Heating body protective coating as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molten salt electrolysis protection materials, in particular to a heating body protection coating and a preparation method and application thereof. The protective coating is prepared from the following raw materials: 30%-50% of aluminum oxide, 10%-30% of feldspar powder, 20%-30% of sodium silicate, 5%-20% of phosphate, 6%-12% of potassium fluoroaluminate, 1%-5% of silica powder and 0%-20% of a hydrophilic solvent. According to the protective paint, through the synergistic effect of all the components, excellent oxidation resistance, corrosion resistance, thermal stability and repairability are achieved, and a protective coating formed by the protective paint can be stably used for 1000 h or above in an electrolysis experiment without generating corrosion spots.

Description

Technical Field

[0001] This application relates to the technical field of molten salt electrolysis protection materials, and particularly relates to a heating body protection coating, a preparation method thereof, and an application thereof. Background Art

[0002] The key equipment for salt method electrolytic production of aluminum is an electrolytic cell using direct current. In the electrolytic cell, the aluminum salt generates heat by relying on the direct current carrier, and heat is also generated between the cathode and anode of the electrolytic cell through electrolysis. These heats can promote the electrolyte to maintain a dynamic molten state at about 945°C. And the molten electrolyte can provide a stable environment for aluminum electrolysis. Generally, an experimental-level molten salt electrolytic aluminum test device is used to study the physical and chemical phenomena during the molten salt electrolytic aluminum process to optimize the electrolysis process. At present, traditional experimental-level molten salt electrolytic aluminum experimental devices generally use small aluminum electrolysis equipment for electrolysis experiments. However, due to the limited number, current magnitude, and reaction area of the cathode and anode electrodes of the small aluminum electrolysis equipment, during the electrolysis experiment, the heat generated by the direct current electrolysis reaction and the heat generated by the direct current itself are far less than the heat dissipated by the electrolytic cell. Therefore, in order to accurately simulate the traditional large electrolytic cell, an additional heating device needs to be set on the small aluminum electrolysis equipment to ensure that the heat of the small aluminum electrolysis equipment meets the simulation requirements of the traditional large electrolytic cell.

[0003] With the introduction of the additional heating device, the small aluminum electrolysis equipment is in an uninterrupted high-temperature operation state. In this high-temperature operation state, due to the existence of corrosive substances such as atomic oxygen atmosphere, hydrogen fluoride, and alkaline volatiles, the heating body of the test tank of the small aluminum electrolysis equipment will be corroded and damaged. On the one hand, the corrosion layer formed by the heating body will continuously thicken, seriously affecting the heating efficiency of the heating body. On the other hand, the severe corrosion layer will cause the heating body to break and separate, resulting in a sharp drop in the temperature of the test tank and causing the test to be interrupted. In addition, the corrosion and damage of the heating body will affect the effective development of inspection tests such as material corrosion resistance, corrosion rate, and durability of key parts, seriously restricting the in-depth development of such inspection tests. Although there are currently antioxidant and corrosion-resistant coatings for different heating bodies, the antioxidant and corrosion-resistant capabilities of these coatings can only be targeted at specific environments and are difficult to meet the service environment requirements of the heating body in the molten salt electrolysis experiment.

[0004] Currently, the technologies related to the coatings for heating elements are as follows: (1) High-temperature resistant and oxidation-resistant coatings. The characteristics of this oxidation-resistant coating are strong oxidation resistance, good heat insulation, and easy cleaning of the coating under high-temperature conditions; (2) Special coatings for high-temperature resistant and oxidation-resistant barbecue stoves. The characteristics of this special coating are that the coating is composed of six ceramic layers, namely, oxidation-resistant, heat-insulating, heat-preserving, and energy-gathering layers, respectively, and has good heat resistance; (3) Coatings with high heat resistance and oxidation-resistant characteristics. The characteristics of this characteristic coating are good mechanical properties and oxidation resistance. Practical tests have proved that this characteristic coating can withstand high temperatures up to 800 °C; (4) Water-based coatings with high temperature resistance for metal surfaces. The characteristics of this water-based coating are multiple color options, certain mechanical properties, and high temperature resistance, etc. Summary of the Invention

[0005] This application provides a protective coating for heating elements, its preparation method and application, to solve the following technical problems: how to simultaneously improve the oxidation resistance and corrosion resistance of the protective coating in the molten salt electrolysis experiment.

[0006] In the first aspect, an embodiment of this application provides a protective coating for heating elements. Calculated by mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 30% - 50%, feldspar powder: 10% - 30%, sodium silicate: 20% - 30%, phosphate: 5% - 20%, potassium fluoroaluminate: 6% - 12%, silica powder: 1% - 5% and hydrophilic solvent: 0% - 20%.

[0007] Optionally, the phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 5% - 10%, and the mass fraction of sodium tripolyphosphate is 4% - 8%.

[0008] Optionally, the particle size of the feldspar powder is 10 μm - 35 μm.

[0009] Optionally, the particle size of the silica powder is 1500 mesh - 1800 mesh.

[0010] In the second aspect, an embodiment of this application provides a method for preparing the protective coating described in the first aspect. The method includes:

[0011] Mix the defoamer, sodium silicate, hydrophilic solvent and part of the liquid phosphate to obtain a liquid raw material;

[0012] Mix alumina, feldspar powder, potassium fluoroaluminate, silica powder and the remaining solid-phase phosphate to obtain a solid-phase raw material;

[0013] Stir the solid-phase raw material and the liquid raw material to obtain a mixed slurry;

[0014] Mix the thickener and the mixed slurry to obtain a protective coating.

[0015] Optionally, the mass of the defoamer is 0.05% to 0.10% of the mass of the liquid raw material.

[0016] Optionally, the mass m1 of the thickener and the mass m2 of the mixed slurry satisfy the relationship: m1:m2 = (0.5 - 1.2):(99.5 - 98.8).

[0017] In a third aspect, an embodiment of the present application provides a heating element protection coating, and the protection coating is prepared from the protection coating material described in the first aspect.

[0018] Optionally, the thickness of the protection coating is 50 μm to 150 μm.

[0019] In a fourth aspect, an embodiment of the present application provides a method for preparing the protection coating described in the third aspect, and the method includes:

[0020] Spraying the protection coating material described in the first aspect on the surface of the heating element to obtain a coated slurry;

[0021] Drying the coated slurry to obtain the protection coating.

[0022] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0023] A heating element protection coating material provided by an embodiment of the present application. In this protection coating material, alumina with a mass fraction of 30% to 50% can serve as the main framework. Based on the antioxidant property of alumina, the antioxidant property of the protection coating material can be improved. In addition, the main framework can form mullite phases with sodium silicate with a mass fraction of 20% to 30% under high-temperature conditions. These mullite phases can refine the distribution of other components of the protection coating material and improve the denseness and high-temperature stability of the coating formed by the protection coating material. In addition, feldspar powder with a mass fraction of 10% to 30% can form an inert bonding interface in the protection coating material after melting to avoid cracking of the coating formed by the protection coating material. At the same time, the inert bonding interface will hinder the corrosion of molten salt electrolyte and improve the corrosion resistance of the protection coating material. In addition, phosphate with a mass fraction of 5% to 20% can form glassy substances with potassium fluoroaluminate with a mass fraction of 6% to 12% under high-temperature conditions. These glassy substances will fill the microcracks of the protection coating formed by the protection coating material to block the infiltration of corrosive molten salt and improve the corrosion resistance of the protection coating material. And the fluorine element of potassium fluoroaluminate will improve the thermal stability of the protection coating material under high-temperature conditions. In addition, silicon micropowder with a mass fraction of 1% to 5% has a good thermal expansion coefficient, enabling the protection coating material to exist stably under high-temperature conditions, avoiding peeling due to expansion, and improving the thermal stability of the protection coating material. In addition, silicon micropowder and sodium silicate will provide a silica phase for the protection coating material, and the silica phase has good thermal stability and antioxidant property, which can improve the antioxidant property of the protection coating material. Brief Description of the Drawings

[0024] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments in line with this application, and are used together with the specification to explain the principles of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 Schematic flow diagram of a method for preparing a protective coating provided by an embodiment of this application;

[0027] Figure 2 Schematic diagram of a physical object of a heating element protection coating provided by an embodiment of this application;

[0028] Figure 3 Schematic flow diagram of a method for preparing a protective coating provided by an embodiment of this application;

[0029] Figure 4 Schematic diagram of a heating element in a molten salt electrolysis test for more than 1220 h of a protective coating formed by the protective coating provided by Embodiment 3 of this application;

[0030] Figure 5 Schematic diagram of a heating element of a blank group provided by this application after a molten salt electrolysis experiment;

[0031] Figure 6 Schematic diagram of spraying in a single-row spraying method in different directions provided by this application. Detailed Description of the Embodiments

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

[0033] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0034] In this document, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one kind", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single item (s) or plural item (s); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as parts by weight, parts by mass, etc. represent the proportional relationship between each component. In the proportional relationships involved in this document, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0035] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this document can be obtained through market purchase or can be prepared by existing methods.

[0036] It should be noted that for the existing technologies (1) to (4) described in the background art, the inventors found that although these coatings have their respective advantages and all have good antioxidant and corrosion resistance capabilities, in the service environment of molten salt electrolysis, these coatings are difficult to resist the high oxidation and high corrosion capabilities of molten salt, resulting in relatively low heat insulation and heat preservation performance. Moreover, the use temperature of these coatings is relatively low, and the spraying process is relatively complex, making it difficult to meet the service environment requirements of the heating element in molten salt electrolysis experiments.

[0037] An embodiment of the present application provides a protective coating for a heating element. In terms of mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 30% - 50%, feldspar powder: 10% - 30%, sodium silicate: 20% - 30%, phosphate: 5% - 20%, potassium fluoroaluminate: 6% - 12%, silica powder: 1% - 5% and hydrophilic solvent: 0% - 20%.

[0038] It should be noted that SF-400SAC type feldspar powder can be used for this feldspar powder.

[0039] It should be noted that micron-sized silicon dioxide powder can be used for this silica powder.

[0040] It should be noted that this hydrophilic solvent can be softened water.

[0041] It should be noted that an embodiment of the present application provides a protective coating for a heating element. Through the synergistic effect of each component, this protective coating achieves excellent antioxidant property, corrosion resistance, thermal stability and reparability. The following is a specific description of the action mechanism and performance optimization of each component:

[0042] 1. Alumina (30% - 50%) - Main body framework and antioxidant core:

[0043] (1) Antioxidant property: Alumina (Al2O3) has extremely high chemical stability and can still maintain the inertness of the protective coating in an environment where the protective coating is at high temperature and under molten salt corrosion, so as to effectively block the erosion of oxygen and corrosive gases on the protective coating.

[0044] (2) Framework support effect: As the main structural phase of the protective coating, alumina particles will form a three-dimensional network framework, and this network framework will improve the mechanical strength and thermal shock resistance of the protective coating formed by the protective coating.

[0045] (3) Formation of mullite phase: At high temperature, alumina will react with sodium silicate to form mullite phase (3Al2O3·2SiO2). This mullite phase has extremely high thermal stability and chemical inertness, and can significantly improve the denseness and molten salt penetration resistance of the protective coating formed by the protective coating.

[0046] 2. Sodium silicate (20% - 30%) - Binder and mullite precursor:

[0047] (1) Low - temperature bonding effect: Sodium silicate can melt under high - temperature conditions, forming a liquid phase to promote the bonding between the protective coating formed by the protective paint and the substrate, improving the adhesion and densification of the initial protective coating.

[0048] (2) High - temperature mullitization: At higher temperatures, sodium silicate will decompose to generate SiO2, which reacts with alumina to form mullite phase, refining the microstructure of the protective coating, reducing the porosity of the protective coating, and improving the thermal shock resistance and molten salt corrosion resistance of the protective coating.

[0049] (3) Contribution of silica phase: The SiO2 provided by sodium silicate can form a stable glass phase at high temperatures, further enhancing the oxidation resistance and corrosion resistance of the protective coating.

[0050] 3. Feldspar powder (10% - 30%) - Melting bonding and crack - resistance enhancement:

[0051] (1) Melting filling effect: Feldspar powder (mainly composed of KAlSi3O8 or NaAlSi3O8) will melt under high - temperature conditions, forming a low - viscosity liquid phase to fill the micropores of the protective coating, so as to improve the densification of the protective coating.

[0052] (2) Inert bonding interface: The molten feldspar can form a glassy bonding phase after cooling, reducing the thermal stress between the protective coating and the substrate, and preventing the protective coating from cracking and spalling.

[0053] (3) Resistance to molten salt corrosion: The aluminosilicate phase formed after the melting of feldspar has excellent resistance to molten salt corrosion, which can effectively block the penetration of electrolytes and improve the corrosion resistance of the protective coating.

[0054] 4. Phosphate (5% - 20%) and potassium fluoroaluminate (6% - 12%) - Glass - state sealing and thermal stability strengthening:

[0055] (1) Glass - phase formation: Phosphate (such as AlPO4) and potassium fluoroaluminate (KAlF4) will react to form a low - melting - point glass phase at high temperatures. This glass phase will flow to fill the micro - cracks of the protective coating formed by the protective paint, improving the self - repair ability of the protective coating.

[0056] (2) Role of fluorine element: The F - ions in potassium fluoroaluminate can reduce the viscosity of the glass phase, promote its fluidity at high temperatures, and enhance the sealing effect of the protective coating. At the same time, F - can stabilize the Al2O3 lattice and improve the thermal stability of the coating.

[0057] (3) Resistance to molten salt penetration: The formed glass phase has an extremely low solubility in molten salt, which can effectively block the erosion of molten salt electrolyte.

[0058] 5. Silica fume (1% - 5%) - Thermal expansion matching and thermal conductivity optimization:

[0059] (1) Adjustment of thermal expansion coefficient: The thermal expansion coefficient of silica fume (nano-SiO2) can form a gradient match with the heating element, reducing the spalling of the protective coating caused by thermal stress.

[0060] (2) Enhancement of thermal conductivity: Silica fume and alumina jointly construct a thermal conductivity network, improving the thermal conductivity of the protective coating, ensuring uniform distribution of the heat of the heating element, and avoiding local overheating damage.

[0061] (3) Contribution of silica phase: Silica fume can be partially transformed into cristobalite (SiO2) at high temperatures, further enhancing the oxidation resistance of the protective coating.

[0062] 6. Hydrophilic solvent (0% - 20%) - Optimization of construction performance and convenience of repair:

[0063] (1) Construction adaptability: The aqueous solvent can adjust the viscosity of the protective coating, suitable for brushing, dipping or spraying processes, ensuring uniform coverage of the protective coating.

[0064] (2) Convenience of repair: In the case of local damage to the protective coating, the hydrophilic solvent can enable the new coating to form a chemical bond with the old coating, realizing in-situ repair.

[0065] In summary, a protective coating for a heating element provided by an embodiment of the present application has the following improved comprehensive performance:

[0066] (1) Oxidation resistance: The synergistic effect of mullite phase + glass phase significantly improves the oxidation resistance of the protective coating formed by the protective coating under high-temperature conditions;

[0067] (2) Corrosion resistance: Dense coating + glass phase sealing reduces the corrosion rate of the heating element in molten salt electrolyte;

[0068] (3) Thermal stability: Thermal expansion matching + thermal conductivity optimization ensure that the protective coating does not spall under high-temperature conditions of thermal cycling;

[0069] (4) Economy and reparability: The protective coating can reduce the use cost of industrial-grade raw materials, and supports multiple repairs, which can extend the total life of the heating element;

[0070] Therefore, through the synergistic optimization of multiple components, this protective coating system has successfully solved the problem of easy corrosion and damage of the heating element in molten salt electrolysis experiments, and has broad application prospects.

[0071] It should be noted that the shelf life of the protective coating is 12 months under the storage temperature condition of not less than 0 °C.

[0072] The mass fraction of the alumina can be 30%, 31%, 32%, 33%, 34%, 35%, 40%, 45% or 50%.

[0073] The mass fraction of the feldspar powder can be 10%, 11%, 12%, 13%, 14%, 15%, 20%, 25% or 30%.

[0074] The mass fraction of the sodium silicate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0075] The mass fraction of the phosphate can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0076] The mass fraction of the potassium fluoroaluminate can be 6%, 7%, 8%, 9%, 10%, 11% or 12%.

[0077] The mass fraction of the silica fume can be 1%, 2%, 3%, 4% or 5%.

[0078] The mass fraction of the hydrophilic solvent can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15% or 20%.

[0079] In some alternative embodiments, the phosphate further includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of the aluminum dihydrogen phosphate is 5% - 10%, and the mass fraction of the sodium tripolyphosphate is 4% - 8%.

[0080] In these embodiments, the aluminum dihydrogen phosphate with a mass fraction of 5% - 10% and the sodium tripolyphosphate with a mass fraction of 4% - 8% have the following principles:

[0081] 1. High - temperature bonding and densification:

[0082] Aluminum dihydrogen phosphate decomposes under high - temperature conditions to form an AlPO4 glass phase, which reacts with alumina to form an aluminum phosphate network structure, enhancing the chemical bonding force between the protective coating formed by the protective coating and the substrate, and reducing the risk of cracking of the protective coating under high - temperature conditions.

[0083] Sodium tripolyphosphate, as a dispersant, can refine the distribution of raw material particles, promote the uniform formation of mullite phase during sintering, and reduce the porosity of the protective coating formed by the protective coating.

[0084] 2. Enhancement of corrosion resistance:

[0085] The aluminophosphate glass phase can fill the microcracks of the protective coating formed by the protective paint, block the penetration of molten salt, and improve the corrosion resistance of the protective coating.

[0086] The complexing effect of sodium tripolyphosphate can stabilize metal ions, reduce the formation of metal oxides under high-temperature conditions, and lower the electrochemical corrosion rate of the protective coating.

[0087] 3. Process Optimization and Cost Control:

[0088] The water solubility of aluminum dihydrogen phosphate makes it easy to mix with other water-based components (such as sodium silicate), simplifying the construction process.

[0089] The addition amount of sodium tripolyphosphate only needs to be 4% - 8% to achieve the dual functions of raw material dispersion and sintering aid, reducing the cost of the overall protective paint.

[0090] 4. Synergistic Enhancement of Thermal Stability:

[0091] The composite phosphate glass phase formed by the two at high temperature has a coefficient of thermal expansion that matches the alumina skeleton, which can prevent the protective coating formed by the protective paint from peeling off during thermal cycling under high-temperature conditions.

[0092] Na2O generated by the decomposition of sodium tripolyphosphate can promote the melting of feldspar powder and accelerate the low-temperature densification of the protective coating formed by the protective paint.

[0093] The mass fraction of the aluminum dihydrogen phosphate can be 5%, 6%, 7%, 8%, 9% or 10%.

[0094] The mass fraction of the sodium tripolyphosphate can be 4%, 5%, 6%, 7% or 8%.

[0095] In some alternative embodiments, the particle size of the feldspar powder is 10 μm - 35 μm.

[0096] In these embodiments, the particle size of the feldspar powder can be 10 μm - 35 μm, enabling the feldspar powder to be fully mixed with other components of the protective paint to form a dense, oxidation-resistant and corrosion-resistant protective coating.

[0097] The particle size of the feldspar powder can be 10 μm, 15 μm, 25 μm, 30 μm or 35 μm.

[0098] In some alternative embodiments, the particle size of the silica fume is 1500 mesh - 1800 mesh.

[0099] In these embodiments, the silica fume with a particle size of 1500 mesh - 1800 mesh makes

[0100] The particle size of the silica fume can be 1500 mesh, 1550 mesh, 1600 mesh, 1650 mesh, 1700 mesh, 1750 mesh or 1800 mesh.

[0101] Figure 1 Exemplarily shown is a schematic flow chart of a method for preparing a protective coating provided by an embodiment of the present application;

[0102] Based on a general inventive concept, as Figure 1 shown, an embodiment of the present application provides a method for preparing the protective coating, and the method includes:

[0103] S1. Mix an antifoaming agent, sodium silicate, a hydrophilic solvent, and a part of liquid phosphate to obtain a liquid raw material;

[0104] S2. Mix alumina, feldspar powder, potassium fluoroaluminate, silica fume, and the remaining solid-phase phosphate to obtain a solid-phase raw material;

[0105] S3. Stir the solid-phase raw material and the liquid raw material to obtain a mixed slurry;

[0106] S4. Mix a thickener and the mixed slurry to obtain a protective coating.

[0107] This method is for the preparation method of the above-mentioned protective coating. The specific composition of the protective coating can refer to the above embodiments. Since this preparation method adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0108] It should be noted that in this method, the liquid-phase components are first mixed, and an antifoaming agent is added simultaneously to avoid the formation of bubbles during the mixing stage of the liquid-phase components, which may affect the mixing uniformity between sodium silicate, the hydrophilic solvent, and a part of the liquid phosphate.

[0109] It should be noted that in this method, a thickener is also mixed with the mixed slurry. The thickener can improve the viscosity of the mixed slurry to improve the forming performance of the mixed slurry and facilitate the final formation of a dense protective coating by the mixed slurry.

[0110] It should be noted that the mixing stage of this method is carried out by mechanical stirring, and manual batching or an automated batching system can be used for batching before mixing the materials.

[0111] In some alternative embodiments, the mass of the antifoaming agent is 0.05% - 0.10% of the mass of the liquid raw material.

[0112] In these embodiments, an antifoaming agent accounting for 0.05% to 0.10% of the mass of the liquid raw material can effectively improve the uniform mixing among sodium silicate, a hydrophilic solvent, and a partial liquid phosphate, such that these materials in the liquid raw material are fully and uniformly dispersed.

[0113] The mass of the antifoaming agent is 0.05%, 0.06%, 0.07%, 0.08, 0.09% or 0.1% of the mass of the liquid raw material.

[0114] In some alternative embodiments, the mass m1 of the thickener and the mass m2 of the mixed slurry satisfy the relational expression: m1:m2 = (0.5 - 1.2):(99.5 - 98.8).

[0115] In these embodiments, the mass ratio of the thickener to the mixed slurry is m1:m2 = (0.5 - 1.2):(99.5 - 98.8). The thickener can improve the viscosity of the mixed slurry to enhance the forming performance of the mixed slurry, facilitating the ultimate formation of a dense protective coating by the mixed slurry.

[0116] The value of the mass m1 of the thickener can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or 1.2.

[0117] The value of the mass m2 of the mixed slurry can be 98.8, 98.9, 99.0, 99.1, 99.2, 99.3, 99.4 or 99.5.

[0118] Figure 2 Exemplarily shown is a physical schematic diagram of a heating element protective coating provided by an embodiment of the present application;

[0119] Based on a general inventive concept, as Figure 2 shown, an embodiment of the present application provides a heating element protective coating, and the protective coating is prepared from the protective coating material.

[0120] The protective coating is realized based on the above-mentioned protective coating material. The specific composition of the protective coating material can refer to the above embodiments. Since the protective coating adopts some or all of the technical solutions of the above embodiments, it thus has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated herein one by one.

[0121] It should be noted that the protective coating is prepared using the protective coating material as the raw material.

[0122] In some alternative embodiments, the thickness of the protective coating is 50 μm to 150 μm.

[0123] In these embodiments, the protective coating with a thickness of 50 μm to 150 μm has good compactness and thickness, and can effectively resist the corrosion of molten salt electrolyte to improve the corrosion resistance of the protective coating.

[0124] The thickness of the protective coating can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm.

[0125] Figure 3 Exemplarily shown is a schematic flow chart of a method for preparing a protective coating provided by an embodiment of the present application;

[0126] As Figure 3 shown, based on a general inventive concept, an embodiment of the present application provides a method for preparing the protective coating, and the method includes:

[0127] S1. Spraying the protective coating material on the surface of the heating body to obtain a coated slurry;

[0128] S2. Drying the coated slurry to obtain a protective coating.

[0129] This method is for the preparation method of the above-mentioned protective coating. The specific composition of the protective coating can refer to the above embodiments. Since this method adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, and will not be elaborated one by one here.

[0130] It should be noted that for this spraying, a negative pressure spray gun can be used as the equipment and compressed air can be used as the power source to evenly spray the protective coating material on the exposed outer surface of the heating body.

[0131] It should be noted that the spraying method can be carried out in a single-row spraying manner for different directions of the heating body. Specifically, it can be carried out in sequence through different regions of the heating body in the left, middle and right directions in the manner shown Figure 6 to enable the protective coating material to evenly cover the surface of the heating body.

[0132] The present application will be further described below in conjunction with specific embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0133] Example 1

[0134] A heating element protection coating. In terms of mass fraction, the raw materials of 30 kg of the protection coating consist of the following components: alumina: 30%, SF-400SAC type feldspar powder: 20%, sodium silicate: 25%, phosphate: 13%, potassium fluoroaluminate: 9%, silica fume: 3%, and hydrophilic solvent: 0%.

[0135] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 7%, and the mass fraction of sodium tripolyphosphate is 6%.

[0136] The particle size of the feldspar powder is 10 μm to 35 μm.

[0137] The particle size of the silica fume is 1500 mesh to 1800 mesh.

[0138] As Figure 1 shown, a method for preparing the protection coating is carried out under the condition of room temperature 23 °C as follows:

[0139] S1. Mix the defoamer, sodium silicate, hydrophilic solvent and part of the liquid phosphate to obtain a liquid raw material;

[0140] S2. Mix the alumina, feldspar powder, potassium fluoroaluminate, silica fume and the remaining solid-phase phosphate to obtain a solid-phase raw material;

[0141] S3. Stir the solid-phase raw material and the liquid raw material to obtain a mixed slurry;

[0142] S4. Mix the thickener and the mixed slurry to obtain the protection coating.

[0143] The mass of the defoamer is 0.05% of the mass of the liquid raw material.

[0144] The mass m1 of the thickener and the mass m2 of the mixed slurry satisfy the relationship: m1:m2 = 1.2:98.8.

[0145] As Figure 2 shown, a heating element protection coating is prepared from the protection coating.

[0146] The thickness of the protection coating is 150 μm.

[0147] As Figure 3 shown, a method for preparing the protection coating includes:

[0148] S1. Spray the protection coating on the surface of the heating element to obtain a coated slurry;

[0149] S2. Naturally dry the coated slurry for 24 h to obtain the protection coating.

[0150] Example 2

[0151] Compared with Example 1, this example has the following differences, and the rest are the same:

[0152] By mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 50%, feldspar powder: 10%, sodium silicate: 20%, phosphate: 9%, potassium fluoroaluminate: 6%, silica powder: 1% and hydrophilic solvent: 4%.

[0153] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 5%, and the mass fraction of sodium tripolyphosphate is 4%.

[0154] Example 3

[0155] Compared with Example 1, this example has the following differences, and the rest are the same:

[0156] By mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 36%, feldspar powder: 18%, sodium silicate: 18%, phosphate: 10%, potassium fluoroaluminate: 10%, silica powder: 5% and hydrophilic solvent: 3%.

[0157] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 6%, and the mass fraction of sodium tripolyphosphate is 4%.

[0158] Example 4

[0159] Compared with Example 1, this example has the following differences, and the rest are the same:

[0160] The protective coating stored for 12 months is used to prepare a protective coating according to the method of Example 1.

[0161] Comparative Example 1

[0162] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0163] Feldspar powder is not added. By mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 30%, sodium silicate: 25%, phosphate: 13%, potassium fluoroaluminate: 9%, silica powder: 3% and hydrophilic solvent: 20%

[0164] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 7%, and the mass fraction of sodium tripolyphosphate is 6%.

[0165] Comparative Example 2

[0166] Compared with Example 1, this comparative example has the following differences, and the rest are the same:

[0167] No phosphates are added. By mass fraction, the raw materials of the protective coating consist of the following components: alumina: 30%, feldspar powder: 20%, sodium silicate: 25%, potassium fluoroaluminate: 9%, silica fume: 3% and hydrophilic solvent: 13%.

[0168] Comparative Example 3

[0169] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0170] No aluminum dihydrogen phosphate is added, and the mass fraction of sodium tripolyphosphate is 13%.

[0171] Comparative Example 4

[0172] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0173] No sodium tripolyphosphate is added, and the mass fraction of aluminum dihydrogen phosphate is 13%.

[0174] Comparative Example 5

[0175] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0176] No potassium fluoroaluminate is added. By mass fraction, the raw materials of 30 kg of the protective coating consist of the following components: alumina: 30%, SF-400SAC type feldspar powder: 20%, sodium silicate: 25%, phosphate: 13%, silica fume: 3% and hydrophilic solvent: 9%.

[0177] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 7%, and the mass fraction of sodium tripolyphosphate is 6%.

[0178] Comparative Example 6

[0179] Compared with Example 1, the differences of this comparative example are as follows, and the rest are the same:

[0180] No silica fume is added. By mass fraction, the raw materials of 30 kg of the protective coating consist of the following components: alumina: 30%, SF-400SAC type feldspar powder: 20%, sodium silicate: 25%, phosphate: 13%, potassium fluoroaluminate: 9% and hydrophilic solvent: 3%.

[0181] The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 7%, and the mass fraction of sodium tripolyphosphate is 6%.

[0182] Related experiments and effect data:

[0183] The protective coatings of Examples 1 to 4 and Comparative Examples 1 to 2 were respectively sprayed on the surface of the heating element in the manner of Example 1. Then, a heating element without spraying any protective coating was used as the blank group. These heating elements were loaded into the molten electrolyte, and the temperature of the molten electrolyte was maintained at 900 °C. After electrolysis test drying, the time when corrosion spots appeared on the heating element was counted, and the results are shown in Table 1.

[0184] Table 1 Electrolysis experiment situation table of protective coatings of each example and comparative example forming protective coatings

[0185]

[0186]

[0187] As can be seen from Table 1, compared with Example 1, feldspar powder is not added in Comparative Example 1, phosphate is not added in Comparative Example 2, aluminum dihydrogen phosphate is not added in Comparative Example 3, sodium tripolyphosphate is not added in Comparative Example 4, potassium fluoroaluminate is not added in Comparative Example 5, and silica powder is not added in Comparative Example 6, all of which will have a serious impact on the protection of the heating element, and the time when corrosion spots appear is greatly shortened, indicating that these components have a certain impact on the protection function of the protective coating.

[0188] In addition, it was actually found in the experiment that the heating element of Example 3 after more than 1220 h of molten salt electrolysis experiment is as Figure 4 shown, indicating that the heating element of Example 3 did not show corrosion or damage during the molten salt electrolysis experiment; although corrosion spots appeared on the heating element of Example 4 at 1190 h, this may be due to partial aging during the long-term storage stage of the protective coating, but the corrosion spots were polished later and the protective coating was used for repair again.

[0189] In addition, after 356 h of electrolysis experiment on the blank group, the results are as Figure 5 shown. The temperature of the electrolyte dropped sharply, and it was necessary to stop the electrolytic cell for treatment. Subsequent inspection found that a large amount of corrosion layer appeared on the heating element, and these corrosion layers filled the inner wall gaps of the heating element. In addition, fractures appeared in some areas of the heating element, indicating that the heating element was stopped passively due to fractures and the experiment was not completed.

[0190] In summary, a protective coating for a heating element provided in the embodiments of the present application realizes excellent oxidation resistance, corrosion resistance, thermal stability and reparability through the synergistic effect of each component, so that the protective coating formed by the protective coating can be stably used for more than 1000 h in the electrolysis experiment without the appearance of corrosion spots.

[0191] In addition, a protective coating for a heating element provided by an embodiment of the present application can effectively improve the antioxidant and corrosion resistance of the heating element in a complex atmosphere. The protective coating formed in the molten salt electrolysis experiment can effectively ensure the adaptability of the heating element under long-term high-temperature conditions and complex gas corrosion atmosphere conditions, and extend the service life of the heating element by three times or more.

[0192] Furthermore, a protective coating for a heating element provided by an embodiment of the present application still has a normal protective function after long-term storage. Moreover, in the case where corrosion spots appear on the heating element later, after simple repair with this protective coating, the protective coating can still be used normally, effectively solving the common problem that the heating element in the molten salt electrolysis experiment is easily damaged by oxidation and molten salt corrosion.

[0193] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A heating element protective coating. In terms of mass fraction, the raw materials of the protective coating are composed of the following components: alumina: 30% - 50%, feldspar powder: 10% - 30%, sodium silicate: 20% - 30%, phosphate: 5% - 20%, potassium fluoroaluminate: 6% - 12%, silica fume: 1% - 5% and hydrophilic solvent: 0% - 20%.

2. The protective coating according to claim 1, characterized in that, The phosphate also includes aluminum dihydrogen phosphate and sodium tripolyphosphate; the mass fraction of aluminum dihydrogen phosphate is 5% - 10%, and the mass fraction of sodium tripolyphosphate is 4% - 8%.

3. The protective coating according to claim 1, characterized in that, The particle size of the feldspar powder is 10μm - 35μm.

4. The protective coating according to claim 1, characterized in that, The particle size of the silica fume is 1500 mesh - 1800 mesh.

5. A method for preparing the protective coating according to any one of claims 1 to 4, the method comprising: Mixing an antifoaming agent, sodium silicate, a hydrophilic solvent and a part of liquid phosphate to obtain a liquid raw material; Mixing alumina, feldspar powder, potassium fluoroaluminate, silica fume and the remaining solid-phase phosphate to obtain a solid-phase raw material; Stirring the solid-phase raw material and the liquid raw material to obtain a mixed slurry; Mixing a thickening agent and the mixed slurry to obtain a protective coating.

6. The method according to claim 5, characterized in that, The mass of the antifoaming agent is 0.05% - 0.10% of the mass of the liquid raw material.

7. The method according to claim 5, wherein The mass m1 of the thickening agent and the mass m2 of the mixed slurry satisfy the relationship: m1:m2 = (0.5 - 1.2):(99.5 - 98.8).

8. A heating element protective coating, the protective coating is prepared from the protective coating according to any one of claims 1 to 4.

9. The protective coating according to claim 8, wherein, The thickness of the protective coating is 50μm - 150μm.

10. A method for preparing the protective coating according to claim 8 or 9, the method comprising: Spraying the protective coating according to any one of claims 1 to 4 on the surface of a heating element to obtain a coated slurry; Drying the coated slurry to obtain a protective coating.

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