A method for preparing a protective coating for inhibiting the formation of wall-climbing titanium

Abstract

The present invention relates to the field of metal materials technology and provides a protective coating technology for inhibiting the formation of creeping titanium. The coating is applied to the inner surface of a titanium production reactor to inhibit the formation of creeping titanium. The technology comprises the following steps: pre-treating the inner surface of the reactor; applying the coating, the coating material comprising Y2O3; a heat treatment and curing process; and a cooling process. The present invention can reduce the amount of creeping titanium, improve the quality of titanium sponge, and extend the service life of the equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a method for preparing a protective coating for inhibiting the generation of wall-climbing titanium. Background Art

[0002] Currently, the Kroll process is commonly used in the industrial production of titanium sponge. This involves reducing titanium tetrachloride with liquid magnesium at high temperatures to produce metallic titanium and magnesium chloride as byproducts. The reaction takes place in a sealed, high-temperature-resistant metal reactor, typically controlled between 800 and 950°C. During the reduction process, the chemical reaction is highly exothermic, leading to dramatic local temperature fluctuations. This, coupled with significant vapor diffusion of titanium tetrachloride and liquid level fluctuations, can easily cause the reduction product (titanium) to deposit along the reactor walls, forming "wall-climbing titanium."

[0003] The formation of wall-climbing titanium not only reduces titanium recovery, but also increases the intensity of subsequent slag cleaning operations, increases equipment wear, and can even cause localized expansion and deformation of the reactor wall, shortening equipment life. Traditional measures to suppress wall-climbing titanium, such as optimizing feed rates, controlling reaction temperature fields, and adjusting gas flow fields, have some success, but their effectiveness is limited and they fail to fundamentally eliminate titanium's tendency to adhere to the metal reactor walls.

[0004] Chinese patent CN112323011A discloses a plasma spraying process for VW75 rare earth magnesium alloy. The process involves first cleaning the VW75 rare earth magnesium alloy substrate surface with acetone, applying compressive stress to induce lattice distortion of 1-10%, and performing a sandblasting pretreatment. Dry compressed air is then used to remove grit or dust adhering to the roughened surface, ensuring that the sandblasted surface exhibits no reflective bright spots when viewed from all angles. Within 1-3 hours after sandblasting, a bonding layer made of NiCrAlY alloy powder is sprayed onto the roughened substrate surface. A topcoat made of nanoparticle agglomerated yttria-particulate partially stabilized zirconia powder is then sprayed over the bonding layer. After spraying, the sample is slowly cooled to room temperature to reduce internal stress. This method allows for the production of a coating with a higher heat resistance on the VW75 magnesium alloy surface, which can significantly improve overall performance for samples with large insulation thicknesses. However, this method is different from the process of the present invention, and the coating is not suitable for suppressing the formation of wall-climbing titanium.

[0005] Chinese patent CN115895311A discloses a protective coating suitable for use with high-sulfur, high-alkali coal and a method for preparing the coating. The coating comprises a basecoat and a topcoat, and also discloses a method for preparing a double-layer protective coating. This invention addresses the issue of corrosion and coking on boiler heating surfaces. Although the raw materials contain yttrium oxide, its process and intended effects differ from those of the present invention.

[0006] It can be seen that a method for preparing a protective coating for inhibiting the formation of wall-climbing titanium is needed to meet actual production needs. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing a protective coating for inhibiting the formation of creeping titanium, which is specifically used in the preparation and application of an anti-titanium adhesion coating on the inner wall of a reactor during the production of sponge titanium, thereby reducing the amount of creeping titanium generated, improving the authenticity rate of sponge titanium and extending the service life of the equipment.

[0008] To achieve the above-mentioned object, the present invention provides a method for preparing a protective coating for inhibiting the formation of wall-climbing titanium. The technical solution of the present invention is achieved as follows:

[0009] A method for preparing a protective coating for inhibiting the formation of wall-climbing titanium, wherein the coating is applied to the inner surface of a titanium production reactor to inhibit the formation of wall-climbing titanium, comprising the following steps:

[0010] S1: pretreatment of the inner surface of the reactor;

[0011] S2: applying a coating, wherein the coating material includes Y2O3;

[0012] S3: heat treatment curing process;

[0013] S4: Cooling treatment.

[0014] The present invention can form a stable, dense protective layer with excellent anti-titanium adhesion performance on the inner wall of the reactor. By utilizing its low wettability and chemical inertness, the contact between the product titanium and the metal wall is blocked, effectively preventing titanium from depositing on the wall surface, and significantly reducing the amount of wall-climbing titanium generated, thereby increasing the titanium recovery rate, improving the thermal field distribution of the reduction system, and extending the service life of the equipment.

[0015] Furthermore, in step S2, the coating material further comprises MgO. After the addition of MgO, the mechanical strength of the coating is improved, taking into account both the titanium adhesion resistance of Y2O3 and the thermal shock resistance of MgO.

[0016] Furthermore, in step S2, the coating has a double-layer structure: Y2O3 is the surface layer and MgO is the bottom layer. This structure is stable, can effectively prevent the adhesion and diffusion of titanium, improves the overall bonding strength, and is easy to remove, reprocess, and repair.

[0017] Furthermore, in step S2, the coating has a sandwich structure: Y2O3 is the surface layer and the bottom layer, and MgO is the middle layer. The surface layer prevents the adhesion and diffusion of titanium, the interlayer prevents the coating from cracking and has strong impact resistance, and the bottom layer provides further buffering effect.

[0018] Furthermore, in step S2, the coating material is 99.9% Y2O3 powder. Y2O3 is used as the anti-titanium adhesion material to ensure that it maintains a stable structure under high-temperature reaction environment. At the same time, Y2O3 has the characteristics of low wettability, high-temperature stability and chemical inertness.

[0019] Furthermore, in step S2, the coating is applied at the upper half of the inner wall of the reactor. During production, wall-climbing titanium is easily generated in this area, and the coating is applied to the area where wall-climbing titanium is concentrated.

[0020] Furthermore, in step S2, the coating thickness is 50-200 μm, which provides a dense coating structure without pores and is not easy to fall off.

[0021] Furthermore, in step S2, the coating is applied by thermal spraying or plasma spraying process to meet the requirements of reactor structure and coating uniformity.

[0022] Furthermore, in step S3, the material is first heated to 800-900°C and held for 10-14 hours, then raised to 900-1000°C and held for 2-6 hours to ensure that internal stress in the material is effectively released and promote the full chemical reaction. This method can effectively avoid material cracking or performance degradation caused by sudden temperature changes, thereby improving product quality and process stability.

[0023] Furthermore, in step S4, indirect water cooling is first used for 4 to 8 hours, and then direct water cooling is used for 2 to 6 hours. By slowly lowering the temperature, the coating is densified and internal stress is eliminated, thereby improving the adhesion strength.

[0024] Compared with the prior art, the method for preparing a protective coating for inhibiting the formation of wall-climbing titanium described in the present invention has the following advantages:

[0025] ① Significantly reduce the amount of wall-climbing titanium generated, reduce the thickness of the titanium deposition layer on the reactor wall by more than 60%, and reduce the intensity of manual cleaning.

[0026] ② The low wettability of the coating is conducive to the uniform distribution of the temperature field and the optimization of thermal control of the reaction process. Combined with online monitoring and control, it improves product quality and increases the authenticity rate of sponge titanium.

[0027] ③ Not easy to corrode and deform, effectively preventing direct contact between the product titanium and the steel matrix, reducing the risk of corrosion and deformation of the reactor wall, and extending the service life of the reactor.

[0028] ④The coating has good stability and effectively supports the coordinated work of the automatic feeding and temperature control systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is a schematic structural diagram of the coating according to Example 1 of the present invention applied to the inner wall of a reduction reactor;

[0030] Figure 2 This is a schematic diagram of the location for adding the coating inside the reactor described in Example 1 of the present invention.

[0031] Description of reference numerals:

[0032] 1. Reactor; 2. Coating; 3. Product titanium deposition; 4. Furnace shell; 11. Reactor flange. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described are part of the embodiments of the present invention, rather than all of the embodiments. The specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. It should be noted that, unless there is a conflict, the features in the embodiments and embodiments of the present invention may be combined with each other.

[0034] A method for preparing a protective coating for suppressing the formation of wall-climbing titanium according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] A method for preparing a protective coating for inhibiting the formation of wall-climbing titanium, wherein the coating 2 is applied to the inner surface of a titanium production reactor 1 to inhibit the formation of wall-climbing titanium, comprising the following steps:

[0037] S1: Pretreatment of the inner surface of reactor 1.

[0038] The titanium production reactor 1 is usually made of stainless steel or alloy steel. The inner wall of the reactor 1 is sandblasted or mechanically polished. The original oxide scale, carbon deposits, residues, etc. are removed to improve the surface roughness of the substrate to enhance the mechanical bonding force of the coating 2. The surface roughness of the substrate is preferably Ra = 2 to 4 μm. Al2O3 sand with a particle size of 60 to 120 μm is preferred for sandblasting. An interfacial reaction will occur between the Y2O3 coating and Al2O3 at high temperatures, and the reaction product is Y3Al5O 12 , so that the layers can maintain good bonding and are not easy to peel off and break.

[0039] S2: Apply coating 2.

[0040] Coating 2 is made from Y2O3, preferably industrial-grade 99.9% high-purity Y2O3 powder with an average particle size of 5 to 25 μm. Y2O3 can withstand temperatures up to 2000°C in inert or reducing atmospheres, and its chemical stability is significantly superior to that of Al2O3, ZrO2, and other materials. Y2O3 is used as the titanium-resistant material to ensure a stable structure in high-temperature reaction environments. Y2O3 also exhibits low wettability, high-temperature stability, and chemical inertness. Y2O3 coating 2 exhibits particularly excellent non-wettability toward molten metal. Experiments have shown that the contact angle between Y2O3 and high-temperature molten metal is typically greater than 140°, and in some cases can reach 157°. This indicates that its surface has a significant repellency to liquid metal. This non-wettability effectively prevents titanium from adhering to and diffusing the inner wall of reactor 1.

[0041] Coating 2 can also include MgO as its raw material. Y2O3 and MgO powders are sprayed together in a mixed mass ratio (e.g., 7:3, 4:1, or 3:1) to create a dual-phase coating. MgO, a high-melting-point metal, is stable at high temperatures. Furthermore, Y2O3 and MgO do not undergo a violent chemical reaction at high temperatures, allowing them to coexist and form a stable solid solution. Furthermore, the close thermal expansion coefficients of Y2O3 and MgO provide good thermal stress compatibility when combined, preventing damage to Coating 2 due to cyclic heating. The addition of MgO enhances Coating 2's mechanical strength, balancing the titanium adhesion resistance of Y2O3 with the thermal shock resistance of MgO.

[0042] Coating 2 can be sprayed in a single layer or in a composite multilayer structure. The composite multilayer structure includes the following two structural forms:

[0043] Coating 2 has a double-layer (gradient layer) structure, with Y2O3 as the surface layer and MgO as the bottom layer. This structure is stable, effectively prevents the adhesion and diffusion of titanium, improves overall bonding strength, and is easy to remove, reprocess, and repair.

[0044] Coating 2 has a sandwich structure: Y2O3-MgO-Y2O3. Y2O3 forms the top and bottom layers, while MgO forms the middle layer. The top layer prevents titanium from adhering and diffusing, while the sandwich layer prevents cracking and provides strong impact resistance. The bottom layer provides further cushioning.

[0045] At the same time, the multi-layer structure of the coating 2 produces a synergistic effect, which can improve the ductility of the coating 2, reduce the possibility of crack propagation, and also improve the fatigue resistance of the coating 2 and extend the fatigue life.

[0046] like Figure 2As shown, coating 2 is applied to the upper half of the reactor 1 inner wall below reactor flange 11, preferably in an annular region of the reactor 1 inner wall 500 to 1600 cm from the lower edge of reactor flange 11. During production, wall-climbing titanium is most likely to form in this region, so coating 2 is applied to this concentrated region. The remaining areas of the inner wall are titaniumized by spraying titanium powder.

[0047] Thermal spraying or plasma spraying is used to uniformly apply the coating 2 on the inner wall to meet the requirements of the reactor 1 structure and the uniformity of the coating 2. Preferably, in Ar / H2 or Ar / H e The yttrium oxide coating 2 is prepared under ion gas conditions, which can facilitate powder melting and enhance the density and corrosion resistance of the coating 2. Preferably, the coating thickness is 50 to 200 μm. Experiments have shown that the coating 2 with this thickness has a dense structure, no pores, and is not easy to fall off.

[0048] During the application of Coating 2, an intelligent sensor monitors temperature and pressure changes in real time, ensuring reliable application. This intelligent sensor not only monitors temperature fluctuations but also provides an alarm for abnormalities. If an abnormality is detected during operation, the intelligent sensor will promptly issue an alarm, alerting the operator and prompting appropriate action, effectively improving process stability.

[0049] S3: Heat treatment curing process.

[0050] The heat treatment curing process utilizes a staged temperature ramp-up and temperature-holding control method. During the heat treatment curing process, the temperature is gradually increased in predetermined stages, with specific holding times set at each stage to ensure the effective release of internal stresses in the material and promote the full chemical reaction. This method effectively avoids material cracking or performance degradation caused by sudden temperature changes, thereby improving product quality and process stability.

[0051] Specifically, after the coating 2 is applied, the reactor 1 is evacuated to exhaust the exhaust gas, and the coating application area of ​​the reactor 1 is heated to 800-900°C. During the reduction process of sponge titanium production, the temperature in the furnace is controlled to reach about 860°C. This temperature range is set to allow the coating 2 to adapt to the temperature of normal production. Next, argon gas is filled to ensure that the reactor 1 is under positive pressure, and the temperature is kept warm for a first preset time to promote the physical / chemical bonding between the coating 2 and the substrate. The first preset time is 10-14 hours, preferably 12 hours. Further, the temperature is raised to 900-1000°C and kept warm for a second preset time to improve the thermal stability and peel strength of the coating 2. The second preset time is 2-6 hours, preferably 2 hours.

[0052] S4: Cooling treatment.

[0053] The coating 2 is cooled using a slow cooling process. By slowly lowering the temperature, the coating 2 densifies, eliminates internal stress, and improves adhesion strength. Preferably, indirect water cooling is first used for a third preset time, followed by direct water cooling for a fourth preset time. During the cooling process, the reactor 1 is filled with argon to maintain a positive pressure. The third preset time is 4 to 8 hours, preferably 6 hours; the fourth preset time is 2 to 6 hours, preferably 4 hours.

[0054] S5: Regular inspection and maintenance.

[0055] During production breaks, use ultrasound or a coating thickness gauge to check the integrity of coating 2. If damage is found, re-spray immediately to ensure the continued stability of coating 2's protective capabilities. Data on the process status of coating 2 additions is input into the automated DCS control system to enable dynamic maintenance scheduling.

[0056] The technology of the present invention can form a stable, dense protective layer with excellent anti-titanium adhesion performance on the inner wall of the reactor 1. By utilizing its low wettability and chemical inertness, it blocks the contact between the product titanium and the metal wall, effectively prevents the deposition of titanium on the wall, and significantly reduces the amount of wall-climbing titanium generated, thereby increasing the titanium recovery rate, improving the thermal field distribution of the reduction system, and extending the service life of the equipment.

[0057] The coating 2 technology of the present invention has been experimentally applied in a reduction distillation reactor. The experimental results show that compared with the traditional titanium sponge production process, the technology has demonstrated significant advantages.

[0058] First, the titanium wetting angle on the surface of coating 2 is significantly increased, reducing the probability of titanium nucleation and adhesion on the wall; according to actual measurement data, the thickness of the titanium deposition layer on the reactor wall is reduced by more than 60%, and the titanium climbing the wall after the product is out of the furnace is significantly reduced, reducing the cleaning workload of reactor 1. Second, the low wettability of coating 2 is conducive to the uniform distribution of the temperature field, the reduction of by-products, and the increase in the proportion of genuine products, which has good economic value. Third, after the present invention is applied to production, there is no obvious corrosion and expansion deformation on the inner wall of reactor 1, and the integrity rate of coating 2 exceeds 95%, which effectively prevents direct contact between the product titanium and the metal substrate of reactor 1, reduces the risk of corrosion and deformation of the reactor wall, and extends the service life of reactor 1. Fourth, coating 2 has good stability and effectively supports the coordinated work of the automatic feeding and temperature control systems.

[0059] It should be noted that all terms used in the present invention to indicate direction and position, such as "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside", "top", "low", "tail end", "head end", "center", etc., are only used to explain the relative position relationship and connection status of various components in a certain specific state, and are only for the convenience of describing the present invention, but do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

[0060] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for preparing a protective coating for inhibiting the formation of wall-climbing titanium, characterized in that: The coating (2) is a single-layer spray coating or a multi-layer structure, applied on the inner surface of the titanium production reactor (1) to inhibit the formation of wall-climbing titanium, comprising the following steps: S1: pretreatment of the inner surface of the reactor (1); sandblasting using Al2O3 sand; S2: applying a coating (2) by a thermal spraying or plasma spraying process, wherein the raw materials of the coating (2) are composed of Y2O3 and MgO; S3: Heat treatment curing process: first heat to 800-900°C, fill with argon gas to ensure positive pressure in the reactor 1, keep warm for 10-14 hours, then raise the temperature to 900-1000°C, keep warm for 2-6 hours; S4: Cooling treatment.

2. The method for preparing a protective coating according to claim 1, wherein: In step S2, the coating (2) is a double-layer structure: Y2O3 is the surface layer and MgO is the bottom layer.

3. The method for preparing a protective coating according to claim 1, wherein: In step S2, the coating (2) is a sandwich structure: Y2O3 is the surface layer and the bottom layer, and MgO is the middle layer.

4. The method for preparing a protective coating according to any one of claims 1 to 3, characterized in that: In step S2, the raw material of the coating (2) is 99.9% Y2O3 powder with an average particle size of 5 to 25 μm.

5. The method for preparing a protective coating according to claim 1, wherein: In the step S2, the coating (2) is applied to the upper half of the inner wall of the reactor (1).

6. The method for preparing a protective coating according to claim 1, wherein: In the step S2, the thickness of the coating (2) is 50 to 200 μm.

7. The method for preparing a protective coating according to claim 1, wherein: In step S4, indirect water cooling is first used for 4 to 8 hours, and then direct water cooling is used for 2 to 6 hours.

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