Characterization of Ni-Al Solar Absorber Prepared by Flame Spray Technique

Abstract

In this research, a Ni-Al solar absorber was successfully prepared by the flame spray technique with Ni-5 wt.%Al particles as a starting material. The Ni-5 wt.%Al particles were melted and sprayed onto the outer surface of a stainless steel 316L tube in order to form a Ni-Al composite coating. The phase, morphology and reflectance (R) spectrum of the Ni-Al solar absorber were characterized by X-ray Diffraction (XRD), a Scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) analyzer and an Ultraviolet-visible-near infrared spectrophotometer at the wavelength 300-2500 nm. The results revealed that the surface of the Ni-Al solar absorber was rough, and its cross section was overlapped layer by layer. The Ni-Al solar absorber was composed of Nickel (Ni) and aluminum (Al) phases. NiO and Al2O3 phases were also found on the surface. The chemical composition of the Ni-Al solar absorber was Ni (72.94 wt.%), Al (11.76 wt.%) and O (15.29 wt.%). The solar absorptance (α)of this solar absorber was 0.77. This demonstrates that a Ni-Al composite coating can be applied as a solar absorber material for solar collector at high operating temperatures.

Influence of Ni–Al coating thickness on spectral selectivity and thermal performance of parabolic trough collector

“…The Ni-Al coating is built up layer by layer as the result of the individual melted Ni and Al particles in the form of splat sprayed from a spray gun. This microstructure is similar to those of Ni-Al composite coatings prepared by other people using the same and other techniques [14,19,20]. However, it can be observed that the samples with different thicknesses have different pore sizes and interlamellar porosity.…”

“…The pores occurred after cutting and polishing the samples, indicating that these areas had a low-density microstructure due to the weak bond between the melted Ni and Al particles. According to previous studies, this is caused by imperfectly melted and un-melted particles of raw materials during the flame spraying process [13,14]. Moreover, there are cracks at the interface between the Ni-Al coating and the outer surface of the SS tube as the result of a residual stress from the thermal expansion mismatch between the coating and the SS tube.…”

“…To prepare the tube, the Ni-5wt% Al powder was coated onto the outer surface of the SS tube using CastoDyn DS 8000 flame spray equipment (Castolin Eutectic, Switzerland). The flame spray setup and fuel condition for the coating process were previously proposed [14]. The variation of Ni-Al coating thickness was carried out by the flame spray process for 120, 180, and 300 s under the same conditions.…”

“…The α was determined from the measured R spectrum, as expressed in Eq. (1) [14,15], where R(λ) is the observed reflectance spectrum of the coating at a specific wavelength of 300-2500 nm, and I s (λ) is the solar spectral irradiance at air mass (AM) 1.5 [16].…”

“…Ni-Al composite coatings are particularly applied to numerous special applications that required a high melting point, lowdensity (5890 kg m −3 ), high thermal conductivity, excellent anticorrosion, high-temperature oxidation, high thermal stability, and high-temperature mechanical properties [11][12][13]. A previous study by this researcher has successfully prepared Ni-Al solar absorber using a flame spray technique, especially, the α of the Ni-Al solar absorber was 0.77 [14]. However, the effect of Ni-Al coating thickness on spectral selectivity and thermal performance of PTC is uncertain at present, and further research in this area is necessary.…”