Science: Revolution in Magnesium

Into each of the 500-odd warplanes produced in the U.S. last week went many times as much magnesium as the total U.S. production of this soft, silvery metal in 1914. And thereby hangs a tale:

> Of how aviation created a market for the world’s least-wanted metal;

> Of how magnesium became, for a brief moment, one of the great bottlenecks of rearmament;

> Of chemical ingenuity which will not only smash the bottleneck but may soon cut the price of magnesium from 27¢ to 10¢ a lb. and make magnesium a goodly post-war competitor of both aluminum (now 15¢) and plastics.

Magnesium is everywhere. It is a vital ingredient of chlorophyll, and without it leaves would not be green. Every cubic mile of sea water contains 5,700,000 tons of it. Whole mountains of its ores lie among the Austrian Alps, the southern Appalachians, the Sierra Nevada. The far Western States are strewn with it; salt lakes are saturated with it. But until aviation came along, nobody wanted it.

In small quantities the pure metal was used for photographers’ flashlights, for fireworks, for star shells, as a scavenger to remove oxygen from other metals while molten, in organic synthesis. In compounds it was used medicinally for milk of magnesia and Epsom salts. But today the fact that magnesium is only two-thirds as heavy as aluminum and less than one-fourth as heavy as steel has brought it into great demand. And from almost everything except green leaves chemists are now extracting the pure metal—some 24,000 tons this year in the U.S., twice last year’s production but probably only half as much as next year’s.

Mining the Ocean. A year ago magnesium was extracted from only one source, Michigan’s brine wells; by only one enterprising producer, Dow Chemical Co.; and by only one method, electrolysis of molten magnesium chloride recovered from salt water. This is a chemical trick so old that it is known as a prior art and is not patentable. Last winter Trust-Buster Thurman Arnold’s division of the Department of Justice sued Dow as a monopoly, but the chief reason that Dow had magnesium all to itself was that before the U.S. began rushing warplanes there was too little demand to inspire competition.

Until this spring, Dow drew all its magnesium from its inexhaustible brine wells at Midland, Mich. From these it is now extracting magnesium at the rate of 12,000 tons a year—26 times as much as in 1929. This spring Dow tapped a new source which has stirred everyone’s imagination : it began mining sea water for magnesium at a great $15,000,000 plant at Freeport, Tex., which by year’s end will be sucking in 12,000,000 gallons a day (enough water for a city of 120,000) and turning out 50 tons of metal—a rate of some 18,000 tons a year. This is 50% more than Dow’s Michigan wells are producing, yet it would take 316 years at this rate to extract the magnesium from a single cubic mile of sea water.

While Dow has been pioneering the extraction of magnesium from water, others have been studying how to extract magnesium from rock. TVA scientists are working on the Carolinas’ abundant magnesium silicate called olivine, of which 27% is recoverable magnesium (in contrast to sea water’s .1%). When this ore is mixed with hydrochloric acid, magnesium chloride is formed which can be treated by electrolysis just like that from water. Because olivine is so rich in metal and TVA power sells cheaply, experiments have been launched at Georgia Tech in the hope of making this a major U.S. source of cheap magnesium.

Danger Up, Price Down. A radically different “carbothermic” process is being tried in the West on two other very common ores, brucite (Mg(OH)2) and magnesite (MgCO3). When either of these is baked it forms magnesium oxide, and the trick is first to vaporize this by heating it to 3,800° F. in the presence of carbon and then cool it to around 380° in 1/1000th of a second with a blast of cold gas. During the heating, the carbon takes the oxygen away from the magnesium, and during the cooling the magnesium is precipitated as a fine powder too fast to recombine with the oxygen. This is called the Hansgirg process, and RFC has financed a $9,250,000 plant at Los Altos, near Palo Alto, Calif., to make 15,000 tons a year. The difficulty with the process is that the hot powdered magnesium is violently explosive. Already there has been a fatal magnesium explosion at Los Altos.

A variation of this process is being perfected by Metallurgist Henry Alfred Doerner of the U.S. Bureau of Mines who claims that when a chill spray of oil is substituted for the Hansgirg cooling gas the magnesium is rendered nonexplosive by an easily removable oily film which forms on the powder grains. The process has been developed at Washington State College and will probably be used in a 12,000-ton plant at Spokane where magnesium deposits adjoin Grand Coulee’s cheap power.

The backers of both these processes hope to get magnesium for 12¢, 10¢, perhaps even less a pound. Dow is skeptical about the Hansgirg process (Dow turned it down), but Dow itself has cut the price of magnesium from $5 in 1915 to 50¢ in 1925 to 30¢ in 1931 and is said to have sold magnesium to Germany before the war as low as 21¢ a lb. Dow’s magnesium costs are inextricably tied up with other chemicals, notably bromine, which are recovered simultaneously. If some of Dow’s first costs can be written off against emergency production for rearmament, most chemists expect Dow can keep its prices well in line with competition.

Blown Up, Flown Up. Although powdered magnesium is explosive, solid magnesium is no more combustible than aluminum or iron, both of which also burn in foil or powder form. (To prove this point one metallurgist went about smoking a magnesium pipe.) But today less than 5% of U.S. magnesium goes into military pyrotechnics and scavenging; 95% goes into definitely nonflammable alloys of which about 80% goes into airplanes.

Pure magnesium is soft and weak but alloyed with small amounts of aluminum (forming Dowmetal) its tensile strength and hardness increase six times. A bar of such a magnesium-base alloy is stronger than three times its weight in ordinary steel. It is not as strong as the same weight of an aluminum-base alloy (using .5% magnesium and 95% aluminum, making duralumin). Consequently airplane parts, where strength is important, are principally made of aluminum-base alloys, and Dowmetal is used primarily for engine castings, doors, hatches, floors, seats, brake assemblies, etc. Aluminum is usually used with some percentage of magnesium—partly for greater strength and partly because magnesium makes aluminum easier to work. Wherever strength is not essential the lighter magnesium gets the call.

After the war, cheap magnesium will compete in many markets which were closed to the more expensive metal of 1939. For example:

> White Sewing Machine Co. has made a portable machine weighing only 13 lb. as compared with 65 1b. for cast iron.

>Giant motor busses and trailers have been built in the U.S. with a deadweight saving of four to five tons through magnesium alloys.

> The European auto industry (before World War II) used thousands of tons of magnesium alloys in cars, though the U.S. industry has so far used little. Often this purpose was not so much to save dead weight as to give moving parts reduced inertia and centrifugal force, prevent vibration, fatigue, etc.

> Many fabricators would prefer a lightweight metal, if it is as cheap as magnesium promises to be, to any plastic.