Aluminum

Aluminum is a light, strong, somewhat ductile silvery metal, atomic number 13. It is the best conductor of electricity after copper and silver, and its alloys have a higher tensile strength than those of any metals except iron and copper. It is more resistant to corrosion than iron and has a better strength to weight ratio, making it indispensable for construction of aircraft. However, it does not wear as well as iron, being considerably softer.

Aluminum is the most abundant metal in the earth’s crust, but it is so difficult to extract from its ores that the price was $374 per ton in 1941, much higher than the price of either steel ($43 a ton) or copper ($240 a ton). Its only economical ore is bauxite, a mixture of hydrous aluminum oxides formed in tropical climates when heavy rainfall leaches the more soluble minerals from aluminum-rich soil. Bauxite is first dissolved in alkali, which leaves behind iron oxides and silica (the principal impurities), then the solution is precipitated with acid to form nearly pure aluminum oxide. This is dissolved in molten aluminum fluoride (cryolite) and reduced by electrolysis, a process requiring large amounts of electrical power. The cryolite is recycled so that only small quantities of fluorine are required to maintain production. Fluorite, the principal ore of fluorine, is widespread in nature, and Japan stockpiled sufficient supplies so that it was never a limiting resource. The United States likewise had access to ample supplies of cryolite, mostly from mines in Greenland.

In 1941, bauxite was mined in Arkansas, the Caribbean, and South America. Smaller amounts were produced in India. The only source under Japanese control at the start of the Pacific War was in the Palau Islands. However, Japan seized rich deposits in Malaya and the Netherlands East Indies early in the war. When these became inaccessible due to the submarine blockade later in the war, attempts were made to use aluminiferous shale from Manchuria, but this proved to be a poor source of aluminum, and production plummeted.

Japanese production of aluminum in 1941 was 71,740 metric tons and peaked at 103,000 tons in 1943, while U.S. production was 309,100 tons in 1941 and peaked at 920,200 tons in 1943. At the time war broke out, Japan had stockpiled 254,740 tons of bauxite.

References

Cohen (1949)

Van Royen and Bowles (1952)

U.S. Geological Survey (accessed 29 December 2006)