DARK COATINGS

摘要

A composition comprising semiconductor particles in a binder provides a dark coating with infra-red characteristics arranged to prevent undesirable temperature rises when exposed to solar radiation. Preferably the coating has a visible diffuse reflectivity of no more than 10 %, a direct solar hemispherical reflectivity in the near infra-red region of no less than 60 %, and a thermal hemispherical emissivity ϵMIR25 of no less than 50 %. The particles are preferably of crystalline silicon, amorphous silicon, hydrogenated silicon, CdSe, CdTe or GaAs, with an optical dimension of 0.6 to 2 microns. The coating may exhibit an absorption edge with a knee at which the second derivative of reflectivity with wavelength is a positive maximum occurring within the waveband 0.6 to 0.85 microns.