We continue to review some of the most important materials in heat treatment and metallurgy.
Titanium (Chemical symbol: Ti)
Titanium was discovered in 1791 within black sand known as ilmenite – a mixture of iron oxides and titanium oxides. The original discoverer was William Gregor of Cornwall, Great Britain, and it was later named titanium by Martin Heinrich Klaproth, an accomplished German chemist who also discovered uranium, zirconium and cerium. Klaproth named titanium after the Titans of Greek mythology. Titanium is most commonly found as an ore. Pure titanium (Fig. 1) was not isolated until 1910 by Matthew Hunter of New Zealand. Hunter was the inventor of the Hunter process for producing titanium.
Perhaps the most striking property of titanium is its strength-to-density ratio, the highest of any metallic element. It is as strong as steel but 45% lighter. Titanium is twice as strong as aluminum and only 60% heavier. Just as notable is titanium's corrosion resistance. It is resistant to organic acids, dilute sulfuric and hydrochloric acids, chlorine gas and chloride solutions.
Today, 95% of all titanium is used in the production of titanium dioxide, a very bright white pigment used in paper, paints, plastics and toothpaste among others. It is an excellent reflector of infrared radiation and titanium-dioxide paints are used in solar observatories.
Titanium is also considered bio-inert and is commonly used for medical screws and implants such as orthopedic rods, pins and plates, as well as dental implants and surgical tools. The most common titanium used in medicine is 6AL4V and 6AL4V ELI, alloys made of 6% aluminum and 4% vanadium.
Titanium also has an innate ability to join with human bone, referred to as Osseointegration, a unique phenomenon where the body’s natural bone and tissue actually bond to the metal. This makes it ideal for hip and knee replacements and as a material for surgical fasteners (Fig. 2). Furthermore, it is only weakly ferromagnetic, which allows patients with titanium implants to be scanned with MRIs and NMRIs.
Titanium’s light weight and high strength make it a common material in aerospace structures. It is used in aircraft as engine supports, firewalls, landing-gear components and hydraulic tubing, as well as the compressor blades, disks and housing of jet engines.
According to Boeing, their 737 Dreamliner is made of 15% titanium. Overall, a typical commercial jet uses 3,500-12,000 kg (7,700-26,400 pounds) of the metal. The use of titanium has made space exploration feasible (Fig. 3), and it was extensively used in the Mercury, Gemini and Apollo capsules. The space shuttle has many titanium parts, as does the International Space Station. Titanium is also widely used in military hardware such as jet fighters, missiles, tanks, ships and submarines.
Here are a few important facts about titanium.
- Atomic number: 22
- Atomic mass: 47.867 amu
- Density @ 293 K: 4.54 g/cm3
- Melting point: 1660°C (1933 K)
- Boiling point: 3287°C (3560 K)
- Crystal structure: Hexagonal
- Number of protons/electrons: 22
- Number of neutrons: 26