CN115125525A - Low-cost hexagonal boron nitride surface chemical nickel plating pre-palladium-free activation method - Google Patents

Abstract

The invention discloses a low-cost palladium-free activation method before electroless nickel plating on the surface of hexagonal boron nitride. The hexagonal boron nitride is subjected to acid-base etching treatment on the surface, and then the residual impurities on the surface are removed by heat treatment. The heat-treated hexagonal boron nitride is placed in the dispersant solution to make it uniformly dispersed. Silver nitrate and sodium citrate were added in proportion, activated in ultrasonic vibration, then washed with absolute ethanol and filtered. The invention is a low-cost activation method, the cost is about 1/20 of that of palladium chloride activation, the process engineering is simple, the activation effect is good, and the uniform coating of the subsequent nickel layer can be realized; the nano-silver layer produced by the activation is also Excellent solid lubricant; the activation process uses conventional chemicals, which can be suitable for continuous production in large quantities.

Description

A kind of low-cost hexagonal boron nitride surface electroless nickel plating without palladium activation method

technical field

The invention relates to a surface treatment method, in particular to an activation method before electroless nickel plating on the surface of hexagonal boron nitride.

Background technique

With the development and progress of science and technology, the performance of materials is not the only pursuit, but also requires energy saving. The loss caused by friction and wear is inevitable when using equipment tools, which directly determines the service life of equipment tools and causes great energy loss. The study of metal matrix self-lubricating composites is an important means to solve this problem. This kind of composite material not only has the mechanical properties of metal matrix, but also has the tribological properties of solid lubricant. However, as an additive, solid lubricant is difficult to combine with metal matrix. Therefore, surface modification of solid lubricants is a potential approach.

Compared with uncoated solid lubricant powders, the microstructure-modified composite powder materials exhibited better mechanical and antiwear properties. There are many ways to synthesize core-shell composite powders with metal shells. Among them, electroless plating is considered to be one of the most convenient and effective techniques. Electroless plating is a plating method in which metal ions are reduced into metal elements and deposited on the surface with catalytic activity by using reducing agents in the plating solution under the condition of no applied current.

Hexagonal boron nitride (h-BN) in common solid lubricants is a white crystalline powder, commonly known as white graphite. It belongs to the hexagonal crystal system and has a layered structure. There is a small intermolecular van der Waals force between the layers, so the shear strength is low. It is easy to form a lubricant transfer film on the contact surface under the action of friction, reducing the friction pair. friction coefficient and reduce wear. In recent years, h-BN has been widely used in mold making, aviation and aerospace turbine engines and other fields. Related research reports show that h-BN has been relatively least studied in developing surface-tailored composite coatings in tribology due to its poor wettability with metal/ceramic substrates and its insufficient thermal oxidation properties. In addition, h-BN coatings have been shown to be poor applications for high temperature metalworking lubrication. Studies have shown that the wetting properties of h-BN can be improved by adding h-BN lubricant particles to the matrix layer of active metals such as nickel. Based on this viewpoint, the physical and chemical behaviors of h-BN were improved by electroless nickel plating to expand its performance window, leading to the development of an efficient composite coating system.

Because h-BN is chemically stable and has no defects and functional groups on its surface, it is difficult to form crystalline nuclei for electroless nickel plating on its surface. However, in the pretreatment of traditional electroless nickel plating, palladium is expensive and complicated to operate, and highly corrosive hydrochloric acid needs to be used. Although its activation effect is good, in large-scale production, the consumption is relatively large, accounting for 20~40% of the total cost of electroless plating, resulting in high cost of electroless plating.

SUMMARY OF THE INVENTION

Purpose of the invention: In view of the deficiencies in the prior art, the purpose of the present invention is to provide a low-cost hexagonal boron nitride surface electroless nickel-plating method without palladium activation, the process engineering is simple, the nano-silver loading is uniform, the activation effect is good, and the Uniform deposition of subsequent nickel layers.

The technical solution of the present invention is shown below.

A method for palladium-free activation before electroless nickel plating on the surface of low-cost hexagonal boron nitride, which is characterized by comprising the following steps:

(1) Put the hexagonal boron nitride into the mixed solution of KOH and NaOH, continue to ultrasonically stir, perform one etching treatment, and rinse with deionized water until neutral after one etching is completed;

(2) Move the hexagonal boron nitride etched once to the dilute nitric acid solution, neutralize the residual acid and alkali, and perform secondary etching. After the secondary etching is completed, rinse it with deionized water to neutrality and filter, and then use a specific Process parameters for heat treatment;

(3) Using nonylphenol polyoxyethylene ether (N=40) as a dispersant, adding it into deionized water and stirring continuously to form a uniform solution, adding the heat-treated hexagonal boron nitride into the solution, and continuously ultrasonically stirring it to make a uniform solution. Hexagonal boron nitride is uniformly dispersed;

(4) adding silver nitrate and sodium citrate to the homogeneous solution described in step (3) in a specific proportion, activating the hexagonal boron nitride, washing with absolute ethanol and filtering after finishing the treatment.

In step (1), the mass of h-BN is 1-10 g, the concentration of KOH solution is 5-20 mol/L, the concentration of NaOH solution is 5-20 mol/L, the solution volume is 100 mL, and the etching treatment The time is 1~10 h, and the etching temperature is 50~100 °C. The main purpose of etching is to remove surface contamination, and the resulting pores and defects can serve as crystalline regions for subsequent activation and nickel plating. The appropriate volume ratio of h-BN determines the quality of the etching effect. Too much h-BN will easily form agglomerates. Due to the chemical stability of h-BN, a sufficient concentration of alkaline solution is required for successful etching.

In step (2), the concentration of dilute nitric acid is 0.1~1.5 mol/L, the volume of the solution is consistent with the volume of the alkali treatment solution in step (1), the etching time is 5~40 min, the heat treatment temperature is 500~900 ° C, and the heat treatment The time is 1-10 h, and the tube furnace is evacuated until the pressure is lower than 5 Pa. The main purpose of the acid treatment is to remove residual alkali, and as an additional supplemental etch to the alkali treatment. The main purpose of heat treatment is to evaporate residual liquid and decompose residual impurities.

In step (3), the concentration of nonylphenol polyoxyethylene ether (N=40) is 100-500 ppm, the solution volume is 100 mL, and the stirring time is 10-50 min. The main purpose of adding nonylphenol polyoxyethylene ether (N=40) is to uniformly disperse h-BN and reduce agglomeration. It can also reduce its surface energy, preventing it from forming a film with water and floating on the water surface.

In step (4), the concentration of silver nitrate is 0.1~10 g/L. The concentration of sodium citrate is 10-20 times that of silver nitrate, the activation temperature is 20-60 ℃, and the activation time is 20-100 min. When the concentration of silver nitrate is less than 0.1 g/L, the activation effect is insufficient, and it is difficult to plate nickel on the surface of h-BN. When the concentration of silver nitrate is greater than 10 g/L, the activation effect is too strong, and large-sized silver clusters appear in the powder, which will lead to nickel plating on the silver clusters, or even the nickel clusters are too large, resulting in shedding.

Further, the h-BN substrate after the above activation treatment is subjected to subsequent electroless nickel plating treatment.

Beneficial effects:

(1) the activation of the present invention does not need to use expensive palladium, and the activation effect is good, and the cost is lower;

(2) the process engineering of the present invention is simple, the stability is good, and does not need to use the fluoride that has great harm to the environment and human body;

(3) In the method provided by the present invention, the nano-silver generated in the activation is used as an active site, which can provide a crystal nucleus for subsequent nickel plating. Moreover, silver, as a solid lubricant, can also provide beneficial effects on tribological behavior;

(4) In the method provided by the present invention, nano-silver can only be produced on the surface of h-BN, and the silver ions in the solution do not undergo a comprehensive reduction reaction, so that most of the silver ions are preserved, the solution can be reused, and the cost is reduced .

Description of drawings

Figure 1 is an SEM image of the surface microstructure of the h-BN composite powder after nickel plating.

Figure 2 is the XRD pattern of the h-BN composite powder after nickel plating.

Figure 3 is the full range XPS spectrum of h-BN composite powder after nickel plating.

Figure 4 is the Ni 2p XPS narrow spectrum of h-BN composite powder after nickel plating.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments.

Example 1:

A low-cost palladium-free activation method before electroless nickel plating on the surface of hexagonal boron nitride in this embodiment includes the following steps.

(1) Etching treatment

Add 30 g KOH and 25 g NaOH to a beaker and add deionized water to 100 mL. Then 2.5 gh-BN was added to the solution, and ultrasonic stirring was continued at 75 °C for 2 h. After the etching process is completed, rinse with deionized water until neutral.

(2) Acid treatment and heat treatment

100 mL of 0.3 mol/L dilute nitric acid solution was prepared, and the alkali-treated h-BN was placed in it. After etching for 20 min, it was washed with deionized water until neutral and filtered. It was then heat-treated at 700 °C for 1 h.

(3) Activation treatment

Take 0.03 g of nonylphenol polyoxyethylene ether (N=40) and dissolve it in 100 mL of deionized water. The treated h-BN powder was added to it, and after ultrasonic stirring for 20 min, 0.1 g silver nitrate and 1.3 g sodium citrate were added. After ultrasonic vibration at 30 °C for 30 min, suction filtration was performed, then washed with absolute ethanol for 3 times, and finally dried in a vacuum oven at 40 °C for 10 h.

(4) Electroless nickel plating

The activated h-BN powder was added to the electroless nickel plating solution, and 25 mL of hydrazine hydrate was added dropwise while stirring. Then put it into a water bath at 75 °C, keep stirring, and control the pH value around 12. Continue heating until no bubbles appear. The powder was washed to neutrality with deionized water, then rinsed twice with absolute ethanol. Finally, it was dried in a vacuum oven at 60 °C for 10 hours. The formula of the plating solution is as follows: nickel sulfate: 30 g/L, hydrazine hydrate: 50 mL/L, sodium citrate: 30 g/L, pvp: 0.05 g/L.

The microstructure characterization of the h-BN composite powder after nickel plating. The surface morphology of the h-BN composite powder after nickel plating was observed by SEM, and the results are shown in Figure 1. The translucent flake particles are h-BN particles, and the spherical small particles are Ni particles. Most of the powder surface is coated with Ni, and there are only a few 1-2 μm nickel-free h-BN particles. Since the particle size of the h-BN raw material is less than 3 μm, there are a large number of nano-flaky h-BN particles in it. Therefore, it can be observed that the nickel-plated layer is co-deposited by nano-nickel balls and nano-flaky h-BN particles, and the surface nickel layer of the Ni-coated h-BN powder with a particle size of about 3 μm is relatively uniform.

The composition analysis of the h-BN composite powder after nickel plating was carried out by XRD, and the results are shown in Figure 2. The diffraction peaks of Ni are obviously stronger than those of h-BN, indicating that most of the surfaces of the composite powders are Ni particles. It can be seen that there are broad and short diffraction peaks of metallic silver on the curve, indicating that there are a small amount of Ag particles as active sites, forming an uneven layer. The more active sites, the more it can promote the electroless nickel plating reaction and form a more uniform and thicker nickel layer.

The surface element composition and chemical state of the nickel-plated h-BN composite powders were probed by XPS characterization. From the full-range spectra, it can be observed that the peaks at 190.6 and 398.2 eV correspond to the B 1s and N 1s peaks in h-BN, respectively (Fig. 3). While the C 1s and O1s peaks are due to the introduction of contamination sources and partial oxidation. The peak at 368.2 eV corresponds to Ag 3d, indicating that Ag particles are adsorbed on the powder as a catalyst for nickel plating. The characteristic peaks corresponding to Ni 3p, Ni 3s, Ni 2p3/2, and Ni 2p1/2 are located at 67.5, 112.5, 855.8, and 873.2 eV, respectively. In the high-resolution Ni 2p spectrum (Fig. 4), characteristic peaks of nickel oxides are generated at 855.8, 861.2, 879.4 eV due to partial oxidation. At 873.2 and 852.4 eV, they correspond to the nickel element and the nickel-boron compound, respectively. It shows that nickel is successfully plated on the surface of h-BN.

Example 2:

The basic steps of this example are basically the same as those of Example 1, except that the solution concentration of silver nitrate is reduced to 0.5 g/L. The SEM observation analysis showed that more h-BN surfaces were not successfully plated with nickel, and the doping amount of h-BN nanosheets on the surface of large-sized particles became larger. It shows that the activation degree is not enough, and the formed nickel layer has many defects.

Example 3:

The basic steps of this example are basically the same as those of Example 1, except that the concentration of the solution of silver nitrate is increased to 5 g/L. SEM observation and analysis show that there are many h-BN surfaces that are not successfully plated with nickel, and more nickel clusters almost entirely composed of nano-nickel are added around. However, the large size h-BN of 3-5 μm is plated with a uniform and thick nickel layer. The reason for this phenomenon is probably due to excessive activation, and the growth rate of nickel clusters on the surface of h-BN is too fast.

Comparative Example 1:

The basic steps of this comparative example are basically the same as those of Example 1, except that the solution concentration of silver nitrate is reduced to 0.1 g/L. SEM observation and analysis showed that a large number of h-BN surfaces were not successfully plated with nickel, and it was difficult to find a complete nickel layer on the surface of h-BN with large particles, indicating that the concentration of silver ions was too low, resulting in poor activation effect. forming a large number of active sites.

Comparative Example 2:

The basic steps of this comparative example are basically the same as those of Example 1, except that the concentration of the solution of silver nitrate is increased to 10 g/L. SEM observation and analysis showed that a large number of h-BN surfaces were not successfully plated with nickel, and there were a large number of nickel clusters almost entirely composed of nano-nickel in the composite powder. The reason for this phenomenon is probably due to excessive activation, and the growth rate of nickel clusters on the surface of h-BN is too fast.

Claims (8)

1. a low-cost hexagonal boron nitride surface chemical nickel plating without palladium activation method, is characterized in that, comprises the following steps: (1) Put the hexagonal boron nitride into the mixed solution of KOH and NaOH, continue to ultrasonically stir, perform one etching treatment, and rinse with deionized water until neutral after one etching is completed; (2) Move the hexagonal boron nitride etched once to the dilute nitric acid solution, neutralize the residual acid and alkali, and perform secondary etching. After the secondary etching is completed, rinse it with deionized water to neutrality and filter, and then use a specific Process parameters for heat treatment; (3) Using nonylphenol polyoxyethylene ether NP-40 as a dispersant, adding it into deionized water and stirring continuously to form a uniform solution, adding the heat-treated hexagonal boron nitride to this solution, and continuously ultrasonically stirring to make the hexagonal nitrogen Boronide is uniformly dispersed; (4) adding silver nitrate and sodium citrate to the homogeneous solution described in step (3) in a specific proportion, activating the hexagonal boron nitride, washing with absolute ethanol and filtering after finishing the treatment. 2. palladium-free activation method before low-cost hexagonal boron nitride surface electroless nickel plating according to claim 1, is characterized in that: in step (1), the quality of hexagonal boron nitride is 10～100 g/L, KOH The concentration of the solution is 5~20 mol/L, and the concentration of the NaOH solution is 5~20 mol/L. 3. the palladium-free activation method before the low-cost hexagonal boron nitride surface electroless nickel plating according to claim 1, is characterized in that: in step (1), the time of etching treatment is 1～10 h, and the etching temperature is 50～10 h 100°C. 4. the low-cost hexagonal boron nitride surface electroless nickel plating without palladium activation method according to claim 1, is characterized in that: in step (2), dilute nitric acid concentration is 0.1～1.5 mol/L, solution volume and step The volume of the alkaline treatment solution in (1) remains the same. 5. the low-cost hexagonal boron nitride surface electroless nickel plating without palladium activation method according to claim 1, is characterized in that: in step (2), etching time is 5～40 min, and heat treatment temperature is 500～900 ℃ , the heat treatment time is 1~10 h, and the vacuum is evacuated in the tube furnace until the pressure is lower than 5 Pa. 6. the low-cost hexagonal boron nitride surface electroless nickel plating without palladium activation method according to claim 1, is characterized in that: in step (3), the concentration of nonylphenol polyoxyethylene ether NP-40 is 100 ~ 500 ppm, the volume of the solution is consistent with the volume of the alkali treatment solution in step (1), and the stirring time is 10-50 min. 7. the low-cost hexagonal boron nitride surface electroless nickel plating without palladium activation method according to claim 1, is characterized in that: in step (4), the concentration of silver nitrate is 0.1～10 g/L, and sodium citrate The concentration of silver nitrate is 10 to 20 times that of silver nitrate. 8. the low-cost hexagonal boron nitride surface electroless nickel plating method without palladium activation according to claim 1, is characterized in that: in step (4), the temperature of activation treatment is 20～60 ℃, and activation treatment time is 20 ℃ ~100 min.

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