Titanium dioxide (TiO2) (EU) is a white pigment used to give whiteness and hiding power to a coating. The pigment is considered as being expensive, especially when volume prices of systems are used. The high volume price is caused by the high density of TiO2.
Scattering by Solid Particles
Particles in a matrix, like a binder system in a coating, can change the direction of light when the particles and the medium have a different refractive index (n). This phenomenon, called scattering, results in both the white color and hiding power of the coating. Scattering efficiency is governed by a few properties:
- Scattering is strong when the difference in refractive index of particle and matrix, Δn = np – nm, is big.
- For a specific wavelength of light, λ, there is an optimum with respect to particle size.
The refractive index of binders used in coatings is around 1.6. TiO2 is preferably used as scattering source because the pigment has a high refractive index, depending upon the crystal structure of the pigment:
TiO2 particles having a diameter of around 300 nm scatter visible light, λ ≈ 400 – 800 nm, most effectively.
Optimizing scattering efficiency of TiO2
Several measures can be taken in order to maximize the efficiency of expensive TiO2 pigment:
- Select rutile TiO2 with average primary particle diameter, called d-50, of around 300 nm. Both crystal structure and particle size can be found in the technical documentation of the pigment supplier.
- Separate the primary particles as much as possible during the dispersion process and stabilize the particles with dispersant to prevent flocculation:
- Assure that the TiO2 particles are distributed uniformly over the complete system. This is called spacing. An approach to prevent crowding, the opposite of spacing, is to use a suitable filler. The filler particles, filling the spaces between the TiO2 particles, act as spacers.
Often a lot of money can be saved, especially by improving the separation process and/or by changing the type or amount of dispersant.
The views, opinions and technical analyses presented here are those of the author, and are not necessarily those of UL, ULProspector.com or Knowledge.ULProspector.com. While the editors of this site make every effort to verify the accuracy of its content, we assume no responsibility for errors made by the author, editorial staff or any other contributor. All content is subject to copyright and may not be reproduced without prior authorization from Prospector.