What is Aluminum?

Aluminum (or Aluminum) is a silvery-white in color metal. The chemical symbol of aluminum is Al and it has an atomic number (Z) of 13 in the periodic table. The aluminum name for this metal is derived from the Latin word ‘alumen’, which means bitter salt. Aluminum was discovered in the year 1825 by Hans Oersted, and later Friedrich Wöhler isolated aluminum. It is the most commonly found metal in the earth’s core, which is around 8% of the total core mass. Moreover, it is the third most commonly found element on earth after oxygen and silicon. Electron distribution of aluminum per shell is 2, 8, and 3 with a valency of 3. Atomic weight is nearly 26.9815 u.

Industrial production of aluminum first started in the year 1856 and later in 1954, surpassing copper, aluminum became the most produced non-ferrous, non-sparking metal. Aluminum is found in igneous as feldspar and mica. Due to weathering, a hydrated aluminum oxide, bauxite is formed, which is the major ore of aluminum. Alumina does not dissolve in water but dissolves in molten cryolite.

Properties of Aluminum

The density of aluminum is 2710 kg/m³ with a specific gravity of 2.71. Aluminum in its high-purity form has a silvery-white color. Pure aluminum element (Al) lies in the p-block of the periodic table. Pure aluminum is a very soft, malleable metal, and also reflects light. Aluminum readily binds with other elements and consequently, does not occur in pure form. Aluminum sulfates are the most commonly found form of aluminum in nature.

Aluminum is lightweight and non-magnetic. It is the second most malleable and the sixth most ductile metal. Malleability is the property of a metal, which allows it to be hammered or rolled into thin sheets. On the other hand, ductility is a property that indicates the ability of the metal to be deformed into thin wires. In other words, malleability is the ability to deform under compressive stresses and ductility is to deform under tensile stresses.

Aluminum has the following chemical properties, namely, it has a melting point of 660.323°C (933.47 K and 1220.58° F) and a boiling point of 2470°C (2743 K and 4478° F). Consequently, at a standard temperature of 20°C, it is found in a solid-state in nature. Young’s modulus, shear modulus, and bulk modulus of aluminum are 70 GPa, 26 GPa, and 76 GPa, respectively.

Aluminum provides a good corrosion resistance toward many chemicals naturally, but it has a great affinity toward oxygen, which results in the formation of an oxide layer on the surface of a metal when exposed to the atmosphere. This oxide layer forms a protective coating, which prevents further corrosion.

 Aluminum has a stable cubical structure that remains stable until it is heated up to the melting point. The surface of this metal is less lustrous and is very reflective. The expansion coefficient of aluminum due to heating is 23.2.            

The mechanical properties of aluminum are also noteworthy. Its elasticity has a value of around 10,000 Ksi and its tensile strength is around 13,000 Psi. The yield strength of aluminum is 5,000 Psi and its bearing yield strength is around 23,100 Psi. The shear strength of aluminum is about 9,000 Psi and the fatigue strength has a value of 5,000 Psi. The Poisson ratio of aluminum is 0.35.

Different industrial use of Aluminum

The most important application of aluminum is for the construction of airplanes in which aluminum alloyed with copper, manganese, magnesium, and silicon is used, making the alloy lightweight yet strong as pure aluminum, which is not particularly strong.

Aluminum is a lightweight metal with a density of 2.71 gm/cm³, which is just 1/3^rd of that of steel, and also much lower than that of other metals. It stands out as a great potential for application in places where lightweight parts are needed, as in aircraft.

Moreover, aluminum is also used in the construction of ships because of its property of corrosion resistance. It is also used in window frames, high-rise buildings, trains, spacecraft components, and so on. The roofing sheets for houses are made up of aluminum.

Aluminum alloy

Aluminum is also alloyed with other metals that enhance the properties of aluminum even more. In aluminum alloy, aluminum is combined with magnesium, manganese, tin, silicon, and zinc with major domination of aluminum itself (about 85%). Heat-treatable aluminum alloys consist of pure aluminum that is heated up to a certain temperature. At  elevated temperatures, aluminum alloys become weaker and weaker.

The aluminum alloys are lightweight as compared to copper, brass, nickel, and steel. It also has good corrosion resistance. Due to good thermal conductivity and electrical conductivity, it has application in kitchen appliances and for wiring of electronic appliances as well. The electrical conductivity of aluminum is approximately equal to $36.9 \times {10}^6$Siemens/meter. Aluminum is also cheaper than copper and almost as good as copper in the case of electric conduction, so it is used in transmission lines.            

Duralumin is an alloy of aluminum and copper and is widely used. Chemical composition of duralumin, aluminum 94%, copper 4%, manganese, and magnesium are 0.4 - 0.7%. Aluminum when mixed with magnesium provides a lightweight alloy with higher fire protection. Other aluminum alloys are Al-Li (combination of aluminum and lithium), alnico (Aluminum+ nickel + copper), magnalium (Aluminum + magnesium), silumin (aluminum + silicon), and so on.

Aluminum foil

One major application of aluminum is in making aluminum foil, which is used for packaging food items. Aluminum metal is rolled under great pressure in foil rolling mills to obtain thin to very thin foils of an almost paper-size thickness (thickness>25 µm).

Aluminum is highly ductile and does not allow light, oxygen, moisture, and bacteria to pass through it, additionally acting as a barrier. These characteristics of aluminum make it suitable for use in foils for food packaging and also for pharmaceutical packaging of tablets and pills. Aluminum foil, being shiny, is also used for artistic and decorative purposes.

Context and Applications

The concept holds relevance in various diplomas, undergraduates, and postgraduates courses like

• Bachelor of Science in Mechanical Engineering
• Master of Science in Mechanical Engineering
• Metal casting training by American foundry society

Practice Problems

1. What is the yield strength of aluminum? (Given $1psi = 6.894 \times {10}^{-9}\mu m$)

1. $6.894 \times {10}^{-9}\mu m$ 
2. $3.447\times {10}^{-6}\mu m$
3. $4.447 \times {10}^{-5}\mu m$
4. $4.447 \times {10}^{-6}\mu m$  

Answer- Option b

Explanation- The yield strength of aluminum is 5,000 psi and $1psi = 6.894 \times {10}^{-9} \mu m$. So, 5000 psi becomes $3.447 \times {10}^{-6} \mu m$.

2. How does aluminum react at high temperatures?

1. Generally weak           
2. Densest   
3. Strongest                     
4. No change is observed

Answer- Option a

Explanation- The melting point of aluminum is about 1,260 ^o F and it loses its strength by 50% when it is heated at 600 ^o F. Moreover, it can be concluded that as temperature increases, the strength of aluminum decreases.

3. What is the melting point of aluminum?

1. 100°C                             
2. 550.323°C 
3. 660.323°C                   
4. 1000°C

Answer- Option c

Explanation- The melting point of aluminum is about 1,260 ^o F, that is, 660 ^o C.

4. What is the most important chemical property of aluminum?

1. Brittle                             
2. Soft       
3. Hard                         
4. Magnetic

Answer- Option b

Explanation- Aluminum is not brittle/hard it is very soft and it is non-magnetic.

5. What is the weight of aluminum as compared to that of steel?

1. Lighter than steel                   
2. Equal in weight
3. Heavier than steel                       
4. Depends upon alloyed metal

Answer- Option a

Explanation- Aluminum is a lightweight metal with a density of 2.71 gm/cm³, which is just 1/3^rd of that of steel.

Common Mistakes

Students might get confused between aluminum and steel because they both look similar; but, when it comes to usage, aluminum needs more care. It is one of the best options to use for outdoor signs, and it is also better weather resistant than steel. They may also get confused between different isotopes of aluminum, as it has nine isotopes, whose mass ranges from 23 - 30 but ²⁷Al (which is a stable isotope) and ²⁶Al (which is a radioactive isotope) are the only naturally occurring ones.

Related Concepts

• Chemical elements
• Aluminum alloy
• Corrosion
• Steel