High-temperature-resistant coating for graphite crucible as well as preparation method and application of high-temperature-resistant coating

Abstract

The invention provides a high-temperature-resistant coating for a graphite crucible as well as a preparation method and application of the high-temperature-resistant coating, and belongs to the field of high-temperature-resistant coatings. The high-temperature-resistant coating is an isolating layer covering the inner wall of the graphite crucible and is prepared from the following raw materials: 90-98% of aluminum oxide powder and 2-10% of a high-temperature-resistant adhesive. The high-temperature-resistant adhesive comprises one or more of a phosphate adhesive, dextrin and silica sol. According to the application, an effective isolation barrier is introduced between the inner wall of the graphite base and the high-temperature slag, so that the adhesion between the slag and the graphite substrate is remarkably reduced or eliminated, and the slag can be quickly and effectively stripped from the inner wall of the graphite substrate, so that the repeated utilization of the graphite base is realized, and the service life of the graphite base is prolonged. Finally, the purposes of reducing the detection cost and reducing the resource consumption are achieved.

Description

Technical Field

[0001] This application relates to the field of high-temperature resistant coating technology, and in particular to a high-temperature resistant coating for graphite crucibles, its preparation method, and its application. Background Technology

[0002] In high-temperature load reduction and softening drip tests of iron ore, graphite crucibles are commonly used as containers to collect the high-temperature molten slag, primarily due to the excellent high-temperature resistance and thermal shock resistance of graphite. However, the high-temperature molten slag generated during the test exhibits extremely high chemical reactivity and adhesiveness. When the slag directly contacts the inner wall of the graphite crucible, a complex physicochemical reaction occurs between the two at high temperatures, resulting in an extremely tight and firm adhesion layer between the slag and the graphite inner wall after cooling and solidification. This adhesion layer is difficult to remove effectively using conventional mechanical or chemical methods, causing the graphite crucible to be scrapped after a single test due to its inability to be cleaned, thus becoming a disposable consumable. This not only significantly increases the testing cost per test but also results in serious resource waste.

[0003] Therefore, how to effectively increase the number of times graphite crucibles used in high-temperature load reduction softening drip tests of iron ore, thereby reducing test costs and saving resources, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides a high-temperature resistant coating for graphite crucibles, its preparation method, and its application, in order to solve the following technical problem: how to increase the number of times a graphite crucible can be used in the high-temperature load reduction softening drip test of iron ore.

[0005] In a first aspect, embodiments of this application provide a high-temperature resistant coating for a graphite crucible. The high-temperature resistant coating is an insulating layer covering the inner wall of the graphite crucible. By mass fraction, the high-temperature resistant coating is composed of the following raw materials: alumina powder: 90%–98%, and high-temperature resistant binder: 2%–10%. The high-temperature resistant adhesive includes one or more of the following: phosphate adhesives, dextrin, and silica sol.

[0006] Optionally, the thickness of the high-temperature resistant coating is 0.1 mm to 0.5 mm.

[0007] Optionally, the high-temperature resistant coating has a melting point >2050℃.

[0008] Optionally, the purity of the alumina powder is ≥99%.

[0009] Optionally, the phosphate binder is aluminum dihydrogen phosphate.

[0010] Secondly, embodiments of this application provide a method for preparing the high-temperature resistant coating according to any one of the first aspects, the method comprising: Alumina powder, high-temperature resistant binder, and solvent are mixed to obtain a coating slurry; The coating slurry is applied to the inner wall surface of the pretreated graphite crucible to form a wet film; The graphite crucible coated with a wet film is dried and heat-treated to obtain a graphite crucible with the high-temperature resistant coating.

[0011] Optionally, the drying temperature is 80℃~150℃, and the drying time is 1h~3h.

[0012] Optionally, the heat treatment temperature is 450℃~600℃, and the heat treatment holding time is 1h~2h.

[0013] Thirdly, embodiments of this application provide an application of the high-temperature resistant coating described in any of the first aspects, wherein a graphite crucible with the high-temperature resistant coating is used in a high-temperature load reduction softening drip test of iron ore.

[0014] Optionally, the graphite crucible with the high-temperature resistant coating can be reused ≥9 times when used in the high-temperature load reduction softening drip test of iron ore.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a high-temperature resistant coating for graphite crucibles. By applying a high-temperature resistant coating composed of specific raw materials to the inner wall of the graphite crucible, the number of times it can be used in high-temperature load reduction softening drip tests of iron ore is significantly increased. The core principle is that the coating forms a highly efficient physical and chemical isolation barrier between the slag and the graphite matrix.

[0016] Specifically, the high-temperature resistant coating is mainly composed of alumina powder (90%–98%). The inherently extremely high melting point and excellent chemical inertness of alumina ensure that the coating does not soften, melt, or chemically react with the molten slag when in contact with it. This fundamentally avoids the strong chemical bonding and alloying that could form between the molten slag and the graphite matrix due to direct contact at high temperatures, transforming the interfacial bonding into a relatively weak physical contact between the molten slag and the surface of the inert coating.

[0017] Meanwhile, the key function of the high-temperature resistant adhesive (2%–10%, selected from one or more of phosphate adhesives, dextrin, and silica sol) is that, after curing, it can bond the alumina powder particles into a continuous and dense whole, and firmly adhere the coating to the inner wall of the graphite crucible. This gives the coating sufficient mechanical strength and bonding force to withstand the thermal stress during the test and the physical force applied to separate the solidified slag after the test, thus ensuring that the coating itself is not damaged or peeled off from the substrate after a single use.

[0018] Therefore, after a test, the solidified slag mainly bonds to the inert and weakly bonded coating surface, making it easy to peel off entirely using external physical force. After peeling, the intact coating can continue to provide the same protection for the next test. The above-mentioned ratio of alumina powder to high-temperature resistant adhesive ensures that the coating has both stable isolation function and reliable durability at extreme high temperatures, allowing the graphite crucible to be transformed from a disposable consumable into a reusable container, directly resulting in an effective increase in the number of uses. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram of the structure of a graphite crucible with a high-temperature resistant coating provided in an embodiment of this application; Figure 2 This is a schematic flowchart illustrating the preparation method of the high-temperature resistant coating provided in the embodiments of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0024] Figure 1 This is a schematic diagram of the structure of a graphite crucible with a high-temperature resistant coating provided in an embodiment of this application.

[0025] like Figure 1 As shown in the embodiment of this application, a high-temperature resistant coating for a graphite crucible is provided. The high-temperature resistant coating is an isolation layer covering the inner wall of the graphite crucible. By mass fraction, the high-temperature resistant coating is composed of the following raw materials: alumina powder: 90% to 98%, and high-temperature resistant binder: 2% to 10%. Among them, high-temperature resistant adhesives include one or more of phosphate adhesives, dextrin, and silica sol.

[0026] In some implementations, the high-temperature resistant coating has a melting point >2050°C.

[0027] In some embodiments, the phosphate binder is aluminum dihydrogen phosphate.

[0028] It should be noted that the high-temperature resistant coating provided in this application serves as an isolation barrier applied to the inner wall of a graphite crucible. Its core function is to physically isolate the direct contact between the high-temperature molten slag and the graphite substrate, and to utilize the specific properties of the coating material itself to enable the cooled molten slag to be completely peeled off from the coating surface, thereby achieving the reuse of the graphite crucible.

[0029] The core role of alumina powder: As the main component of the coating (accounting for 90%–98% of the total solid content), alumina powder undertakes the primary functions of high-temperature resistance and anti-adhesion. First, alumina has an extremely high melting point (>2050℃) and excellent thermal stability, ensuring that the coating does not soften, melt, or decompose in the high-temperature environment of iron ore softening and dripping tests (typically reaching above 1500℃), maintaining its structural integrity. Second, alumina is highly chemically inert and does not easily react with high-temperature slags such as ferrates, thus fundamentally avoiding strong chemical adhesion formed by interfacial chemical reactions. Third, alumina has a low surface energy, resulting in poor wettability of high-temperature slag on its surface. This facilitates the natural stress generated at the interface between the slag and the coating during the cooling and solidification process due to shrinkage, creating conditions for subsequent physical peeling. For example, the percentage of alumina powder can be 90%, 91%, 92%, 93%, 95%, 96%, 97%, 98%, etc.

[0030] The key role of the high-temperature resistant adhesive: The high-temperature resistant adhesive (comprising 2%–10% of the total solid content by mass) is selected from one or more of phosphate-based adhesives (such as aluminum dihydrogen phosphate), dextrin, or silica sol. Its core function is to firmly bond loose alumina powder particles into a continuous, dense whole through physical and chemical bonding, ensuring that this whole adheres tightly and stably to the graphite matrix surface. The adhesive network formed by the adhesive imparts the necessary mechanical strength to the coating to resist thermal stress and minor mechanical impacts during operation, preventing the coating from detaching from the graphite matrix or pulverizing before or during use. For example, the percentage of high-temperature resistant adhesive can be 2%, 3%, 4%, 5%, 7%, 8%, 9%, 10%, etc.

[0031] In some embodiments, the thickness of the high-temperature resistant coating is 0.1 mm to 0.5 mm.

[0032] Limiting the coating thickness to 0.1mm to 0.5mm ensures the formation of a uniform, continuous, and sufficiently barrier-like insulating layer. If the thickness exceeds 0.5mm, the coating process becomes more complex, drying is more prone to cracking, and the excessively thick coating may increase the risk of peeling off under thermal shock due to the significant difference in thermal expansion coefficients between it and the graphite substrate. If the thickness is less than 0.1mm, a complete and defect-free continuous insulating layer may not be formed, and local weak points are easily penetrated or damaged by molten slag, leading to protective failure. For example, the thickness of the high-temperature resistant coating can be 0.1mm, 0.15mm, 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.5mm, etc.

[0033] In some embodiments, the purity of the alumina powder is ≥99%.

[0034] By limiting the purity of alumina powder to ≥99%, the alumina components are ensured to have the highest possible melting point and chemical inertness. This minimizes the risk of impurities causing a decrease in melting point or side reactions with slag, thus guaranteeing the reliability of coating performance.

[0035] Figure 2 This is a schematic flowchart illustrating the preparation method of the high-temperature resistant coating provided in the embodiments of this application.

[0036] Based on a general inventive concept, such as Figure 2 As shown in the embodiment of this application, a method for preparing a high-temperature resistant coating according to any one of the above-mentioned methods is provided, the method comprising: S1. Mix alumina powder, high-temperature resistant adhesive and solvent to obtain coating slurry; S2. Apply the coating slurry to the inner wall surface of the pretreated graphite crucible to form a wet film; S3. The graphite crucible coated with a wet film is dried and heat-treated to obtain a graphite crucible with a high-temperature resistant coating.

[0037] In some embodiments, the drying temperature is 80°C to 150°C, and the drying time is 1 hour to 3 hours.

[0038] In some embodiments, the heat treatment temperature is 450°C to 600°C, and the heat treatment holding time is 1 hour to 2 hours.

[0039] The method for preparing the high-temperature resistant coating provided in this application, through a series of carefully designed steps and process parameter control, aims to transform alumina powder and high-temperature resistant binder in a specific ratio into a dense and functionally stable isolation coating that adheres firmly to the inner wall of a graphite crucible.

[0040] The core of step S1 (slurry preparation) lies in obtaining a coating slurry with uniform composition, stable dispersion, and suitable viscosity. Alumina powder, high-temperature resistant binder, and solvent (such as deionized water) are mixed to ensure that the binder and solvent fully wet and coat each alumina powder particle, forming a uniform suspension system. A uniform slurry is a prerequisite for obtaining a coating with consistent composition and stable performance, ensuring uniform high-temperature resistance, chemical inertness, and mechanical properties throughout the coating.

[0041] Step S2 (coating and forming) transforms the liquid slurry into an initial coating (wet film) of a predetermined shape and thickness. The slurry is coated onto the pre-cleaned (possibly including polishing) inner wall of a graphite crucible, its direct effect being to construct a continuous wet film containing all functional components on the substrate surface. The uniformity of the coating directly determines the consistency of the final coating thickness, and controlling the thickness of the wet film (typically corresponding to 0.1–0.5 mm of dry film) ensures that the final sintered and cured coating has an optimized thickness sufficient to effectively isolate slag without being too thick and prone to cracking.

[0042] Step S3 (drying and heat treatment) is a key transformation process that enables the coating to achieve its final performance. It is divided into two stages: drying and heat treatment, each with its own emphasis.

[0043] The purpose of the drying treatment (80℃~150℃, holding time 1h~3h): The main objective of this stage is to gently and thoroughly remove solvents (such as water) from the coating slurry. Holding at a temperature range of 80℃ to 150℃ for 1 to 3 hours allows the solvent to evaporate at a gradual rate, preventing the wet film from shrinking and cracking, creating pores or blistering due to excessively rapid evaporation, thus ensuring that the coating obtains a smooth and dense initial solid structure. For example, the drying temperature can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc.; for example, the holding time can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.3h, 2.6h, 3h, etc.

[0044] The role of heat treatment (450℃~600℃, holding for 1h~2h): This stage is the decisive step for the coating to obtain high strength and high stability. Holding at 450℃ to 600℃ for 1 to 2 hours allows the high-temperature resistant binders (such as aluminum dihydrogen phosphate, dextrin, etc.) to undergo sufficient chemical transformation and sintering. For phosphate binders, this temperature range promotes the formation of a condensed phosphate glass phase network with high-temperature resistance; for organic binders such as dextrin, it completes their carbonization and decomposition, forming residual carbon binders. This process greatly enhances the bonding strength of the binder to alumina particles, improves the coating's density, mechanical strength, and adhesion to the graphite matrix, and stabilizes the coating structure, making it sufficient to withstand high-temperature thermal shock during subsequent use. For example, the heat treatment temperature can be 450℃, 470℃, 490℃, 510℃, 530℃, 550℃, 580℃, 600℃, etc.; for example, the heat treatment holding time can be 1h, 1.1h, 1.3h, 1.5h, 1.6h, 1.7h, 1.9h, 2h, etc.

[0045] The product prepared by the method of preparing the high-temperature resistant coating is the high-temperature resistant coating mentioned above. The chemical composition of the high-temperature resistant coating prepared by the method of preparing the high-temperature resistant coating can be referred to the above embodiments. Since the method of preparing the high-temperature resistant coating adopts some or all of the technical solutions of the high-temperature resistant coating embodiments, it has at least all the beneficial effects brought about by the technical solutions of the high-temperature resistant coating embodiments, which will not be elaborated here.

[0046] Based on a general inventive concept, embodiments of this application provide an application of any of the above-mentioned high-temperature resistant coatings, using a graphite crucible with a high-temperature resistant coating for a high-temperature load reduction softening drip test of iron ore.

[0047] In some embodiments, graphite crucibles with high-temperature resistant coatings can be reused ≥9 times when used in high-temperature load reduction softening drip tests of iron ore.

[0048] In this application, the graphite crucible with a high-temperature resistant coating can be reused ≥9 times, which is achieved through the coating's formulation design, structural characteristics, and precise matching with the operating conditions.

[0049] First, the coating uses high-purity (≥99%) alumina as the main component (accounting for 90%–98% of the solid content by mass), which fundamentally endows the coating with the ability to survive in the extreme environment of high-temperature load reduction softening drip test of iron ore. The inherently extremely high melting point of alumina (>2050℃) ensures that the coating remains solid at the high test temperature (e.g., 1580℃ in the example), without softening or melting; its excellent chemical inertness makes the coating less likely to react chemically with the high-temperature molten slag, thereby completely avoiding the formation of strong chemical bonds at the interface. This is the chemical basis for achieving peelable rather than firmly bonded slag.

[0050] Secondly, a specific proportion (2%–10% of the solid content by mass) of high-temperature resistant binder (such as aluminum dihydrogen phosphate or dextrin) and optimized preparation process jointly ensure the mechanical integrity of the coating and its firm adhesion to the graphite matrix. The adhesive network formed after heat treatment tightly binds and anchors the alumina particles to the inner wall of the graphite crucible, forming a dense and robust isolation layer. This coating can withstand the thermal stress impact during testing and the physical force of slag removal after cooling, preventing it from cracking or peeling off from the substrate. The coating thickness is controlled within the range of 0.1 mm to 0.5 mm, ensuring the formation of a continuous, defect-free isolation barrier while avoiding increased internal stress and vulnerability risks due to excessive thickness.

[0051] Finally, the physical properties of the coating surface directly contribute to the efficient removal of the slag. Due to the low surface energy of alumina, the high-temperature slag exhibits poor wettability on the coating surface. When the experiment ends and cooling occurs, the difference in thermal expansion coefficients between the solidified slag and the coating, coupled with the fact that their interface is only in physical contact without strong chemical bonding, makes it easier for the slag to generate separation stress at the interface during cooling and shrinkage. At this point, applying a slight physical force (such as gently tapping the outer wall of the crucible) can overcome this residual adhesion, causing the entire piece of slag to peel completely off the coating surface without damaging the coating itself or the graphite matrix.

[0052] In summary, the high-temperature resistant coating resists the erosion and melting of molten slag through its high-temperature resistance and chemical inertness, ensures its integrity under repeated thermal cycles and physical operations through its excellent mechanical strength and adhesion, and facilitates the easy removal of solidified slag through its surface properties that discourage slag wetting and adhesion. These three synergistic properties enable the coating to repeatedly and effectively perform the "isolation-bearing-removal" functional cycle after a single application, thus supporting the graphite crucible to stably achieve and exceed nine reuse cycles under harsh experimental conditions.

[0053] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0054] Example 1 The preparation and application methods for high-temperature resistant coatings are implemented as follows: S1. Preparation of coating slurry: Weigh 45 parts by weight of alumina powder (Al2O3 content of 99.5%), 5 parts by weight of dextrin (solid content of 99.3%) as a high-temperature resistant binder, and 5 parts by weight of deionized water. Mix them and stir evenly to obtain a uniform coating slurry.

[0055] S2. Pretreatment of graphite crucible: Clean the inner wall of the graphite crucible used for the standard soft melting drop test, then lightly polish the inner wall surface with 400-grit sandpaper, and finally wipe it with alcohol and dry it to remove impurities and increase surface adhesion.

[0056] S3. Coating and Heat Treatment: The coating slurry prepared in step S1 is uniformly brushed onto the inner wall surface of the pretreated graphite crucible, controlling the wet film thickness to be approximately 0.4 mm. Subsequently, the coated graphite crucible is dried at 100°C for 2 hours, then heated to 500°C at a heating rate of 2°C / min, and held at this temperature for 1.5 hours. Finally, it is cooled with the furnace, thereby forming the high-temperature resistant coating on the inner wall of the graphite crucible.

[0057] S4. Usage and Results: The coated graphite crucible was used in a high-temperature load reduction softening drip test of iron ore, with a maximum test temperature of 1580℃. After the test, the cooled slag could be completely peeled off from the coating surface. After the graphite crucible was reused approximately 9 times, the coating surface became slightly rough and showed minor wear in some areas; however, it could be reused after repair.

[0058] Example 2 The preparation and application method of the high-temperature resistant coating shall be implemented according to the following specific steps: S1. Preparation of coating slurry: Weigh 85 parts by weight of alumina powder (Al2O3 content is 99.6%), 6 parts by weight of aluminum dihydrogen phosphate solution (solid content 50%) as a high temperature resistant binder (equivalent to 3 parts by weight of solid aluminum dihydrogen phosphate), and 9 parts by weight of deionized water, mix them and stir evenly to obtain a uniform coating slurry.

[0059] S2. Pretreatment of graphite crucible: Clean the inner wall of the graphite crucible used for the standard soft melting drop test, then lightly polish the inner wall surface with 400-grit sandpaper, and finally wipe it with alcohol and dry it to remove impurities and increase surface adhesion.

[0060] S3. Coating and Heat Treatment: The coating slurry prepared in step S1 is uniformly brushed onto the inner wall surface of the pretreated graphite crucible, controlling the wet film thickness to be approximately 0.3 mm. Subsequently, the coated graphite crucible is dried at 100°C for 2 hours, then heated to 500°C at a heating rate of 2°C / min, and held at this temperature for 1.5 hours. Finally, it is cooled with the furnace, thereby forming the high-temperature resistant coating on the inner wall of the graphite crucible.

[0061] S4. Application and Results: The coated graphite crucible was used in a high-temperature load reduction softening drip test of iron ore. After the test, the cooled slag could be peeled off entirely by gently tapping the outer wall, while the inner coating remained intact and smooth. The graphite crucible was successfully reused more than 15 times, with the coating remaining intact and the peeling effect stable.

[0062] Example 3 The preparation and application method of the high-temperature resistant coating shall be implemented according to the following specific steps: S1. Preparation of coating slurry: Weigh 98 parts by weight of alumina powder (Al2O3 content is 99%), 2 parts by weight of dextrin (solid content is 99%) as a high temperature resistant binder, and 10 parts by weight of deionized water. Mix them and stir evenly to obtain a uniform coating slurry.

[0063] S2. Pretreatment of graphite crucible: Clean the inner wall of the graphite crucible used for the standard soft melting drop test, then lightly polish the inner wall surface with 400-grit sandpaper, and finally wipe it with alcohol and dry it to remove impurities and increase surface adhesion.

[0064] S3. Coating and Heat Treatment: The coating slurry prepared in step S1 is uniformly brushed onto the inner wall surface of the pretreated graphite crucible, controlling the wet film thickness to be approximately 0.3 mm. Subsequently, the coated graphite crucible is dried at 80°C for 1 hour, then heated to 450°C at a heating rate of 2°C / min and held at this temperature for 1 hour. Finally, it is cooled with the furnace, thereby forming the high-temperature resistant coating on the inner wall of the graphite crucible.

[0065] S4. Application and Results: The coated graphite crucible was used in a high-temperature load reduction softening drip test of iron ore. After the test, the cooled slag could be easily peeled off from the coating surface. Due to the low binder content in the coating, its resistance to mechanical impact was slightly weaker. After approximately 12 repeated uses, minor peeling occurred at the edges of the coating due to operational impacts, but the function of the main coating was not affected.

[0066] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) Reliable performance: The high-temperature resistant coating with alumina as the main component has excellent high-temperature resistance, good chemical inertness and moderate thermal shock resistance. It can effectively isolate slag from graphite matrix and ensure stable function during repeated use.

[0067] (2) Reduced cost: By enabling the reuse of graphite crucibles (usually up to 9 times or more), the cost of a single test is significantly reduced.

[0068] (3) Easy to operate: The preparation and coating process of the coating are relatively simple, easy to implement and promote.

[0069] (4) Application innovation: Through creative formulation system and special application method, the problem of graphite crucibles being scrapped once due to slag adhesion has been solved, forming a complete method chain from "disposable" to "reusable".

[0070] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A high-temperature resistant coating for graphite crucibles, characterized in that, The high-temperature resistant coating is an isolation layer covering the inner wall of the graphite crucible. By mass fraction, the high-temperature resistant coating is composed of the following raw materials: alumina powder: 90%–98%, high-temperature resistant binder: 2%–10%. The high-temperature resistant adhesive includes one or more of the following: phosphate adhesives, dextrin, and silica sol.

2. The high-temperature resistant coating according to claim 1, characterized in that, The thickness of the high-temperature resistant coating is 0.1 mm to 0.5 mm.

3. The high-temperature resistant coating according to claim 1, characterized in that, The melting point of the high-temperature resistant coating is >2050℃.

4. The high-temperature resistant coating according to claim 1, characterized in that, The purity of the alumina powder is ≥99%.

5. The high-temperature resistant coating according to claim 1, characterized in that, The phosphate binder is aluminum dihydrogen phosphate.

6. A method for preparing a high-temperature resistant coating according to any one of claims 1 to 5, characterized in that, The method includes: Alumina powder, high-temperature resistant binder, and solvent are mixed to obtain a coating slurry; The coating slurry is applied to the inner wall surface of the pretreated graphite crucible to form a wet film; The graphite crucible coated with a wet film is dried and heat-treated to obtain a graphite crucible with the high-temperature resistant coating.

7. The method according to claim 6, characterized in that, The drying temperature is 80℃~150℃, and the drying time is 1h~3h.

8. The method according to claim 6, characterized in that, The heat treatment temperature is 450℃~600℃, and the heat treatment holding time is 1h~2h.

9. The application of the high-temperature resistant coating according to any one of claims 1 to 5, characterized in that, The graphite crucible with the high-temperature resistant coating was used in the high-temperature load reduction softening drip test of iron ore.

10. The application according to claim 9, characterized in that, The graphite crucible with the high-temperature resistant coating can be reused ≥9 times when used in the high-temperature load reduction softening drip test of iron ore.

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