ELEMENT OF THE MONTH
Each month we will explore elements of interest from the periodic table, with a brief history of discovery and development, and a review of uses and applications.
TITANIUM – ATOMIC NUMBER: 22 – CHEMICAL SYMBOL: TI
Titanium is a relatively hard, bright metallic element, with high strength and low density. Thermal and electrical conductivity is low but it becomes superconducting at very low temperatures.
It was discovered in Cornwall in 1791 by Reverend William Gregor as the black mineral Menaccanite. Gregor concluded that the mineral was made up of oxides of iron and another unknown element.
Four years later in Berlin, Martin Klaproth analysed a sample of red ore from Hungary and concluded that it was the oxide of a previously unknown element that he named Titanium. He analysed Menaccanite and confirmed that it too was an oxide of Titanium.
Titanium is mostly present in igneous rocks, and occurs in the minerals, ilmenite, rutile, sphene, and many iron ores. It is the ninth most abundant element on earth
Titanium resists corrosion by seawater and this property is exploited in many marine applications.
It connects well with bone producing a strong and stable interface, and is widely used in replacement hip and knee joints, as well as dental implants.
Its high strength and low density make it ideal for aerospace applications, either as an alloying element, or as a titanium-based alloy such as Grade 5 Ti-6Al-4V.
Canada, Australia, and South Africa are the top 3 titanium producers.
WHERE IS TITANIUM USED?
As a Pure Element
Pure titanium is used in heat exchangers and piping for petrochemical plants, thermal/nuclear power plants, and sea water desalination plants, where its natural resistance to corrosion is invaluable.
As an Alloy
Titanium can be alloyed with a wide range of elements, the most common of which are vanadium and aluminium. Addition of these elements can improve strength, corrosion resistance, and welding/fabrication characteristics, and can increase the material hardness when combined with heat treatment. Applications are widespread in aerospace airframe and engine components.
There are nearly 40 different titanium alloy grades including Grade 38 that was developed for use in armour plating, and grade 36 that includes ~50% niobium for super-conductor wire and magnet applications. The most commonly used alloy is grade 5 Ti-6Al-4V.
As a Compound
Titanium is very reactive and forms an oxide layer a few nano-metres thick on exposure to air. The oxide layer may reach a thickness of 25 nano-metres after continued exposure, which gives excellent resistance to corrosion in air. Titanium compounds are also formed with chlorine and other halogens.
Titanium will burn in a nitrogen atmosphere at a temperature of 800C to form Titanium Nitride (TiN), a hard ceramic material.
A common practical use of TiN is as a thin wear resistant coating on cutting tools such as drill bits. Often deposited by Physical Vapour Deposition (PVD), it is characterised by its yellow-gold colour, which can also be used for cosmetic purposes as well as wear resistance in automotive trims, domestic plumbing fittings, pens, etc.
The most widely used titanium compound is titanium oxide, a bright white pigment used in paint, paper, and plastics. Nano-particles of the oxide are used in sunscreens to reflect ultra-violet light.
Here are some key parameters for Titanium, quantifiable using instruments from Helmut Fischer GmbH
- Thickness of hard PVD coatings such as TiN, TiAlN, TiCN, on high speed tool steels, in the range 1µm to 5µm , measurable with a non-destructive XRF based instrument such as the Fischerscope XDLM
- Composition analysis and material identification of titanium alloys such as grade 5 TiAl6V4, to verify to specification in aerospace applications, using a portable XRF based instrument such as the XAN 500
- Determination of hardness, creep, and elasticity of PVD coatings such as TiN, TiAlN, TiCN, using the Fischer Nano-Indentation instrument HM2000