June/July 2012

Metallothermic reactions (Part 2)

A short history

By Fathi Habashi, Laval University, Quebec City

Part 1 explained how the discovery and isolation of alkali metals led to a more in-depth investigation of the potential of metallothermic reactions. Below are some of the metals chemists were able to obtain. This reaction is the basis of the Thermit process, introduced by German chemist Hans Goldschmidt in 1899 to weld rails. The same reaction was also used to make incendiary bombs.

Boron After the isolation of elemental boron in 1808, German chemist Friedrich Wöhler obtained crystalline boron in 1856 by dissolving amorphous boron in molten aluminum. On cooling, crystalline boron separates out and can be recovered by dissolving aluminum in sodium hydroxide.

Silicon In 1811, Joseph-Louis Gay-Lussac and Louis-Jacques Thénard prepared impure amorphous silicon by heating silicon tetrafluoride with potassium, but they did not purify and characterize the product. Silicon, in its more common crystalline form, was prepared in 1854 by Henri Étienne Sainte-Claire Deville by electrolyzing impure sodium-aluminum chloride containing around 10 per cent silicon.

Zirconium In 1789, German chemist Martin Heinrich Klaproth analyzed a sample of zircon from the island of Ceylon (now Sri Lanka) and discovered a new element, which he named Zirkonerde. Zirconium metal was first obtained in an impure form by Swedish chemist Jöns Jacob Berzelius in 1824 by heating a mixture of potassium and potassium zirconium fluoride in an iron tube. The iodide process was the first industrial process for the commercial production of metallic zirconium. This method was superseded by the Kroll process, developed by Wilhelm Kroll in 1845, in which zirconium tetrachloride was reduced by magnesium.

Titanium was first isolated by Berzelius in 1825 by reducing K2TiF6 with potassium. In 1887, Lars Nilson and Sven Otto Pettersson in Stockholm isolated the metal in 95 per cent purity by reducing TiCl4 with sodium. In 1910, Matthew A. Hunter prepared 99.9 per cent pure titanium metal by reducing TiCl4 with sodium in a steel bomb. In 1938, Wilhelm J. Kroll produced pure titanium by reducing TiCl4 with magnesium. In 1942, under Kroll’s direction, the US Bureau of Mines operated a pilot plant in Boulder City, Nevada, for the production of titanium based on his process. In 1948, E. I. du Pont de Nemours & Company produced the first commercial ­titanium.

Magnesium was discovered and isolated by Sir Humphry Davy in 1808 by fused salt electrolysis of MgCl2. Antoine Alexandre Brutus Bussy prepared a sample in 1831 by heating magnesium chloride and potassium in a glass tube. When he washed out the potassium chloride, small, shining globules of magnesium remained. The first industrial production of magnesium by electrolysis of molten carnallite from Stassfurt deposits began in 1886 near Bremen, Germany. In 1915, Dow Chemical Company started producing magnesium from naturally occurring subterranean brine in Midland, Michigan. The use of magnesium in the aircraft industry in World War II resulted in a greater demand and large-scale production methods had to be found. In 1941, the Dow Chemical Company produced an ingot of magnesium at Freeport, Texas – the first metal ever to be taken from sea water.

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