CN101871093B - Preparation method of selective absorption coating for steel core of solar collector tube - Google Patents

Abstract

The invention discloses a method for preparing a selective absorption coating for a steel core of a solar heat collecting tube, which belongs to the field of solar energy application. This selective absorbing coating preparation method is designed on the basis of simulated theoretical calculations to design solar selective absorbing coatings and the best process for preparing film layers. The process is simple, easy to operate, reliable in product quality, and suitable for organizing large-scale industrial production. The coating preparation method improves the performance of the solar selective absorption coating on the heat collecting tube and the working temperature of the coating exceeds 400° C., and can improve the solar light-to-heat conversion efficiency.

Description

Preparation method of selective absorption coating for steel core of solar collector tube

technical field

The invention relates to a method for preparing a selective absorption coating for a steel core of a solar heat collecting tube, belonging to the field of solar energy applications.

Background technique

The trough solar thermal power generation system uses a trough parabolic concentrator to focus sunlight on a line, and a tubular heat absorber (collector tube) is installed on this focal line to absorb the focused solar radiation energy. After the fluid in the tube is heated by the converted solar energy, it flows through the heat exchanger to heat the working fluid, and converts it into high-temperature and high-pressure hot steam, and then generates electricity by means of steam cycle power. The trough solar thermal power generation technology is relatively mature, so it has been widely promoted and applied in the world. This type of power station is distributed in Algeria, Australia, Egypt, India, Iran, Italy, Morocco, Mexico, Spain, the United States and other countries with rich solar energy resources. The high-temperature vacuum tube receiver in this system is the core component of the whole system, provided by Israel Solel Company (formerly known as LUZ Company). German Schott company has improved the high-temperature vacuum tube: first, to prevent the high temperature at both ends from affecting the sealing quality, a solar radiation reflection circle is added locally; ; The third is to adjust the relevant glass material formula, so that Kovar alloy and glass tube can be sealed better. In trough parabolic concentrating power generation, improving the performance of the solar selective absorption coating on the heat collecting tube and increasing the working temperature of the coating to exceed 400°C can improve the efficiency of converting solar energy into heat energy.

Contents of the invention

The invention provides a method for preparing a selective absorption coating for a steel core of a solar heat collection tube. The coating preparation method should improve the performance of the solar selective absorption coating on the heat collecting tube and can improve the solar light-to-heat conversion efficiency when the working temperature of the coating exceeds 400°C.

The technical solution adopted in the present invention is: a method for preparing a selective absorption coating for a solar collector tube steel core, the preparation method adopts a DC sputtering metal target material, a radio frequency sputtering oxide target material and a reactive co-sputtering method. Selectively coated reflective metal layer, absorbing layer and anti-reflection layer; the equipment used mainly includes vacuum system, planar magnetron sputtering, columnar magnetron sputtering, bias power heating system, gas supply system and water cooling system. The stainless steel tube is installed on the revolution and rotation work frame in the water-cooled vacuum chamber, and the preparation steps of the X-Y film system on the stainless steel tube are as follows:

1. Design the film structure

1. First prepare single-layer X film and Y film, measure the refractive index n and extinction coefficient k,

2. Calculate the optical parameters of X film and Y film with different components,

3. Modeling with TFC film design software to simulate the structure of the optimal solar selective absorption coating,

4. Invert the theoretical simulation calculation results to the preparation process. Use the film thickness meter to accurately detect, regulate and adjust to prepare X film/highly doped X-Y film/lowly doped X-Y film/pure Y film,

5. Using Lambda 950 spectrophotometer, infrared emissivity detector and other testing equipment to measure reflectivity, transmittance, emissivity and other multi-layer film optical parameters,

6. The theory and the results are confirmed and compared with each other, and the best process for preparing the film layer that meets the requirements is obtained;

2. The process of preparing X-Y film system:

1. Vacuum chamber pumping process:

(1) Turn on the water valve switch. And check whether the water flow of each pipeline is smooth,

(2) Turn on the mechanical pump,

(3) Open the pre-extraction valve, pump air to 500Pa, turn on the Roots pump, and then pump air to 5Pa, turn on the power of the molecular pump for 4 to 5 minutes during the pumping process,

(4) Close the pre-pumping valve, open the front valve for 1 minute, open the high valve, and open the molecular pump to pump high vacuum until the pressure meets the process requirements.

2. According to the operating procedures, heat, turn on the rack,

3. According to the process regulations, send Ar gas,

4. Clean the stainless steel tube with plasma,

5. The X reflective layer is prepared by planar magnetron sputtering X target sputtering deposition,

6. Using radio frequency magnetron sputtering Y sputtering deposition Y and planar magnetron sputtering X target sputtering deposition X, depositing and forming an absorbing layer at the same time, the ratio and deposition rate of X and Y depend on the sputtering power,

7. The Y film is deposited by radio frequency magnetron sputtering alone, and the deposition rate depends on the sputtering power.

X in the XY film system is W, Mo or Al metal, and Y is SiO ₂ , Al ₂ O ₃ or AlN ceramic.

The above-mentioned theoretical basis for the simulation calculation of the X film and the Y film is: the equivalent medium theory believes that when one material particle is uniformly embedded in another matrix material to form a composite material with uniform macrostructure, the dielectric properties of the material can be used. The dielectric properties of a homogeneous material are equivalent, and the dielectric constant of this material is the equivalent dielectric constant of the heterogeneous material under study. The MG theory was proposed by Maxwell and Garnett in 1904 and 1906 respectively, starting from the Clausius-Mossotti formula, which is applicable to the cermet system with spherical metal particles embedded in the dielectric matrix and made the following assumptions:

(1) A very small amount of metal particles are dispersed in the medium matrix, the distance between the particles is relatively large, there is no interaction between the particles, and they are scattered separately;

(2) The particles are polarized by transient field induction;

(3) The outer field can be corrected by the Lorentz local field

If the dielectric constant of the medium is ε1 and the dielectric constant of the metal spherical particles is ε2, then the dielectric constant ε of the two-phase composite system can be expressed by the formula:

$\mathrm{<span\; class="notranslate">\; \&epsiv;MG</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

where f is the metal volume fraction.

The relationship between the complex refractive index N of the composite system and the equivalent complex permittivity ε in the optical frequency range can be expressed by formula 3-2:

$\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; ik</span>}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}$

where n and k are the optical refractive index and extinction coefficient of the composite system, respectively

The beneficial effects of the present invention are: the method for preparing the selective absorption coating of the steel core of the solar heat collecting tube obtains the optimum process for preparing the film layer meeting the requirements on the basis of simulation theoretical calculation, the process is simple, the operation is convenient, and the product quality is high. Reliable and suitable for organizing large-scale industrial production. The coating preparation method improves the performance of the solar selective absorption coating on the heat collecting tube and can improve the conversion efficiency of solar energy into electric energy when the working temperature of the coating exceeds 400 DEG C, and reduce its power generation cost.

Description of drawings

Fig. 1 is a front view of a selective absorption coating equipment for a solar collector tube steel core.

Fig. 2 is a top view of a selective absorption coating equipment for a solar collector tube steel core.

Figure 3 is a structural diagram of the vacuum chamber.

In the figure: 1. Water-cooled vacuum chamber, 2. Revolving and rotating workpiece frame, 3. Insulation of bracket drive shaft, 4. Coated stainless steel tube, 5. Heater, 6. Columnar magnetron sputtering target, 7. Drive shaft, 8 , Turret power motor, 9, 10, metal magnetron sputtering source, 11, 12, radio frequency magnetron sputtering target, 13, vacuum chamber door, 14, temperature measuring thermocouple, 15, film thickness tester, 16, High valve, 17, molecular pump, 18, backing valve, 19, pre-pumping valve, 20, bypass valve, 21, Roots pump, 22, mechanical pump.

Detailed ways

Figures 1, 2, and 3 show a diagram of a selective absorption coating equipment for a solar collector tube steel core. This metal-ceramic coating equipment mainly includes a vacuum chamber and a vacuum system, the vacuum chamber and the vacuum system are connected together by pipelines, and the coated stainless steel tube 4 is installed on the turntable mechanism driven by an external motor in the vacuum chamber; it It also includes metal magnetron sputtering sources 9, 10 and radio frequency magnetron sputtering targets 11, 12 installed on the vacuum chamber; a heater 5, a columnar magnetron sputtering target 6, a temperature measuring thermocouple 14, Film thickness tester 15; the vacuum system is connected to the vacuum chamber through a high valve 16, the outlet of the high valve 16 is provided with a pre-exhaust valve 19, and the outlet of the pre-exhaust valve 19 is connected to the mechanical pump 22 and the Roots pump through a bypass valve 20 21. The other path is connected to the molecular pump 17 through the fore valve 18, and the outlet of the pre-pumping valve 19 is also directly connected to the Roots pump 21.

The turret mechanism adopted by the water-cooled vacuum chamber 1 is located at the bottom of the vacuum chamber, the turret power motor 8 is located outside the vacuum chamber, and a vacuum chamber door 13 is provided on one side of the vacuum chamber. The equipment can conveniently prepare various metal films or ceramic films, etc.

Embodiment 1: Metal thin film preparation method

1. Vacuumize, heat, and turn on the rack according to the operating procedures;

2. According to the process regulations, send Ar gas;

3. Plasma cleaning workpiece;

4. Prepare thin films by planar magnetron sputtering metal targets, open the baffle, and use two DC power supplies or intermediate frequency power supplies to prepare metal thin films separately (composite metal alloy thin films are the same);

5. Columnar magnetron sputtering target, using DC power supply, to prepare metal thin film;

6. For the preparation of metal thin films or composite metal alloy thin films, intermediate frequency power sputtering planar metal targets and DC power sputtering columnar metal targets can be used in combination. The deposition rate is controlled by vacuum gas pressure and sputtering current.

Embodiment 2: preparation method of ceramic thin film

The ceramic thin film is prepared by radio frequency sputtering deposition of ceramic target material or planar magnetron sputtering reactive sputtering deposition method.

Embodiment 3: SiO2 thin film preparation method

1. Vacuumize, heat, and turn on the rack according to the operating procedures;

2. According to the process regulations, send Ar gas;

3. Plasma cleaning workpiece;

4. Using radio frequency magnetron sputtering (SiO2) target, open the baffle, radio frequency plasma sputtering deposition. The deposition rate mainly depends on the RF power.

Embodiment 4: Al-N film preparation method

1. Vacuumize, heat, and turn on the rack according to the operating procedures;

2. According to the process regulations, send Ar gas;

3. Plasma cleaning workpiece;

4. The columnar magnetron sputtering aluminum target adopts DC power supply sputtering reaction deposition or intermediate frequency power supply sputtering reaction deposition process. The reaction gas is composed of Ar and N2 gas mixture, and the phase composition and structure of the formed film depend on the gas ratio. and sputtering voltage-current.

Embodiment 5: Mo-SiO2 thin film preparation method

1. Vacuumize, heat, and turn on the rack according to the operating procedures;

2. According to the process regulations, send Ar gas;

3. Plasma cleaning workpiece;

4. Use planar magnetron sputtering Mo target to sputter deposit metal Mo to prepare metal reflective layer;

5. Use radio frequency magnetron sputtering (silicon oxide target) to sputter deposit _SiO2 and planar magnetron sputtering Mo target to sputter deposit metal Mo to form an absorbing layer at the same time. The ratio and deposition rate of metal and _SiO2 depend on sputtering power;

6. The _SiO2 thin film is deposited by radio frequency magnetron sputtering alone, and the deposition rate depends on the sputtering power.

Embodiment 6: Preparation method of Mo-AlN film

1. Vacuumize, heat, and turn on the rack according to the operating procedures;

2. According to the process regulations, send Ar gas;

3. Plasma cleaning workpiece;

4. Use planar magnetron sputtering Mo target to sputter deposit metal Mo to prepare metal reflective layer;

5. Introduce Ar and N2 mixed gas, and use columnar magnetron sputtering (Al target) to sputter deposit AlN and

Planar magnetron sputtering Mo target sputtering deposits metal Mo co-deposition to form absorber layer, the ratio and deposition rate of metal and AlN depend on sputtering power and gas ratio;

6. The AlN anti-reflection film is deposited by sputtering with a columnar magnetron sputtering target alone. The phase structure and composition depend on the gas ratio and sputtering power.

Claims (2)

1. A method for preparing a selective absorbing coating on a steel core of a solar collector tube, the preparation method adopts a DC sputtering metal target, a radio frequency sputtering oxide target and reactive co-sputtering to prepare the reflective metal of the selective coating layer, absorbing layer and anti-reflection layer; the equipment used mainly includes vacuum system, planar magnetron sputtering, columnar magnetron sputtering, bias power heating system, gas supply system and water cooling system, and the stainless steel pipe (4) is installed on On the revolution and rotation work frame (2) in the water-cooled vacuum chamber (1), an X-Y film system is prepared on a stainless steel tube (4); it is characterized in that: the preparation steps of the X-Y film system are: 1. Design the film structure 1. First prepare single-layer X film and Y film, measure the refractive index n and extinction coefficient k, 2. Calculate the optical parameters of X film and Y film with different components, 3. Modeling with TFC film design software to simulate the structure of the optimal solar selective absorption coating, 4. Invert the theoretical simulation calculation results to the preparation process, and use the film thickness meter to accurately detect, regulate and adjust the preparation of X film/highly doped X-Y film/lowly doped X-Y film/pure Y film, 5. Use spectrophotometer and infrared emissivity detector to measure reflectivity, transmittance, emissivity multilayer film optical parameters, 6. The theory and the results are confirmed and compared with each other, and the best process for preparing the film layer that meets the requirements is obtained; 2. The process of preparing X-Y film system: 1. Vacuum chamber pumping process: (1) Turn on the water valve switch and check whether the water flow of each pipeline is smooth, (2) Turn on the mechanical pump (22), (3) Open the pre-extraction valve (19), pump air to 500Pa, turn on the Roots pump (21), and then pump air to 5Pa, turn on the power supply of the molecular pump (17) for 4 to 5 minutes during the pumping process , (4) Close the pre-pumping valve (19), open the front valve (18) for 1 minute, open the high valve (16), and open the molecular pump (17) to pump high vacuum until the pressure reaches the process requirements, 2. According to the operating procedures, heat, turn on the rack, 3. According to the process regulations, send Ar gas, 4. Clean the stainless steel tube (4) with plasma, 5. The X reflective layer is prepared by planar magnetron sputtering X target sputtering deposition, 6. Use radio frequency magnetron sputtering Y sputtering deposition Y and planar magnetron sputtering X target sputtering deposition X, depositing and forming an absorbing layer at the same time, the ratio and deposition rate of X and Y depend on the sputtering power, 7. The Y film is deposited by radio frequency magnetron sputtering alone, and the deposition rate depends on the sputtering power. 2. The method for preparing a selective absorption coating for a steel core of a solar collector tube according to claim 1, wherein X in the XY film system is W, Mo or Al metal, and Y is SiO ₂ , Al ₂ O ₃ or AlN ceramics.

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