Non-Invasive Optical Topographic Evaluation of Cr-Cr_2O_3 Cermet Solar Absorbers

摘要

The importance of renewable energy sources is currently attracting widespread attention due to the limited availability of fuels and major environmental impacts. A great deal of effort is put our days on the development of new efficient solar energy collectors either by quantum or thermal conversion. On this communication we will focus on the roughness and microtopographic inspection of surface thin films and spectrally selective coatings for these types of applications. Physically Vapour Deposited (PVD) coatings like sputter deposited metal oxide and nitride thin multilayered and graded ones can be used in spectrally selective surfaces for thermal collectors and energy-efficient windows. The efficiency of Cr-Cr_2O_3 cermet solar absorbers for both static and dynamic control of radiative heat transfer through absorbing surfaces will depend on the chemical and physical structural characteristics and related optical properties like reflectance, emittance, absorbance and transmittance. The topographic characteristics of the produced coatings will greatly condition its relevant properties. A careful integral evaluation of the micro-relief structure of these Cr-Cr_2O_3 cermet coatings needs to be performed in a non-destructive, non-invasive way. Two optical inspection system suitable for the type of surfaces and range of roughness involved were employed: the MICROTOP.03.MFC an active optical triangulation sensor developed by the principal author at the Universidade do Minho; and, the Rodenstock' RM100 focus sensing based system. Not only the roughness values and roughness regimes of the surfaces are meaningful but also all other microtopographic characteristics including lay and form. The Fourier analysis of the different obtained profiles was performed and frequency filtering and extracting applied as a major source of meaningful microtopographic information.