Aging of solar selective Cr-SiO absorbers

摘要

Thin films of CR-SiO-cermets produced by evaporation on metal substrates show spectral selectivity. This property depends not only on the substrate material,m the average composition and the thickness of the film but also on the conditions of the preparation. In particular the temperature of the substrate during preparation has a strong influence on the change of selectivity during ageing. Ageing processes have been investigated in the temperature range 400 to 800$DGR@C in Ar-atmosphere for time periods up to 42 days by means of optical measurements, X-ray analysis and other properties. The main effect is the decrease of the thickness of the film and a change of the structure. By dissociation of the SiO into Si and SiO$-2$/ all chromium-silicides have been observed which are known from the binary Cr-Si-constitution diagram with the exception of CrSi. Some formation of Cr$-2$/O$- 3$/ was observed not because of the development of oxygen by the reduction of SiO$-2$/ but by residual oxygen in the Ar-atmosphere.