The Effects of Using Some Common White Pigments on Thermal and Aesthetic Performances of Pigmented Coatings

Abstract

A coated surface with high reflectance in the near infrared (NIR) region and low reflectance in the visible (VIS) region can both stay cool in the sun and retain its appearance by reducing the glare of reflected sunlight. To design such coatings, an optimization method that embraces both thermal and aesthetic effects is introduced. White pigments are widely used in designing cool coatings due to their relatively high reflectance of sunlight. However, using white pigments may produce glare, which can cause visual discomfort. It is possible to control these effects by controlling the size of pigment particles, volume concentration of pigments and coating thickness. Among the various white pigments that are available, we chose titanium dioxide, zinc oxide and alumina for this study. Radiative heat transfer in an anisotropic scattering, monodisperse pigmented layer was analyzed using the radiation element method by ray emission model (REM 2 ). Both collimated and diffuse solar irradiations were considered. The CIE (International Commission on Illumination) colorimetric system was used for color analysis. Finally, the optimum values of particle size, volume fraction of pigment, and coating thickness were obtained and compared for the three mentioned pigments.

Painting by Numbers: Nanoparticle‐Based Colorants in the Post‐Empirical Age

“…This could potentially lead to the same issue as noted in the literature review for the analytical optimization carried out by Baneshi et al (Figure 5 d-f), [ 36 ] namely that when reducing the undesirable property, the desirable is also degraded. To counter this we are implementing multi-objective criterion optimization which maximizes the extinction efficiency in the UV spectral range whilst minimizing it in the visible range as before.…”

“…Moreover, Figure 5 a illustrates that such a coating should ideally perform further functions such as permitting IR radiation to dissipate (particularly relevant for the cooling of spacecraft) or refl ecting UV radiation which can lead to degradation of organic binders. [ 36 ] Indeed, so-called "cool color" coatings are a good example of our increasing slant towards multifunctional materials but the question remains as to whether the desirable functions can be provided by a designed particle or through a designed "synergy" of different particles. Supporting the latter idea is the work of Levinson and coworkers, who, at the Lawrence Berkeley National Laboratory have undertaken a very signifi cant collaborative project with pigment and roofi ng industries in order to select materials which can be combined in single or multilayer coatings in order to signifi cantly increase the near-IR refl ectance of roofs.…”

“…[ 40 ] Furthermore, Baneshi and co-workers attempted to optimize, by purely theoretical means, the particle size and coating thickness of a "cool" pigment layer comprising titanium dioxide, zinc oxide or aluminum oxide particles. [ 36 ] The optimization parameter used was defi ned as: e.g. in the form of magnetic, electrical or thermal properties.…”

The Effect of Dispersed State to Control of Radiative Properties of Coatings Pigmented with Nanoparticles

“…1. Concept of a spectral selective coating To achieve this spectral behavior, the authors proposed making the coating on a black substrate with controlled size and concentration of pigment particles (5,6) . We introduced a parameter, R, as the ratio of solar reflected energy in the NIR region to the reflected energy in the VIS region weighted by the standard visual sensitivity of the human eye.…”

“…To achieve an optimum coating, this parameter should be maximized. In previous works (5,6) , the white pigments such as TiO 2 , ZnO and Al 2 O 3 were optimized. Moreover, we optimized the dark red coatings pigmented with Fe 2 O 3 (7) .…”