The Kroll process converts ore into titanium metal, which is used in various industries due to its strength and lightness. The process involves removing impurities from minerals such as rutile and ilmenite. William Kroll developed the Kroll method in 1938, which involves passing chlorine gas through rutile to produce titanium tetrachloride. The titanium tetrachloride is then turned into a metallic sponge, which is melted and solidified in a vacuum to produce an ingot of titanium. The Kroll process is expensive but is used to produce titanium for medical implants, construction, and aircraft design.
The Kroll process is a method used to convert ore into titanium metal. Engineers, manufacturing companies, and medical companies use titanium for a variety of different purposes because it’s as strong as steel but is lighter. Traces of titanium can be found in minerals such as rutile and ilmenite, but the Kroll pyrometallurgical process removes impurities and produces a metal that can be used in medical implants, construction and aircraft design.
Titanium was discovered in Great Britain in 1791 by a man named William Gregor. A German scientist named Martin Heinrich Klaproth named it after the Greek god Titan during the same year. Scientists began developing ways to extract the newly discovered element from rutile and ilmenite, and in 1910, a chemist named Matthew Hunter developed a method of making titanium metal by mixing rutile with coke and chlorine. The Hunter process became the first industrial scale process for producing this metal.
During the 1930s, a Luxembourg scientist named William Kroll began experimenting with titanium. In 1938 he developed what later became known as the Kroll Method. Kroll moved to the United States after the outbreak of World War II and his process for making titanium metal was patented in the United States in 1940. The patent was later canceled by the federal government because Kroll was not a citizen of the United States. He got into a seven-year legal battle that culminated in the reinstatement of the patent.
The Kroll process begins by passing chlorine gas through rutile in a chlorinator. During the first stage of the process, titanium tetrachloride and chlorides are produced from the ore. The oxygen is removed from the titanium tetrachloride through a distillation process, and this leaves the titanium tetrachloride in liquid form. Scientists add liquid magnesium or sodium to titanium tetrachloride, and the end result is a metallic sponge.
This titanium sponge is crushed and then put into a vacuum arc furnace for consumable electrodes. The sponge melts inside the furnace but, unlike other metals, it is not cast because it solidifies in a vacuum. An ingot of titanium produced during the Kroll process can weigh over 5,000 kilograms (5.51 tons). The multiple stages of the Kroll process mean that titanium is much more expensive to produce than similar types of metal, such as steel.
After developing the Kroll process, William Kroll used a similar technique to create zirconium metal. Both titanium and zirconium are now used to make space ship parts. Titanium, unlike zirconium, is not dangerous to health and is therefore also used for medical implants.
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