Titanium was first discovered in 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.
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Gregor&#;s achievements neglected, titanium was rediscovered in 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 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 . 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 .
Finding a method of preventing Titanium bonding with nitrogen was critical. In 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 s 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 and .
The slightest of defects in titanium output can have dire consequences. The Sioux air disaster of 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 s. The FAA mandated a switch from Argon Remelting to double vacuum arc remelting in . 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 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-s 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 saw further industry-wide effort in the s 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 s and reached widespread usage in the s 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 s. 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.
In , Michael Suisman, president of Suisman & Blumenthal, sounded a stern warning that a &#;titanium disease&#; was spreading throughout the land. His clinical description was as follows:
&#;Symptoms: The patient is completely overcome by the metal titanium. He or she tends to eat and sleep titanium, pushing all other metals out of his or her system. The patient will talk for hours about the virtues of titanium, extolling its remarkable qualities. Any blemish on titanium&#;s image, any negative characteristic will tend to be dismissed. Titanium&#;s feast-or-famine existence seems to only intrigue the patient.
Earliest known causes: In the s, a number of patients were overcome with titanium, describing it as the &#;Wonder Metal.&#; The side effects of the &#;Wonder Metal&#; syndrome took many years to disappear.
Similar disease: See infatuation.
Length of disease: Lifetime.
Cure: None known.&#;
After working with titanium for more than two decades, I have fallen victim to the &#;titanium disease.&#; What makes this metal so unique? With a quick look at the history and distinctive properties, one can easily recognize the attraction.
History
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Titanium was discovered by an English pastor named William Gregor in the &#;s. In the &#;s small quantities of the metal were produced. Before World War II, titanium as a useful metal was only a tantalizing laboratory curiosity. At that time, titanium was only valuable as an additive to white paint in its oxide form. It took the long and expensive arms race between the United States and the Soviet Union in the &#;s to create the need to solve many of the titanium complex problems.
Since the end of the Cold War, titanium has matured primarily as an aerospace material. However, this &#;Wonder Metal&#; has expanded to commercial markets such as artificial body implants, golf clubs, tennis rackets, bicycles, jewelry, heat exchangers, and battery technologies.
Titanium&#;s unusual metal attributes include a strength comparable to steel but 45% lighter. It is twice as strong as aluminum but only 60% heavier. It is both biologically and environmentally inert. It will not corrode. The metal is nonmagnetic and can hold strength at high temperature because it has a relatively high melting point. Finally, titanium has a very low modulus of elasticity and excellent thermal conductivity properties. For thermal processors, these &#;spring like &#;properties allow titanium to be readily formed or flattened with heat and pressure.
Problems
For all of its outstanding attributes, titanium is still the problem child of the metallurgical family. It is exceedingly difficult to obtain from its ore, which commonly occurs as black sand. If you scoop up a handful of ordinary beach sand and look closely, you will likely see that some of the grains are black; this is a titanium ore. In certain places in the world, especially Africa and Australia, there are vast black sand deposits. Although titanium is the ninth most abundant element on the earth, turning that handful of sand into a critical jet engine blade or body implant is a significant undertaking. The refining process is about 10,000 times less efficient than making iron, which explains why titanium is costly.
Titanium never occurs alone in nature, and it is a highly reactive metal. Known as a &#;transition metal,&#; it can form bonds using electrons from more than one of its shells or energy levels. Therefore, titanium is known as the &#;streetwalker metal.&#; Metallurgists are aware that titanium is renowned to &#;pick up&#; other elements quite readily during many downstream thermal and chemical processes. These reactions are often harmful to the advantageous properties of titanium and should be avoided at all times.
Solution
Since titanium has a tremendous affinity to pick up other elements at elevated temperatures, primarily oxygen and hydrogen, the only way to heat treat titanium successfully is to utilize high vacuum atmospheres. High vacuum levels of x10-5 Torr minimum and low leak rates of five microns per hour maximum are the parameters needed to retain this metal&#;s desired properties. An oxygen-rich atmosphere results in a hard &#;alpha case&#; surface condition. A hydrogen atmosphere results in a hydrided condition, which makes titanium very brittle to the core. Both conditions can be extremely detrimental to any critical titanium component.
With high pumping capability and tight pyrometric controls, vacuum furnaces successfully provide various treatments on the &#;wonder metal&#; while avoiding the &#;streetwalker&#; syndrome. They include inert stress relieving, solution treating, aging, and degassing treatments. After proper processing, bright and clean parts with low hydrogen content and zero alpha case are the norm.
The recycling of titanium is of a different order of magnitude than it is for other metals due to its value. It took a shortage of titanium in the s, and some innovative metallurgy, to transform valuable titanium scrap back into a qualified ingot. To do this, metallurgists used the reactiveness of the metal to their advantage. Since titanium is very ductile and extremely hard to grind into powder, metallurgists learned how to use hydrogen to their advantage. Adding hydrogen to turnings and scrap makes the titanium brittle and enables the material to be pulverized into fine powders. The final product must then be thoroughly degassed or dehydrided to enter back into the revert stream because every pound of titanium is precious.
The reactiveness of titanium also assists the metallurgist to apply various surface treatments. Nitrided and carbide surfaces, when used, add further protection to the titanium while making the exterior harder.
Alloys
Titanium alloys are divided into four distinct types: commercially pure, alpha, beta, and alpha-beta. Commercially pure grades have no alloy addition, and therefore they have very little strength. This grade of titanium is used when corrosion resistance is of greater importance. Alpha alloys are created with alpha stabilizers such as aluminum. They are easy to weld and provide a reliable strength at elevated temperatures. Beta alloys use stabilizers such as molybdenum or silicon which makes these alloys heat treatable to higher tensile strengths. Finally, the most used titanium alloy are the alpha-beta alloys. These heat treatable alloys are made with both alpha and beta stabilizers creating an excellent balance between strength, weight, and corrosion resistance.
Summary
For all the advances, titanium and its many alloys, has not reached its apex in popularity in the world. Is there any other element that calls to mind the notion of strength quite like titanium? For what reason has this metal, named after the Titans of Greek mythology, never reached its full potential? If it were not for the expense, we would undoubtedly have titanium cars, houses, jets, bridges, and ships. Unfortunately, the cost of titanium keeps the &#;Titanium Disease&#; at bay.
Author: Robert Hill, FASM &#; President, Solar Atmospheres of Western PA
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