White titanium dioxide is frequently used in the form of nanoparticles. There is a real chance now that black titanium dioxide in the form of nanotubes will see its first industrial application; it will appear on a clock face of a famous watch manufacturer.
When approached by this manufacturer, the team of Dr. Jan Macák conceived of the idea of producing black titanium dioxide. “We always strive for our materials having a variety of applications thanks to their properties. That is one of the reasons why our research involves cooperation with business partners,” says Dr.-lng. Jan Macák, who is the CEMNAT specialist in synthesis of low-dimensional structures such as nanotubes, nanoparticles and nanofibers.
It took the researchers a year to synthesise the material for manufacturing the blackest clock face, and it involved a cooperation with the Central European Institute of Technology of Brno University of Technology (CEITEC).
“Thanks to their optical properties, it was clear from the very beginning that we have to use a layer of nanotubes. What we had do develop, however, was a way for the tubes from titanium dioxide to become black enough. And that was not easy,” says Dr. Macák.
We know from our experience and literature that carbon nanotubes with a similar structure are almost perfectly black thanks to their composition, architecture and light absorption system.
Never before has black titanium dioxide been used in such a form and on such a surface like a clock face. That is why the researchers are careful not to disclose the process. “The black form we have developed is very specific in terms of its preparation. It contains a few defects of the crystalline grid, which have a major impact on the refractive index. Optically, the white material turns into black material. The reaction can be controlled and different shades of gray can be prepared as well,” says Dr. Macák.
He also adds: “Titanium dioxide could be compared to a chameleon. The colour can change without having to use different ingredients with a different chemical composition. I am happy to say we have succeeded. What we still test is the stability of the black form as the clock faces are supposed to last unchanged for dozens of years.”
Compounds of oxide and titanium can be found in the nature in minerals. For industrial use, small particles of white titanium dioxide are produced using either the chloride or sulfate process. More than 4 million tons of pigment are used every year in automotive industry, or food industry as well as for manufacturing stationary products, cosmetics, dyes, pharmaceuticals or suntan lotions. The white dye is insoluble in water, it absorbs UV radiation that can be turned into heat, it reflects sun and has high brightness and colour stability.