CR2016 battery.Study on the preparation method of solar selective absorption coating

　　Study on the preparation method of solar selective absorption coating

　　The preparation methods of solar selective absorption coating include painting method, aqueous solution chemical conversion method, sol-gel method, electrochemical deposition method, vapor deposition method and vacuum coating method, etc., metal-ceramic composite plating, plastic plating and electric brush plating, etc. The method is a new process developed in recent years.

　　Metal-ceramic composite high-selectivity heat-absorbing film

　　The cermet composite selective absorption film produced by high-pressure and strong magnetic condensation technology - black titanium high-selectivity solar heat absorption film is a functional metal-based composite material, a new inert electrode material and a special functional composite powder material, nano-metal The application of composite material processing and preparation technology relies on the organic chemical industry. It uses the principle of strong magnetic, high-speed eddy current, high-pressure heteropolar adsorption to form a layer of near-infrared and mid-infrared light below 500 nanometers on the surface of the substrate in an electrostatic high-voltage environment. A dense ultra-thin film layer with selective absorption function. The film passed the national testing center test, α>94%, ε<10%, neutral salt spray resistance, 5% sodium chloride, 35°C test time of 280 hours, without any change. High temperature aging resistance: 250℃ test time 100 hours, the absorption ratio will not change, but the emission ratio will reduce to less than 5%. Resistance to accelerated UV aging for 3,000 hours without any change after the test. Washing resistance test with 50% sandstone slurry and brown brush for 300,000 times without any change after the test. There is no change after the high and low temperature shock test. There was no change after 1,000 hours of testing in an 85% humidity, 85°C experimental chamber.

　　electrochemical deposition

　　The method of preparing selective absorbing coatings by electroplating is called electrochemical deposition. The prepared coatings include electrodeposition films and electrochemical conversion films.

　　(1) Electroplating method: Black nickel is one of the earliest typical coatings prepared by the electroplating process. Most black nickel coatings are nickel alloy coatings. There are two commonly used electroplating solutions for black nickel, namely zinc sulfate electroplating solutions and molybdenum-containing electroplating solutions. salt plating solution. Black nickel produced from chloride electrolyte is mainly composed of pure nickel, with α>92% and ε<25%. The coating is composed of two films with different porosity and non-overlapping pores. The black nickel deposited on different substrates was heated to 200°C, maintained for 80 hours, and then wet-aged in a humid room for 500 hours. The optical properties remained unchanged.

　　Black chrome coating is another typical example of electrodeposition coating. It is not only highly selective, but also has good temperature and moisture resistance. It is a selective absorption coating with excellent comprehensive performance. The black chrome process needs to operate at high current density (15~200A/dm2) and low temperature (25℃). Due to the poor conductivity of the solution, a large amount of Joule heat will be generated during production, and cooling is required to maintain production.

　　Black cobalt coating can also be used for solar photothermal conversion, such as as a heat-absorbing plate coating for heat pipe vacuum collectors. Its base is pre-copper-plated or electroless nickel-plated glass. Generally, the main component of black cobalt coating is CoS, which has a honeycomb network structure with α = 84% to 90% and ε = 22% to 24%. The optical properties are stable after a 220°C heat resistance test.

　　(2) Electrochemical conversion method: The most mature process in electrochemical conversion film is aluminum anodized film. Anodizing of aluminum and aluminum alloys can be carried out in sulfuric acid or phosphoric acid media, but phosphoric acid oxide films are mainly used in solar photothermal conversion. Aluminum anodized film is a colorless and transparent porous film with a porosity of up to 22%.

　　physical vapor deposition

　　Vacuum evaporation, sputtering coating and ion plating, often called Physical Vapor Deposition (PVD method for short), are one of the basic thin film production technologies. They all require a certain degree of vacuum in the space where the film is deposited.

　　(1) The vacuum evaporation coating method is a method in which the raw materials of the film in the evaporation container are heated in a vacuum chamber to cause the molecules or atoms to vaporize and escape from the surface, forming a vapor flow, which is incident on the solid surface and condenses to form a solid film.

　　(2) Sputtering deposition: The so-called sputtering refers to the phenomenon in which charged particles bombard the solid surface, causing solid atoms (or molecules) to be ejected from the surface. Most of the ejected particles are in the atomic state and are often called sputter atoms. Since ions are directly sputtered, this coating technology is also called ion sputtering coating. Compared with vacuum evaporation, magnetron sputtering has simpler vacuum equipment, more convenient process control, and it is easy to obtain a uniform selective absorption coating on a large area. Magnetron sputtering technology is often combined with optical design to prepare high-performance selective absorption coatings because it is relatively easy to control film composition and thickness.

　　At present, solar selective absorption coatings with operating temperatures above 500°C are usually prepared by radio frequency sputtering process of vacuum coating. Cermet membranes developed in the 1980s usually use Al2O3 medium as the base material, mainly including Ni-Al2O3, Co-Al2O3, Pt-Al2O3, Mo-Al2O3 and Fe-Al2O3. However, compared with DC sputtering technology, RF sputtering technology has complex equipment and low production efficiency, so the coating cost is expensive. On the basis of gradient AlN-Al, a cermet selective absorption coating with AlN dielectric as the matrix was developed. The AlN dielectric was deposited by DC reactive sputtering, and stainless steel, tungsten and other metal particles were injected into the dielectric matrix using the DC co-sputtering method. , improves the sputtering rate and greatly reduces the cost of the film layer. Its α>91%, ε<22% (500℃), is suitable for the use requirements of medium and high temperature collectors. However, in the field of medium and low temperature utilization, this film layer has extremely strict requirements on the application environment. In terms of the current domestic environment, the The service life of the coating is very short, and the coating is easily corroded by the outside world.

　　Aqueous solution chemical conversion method

　　Chemical methods are used to generate black metal oxides or sulfides with selective absorption films on the metal surface. Copper black, zinc black, etc. are usually produced by spraying or spray dipping. The absorption ratio of the coating is above 90%, and the emission ratio is around 10%. The production equipment is simple, easy to operate, low cost, and has little pollution. It is an important and effective method for researching coatings.

　　Other methods

　　(1) Rapid atomic etching method: In 2003, Hitoshi Saia and others studied the spectral properties and thermal stability of submicroperiodic two-dimensional W surface gratings to prepare solar energy selective absorption surfaces suitable for high-temperature applications. Results The surface microhole grating has good spectral selectivity and is suitable for high temperature applications. They exhibit good spectral selectivity and sufficient thermal stability in vacuum at 897°C. α can exceed 85%, ε=7.5% (527℃), ε=14.2% (927℃).

　　(2) Chemical vapor deposition method: Chemical vapor deposition is a chemical vapor growth method, referred to as CVD technology. The required film is produced by gas phase action or chemical reaction (thermal decomposition or chemical synthesis) on the substrate surface. Berghaus et al. used a low-pressure cold wall CVD system to simultaneously thermally decompose W(CO)6 and Al(C3H7O)3(ATI) to prepare amorphous W-WOX-Al2O3 thin films. The film formed on the copper substrate has an α of 85% and an ε of 4%. The absorption ratio of the film layer can be improved by methods such as gradient changes in the tungsten content in the absorption film, adding and subtracting reflective layers, and roughening the surface of the substrate and film. The ceramic film can withstand temperatures of at least 500°C.

　　(3) Sol-gel method: The required oxide film can be obtained by hydrolyzing a solution of an appropriate metal organic compound. Films prepared by the sol-gel method have the advantages of uniform mixing of multiple components, easy control of ingredients, uniform film formation, large-area implementation, low cost, short cycle, and ease of industrial production. Leon Kalulza et al. obtained black CuFeMnO4 spinel structure powder and film through sol-gel method by dipping manganese acetate, ferric chloride and copper chloride precursors and heat treatment at 500°C. The α and ε values of CuFeMnO4 (500°C) and (Mn:Cu:Fe)/TEOS film (500°C) indicate that the CuFeMnO4 film is a potential absorbing coating in solar thermal collection systems. (Wang Junhua, chief engineer of Anhui Haitaike New Energy Technology Co., Ltd.)

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