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[Display omitted] • The spectral positions of photonic bandgaps were estimated by theoretical simulation. • The first-order photonic bandgap was verified to be located in the infrared region. • The formation of the photonic bandgaps appreciably improved the overall properties. • A small amount of CuAl 2 O 4 was produced by controlling electrodeposition voltage. • The CuAl 2 O 4 formation enhanced the thermal stability of the coating properties. Solar selective absorption coatings based on anodic aluminum oxides (AAO) were prepared via an anodization technique and a subsequent alternating current electrodeposition of Cu-Ni nanoparticles at the bottom. The phase structure, microstructure and solar selective absorption properties of the AAO coatings were investigated with respect to their preparation conditions. Moreover, the dependence of the solar selective absorption properties on thermal annealing history was examined. One-dimensional AAO photonic crystal coatings were produced by anodization under period pulse voltages. The spectral positions of photonic bandgaps were estimated for the AAO photonic crystal coatings. The first-order photonic bandgap was verified to be located in the infrared region. The construction of the photonic crystal structure appreciably lowered the infrared emittance and as a result improved the overall properties of the AAO photonic crystal coatings. A small amount of CuAl 2 O 4 was formed in the electrodeposition layer of AAO photonic crystal coatings by controlling the amplitude of applied electrodeposition voltage at 14 V. The formation of the CuAl 2 O 4 minimized the oxidization of the Cu-Ni nanoparticles at elevated temperatures and thereby enhanced the thermal stability of the solar selective absorption properties. The AAO photonic crystal coating prepared under the electrodeposition voltage showed a solar absorptance of 0.90, an infrared emittance of 0.11 and a spectral selectivity of 8.12 at room temperature, while retaining a spectral selectivity of 6.47 after being annealed at 300 °C for 24 h. [ABSTRACT FROM AUTHOR]

Solar selective absorption films based on anodic aluminum oxide (AAO) photonic crystals were prepared by an anodization under periodic current-pulses, subsequently with an alternating current electrodeposition of Co and Ag in sequence. The phase structure, microstructure, and solar selective absorption properties of the Co–Ag electrodeposited film were investigated in comparison with a Co electrodeposited counterpart. Moreover, the stability of the properties against thermal annealing was examined for the two films. A one-dimensional photonic crystal structure was verified for the AAO part in both films, with the first-order photonic bandgap occurring at around 4 μm, while the metals were confirmed to be deposited at the bottom of the AAO part in the form of nanoparticles. For the Co–Ag electrodeposited film, the Ag nanoparticles were deposited over those of Co. The Ag electrodeposition not only was contributive to the solar selective absorption properties, but also substantially improved the stability of the properties against thermal annealing. The Co–Ag electrodeposited film exhibited an infrared emissivity of 0.12, a solar absorptivity of 0.94, and a spectral selectivity of 7.83 before experiencing thermal annealing, while retained a decent spectral selectivity of 6.00 after being annealed in air at 300 °C for 24 h. • An AAO photonic crystal structure was constituted under periodic current-pulses. • The first-order photonic bandgap was verified to be located at around 4 μm. • The Ag in the Co–Ag electrodeposited film was deposited over the Co. • The Ag electrodeposition benefited the solar selective adsorption properties. • The Ag electrodeposition improved the thermal stability of the properties. [ABSTRACT FROM AUTHOR]

The 2 wt% Al 2 O 3 reinforced CoCrAlYTa coatings (referred to as 2Al 2 O 3 -CoCrAlYTa) were manufactured by laser-induction hybrid cladding. And the oxidation behavior of the coatings was investigated using a thermogravimetric analyzer (TGA) at different oxidation temperatures (950 °C, 1000 °C, 1100 °C, and 1200 °C) in an air atmosphere with a test time of 200 min. The composition and microstructure of the oxide scales formed at different temperatures were characterized and investigated. Additionally, the microstructure evolution of the coating, failure mechanism of the oxide scales, and elemental diffusion at the different temperatures were also discussed. It was found that after oxidation, Al depleted zones appeared in the 2Al 2 O 3 -CoCrAlYTa coatings. When oxidation temperature was 950 °C, fine-equiaxed oxide grains were formed on the coating. Moreover, at 950 °C, 1000 °C, and 1100 °C, the oxide scales were intact, and no large voids were found in the oxide scale/coating interface. As the temperature reached 1200 °C, the oxide scale formed on the surface of the coating became thicker and consisted of an outer layer of fine equiaxial crystals and an inner layer of coarse columnar crystals, and large voids developed at the oxide scale/coating interface, causing the oxide scales to delaminate from the coating. [Display omitted] • 2Al 2 O 3 -CoCrAlYTa (ODS) coatings were produced by laser-induction hybrid cladding (LIHC). • At 950 °C, 1000 °C and 1100 °C, a continuous Al 2 O 3 scale formed on the coatings surface. • The rapid outward-diffusion of Al caused the formation of voids at the scale/coating interface at 1200 °C. • The excessive internal stress superimposed massive voids leads to the cracking and delamination of scale at 1200 °C. [ABSTRACT FROM AUTHOR]

In this study, an anodic aluminum oxide (AAO)-based photonic crystal, with a branched channel structure and deposited Cu-Ni composite nanoparticles, is fabricated for solar thermal absorption. The infrared-wave emission properties can be finely tuned by adjusting photonic band gap of the photonic crystal, facilitating the production of an excellent solar heat-absorbing material. Such a channel structure, as generated by anodic oxidation, possesses layers with high and low porosities, featuring a periodical change. The programmed power source (with periodically changed voltage and hence step-change current) enables sharp alteration of the porosity, forming the AAO-based photonic crystal oxidation film (with a complete photonic band gap). Subsequently, Cu-Ni composite nanoparticles are deposited into the pores of the AAO-based film at an alternating current (AC) frequency under different conditions. The optimized conditions (including periodical oxidation time, voltage, oxidation period, AC deposition voltage, time, and temperature) lead to the generation of a solar heat-absorbing composite coating that exhibits solar absorptance, thermal emissivity, and quality factor reaching values of 0.95, 0.13 and 7.3, respectively. In addition, the composite oxidation coating, with the AAO-based photonic crystal layer, shows a significantly lower thermal emissivity as compared to the counterpart in the absence of the AAO-based photonic crystal layer. [ABSTRACT FROM AUTHOR]

The microstructure and isothermal oxidation behaviour of CoCrAlYTa coatings containing different Al 2 O 3 contents produced by laser-induced hybrid cladding (LIHC) were investigated. The results showed that the addition of Al 2 O 3 particles to the CoCrAlYTa coatings reduced the critical concentration of Al due to the increased diffusion coefficient of Al, which promoted the formation of continuous and complete Al 2 O 3 scales. However, the growth of tantalum oxide in the CoCrAlYTa coating resulted in cracking of the surrounding oxide scales. Interestingly, a CoCrAlYTa coating made of the optimal content of 2 wt% Al 2 O 3 formed an oxide scale with good compactness after high-temperature oxidation. • CoCrAlYTa coatings are produced by laser-induction hybrid cladding (LIHC). • Adding alumina particles can promote the formation of a continuous and intact Al 2 O 3 scale. • The optimal addition amount of alumina particles is 2 wt% in this work. • The growth of tantalum oxide can cause cracking of the surrounding scales. [ABSTRACT FROM AUTHOR]

• Elevating anodizing temperature induces thinner pore walls and breakdown of AAO films. • Introducing organic acid into electrolyte prevent AAO film from breakdown at 30°C. • Lower the electronic current and suppress the formation of oxygen bubbles. • Scour effect of O 2 on the porous-type and barrier-type AAO layers was alleviated. Anodic aluminum oxide films, industrially produced by anodizing aluminum alloys under the galvanostatic mode at a relatively low temperature of 20°C (electrolyte bath temperature), present the reliable anticorrosive effect for numerous applications. For fabricating anodic aluminum oxide films with the promising corrosion resistance as well as high growth rate in a wide temperature range, the effect of anodizing temperatures on the structure and growth mechanism of anodic aluminum oxide films was investigated. As the temperature increases up to 30°C, the stress-driven breakdown of porous-type anodic aluminum oxide layers induced by their thinner pore walls was estimated. This phenomenon is interpreted by an increase of electronic current and thus a strong scour effect of O 2 bubbles on the porous-type anodic aluminum oxide layers. Moreover, with the addition of composite organic acid into the sulfuric acid-based electrolyte solution, the anions ( C 6 H 5 O 7 3 − , C 4 H 4 O 6 2 − ) that incorporated into the anodic oxide contribute to lowering the electronic current and thus suppressing the formation of oxygen bubbles, resulting in a thicker barrier-type anodic aluminum oxide layer. This is assumed to be responsible for the enhanced corrosion resistance of anodic aluminum oxide films prepared at 30°C with 50 g/L organic acid addition. [ABSTRACT FROM AUTHOR]