Charles Martin Hall
Charles Martin Hall was an American chemist and inventor notable for his pioneering work in aluminum production. Born in 1863, he studied at Oberlin College, where he developed an interest in aluminum while conducting experiments in a makeshift laboratory. In 1886, Hall discovered an innovative electrolytic process for extracting aluminum from its oxide using cryolite as a solvent, a significant breakthrough that led to a reduction in aluminum production costs. This method allowed for the efficient production of aluminum, which was previously expensive and challenging to obtain.
Hall's contributions to the aluminum industry included founding the Pittsburgh Reduction Company, which later became the Aluminum Company of America (ALCOA). His work not only advanced the metallurgical field but also played a crucial role in making aluminum more accessible for various applications. For his contributions, Hall was recognized with the Perkin Medal in 1911. The Hall-Héroult process, named after him and his contemporary Paul Héroult, remains the primary method for aluminum production today, marking Hall's lasting impact on the industry and resource utilization.
On this Page
Subject Terms
Charles Martin Hall
Inventor
- Born: December 6, 1863
- Birthplace: Thompson, Ohio
- Died: December 27, 1914
- Place of death: Daytona Beach, Florida
Aluminum was well known by the middle of the nineteenth century, but it was expensive to obtain. Charles Martin Hall developed a method of reducing aluminum oxide cheaply by electrolysis of a molten salt mixture—essentially the same method used in the twenty-first century. World production of aluminum by the electrolytic process has risen into the range of billions of kilograms annually.
Biographical Background
In 1873, Charles Martin Hall’s parents moved from Thompson to Oberlin, Ohio, where Hall studied at Oberlin College, graduating with a bachelor of arts degree in 1885. He became interested in the production of aluminum and started to do research in the college laboratory. After graduation, Hall continued his research in a woodshed behind the family home, assisted from time to time by his sister Julia. He constructed his own equipment, even the voltaic cells, for a source of electricity. A key discovery was the use of the mineral cryolite (sodium hexafluoroaluminate) as a solvent for aluminum oxide at an elevated temperature. By the summer of 1886, Hall had obtained his first samples of aluminum and submitted a patent application for his process. The electrolytic method was discovered virtually simultaneously by Paul Héroult (1863-1914) in France.
Hall went on to found an aluminum industry, first at the Pittsburgh Reduction Company and later at the Aluminum Company of America (ALCOA). He was awarded the Perkin Medal of the American Section of the Society of Chemical Industry in 1911.
Impact on Resource Use
Aluminum compounds are abundant in the Earth’s crust, firmly united with oxygen in minerals such as bauxite, clay, and feldspar. bauxite is the only important ore. Freeing the metal from oxygen constitutes the essential problem for aluminum production. Electrolysis of water solutions of aluminum compounds failed to produce the metal. Early commercial processes involved electrolysis of sodium chloride to form sodium metal, which was then used to produce aluminum from its chloride, a relatively inefficient and costly arrangement.
Hall’s discovery of the direct electrolytic process, and its refinements over the years of 1889 to 1914, made possible a dramatic reduction of the price of aluminum to about $0.08 per kilogram. The process operates at about 1,220 kelvins (947° Celsius) and involves passage of electric current between carbon electrodes through a molten electrolyte of aluminum oxide (alumina) dissolved in the mineral cryolite (sodium hexafluoroaluminate). The alumina used is made from bauxite by the Bayer process. Resistive heating is sufficient to keep the electrolyte liquid, and the aluminum metal is formed as a liquid at the cathode and tapped off periodically at the bottom of the electrolysis cell. Oxygen gas is formed at the anode and combines with the carbon of the electrode. The process is a heavy consumer of electric power and most economical where power is inexpensive.