Hall-Héroult process

On this day in 1886 Charles Martin Hall of Oberlin, Ohio, used an electrochemical process to make aluminum from aluminum oxide. Around the same time, Paul Héroult of Thury-Harcourt, France, independently discovered the same process. (In the photos, Hall is clean-shaven; Héroult is bearded.) Because of its high melting point, aluminum oxide is impractical to smelt by heat alone. Before the Hall-Héroult process was invented, aluminum was more expensive to produce than silver. Afterward, aluminum’s production cost was reduced by two orders of magnitude. The process works by dissolving the oxide in cryolite, Na3AlF6, to lower its melting point and then passing an electric current through the mixture to reduce the oxide. Hall industrialized the process and founded Alcoa (Aluminum Company of America). Héroult went on to invent the first commercially successful electric arc furnace for steel.

Date in History: 23 February 1886