In this thesis, high solar absorber coatings of Ni-P on aluminum substrate have been fabricated by electroless technique as an alternative to sophisticated PVD coatings. For this purpose, nickel-phosphorus coating was deposited on commercially pure aluminum and then blacking process was carried out. The effect of various parameters on microstructure, hardness, adhesion, optical properties and durability of the coatings was studied. These parameters were phosphorous content, heat treatment, substance’s roughness, thickness of coating, blackened acid and CNT. The phase structure of the coatings was studied by X-ray diffraction; the crystallite size measured by using Sherrer method indicated an average crystallite size of about 15 nm with an increase in hardness. Microstructural examinations of the coatings were performed by scanning electron microscopy. The coatings generally had sound, crack-free surfaces. The topography of the coatings was studied by Atomic force microscopy. The optical properties of the coatings were determined by means of spectrophotometer and FTIR. Absorption and emission coefficients of the coatings were measured in range of 0.3-1.7µm and 2.5-25µm respectively. The ultra high absorption of the coatings is associated with unique surface morphology and formation of nickel oxides (NiO, Ni 2 O 3 ) and some nickel phosphate. The surface morphology consisting of a dense array of microscopic, conical pores perpendicular to the surface. This structure produce by selective etch act as light traps, is capable of absorbing over 98% light in solar region. The results indicated that after heat treatment, emission coefficient was decreased. CNTs improved absorption and emission of the coatings. Emission coefficient of coating was 0.34 while after embed CNTs, it reduced to 0.22. Prepared samples were subjected to an accelerated lifetime test. In the test procedure the temperature of the environment was set to 40 ? C and the relative humidity to 95%. Durability test showed that high phosphorous coatings had good long-term optical performance. The results of this study indicate that the coating process described here is a good method to produce solar absorber coatings on aluminium.
