What is titanium dioxide?

Titanium dioxide is a white inorganic compound, which has been used for around 100 years in a vast number of diverse products. It is depended on it for its non-toxic, non-reactive and luminous properties, which safely heighten the whiteness and brightness of many materials.

It is the whitest and brightest of known pigments, with reflective qualities; it can also both scatter and absorb UV rays.

What is titanium dioxide used for?

Its ultra-white colour, highly-refractive and UV-resistant properties make TiO2 enormously popular with both the industrial and consumer sectors, appearing in dozens of products that people use and see on a daily basis.

Beyond paints, catalytic coatings, plastics, paper, pharmaceuticals and sunscreen, some lesser-known applications include packaging, commercial printing inks, other cosmetics, toothpastes, and food (where it is listed as the food colourant E171).

Paints, coatings and plastics

When used specifically as a pigment in paints, TiO2 is called titanium white, Pigment White 6 or CI 77891. It is also known as ‘the perfect white’ or ‘the whitest white’ due to its powerful, pure whitening qualities.

Until laws changed in the 1920s, most commercial paint manufacturers used highly toxic white lead as a whitener and did not initially convert to using titanium dioxide, partly due to its higher cost. Zinc oxide (ZnO) is also used as a white pigment but is not as effective.

Titanium dioxide is now one of the most common pigments in global use, and is the basis for most paint colours. It is also found in coatings and plastics. These uses of titanium dioxide account for more than 50 percent of its global usage.

Its high refractive index means that, as a pigment, it is able to scatter visible light. This results in an opaque colour and creates a bright, reflective quality when applied to a surface or incorporated into a product.

A key example of its use in these applications is as a coating for wind turbines, providing both a suitable white colour and protection from UV degradation. For the same reasons, it is also found in plastic window frames.

Food

In food, TiO2 is used in pigment grade (see below) and called E171. In many food products it acts as a whitener, but also as a colour and texture enhancer. E171 can give smoothness, when used in some chocolates, or can help give an abrasive effect, as used in some sweets.

Cosmetics and skin care

In skin care and makeup products, titanium dioxide is used both as a pigment and as a thickener for creams. As a sunscreen, ultra-fine TiO2 is used because of its transparency and UV absorbing abilities.

Environmental benefits

Due to its various properties, titanium dioxide has been found to be useful for many different environmentally friendly applications.

When used in a paint coating on the outside of buildings in warm and tropical climates, the white, light-reflecting qualities of TiO2 can lead to considerable energy savings, as it reduces the need for air-conditioning.

Also, its opaqueness means it doesn’t need to be applied in thick or double coats, improving resource efficiency and avoiding waste.

As a photocatalyst, titanium dioxide can be added to paints, cements, windows and tiles in order to decompose environmental pollutants. As a nanomaterial (see below), it can also be used as a crucial DeNOx catalyst in exhaust gas systems for cars, trucks and power plants, thus minimising their environmental impact.

Researchers are discovering new potential uses for titanium dioxide in this form. This includes clean energy production.

As a photocatalyst, it has also been shown that TiO2 can carry out hydrolysis (breaking water into hydrogen and oxygen), and the collected hydrogen can be used as a fuel.

Also, a type of solar power cell available for use – known as Gr?tzel cells – utilises nano-grade titanium dioxide to produce solar energy in a process similar to photosynthesis in plants.

What are the physical properties of titanium dioxide?

Titanium dioxide has a number of unique characteristics that make it ideally suited to many different applications.

It has an extremely high melting point of 1,843oC and boiling point of 2,972oC, so occurs naturally as a solid, and, even in its particle form, it is insoluble in water. TiO2 is also an insulator.

Unlike other white materials that may appear slightly yellow in light, because of the way TiO2 absorbs UV light, it doesn’t have this appearance and appears as pure white.

Importantly, titanium dioxide also has a very high refractive index (its ability to scatter light), even higher than diamond. This makes it an incredibly bright substance and an ideal material for aesthetic design use.

Another crucial property of titanium dioxide is that it can show photocatalytic activity under UV light. This makes it effective for environmental purification, for different kinds of protective coatings, sterilisation and anti-fogging surfaces, and even in cancer therapy.

Brilliant

Brilliance, colour strength, opacity and pearlescence unlike any other substances.

Resistant

Stability to heat, light and weathering prevents degradation of paint, in films and embrittlement of plastics.

Protective

Ability to scatter and absorb UV radiation makes TiO2 a crucial ingredient for sunscreen, protecting the skin from harmful, cancer-causing UV rays.

Powerful

Is used as a photocatalyst in solar panels as well as reducing pollutants in the air.