Titanium is a strong and lightweight refractory metal. Alloys of titanium are critical to the aerospace industry but, due to their numerous unique properties, are also used in medical, chemical and military applications, as well as in sporting goods.
Properties:
- Atomic Symbol: Ti
- Atomic Number: 22
- Element Category: Transition Metal
- Density: 4.506/cm3
- Melting Point: 3034°F (1668°C)
- Boiling Point: 5949°F (3287°C)
- Moh's Hardness: 6
Characteristics:
Alloys containing titanium are known for their high strength, light weight and exceptional corrosion resistance.
Despite being as strong as steel, titanium is about 40% lighter in weight, which, along with its resistance to cavitation and erosion, makes it an essential structural metal for aerospace engineers.
Titanium is also formidable in its resistance to corrosion by both water and chemical media. It does this by forming a thin layer of titanium dioxide (TiO2) on its surface that is extremely difficult for these materials to penetrate.
Having a low modulus of elasticity means that titanium is not also very flexible, but returns to its original shape after bending, resulting in its importance to shape memory alloys.
Titanium is non-magnetic and biocompatible (non-toxic, non-allergenic), which has led to its increasing use in the medical field.
History:
The use of titanium metal, in any form, only really developed after World War II. In fact, titanium was not isolated as a metal until the American chemist Matthew Hunter produced it by reducing titanium tetrachloride (TiCl4) with sodium in 1910; A method now known as the Hunter process.
Commercial production, however, did not come until after William Justin Kroll showed that titanium could also be reduced from chloride using magnesium in the 1930s. The Kroll process remains the most important commercial production method to this day.
After a cost-effective production method was developed, titanium's first major use was in military aircraft. Both Soviet and American military aircraft and submarines (e.g. Soviet Alfa and Mike Class submarines and the USAF F100 Super Sabre and Lockheed A-12) designed in the 1950s and 1960s began making use of titanium alloys. By the early 1960s, titanium alloys started to be used by commercial aircraft manufacturers as well.
The medical field, particularly dental implants and prosthetics, awoke to titanium's usefulness after Swedish doctor Per-Ingvar Brånemark's studies dating back to the 1950s showed that titanium triggers no negative immune response in humans, allowing the metal to integrate into our bodies in a process he termed osseointegration.
Production:
Although titanium is the fourth most common metal elements in the earth's crust (behind aluminum, iron and magnesium), production of titanium metal is extremely sensitive to contamination, particularly by oxygen, which accounts for its relatively recent development and high cost.
The main ores used in the primary production of titanium are ilmenite, which accounts for about 90% of production, and rutile, which accounts for the remaining 10%. About 6.3 million tonnes of titanium mineral concentrate was produced in 2010, although only a small fraction (about 5%) of titanium concentrate produced each year ultimately ends-up in titanium metal. Instead, most is used in the production of titanium dioxide (TiO2), a whitening pigment used in paints, foods, medicines and cosmetics.
In the first step of the Kroll process, titanium ore is crushed and heated with coking coal in a chlorine atmosphere to produce titanium tetrachloride (TiCl4). The chloride is then captured and sent through a condenser, which produces a titanium chloride liquid that is more 99% pure.
The titanium tetrachloride is then sent directly into vessels containing molten magnesium. In order to avoid oxygen contamination, this is made inert through the addition of argon gas.
During the consequent distillation process, which can take a number of days, the vessel is heated to 1832°F (1000°C). The magnesium reacts with the titanium chloride, stripping the chloride and producing elemental titanium and magnesium chloride.
The fibrous titanium that is produced as a result is referred to as titanium sponge. To produce titanium alloys and high purity titanium ingots, titanium sponge can be melted with various alloying elements using electron beam, plasma arc or vacuum-arc melting.
In the hope of reducing titanium's extraction costs, electrolytic and other processes for producing titanium metal continue to be actively researched.
Due to its strategic nature, statistics on titanium metal production can be difficult to come-by. However, it is estimated that total world titanium sponge production was about 150,000 tonnes in 2010. The largest producing countries are China, Japan, Russia, Kazakhstan and the United States. Large titanium sponge producers include VSMPO (Russia), Titanium Metals Corp. (USA), RTI Intl. (USA), Fushun Jinming Titanium Industry (China), Luoyang Sunrui Wayi Titanium Co. (China) and Osaka Titanium Technology Co. (Japan).
Applications:
Titanium metal alloys are primarily used in the following industries:
- Aerospace
- Military
- Medical
- Chemical
- Sporting goods
Over the past few decades, aircraft manufacturers have increasingly turned to titanium as a key structural component. From its first uses in the early 1960s, the average titanium content in Boeing's commercial airlines has increased from about 2% of bodyweight to approximately 15%.
Airplane frames and bodies, as well as wing access panels, landing gear, brackets and many frame components rely on the strength and lightweight of titanium alloys.
The ability of some titanium alloys to operate at temperatures greater than 1112°F (600°C) makes them ideal for jet engine casings, compressor discs and blades, where high temperature stress would fatigue and crack most metal alloys.
With higher technical requirements and a greater cost, military aircraft generally contain even more titanium alloy components than commercial aircraft. A single B2 stealth bomber is constructed using more than 91 tonnes of titanium alloy, while 25% of Tornado class fighter jets is comprised of titanium alloys.
Helicopter rotor heads, blade attachments and, in military models, weapon carriers, all make use of titanium. Other military applications include mortar bases as well as body and vehicle armor.
Titanium metal's excellent corrosion resistance, particularly to gases, has led to its use in industrial chemical facilities, including petrochemical and papermaking plants, as well as those making acetic and benzoic acids.
Titanium-containing alloys are also more resistant to salt water corrosion than regular stainless steels, resulting in their use in desalination plants, submarine hulls and ship propellers, as well as in piping and drilling tools for offshore rigs.
The human body's acceptance of titanium, as mentioned, resulted in the first titanium dental implants in the 1950s. Now, alloys of the metal are used in artificial hips, dental implants, stents (braces to strengthen blood vessels) and various other prosthetic body parts.
High performance automotive engines also make use of titanium's ability to withstand high temperatures. Alloys are used to form connecting rods, crankshafts and camshafts. Other automotive uses include suspension springs and exhaust systems.
Sporting equipment and manufacturers often turn to titanium alloys because of their high strength to weight ratio. Most often, these alloys are used in golf clubs and bicycle frames.
Other uses for titanium alloys include:
- Architectural
- Storage of radioactive waste (crystalline silicate)
- Eyeglass frames (shape memory alloys)
- Chlor-alkali processing
- Cryogenic equipment
- Logging equipment
- Electrochemical anodes
- Flue gas desulphurisation
- Geothermal plant
- Heat exchangers
- Jewellery manufacture
- Metal extraction equipment
- Metal matrix composites (e.g. titanium carbide, TiC)
- Offshore piping systems
- Springs
- Steam turbines
- Ultracentrifuges
- Wet air oxidation
Sources:
TIMET Video: The Kroll Process. Available on the International Titanium Association website: http://www.titanium.org
The US Geological Survey: Titanium. http://minerals.usgs.gov/minerals/pubs/commodity/titanium/
Vulcan, Tom. 2010. Titanium: The Metal of the Gods. Hardassetinvestor.com.
