The Kroll Process of Refining Titanium
Billions of years ago, a star in our vicinity spent its dramatic finale in a burst of light that gave birth to the element titanium. Titanium can only be created by the largest of cosmic explosions: the supernova. Its momentous origin underscores its superiority as a metal and foreshadows its undeniable allure.
One cannot simply stroll along the beach picking up specimens of this noble wonder of nature. In fact, it has taken decades of research and technology coupled with billions of dollars in equipment and testing to bring titanium to the forefront of metallurgy. A trace element commonly used in locating diamonds, titanium is typically found in the form of ores such as rutile and ilmenite.
Before titanium can be used to create the huge array of products that have vastly improved our lives, it must first endure a costly and difficult process to extract the pure material from its ore state. The most common way that this is achieved is through a procedure called the Kroll process.
To produce a useable form of titanium, the basic ore, usually rutile, is converted to sponge by charging the ore in a chlorinator, then passing chlorine gas through the charge. This results in titanium tetrachloride. The oxygen is removed as CO or CO², resulting in a colorless liquid form of TiCl4 crude that is purified by continuous fractional distillation. It is then reacted with either magnesium or sodium under an inert atmosphere to yield a metallic titanium sponge and magnesium or sodium chloride. The chloride is then reprocessed and recycled.
The next stage of the process requires the titanium sponge to be crushed and pressed before being melted in a consumable electrode vacuum arc furnace at extreme heat. The melted ingot, each weighting as much as 12,000 lbs, is not poured but solidifies under vacuum conditions in the furnace.