CN109252204B - Method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating - Google Patents
Method for preparing magnesium phosphate/Super-P composite corrosion-resistant coating Download PDFInfo
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- CN109252204B CN109252204B CN201810992289.8A CN201810992289A CN109252204B CN 109252204 B CN109252204 B CN 109252204B CN 201810992289 A CN201810992289 A CN 201810992289A CN 109252204 B CN109252204 B CN 109252204B
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- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
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- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
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- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
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Abstract
The invention discloses a method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating, and belongs to the field of surface electroplating of neodymium iron boron permanent magnet materials. The method comprises 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. The method is simple, environment-friendly and pollution-free, and the obtained coating is thick, uniform and compact and has good associativity; the Super-P is added to obviously improve the corrosion resistance of the coating and protect the neodymium iron boron substrate.
Description
Technical Field
The invention relates to a method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating, belonging to the field of surface electroplating of neodymium iron boron permanent magnet materials.
Background
The neodymium iron boron magnet is considered as a third-generation rare earth permanent magnet due to good magnetic performance and cost performance, but the corrosion resistance of the neodymium iron boron magnet in most environments is poor due to the fact that the neodymium iron boron magnet has a multi-phase structure; this drawback greatly restricts the development of the industry.
Many people have done research on improving the corrosion resistance of the neodymium iron boron permanent magnet material at home and abroad, such as an alloying method and a plating protection method; research shows that the addition of the alloy elements can promote the formation of intermetallic compounds at the grain boundary and improve the potential of the magnet intergranular phase, thereby improving the corrosion resistance of the neodymium iron boron magnet. However, the addition of the alloying elements results in a decrease in the magnetic properties of the magnet. Alloy elements such as Co form compounds at grain boundaries to reduce the reactivity of grain boundary phases, but the formation of these non-magnetic phases reduces the magnetic energy and coercive force of the magnet, resulting in a reduction in the magnetic properties of the magnet. The plating protection method is the most important method for improving the corrosion resistance of the neodymium iron boron magnet, and is also the most effective corrosion resistance means in practical application. Chinese invention patent, application number: 201210481482.8, the research of improving the corrosion resistance of the phosphating film on the surface of the neodymium iron boron permanent magnet is carried out, the composition of the phosphating solution is complex, the operation is not easy, the phosphating time is long, and the obtained phosphating film is thin.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the traditional neodymium iron boron phosphate film has low corrosion resistance, the binding force between a coating layer and a base material is poor, and the thickness of the coating layer is thin.
The invention aims to provide a method for preparing a magnesium phosphate/Super-P composite corrosion-resistant coating, which comprises the following specific 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 magnesium oxide, 10-15 g/L, Super-P200-250 mg/L phosphoric acid, 50-55 mg/L surfactant (nonionic surfactant).
Preferably, the electrodeposition conditions of the present invention are: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 ℃.
Preferably, in the alkali washing oil removal 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.
Preferably, in the acid pickling rust removal process, the formula of the acid 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.
Preferably, the sanding process of the present invention begins with 400 sandpaper to 2000 sandpaper.
The invention has the advantages and effects that:
(1) according to the invention, a compact magnesium phosphate/super-P composite coating is electrodeposited on the neodymium iron boron substrate, so that the corrosion resistance of the coating is improved, and the protection effect of the composite coating on the neodymium iron boron substrate is better than that of magnesium phosphate, zinc phosphate and a common coating; the obtained coating is compact, the thickness is increased, the corrosion resistance is improved, and a stable insulating layer is provided for the neodymium iron boron substrate.
(2) The super-P is extremely stable nano conductive particles, does not participate in electrochemical reaction in the process of electrodepositing the magnesium phosphate coating, but extremely fine super-P particles can be well dispersed among the magnesium phosphate coatings to form a magnesium phosphate/super-P composite coating; the nano particles dispersed among the coatings can not only improve the structure of the coatings and play a role of enhancing phases, but also endow the magnesium phosphate coatings with the special performance of conductivity; therefore, the phosphating reaction can be continuously carried out, the super-P particles are discontinuous conductive media, the conductor path in the coating is continuously reduced along with the continuous electrolytic phosphating reaction, the conductivity is gradually reduced, the voltage is also rapidly increased finally due to the poor conductivity of the coating, and the thickness of the coating deposited when the limit value is reached is certainly larger.
Drawings
FIG. 1 is a graph of potential-time curve (80 ℃) during electrolytic phosphating of a composite coating of example 4;
FIG. 2 is an XRD pattern of a sample after electrolytic phosphating in example 3;
FIG. 3 is a graph showing the polarization curves of the sample of example 2 in a NaCl solution (a: matrix; b: magnesium phosphate; c: magnesium phosphate/Super-P);
FIG. 4 is an electrochemical impedance spectrum of the sample of example 2 in a NaCl solution;
FIG. 5 is an electrochemical impedance spectrum of a magnesium phosphate coating prepared at different temperatures for samples of each example (a: substrate; b: 50 ℃; c: 60 ℃; d: 70 ℃; d: 80 ℃);
FIG. 6 is a sample morphology graph after electrolytic phosphating.
Detailed Description
The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
The method for preparing the magnesium phosphate/Super-P composite corrosion-resistant coating by electrolytic phosphating comprises the following specific steps: before plating the magnesium phosphate/Super-P composite coating, performing alkali washing oil removal, acid washing rust removal and sand paper polishing on the neodymium iron boron substrate; then carrying out electrodeposition on magnesium phosphate/Super-P composite coating; the method comprises the following specific steps: firstly, sanding the surface of neodymium iron boron by using sand paper, roughly grinding 400 grains of sand paper until 2000 grains of sand paper are finely ground to be bright, then washing by using deionized water, and then carrying out SEM (scanning Electron microscope) detection → corrosion resistance detection on a sample according to the steps of alkaline washing oil removal → deionized water washing → acid washing rust removal → deionized water washing → electrodeposition → clear water washing → blow drying → carrying out SEM on the sample.
The preparation process of the electrolyte comprises the following steps: weighing magnesium oxide with an electronic balance, putting into a clean beaker, and adding 200ml of distilled water into the beaker filled with the magnesium oxide; putting the beaker on a magnetic stirrer, uniformly stirring, measuring the pH value of the solution, slowly adding phosphoric acid (dropping by using a rubber head dropper) into the solution in the stirring process until the solution becomes clear, and finally measuring the pH value and generally maintaining the pH value between 4.4 and 4.6; weighing Super-p, pouring into the clear solution, and adding a surfactant; and (3) putting the beaker into an ultrasonic cleaning instrument, and uniformly dispersing and mixing the Super-p in the solution to obtain the electroplating solution.
Example 1
(1) Preparing a sample of neodymium iron boron, wherein the sample size is as follows: 10mm by 5 mm.
(2) Alkali washing oil removal and process conditions are as follows: 3g/L of sodium hydroxide, 30g/L of sodium carbonate, 50g/L, op-10 g of sodium phosphate, 0.5g/L of emulsifier and the balance of water, wherein the temperature is 30 ℃, and the treatment time is 30 s.
(3) Acid pickling for rust removal and process conditions: immersing the deoiled and water-washed sample into a mixed solution containing 3% of nitric acid and 3% of sulfuric acid, and the balance being water; the temperature was room temperature for 10 s.
(4) The components and the process conditions of the electroplating solution are as follows: 2g/L of magnesium oxide, 10g/L, Super-P200 mg/L of phosphoric acid, 50mg/L of surfactant and 200ml of deionized water, wherein the pH value is 4.4, and the current density is 5mA/cm2The time is 20min and the temperature is 50 ℃.
(5) After electrodeposition, the film is washed by clean water and dried by a blower.
The coating obtained by the embodiment is gray and bright, uniform in color and luster, relatively compact and improved in corrosion resistance. The coating has better bonding force with the substrate material, is very firm and is difficult to scrape off by a blade. From FIG. 5, it can be seen that the resistivity of the magnesium phosphate/Super-P composite coating, although lower than the other three temperatures, is much higher than that of the substrate, indicating that the magnesium phosphate/Super-P coating can provide more effective corrosion protection to the substrate.
Example 2
(1) Preparing a sample of neodymium iron boron, wherein the sample size is as follows: 10mm × 10mm × 5 mm;
(2) alkali washing oil removal and process conditions are as follows: 5g/L of sodium hydroxide, 35g/L of sodium carbonate, 60g/L, op-10 g of sodium phosphate, 1g/L of emulsifier and the balance of water, wherein the temperature is 30 ℃, and the treatment time is 40 s;
(3) acid pickling for rust removal and process conditions: immersing the deoiled and water-washed sample into a mixed solution containing 3% of nitric acid and 3% of sulfuric acid, and the balance being water; the temperature is room temperature and the time is 15 s;
(4) the components and the process conditions of the electroplating solution are as follows: magnesium oxide 2g/L, phosphoric acid 10g/L, Super-P200 mg-L, 50mg/L of surfactant and 200ml of deionized water, wherein the pH value is 4.5, and the current density is 5mA/cm2The time is 20min and the temperature is 60 ℃.
(5) After electrodeposition, the film is washed by clean water and dried by a blower.
The obtained coating layer is gray and bright, has uniform color and is relatively compact, and the corrosion resistance is improved. From FIG. 3, it can be seen that the corrosion potential (-0.74V) of the magnesium phosphate/super-P composite coating is higher than that (-0.77V) of the magnesium phosphate coating, which indicates that the prepared coating is more thermodynamically stable and corrosion is less likely to occur; meanwhile, the corrosion current of the coating is low, and the coating can generate good protection effect after being tightly covered on the surface of the substrate; the coating has better bonding force with the substrate material, is very firm, and is difficult to scrape off by a blade; from FIG. 4, it is found that the resistance of the magnesium phosphate/Super-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 to the substrate, which is consistent with the results analyzed by the polarization curve; as can be seen from fig. 5, this embodiment has the highest impedance and the best effect.
Example 3
(1) Preparing a sample of neodymium iron boron, wherein the sample size is as follows: 10mm × 10mm × 5 mm;
(2) alkali washing oil removal and process conditions are as follows: 7g/L of sodium hydroxide, 40g/L of sodium carbonate, 70g/L, op-10 g of sodium phosphate, 1.5g/L of emulsifier and the balance of water, wherein the temperature is 40 ℃, and the treatment time is 50 s;
(3) acid pickling for rust removal and process conditions: immersing the deoiled and water-washed sample into a mixed solution containing 3% of nitric acid and 3% of sulfuric acid, and the balance being water; the temperature is room temperature and the time is 20 s;
(4) the components and the process conditions of the electroplating solution are as follows: 3g/L of magnesium oxide, 15g/L, Super-P250 mg/L of phosphoric acid, 55mg/L of surfactant and 200ml of deionized water, wherein the pH value is 4.5, and the current density is 5mA/cm2The time is 15min and the temperature is 70 ℃.
(5) After electrodeposition, the film is washed by clean water and dried by a blower.
The obtained coating layer is gray and bright, uniform in color and very compact, and the corrosion resistance is improved; the coating has better bonding force with the substrate material, is very firm, and is difficult to scrape off by a blade; as is apparent from FIG. 2, after the super-P is added into the electrolyte, the diffraction peak intensity of the neodymium iron boron substrate in the XRD spectral line of the prepared magnesium phosphate/super-P composite coating is obviously weakened, which is caused by the fact that the diffraction peak intensity of the substrate is reduced due to the increase of the coating thickness; from FIG. 5, it can be seen that the impedance is between 50 ℃ and 60 ℃ for the samples and higher than that of the magnesium phosphate, indicating that the magnesium phosphate/Super-P coating provides more effective corrosion protection to the substrate.
Example 4
(1) Preparing a sample of neodymium iron boron, wherein the sample size is as follows: 10mm × 10mm × 5 mm;
(2) alkali washing oil removal and process conditions are as follows: 10g/L of sodium hydroxide, 50g/L of sodium carbonate, 80g/L, op-10 g of sodium phosphate, 2.5g/L of emulsifier and the balance of water, wherein the temperature is 40 ℃, and the treatment time is 60 s;
(3) acid pickling for rust removal and process conditions: immersing the deoiled and water-washed sample into a mixed solution containing 3% of nitric acid and 3% of sulfuric acid, and the balance being water; the temperature is room temperature and the time is 20 s;
(4) the components and the process conditions of the electroplating solution are as follows: 3g/L of magnesium oxide, 15g/L, Super-P250 mg/L of phosphoric acid, 55mg/L of surfactant and 200ml of deionized water, wherein the pH value is 4.6, and the current density is 5mA/cm2The time is 15min and the temperature is 80 ℃.
(5) After electrodeposition, the film is washed by clean water and dried by a blower.
The obtained coating layer is gray and bright, has uniform color and very compact structure, and has improved corrosion resistance. As can be seen from FIG. 1, in the case of otherwise identical reaction conditions, the coating obtained is faster with the same thickness due to the presence of Super-P, the longer the reaction time, the greater the thickness of the coating deposited is bound to be; the coating has better bonding force with the substrate material, is very firm, and is difficult to scrape off by a blade; from FIG. 5, it can be seen that the impedance is between 50 ℃ and 60 ℃ for the samples and higher than that of the magnesium phosphate, indicating that the magnesium phosphate/Super-P coating provides more effective corrosion protection to the substrate.
The invention adopts the method of preparing the magnesium phosphate/Super-P composite corrosion-resistant coating by electrolytic phosphating, and mainly solves the problems of thinner phosphating coating and lower corrosion resistance; the method is simple to operate and environment-friendly, and the obtained coating is thick, gray, uniform and compact in color and luster, good in associativity and capable of improving 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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| CN101182639A (en) * | 2007-09-13 | 2008-05-21 | 上海大学 | Steel phosphating liquid containing magnesium and nickel and phosphating method thereof |
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| CN104250747A (en) * | 2013-06-26 | 2014-12-31 | 无锡洛社科技创业有限公司 | Preparation method of phosphating liquid used in automobile painting |
| CN104357818B (en) * | 2014-11-14 | 2016-11-23 | 浙江迪特高强度螺栓有限公司 | A kind of compositions for steel iron phosphatising and preparation method thereof |
| CN107740168A (en) * | 2017-09-30 | 2018-02-27 | 华南理工大学 | A kind of efficient corrosion resisting Zinc phosphating solution and preparation method thereof |
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