Development of highly reflective composite surfaces

Reflective thin films have a variety of application areas such as solar collector systems for thermal and photovoltaic applications, optical mirrors, illumination armatures, laser applications, etc. Silver and aluminum coatings are commonly used reflective materials used in concentrating solar power systems although silver is the most reflective material in the visible region. Silver films can be deposited on substrate surfaces by various methods. However, they must be carried out under high vacuum environment and also can not be used in large-scale coatings. Electroless plating method is a promising option for silver deposition on arbitrary substrates at low cost, under low temperature and with easy controlled process parameters. This work focuses on development of highly reflective surfaces produced by silver coating for use in solar collector systems. Silver coatings were deposited in aqueous medium using silver mirror reaction. The method is based on adsorption of [Ag(NH3)2]+ complex ions onto the substrate surface and then the reduction to elemental silver Ag0 with the addition of an aldehyde as reductant. Parameters such as sensitization time, concentration of OH-, concentration of glucose, concentration of [Ag+], reduction time, effect of additives (such as alcohols, capping agent, etc.) were investigated within this study. Surface morphology of the silver film coatings were characterized by scanning electron microscopy, and their crystal structure by X-ray diffraction method. Surface reflectance was measured by UV-Vis spectroscopy. XRD results proved the growth of silver film on the substrates and also showed that no impurities were present in the film. SEM images were used to confirm the measured reflectance values. More evenly distributed and smaller-sized spherulite-shaped crystals were observed for surfaces with high reflectance. Reflectance value of 97% was achieved by optimization of the process parameters. Also, to identify the effect of all processes to mechanical properties of samples, pulling and bending testes had done.