Titanium

Properties

Titanium is a silvery-gray transition metal with an average atomic mass of 47.867. Its density is 4.5 g/cm³, a little over half that of steel, yet its best alloys match many steels in strength. It is also very heat resistant: it melts at 1941 K (1667.85 °C) and boils at 3560 K (3286.85 °C).

Its electron configuration is [Ar] 4s² 3d², so a titanium atom has four electrons beyond the argon core that it can use in bonding. Giving up all four gives the Ti⁴⁺ state, the most common one in its compounds, though +3 and +2 compounds also exist. You can build this configuration step by step with the electron configuration tool. Its Pauling electronegativity is 1.54 and its first ionization energy is 6.828 eV, typical values for an early transition metal.

At room temperature the atoms are packed in a hexagonal close-packed crystal. Heated to about 882 °C, the metal switches to a body-centered cubic structure. Metallurgists exploit this change: adding elements that favor one form or the other is how the main families of titanium alloys are designed. To see how titanium stacks up against its neighbors, try the compare elements tool.

Why it resists corrosion

On paper, titanium is a reactive metal. The reason it survives seawater, chlorine and many acids is a thin, tightly bonded film of oxide that forms on its surface the instant it meets air or water. This layer is only a few nanometers thick, but it seals the metal and re-forms almost instantly if scratched.

That protection has limits. Hot concentrated acids, especially hydrofluoric acid, attack the oxide film directly. At high temperatures the metal also reacts with oxygen and nitrogen, which is why titanium is welded and cast under argon or in a vacuum. Fine titanium powder can even burn, and titanium is one of the few metals that will keep burning in pure nitrogen.

Where it comes from

Titanium is far from rare: it is one of the more abundant elements in Earth’s crust. The two main ores are ilmenite (FeTiO₃), an iron titanium oxide, and rutile (TiO₂). Both are often mined from heavy-mineral beach sands, where waves and currents have concentrated these dense grains.

The hard part is getting the metal out. Heating the oxide with carbon, the trick used for iron, doesn’t work, because titanium grabs carbon, oxygen and nitrogen and ends up brittle. The standard route today, the Kroll process, first converts the ore to titanium tetrachloride (TiCl₄) by heating it with chlorine and carbon. The purified TiCl₄ is then reduced with molten magnesium under an inert atmosphere, leaving a porous solid called titanium sponge. The sponge is melted, often with alloying metals, into ingots. These many energy-hungry steps are why titanium costs far more than steel or aluminum.

Compounds

By tonnage, most mined titanium never becomes metal. It becomes titanium dioxide, TiO₂, a white solid with a very high refractive index. That property lets it scatter visible light strongly, which gives paints, paper and plastics their bright, opaque whiteness. TiO₂ occurs as the minerals rutile and anatase, which share the same formula but differ in crystal structure. Anatase in particular is a photocatalyst: under ultraviolet light it can break down organic grime, an effect used in some self-cleaning glass and coatings.

Titanium tetrachloride, TiCl₄, is a colorless liquid at room temperature and a key industrial intermediate for both the metal and the pigment. It reacts vigorously with water, and in moist air it hydrolyzes into a dense white cloud of TiO₂ particles and hydrogen chloride.

Titanium nitride, TiN, is a very hard, gold-colored ceramic used to coat drill bits and cutting tools. Compounds of Ti³⁺ are also worth knowing: their solutions are violet, and they act as reducing agents because Ti³⁺ is easily oxidized to Ti⁴⁺.

Uses

Titanium’s combination of low density, high strength, and corrosion resistance makes it a favorite in aerospace engineering. It goes into airframes, fasteners and jet-engine parts that must handle stress and heat without adding weight. The workhorse aerospace alloy contains about 6% aluminum and 4% vanadium.

Its biocompatibility makes it a standard material for medical implants, including hip and knee replacements, dental implants and bone plates. The same corrosion resistance explains its use in chemical plants, desalination equipment, heat exchangers and ship parts exposed to seawater.

Titanium dioxide has an even wider market as the dominant white pigment, and in mineral sunscreens very fine TiO₂ particles help scatter and absorb ultraviolet light.

Safety and the body

Titanium has no known biological role, and the bulk metal is considered nontoxic, which is part of why it works so well in implants. The main hazards are industrial. Fine titanium powder and machining swarf can ignite, and a titanium fire cannot be put out with water. TiCl₄ is corrosive because it releases hydrogen chloride on contact with moisture. The European Union stopped allowing titanium dioxide as a food additive in 2022 after reviewing its safety.

History

Titanium was first identified in 1791 by English clergyman and mineralogist William Gregor, who found an unfamiliar substance in a black sand mineral in Cornwall and initially called it “menachanite.” A few years later, in 1795, German chemist Martin Heinrich Klaproth independently identified the same element in a different mineral, rutile, and gave it the name titanium, after the Titans of Greek mythology.

Because the metal proved so difficult to extract in pure form, it remained largely a laboratory curiosity for more than a century. Reasonably pure titanium was first made in 1910 by reducing TiCl₄ with sodium. The industrial breakthrough was William Kroll’s magnesium-reduction process, scaled up after World War II as military aircraft created demand.