Titanium: The Element

Discovery and Properties
Titanium (Ti) is a fundamental element in the periodic table with atomic number 22 and average atomic weight 47.9gm. Its electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d² with 2 unpaired electrons in the d-shell. In its pure form, titanium is a silver-colored transition metal. The melting point and the boiling point of titanium are 1668 degree Celsius and 3287 degree Celsius respectively.

Pure titanium has very low density (4.506 gm/cm³ at room temperature) compared to other metals and has more than average strength. Its most important property is that it is highly resistant to corrosion compared to other metals. It can withstand dilute sulphuric and hydrochloric acids, sea water, chlorine compounds as well as gaseous chlorine and organic acids without corrosion. Titanium forms strong, light alloys with aluminum, iron, vanadium and molybdenum. Compared to steel, titanium is comparable in strength yet it is 45% lighter!

It is found in the Earth's crust in the form of compounds and is ranked ninth in terms of abundance. Modern studies have revealed that Earth and the moon share geological history. Not surprisingly, rock samples from the moon collected through the Apollo missions show an abundance of titanium compounds. In future, the Moon may be mined for titanium. Traces of titanium compounds have also been found in the Sun's composition through spectroscopic studies. In fact titanium compounds are found in most of the dwarf M-type stars like the Sun. Traces of titanium are also found in the human body and plants but it is non-reactive and therefore plays no biological role. This very property and its ductility makes it an ideal element for building surgical implants.

Titanium has an average atomic weight because it has 5 isotopes with atomic weights ranging from 46 to 50, out of which 48Ti is the most abundant. It is known to be dimorphic, which means it occurs in two crystalline forms. Below 880 degree Celsius, it exists in the hexagonal alpha form and above that temperature it exists in the cubic beta form. It is one of the costliest metals today.

The discovery of titanium was first made by an English priest and mineralogist William Gregor in 1791, while studying mineral deposits in the Manaccan Valley in Cornwall, England. He realized that he had isolated the residue of an entirely new metal from a steel gray mineral called 'ilmenite' known as crystalline form of iron titanium oxide (FeTi O₃) now. He named it after the place of discovery as, 'Mannacanite'. Still this name did not stick because in the same year a German chemist Martin Heinrich Klaproth, discovered the same metal element from another mineral called 'rutile', now known to be mainly composed of titanium dioxide (TiO₂). He named the new metal more imaginatively as 'titanium' after the famous 'Titans' in Greek mythology. As Klaproth was a popular, well-established chemist who was well connected, the name stuck, although Gregory is credited for discovering it first.

Still nobody was able to isolate a high purity sample of titanium in the 18th or 19th century.

Hunter Process
Flash forward to 1910, Matthew Hunter, a Kiwi chemist refined and modified a chemical process developed in 1887 by Nilsen and Pettersen using sodium which extracted 99.9% pure metallic titanium that had the property of ductility. This made titanium available for a range of applications for the first time.

The first step in the Hunter process, as it is known today, consists of heating a mixture of chlorine, coke and rutile which gives a product consisting of titanium tetrachloride (TiCl₄) and carbon dioxide at a very high temperature:

TiO₂ (solid) + 2Cl₂ (solid) + C (solid) → TiCl₄ + CO₂ (gaseous)

The second step is heating the titanium tetrachloride from the previous step with liquid sodium (Na) in a high temperature-resistant steel enclosure at 700 - 800 degree Celsius. In this process known as 'reduction', reduction of titanium tetrachloride by sodium gives 99.9% pure metallic titanium along with salt (NaCl) :

TiCl₄ (liquid) + 4Na (liquid) → 4NaCl (liquid) + Ti (solid)

Kroll Process
Although the Hunter process was the pioneering process of titanium extraction, it was replaced by the Kroll process later. It was developed by William Kroll in 1940 during World War II. The first step in the process consists of reducing either of the titanium minerals ilmenite or rutile by coke at a temperature of 1000 degree Celsius. The mixture so formed is then subjected to chlorine and titanium tetrachloride. Then through the process of fractional distillation many of the excess components of the mineral are removed. In the last stage TiCl₄ is reduced by magnesium in liquid form at a temperature of 800 - 850 degree Celsius again in a high temperature-resistant steel enclosure to give titanium:

2Mg (liquid) + TiCl₄ (gaseous) → 2MgCl₂ (liquid) + Ti (solid)

Further processing is required to extract titanium from the mixture of resultant products. This can be achieved through vacuum distillation. Titanium acquired through this process is highly pure and ductile. This is the established commercial process for titanium production all over the world now.

Uses of Titanium
Due to its high tensile strength, low density and light weight, titanium is the premier choice of metal for space vehicles and missile programs. Its ability to form high strength alloys with other metals enhances its usability in making surgical instruments and prosthetics.

Due to its anti-corrosive properties in sea water, it is used for crucial parts of new age distillation plants built on the seashore. Titanium dioxide is widely used in paints used by artists and also in wall paints. Titanium paint reflects infra red radiation as it does not fall into its absorption band. This property is exploited to make many buildings, heat-resistant.

Thus titanium justifies its naming after the Titans as it makes building of robust space vehicles possible. It makes mankind's leap into outer space possible!