History of Titanium
Titanium was first discovered in 1791 by William Gregor a Cornish Clergyman and amateur mineralogist; while studying sand deposits in the Manaccan valley. In his sample he identified an oxide of iron and an unknown metal; he called it ‘menachanite’. Sadly his contribution to titanium’s discovery was forgotten. The oxide he examined, now known as ilmenite is titanium’s most important commercial ore and accounts for 92% of all titanium extraction.
Gregor’s achievements neglected, titanium was rediscovered in 1795 by Martin Heinrich Klaproth a renowned German chemist who is also credited with the discovery of uranium. Klaproth was investigating rutile and named the unidentified metal after the Titans of Hellenic mythology. Contrary to popular conception his choice of name does not refer to the element’s properties of strength and durability, his notes show that he chose the name due to its neutrality, as advocated by Antoine Lavosier.
“Whenever no name can be found for a new fossil which indicates its peculiar and characteristic properties (in which situation I find myself at present) I think it best to choose such a denomination as means nothing of itself, and thus can give no rise to any erroneous ideas. (as Lavoisier had suggested) In consequence of this, as I did in the case of Uranium, I shall borrow the name for this metallic substance from mythology, and in particular from the Titans, the first sons of the earth. I therefore call this new metallic genus Titanium.”
Isolating Titanium prove problematic with many scientists including Klaproth himself trying and failing. But, in 1887 94 years after Gregor’s initial discovery metallic titanium was isolated by Lars Nilson and Otto Pettersson, who achieved a purity of 95%. Their method using sodium was later refined into the hunter process.
Henry Moissan managed 98% purity using an electric furnace in 1896. The product was heavily contaminated with interstitials (oxygen, nitrogen, and carbon) making it brittle. Titanium’s high affinity for Nitrogen at high temperatures was documented in 1908.
Finding a method of preventing Titanium bonding with nitrogen was critical. In 1910 Matthew A. Hunter achieved 99.9% purity in collaboration with General Electric at Rensselaer Polytechnic Institute. Ilmenite was reduced via the chloride process to make titanium tetrachloride. Then using what is now known as the Hunter Process reacted the TiCl4 with sodium in an evacuated blast furnace at 700-800 degrees Celsius.
The Kroll Process developed by William J. Kroll in Luxemburg in the 1930s displaced the Hunter Process. Using magnesium instead of sodium reduced the cost of the process, which aided titanium’s widespread entrance into the aerospace market after the Second World War. The reliability of Titanium depends entirely upon its supply chain; incremental improvements have seen the purity of titanium used in aerospace improved in excess of 100 fold between 1950 and 2010.
The slightest of defects in titanium output can have dire consequences. The Sioux air disaster of 1989 being one such example, the accident occurred when the titanium engine bore in US airline Flight 232 cracked. The resulting “uncontained engine failure” immobilised the plane’s hydraulic systems and its backups. The crew was forced to improvise, using the thrust of the plane’s two remaining engines to roll and pitch the plane towards Sioux City airport. They received praise for their actions in the United States’ National Transportation Safety Board investigation. 185 of the 296 people aboard survived. The crack in question arose from a “hard alpha” inclusion in the Ti 6al 4V alloy, which had grown in size during the planes 18 years of service.
Titanium’s risk of fracture can be reduced by managing its mechanics and microstructure. Changes were first implemented by the industry in the 1970s. The FAA mandated a switch from Argon Remelting to double vacuum arc remelting in 1972. The reasoning for this was that the vacuum helps to remove dissolved oxygen improving the quality of the ingot, though it is not enough to remove the hard alpha inclusions like those in the engine bore of Flight 232. The OPEC oil crisis of 1973 was a contributing factor in the mass uptake of Titanium in the industry. The rising cost of fuel meant that titanium’s efficiency improvements made the metal more desirable.
The mid-1980s saw further improvements with the switch to triple melt VAR which is now the minimum standard for titanium metal used in aerospace. The investigation into the Sioux accident of 1989 saw further industry-wide effort in the 1990s to improve the production process across the board from handling, electrode welding and vacuum, and water leaks; Leaks are particularly problematic during the Kroll process where oxygen reacts into the melt causing hard alpha inclusions which cannot be removed easily removed through VAR.
A solution to this problem was the skull melting process also known as Electron Beam Cold Hearth Remelting which was patented in the 1980s and reached widespread usage in the 2000s is an alternative to the third step in the triple melt process. Unlike VAR it super heats the metal melting hard alpha defects and allowing contaminated feedstocks to be repurposed into a high quality ingot, impurities form on the surface of the ingot and can be removed easily. The process is useful because it allows waste chips, created and contaminated by machining the metal to melted back down and have its contaminants removed and be used in high-grade applications.
Kroll predicted electrolysis would supersede his own pioneering process within 15 years. 80 years later, Chen, Fray, and Farthing developed the necessary method at the University of Cambridge in the late 1990s. The FFC Cambridge process is expected to reduce the cost of titanium manufacture considerably by allowing the purified oxide ore of a metal to be electrolysed into the desired metal or alloy. The process is similar to the one currently used in aluminium, but the higher melting point of Ti makes the matter more challenging. You can learn more about titanium on our properties page.