ELEMENT OF THE MONTH
Each month we will explore elements of interest from the periodic table, with a brief history of discovery and development, and a review of uses and applications.
ALUMINIUM – ATOMIC NUMBER: 13 – CHEMICAL SYMBOL: AL
Aluminium is the third most abundant element after oxygen and silicon, and the most abundant metallic element at just over 8% of the earth’s crust. It exists in nature as a range of compounds but not in a pure element form.
It was first produced in an impure state by Hans Christian Oersted in 1825, in a relatively expensive process that heated aluminium chloride with potassium.
German chemist Friedrich Wohler perfected the method in 1827 but could only produce small quantities at prohibitive expense.
Aluminium was more expensive than gold at $1200 per kg until 1854 when Henri Saint-Claire Deville found a way to substitute sodium for potassium to give a cost reduction, but not by enough to stimulate wider use of the metal.
It was not until 1886 that American Charles Martin Hall and Frenchman Paul Heroult simultaneously developed a process to isolate aluminium from its oxide by electrolysis. In 1888 the invention of a new process by Austrian chemist Joseph Bayer allowed low-cost extraction of aluminium oxide from bauxite, so that by 1895 the cost of aluminium was down to $1.20 per kg, at which point its use became more widespread.
WHERE IS ALUMINIUM USED?
As a Pure Element
High purity aluminium is soft and weak, but it has high electrical and thermal conductivity. It is commonly used in aluminium foil, electrical conductor cables and busbars, where its high conductivity relative to weight and lower cost give it a significant advantage over copper.
As an Alloy
Small quantities of magnesium, silicon, manganese, copper, zinc, and other elements, can be alloyed with aluminium to improve strength, hardness, or toughness. Aluminium alloys with a high strength to weight ratio are important structural materials widely used in aerospace and transportation.
Aluminium alloys are commonly used in heat exchange applications where high thermal conductivity and light weight offer a significant advantage over steel or copper.
Alloys are non-toxic so can be used in cookware, and even heat distribution is one of the benefits.
Specific mechanical characteristics such as tensile and shear strength, hardness, and fatigue resistance, can be obtained from a wide range of alloy formulations, and some alloys can be further improved by either cold working or heat treatment.
As a Compound
All aluminium on Earth has previously combined with other elements to form aluminium compounds. Aluminium oxide exists naturally in the gemstones ruby and sapphire, and synthesised versions of these gems are used in lasers.
As a Coating
Thermal Spray Aluminium (TSA) coatings offer excellent corrosion resistance in harsh subsea, marine, and high temperature environments in oil and gas industries.
Although not strictly a coating, aluminium oxide can be grown on the surface of some aluminium alloys to protect the surface from cosmetic or functional deterioration, or provide enhanced wear or corrosion resistance.
Here are some key parameters for Aluminium, quantifiable using instruments from Helmut Fischer GmbH
- Composition of aluminium alloys, measurable with a non-destructive XRF based instrument such as the XAN 250
- Hardness of heat-treated aluminium alloys in the aerospace industry using the HM2000 nano-indentation system
- Electrical conductivity of aluminium alloys pre and post heat treatment to verify correct treatment, using SMP350
- Thickness determination of Thermally Sprayed Aluminium (TSA) coatings on steel and stainless steels, using Phascope PMP10
- Thickness of anodised layers on convex and concave aluminium extrusions without the need for re-calibration, using FMP100 with FTD3.3 probe