Aluminum

Aluminium is a silvery-white element known for its softness, ductility, and non-magnetic properties. It makes up about 8% of the Earth's crust, making it the third most abundant element and the most abundant metal found there. However, its presence decreases as you go deeper into the Earth's mantle. The primary source of aluminium is the ore bauxite.

1.0Introduction

Aluminium has gained significant importance due to its ideal physical and chemical properties, making it suitable for various applications, including heat resistance, lightweight construction, and higher durability and strength requirements. 

A notable aspect of aluminium is its versatility; it can be used as a standalone metal or alloyed with other elements. This adaptability has enabled aluminium to replace several different materials in various industries.

Aluminium metal is highly reactive, making native specimens exceedingly rare. The rapid oxidation rate of aluminium poses challenges in refining the metal. Despite this, aluminium is known for its low density and remarkable ability to resist corrosion due to passivation, where a protective oxide layer forms on its surface. Interestingly, although aluminium is abundant in the environment, no known life form uses it biologically.

2.0Occurrence and Extraction 

Aluminium is highly reactive and does not occur in its free state. Instead, it is always found in compound forms, bonding its atoms with other elements. For example, the metal is combined with oxygen in bauxite, the primary ore of aluminium. This means that pure aluminium metal is not found naturally, regardless of the source.

Metallurgical Extraction of Aluminium

Since bauxite has the highest aluminium concentration, it is considered a metallic ore. The extraction of aluminium from bauxite involves several steps:

• Hydration Reactions: Bauxite undergoes a series of hydrating reactions to form aluminium oxide (alumina). Since the density of aluminium in this oxide is low, the resulting silvery-white powder is often separated for various purposes.
• Electrolysis Preparation: Aluminium's high melting point makes it unsuitable for direct electrolysis. Instead, cryolite (an aluminium compound with a lower melting point) facilitates the process by allowing ions to move freely within the electrolytic cell.
• Electrolysis: Graphite is used as the cathode and anode in the process, chosen for its efficient heat conduction. During electrolysis, crude aluminium is deposited on the cathode (the cell's negative terminal), while the anodes gradually need replacement..

3.0Compounds of Aluminium

Some major compounds that can be made with aluminium:

• Aluminium Oxide: This is one of the most abundant compounds containing aluminium. Although aluminium readily reacts with oxygen, a layer of aluminium oxide forms on the metal’s surface, creating a hard crust that prevents further reactions.
• Aluminium Sulfate: Commonly used in the paper industry, aluminium sulfate binds dye molecules to paper surfaces and fills surface pores.
• Alum: A conjugated compound formed by combining aluminium sulfate with water molecules and potassium sulfate. Alum has various medicinal properties, including its ability to stop bleeding.
• Aluminium Chloride: Widely used as a catalyst in the Friedel-Crafts reaction, aluminium chloride plays a crucial role in the formation of organic compounds.

4.0Physical Properties of Aluminium

• Aluminium typically appears as a silver or light grey powdered metal.
• It is highly flammable and produces an intense flame when it burns.
• The uncoated powder form is a light grey solid that is denser than water.
• Contact with mucous membranes, eyes, or skin can cause burns, and aluminium may be toxic if inhaled or ingested.
• Aluminium is naturally odourless.
• Boiling point: 4221°F (2327°C) at 760 mmHg.
• Melting point: 1220°F (660°C).
• Insoluble in organic solvents and water.
• Soluble in dilute hydrochloric acid, hot water, and alkalis.

5.0Chemical Properties of Aluminium

Some common chemical properties of aluminium:

• Reaction with Air: Aluminium does not react with air because it forms a thin oxide layer on its surface, which protects it from further oxidation.
• Reaction with Mineral Acids: Aluminium reacts readily with mineral acids, forming a solution containing free Al³⁺ ions and liberating hydrogen gas.

2Al(s) + 6HCl(aq) → 2Al³⁺(aq) + 6Cl⁻(aq) + 3H₂(g)

• Reaction with Nitric Acid: Aluminium reacts passively with nitric acid due to its oxidative action, which results in the formation of a protective layer of aluminium oxide on its surface.
  Al₂O₃ + 6HNO₃ → 2Al(NO₃)₃ + 3H₂O
• Reaction with Alkalis: Aluminium reacts with alkalis to form aluminates, releasing hydrogen gas.
  2Al(s) + 2NaOH(aq) + 6H₂O → 2Na⁺(aq) + 2[Al(OH)₄]⁻(aq) + 3H₂(g)
• Reaction with Halogens: Aluminium reacts vigorously with halogens, forming aluminium halides.
  2Al(s) + 3X₂(g) → 2AlX₃(s)                              (X = Cl, Br, I)
• Reaction with Ferric Oxide: Aluminium reacts directly with ferric oxide to form aluminium oxide, releasing free iron atoms.
  2Al(s) + Fe₂O₃(s) → 2Fe(s) + Al₂O₃

6.0Uses of Aluminium

• Alloying: Aluminium is added to certain metals, such as aluminium bronzes and most magnesium-based alloys, to enhance their properties. In aluminium-base alloys, significant amounts of other metals and silicon are added to improve specific qualities.
• Manufacturing: Aluminium and its alloys are extensively used in producing aeroplane, building materials, consumer durables (like refrigerators, air conditioners, and kitchen utensils), electrical conductors, and chemical and food-processing equipment.
• Packaging: Aluminium is commonly used in the packaging industry to make coils, cans, foils, and other wrapping materials.
• Everyday Products: Aluminium is found in many everyday items, such as kitchenware and timepieces.
• Construction: The building industry utilizes aluminium for making doors, windows, cables, and roofing.
• Transportation: Aluminium is extensively used in the transportation industry for manufacturing bicycles, spacecraft, vehicle bodywork, aircraft, and marine equipment.
• Currency: Many coins are made from alloys containing aluminium.
• Other Applications: Aluminium is also used to produce paints, reflecting surfaces, and wires.