easy shaping and corrosion resistance make aluminiuma good material for drink cans and roofing materials.
*Corrosion resistance and low density leads to its use for greenhouses and window frames.
*Good conduction of heat leads to its use for boilers, cookers and cookware.
*Good conduction of electricity leads to its use for overhead power cables hung from pylons(low density gives it an advantage over copper).
*High reflectivity makes aluminium ideal for mirrors, reflectors and heat resistant clothing for fire fighting.
Published by Ravindra.K(Mechanical Engineering)
Basic information about and classifications of aluminium:
*Name: Aluminium
*Symbol: Al
*Atomic number: 13
*Atomic weight: 26.9815386 (8)
*Standard state: solid at 298 K
*CAS Registry ID: 7429-90-5 Group in periodic table: 13
*Group name: (none)
*Period in periodic table: 3
*Block in periodic table: p-block
*Colour: silvery
*Classification: Metallic
History & Production:
From Latin alumen, meaning bitter salt. It derives its name from alum, KAl(SO4)2.12H2O, where the ancient Greek and Roman used it in medicine as an astringent and as a mordant in dyeing. In 1807, H. Davy, who was not able to isolate the metal, proposed the name alumium and later changed to aluminum.It was then modified again to the name aluminium. The impure metal was first isolated by H.C. Oersted using the reaction of dilute potassium amalgam on aluminium(III) chloride, in 1825. Nowadays, it can be obtained by electrolysis of alumina (Al2O3) dissolved in cryolite. The former can be obtained from bauxite mineral via the Bayer process, while cryolite has been largely synthesized since the natural mineral is rather rare. Aluminium is used for kitchen utensils, and a variety industrial and building materials. When alloyed with small amount of other metals such as magnesium, copper, manganese etc, it is used for construction of aircrafts and rockets. It is also used in coating applications in telescope mirrors, packages, etc.
Biological Role:
Aluminium has no known biological role. It can be accumulated in the body from daily intake, and at one time was suggested as a potential causative factor in Alzheimer’s disease (senile dementia), although some studies have disproved this theory. Only a small amount of what we take in with our food is absorbed by our bodies. Foods with above average amounts of aluminium are tea, processed cheese, lentils and sponge cakes (where it comes from the rising agent). Cooking in aluminium pans does not greatly increase the amount in our diet except when cooking acid foods such as rhubarb. Some indigestion tablets are pure aluminium hydroxide.
Natural Abudance:
Aluminium is not found uncombined in nature, but is the most abundant metal in the Earth’s crust (8.1%) in the form of minerals such as bauxite and cryolite. Most commercially produced aluminium is obtained by the Bayer process of refining bauxite. In this process the bauxite is refined to pure aluminium oxide, which is mixed with cryolite and then electrolytically reduced to pure aluminium. A lot of energy is needed to extract it from its ores: however, this is worthwhile because it does not rust and is fairly easy to recycle.
Aluminium Properties:
After iron, aluminium is now the second most widely used metal in the world. This is because aluminium has a unique combination of attractive properties. Low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity are amongst aluminium’s most important properties. Aluminium is also very easy to recycle.
Weight:Aluminium is light with a density one third that of steel, 2.700 kg/m3.
Strength:Aluminium alloys commonly have tensile strengths of between 70 and 700 MPa. The range for alloys used in extrusion is 150 – 300 MPa. Unlike most steel grades, aluminium does not become brittle at low temperatures. Instead, its strength increases. At high temperatures, aluminium’s strength decreases. At temperatures continuously above 100°C, strength is affected to the extent that the weakening must be taken into account.
Linear expansion:Compared with other metals, aluminium has a relatively large coefficient of linear expansion. This has to be taken into account in some designs.
Machining:Aluminium is easily worked using most machining methods – milling, drilling, cutting, punching, bending, etc. Furthermore, the energy input during machining is low.
Formability:Aluminium’s superior malleability is essential for extrusion. With the metal either hot or cold, this property is also exploited in the rolling of strips and foils, as well as in bending and other forming operations.
Conductivity:Aluminium is an excellent conductor of heat and electricity. An aluminium conductor weighs approximately half as much as a copper conductor having the same conductivity.
Joining:Features facilitating easy jointing are often incorporated into profile design. Fusion welding, Friction Stir Welding, bonding and taping are also used for joining.
Reflectivity:Aluminium is a good reflector of both visible light and radiated heat.
Screening EMC:Tight aluminium boxes can effectively exclude or screen off electromagnetic radiation. The better the conductivity of a material, the better the shielding qualities.
Corrosion resistance:
Aluminium reacts with the oxygen in the air to form an extremely thin layer of oxide. Though it is only some hundredths of a (my)m thick (1 (my)m is one thousandth of a millimetre), this layer is dense and provides excellent corrosion protection. The layer is self-repairing if damaged.
Anodising increases the thickness of the oxide layer and thus improves the strength of the natural c orrosion protection. Where aluminium is used outdoors, thicknesses of between 15 and 25 ¥ìm (depending on wear and risk of corrosion) are common.
Aluminium is extremely durable in neutral and slightly acid environments.
In environments characterised by high acidity or high basicity, corrosion is rapid.
Further details are given in Corrosion Resistance.
Non-magnetic material:Aluminium is a non-magnetic (actually paramagnetic) material. To avoid interference of magnetic fields aluminium is often used in magnet X-ray devices.
Zero toxicity:After oxygen and silicon, aluminium is the most common element in the Earth’s crust. Aluminium compounds also occur naturally in our food.
Applications:
*Low density and strength make aluminium ideal forconstruction of aircraft, lightweight vehicles, and
ladders.An alloy of aluminium called duralumin is often usedinstead of pure aluminium because of its improved properties.
*Easy shaping and corrosion resistance make aluminiuma good material for drink cans and roofing materials.
*Corrosion resistance and low density leads to its use for greenhouses and window frames.
*Good conduction of heat leads to its use for boilers, cookers and cookware.
*Good conduction of electricity leads to its use for overhead power cables hung from pylons(low density gives it an advantage over copper).
*High reflectivity makes aluminium ideal for mirrors, reflectors and heat resistant clothing for fire fighting.
Published by Ravindra.K(Mechanical Engineering)
No comments:
Post a Comment
Thank Q Your Feedback is Valuable........