Selective Coatings Research Articles

Thermal stability of AlCrO antireflection layer for high-temperature cermet-based solar selective absorber applications

Highly stabled antireflection layers play a crucial role in enhancing the optical and thermal performance of cermet-based solar selective absorbing coatings. Few state-of-the-art antireflection layers are qualified for high-temperature (>873 K) utilizations due to the insufficient thermal stability and increased infrared emissivity. Herein, a highly stable multilayer cermet-based absorber with an AlCrO antireflection layer is developed using cathode arc ion plating. The deposited coating exhibits a solar absorptivity of 0.908 ± 0.005 and a thermal emissivity of 0.144 ± 0.004 even after annealing at 923 K for 2000 h in air, compared to the pristine coating with a spectral selectivity of 0.898 ± 0.002/0.186 ± 0.003. After undergoing the extensive annealing treatments, abundant particles with an average size of approximately 8 μm have been detected on the coating surface. However, the AlCrO layer exhibits a remarkably flawless and dense surface topography devoid of any cracks or voids. Based on the GI-XRD and TEM evaluations, the particles have been identified as Mn2O3 nanocrystals. The formation of Mn2O3 particles originates from the diffusion of Mn atoms from the stainless-steel substrate to the surface of the AlCrO layer, where they undergo oxidation. The presence of Mn2O3 can enhance the solar absorptivity by increasing transmittance in the visible light spectrum and reduce the emittance by enhancing reflection of infrared radiation. Then, the impact of Mn2O3 on spectra selectivity and thermal stability is discussed. These results indicate that the AlCrO layer exhibits remarkable durability when subjected to high-temperature annealing in an air environment, thereby significantly enhancing the thermal stability and optical performance of cermet-based solar selective absorbing coatings. These findings suggest that the AlCrO layer exhibits exceptional durability under high-temperature annealing in an air environment, thereby significantly enhancing the thermal stability and optical performance of cermet-based solar selective absorbing coatings.

Parabolik Oluklu Solar Kollektörlerin Termal Verimliliğinin Artırılması: Genel Bakış

This article examines various methods to enhance the thermal efficiency of parabolic trough solar collectors (PTCs), both theoretically and experimentally. These methods include increasing the surface area of the absorber tube to increase its ability to absorb solar energy, placing a tube inserts inside the tube to induce turbulence and hence improve heat transfer. Among other methods are also minimization of reflection by using selective coatings on the surface of the absorber tube. Additionally, increasing the thermal conductivity of the working fluid, or modifying or altering the shape of the absorber tube or the reflective surface have also been shown to have improved thermal performance by minimizing energy losses due to conduction, convection, and radiation. All these and similar approaches that address and improve system parameters lead to improved efficiency and thermal performance, but they also entail a pressure drop and increase the cost of the system. In this study, the techniques that are used to improve the thermal efficiency of PTCs are addressed and presented in detail along with the findings of previous studies.

Sustainable Energy Progress via Integration of Thermal Energy Storage and Other Performance Enhancement Strategies in FPCs: A Synergistic Review

Flat plate collectors (FPCs) are the leading solar thermal technology for low-medium range temperature applications. However, their expansion in developing countries is still lacking because of their poor thermal performance. Improving the thermal performance of flat plate collectors (FPCs) is a crucial concern addressed in this review This study comprehensively discussed the performance improvement methods of FPCs, such as design modification, reflectors, working fluid, and energy storage materials, by covering current issues and future recommendations. Design factors such as coating and glass cover thickness, thickness of absorber plate and material, air gap between the glass cover and absorber plate, and riser spacing, along with insulation materials, are examined for their impact on FPC performance. Absorber design changes with selective coatings for improving the heat transmission rate between the working fluid and absorber are critical for enhancing collectors’ thermal output. The nanofluids utilization improved FPC’s thermal performance in terms of energetic and exergetic outcomes in the 20–30% range. Moreover, adding a heat storage unit extends the operating hours and thermal output fluctuations of FPCs. Research suggests that employing turbulators and nanofluids as heat transfer fluids are particularly effective for enhancing heat transfer in FPCs. This comprehensive review serves as a critical tool for evaluating and comparing various heat transfer augmentation techniques, aiding in the selection of the most suitable option.

Facile dip-coating assisted preparation of reduced graphene oxide-copper oxide nanocomposite thin films on aluminum substrate for solar selective absorber

Reduced graphene oxide integrated copper oxide nanocomposite thin film (rGO-CuO NC TF) solar selective absorber coatings were devised on aluminum substrate using dip-coating procedure. The prepared coatings were subjected to characterization by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, PL spectroscopy, UV–vis–NIR spectrophotometer, Emissometer and Raman spectroscopy. XRD and Raman analyses disclosed presence of mono-phase with highly crystalline monoclinic structured CuO in the rGO-CuO NC TFs. The SEM images revealed grain-like morphology of CuO, which are randomly distributed on rGO sheets. EDX and XPS investigations confirmed presence of anticipated chemical constituents and chemical composition, respectively in the NC TFs. The rGO-CuO NC TF with 1.0 wt% GO disclosed absorptance (α) of 79.92% and emittance (ε) of 4.2% with a highest selectivity (ξ) of 19.03 that suggests its promising prospect for solar absorber coating in solar thermal devices.

Selective Detection of Erythrocytes with QCMs-ABO Blood Group Typing.

Blood transfusion, as well as organ transplantation, is only possible after prior blood group (BG) typing and crossmatching. The most important blood group system is that of Landsteiner's ABO classification based on antigen presence on the erythrocyte surfaces. A mass sensitive QCM (quartz crystal microbalance) sensor for BG typing has been developed by utilizing molecular imprinting technology. Polyvinylpyrrolidone (crosslinked with N,N-methylenebisacrylamide) is a favorable coating that was imprinted with erythrocytes of different blood groups. In total, 10 MHz quartz sheets with two resonators, one for MIP (molecularly imprinted polymer) and the other for NIP (non-imprinted polymer) were fabricated and later used for mass-sensitive measurements. The structure of erythrocyte imprints resembles a donut, as identified by AFM (atomic force microscope). All the erythrocytes of the ABO system were chosen as templates and the responses to these selective coatings were evaluated against all blood groups. Each blood group can be characterized by the pattern of responses in an unambiguous way. The results for blood group O are remarkable given that all types of erythrocytes give nearly the same result. This can be easily understood as blood group O does not possess neither antigen A nor antigen B. The responses can be roughly related to the number of respective antigens on the erythrocyte surface. The imprints generate hollows, which are used for reversible recognition of the erythrocytes. This procedure is based on molecular recognition (based on supramolecular strategies), which results from size, shape and enthalpic interactions between host and guest molecules.

Development of a Selective Layer Via Ultrasonic Spray Coating for Vanadium Redox Flow Batteries: Analysis of Ink Composition and Component Scale-up

Vanadium Redox Flow Battery (VRFB) is a promising technology for stationary energy storage because of its long cycle life and independent energy to power ratio. However, the competitiveness of the technology is hindered by some technological issues, such as vanadium cross-over. Vanadium cross-over is the undesired transport of vanadium ions trough the ion-exchange membrane, causing capacity loss and electrolyte imbalance. Usually, to mitigate cross-over fluxes between the two half-cells, relatively thick membranes (>50 µm) are employed in the commercial applications, meaning increased ohmic losses, reduced energy efficiency and higher system capital cost: indeed, the membrane can contribute up to 50% the cost of the stack [1]. The state-of-the-art membranes for VRFB are made of NafionTM because of its high conductivity, but its not-ideal selectivity towards vanadium ions prevents the use of thin membranes. Alternative cation exchange membranes like SPEEK or SPI are promising because of their reduced permeability, but the low conductivity limits system power density. Instead, anion exchange membranes are still limited by the poor chemical stability and low conductivity [2].The authors in a recent work [3] successfully demonstrated the possibility of mitigating vanadium cross-over though an innovative additional selective layer directly deposited on the membrane. The selective layer, termed as barrier, is a porous component whose pores size tortuous path, thickness and composition are designed to improve ion/proton selectivity. As reported in Cecchetti et al., the barrier layer, manufactured through Reactive Spray Deposition Technology (RSDT) significantly reduced battery self-discharge without hindering the efficiency of the battery [3].In this work, the possibility of manufacturing the barrier via Ultrasonic Spray Coating (USC) is investigated. USC is a commercial and easily scalable technique that exploits the ultrasonic vibration of the nozzle tip to uniformly atomize and spray an ink on a substrate [4]. In particular, the influence of the process parameters and ink composition on the selectivity of the barrier layer and efficiency of the battery were investigated through both morphological and electrochemical characterization in batteries of 4 cm2 and 25 cm2 active area. The deposited barrier layers were directly deposited on NafionTM 212 to form thin layers of 10 µm thickness (Figure 1). The barriers were composed of commercial silica and Vulcan® XC-72R nanoparticles, that introduce a tortuous path for the vanadium ions through the separators, and NafionTM ionomer, acting as a binder and ensuring proton conductivity.After identifying the combination of process parameters and ink composition that ensures the lowest self-discharge of the battery, the scale-up of the barrier at commercial scale was investigated by directly deposition the barrier on NafionTM 212 to obtain an active area of 100 cm2. The 100 cm2 barrier was tested in a VRFB in cycles of charge-discharge cycles with cut-off voltages of 1.65 V and 1 V showing a capacity decay rate of 0.11 % cycle-1 at 50 mA cm-2: four time lower than the reference value (0.44 % cycle-1) reported by Rodby et al. for VRFB in the same range of current density [5].

Enhanced high-temperature thermal stability of the novel MoAlSiN-based solar selective absorbing coatings by optimizing the multilayer structure

Solar selective absorbing coating (SSAC) plays an important role in the high-temperature concentrated solar power system. The high thermal stability of SSAC above 600 °C has been a big open question for molten salt concentrated solar power projects. In our work, the TiN/Mo/MoAlSiN/MoAlSiON/SiO2 and the TiN/Mo/MoAlSiN/Si3N4/SiO2 SSACs are developed for getting high-temperature thermal stability, besides excellent spectral selectivity. The solar spectral absorptivities of the MoAlSiN/MoAlSiON and MoAlSiN/Si3N4 SSACs are 95.2% and 93.2%, respectively. While the infrared emissivities of the MoAlSiN/MoAlSiON and MoAlSiN/Si3N4 SSACs are controlled below 10.6% and 10.5% at 400 °C, respectively. The novel MoAlSiN/Si3N4 SSAC deposited on quartz can maintain thermal stability even after heat treatment at 800 °C for 200 h in vacuum, which is one of the best results in the research field for high-temperature SSACs. It is found that the choice of suitable materials without oxygen and the elimination of interfacial thermal stress are very important for improving thermal stability. Furthermore, the practical total energy conversion efficiencies of the MoAlSiN/Si3N4 SSAC at 600 °C–800 °C are always above 57%. When the activation energy is assumed as 180 kJ/mol, the estimated service life of the MoAlSiN/Si3N4 SSAC at 600 °C is more than 25 years.

Enhancing Nasopharyngeal Carcinoma Cell Separation with Selective Fibronectin Coating and Topographical Modification on Polydimethylsiloxane Scaffold Platforms.

The extracellular matrix (ECM) serves as a complex scaffold with diverse physical dimensions and surface properties influencing NPC cell migration. Polydimethylsiloxane (PDMS), a widely used biocompatible material, is hydrophobic and undesirable for cell seeding. Thus, the establishment of a biomimetic model with varied topographies and surface properties is essential for effective NPC43 cell separation from NP460 cells. This study explored how ECM surface properties influence NP460 and NPC43 cell behaviors via plasma treatments and chemical modifications to alter the platform surface. In addition to the conventional oxygen/nitrogen (O2/N2) plasma treatment, O2 and argon plasma treatments were utilized to modify the platform surface, which increased the hydrophilicity of the PDMS platforms, resulting in enhanced cell adhesion. (3-aminopropyl)triethoxysilane and fibronectin (FN) were used to coat the PDMS platforms uniformly and selectively. The chemical coatings significantly affected cell motility and spreading, as cells exhibited faster migration, elongated cell shapes, and larger spreading areas on FN-coated surfaces. Furthermore, narrower top layer trenches with 5 µm width and a lower concentration of 10 µg/mL FN were coated selectively on the platforms to limit NP460 cell movements and enhance NPC43 cell separation efficiency. A significantly high separation efficiency of 99.4% was achieved on the two-layer scaffold platform with 20/5 µm wide ridge/trench (R/T) as the top layer and 40/10 µm wide R/T as the bottom layer, coupling with 10 µg/mL FN selectively coated on the sidewalls of the top and bottom layers. This work demonstrated an innovative application of selective FN coating to direct cell behavior, offering a new perspective to probe into the subtleties of NPC cell separation efficiency. Moreover, this cost-effective and compact microsystem sets a new benchmark for separating cancer cells.

Design and scalable fabrication of core-shell nanospheres embedded spectrally selective single-layer coatings for durable daytime radiative cooling

Daytime radiative cooling (DRC) can spontaneously cool a surface without consuming energy by reflecting sunlight and emitting thermal radiation to the outer space through atmospheric transmission windows. However, the manufacturing of efficient DRC designs with low cost, high scalability, strong applicability, and along with achieving great weather resistance for practical applications remains a challenge. Here, we report a facile strategy to fabricate spectrally selective single-layer DRC coatings by facilely embedding hydrophobically modified TiO2@SiO2 nanospheres in commercially available fluorocarbon resin matrix for improving daytime cooling. The TiO2 shell thickness, pigments volume fraction, and coating thickness are optimized using finite difference time-domain (FDTD) simulation to maximize the sunlight scattering efficiency with minimal material usage. The coating prepared with a spaying time of 40 s reflects above 93% of solar irradiance and exhibits an infrared emissivity of ∼94% at atmospheric transmittance window wavelength, leading to a desirable daytime sub-ambient temperature drop of ∼10.9 °C. Building energy simulations demonstrates that 32.6% of cooling energy can be saved per year in China when the coating is used as building envelopes. The coatings also show improved scalability, peel strength, self-cleaning, and weather resistance, which makes them attractive candidates for long period outdoor DRC applications. This work paves a new way to design radiative cooling coatings with low cost and ease of application for the development of highly energy-efficient cooling technology.

Enhanced Performance of Nickel–Cobalt Oxides as Selective Coatings for Flat-Plate Solar Thermal Collector Applications

Solar thermal collectors represent a practical option to capture energy from the sun, providing low-cost domestic and industrial heating and decreasing the dependency on fossil fuels. Spinel-type metal oxides show interesting physicochemical properties and so can be used as active materials for converting solar energy to electrical, chemical, and heat energy. We report the synthesis and characterization of nickel–cobalt mixed metal oxides used as an active phase in selective paints for solar absorber coatings applied to a domestic flat collector. The nickel–cobalt mixed oxides crystallized in the cubic phase related to the spinel structure, exhibiting good thermal stability and reproducibility. These mixed oxides presented oxidation states (2+ and 3+) for both nickel and cobalt. The coatings fabricated from the selective paints based on nickel–cobalt mixed oxides showed a solar absorptance value of 94%, while for the commercial paint Solkote®, the value was 93%. A representative coating based on the NiCo2O4 composition was evaluated for the first time in a domestic-type flat solar collector for water heating under real operating conditions, achieving an outstanding performance that competes with that of commercial collectors. The potential application of nickel–cobalt mixed oxides in solar collectors opens up new opportunities for future innovations and developments in functional absorber coatings.

Review of Surface Acoustic Wave Sensors for the Detectionand Identification of Toxic Environmental Gases/Vapours

Detection and identification of toxic environmental gases have assumed paramount importance precisely in the defense, industrial and civilian security sector. Numerous methods have been developed for the sensing of toxic gases in the environment ever since surface acoustic wave (SAW) technology came into existence. Such SAW sensors called electronic nose (E-Nose) sensor use the frequency response of a delay line/resonator. SAW device is focused and given importance. The selective coating between input and output interdigital transducers (IDTs) in the SAW device is responsible for corresponding changes in operating frequency of the device for a specific gas/vapour absorbed from the environment. A suitable combination of well-designed SAW delay lines with selective coatings not only help to improve sensor sensitivity and selectivity but also leads to the minimization of false frequency alarms in the E-Nose sensor. This article presents a comprehensive review of design, development, simulation and modelling of a SAW sensor for potential sensing of toxic environmental gases.

Realizing an Optical Micro‐Cavity in a CuCo2O4‐W‐CuCo2O4 Thin Film Stack for Spectrally Selective Solar Absorbers

AbstractTapping the potential of solar thermal energy requires spectrally selective solar absorber coatings, which lead to high photothermal efficiency. Micro‐cavities are known to dramatically enhance or suppress light absorption and emission in a directional manner and are used in nanophotonics, photodetectors, lasing, etc. Here, a dielectric‐metal‐dielectric multilayer stack with an optical micro‐cavity of a 12 nm tungsten layer formed between two dielectric layers of transition metal oxide CuCo2O4 (CCO) is designed. The CCO‐W‐CCO thin film multilayers deposited on stainless steel substrate by DC‐radio frequency magnetron sputtering achieve a 90% solar absorptance for the entire solar spectrum and a thermal emittance of 19% for the infrared spectrum. Optimization of thicknesses of individual layers is achieved by numerical simulations done in COMSOL Multiphysics, thereby reproducing the optical properties of each layer. The simulation results satisfactorily reproduce the experimental reflectance and demonstrate maximum power dissipation in the metallic layer in visible as well as NIR regions. Nevertheless, CCO material characterizations reveal that the enhanced absorption over the entire solar spectrum could be attributed to the underlying spinel crystal structure and the nanostructure film morphology.

Improved optical and mechanical characteristics of multilayered Cu/TiON/CrO2 coating via heat treatment for solar absorbing applications

In the last few decades, growing interest has been shown in the development of new solar selective coatings based on transition metal nitride and/or oxinitride for solar absorbing applications. Solar thermal collectors are well thought out to be the most effective process of converting and harvesting solar radiation. In this investigation, Cu/TiON/CrO2 multilayered solar selective absorber coatings have been coated onto Al substrates using the dip-coating process followed by an annealing process at (400, 450, 500, 550, and 600 °C. The XRD analysis showed excellent crystalline quality for the prepared thin films along with enhanced surface features as proved by FESEM images, and the grains are in the range of (27–81) nm. The optical investigations revealed that the film annealed at 600 °C exhibits improved solar absorptance, thermal emittance, and solar selectivity of ~ (90.7 %), (5.8 %) and 15.6, respectively. Also, the highest values of hardness ~ (26.8 GPa) and Young’s modulus ~ (250 GPa) were assigned for the film annealed at the highest temperature. Calculated optical band gaps of fabricated thin multilayered Cu/TiON/CrO2 films were found to be in the range of (1.8 – 2.10) eV.

Extracting Optical Parameters of Cu–Mn–Fe Spinel Oxide Nanoparticles for Optimizing Air-Stable, High-Efficiency Solar Selective Coatings

High-temperature Cu–Mn–Fe spinel-oxide nanoparticle solar selective absorber coatings are investigated experimentally and theoretically. A general realistic approach to evaluate absorption coefficient spectra from the optical measurements of the nanoparticle-pigmented coatings is developed by solving the inverse problem of the four-flux-radiative transfer model. The derived absorption properties are utilized to elucidate the direct and indirect bandgap transitions in the visible spectral regime as well as the sub-bandgap absorption in the infrared range. Furthermore, the optical properties of NP materials can be directly applied to optimize the solar selective coating design and analyze thermal degradation mechanisms. The analysis reveals that the Cu–Mn–Fe spinel oxides are semiconductors with an indirect bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap material with Eg = 1.84 eV. With the same coating thickness and nanoparticle load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 < CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a high optical-to-thermal energy conversion efficiency of ∼93.5% under 1000× solar concentration at 750 °C, and long-term endurance upon thermal cycling between 750 °C and room temperature in air. The optical parameter analysis approach can be easily extended to other material systems to facilitate the search and optimization of high-temperature nanoparticle-pigmented solar selective coatings.

Aptamer-functionalized stir bar sorptive extraction for selective isolation, identification, and determination of concanavalin A in food by MALDI-TOF-MS

An aptamer-functionalized stir bar sorptive extraction (SBSE) coating is described for the first time devoted to selective isolation and preconcentration of an allergenic food protein, concavanalin A (Con A), followed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF-MS) determination. For this purpose, the polytetrafluoroethylene surface of commercial magnetic stir bars was properly modified and vinylized to immobilize a thiol-modified aptamer against Con A via straightforward “thiol-ene” click chemistry. The aptamer-functionalized stir bar was employed as SBSE sorbent to isolate Con A, and several parameters that can affect the extraction efficiency were investigated. Under the optimized conditions, Con A was extracted and desorbed during 30 and 45 min, respectively, at 25 °C and 600 rpm. The SBSE MALDI-TOF-MS method provided limits of detection of 0.5 μg mL−1 for Con A. Furthermore, the SBSE coating was highly selective to Con A compared to other lectins. The developed method was successfully applied to the determination of low levels of Con A in several food matrices (i.e., white beans as well as chickpea, lentils, and wheat flours). Recoveries ranged from 81 to 97% with relative standard deviations below 7%. The aptamer-based stir bars presented suitable physical and chemical long-term stability (1 month) and a reusability of 10 and 5 extraction cycles with standards and food extracts, respectively. The developed aptamer-affinity extraction devices open up the possibility of developing novel highly selective SBSE coatings for the extraction of proteins and peptides from complex samples.Graphical abstract

New spectrally selective coatings for CSP linear receivers operating in air at high temperature

AbstractAn attractive candidate to reduce dependence on fossil fuels and replace them by renewable sources is represented by concentrated solar power (CSP) technology, whose wide deployment is still hindered by its high investment costs. In CSP linear collector plants, a key component with high technological content may be identified in receiver tubes, that are traversed by heat transfer fluid and located on focal line on which solar radiation is concentrated by mirrors. The proposed work aims at developing spectrally selective coatings for receiver tubes able to overcome state‐of‐the‐art technological limitation in terms of both vacuum encapsulation and maximum operative temperature, currently limited at 550°C for molten salts CSP plants. To this aim, a multilayer structure was designed and developed for coating a receiver tube to be employed in open‐air environment at temperature of 600°C. The multilayer coating is based on tungsten chromium titanium infrared reflector and includes a solar absorber layer developed with two alternative methods of reactive sputtering and thermal oxidation respectively, finally covered by antireflective and barrier bi‐layer of aluminum oxide and silica. Thermal stability was demonstrated of the new developed coatings, since only small variations were measured of the optical parameters after more than 2000 h of aging in open air conditions at temperature of 600°C (on average less than 5%), with final measured solar absorptance αs of 73% and 87% and thermal emissivity εth at 600°C of 18% and 27% for aged multilayer structures including the absorber layer obtained through thermal oxidation and sputtering process, respectively. These results pave the way for further improvement in terms of both optical performance and operative temperature increase, allowing to enhance efficiency and lower costs, thus contributing to ease to deployment of CSP technology.

High-temperature thermal stable solar selective absorbing coating based on the dielectric-metal-dielectric structure

Obtaining high-temperature thermal stable solar selective absorbing coatings is a big challenge for ultra-high temperature solar-thermal conversion applications. In this paper, a dielectric-metal-dielectric (DMD) structured solar selective absorbing coating (SSAC), AlN/TiB2/AlN/Mo/AlN/substrate is proposed and then prepared by direct current magnetron sputtering. The as-deposited SSACs have a high absorptance of 93.4% and a low emittance of 6.9% at room temperature. The SSACs with the DMD structure deposited on the stainless steel (SS) substrate can maintain stability at 800 °C for 200 h in vacuum. The performance criterion (PC) value, a key factor to evaluate thermal stability, is only 0.010 for the coatings after heat treatment. The SSACs deposited on the quartz substrate can even remain stable at 900 °C with a low PC value of 0.008. Our findings will have great potential applications in ultra-high-temperature solar-thermal conversion, and satisfy fully the requirements of thermal stability for current CSP projects.

Versatility of infrared properties of MXenes

Selective and ultrathin films and coatings capable of controlling infrared (IR) emission are crucial for highly integrated thermal management systems, but are challenging produce using conventional materials. Here, we report that the MXene family of two-dimensional carbides and carbonitrides offers a broad range of IR emissivity values (∼0.06–0.59) with diverse colors, varying with MXene composition and structure. Specifically, 200 nm thick purple Ti3C2Tx coating has an average IR emissivity of 0.06, while gold Nb2CTx coating is 0.59 at wavelengths from 3-25 μm. We demonstrate that the IR emissivity can be finely tuned by combining different metals in solid-solution MXenes. Furthermore, the IR identification capability at varying temperatures was validated using different MXene coatings and patterned MXene fabrics. The versatility of MXenes at optical and infrared wavelengths provides a platform for developing MXene-based smart, flexible devices and wearables capable of selective and localized thermal management, aiming at radiative heating/cooling, IR identification, photothermal conversion, and thermal imaging.

Structural and optical properties of DC sputtered AlxOy/Cr/AlxOy multilayer selective absorber coatings

AlxOy/Cr/AlxOy multilayered selective absorber was theoretically optimized using the individual layers’ optical constants acquired through fitting the transmittance and reflectance measurements into SCOUT software. The optimized multilayer was deposited onto polished aluminium substrates by DC magnetron sputtering at room temperature. The structural analysis of the multilayer stack revealed low crystalline diffraction peaks of Cr at 2θ ≈ 43.3° ascribed to (110) diffraction plane of BCC Cr metal. However, due to the amorphous nature of the deposited films, no AlxOy phase was detected by XRD. SEM and AFM analysis revealed the uniformly and densely distributed small grains with a considerably average surface roughness of ∼5.6 nm. The deposited AlxOy/Cr/AlxOy multilayered stack was found to have an optical absorptance of 0.91 and thermal emittance of 0.12 at a temperature of 373 K, which is potential and suitable for selective solar absorbers applications.

Influence of different thermal degradation processes on the optical property of Pyromark-2500

Concentrating solar power (CSP) is emerging as an increasingly important component of renewable energy. CSP systems are being widely adopted in the establishment of large-scale thermal power plants, with an increase in the number of successfully operating demonstration systems.Special coatings are generally used in various types of receivers for solar collector systems. Selective coatings are used for receivers intended to be operated at low or medium temperatures. Similar selective coatings are not currently available for application under high temperatures. In such cases, high-temperature absorbing coatings are generally used to improve the thermal efficiency of the receiver and protect their tubes from oxidation. It is worthwhile to observe the behaviour of such coatings when exposed to high fluxes for extended periods, in order to develop more efficient technologies.Currently, the essential properties for characterizing the paint are absorptivity, emissivity, and structural integrity of the coating (adhesion and cohesion). Good understanding of the behaviour of this paint under representative operating conditions would help to improve the design of the plant, maintain its performance and maintain the thermal efficiency of the receiver. The principal objective of this study was to provide extensive knowledge of the durability and variation of the optical properties of Pyromark when it is consolidated with improved methods. No degradation or loss of optical performance was observed at temperatures under 700 °C. The substrate affected the crystalline structure of an initial coating at high temperatures owing to the diffusion of metal ions. Concentrated solar radiation was the main factor that affected the integrity of the coating. At concentrations higher than 550× suns, a significant area of the irradiated samples was found to be uncoated. These results can be used to design more accurate latest generation receivers to improve the performance of this technology.