CN113604079B - Thermochemical protective coating material and preparation method thereof - Google Patents

Abstract

The invention provides a thermochemical protective coating material, the thermochemical protective coating material comprises ABO ₃ perovskite material or ternary composite metal oxide doped with lithium, the A site of the ABO ₃ perovskite material is La , any combination of two or more of Ca, Ba, Sr and K, and/or, the B site of the ABO ₃ perovskite material is a combination of any two or three of Mn, Fe and Co. The thermochemical protective coating material can adjust the reaction temperature by changing the molar ratio of the composite metal oxide according to different requirements, thereby overcoming the shortcoming of the narrow temperature range of the single metal oxide heat storage material, and spraying the thermochemical protective coating The material is sprayed onto the surface of the heat absorber, which can improve the heat resistance of the heat absorber itself and prolong the service life of the heat absorber.

Description

A kind of thermochemical protective coating material and preparation method thereof

technical field

The invention relates to the technical field of thermochemical heat storage, in particular to a thermochemical protective coating material and a preparation method thereof.

Background technique

At present, solar power generation technology is an effective means to alleviate energy crisis, environmental degradation and reduce carbon emissions. Solar power generation technologies mainly include photovoltaic power generation and solar thermal power generation. Solar thermal power generation can cut peaks and fill valleys through low-cost heat storage to ensure stable power generation, and has the potential to serve as basic power loads or peak-shaving units. Solar thermal power generation technology uses a large-scale array of parabolic or dish mirrors to collect solar heat, provides steam through a heat exchange device, and combines traditional turbogenerator technology to achieve the purpose of power generation.

There are a large number of heat absorbers and heat exchange pipes in the solar thermal power generation system, and the working environment is harsh. Long-term exposure to the external environment will cause the metal surface to be damaged due to oxidation. At the same time, the temperature difference between the inside and outside of the heat exchanger is large, resulting in more environmental heat loss. At the same time, the working state is affected by environmental changes. Solar radiation is the energy source of the system. Frequent fluctuations in solar radiation will cause thermal shock and thermal fatigue, which will have a serious impact on the stable operation and life of the heat sink. Especially when there is a strong wind, the external convection heat dissipation of the heat sink is strengthened, and the strong wind may cause physical damage to the exposed heat absorption pipe. Therefore, severe weather changes will reduce the efficiency of the heat sink, shorten its life, and even damage it, causing safety accidents.

In this regard, for example, in CN 108302796A, a chemical energy storage device is added to perform deep peak regulation to avoid excessive local temperature of the heat absorber and prolong the service life of the heat absorber; layer to reduce the heat loss of the heat absorber, weaken the temperature impact of the heat absorber, and enhance the adaptability of the heat absorber to weather changes.

However, the above method can only alleviate the harsh environment of the heat absorber and heat exchange pipes from the external conditions to a certain extent, but cannot improve the heat resistance and heat storage capacity of the heat absorber and heat exchanger itself. In order to improve the power generation efficiency of the solar power generation system, a higher concentration ratio is required. And enhancing the heat resistance and heat storage capacity of the heat absorber itself plays an important role in increasing the temperature of the heat absorber under high concentration ratio and maintaining the stable and safe operation of the system.

Contents of the invention

The purpose of the present invention is to disclose a thermochemical protective coating material and its preparation method, which can not only protect the heat absorber from thermal shock, but also improve the working stability of the system by using its own heat storage capacity, thereby improving the power generation efficiency.

The invention provides a thermochemical protective coating material, comprising: ABO ₃ perovskite material or a ternary composite metal oxide doped with lithium, wherein the A position of the ABO ₃ perovskite material is La, Ca, Ba, A combination of any two or more of Sr and K, and/or, the B site of the ABO ₃ perovskite material is a combination of any two or three of Mn, Fe and Co.

Specifically, the thermochemical protective coating material provided by the present invention includes an ABO ₃ perovskite material suitable for medium-high temperature heat storage or a ternary composite metal oxide doped with lithium. By changing the ratio of A-site or B-site doping elements of the ABO ₃ perovskite material and the molar ratio of each element in the ternary composite metal oxide, the reaction temperature of the composite metal oxide can be adjusted, so that the added element can be flexibly selected according to needs. ratio to obtain a specific reaction temperature. Thermochemical protective coating materials with thermochemical heat storage capacity can improve the protection of inner layer materials to reduce thermal shock, and use their own heat storage capacity to improve the working stability of the system. Preferably, the ternary composite metal oxide is manganese-iron-lithium ternary composite metal oxide, cobalt-copper-lithium ternary composite metal oxide or copper-aluminum-lithium ternary composite metal oxide.

According to the above technical scheme, the reaction temperature is changed by changing the three elements of manganese, iron and lithium, the three elements of cobalt, copper and lithium or the molar ratio of the three elements of copper, aluminum and lithium.

Preferably, the thermochemical protective coating material also includes silicon carbide.

According to the above technical solution, adding an appropriate amount of silicon carbide to the thermochemical coating material can improve the thermal conductivity of the coating and reduce heat loss.

Preferably, the thermochemical protective coating material also includes polysilazane organic polymers.

According to the above technical scheme, ceramic precursors such as polysilazane-based organic polymers are added to the thermochemical coating material, and ceramic transformation can be realized during the heat treatment process, and the prepared ceramic coating has high hardness and excellent superstructure. Hydrophobic and corrosion resistant.

Preferably, the thermochemical protective coating is a coating formed by spraying a thermochemical protective coating material.

According to the above technical scheme, the thermochemical protective material is applied to the surface of the heat absorber by spraying, which can not only obtain a coating film with excellent performance, but also improve the absorption efficiency, friction resistance, and impact resistance of the heat absorber, and prolong the absorption time. service life of the heater.

Preferably, the thermochemical protective coating also includes a black chrome layer.

According to the above technical scheme, electroplating a layer of black chromium on the pretreated workpiece can increase the radiation absorption rate of the coating, reduce the emissivity, and improve the utilization rate of solar energy.

Preferably, the thermochemical protective coating is a microporous membrane with a thickness of 50-80 μm.

According to the above technical solution, the microporous membrane can increase the contact area between the protective material and the gas, and improve the reactivity of the thermochemical protective coating material.

Preferably, the working temperature range of the thermochemical protective coating is 500-900°C.

According to the above technical solution, by changing the type and proportion of the elements of the composite metal oxide, the reaction temperature range of the obtained thermochemical protective coating material is from 500°C to 900°C.

Preferably, the thermochemical protective coating is sprayed by an electrostatic powder spraying system.

According to the above technical scheme, the coefficient of thermochemical coating material and air can be set through the control system of the electrostatic powder spraying system, and the powder output and the atomization state of the thermochemical protective material can be changed, so as to achieve different spray film thicknesses and meet different requirements. product needs.

The present invention also provides a kind of preparation method of thermochemical protection coating material, comprises the following steps:

Step 1: Mix nitrate, citric acid, and ethylene glycol in a certain proportion, heat and stir until a gel is formed;

Step 2, drying the gel formed in Step 1 in an environment of 180-220°C to obtain a sample;

Step 3, calcining the sample in step 2 in an environment of 300-500°C, and then performing high-temperature heat treatment in an environment of 800-1000°C;

In step 4, the sample calcined in step 3 is taken out and ground into powder to obtain a thermochemical protective coating material.

According to the above technical scheme, the thermochemical protective coating material made by the above method can be obtained. The thermochemical protective coating material has a micron-scale porous structure, which can increase the contact area between the heat storage material and the gas, and improve the thermal efficiency of the composite metal oxide. Reactivity of chemical energy storage materials.

The composite metal oxide thermochemical protective coating material of the invention is suitable for thermochemical protection on the surface of a heat absorber for medium-high temperature solar thermal power generation. The thermochemical protective coating material can fill the shortcoming of the narrow temperature range of a single metal oxide heat storage material, and adjust the reaction temperature by changing the molar ratio of the composite metal oxide according to different needs, so that the reaction temperature zone and the actual temperature can be better matched , reduce heat loss and improve thermal efficiency. The thermochemical protective coating material is sprayed onto the surface of the heat absorber by spraying, which can not only obtain a coating surface with excellent performance, but also improve the absorption rate of the heat absorber, abrasion resistance, impact resistance, adhesion, Toughness, corrosion resistance, etc. are enhanced to prolong the service life of the heat absorber.

Description of drawings

Fig. 1 is the thermogravimetric curve of the perovskite structure BaCo1 _{- xMnxO3} provided by the embodiment of the present invention _;

Fig. 2 is the thermogravimetric curve of the ferromanganese lithium ternary composite metal oxide thermochemical heat storage material provided by the embodiment of the present invention;

Fig. 3 is a diagram of the thermochemical protection system of the air heat absorber provided by the embodiment of the present invention;

Fig. 4 is a schematic structural diagram of an air heat absorber provided by an embodiment of the present invention;

Fig. 5 is a cross-sectional view of a heat absorber without a thermochemical protective coating provided by an embodiment of the present invention;

Fig. 6 is a cross-sectional view of a heat absorber for spraying a thermochemical protective coating according to an embodiment of the present invention;

Fig. 7 is a temperature gradation diagram of a heat absorber without a thermochemical protective coating and a heat absorber sprayed with a thermochemical protective coating according to an embodiment of the present invention.

reference sign

1 Thermochemical protective coating

2 air compressors

3 pressure reducing valve

4 flow meters

5 valves

6 Solar Simulation Lights

7 heat sink

a Air inlet

b Air outlet

T1～T5 thermocouple

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The invention provides a thermochemical protective coating material, comprising: ABO ₃ perovskite material or a ternary composite metal oxide doped with lithium, wherein the A position of the ABO ₃ perovskite material is La, Ca, Ba, A combination of any two or more of Sr and K, and/or, the B site of the ABO ₃ perovskite material is a combination of any two or three of Mn, Fe and Co.

Specifically, the thermochemical protective coating material provided by the present invention includes an ABO ₃ perovskite material suitable for medium-high temperature heat storage or a ternary composite metal oxide doped with lithium. By changing the ratio of A-site or B-site doping elements of the ABO ₃ perovskite material and the molar ratio of each element in the ternary composite metal oxide, the reaction temperature of the composite metal oxide can be adjusted, so that the added element can be flexibly selected according to needs. ratio to obtain a specific reaction temperature. Thermochemical protective coating materials with thermochemical heat storage capacity can improve the protection of inner layer materials to reduce thermal shock, and use their own heat storage capacity to improve the working stability of the system.

Example 1

This embodiment provides an ABO ₃ perovskite structure metal oxide thermochemical protective coating material. In the perovskite structure, the A site is mostly an alkali metal element, such as La, Ca, Ba, Sr, etc., and the B site is mostly a transition metal element, such as Mn, Co, Fe, etc. The actual perovskite material Typically there will be a non-stoichiometric ratio of oxygen. By doping other elements in different proportions at the A site or the B site, the temperature regulation of the oxidation and reduction reactions can be realized.

In this embodiment, the ABO ₃ perovskite material with doping elements is BaCo _1-x Mn _x O ₃ , wherein Ba and Co are in-situ elements, and Mn is a doping element. The content of Mn can vary between 0-0.4, that is, x can be any value between 0 and 0.4. Figure 1 is the thermogravimetric curve of BaCo _1-x Mn _x O _3. It can be seen from Figure 1 that when x changes in the range of 0 to 0.4, the reaction temperature changes in the range of 500-720 ° C, and with the increase of x increase and rise.

The preparation method of the metal oxide thermochemical protective coating material of the _ABO3 perovskite structure provided in this embodiment includes the following steps:

Step 1: Mix nitrate, citric acid and ethylene glycol in a certain proportion, heat and stir until a gel is formed. Specifically, weigh the required nitrate, citric acid, ethylene glycol, deionized water, etc. according to the calculated ratio, put them into a beaker, stir at 70°C for 3 hours, adjust the pH to 8 with ammonia water, and then Ethylene glycol was added at a molar ratio of citric acid: ethylene glycol = 3:2, and stirred at 90° C. for 2 h until a gel was formed.

Step 2: Pour the formed gel into a crucible, and dry in a drying oven at 200° C. for 3 hours.

Step 3: Put the dried sample into a tube furnace for calcination at 300°C for 3 hours, then raise the temperature to 1000°C, and calcine at high temperature for 5 hours.

Step 4: Cool the calcined sample to room temperature, take it out and grind it into powder to obtain the thermochemical protective coating material.

Example 2

This embodiment provides a ternary composite metal oxide thermochemical protective coating material. The ternary composite metal oxide described in this embodiment is a ternary composite metal oxide of manganese, iron and lithium. The reaction temperature is changed by changing the molar ratio of the three elements of manganese, iron and lithium. The molar ratio of the elements is different, the reaction initiation temperature and the maximum reaction rate temperature are all different.

In this embodiment, the molar ratio of manganese, iron, and lithium in the manganese-lithium ternary composite metal oxide is x:y:z, where (x+y):z is 1:1-1.5:1 , the molar ratio x:y of ferromanganese is 2:1～4:1. Fig. 2 is the thermogravimetric curve of the manganese-lithium ternary composite metal oxide. It can be known from Fig. 2 that the reaction temperature of the manganese-lithium ternary composite metal oxide is 600-900°C.

The manganese-iron-lithium ternary composite metal oxide thermochemical protective coating material provided in this example is prepared by a sol-gel method, including the following steps:

Step 1: Mix manganese, iron, lithium nitrate, citric acid, and ethylene glycol in a certain proportion, heat and stir until a gel is formed;

Step 2: drying the gel formed in Step 1 at 200°C to obtain a sample;

Step 3: calcining the sample in an environment of 450°C, and then calcining in an environment of 800°C;

Step 4: Take out the calcined sample and grind it into powder to obtain the thermochemical protective coating material.

The composite metal oxide thermochemical heat storage material prepared by the sol-gel method in this example has a porous structure with micron-sized pores, which can increase the contact area between the heat storage material and the gas, and improve the reaction of the composite metal oxide thermochemical heat storage material. active.

Example 3

This embodiment provides a preparation step of a thermochemical protective coating.

The preparation steps of the workpiece thermochemical protective coating include preparation before spraying and electrostatic powder spraying. The preparation steps before spraying are as follows:

Before coating, the workpiece to be sprayed needs to be pretreated. Pretreatment can make the characteristics of the thermochemical protective coating fully developed, and can also prolong the service life of the thermochemical protective coating. The preprocessing steps are as follows:

Step 1: Purify the surface of the workpiece to be sprayed, and remove the stains, paints and oxides attached to the surface;

Step 2: Carry out surface preprocessing, reserve a certain thickness of the sprayed layer, so that the workpiece meets the design size requirements after spraying;

Step 3: roughen the surface of the pre-sprayed workpiece by sandblasting. The sandblasting material can be selected through the surface hardness of the pre-sprayed workpiece. The sandblasting material in this embodiment can be polygonal condensed cast iron sand (suitable for the surface of the pre-sprayed workpiece with a hardness of about HRC50), corundum sand (suitable for a hardness of about HRC40 The surface of the pre-sprayed workpiece) and quartz sand (suitable for the surface of the pre-sprayed workpiece with a hardness of about HRC40), can also be roughened by machining;

Step 4: Warm up. After the surface is roughened, it needs to be preheated to improve the surface bonding strength;

Step 5: Spray and combine the bottom layer. In order to improve the bonding strength between the thermochemical protective coating and the sprayed workpiece, a layer of bonding bottom layer can be sprayed after the pretreatment of the sprayed workpiece. The thickness of the bonding bottom layer is determined according to the specific size of the workpiece. In the case of thin workpieces and easy deformation of sandblasting , combined with a bottom layer thickness of 50-100 μm;

Spray thermochemical protective coating. Use an electrostatic spraying machine to spray a thermochemical protective coating on the surface of the workpiece to be sprayed. The spraying steps are as follows:

Step 1: Using the principle of electrostatic adsorption, evenly spray a layer of thermochemical protective powder coating on the surface of the workpiece;

Step 2: Place the sprayed workpiece in a high-temperature furnace at about 200°C for 20 minutes to melt, level and solidify the powder.

The thickness of electrostatic powder spraying can reach 50-80μm in one spraying. The parameters of thermochemical protective coating material and air can be set through the control system, and the powder output and atomization state of thermochemical protective material can be changed, so as to achieve different coating thicknesses. , to meet the thickness requirements of different spray coatings.

The thermochemical protective coating with electrostatic powder spraying has the long-lasting performance of the coating film. In addition to the thermochemical protective coating itself has a certain thermochemical protection ability, other properties have also been greatly improved, including abrasion resistance and impact resistance. , Adhesion, toughness, corrosion resistance.

Example 4

This embodiment provides a method of using the perovskite material coating to protect the air heat absorber 8, and using the above perovskite material to realize heat storage/radiation characteristics in a medium-high temperature environment, and to protect the heat absorber Thermochemical protection.

Fig. 3 is the thermochemical protection system diagram of heat absorber 8, as shown in Fig. 3, this thermochemical protection system comprises: air compressor 2, decompression valve 3, flow meter 4, valve 5, solar simulation lamp 6, heat absorption Device 7, T1-T5 are thermocouples, a is the air inlet, b is the air outlet. Fig. 4 is a schematic structural diagram of the heat absorber 7, and Fig. 5 and Fig. 6 are respectively cross-sectional views of the heat absorber without a thermochemical protective coating and after spraying a thermochemical protective coating.

Spray the above-mentioned perovskite material on the heat absorber 7 by electrostatic powder spraying method, the coating thickness is 60 μm, heat it under the solar simulation lamp 6, keep the air flow rate at 6m ³ /h, and turn on one lamp every ten minutes For the simulated lamp 6, when the sixth solar simulated lamp 6 is turned on, the temperature is measured with an infrared thermometer every one minute, and compared with the temperature of the heat absorber 7 that is not coated with the thermochemical protective coating 1, the experimental results As shown in FIG. 7 , where dg is the temperature measured without the thermochemical protective coating 1 , that is, the temperature of the light pipe, and hk is the temperature after spraying the thermochemical protective coating 1 .

It can be seen from Figure 7 that when there is no thermochemical protective coating 1, the temperature of the sixth simulated lamp 6 just after turning on is 560°C, and after the thermochemical protective coating 1 is sprayed, the temperature of the sixth simulated lamp 6 is 580°C , to be higher than the temperature when there is no thermochemical protective coating 1, because the coating is black, and the radiation absorption rate of the heat absorber 7 increases after spraying the coating, absorbing more radiation energy and increasing the temperature. Three minutes after turning on the sixth simulated lamp 6, the temperature of the heat absorber 7 without the thermochemical protective coating 1 rose to 657°C, while the temperature of the heat absorber 7 sprayed with the thermochemical protective coating 1 was basically stable at 640°C , at this time, the thermochemical protective coating 1 starts to react to absorb heat, so as to prevent the heat absorber 7 from overheating.

In this embodiment, the temperature of the heat absorber 7 sprayed with thermochemical protective coating 1 is finally stabilized at 640°C, indicating that the reaction temperature of the coating is about 640°C. The types and proportions of oxides are used to prepare thermochemical protective coatings 1 at corresponding reaction temperatures.

The specific examples of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, although in the embodiments of the present invention, the composite metal oxide thermochemical protective coating material is a ternary composite Metal oxides are described as examples, but those skilled in the art can understand that the use of lithium-doped quaternary and above composite metal oxides as protective coating materials should also belong to Within the protection scope of the present invention, and those skilled in the art can make various changes and modifications within the scope of the claims, which does not affect the essential content of the present invention. In the case of no conflict, the embodiments of the application and The features in the embodiments can be combined with each other arbitrarily.

Claims (4)

1. A thermochemical protective coating is characterized by being formed by spraying thermochemical protective coating materials, wherein the thermochemical protective coating materials comprise ternary composite metal oxides doped with lithium,

the thermochemical protective coating material is sprayed on the surface of the heat absorber;

changing the molar ratio of metal elements in the ternary composite metal oxide to obtain the thermochemical protective coating material with specified reaction temperature, wherein the specified reaction temperature is adapted to the temperature requirement of the heat absorber;

the lithium-doped ternary composite metal oxide is a manganese-iron-lithium ternary composite metal oxide, and the molar weight ratio of manganese to iron to lithium is x: y: z (x + y) is 1-1.5, and the molar weight ratio of ferromanganese x to y is 2;

the thermochemical protective coating is a microporous membrane with the thickness of 50-80 mu m formed by spraying of an electrostatic powder spraying system.

2. The thermochemical protective coating of claim 1, wherein the thermochemical protective coating material further comprises silicon carbide.

3. The thermochemical protective coating of claim 1, wherein the thermochemical protective coating material further comprises a polysilazane-based organic polymer ceramic precursor.

4. Thermochemical protective coating according to claim 1, characterized in that it further comprises a black chrome layer.

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