Preparation method of spherical nanometer barium titanate coated nickel powder

Abstract

The application discloses a preparation method of spherical nano-barium titanate coated nickel powder and belongs to the technical field of MLCC internal electrode materials. The method comprises the following steps: dispersing nano-nickel powder in water and performing ultrasonic treatment; adding titanium tetrachloride into the water, and then adding a nickel powder dispersion liquid; then adding a barium source, adjusting the pH to alkaline by using lye, stirring and reacting at 60-80 DEG C under normal pressure and in an air atmosphere, and separating and drying to obtain the product. The barium source is barium hydroxide, barium chloride or barium acetate. The application uses cheap titanium tetrachloride as a titanium source to synthesize the barium titanate coated nickel powder with a core-shell structure in an aqueous solution in one step, and the reaction condition is mild, and no organic solvent and inert atmosphere protection are needed, so that the process is simple and the cost is low. The obtained product has a continuous and dense coating layer, the oxidation starting temperature is above 385 DEG C, the volume shrinkage rate at 1200 DEG C is less than or equal to 9.1%, the oxidation resistance and sintering shrinkage matching property of the nickel powder are significantly improved, and the product is suitable for MLCC internal electrode materials.

Description

Technical Field

[0001] This invention belongs to the field of metal powder material preparation technology, specifically relating to a method for preparing spherical nano-barium titanate coated nickel powder and its application in the internal electrode material of multilayer ceramic capacitors (MLCCs). Background Technology

[0002] Multilayer ceramic chip capacitors (MLCCs) are an important component of electronic components, and the development of their internal electrode materials has shifted from noble metals (such as platinum and palladium) to base metals (such as nickel and copper). Among them, nickel powder has become the mainstream material for MLCC internal electrodes due to its advantages such as low cost, high conductivity, good corrosion resistance, and matching co-firing temperature with ceramic dielectrics.

[0003] However, nickel powder still faces two major technical challenges in practical applications: first, nickel is easily oxidized to nickel oxide (NiO) during high-temperature sintering, leading to a decrease in electrode conductivity; second, the shrinkage behavior of the nickel internal electrode and the barium titanate (BaTiO3) ceramic dielectric layer is mismatched during sintering, easily causing structural defects such as delamination, warping, and even cracking in MLCCs. To solve these problems, researchers proposed coating the surface of nickel powder with a layer of barium titanate ceramic. Utilizing the advantage that barium titanate is made of the same material as the dielectric layer, this approach can both prevent nickel powder oxidation and improve the matching of sintering shrinkage.

[0004] Currently, methods for preparing barium titanate-coated nickel powder have been reported. For example, CN119634725A discloses a method for synthesizing barium titanate-coated Ni particles using spray drying technology. This method uses metatitanic acid and barium hydroxide as raw materials, mixes nickel powder with the raw materials, and then spray-dries the mixture to obtain an intermediate. The intermediate is then heat-treated in a tube furnace at 500-700℃ under a N2 atmosphere to form the coating layer. Although this method can be mass-produced, it requires spray drying equipment and a tube furnace, and must be processed at high temperatures under an inert atmosphere, resulting in high equipment investment and energy consumption.

[0005] CN103508736A discloses two chemical coating methods for preparing barium titanate-coated nickel nanopowder: one is atmospheric pressure coating followed by hydrothermal crystallization (140~240℃), and the other is atmospheric pressure coating followed by atmospheric pressure crystallization. Both methods use tetrabutyl titanate as the titanium source and require the use of organic solvents (such as isopropanol and n-butanol) and various additives such as triethanolamine, glycerol, and polyethylene glycol. Tetrabutyl titanate is expensive, the use of organic solvents increases costs and environmental pressure, and the hydrothermal crystallization step requires a high-pressure reactor, which is not conducive to continuous production.

[0006] Furthermore, CN114477273A discloses a hydrothermal method for preparing tetragonal phase barium titanate nanopowder, using titanium tetrachloride and barium salt as raw materials, to synthesize barium titanate powder under hydrothermal conditions of 220-350℃ and pH≥13. However, this method only addresses the preparation of barium titanate powder and does not involve forming a coating layer on the surface of nickel powder. Moreover, the hydrothermal reaction conditions are harsh, making it difficult to directly apply to the preparation of core-shell structured composite powders.

[0007] In summary, the existing methods for preparing barium titanate-coated nickel powder still have the following shortcomings: (1) they require expensive organic titanium sources or organic solvents, which are costly and environmentally unfriendly; (2) they rely on complex equipment or harsh conditions such as spray drying, hydrothermal crystallization, or high-temperature inert atmosphere heat treatment; and (3) they involve many process steps, which are not conducive to large-scale production. Therefore, developing a simple, low-cost method for preparing barium titanate-coated nickel powder at low temperatures under normal air pressure has significant practical application value. Summary of the Invention

[0008] To address the shortcomings of existing barium titanate-coated nickel powder preparation methods, such as high cost, complex processes, and the need for organic solvents or high-temperature inert atmospheres, this invention provides a method for preparing spherical nano-barium titanate-coated nickel powder. This method is based on a low-temperature liquid-phase method that completes the coating in one step in an aqueous solution system using inexpensive inorganic raw materials.

[0009] The technical solution adopted in this invention is as follows: A method for preparing spherical barium titanate nano-coated nickel powder includes the following steps: S1: Disperse nano-nickel powder in water and subject it to ultrasonic treatment to obtain a nickel powder dispersion. The median particle size D50 of the nano-nickel powder is preferably 80~150 nm, and the ultrasonic treatment time is preferably 20~40 min to fully break up the nickel powder agglomerates and achieve single-particle dispersion.

[0010] S2: Add titanium tetrachloride to water and stir until homogeneous to obtain an aqueous solution of titanium tetrachloride. Then add the nickel powder dispersion obtained in step S1 to obtain a mixed solution. Among them, titanium tetrachloride is used as the titanium source, and its molar ratio with nano-nickel powder is preferably 1:20~1:100. This ratio can effectively control the thickness and coating amount of the barium titanate coating layer.

[0011] S3: Add a barium source to the mixed solution from step S2, and adjust the pH of the system to alkaline (preferably pH = 12~14) with an alkaline solution. Then, heat the mixture to 60~80℃ under normal pressure and air atmosphere and stir for 2~6 h. After the reaction is complete, separate and dry the mixture to obtain barium titanate-coated nickel powder. The barium source is at least one of barium hydroxide, barium chloride, or barium acetate; the alkaline solution is preferably a sodium hydroxide solution.

[0012] In this invention, titanium tetrachloride hydrolyzes in water to generate titanium hydroxyl oxides, while a barium source provides barium ions. Under alkaline conditions, the titanium hydroxyl oxides react with the barium ions to generate barium titanate (BaTiO3) nanoparticles in situ on the surface of nickel powder, gradually forming a continuous and dense coating layer. The entire reaction process is carried out in an aqueous solution without any organic solvents; the reaction temperature is 60-80℃, under normal pressure, without the need for an inert atmosphere; and the reaction time is only 2-6 hours to obtain a core-shell structured composite powder with a continuous and uniform coating layer.

[0013] As a preferred embodiment, the barium titanate coating layer accounts for 5-15% of the total mass of the composite powder, and the coating layer thickness is 20-50 nm. The thickness and amount of the coating layer can be controlled by adjusting parameters such as the molar ratio of titanium tetrachloride to nickel powder, reaction temperature, and pH value.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention uses inexpensive titanium tetrachloride as the titanium source to synthesize core-shell structured barium titanate-coated nickel powder in an aqueous solution in one step. The reaction conditions are mild (60-80°C, normal pressure, air atmosphere), requiring no organic solvents or inert atmosphere protection. The process is simple, low-cost, and easy to scale up. Figure 1 As shown, the nickel powder obtained in Example 1 is coated with a continuous and dense barium titanate layer with a uniform thickness (20~50 nm); Figure 2 As shown, the XRD pattern simultaneously exhibits characteristic peaks of cubic BaTiO3 and face-centered cubic Ni, with no impurities, indicating high crystallinity and purity of the product. Performance tests show that the barium titanate-coated nickel powder prepared in Examples 1-7 of this invention has an oxidation initiation temperature ≥385℃ and a volume shrinkage rate ≤9.1% at 1200℃. Compared with uncoated pure nickel powder (oxidation initiation temperature approximately 251℃, shrinkage rate 24.8%), it significantly improves oxidation resistance and enhances the sintering shrinkage matching with the BaTiO3 ceramic dielectric layer. The comparative examples further verify the indispensability of the alkaline environment, inorganic titanium source, and barium source. Therefore, this invention provides a high-quality, low-cost barium titanate-coated nickel powder and its preparation method, which has broad application prospects in the field of MLCC internal electrode materials. Attached Figure Description

[0015] Figure 1 A scanning electron microscope (SEM) image of the barium titanate-coated nickel powder prepared in Example 1 of this invention; Figure 2 The image shows the X-ray diffraction (XRD) pattern of the barium titanate-coated nickel powder prepared in Example 1 of this invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of this invention is not limited to the following embodiments.

[0017] The testing methods and instruments used are all existing general testing methods and commercial instruments.

[0018] Example 1 A method for preparing spherical barium titanate nano-coated nickel powder includes the following steps: S1: Weigh 5.8 g of spherical nickel powder with a median particle size D50 = 100 nm, add it to 100 mL of deionized water, and ultrasonically disperse for 30 min to obtain a nickel powder dispersion.

[0019] S2: At room temperature, 0.71 g of titanium tetrachloride was slowly added to 20 mL of deionized water and stirred until completely dissolved to obtain an aqueous solution of titanium tetrachloride. Then, the nickel powder dispersion obtained in step S1 was added to this solution, and stirring was continued for 10 min to obtain a mixed solution.

[0020] S3: Add 0.58 g of barium hydroxide (Ba(OH)2·8H2O) to the above mixed solution and stir until completely dissolved. Then adjust the pH of the system to 13 with 1 mol / L sodium hydroxide solution. Transfer the mixed solution to a water bath, heat to 60℃, and stir the reaction for 4 h under normal pressure and air atmosphere. After the reaction is completed, centrifuge to separate the solid. Wash the obtained solid three times each with deionized water and ethanol, and dry it in a 70℃ forced-air drying oven for 6 h to obtain barium titanate coated nickel powder composite powder.

[0021] SEM images of the barium titanate-coated nickel powder prepared in this embodiment are shown below. Figure 1 As shown. By Figure 1 As can be seen, the powder is spherical and uniformly coated with a layer of barium titanate nanoparticles. The coating layer is continuous and dense, with a thickness of about 30~45 nm.

[0022] Figure 2 This is the XRD pattern of the product from this embodiment. Figure 2 It can be seen that the diffraction peaks correspond to the face-centered cubic Ni and the cubic BaTiO3 phase, respectively, with no other impurity phase peaks, indicating that the barium titanate coating layer was successfully synthesized.

[0023] TG-DSC testing showed that the oxidation onset temperature of the product in this embodiment was 392°C, which is 142°C higher than that of uncoated pure nickel powder (oxidation onset temperature of approximately 250°C). TMA testing showed that the volume shrinkage rate of the product in this embodiment at 1200°C was 8.2%, significantly lower than the 24.8% of the uncoated pure nickel powder, and the difference in shrinkage between the product and the BaTiO3 ceramic medium (shrinkage rate of approximately 4.2%) was significantly reduced.

[0024] Example 2 The only difference from Example 1 is that the amount of nickel powder used in step S1 is changed to 2.9 g. The remaining steps are the same as in Example 1.

[0025] The barium titanate-coated nickel powder prepared in this embodiment has a barium titanate mass fraction of approximately 14% (calculated based on the feed ratio). TG-DSC testing showed an oxidation initiation temperature of 398°C; TMA testing showed a volume shrinkage rate of 7.5% at 1200°C.

[0026] Example 3 The only difference from Example 1 is that the amount of nickel powder used in step S1 is changed to 8.7 g. The remaining steps are the same as in Example 1.

[0027] The barium titanate-coated nickel powder prepared in this embodiment has a barium titanate mass fraction of approximately 5%. The oxidation initiation temperature is 385℃, and the volume shrinkage rate at 1200℃ is 9.1%.

[0028] Example 4 The only difference from Example 1 is that the barium source in step S3 is replaced with barium chloride (BaCl2·2H2O), and the amount added is 0.39 g. The remaining steps are the same as in Example 1.

[0029] The barium titanate-coated nickel powder prepared in this embodiment has an oxidation initiation temperature of 388℃ and a volume shrinkage rate of 8.5% at 1200℃.

[0030] Example 5 The only difference from Example 1 is that the barium source in step S3 is replaced with barium acetate, and the amount added is 0.48 g. The remaining steps are the same as in Example 1.

[0031] The barium titanate-coated nickel powder prepared in this embodiment has an oxidation initiation temperature of 390℃ and a volume shrinkage rate of 8.3% at 1200℃.

[0032] Example 6 The only difference from Example 1 is that the reaction temperature in step S3 is changed to 70°C. The remaining steps are the same as in Example 1.

[0033] The barium titanate-coated nickel powder prepared in this embodiment has an oxidation initiation temperature of 395℃ and a volume shrinkage rate of 8.0% at 1200℃.

[0034] Example 7 The only difference from Example 1 is that the amount of barium hydroxide added in step S3 is changed to 0.64 g (Ba:Ti molar ratio is approximately 1.1:1). The remaining steps are the same as in Example 1.

[0035] The barium titanate-coated nickel powder prepared in this embodiment has an oxidation initiation temperature of 396℃ and a volume shrinkage rate of 7.8% at 1200℃.

[0036] Comparative Example 1 The only difference from Example 1 is that sodium hydroxide is not added in step S3 to adjust the pH; instead, dilute hydrochloric acid is used to adjust the pH of the system to 4 (acidic conditions). The remaining steps are the same as in Example 1.

[0037] The obtained product, as tested by TG-DSC, showed an oxidation initiation temperature of only 268℃, similar to that of pure nickel powder. This comparative example demonstrates that an alkaline environment is a necessary condition for the in-situ formation of barium titanate.

[0038] Comparative Example 2 The only difference from Example 1 is that titanium tetrachloride in step S2 is replaced with an equimolar amount of tetrabutyl titanate (approximately 1.2 g). Since tetrabutyl titanate is insoluble in water, it must first be dissolved in 20 mL of anhydrous ethanol before being added. The remaining steps are the same as in Example 1.

[0039] The obtained product, as determined by TG-DSC, had an oxidation initiation temperature of 312°C, lower than that of Example 1. This comparative example demonstrates that the inorganic titanium tetrachloride source used in this invention exhibits higher reactivity than the organic titanium source.

[0040] Comparative Example 3 The same nickel powder (D50=100 nm) as in Example 1 was used directly without any coating treatment.

[0041] TG-DSC testing showed an oxidation initiation temperature of 251℃; TMA testing showed a volume shrinkage rate of 24.8% at 1200℃. This comparative example serves as a blank control to demonstrate the effectiveness of the coating effect of this invention.

[0042] Comparative Example 4 5.8 g of nickel powder (D50=100 nm) and 0.45 g of commercially available nano barium titanate powder (D50=50 nm, equivalent to the theoretical mass of the coating layer in Example 1) were ground and mixed in an agate mortar for 30 min to obtain a mechanically mixed powder.

[0043] The resulting product, as tested by TG-DSC, showed an oxidation initiation temperature of 285°C, significantly lower than that of Example 1; however, TMA testing revealed a volume shrinkage rate of 18.5% at 1200°C, still significantly higher than that of Example 1. This comparative example demonstrates that the one-step liquid-phase in-situ coating method of the present invention, compared to simple physical mixing, can form a tightly bound core-shell structure, significantly improving antioxidant properties and shrinkage matching.

[0044] Comparative Example 5 The only difference from Example 1 is that no barium source (barium hydroxide) is added in step S3; the rest of the steps are the same as in Example 1.

[0045] The obtained product was tested by TG-DSC, and the oxidation initiation temperature was 276℃. This comparative example demonstrates that the participation of a barium source is a necessary condition for the formation of a barium titanate coating layer, and the TiO2 coating layer generated by the hydrolysis of a titanium source alone has limited antioxidant effect.

[0046] Test case Overall performance comparison The products of Examples 1-7 and Comparative Examples 1-5 were subjected to comprehensive performance tests, and the results are summarized in Table 1.

[0047] Table 1. Performance comparison of the products of each embodiment and comparative example.

[0048] As can be seen from Table 1, the barium titanate coated nickel powder prepared in Examples 1 to 7 of the present invention has an oxidation initiation temperature ≥385℃ and a volume shrinkage rate ≤9.1% at 1200℃. Compared with uncoated pure nickel powder (Comparative Example 3) and existing technical methods (Comparative Examples 1, 2, 4, 5), it exhibits significantly superior antioxidant properties and shrinkage matching properties.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing spherical barium titanate nano-coated nickel powder, characterized in that, Includes the following steps: S1: Disperse nano-nickel powder in water and subject it to ultrasonic treatment to obtain a nickel powder dispersion; S2: Add titanium tetrachloride to water, stir until homogeneous, and then add the nickel powder dispersion obtained in step S1 to obtain a mixed solution; S3: Add a barium source to the mixed solution in step S2, and adjust the pH of the system to alkaline with an alkaline solution. Then, heat the mixture to 60-80℃ under normal pressure and air atmosphere and stir to react. After the reaction is completed, separate and dry the mixture to obtain barium titanate coated nickel powder. The barium source is at least one of barium hydroxide, barium chloride, or barium acetate.

2. The method according to claim 1, characterized in that, In step S1, the median particle size D50 of the nano-nickel powder is 80-150 nm, and the ultrasonic time is 20-40 min.

3. The method according to claim 1, characterized in that, In step S2, the molar ratio of titanium tetrachloride to nano-nickel powder is 1:20 to 1:

100.

4. The method according to claim 1, characterized in that, In step S3, the barium source is barium hydroxide, and the mass ratio of barium hydroxide to titanium tetrachloride is 1:1 to 1.1:

1.

5. The method according to claim 1, characterized in that, In step S3, the alkaline solution is a sodium hydroxide solution, and the pH of the system is adjusted to 12-14.

6. The method according to claim 1, characterized in that, In step S3, the temperature for heating and stirring the reaction is 60-80℃, and the time is 2-6 h.

7. The method according to claim 1, characterized in that, In step S3, the drying temperature is 60-80℃ and the drying time is 4-8 h.

8. The method according to claim 1, characterized in that, The barium titanate coating accounts for 5-15% of the total mass of the composite powder, and the coating thickness is 20-50 nm.

9. A spherical nano-barium titanate coated nickel powder, characterized in that, The barium titanate-coated nickel powder is prepared by any one of claims 1 to 8; the barium titanate-coated nickel powder has a core-shell structure, wherein nickel is the core and barium titanate is the shell, and the barium titanate coating layer is a cubic phase.

10. The application of the spherical nano-barium titanate coated nickel powder according to claim 9 in the internal electrode material of multilayer ceramic capacitors (MLCCs).

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