The Effect of Annealing under Non-vacuum on the Optical Properties of TiAlN Non-vacuum Solar Selective Absorbing Coating Prepared by Cathodic Arc Evaporation

TiAIN solar selective absorbing coatings which were deposited on 304L stainless steel using cathodic arc evaporation method were annealed under non-vacuum at different temperatures with different times. The optical properties （absorptance and emittance） of the coatings were measured by a spectrophotometer. It was found that, after being annealed for 2 hours at different temperatures, the absorptance of the coatings reached the highest value of 0.92 at 700 ℃ while the emittance got the lowest value of 0.38 at 800 ℃. When the coatings were annealed at 600 ℃ for 24 hours, the optical properties changed to 0.92/0.44 （absorptance/ emittance）. By measuring the structure, morphology, elements and surface roughness of the coatings, it was found that both the elemental composition and the surface roughness of the coatings changed as a result of annealing, and these changes caused the change of the optical properties of the coatings.

THE PREPARATION AND CHARACTERISTICS STUDY OF TiN_xO_y SPECTRAL SELECTIVE ABSORBING FILM BY MAGNETRON SPUTTERING

Spectral selective absorbent film is a crucial factor for the solar heating devi ce. There are many kinds of spectral selective absorbing film made by different ways. TiNxOy thin film with excellent spectral selecting absobent property were successfully prepared by DC magnetron sputtering with Ar as working gas, N2 and O2 as reactive gas, 99.9% titanium as the target and is copper slice as the subs trate. In this article, the optical characteristics and microstructure of TiNxO y thin film were studied. Inputing O2 can decrease the reflection of the visible lights, and double layer film can get good absorption for solar energy.

Thickness Dependence of Structural and Optical Properties of Chromium Thin Films as an Infrared Reflector for Solar-thermal Conversion Applications

The thermal emittance of Cr film, as an IR reflector, was investigated for the use in SSAC. The Cr thin films with different thicknesses were deposited on silicon wafers, optical quartz and stainless steel substrates by cathodic arc ion plating technology as a metallic IR reflector layer in SSAC. The thickness of Cr thin films was optimized to achieve the minimum thermal emittance. The effects of structural, microstructural, optical, surface and cross-sectional morphological properties of Cr thin films were investigated on the emittance. An optimal thickness about 450 nm of the Cr thin film for the lowest total thermal emittance of 0.05 was obtained. The experimental results suggested that the Cr metallic thin film with optimal thickness could be used as an effective infrared reflector for the development of SSAC structure.

PARAMETRIC MATCHING SELECTION OF MULTI-MEDIUM COUPLING SHOCK ABSORBER

To achieve the dual demand of resisting violent impact and attenuating vibration in vibration-impact-safety of protection for precision equipment such as MEMS packaging system, a theo- retical mathematical model of multi-medium coupling shock absorber is presented. The coupling of quadratic damping, linear damping, Coulomb damping and nonlinear spring are considered in the model. The approximate theoretical calculating formulae are deduced by introducing transformation-tactics. The contrasts between the analytical results and numerical integration results are developed. The resisting impact characteristics of the model are also analyzed in progress. In the meantime, the optimum model of the parameters matching selection for design of the shock absorber is built. The example design is illustrated to confirm the validity of the modeling method and the theoretical solution.

A review of high-temperature selective absorbing coatings for solar thermal applications

Solar selective absorbing coatings directly harvest solar energy in the form of heat.The higher temperatures are required to drive higher power-cycle efficiencies in favor of lower costs of energy.According to different dielectrics,high temperature coatings can mainly be divided to double cermet solar selective coatings,transition metal nitride multilayer coatings and transition metal oxide multilayer coatings.This paper assesses the photothermal conversion efficiency and thermal stability,and discusses the challenges and strategies of improving both thermal and optical properties.Double cermet layers can stabilize nanocrystalline structures by alloying,while transition metal nitride/oxide layers generally choose the reliable materials with superior mechanical properties and thermal stability.The purpose of this review is to get the optimized systems,and propose further research directions at higher temperature,such as all-ceramic absorbing coatings.

Thermal Stability and Degeneration Behavior of Solar Selective Absorber Based on WTi-Al_(2)O_(3)Cermet

A WTi-Al_(2)O_(3)cermet-based solar selective absorber was prepared to investigate the atomic diffusion induced spectral selectivity degeneration.The as-deposited coating exhibits superior absorptance(0.934)and low thermal emittance(0.098),as well as excellent thermal stability with a selectivity of 0.900/0.07 even after annealing at 923 K for 400 h in Ar ambient.However,the multilayer coating failed after being subjected to annealing at 923 K for 400 h in an air environment,as indicated by a decrease in solar absorptance to 0.912 and an increase in thermal emittance to 0.634.The microstructure characterizations reveal that the annealed coating exhibits a columnar morphology along the vertical direction of the substrate.The presence of abundant grain boundaries in the multilayer coating promotes the outward diffusion of Cr and Mn atoms in the stainless-steel substrate.The Mn atoms,in particular,possess the capability to migrate towards the surface of the coating and undergo an oxidation reaction with oxygen,facilitating the formation of a thick Mn_(2)O_(3)layer.The roughness of the coating surface was significantly increased in this case,adversely affecting solar absorptance due to amplified sunlight reflection.In addition,the rocketing of thermal emittance is attributed to the destabilization of W infrared reflective layer during the annealing.These findings highlight the importance of considering the outward diffusion of Mn and Cr elements in the stainless-steel substrate when optimizing solar selective absorbers.

Optical Design and Preparation of High Performance Mo/NiAlN/NiAlON/SiO_2 Solar Selective Absorbing Coating

A new solar selective absorbing coating of Mo/NiAlN/NiAlON/SiO_2 multilayer was prepared on stainless steel(SS) substrates by magnetron sputtering for solar thermal power applications. The optical constants and thickness of individual layers were simulated using the Scout software based on the experimentally measured reflectance and transmittance spectra of individual layers. The coating of Mo/NiAlN/NiAlON/SiO_2 with an ideal solar absorptance(α) of 0.945 in the solar spectrum range was designed via the optical constants of each layer in the Scout software. The Mo/NiAlN/NiAlON/SiO_2 coating was deposited via the optimized layer thickness. A good spectral selectivity with absorptance(α=0.936) and emittance(ε=0.09, T=80 ℃) was obtained. This method, which incorporates the optical simulation with the related experiments, provides a convenient approach to obtain the ideal solar selective absorbing coatings.

Preparation of solar selective absorbing CuO coating for medium temperature application

A new method of preparing CuO solar selective absorbing coating for medium temperature is presented.After pretreatment,brass was overlaid with CuO by chemical plating.The effects of reactant concentration,reaction tem-perature and reaction time on the absorptivity of CuO coating were investigated.The optimized condition of preparing CuO coating was obtained.The CuO coating was analyzed with X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM).In order to prolong the period of use,the CuO coating was protected by TiO2.The experi-ment shows that the TiO2/CuO coating is more heat-resistant,acid-resistant,and wear resistant than CuO coating,without losing absorptivity markedly.The TiO2 coating can reduce emissivity and protect the CuO coating.

Perfect solar absorber based on nanocone structured surface for high-efficiency solar thermoelectric generators

Nanostructured surface is a promising photon management strategy to tune spectrum in design of the selective solar absorber.In this paper,we propose a nanocone structured surface as a perfect solar absorber in application of the solar thermoelectric generators(STEGs).The trade-off between the solar absorption and the mid-infrared emission is obtained to maximize the STEG efficiency.The effects of the geometric parameters,thermal concentration,incident angle and polarized state as well as the lattice arrangement are systematically investigated.The results show that the STEGs equipped with our proposed selective solar absorber can achieve a peak efficiency of 6.53%under AM1.5G condition(no optical concentration).Furthermore,the selective solar absorber exhibits insensitive behavior to the incident angle and polarization angle as well.This means that the proposed selective solar absorber can utilize solar energy as much as possible and be generally suitable in equipping the STEGs without optical concentration.

Greatly enhanced solar absorption via high entropy ceramic AlCrTaTiZrN based solar selective absorber coatings

High entropy alloys(HEAs),which is at the expense of high cost compared to traditional alloy,should not be confined to the mechanical properties,but should be employed to devise a novel combination with unique functional and mechanical performances.In this work,high entropy alloy nitride(HEAN)is utilized as a novel double absorption layer to improve solar absorption in the high temperature solar selective absorbing coatings(SSACs).Our primary motivation is to lower thermal emittance(ε)and enhance solar absorptance(a).In order to realize this goal,coating design(CODE)software is employed to design and optimize the proposed HEAN based SSACs using appropriate dielectric function model.The ultimate as-deposited coating shows good optical properties with a high a value of 0.965 and a lowεvalue of 0.086(at 82C).The estimate of thermal stability tests indicates that HEAN based SSACs has the ability to resist instability in high working temperature,which keeps good optical properties(a¼0.925,ε¼0.070)after annealing at 600C for 10 h.

Spectral emittance measurements of micro/nanostructures in energy conversion:a review

Micro/nanostructures play a key role in tuning the radiative properties of materials and have been applied to high-temperature energy conversion systems for improved performance.Among the various radiative properties,spectral emittance is of integral importance for the design and analysis of materials that function as radiative absorbers or emitters.This paper presents an overview of the spectral emittance measurement techniques using both the direct and indirect methods.Besides,several micro/nanostructures are also introduced,and a special emphasis is placed on the emissometers developed for characterizing engineered micro/nanostructures in high-temperature applications(e.g.,solar energy conversion and thermophotovoltaic devices).In addition,both experimental facilities and measured results for different materials are summarized.Furthermore,future prospects in developing instrumentation and micro/nanostructured surfaces for practical applications are also outlined.This paper provides a comprehensive source of information for the application of micro/nanostructures in high-temperature energy conversion engineering.