A couple figures from the original paper:
Fig. 1. An environmentally stable glass coating for daytime passive radiative cooling.
(A) Schematic of the radiative cooling glass coating on a ceramic roofing tile, which can effectively reflect solar radiation (0.3 to 2.5 μm) and emit infrared radiation (i.e., thermal emission) to the cold sky through the atmospheric transparency window (8 to 13 μm). The radiative cooling glass coating features a porous structure (porosity: ~50%), in which low–melting point glass particles (mean diameter: ~6 μm; volume: ~30%) are partially sintered to form a framework decorated with Al2O3 particles (mean diameter: ~0.5 μm; volume: ~20%). The characteristic size of the glass clusters after sintering is ~12 μm. (B) Demonstration of the optical functionality of the glass particles and Al2O3 particles in the composite structure. The scattering and absorption efficiencies as a function of wavelength for glass (blue line) and Al2O3 (red line) particles were calculated on the basis of the Lorenz-Mie theory. The dual-particle design maximizes material and dimensional effects associated with passive radiative cooling, specifically high reflectance in the solar spectrum and high emissivity in the atmospheric transparency window.
Fig. 2. Fabrication and morphology of the radiative cooling glass coating.
(
A) The glass-Al2O3 particle slurry in ethanol, which shows good fluidity. (
B) The radiative cooling glass coating applied on a ceramic tile by means of sintering at ~600°C in a furnace. (
C) The radiative cooling glass coating can be fabricated on a large scale. (
D and
E) SEM images of the glass and Al2O3 particle mixture (D) before and (E) after sintering at ~600°C for ~1 min. After the heat treatment, the Al2O3 particles are dispersed with the softened and merged glass particles, forming a cohesive microporous structure. (
F) SEM image of the cross-sectional morphology of the microporous coating. (
G) SEM image of the cross-sectional morphology of the microporous coating filled with polymeric resin (darker-gray color). (
H) The size distribution of the glass-Al2O3 clusters and pores after sintering. Approximately 60% of the glass-Al2O3 clusters were in the 8 to 13 μm range, while ~80% of the pores were smaller than 10 μm. (
I) XRD patterns of glass particles, Al2O3 particles, and sintered radiative cooling glass coating.
The coating can be applied with a brush or sprayer. It has to be heated after application so more like a ceramic glaze than a paint. The authors mention the possibility of applying as a spray on in-place structures but didn't test this idea as part of this study.