| Materials are important for human society development. With the advancing in technology and economy, they have been payed more and more attention. Due to teir excellent performances and good prospects, the new materials have become the focus of international competition. This thesis focuses the study on two kinds of light-absorbing materials: low reflection film and solar selective absorbing film. The two kinds of materials have similarities and differences. Due to its strong absorbing ability in a certain wavelength, the low reflection film has low reflectivity, which can effectively improve the accuracy of the thermal detector and infrared optical system, improve the clarity of the cameras and telescopes, and increase the accuracy of the optical navigation system. And the solar spectrum selective absorption films(solar selective absorbing films or solar selective absorbers) have high absorption in the solar spectrum(300- 2500 nm) and high reflectivity(i.e. low thermal emissivity) in the mid infrared region, so they can be utilized to selectively absorb solar energy, and be widely used in the thermal-collecting tubes of solar water heater, solar air-conditioning and solar thermal power generation.We successfully designed and constructed the ultra low reflectivity Cu O/Cu in near ultraviolet visible region. The super thick vertical nanowire array was orderly constructed by super long Cu O nanowires on copper substrate. By adjusting the temperature and time of the reaction, the density and the thickness of the Cu O nanowire arrays were successfully controlled. In addition, we also built some arrays assembled by Cu O nanowires with different inclination, and it was found that the vertical alignment structure was the most conducive for light capture. It was also found that the rougher copper substrates were helpful for the growth of denser nanowire arrays. The experimental results show that the Cu O nanowire array plays a key role in the ultra low reflectivity, via improving the reflection and absorption times btween the light and the nanowire. In addition, the nanowire array can be regarded as the effective optical medium which is filled with air, the gradient changing of refractive index is also helpful for increasing the absorption, namely reducing the reflectivity. Through the air thermal oxidation at 450 oC, we prepared the dark black array whose average thickness was 40.5 μm, with the ultra low reflectivity of 0.078% in the wavelength range of 200-700 nm. As the synthesis process of the ultra low reflection nanowire arrays of Cu O/Cu are simple, non-pollution, no by-products, no need of expensive instruments, low cost, so they have a great prospect for industrial application.In order to obtain more sturdy, durable, low-cost low reflection film in wider wavelength range, then we firstly introduced the hydrothermal method for in situ preparing of low reflection film on Fe-Cr alloy substrate. By adjusting the reaction temperature and alkali solution concentration, we obtained the different spinel films with different crystal particle spatial arrangements and micro voids, and realized the controlling of low reflection(from 12.85% to 4.71% in 300nm-2500 nm region, from 23.04% to 6.16% in 2.5-13 μm region). At the same time, we also put forward that the film can be considered as an air-filled effective optical medium which has gradient refractive index, contributing to the absorption. In addition, the surface interface effect and dielectric effect of the nano crystalline grains are also available to the light absorption. Due to their simple operation, lower production cost and no need of complex equipment, these spinel membranes have great value for mass production. As they have low reflection in ultra wide wavelength range, they can be used in solar thermal materials, low-cost optical instruments and military infrared absorbing materials.We also introduced hydrothermal method to prepare the foamed nanostructure solar selective absorbing film on stainless steel. The film has a high absorption in the solar spectral region(300- 2500nm), at the same time, also achievs a high reflectivity in the mid infrared region, obtaining selective absorption for solar light. The absorbing film is assembled by a large number of nano particle aggregates, and it contains a large amount of nano micro pores, which can lead to multiple reflection and absorption for incident light, namely trapping light. At the same time, the gradient refractive index of the membrane is advantageous to improve the absorption of the membrane, and the relatively flat film surface is conducive to reduce the emittance. The foamed nanostructure film has excellent solar thermal performance and thermal stability, it obtains the absorption of 0.92 and the thermal emission of 0.12 before heat treatment. After heat treatment in the air of 450 oC, the film maintains good adhesion to the substrate, and keeps the absorption of 0.834 and the emission of 0.230. After the heat treatment in air for 24 h at different temperatures, it is found that when the heat treatment temperature is 400 oC, the membrane basically keeps a certain selective absorption, its absorption and thermal emission are 0.837 and 0.192, respectively. Other fomed nanostructure films with different thicknesses were also studied. It is found that although the thinner film has lower absorption, yet its base metal can achieve high reflectance in the infrared region, so it is easy to obtain low thermal emissivity. Therefore we should have comprehensive consideration on the absorption and thermal emission to choose the appropriate thickness of the film. Herein, the synthesis of the fomed nanostructure film provides a new strategy for the preparations of the solar selective absorbing films. Besides, as these films have good performance, their preparation process is also simple, low-cost, so they are expected in mass production for thermal collecting tubes of solar water heaters and solar energy photo-thermal generations.In this dissertation, we firstly introduced air thermal oxidation to prepare the ultra-low reflection Cu O nanowire arrays. We also firstly introduced the hydrothermal method to prepare the low reflection spinel membrane in wider wavelength range on the Fe-Cr alloy substrate. Then we also firstly introduced the hydrothermal method to prepare the solar selective absorbing film on the stainless steel. These new synthetic strategies provide new ideas for the preparation of low reflective film and solar selective absorber. And the way that based on the raw material cost, manufacturing cost, market prospects to choose the material preparation system, also provides a reference for the synthesis of other new materials in the future. |
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