CrAlSiN barrier layer to improve the thermal stability of W/CrAlSiNx/CrAlSiOyNx/SiAlOx solar thermal absorber

Abstract

A B S T R A C TThe influence of adding CrAlSiN barrier layer between the back-reflector tungsten (W) and stainless-steel substrate on thermal stability has been investigated. In previous work, after the annealing in vacuum at 600°C, tungsten diffusion from the back-reflection layer towards the stainless-steel substrate was found. In this study, a barrier layer was added and its influence upon the W diffusion was studied. Several designs of multilayer solar selective absorber for high temperature applications were used to test the thermal and chemical stability and oxidation resistance after vacuum annealing. These samples were characterized by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR) and UV-VIS-NIR spectroscopy. All absorber tandems show good thermal stability after vacuum annealing at 600°C and the changes in optical constants solar absorptance (α) and thermal emittance (ε) are negligible. In some cases, small changes in the reflectance curves after the first step of annealing were seen. Some changes were found in the oxide layer, due to the incomplete oxidized Si atoms, as confirmed by FTIR analyses. This cannot justify the increase of NIR reflectance observed in the optical stacks after annealing, which can be due to the phase changes of the back-reflector tungsten layer. All layers of stacks are amorphous, except the tungsten layer, which is polycrystalline and shows a columnar growth. The addition of a CrAlSiN P = 0.11 Pa barrier layer between tungsten and stainless-steel substrate proved to be a good solution to control the diffusion of W atoms towards the substrate, whereas using higher nitrogen partial pressure in the high and the low absorption layers reduce the diffusion of Cr from those layers to surface.

Spectral properties and microstructure of sputtered WOx films for solar conversion applications

“…The SSACs on Cu substrate showed a poor α of 0.88 and ε of 0.062. Such result was different from the traditional four‐layer double‐cermet SSACs, such as W‐Al 2 O 3 , Mo‐SiO 2 , Al‐AlN, and CrAlSiN . Compared with the recently reported multilayer absorbers (Table ), the WO x /SiO 2 SSACs showed similar optical performance, whereas the SSACs presented a simple structure and low process cost.…”

The effect of increasing Si content in the absorber layers (CrAlSiNx/CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability

“…In all cases, the emittance (ε) is improved after annealing in air and in vacuum, which confirms that the tungsten reflection layer is well protected by the other layers, showing good thermal stability against oxidation. The decrease of the emissivity with annealing was already reported and can be due to a W phase transformation during annealing [22,23]. Fig.…”

“…As a result, small amount of tungsten diffused towards the stainless-steel substrate, but the general evaluation shows that no other significant changes are present. However, tungsten diffusion towards the substrate can be easily solved by adding a barrier layer, as studied in the previous work [22].…”

Effect of Silicon Content in Functional Properties of Thin Films

“…Thin films have been widely used in different application fields such as in chemical as diffusion barrier, in electrochemical as films for protection against corrosion, in mechanical as hard and wear resistance coating, in optical as reflection and antireflection coating, and in electronic area as conductor or insulator material [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…Among all these compounds, we find that the transition metal nitrides (MeN) have been widely used in mechanical applications due to their high hardness and wear resistance [2,[13][14][15][16]. However, it has been found that the addition of a third element may improve the physical and chemical properties of MeN due to a change that this new element generates in the microstructure of these materials [1,[17][18][19][20][21][22][23][24][25][26][27][28][29][30]. These structures are called nanocomposite, and there are two different groups of hard nanocomposite films, for instance: (i) crystalline/amorphous nanocomposites and (ii) crystalline/crystalline nanocomposites.…”