The Element Aluminum
Introduction to Aluminum
The element aluminum is a soft, malleable, silvery-white metal. Aluminum gets its name from the classical Latin word “alum”, loosely translating to “bitter”. Aluminum and its compounds are commonly found in many different aspects of our everyday lives. Light, ubiquitous, and inexpensive, aluminum is the first metal to attain worldwide industrial use since the discovery of iron.
Ten Interesting & Fun Facts about Aluminum
- When aluminum was introduced to the world in Paris in 1855, it was more expensive than gold.
- The price of aluminum is dependent on the cost of electricity. It takes three times more electrical energy to produce one ton of aluminum than one ton of steel.
- Aluminum is about one-third as dense as iron or copper, making it ideal for rolling into foil.
- Aluminum is the most abundant metal in the Earth’s crust.
- Many of the most precious, beautiful stones in the world are aluminum compounds. For example, rubies are aluminum oxide with traces of other elements.
- Aluminum was so expensive in the 1860s that Napoleon III of France had his personal dining ware made from it.
- The existence of aluminum was first hypothesized by English scientist Sir Humphry Davy in 1808. However, he was unable to figure out how to extract it.
- Aluminum is rust-resistant because it produces a thin but tough colorless film that protects the metal against further chemical reactions.
- Recycling aluminum products is important because it is so much more cost-efficient and energy-efficient than producing the metal by extraction.
- Aluminum stands up well against most acids, but it is vulnerable to alkalies (such as ammonium and lye).
Aluminum in the Periodic Table
The element aluminum, atomic symbol Al, has an atomic number of 13 and lies in group 13 of the periodic table (to the left of silicon, below boron, and above gallium). Aluminum is classified as a metal, and it lies in the third period. It has three valence electrons and is fairly chemically reactive. Thus, it is not found in nature in its pure state. Aluminum will readily bond with most nonmetals.
Aluminum has an electronegativity of 1.61 on the Pauling scale. Its electron configuration is 1s22s22p63s23p1. Some other metals near aluminum on the periodic table are zinc, copper, nickel, and magnesium.
The Element Aluminum in Our Bodies
Unlike neighboring elements sodium and magnesium, aluminum is non-essential. It is not required as a trace mineral for human nutrition. In fact, it is highly biologically reactive and essentially toxic.
Alloys of the Element Aluminum
Aluminum forms hard, light, corrosion-resistant alloys. It forms alloys with several elements such as copper, zinc, magnesium, tin, manganese, and silicon. Aluminum alloys generally fall into two categories: casting alloys and wrought alloys. The alloys that are 95% aluminum or greater (by composition) are typically used for metal sheets, plates, foils, and chemical equipment. Alloys containing 90-95% aluminum are more often used in aerospace, extrusions, and cryogenics. Aluminum has many sub-classifications of alloys, and this is an ongoing area of research.
The aluminum alloy duralumin is as strong as mild steel. It contains approximately 94.3% aluminum, 4% copper, .5% manganese, .5% magnesium, and .7% silicon. In addition to being stronger than pure aluminum, it is also tougher with the trade-off being that it is less resistant to corrosion. It is often protected by a coat of pure aluminum.
Aluminum Applications in Today’s World
There is no shortage of uses for aluminum in our modern economy. It is used extensively in construction materials, chemical-processing equipment, electrical conductors, aircraft, and consumer items. It is also used in a less central role in fireworks, rocket fuel, and insulation.
Aluminum is uniquely lightweight, which makes it highly practical for consumer products and beyond. It weighs approximately two-thirds less than iron, copper, nickel, or zinc. This makes it indispensable for the manufacture of construction materials, vehicle frames, and aerospace parts. Most engine aircraft are about 90% aluminum by weight.
Aluminum is also a fairly good electrical conductor. This property has allowed it to replace copper and many high-voltage electric transmission lines. Fewer supporting towers are required for aluminum lines since it is so much lighter. This electrical conductivity also makes it a practical material for cooking utensils. When just one side or edge of an aluminum pan is exposed to heat, this heat will spread evenly through the pan. This prevents food from sticking to the pan in certain spots and burning.
While aluminum is indeed a strong conductor, it is also a good insulator (but not in the classical sense). The metal’s shiny surface deflects the sun’s rays rather efficiently. It is also used in silver and mirrors for this reason.
When aluminum is evaporated in a vacuum, it forms a highly reflective coating that is proven resistant to both light and heat. Unlike silver coatings, this aluminum coating does not deteriorate. These coatings are used in telescope mirrors, toys, and product packaging.
When and How Was Aluminum Discovered?
Aluminum’s existence was initially hypothesized in 1808 by English scientist Sir Humphry Davy. However, he was never able to prove his hypothesis because he could not extract aluminum from its ore. Danish chemist Hans Christian Ørsted produced the first pure aluminum sample in 1825. The sample was extremely small and unfit to perform further experimentation. Nevertheless, it was adequate proof of the existence of the element. In 1845, aluminum was isolated by German chemist Friedrich Wöhler. He isolated it in powder form and was the first scientist to discern some of the properties of the element.
Where Is Aluminum Found in the Universe?
There is more aluminum in the Earth’s crust than any other metal. It is not commonly found in outer space, but it is thought that aluminum-26 is produced in stars at the time of their death. When stars explode in an event known as a supernova, Al–26 is spread through the blast. It is possible that one single supernova is responsible for all aluminum deposits in the entire solar system. Aluminum of man-made origin is also found in space. Aluminum is frequently used as a construction material for spacecraft. Solid rocket boosters also use aluminum in their fuel.
Aluminum Chemistry- Compounds, Reactions, Oxidation States, Isolation
Chemical Properties of Aluminum
Aluminum is so chemically reactive that it is not found in its pure form in nature. However, it forms a protective film when exposed to oxygen in the air, making it difficult to spot its reactivity.
Aluminum Reaction with Water
Aluminum reacts intensely with water to produce hydrogen gas. This is one of the mechanisms behind the combustion of rocket fuel.
2Al(s)+6H2O(l) —> 3H2(g)+ 2Al(OH)3(s)
Aluminum Oxide – Al2O3
Also known as alumina, aluminum oxide is found in nature as the mineral corundum. A less pure form of the compound is known as emery. Both corundum and emery are used as abrasives. Pure corundum is colorless, but the precious stones sapphire and ruby are crystalline corundum compounds tainted by small amounts of other metal oxides (such as titanium oxide or chromic oxide). These precious stones can be artificially manufactured by combining these substances at extremely high temperatures. They are indistinguishable from natural stones, save for microscopic air bubbles.
Aluminum Sulfate – Al2(SO4)3
Aluminum sulfate is created through a chemical reaction in which sulfuric acid is used to dissolve aluminum hydroxide.
2Al(OH)3 + 3H2SO4 + 12H2O –> Al2(SO4)3 18H2O
This compound is used in the purification of water and as a mordant in dyeing and printing cloth. Aluminum sulfate is used for the aforementioned tasks due to its ability to produce a gelatinous precipitate of aluminum hydroxide. This precipitate is generated when it is dissolved in slightly alkaline water. This produces the reverse reaction of the one shown above. The gelatinous precipitate helps hold dye in clothing.
In the water purification process, aluminum sulfate absorbs suspended and dissolved impurities, which then settle at the bottom of the reservoir where they can be more easily removed.
When aluminum sulfate is combined with potassium sulfate in a solution, alum-(K) is produced in the form of cubic, colorless crystals. These crystals are used in dying cloth and water purification, as well as in sizing paper.
Aluminum Chloride – AlCl3
Aluminum chloride is an anhydrous salt used in numerous chemical processes. It is manufactured by passing dry chlorine or hydrogen chloride over heated aluminum.
2Al + 3Cl2 –> 2AlCl3
2Al + 6HCl –> 2AlCl3 + 3H2
Aluminum Hydroxide – Al(OH)3
Aluminum hydroxide is used in tandem with magnesium hydroxide and antacids to relieve indigestion and stomach discomfort. Despite this application, aluminum hydroxide is very toxic and is only used clinically in very small doses. It is found in nature as the mineral gibbsite. This compound is amphoteric, meaning it possesses both acidic and basic properties.
Aluminum Phosphate – AlPO4
Aluminum phosphate is found in nature as the mineral berlinite; however, it also has various synthetic forms. It has been a component of vaccines for over 90 years and is currently showing promise as a potential fertilizer. It is odorless, white, and crystalline.
Aluminum Nitride – AlN
Aluminum nitride is a solid nitride of aluminum with a notably high thermal conductivity. It serves as an effective electrical insulator and is currently being researched in a sub-discipline of photonics known as optoelectronics. This compound is also utilized in steel and semiconductor manufacturing.
Aluminum Citrate – AlC6H5O7
Aluminum citrate is a crystalline salt and is white in color. It is produced by mixing citric acid with aluminum chloride hexahydrate. Aluminum citrate serves as a cross-linker for oil polymers and is also found in antiperspirants.
Isolation of Aluminum
In 1866, American scientist Charles Hall and French scientist Paul Héroult almost simultaneously discovered a process for converting aluminum ore into usable aluminum metal in a cost-effective manner. This method is known as the Hall-Héroult process. It is essentially a two-step process of aluminum refining. Bauxite ore is refined to produce aluminum oxide, which is then processed further to produce pure aluminum. It was the efficiency of the second step which had held back aluminum from marketability for so long.
Héroult and Hall discovered that aluminum oxide could be dissolved in molten cryolite, a mineral primarily found in Greenland. After being dissolved, an electric current is passed through the molten mixture. This current is what separates the aluminum from the oxygen (with the aluminum settling at the bottom of the cell). The aluminum yield from aluminum oxide is around 50%.
Aluminum Oxidation States
Aluminum is most commonly found to have an oxidation state of +3, but it can also show oxidation states of +1 and +2.
Physical Properties of Aluminum
- Symbol: Al
- Melting Point: 660.3 Celsius
- Boiling Point: 2470 Celsius
- Density: 2.7 g/cm3
- Atomic Mass: 26.98
- Atomic Number: 13
- Electron Configuration: [Ne] 3s23p1
- Key Isotopes: Al-27, Al-26
- Chief Ore: Bauxite
- Chief Sources: Australia, Jamaica, Brazil, Russia
- Specific Gravity: 2.7
- Toxicity: Essentially toxic
Aluminum in World Events
In 2022, Russia, a country rich in aluminum reserves, invaded the neighboring country of Ukraine. The resulting sanctions caused the price of aluminum and its subsequent products and services to increase around the world.
Additional Information About Aluminum
- While it is true that aluminum is naturally flexible and lightweight, it is not especially strong for a metal. Without going to the trouble of alloying, there is one way to make it stronger. This is through a process known as cold working, which amounts to flattening the metal by rolling or hammering it at room temperature. This compresses the metal, making it harder in the process.
- Powdered aluminum burns so well that it is an ingredient in fireworks. When powdered aluminum is mixed with powdered iron oxide (rust), thermite is created. Thermite burns hot enough to melt steel.
- Because aluminum foil reflects both light and heat, it is ideal for food preservation. It is completely impermeable, so no light, taste, or aroma escapes.
- Aluminum is indefinitely recyclable. Recycling aluminum requires less than 5% of the original production energy. Around 75% of all aluminum ever produced is still in use, due to recycling.
Where Can I Buy Aluminum?
Many consumer products have a high concentration of aluminum, making it relatively easy to get your hands on the element. Aluminum foil, for example, is around 98.5% pure aluminum. Pure aluminum ingots and granules can be bought from online retailers for approximately $1.20 per gram.