Advanced characterization and optical simulation for the design of solar selective coatings based on carbon: transition metal carbide nanocomposites

Abstract

Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as a predictive design tool for nanomaterial-based optical coatings in general.

On the Effect of Thin Film Growth Mechanisms on the Specular Reflectance of Aluminium Thin Films Deposited via Filtered Cathodic Vacuum Arc

“…A set of aluminium thin films was deposited on glass slides and silicon (100) wafers using a 90 • pulsed FCVA equipment (Plasma Technologies, Kowloon, Hong Kong) [15]. Substrates were previously ultrasonicated for 10 min in (a) 0.5% Hellmanex solution in water, (b) acetone, and (c) ethanol.…”

Sustainable Development of Carbon Nanocomposites: Synthesis and Classification for Environmental Remediation

“…They are also nontoxic, making them suitable for biomedical uses. Nanodiamonds are made from explosive molecules that offer carbon source and conversion energy [146]. The approach for the disposal of obsolete weapons such as composition B, while other explosives may also be employed, is ecologically and economically feasible.…”

Multiscale thermo-mechanical analysis of multi-layered coatings in solar thermal applications

“…At the nanoscale, or more precisely the submicroscale, the nanoabsorber is presented as a heterogeneous composite material, with an a-C matrix and TiC embedded particles. Both phases have been characterized at the lowest scale [5]. Thus, this information can be used at the next scale in order to characterize the behavior of the nanoabsorber as a whole.…”

“…One of the most efficient configurations is based on a multi-layer stack, whose composing layers are usually arranged as depicted in Figure 2, and described in the following [5]: a) an antireflective (AR) layer (e.g., Al2O3, SiO2), transparent to solar radiation to increase solar absorption and chemically stable in air at high temperature so as to reduce corrosion; b) an absorber layer (e.g., transition-metal nanocomposites, cermets), which must offer optimal optical properties regarding absorption and conductivity as well as thermomechanical stability; c) an infrared reflective (IR) layer (e.g., metal nitrides) beneath the absorber, with high reflectivity in the infrared region to reduce emissivity; and, finally, d) a substrate (e.g., stainless steel or Ni-based alloys) layer, that hosts the HTF and provides mechanical resistance.…”

“…The composing materials of each of these layers are typically chosen (or designed) according to their particular optical properties ( Figure 3); therefore, major efforts by materials scientists in Abengoa Research have been devoted in the last years to the optical enhancement of SSCs [5].…”