Chapter 10 Aluminum

The element of aluminum was discovered in 1825, and it was a semiprecious metal compared with silver in price before 1886 because the only way to prepare the metal was by the complex and difficult process that culminated in reacting metallic sodium with aluminum chloride. In 1884 when the Washington Monument was completed, a 6-pound pyramid of this costly aluminum was placed at the very top as an ornament. It also served as the tip of the lightning rod system due to its properties of high electrical conductivity and corrosion resistance. However, economical methods were needed to wrest aluminum from its abundant minerals. On February 23, 1886, Charles Martin Hall succeeded in producing aluminum metal by passing an electric current through a solution of aluminum oxide in molten cryolite (Na3Al F6). Hall’s discovery of this economical method to release it from its ore made this light, lustrous, and nonrusting metal readily available and based the aluminum industry in North America.

College Education of Charles Hall

Charles Hall was self-educated in science, and he hoped to become a successful inventor and entrepreneur. He took his first formal course in chemistry as a junior in college. He met with Professor Frank Jewett, who was well educated in chemical science and interested in aluminum metal, on the campus of Oberlin College near Cleveland, Ohio, in 1880. Earlier, with Frank Jewett’s guidance and encouragement, he had worked on aluminum chemistry and other projects in Jewett’s laboratory. He attended Jewett’s lectures on the chemistry of aluminum, learned its values, and declared that he intended to be the person who would develop an economical method for refining aluminum from its oxide ore.

Hall did the first experiments with electricity in Jewett’s laboratory during his senior year of 1884/85. He prepared aluminum fluoride from hazardous hydrofluoric acid in special lead vessels, and he passed a current through aluminum fluoride dissolved in water. Unfortunately, this system produced only unwanted hydrogen gas and aluminum hydroxide at the negative electrode. After many unsuccessful experiments with chemical methods of reducing aluminum ores to the metal, Jewett and Hall turned to electric current, which could provide the powerful reducing conditions that were needed. They assembled enough of Bunsen Grove batteries to provide sufficient electrical energy for aluminum production. The eventual laboratory process used about one pound of zinc electrodes, hand cast by Hall, and they obtained only one ounce of aluminum.

Laboratory Trials and Failures at Home Backyard

After graduation, Charles Hall continued the work in the woodshed laboratory behind his family’s house with the help of his sister Julia. They carefully logged each experimental attempt and its outcome. When he found a promising combination, Charles tried numerous variations until he was sure it wouldn’t work. Encouraged by Richard Gritzel’s success in obtaining magnesium metal by using an electric current in a magnesium chloride melt as reported in the Scientific American in 1885, Charles experimented with molten fluoride salts as water-free solvents because the fluoride salts had the advantage over previously studied chloride salts of not absorbing water from the air. To work with molten fluoride salts, he needed a furnace capable of producing and sustaining higher temperatures than the coal-fired furnace of his earlier experiments. For this purpose, Hall adapted a second-hand, gasoline-fired stove to heat the interior of a clay-lined iron tube. Despite the higher temperature of this furnace, it still could not melt calcium, aluminum, or magnesium fluorides. Potassium and sodium fluorides melted but did not dissolve useful amounts of aluminum oxide. Hall moved on to experiment with cryolite (sodium aluminum fluoride) as a solvent. The melting point of cryolite is 1000℃, an exceptionally high temperature for electrochemistry. He made cryolite, found that it would melt in his furnace, and showed that it would dissolve more than 25% by weight of aluminum oxide. He did this crucial experiment early in February 1886 and repeated it the next day for his sister Julia to witness. Six days later, Hall first attempted to prepare aluminum metal by passing an electric current through a solution of aluminum oxide in molten cryolite. He immersed graphite rod electrodes into the fiery solution in a clay crucible and let the current run for a while. In Julia’s presence, he poured the melt into a frying pan and broke apart the cooled mass but found no aluminum. There was only a grayish deposit on the negative electrode, a deposit that did not have the shiny metallic appearance of aluminum. After repeating this process several times, Hall realized that this deposit was probably silicon from silicates dissolved out of the clay crucible. If Hall had not been acquainted with the appearance of metallic aluminum from seeing Jewett’s sample, he might have been slower to interpret this false result. From a large graphite rod, Hall made a graphite crucible to line the clay crucible. He also lowered the melting point of the cryolite solution by adding aluminum fluoride. The first experiment with this new system was performed on February 23, 1886. The electric current ran for several hours, and once again he cooled the melt and broke it open in the presence of his three sisters and father. This time they found several small silvery globules, which he tested with hydrochloric acid. He took them to Jewett, who confirmed that they were aluminum.

On July 9, 1886, Hall applied for a patent. Meanwhile, Paul L.T. Heroult was granted a French patent on April 23, 1886, for a comparable process based on cryolite and aluminum oxide; he had also applied for a US patent in May. This meant that Hall had to prove that he had made aluminum by the new method before the date of the French patent to obtain patent protection in the United States. Julia Hall’s biggest contribution may have been that she was responsible for the meticulous records of Hall’s experiments. These records were later used to prove the priority of Hall’s invention. Evidence from his family and Jewett, including two postmarked letters to his brother, George, also helped to establish the priority of Hall’s discovery in the United States in a ruling made by the Patent Examiner.

How could it be that Paul Heroult in Paris, France, and Charles Hall in Oberlin, Ohio, made nearly simultaneous, yet independent discoveries of the same process of refining aluminum? Many factors seem to have contributed. Finding an economical process for refining aluminum was widely recognized as a prime target for inventors. Electrochemistry had begun to mature as an applied science. Large electricity-generating dynamos were being developed commercially. Interest had been aroused in the chemistry of fluorine-containing substances. Although Hall was working in a small US college town, he had access to the latest in scientific thought with Jewett as his mentor. Proximity to Cleveland and its emerging technical industries, such as Standard Oil for gasoline, Brush Electric for large graphite rods, and Grasselli for chemicals, was also a contributing factor.

Hall, like Heroult, was a resourceful experimentalist, who not only devised a method of making aluminum metal, but made most of his apparatus and prepared many of his chemicals. Like Heroult, Hall had a burning desire to be a successful inventor and industrialist. In recognition of the contribution these two young men made to the development of this electrochemical process on both sides of the Atlantic, it is now called the Hall-Heroult process.

Launch of Production

Hall worked as relentlessly in finding backers and raising capital as he did in the lab. He made a list of industries that might use aluminum. He prepared drawings and charts to show how the process could be applied. Then he made appointments with various wealthy individuals to show how they’d benefit if they invested in his idea. In the summer of 1888, a group of investors organized by Captain Alfred Hunt, an MIT graduate involved in the metallurgical business in Pittsburgh, provided sustained financial support for Hall. By Thanksgiving Day 1888, with the able assistance of Arthur Vining Davis, Hall was producing aluminum in a pilot plant of Pittsburgh Reduction Company he founded (later renamed to the Aluminum Company of America (ALCOA) in Pittsburgh. The process was soon simplified by using internal heating caused by electrical resistance in the reaction pots to achieve and maintain the molten state. Steam-driven Westinghouse dynamos provided the electricity. Further cost improvements resulted later from the use of hydroelectricity. In 1911 Hall became the fifth recipient of the Perkin Medal, which was awarded for “valuable work in applied chemistry” by the Society of Chemical Industry (American Section) with the support of the Electrochemical Society and the American Chemical Society. Hall donated his large amounts of ALCOA stocks for educational institutions worldwide at the time of his death in 1914.

At first aluminum was a solution in search of a problem, but gradually many uses were found for it, ranging from aircraft and other modes of transportation to power lines for long-distance transmission of electricity, construction, food storage, and decoration. Now the ready availability of this light, lustrous, and nonrusting metal has changed our lives. Notice that three moles of electrons (three faradays of electricity) are needed to produce each mole of aluminum, because there are three positive charges on each aluminum ion that must be neutralized by electrons. As of today, the production of aluminum by the Hall process still consumes huge amounts of electrical energy. One pound of aluminum requires 6-8 kilowatts of electrical energy. This amount of aluminum can be used to make 23 pop cans or one 300 watt light bulb burning for one hour is required to make only one beverage can. Modem industrial production still faces significant challenges of efficient operation by lowering energy consumption and reduction of the environmental emissions. The recycling of beverage cans and other aluminum objects has become an important energy conservation measure.