Tuesday, 3 June 2014

Take a walk on the white side - Titanium dioxide

Elizabeth Henderson
Product Development Manager
This month’s blog discusses the use Itac makes of titanium dioxide.  This material is seen everywhere and never looked at – our principal use for it is as a whitener in our paints and adhesives, but it is also used in paper, fibres, food, and cosmetics. It plays an important role in u-PVC window frames, as it stabilises the polymer mix against UV light. The mineral occurs naturally as ilmenite, and is also seen as rutile inclusions (brown needle-like strands) in gemstones such as rubies and sapphires. Its desirability as a white pigment is based on its high refractive index (rutile 2.6 cf talc 1.6) and its chemical inertness which makes it stable in formulations and biologically acceptable (compare this with one of its predecessors as white pigment, lead oxide). Production and purification of pigment grades is demanding of energy and requires very aggressive chemicals – the two routes normally used require the use of either sulphuric acid or chlorine gas. A nation’s consumption of TiO2 per capita is used as an index of industrialisation, as increasing urbanisation needs more surface coatings and paper products.
The name ‘titanium’ was originally chosen for the metal on account of its high strength/density ratio, which means it can be used for aircraft components and other small-volume applications such as artificial human joints and posts in teeth. The oxide’s good colour strength in paints means that relatively low quantities can be used in pale colours such as magnolia and grey, where iron oxides and carbon black will contribute to the opacity.
Titanium compounds also play major roles in catalytic processes. Nanoparticle TiO2 when exposed to UV light, reacts with water to generate protons which will decompose any organic material they contact. Such particles can be sintered into the surface of glass, making it self-cleaning. There are limitations with incorporating them into paints because they destroy the organic binders, but silicone binders may emerge in future which it will be possible to use. Polypropylene was first discovered in the lab thanks to someone investigating Ziegler-Natta catalysts, based on mixed oxidation state compounds of titanium with chlorine, and finding a strange white material in reaction products. Ziegler-Natta catalysts have been used for this application ever since.
For all the diversity and importance of the applications of titanium and its compounds, the most striking use of titanium metal is at the Guggenheim art museum in Bilbao, which is covered in glittering plates of titanium metal – clean, beautiful and strong.