CN109252204B - A kind of method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating - Google Patents

Abstract

The invention discloses a method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating, which belongs to the field of surface electroplating of NdFeB permanent magnet materials. The method of the invention is as follows: alkali washing and degreasing, pickling and rust removal, sandpaper polishing, and then electrodeposition are performed on the NdFeB substrate, wherein the composition and content of the electrolyte are: magnesium oxide 2-3 g/L, phosphoric acid 10 g/L ~15g/L, Super‑P 200~250mg/L, Surfactant 50~55mg/L. The method of the invention is simple, environmentally friendly and pollution-free, and the obtained coating is thick, uniform and dense, and has good bonding; the addition of Super-P significantly improves the corrosion resistance of the coating, and plays a protective role on the NdFeB matrix.

Description

A kind of method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating

technical field

The invention relates to a method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating, in the field of surface electroplating of NdFeB permanent magnet materials.

Background technique

NdFeB magnets are considered to be the third generation of rare earth permanent magnets due to their good magnetic properties and cost-effectiveness. However, due to the multiphase structure of these materials, they have poor corrosion resistance in most environments; this Defects greatly restrict the development of its industry.

Many people at home and abroad have done research on improving the corrosion resistance of NdFeB permanent magnet materials, such as alloying method and coating protection method; research shows that adding alloying elements can promote the formation of intermetallic compounds at grain boundaries, which can improve the magnet The potential of the intergranular phase, thereby improving the corrosion resistance of NdFeB magnets. However, the addition of alloying elements will lead to a decrease in the magnetic properties of the magnet. Alloying elements such as Co form compounds at the grain boundary, which can reduce the reactivity of the grain boundary phase, but the formation of these non-magnetic phases will reduce the magnetic energy product and coercive force of the magnet, resulting in a decrease in the magnetic properties of the magnet. The coating protection method is the most important method to improve the corrosion resistance of NdFeB magnets, and it is also the most effective anti-corrosion method in practical application. Chinese invention patent, application number: 201210481482.8, has carried out research on improving the corrosion resistance of the phosphating film on the surface of NdFeB permanent magnets. The composition of the phosphating solution is relatively complex, not easy to operate, the phosphating time is long, and the thickness of the phosphating film can be obtained. thinner.

SUMMARY OF THE INVENTION

The technical problems to be solved by the invention are: the traditional NdFeB phosphide film has low corrosion resistance, poor bonding force between the coating layer and the base material, and the thickness of the coating layer is relatively thin.

The purpose of the present invention is to provide a method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating, the specific process is as follows: alkali washing and degreasing, pickling and rust removal, sandpaper polishing, and then electrodeposition on the NdFeB substrate , the composition and content of the electrolyte are: magnesium oxide 2~3g/L, phosphoric acid 10~15g/L, Super-P 200~250mg/L, surfactant 50~55mg/L (non-ionic surfactant) .

Preferably, the electrodeposition conditions of the present invention are as follows: pH value is 4.4~4.6, current density is 5mA/cm ² , time is 15~20min, and temperature is 50~80°C.

Preferably, in the alkaline washing and degreasing process of the present invention, the formula of the alkaline washing and degreasing liquid is: sodium hydroxide 3~10g/L, sodium carbonate 30~50g/L, sodium phosphate 50~80g/L, op- 10 The emulsifier is 0.5~2g/L, and the treatment conditions are: the treatment temperature is 30~40℃, and the treatment time is 30~60s.

Preferably, in the pickling and rust removal process of the present invention, the formula of the pickling and rust removal solution is: a mixture of 3% nitric acid and 3% sulfuric acid, and the treatment conditions are: the temperature is room temperature, and the time is 10-20s.

Preferably, the sanding process of the present invention starts from 400 grit sandpaper and goes to 2000 grit sandpaper.

Advantages and effects of the present invention:

(1) In the present invention, a layer of dense magnesium phosphate/Supper-P composite coating is electrodeposited on the NdFeB substrate, which increases the corrosion resistance of the coating and makes the composite coating better than the NdFeB substrate in protection. Magnesium phosphate, zinc phosphate and general coatings; the resulting coating is dense, the thickness is increased, the corrosion resistance is improved, and a stable insulating layer is provided for the NdFeB matrix.

(2) Supper-P is an extremely stable nano-conductive particle, which does not participate in the electrochemical reaction during the electrodeposition of magnesium phosphate coating, but extremely fine Supper-P particles can be well dispersed in the magnesium phosphate coating. The magnesium phosphate/Supper-P composite coating is formed between the coatings; the nanoparticles scattered between the coatings can not only improve the structure of the coating itself, but also play the role of reinforcing phase, and can also give the magnesium phosphate coating conductivity. Special properties; therefore, the phosphating reaction can continue. Supper-P particles are a discontinuous conductive medium. With the continuous progress of the electrolytic phosphating reaction, the conductor paths in the coating are continuously reduced, and the conductivity is gradually reduced. , and eventually the voltage will rise sharply due to the poor conductivity of the coating. Of course, the thickness of the deposited coating will be larger when the limit value is reached.

Description of drawings

Fig. 1 is a graph of the potential-time curve (80°C) during the electrolytic phosphating process of the composite coating of Example 4;

Fig. 2 is the sample XRD pattern after the electrolytic phosphating of embodiment 3;

Fig. 3 is the polarization curve diagram of the sample of Example 2 in NaCl solution (a: matrix; b: magnesium phosphate; c: magnesium phosphate/Super-P);

Fig. 4 is the electrochemical impedance spectrogram of the sample of embodiment 2 in NaCl solution;

Fig. 5 shows the electrochemical impedance spectra of magnesium phosphate coatings prepared by samples of each example at different temperatures (a: substrate; b: 50 ℃; c: 60 ℃; d: 70 ℃; d: 80 ℃);

Figure 6 shows the morphology of the sample after electrolytic phosphating.

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited by the content.

The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating by electrolytic phosphating according to the present invention comprises the following specific steps: before the magnesium phosphate/Super-P composite coating is plated, the NdFeB substrate is subjected to alkaline washing and degreasing; Pickling and rust removal, sandpaper grinding; then electro-deposited magnesium phosphate/Super-P composite coating; the details are as follows: First, sand the NdFeB surface with sandpaper from 400 grit sandpaper to rough grinding to 2000 grit sandpaper for fine grinding and brightening , and then rinse with deionized water, and then follow the steps of alkali cleaning to remove oil → deionized water rinse → acid cleaning to remove rust → deionized water rinse → electrodeposition → clean water rinse → drying → SEM, XRD detection on the sample → corrosion resistance detection.

The preparation process of the electrolyte is as follows: Weigh magnesium oxide with an electronic balance, put it into a clean beaker, add 200ml of distillation to the beaker containing magnesium oxide; put the beaker on a magnetic stirrer and stir evenly and measure the pH of the solution at the same time. During the stirring process, slowly add phosphoric acid to the solution (drop it with a rubber tip dropper) until the solution becomes clear, and the pH value is generally maintained between 4.4 and 4.6. Weigh the Super-p and pour it into the clear solution, and add surfactant; put the beaker into the ultrasonic cleaner to make the Super-p evenly dispersed and mixed in the solution to obtain the electroplating solution.

Example 1

(1) Prepare the sample NdFeB, the sample size is: 10mm×10mm×5mm.

(2) Alkali washing and degreasing and process conditions: sodium hydroxide 3g/L, sodium carbonate 30g/L, sodium phosphate 50g/L, op-10 emulsifier 0.5g/L, the rest is water, the temperature is 30 ℃, the treatment Time 30s.

(3) Pickling and rust removal and process conditions: Immerse the degreasing and water-washed samples in a mixture containing 3% nitric acid and 3% sulfuric acid, and the rest is water; the temperature is room temperature, and the time is 10s.

(4) Components and process conditions of electroplating solution: magnesium oxide 2g/L, phosphoric acid 10g/L, Super-P 200mg/L, surfactant 50mg/L, deionized water 200ml, pH value 4.4, current density 5mA /cm ² , the time was 20 min, and the temperature was 50°C.

(5) Rinse with water after electrodeposition and dry with a hair dryer.

The coating obtained in this example is gray and bright in color, uniform in color, relatively dense, and has improved corrosion resistance. The coating adheres better to the base material, is strong, and is difficult to scrape off with a blade. It can be seen from Figure 5 that although the impedance of the magnesium phosphate/Supper-P composite coating is lower than that of the other three temperatures, it is much higher than that of the substrate, indicating that the magnesium phosphate/Super-P coating can provide more effective resistance to the substrate. Corrosion protection.

Example 2

(1) Prepare the sample NdFeB, the sample size is: 10mm×10mm×5mm;

(2) Alkali washing and degreasing and process conditions: sodium hydroxide 5g/L, sodium carbonate 35g/L, sodium phosphate 60g/L, op-10 emulsifier 1g/L, the rest are water, the temperature is 30 ℃, the treatment time 40s;

(3) Pickling and rust removal and process conditions: immerse the degreasing and water-washed samples into a mixture containing 3% nitric acid and 3% sulfuric acid, and the rest is water; the temperature is room temperature, and the time is 15s;

(4) Electroplating solution components and process conditions: magnesium oxide 2g/L, phosphoric acid 10g/L, Super-P 200mg/L, surfactant 50mg/L, deionized water 200ml, pH value 4.5, current density 5mA /cm ² , the time was 20 min, and the temperature was 60°C.

(5) Rinse with water after electrodeposition and dry with a hair dryer.

The obtained coating is gray and bright in color, uniform in color, relatively dense, and has improved corrosion resistance. It can be seen from Figure 3 that the corrosion potential (-0.74V) of the magnesium phosphate/Supper-P composite coating is higher than the corrosion potential (-0.77V) of the magnesium phosphate coating, indicating that the prepared coating is more thermodynamically stable and does not corrode. It is easy to occur; at the same time, the corrosion current of the coating is low, and it can provide good protection after being tightly covered on the surface of the substrate; the bonding force between the coating and the substrate material is better, and it is very strong, and it is difficult to scrape it off with a blade ; It can be found from Figure 4 that the impedance of the magnesium phosphate/Supper-P composite coating is about 2 times that of the magnesium phosphate coating, indicating that the magnesium phosphate/Super-P coating can provide more effective corrosion protection for the substrate, which is different from the polarization The results of the curve analysis are consistent; it can be seen from Figure 5 that the impedance of this embodiment is the highest and the effect is the best.

Example 3

(1) Prepare the sample NdFeB, the sample size is: 10mm×10mm×5mm;

(2) Alkali washing and degreasing and process conditions: sodium hydroxide 7g/L, sodium carbonate 40g/L, sodium phosphate 70g/L, op-10 emulsifier 1.5g/L, the rest is water, the temperature is 40 ℃, the treatment time 50s;

(3) Pickling and rust removal and process conditions: immerse the degreasing and water-washed samples into a mixture containing 3% nitric acid and 3% sulfuric acid, and the rest is water; the temperature is room temperature, and the time is 20s;

(4) Electroplating bath components and process conditions: magnesium oxide 3g/L, phosphoric acid 15g/L, Super-P 250mg/L, surfactant 55mg/L, deionized water 200ml, pH value 4.5, current density 5mA /cm ² , the time was 15 min, and the temperature was 70°C.

(5) Rinse with water after electrodeposition and dry with a hair dryer.

The obtained coating is gray and bright in color, uniform in color, very dense, and has improved corrosion resistance; the adhesion between the coating and the base material is better, it is very strong, and it is difficult to scrape it off with a blade; it is obvious from Figure 2. It can be seen that in the XRD spectrum of the prepared magnesium phosphate/Supper-P composite coating after adding Supper-P to the electrolyte, the diffraction peak intensity of the matrix NdFeB is significantly weakened, which is due to the increase of the coating thickness, It is caused by the decrease in the intensity of the diffraction peak of the matrix; it can be seen from Figure 5 that the impedance is between the 50 ℃ and 60 ℃ samples, and is higher than that of magnesium phosphate, indicating that the magnesium phosphate/Super-P coating can provide a more effective substrate for the substrate. corrosion protection.

Example 4

(1) Prepare the sample NdFeB, the sample size is: 10mm×10mm×5mm;

(2) Alkali washing and degreasing and process conditions: sodium hydroxide 10g/L, sodium carbonate 50g/L, sodium phosphate 80g/L, op-10 emulsifier 2.5g/L, the rest is water, the temperature is 40 ℃, the treatment time 60s;

(3) Pickling and rust removal and process conditions: immerse the degreasing and water-washed samples into a mixture containing 3% nitric acid and 3% sulfuric acid, and the rest is water; the temperature is room temperature, and the time is 20s;

(4) Electroplating bath components and process conditions: magnesium oxide 3g/L, phosphoric acid 15g/L, Super-P 250mg/L, surfactant 55mg/L, deionized water 200ml, pH value 4.6, current density 5mA /cm ² , the time was 15 min, and the temperature was 80°C.

(5) Rinse with water after electrodeposition and dry with a hair dryer.

The obtained coating is bright gray, uniform in color, very dense, and has improved corrosion resistance. It can be seen from Figure 1 that under the same conditions of other reaction conditions, the coating with the same thickness can be obtained faster due to the presence of Super-P, and the longer the reaction time, the larger the thickness of the deposited coating must be; The bonding force with the matrix material is better, it is very strong, and it is difficult to scrape it off with a blade; from Figure 5, it can be seen that the impedance is between the 50 °C and 60 °C samples, and is higher than that of magnesium phosphate, indicating that phosphoric acid Magnesium/Super-P coating can provide more effective corrosion protection to the substrate.

The present invention adopts the method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating by electrolytic phosphating, which mainly solves the problems of thin phosphating coating and low corrosion resistance; The coating is thick, gray and bright, uniform in color, uniform and compact, and has good bonding, which improves the thickness and corrosion resistance of the coating.

Claims (5)

1. A method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating is characterized by comprising the following steps: carrying out alkali washing oil removal, acid washing rust removal and abrasive paper polishing on the neodymium iron boron substrate, and then carrying out electrodeposition, wherein the electrolyte comprises the following components in percentage by weight: 2-3 g/L of magnesium oxide, 10-15 g/L, Super-P200-250 mg/L of phosphoric acid and 50-55 mg/L of surfactant.

2. The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating according to claim 1, characterized in that: the conditions of electrodeposition were: the pH value is 4.4-4.6, and the current density is 5mA/cm²The time is 15-20 min, and the temperature is 50-80 ℃.

3. The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating according to claim 1, characterized in that: in the alkali washing oil removing process, the formula of the alkali washing oil liquid is as follows: 3-10 g/L of sodium hydroxide, 30-50 g/L of sodium carbonate, 50-80 g/L, op-10 g/L of sodium phosphate and 0.5-2 g/L of emulsifier, wherein the treatment conditions are as follows: the treatment temperature is 30-40 ℃, and the treatment time is 30-60 s.

4. The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating according to claim 1, characterized in that: in the pickling rust removal process, the formula of the pickling rust removal liquid is as follows: a mixed solution of 3% nitric acid and 3% sulfuric acid, wherein the treatment conditions are as follows: the temperature is room temperature and the time is 10-20 s.

5. The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating according to claim 1, characterized in that: the sanding process started with 400 sandpaper to 2000 sandpaper.

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