The discovery and isolation of aluminum transformed a metal that was once considered more precious than gold into a ubiquitous material. For centuries, its existence was only theorized because it remained tenaciously bound within its compounds. Aluminum has an extremely high chemical affinity for oxygen, meaning its metallic form does not occur naturally in the Earth’s crust, despite being the planet’s most abundant metallic element. Extracting the pure metal required new chemical knowledge and entirely new technological methods, marking a significant scientific breakthrough in the 19th century.
Early Recognition and Naming of the Element
The groundwork for aluminum’s discovery began in the late 18th century when chemists realized a unique metal was hidden within the common compound known as alum. Alum is a hydrated potassium aluminum sulfate. By the early 1800s, scientists were convinced that the base of alum, aluminum oxide (alumina), contained an unknown metallic element.
The English chemist Sir Humphry Davy was among the first to pursue this metal using the voltaic pile for electrolysis. Although Davy had successfully isolated other metals like sodium and potassium, his attempts to separate aluminum from alumina were unsuccessful. Despite failing to isolate a pure sample, Davy established the metal’s existence and proposed a name for it in 1808. He initially suggested “alumium,” which was later standardized to “aluminum” or “aluminium” based on naming conventions for new elements.
The First Successful Isolation
The first concrete step toward isolating the metallic form of aluminum occurred in 1825, carried out by the Danish physicist and chemist Hans Christian Ørsted. Ørsted’s method involved a chemical reduction of aluminum chloride, resulting in a sample of the metal, albeit in an impure form. He described the product as small “chunks” of metal that displayed a metallic luster.
Two years later, the German chemist Friedrich Wöhler refined Ørsted’s technique. Wöhler modified the chemical agents used in the reaction, allowing him to obtain a more identifiable metallic substance. He is often credited with producing the first pure aluminum in the form of a fine powder or small metallic globules.
Ørsted was the first to chemically produce a metallic form of aluminum, while Wöhler was the first to produce the metal in a pure, verifiable state. Wöhler later demonstrated in 1845 that these particles could be fused into larger solid balls of pure aluminum.
The Chemical Process of Initial Isolation
The isolation process pioneered by Ørsted and refined by Wöhler relied on a difficult and energy-intensive chemical reduction reaction. The scientists first needed to produce anhydrous, or water-free, aluminum chloride (AlCl3), a highly reactive compound. Ørsted’s initial attempt involved reacting this aluminum chloride with a potassium amalgam, which is an alloy of potassium and mercury.
The potassium in the amalgam acted as a reducing agent, displacing the aluminum from the chloride compound, and the subsequent distillation of the mercury left behind a small, impure sample of the metal. Wöhler’s refinement involved substituting pure potassium metal for the potassium amalgam, which offered a much stronger chemical reduction. By heating the anhydrous aluminum chloride with pure potassium, he achieved a cleaner reaction.
The chemical equation for Wöhler’s process is represented as AlCl3 + 3K → Al + 3KCl, resulting in metallic aluminum and potassium chloride salt. Because potassium is a highly reactive and difficult metal to handle, this process was extremely challenging, costly, and could only be performed on a small scale. This complex, laboratory-based method explained why aluminum remained a rare and expensive curiosity for decades after its first isolation.
Securing the Future of Aluminum
The high cost of production resulting from the complex chemical reduction methods meant that aluminum was initially priced higher than silver and gold. For instance, the metal was considered so valuable that Napoleon III commissioned aluminum cutlery for his most honored guests. The metal’s status as a precious element finally changed with a revolutionary shift in production methods in the late 19th century.
The breakthrough came with the independent invention of the Hall-Héroult process in 1886 by Charles Martin Hall and Paul Héroult. This new method replaced the costly chemical reduction with an efficient electrolytic process. By dissolving aluminum oxide in molten cryolite and passing a powerful electric current through it, the metal could be produced on a massive, industrial scale. This electrolytic process dramatically lowered the price of aluminum, transforming it from a laboratory curiosity into an indispensable industrial metal.