What is titanium dioxide?
Where does it come from and why do we need it?
Titanium dioxide (TiO2) is a bright white substance used primarily as a vivid colourant in a wide array of common products. It also has a number of lesser-known qualities that make it an extremely useful and important ingredient in our battle to fight climate change and prevent skin cancer.
Prized for its ultra-white colour, ability to scatter light and UV-resistance, TiO2 is a popular ingredient, appearing in hundreds of products we see and use every day, bringing significant benefits to our economy and overall quality of life.
- Across the EU, applications for TiO2 include paints, plastics, paper, pharmaceuticals, sunscreen and food.
- As a photocatalyst, titanium dioxide can be added to paints, cements, windows and tiles in order to decompose environmental pollutants.
- As a white pigment, TiO2 is one of the most important raw materials for paints and coatings. The DIY market for TiO2-containing paints is €3.5 billion alone.
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.
Read more about how titanium dioxide is used in sunscreen.
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 Grätzel cells – utilises nano-grade titanium dioxide to produce solar energy in a process similar to photosynthesis in plants.
Visit uses of titanium dioxide for more information.
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.
What are the forms of titanium dioxide?
TiO2 possesses different qualities depending on whether it is produced as pigment-grade or nanomaterial-grade. Both forms are tasteless, odourless and insoluble.
Pigment-grade TiO2 particles are approximately 200-350nm in dimension and this form accounts for 98 percent of total production. It is used mainly for light scattering and surface opacity applications, such as paint – this includes its use as a base for various colour paints or as a standalone ‘brilliant’ white.
Nano, or ultrafine TiO2 comprises of primary particles sized less than 100nm. In this grade, titanium dioxide is transparent (colourless) and boasts improved UV scattering and absorbing properties compared with larger particle-size, pigment-grade TiO2.
What is titanium dioxide made of?
Titanium is one of the most common metals on earth, but it does not occur naturally in this elemental form. Titanium dioxide – also known as titanium (IV) oxide or titania – is the naturally occurring compound created when titanium reacts with the oxygen in the air. As an oxide, titanium is found in minerals in the earth’s crust. It also found with other elements, including calcium and iron.
Its chemical formula is TiO2, which means it consists of one titanium atom and two oxygen atoms (hence dioxide). It has a CAS (Chemical Abstracts Service) registration number of 13463-67-7.
TiO2 is typically thought of as being chemically inert, meaning it doesn’t react with other chemicals and is, therefore, a stable substance that can be used in many different industries and for a variety of applications.
Where does titanium dioxide come from?
Titanium dioxide itself was officially first named and created in a laboratory in the late 1800s. It wasn’t mass manufactured until the early 20th century, when it started to take over as a safer alternative to other white pigments.
The element titanium and the compound TiO2 are found around the world, linked to other elements such as iron, in several kinds of rock and mineral sands (including a component of some beach sands). Titanium most commonly occurs as the mineral ilmenite (a titanium-iron oxide mineral) and sometimes as the mineral rutile, a form of TiO2. These inert molecular compounds must be separated through a chemical process to create pure titanium dioxide.
How is titanium dioxide extracted?
How pure titanium dioxide is extracted from titanium-containing molecules depends on the composition of the original mineral ores or feedstock. Two methods are used to manufacture pure TiO2: a sulphate process and a chloride process.
The principal natural source of titanium dioxide is mined ilmenite ore, which contains 45-60 percent TiO2. From this, or an enriched derivative (known as titanium slag), pure TiO2 can be produced using the sulphate or chloride process.
Sulphate and chloride methods
Of the two methods of extraction, the sulphate process is currently the most popular method of producing TiO2 in the European Union, accounting for 70 percent of European sources. The remaining 30 percent is the result of the chloride process. On a global level, it is estimated about 40-45 percent of the world’s production is based on the chloride process.
As a widely used substance with multiple applications, research is being carried out to improve the production process to reduce the levels of chemicals used and waste produced, and to recycle any by-products.
The future of titanium dioxide
For a substance that is relatively unknown to the public, it’s amazing how many everyday products titanium dioxide can be found in. Because of its many varied properties, our skin, cities, cars, homes, food and environment are made brighter, safer, more resilient and cleaner by titanium dioxide. With a legacy of 100 years of safe commercial use, titanium dioxide is only going to become more vital as our environment faces greater challenges from a growing population.