Kroll process

The Kroll process exists because carbon fails where titanium is concerned. Unlike iron, which eagerly sheds its oxygen to carbon in a blast furnace, titanium forms titanium carbide instead—a useless ceramic. William Kroll, working from a private laboratory in a fashionable Luxembourg villa, understood that extracting titanium required something more reactive than carbon.

By the 1930s, Kroll had already experimented with calcium reduction, producing small amounts of ductile titanium in 1924. But calcium left oxide impurities. Magnesium, positioned above carbon in reactivity but easier to handle than sodium, offered a better path. In 1938, Kroll produced 50 pounds of titanium and had it machined at a small Luxembourg factory—the first practical demonstration that titanium could become an engineering metal.

The adjacent possible was closing. On February 22, 1940, Kroll arrived in New York, having fled Rotterdam just as German troops prepared to invade Luxembourg. His U.S. patent was granted that June, but war brought complications. The government seized his patent under the Alien Property Custodian Act, wrongly classifying him as an enemy alien. Seven years of litigation followed; legal fees consumed most of his eventual compensation.

Meanwhile, the U.S. Bureau of Mines had begun its own titanium program in 1938, refining Kroll's small-scale process for industrial production. Contrary to popular belief, World War II saw almost no titanium use—commercial extraction methods weren't solved until 1948, when DuPont produced 100 pounds per day. The first real demand came from jet engines: titanium's strength-to-weight ratio and heat resistance made it perfect for compressor blades, though it couldn't go near combustion chambers where it would ignite.

The Cold War created the strangest chapter in titanium's history. The SR-71 Blackbird required 92% titanium construction, but the United States lacked sufficient ore. The solution: CIA shell companies purchased rutile from the Soviet Union under the cover story that it was needed for pizza ovens. Thirty-two spy planes designed to photograph Soviet territory were built from Soviet titanium, with the Russians never suspecting.

Despite sixty years of attempts to replace it—electrolysis, plasma reduction, alternative reductants—the Kroll process remains dominant. Its inefficiencies have been whittled to near-theoretical minimums. Titanium still costs six times more than stainless steel, but it casings lithium-ion pacemakers (inert, strong, light), builds jet engines (350% thrust-to-weight improvement), and provides medical implants that fuse with living bone.