Preparation method for reducing and coating Mo with composite H2 on surface of metal powder through hydro-thermal synthesis

Abstract

The invention provides a preparation method for reducing and coating Mo with composite H2 on the surface of metal powder through hydro-thermal synthesis, and the preparation method comprises the following steps: step 1, before hydro-thermal synthesis, carrying out acid pickling treatment on target metal powder by utilizing an acid solution to remove pollutants and an oxidation film on the surface of the powder; 2, an ammonium molybdate saturated solution is prepared, and MoO3 coated metal powder is prepared through hydrothermal synthesis by means of the ammonium molybdate saturated solution; and 3, Mo-coated metal powder is prepared through H2 atmosphere reduction.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation and material surface protection, and in particular to a method for preparing a composite H2 reduction coating of Mo by hydrothermal synthesis on the surface of metal powder. Background Technology

[0002] In aerospace, weaponry manufacturing, and petrochemical energy sectors, corrosion, oxidation, and wear of metal components often shorten the lifespan of entire equipment systems. Research indicates that depositing a dense, defect-free coating on the surface of metal components using relevant surface coating technologies is an effective method to improve the corrosion resistance, wear resistance, and oxidation resistance of components, thereby extending the service life of the entire system.

[0003] In recent years, thermal spraying technology has become widely used in the preparation of wear-resistant, corrosion-resistant, heat-resistant, oxidation-resistant, conductive, and insulating coatings due to its high production efficiency and simple and flexible operation. Plasma spraying, in particular, with its heat source temperature typically reaching tens of thousands of degrees Celsius, can melt almost all materials. It has found extensive applications in aerospace, weaponry manufacturing, metallurgy, petrochemicals, and energy sectors. For example, plasma-sprayed Ni-based, Fe-based, and Co-based metal alloy coatings are used in industrial applications requiring corrosion resistance, high-temperature oxidation resistance, and wear resistance due to their excellent properties. Traditional thermal spray coatings typically exhibit a layered structure with very limited interlayer bonding between particles. The average interlayer bonding rate is usually less than one-third of the total interfacial area. The interfacial bonding between particles in thermal spray coatings significantly affects various coating properties, such as elastic modulus, fracture toughness, thermal conductivity, and electrical conductivity. Due to the limited interlayer bonding, these properties are significantly lower than one-third of the corresponding bulk materials. Therefore, how to significantly improve the interfacial bonding of coatings through process optimization or material design to prepare dense coatings with good particle-interfacial bonding, thereby significantly improving the service performance of thermally sprayed metal alloy coatings, has always been an important problem that the field of thermal spraying has been trying to solve.

[0004] Numerous studies have shown that it is difficult to significantly improve the interlayer particle bonding within the coating by adjusting the spraying process parameters. For metal powder materials, the design method of preparing core-shell structured composite powders by coating low-melting-point Fe-based or Ni-based alloy powders with high-melting-point metals can not only suppress the evaporation of low-melting-point metal elements in high-temperature plasma jets, but also effectively enhance the interlayer bonding of plasma-sprayed coatings by increasing the temperature of molten particles to raise the interface temperature.

[0005] Common methods for preparing metal-coated core-shell powders include chemical methods (such as electroless plating, hydrogenation reduction, and chemical vapor deposition) and mechanical methods (such as mechanical ball milling). However, electroless plating involves plating solutions containing heavy metal ions, and impurities such as phosphorus and sulfur produced by the decomposition of the reducing agent can reduce the conductivity of the coating layer; the hydrogenation reduction method requires a reaction temperature higher than the precursor decomposition temperature, which can lead to abnormal growth of aggregate powder grains; chemical vapor deposition is costly and difficult to process fine powders with a particle size <10μm. Although mechanical ball milling is simple to operate, the cold welding effect during the ball milling process can cause powder agglomeration, usually requiring the addition of stearic acid, which can easily introduce carbon contamination, and the coating layer is usually mechanically bonded to the metal powder matrix. Summary of the Invention

[0006] To overcome the shortcomings of existing shell-core coated powder preparation methods, the main objective of this invention is to provide a method for preparing Mo coated with composite H2 reduction by hydrothermal synthesis on the surface of metal powder, thereby preparing a Mo coating layer with high bonding strength on the surface of metal powder and solving the technical problems of traditional preparation methods.

[0007] This invention is achieved through the following technical solution: a method for preparing a composite H2-reduced coated Mo by hydrothermal synthesis on the surface of metal powder, comprising: Step 1: Before hydrothermal synthesis, the target metal powder is acid-washed with an acid solution to remove contaminants and oxide film from the powder surface; Step 2: Prepare a saturated ammonium molybdate solution, and use the saturated ammonium molybdate solution to prepare MoO3-coated metal powder via hydrothermal synthesis; Step 3: Prepare Mo-coated metal powder by reduction in H2 atmosphere.

[0008] Specifically, the acid solution is composed of HCl and HNO3, the concentration of HCl is in the range of 5%-20%, the concentration of HNO3 is in the range of 5%-20%, the ratio of HCl to HNO3 is 1:2, and the pickling time is 1 min-20 min.

[0009] Specifically, step 2 includes: Step 2-1: Prepare a saturated ammonium molybdate solution, including: weighing ammonium molybdate and dissolving it in deionized water, and continuously stirring with a constant temperature magnetic stirrer to form a saturated ammonium molybdate solution.

[0010] Step 2-2: Mix the metal powder and the saturated ammonium molybdate solution at a volume ratio of 1:10, and use a magnetic stirrer to thoroughly and evenly mix the metal powder and the saturated ammonium molybdate solution under preset conditions.

[0011] Steps 2-3: Place the uniformly mixed metal powder and saturated ammonium molybdate solution into a reaction vessel and place it in a constant temperature drying oven to prepare MoO3-coated metal powder. After the reaction is completed, collect the obtained MoO3-coated metal powder.

[0012] Steps 2-4: Repeatedly wash the MoO3-coated metal powder described in Step 2-3 with anhydrous ethanol and deionized water, and then dry it.

[0013] Specifically, the magnetic stirrer speed is set to 15-40 r / s, the stirring time is set to 20 min-100 min, the temperature is set to 25℃-50℃, and the pH of the ammonium molybdate saturated solution is adjusted to the range of 1-6 using nitric acid.

[0014] Specifically, the preset conditions are a rotation speed of 15-40 r / s and a temperature of 25℃-50℃.

[0015] Specifically, the temperature range for preparing MoO3-coated metal powder in the constant temperature drying oven is 160℃-230℃, and the time range is 10-30h.

[0016] Specifically, the drying process involves repeated washing 3-6 times and drying at 70°C for 24 hours.

[0017] Specifically, the H2 atmosphere reduction temperature is in the range of 650℃-850℃, the H2 atmosphere reduction time is in the range of 2h-25h, and the H2 atmosphere flow rate is controlled in the range of 50mL / min-200mL / min.

[0018] Specifically, the thickness of the Mo coating layer is in the range of 0.5 μm to 3 μm.

[0019] Specifically, after step 3, the following is also included: Mo-coated metal powder is heated to a molten state using a spraying process. The high-melting-point Mo coating suppresses the evaporation of elements in the molten metal powder and achieves metallurgical bonding between the interlayer interfaces within the coating, thus forming the high-performance metal alloy coating on the surface of the target metal parts.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The Mo coating layer prepared on the surface of metal powder is uniform and its thickness is controllable. The technical solution provided by this invention can uniformly prepare a Mo coating layer on the surface of each metal powder through a hydrothermal synthesis process combined with hydrogen reduction. By adjusting the hydrothermal synthesis time, temperature, and pH of the saturated ammonium molybdate solution, the thickness of the Mo coating layer on the surface of the metal powder can be adjusted, thereby preparing core-shell structured Mo-coated metal powder with controllable thickness.

[0021] The Mo coating exhibits high bonding strength with the metal powder and is not easily peeled off. This invention utilizes a hydrothermal synthesis process to prepare a MoO3 coating with a lamellar structure on the surface of the metal powder. This unique lamellar structure creates stress-relieving channels during subsequent hydrogen reduction, resolving the cracking defects of the Mo coating that occur with traditional methods. Hydrogen reduction enables localized metallurgical bonding between the Mo coating and the metal powder interface, significantly improving the bonding strength between them.

[0022] The process is environmentally friendly and highly efficient. The preparation method used in this invention does not contain heavy metal ions and does not introduce other impurity elements (such as the carbon source in stearic acid) into the metal powder. Furthermore, a single batch of 50 kg of powder can be processed using a 1 m diameter reactor, which is 10 times faster than the gas-phase method. Therefore, the Mo-coated metal powder preparation process provided by this invention is simple, low-cost, and pollution-free. It enables the batch preparation of Mo coatings with uniform surface, controllable thickness, and high bonding strength, facilitating the widespread application of this type of powder in the field of thermal spraying technology. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the operation flow of a method for preparing a composite H2 reduction coated Mo by hydrothermal synthesis on the surface of metal powder provided in an embodiment of the present invention; Figure 2 These are the microstructure images and surface energy dispersive spectroscopy (EDS) results of the hydrothermally synthesized MoO3-coated metal powder provided in the embodiments of the present invention. Figure 3 This is provided by the embodiments of the present invention. Figure 2 Energy spectrum test results at point A; Figure 4 The cross-sectional microstructure diagram and EDS energy dispersive spectroscopy test results of Mo-coated metal powder prepared by hydrogen reduction of MoO3-coated metal powder provided in the embodiments of the present invention are shown. Figure 5 This is provided by the embodiments of the present invention. Figure 4 Energy spectrum test results at point B; Explanation of reference numerals in the attached figures: 1 represents the MoO3 coating layer, 2 represents the metal powder, and 3 represents the Mo coating layer. Detailed Implementation

[0025] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0026] To overcome the shortcomings of existing shell-core coated powder preparation methods, the main objective of this invention is to provide a method for preparing a Mo coating with high bonding strength through hydrothermal synthesis of a composite H2 reduction coating on the surface of metal powder, and its application. This method solves the technical problems of traditional preparation methods by creating a Mo coating layer with high bonding strength on the surface of metal powder. This invention significantly improves the suppression of metal element evaporation and the interfacial bonding between particles in the coating during the application of metal powder in the thermal spraying field, which is of great significance for the application of Mo-coated metal powder in thermal spraying and for significantly improving the service life of metal parts.

[0027] This invention provides a method for preparing Mo-coated metal powder materials for thermal spraying. The preferred embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0028] Example 1 like Figure 1 As shown, this application provides a method for preparing a composite H2-reduced coated Mo by hydrothermal synthesis on the surface of metal powder, comprising: Step 1: Before hydrothermal synthesis, the target metal powder is acid-washed with an acid solution to remove contaminants and oxide film from the powder surface; The acid solution is composed of HCl and HNO3, wherein the concentration of HCl is in the range of 5%-20%, the concentration of HNO3 is in the range of 5%-20%, the ratio of HCl to HNO3 is 1:2, and the pickling time is 1 min-20 min.

[0029] Step 2: Prepare a saturated ammonium molybdate solution, and use the saturated ammonium molybdate solution to prepare MoO3-coated metal powder via hydrothermal synthesis; Specifically, step 2 includes: Step 2-1: Prepare a saturated ammonium molybdate solution, including: weighing ammonium molybdate and dissolving it in deionized water, and continuously stirring with a constant temperature magnetic stirrer to form a saturated ammonium molybdate solution.

[0030] The magnetic stirrer speed was set to 15-40 r / s, the stirring time to 20 min-100 min, and the temperature to 25℃-50℃. The pH of the saturated ammonium molybdate solution was adjusted to the range of 1-6 using nitric acid.

[0031] Step 2-2: Mix the metal powder and the saturated ammonium molybdate solution at a volume ratio of 1:10, and use a magnetic stirrer to thoroughly and evenly mix the metal powder and the saturated ammonium molybdate solution under preset conditions.

[0032] The preset conditions are a rotation speed of 15-40 r / s and a temperature of 25℃-50℃.

[0033] Steps 2-3: Place the uniformly mixed metal powder and saturated ammonium molybdate solution into a reaction vessel and place it in a constant temperature drying oven to prepare MoO3-coated metal powder. After the reaction is completed, collect the obtained MoO3-coated metal powder.

[0034] Steps 2-4: Repeatedly wash the MoO3-coated metal powder described in Step 2-3 with anhydrous ethanol and deionized water, and then dry it.

[0035] The temperature range for preparing MoO3-coated metal powder in the constant temperature drying oven is 160℃-230℃, and the time range is 10-30h.

[0036] The drying process involves repeated washing 3-6 times and drying at 70℃ for 24 hours.

[0037] Step 3: Prepare Mo-coated metal powder by reduction in H2 atmosphere.

[0038] The reduction temperature of H2 atmosphere is in the range of 650℃-850℃, the reduction time of H2 atmosphere is in the range of 2h-25h, and the flow rate of H2 atmosphere is controlled in the range of 50mL / min-200mL / min.

[0039] Specifically, the thickness of the Mo coating layer is in the range of 0.5 μm to 3 μm.

[0040] This application employs a hydrothermal synthesis process to coat the surface of metal powder with MoO3, and then obtains Mo-coated metal powder by reducing the MoO3-coated metal powder in an H2 atmosphere.

[0041] Specifically, the Mo-coated metal powder is used in the field of thermal spraying. The Mo-coated metal powder is heated to a molten state using a spraying process. The high-melting-point Mo coating suppresses the evaporation of elements in the molten metal powder and achieves metallurgical bonding between the interlayer interfaces within the coating, forming the high-performance metal alloy coating on the surface of the target metal parts.

[0042] Example 2 like Figure 1As shown, in this embodiment, firstly, according to S1, the metal powder is acid-washed to remove surface contaminants and oxide film; then, according to S2, a MoO3 coating layer is prepared on the surface of the metal powder using a hydrothermal synthesis process; finally, according to S3, the outer MoO3 coating layer of the metal powder is reduced by H2 atmosphere to prepare Mo-coated metal powder.

[0043] In this embodiment, the metal powder is a Ni-based alloy powder.

[0044] In this embodiment, the Mo-Ni based alloy powder with Mo coating is prepared by hydrothermal synthesis and reduction in a composite H2 atmosphere, and the Mo coating layer and the Ni based alloy powder have excellent bonding strength at the contact surface.

[0045] Combination Figure 1 A method for preparing a composite H2-reduced coated Mo by hydrothermal synthesis on the surface of metal powder includes the following steps: Step 1: The target Ni-based alloy powder is pickled using a 5% HCl and HNO3 solution with a ratio of 1:2 for 20 minutes. Step 2: Weigh out ammonium molybdate and dissolve it in deionized water. Use a constant temperature magnetic stirrer to continuously stir for 20 minutes at a speed of 40 r / s and a temperature of 50℃ to form a saturated ammonium molybdate solution. Adjust the pH of the saturated ammonium molybdate solution to 3 using nitric acid.

[0046] Step 3: Mix the Ni-based metal powder that has been acid-washed in Step 1 with the saturated ammonium molybdate solution prepared in Step 2 at a volume ratio of 1:10. Use a magnetic stirrer at a speed of 40 r / s and a temperature of 25°C to thoroughly mix the Ni-based alloy powder and the saturated ammonium molybdate solution.

[0047] Step 4: The uniformly mixed Ni-based alloy powder / saturated ammonium molybdate solution prepared in Step 3 was placed in a reaction vessel and placed in a constant temperature drying oven to prepare MoO3-coated Ni-based alloy powder. The temperature was set at 200℃ and the hydrothermal synthesis time was 20h. After the reaction, the obtained MoO3-coated Ni-based alloy powder was repeatedly washed 6 times with anhydrous ethanol and deionized water, and dried at 70℃ for 24h to obtain the desired product. Figure 2 The image shows MoO3-coated Ni-based alloy powder.

[0048] Step 5: Place the MoO3-coated Ni-based alloy powder obtained in Step 4 into a tube furnace and reduce it for 20 hours at a temperature of 650℃ and an H2 flow rate of 150 mL / min. The final product is as follows. Figure 4 The image shows a Mo-coated Ni-based alloy powder. The outer Mo coating of the powder is approximately 2 μm thick, and the Mo shell is tightly bonded to the Ni-based alloy powder.

[0049] In summary, this invention discloses a method for preparing a hydrothermal synthesis composite H2 reduction coating of Mo on the surface of metal powder and its application, relating to the fields of metal powder preparation and material surface protection. This method involves preparing a uniform MoO3 coating layer on the surface of a metal alloy powder using hydrothermal synthesis technology; then, the MoO3-coated metal alloy powder is reduced in an H2 atmosphere to prepare a Mo-coated metal composite powder. This invention can achieve uniform Mo coating on the surfaces of different metal alloy powders. The melting point of the Mo coating layer on the outside of the composite powder is higher than that of the coated metal powder. The high melting point of Mo (2620℃) suppresses the evaporation of metal alloy powder elements during thermal spraying, thereby significantly increasing the surface temperature of flying particles during spraying. This increased particle temperature enables the preparation of a high-performance metal coating with interlayer metallurgical bonding, which has significant application value.

[0050] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a composite H2-reduced coated Mo by hydrothermal synthesis on the surface of metal powder, characterized in that, include: Step 1: Before hydrothermal synthesis, the target metal powder is acid-washed with an acid solution to remove contaminants and oxide film from the powder surface; Step 2: Prepare a saturated ammonium molybdate solution, and use the saturated ammonium molybdate solution to prepare MoO3-coated metal powder via hydrothermal synthesis; Step 3: Preparation of Mo-coated metal powder by reduction in H2 atmosphere.

2. The preparation method according to claim 1, characterized in that, The acid solution is composed of HCl and HNO3, wherein the concentration of HCl is in the range of 5%-20%, the concentration of HNO3 is in the range of 5%-20%, the ratio of HCl to HNO3 is 1:2, and the pickling time is 1 min-20 min.

3. The preparation method according to claim 1, characterized in that, Step 2 specifically includes: Step 2-1: Prepare a saturated ammonium molybdate solution, including: weighing ammonium molybdate and dissolving it in deionized water, and continuously stirring with a constant temperature magnetic stirrer to form a saturated ammonium molybdate solution. Step 2-2: Mix the metal powder and the saturated ammonium molybdate solution at a volume ratio of 1:10, and use a magnetic stirrer to thoroughly and evenly mix the metal powder and the saturated ammonium molybdate solution under preset conditions. Steps 2-3: Place the uniformly mixed metal powder and saturated ammonium molybdate solution into a reaction vessel and place it in a constant temperature drying oven to prepare MoO3-coated metal powder. After the reaction is completed, collect the obtained MoO3-coated metal powder. Steps 2-4: Repeatedly wash the MoO3-coated metal powder described in Step 2-3 with anhydrous ethanol and deionized water, and then dry it.

4. The preparation method according to claim 3, characterized in that, The magnetic stirrer speed is set to 15-40 r / s, the stirring time is set to 20 min-100 min, the temperature is set to 25℃-50℃, and the pH of the ammonium molybdate saturated solution is adjusted to the range of 1-6 using nitric acid.

5. The preparation method according to claim 3, characterized in that, The preset conditions are a rotation speed of 15-40 r / s and a temperature of 25℃-50℃.

6. The preparation method according to claim 3, characterized in that, The temperature range for preparing MoO3-coated metal powder in the constant temperature drying oven is 160℃-230℃, and the time range is 10-30h.

7. The preparation method according to claim 3, characterized in that, The drying process involves repeated washing at least three times and drying at 70°C for 24 hours.

8. The preparation method according to claim 1, characterized in that, The H2 atmosphere reduction temperature is in the range of 650℃-850℃, the H2 atmosphere reduction time is in the range of 2h-25h, and the H2 atmosphere flow rate is controlled in the range of 50mL / min-200mL / min.

9. The preparation method according to claim 1, characterized in that, The thickness of the Mo coating layer is in the range of 0.5 μm to 3 μm.

10. The preparation method according to claim 1, characterized in that, Step 3 is followed by: Mo-coated metal powder is heated to a molten state using a spraying process. The high-melting-point Mo coating suppresses the evaporation of elements in the molten metal powder and achieves metallurgical bonding between the interlayer interfaces within the coating, thus forming the high-performance metal alloy coating on the surface of the target metal parts.

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