Slag-free high-temperature manganese phosphating solution, preparation method and application

Abstract

The invention discloses a slag-free high-temperature manganese phosphating solution as well as a preparation method and application thereof. The slag-free high-temperature manganese phosphating solution comprises the following components in percentage by weight: 22.0%-30.5% of phosphoric acid, 3.0%-8.5% of manganous dihydrogen phosphate, 3.5%-8.0% of manganese carbonate, 4.0%-7.0% of nitric acid, 2.0%-5.0% of nickel nitrate, 0.2%-1.5% of nickel carbonate, 0.2%-1.0% of potassium pyrophosphate, 0.2%-1.0% of tartaric acid, 0.2%-1.0% of EDTA (Ethylene Diamine Tetraacetic Acid), 0.2%-1.0% of sodium citrate, 0.2%-1.0% of EDTMP (Ethylene Diamine Tetraacetic Acid) and the balance of pure water. The phosphating solution has the beneficial effects that a uniform and wear-resistant manganese phosphating film can be formed on the surface of a workpiece, the phosphating solution adopts a specific complexing agent combination, the generation of phosphated residues is reduced, the solution system proportion is adjusted, the influence of the complexing agent on the color of a film layer can be counteracted, the blackness of the original film layer is maintained, and the product quality is improved. Meanwhile, when the phosphating solution is applied, an iron ion concentration monitoring mechanism is established, real-time detection is performed through chemical titration or instrumental analysis, and a deslagging agent is added for centralized treatment when iron ions reach an upper limit value. The problem of surface defects caused by the fact that phosphated residues are attached to workpieces is solved.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a slag-free high-temperature manganese phosphating solution, its preparation method, and its application. Background Technology

[0002] In the field of metal surface treatment, high-temperature manganese phosphating technology is widely used in industries such as machinery manufacturing, automotive parts, and hardware tools because it can form a phosphating film with excellent wear resistance and corrosion resistance on the surface of metal workpieces such as steel. However, during the reaction process of traditional high-temperature manganese phosphating agents, the iron ions generated from the dissolution of the metal surface easily combine with phosphate and manganese ions in the phosphating agent to form a large amount of insoluble phosphate precipitate (i.e., phosphating slag). This phosphating slag not only suspends in the phosphating solution, causing unstable solution concentration and reduced film formation efficiency, but also adheres to the surface of the workpiece, causing surface defects such as pitting, scratches, and uneven thickness of the phosphating film, seriously affecting the appearance quality and performance of the workpiece. At the same time, the generation of a large amount of phosphating slag requires frequent tank emptying and slag cleaning, which not only increases the labor intensity of workers, but also leads to reduced utilization of the phosphating solution, increased production costs, and even environmental pressure due to the generated phosphating slag waste.

[0003] To improve the stability of the phosphating solution and reduce the formation of phosphating slag, some existing technologies add complexing agents to the phosphating agent to inhibit precipitation reactions by complexing free iron and manganese ions. However, the addition of most complexing agents will interact with the active ingredients in the phosphating film, causing the color of the phosphating film to gradually lighten from the ideal uniform black to grayish, or even show local color differences, which cannot meet the application scenarios with strict requirements for the appearance of the workpiece (such as precision mechanical parts, appearance parts, etc.). If the amount of complexing agent is reduced in order to maintain the film color, the problem of excessive phosphating slag will reappear, creating a contradiction between "the amount of complexing agent and the quality of film color", which is difficult to achieve simultaneously.

[0004] There is also the problem that solution stability and film-forming performance are difficult to coordinate. Phosphating solutions are difficult to balance among "solution stability, low sludge characteristics, film wear resistance, and film color quality", which restricts the further promotion and application of high-temperature manganese phosphating technology. Therefore, a slag-free high-temperature manganese phosphating solution, its preparation method, and its application are proposed. Summary of the Invention

[0005] To address the above technical problems, this invention provides a slag-free high-temperature manganese phosphating solution, its preparation method, and its application. This solution can form a uniform and wear-resistant manganese phosphating film on the surface of the workpiece while significantly reducing solution sediment.

[0006] The technical solution is as follows: The first aspect of this invention provides a slag-free high-temperature manganese-based phosphating solution, the key point of which is that the phosphating solution comprises the following components by weight percentage: phosphoric acid 22.0%-30.5%; Marif salt 3.0-8.5%; Manganese carbonate 3.5-8.0%; Nitric acid 4.0-7.0%; Nickel nitrate 2.0-5.0%; Nickel carbonate 0.2-1.5%; Potassium pyrophosphate 0.2-1.0%; Tartaric acid 0.2-1.0%; EDTA 0.2-1.0%; Sodium citrate 0.2-1.0%; EDTMP 0.2-1.0%; Pure water balance.

[0007] Preferably, the phosphating solution comprises the following components by weight percentage: Phosphoric acid 25.0%; Marif salt 6.0%; Manganese carbonate 6.0%; Nitric acid 5.0%; Nickel nitrate 3.0%; Nickel carbonate 1.0%; Potassium pyrophosphate 0.5%; Tartaric acid 0.5%; EDTA 0.2%; Sodium citrate 0.3%; EDTMP 0.3%; Pure water balance.

[0008] Preferably, the phosphoric acid is 85% phosphoric acid.

[0009] The potassium pyrophosphate, tartaric acid, sodium citrate, EDTMP, and EDTA are complexing agents that can complex excess metal ions in the solution, stabilize the tank solution, and inhibit sedimentation.

[0010] The second aspect of this invention provides a method for preparing a slag-free high-temperature manganese phosphating solution as described in the first aspect of this invention, comprising the following steps: S1: Potassium pyrophosphate, tartaric acid, sodium citrate and EDTMP were separately pre-dissolved in water to prepare aqueous solutions of potassium pyrophosphate, tartaric acid, sodium citrate and EDTMP, respectively. S2: Add pure water and phosphoric acid to the reactor and start stirring; S3: Add manganese carbonate to the reactor; S4: Add nitric acid to the reaction vessel; S5: Add the pre-dissolved EDTMP aqueous solution to the reactor; S6: Add nickel nitrate and nickel carbonate to the reactor; S7: Add the pre-dissolved tartaric acid aqueous solution to the reactor; S8: Add Marzaff salt and EDTA to the reactor; S9: Finally, add potassium pyrophosphate and sodium citrate aqueous solution to the reactor and stir continuously for a certain period of time to obtain a residue-free high-temperature manganese phosphating solution.

[0011] Preferably, in the preparation process, each step requires waiting for the added material to completely dissolve or react completely before proceeding to the next step.

[0012] Preferably, the stirring speed in step S2 is controlled at 350-450 r / min.

[0013] Preferably, when adding manganese carbonate to the reactor in step S3, the feeding rate of manganese carbonate is controlled to be slow to cope with the reaction that releases a large amount of carbon dioxide gas when manganese carbonate dissolves.

[0014] Preferably, after all materials are added, continue stirring for 11.5-12.5 hours.

[0015] The third aspect of the present invention provides the application of the phosphating solution as provided in the first aspect or the phosphating solution prepared in the second aspect, wherein the phosphating solution can be used for surface treatment of workpieces, and the application temperature is 93°C-97°C.

[0016] Preferably, when the phosphating solution is used to treat the surface of the workpiece, an iron ion concentration monitoring mechanism is established. The iron ion concentration in the phosphating solution is detected in real time by chemical titration or instrumental analysis. When the iron ion concentration reaches the upper limit, a slag remover is added for centralized treatment.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the phosphating solution can form a uniform and wear-resistant manganese phosphating film on the surface of the workpiece. The phosphating solution uses a specific combination of complexing agents to reduce the generation of phosphating slag. By adjusting the ratio of the solution system, the influence of the complexing agent on the film color can be offset, maintaining the original blackness of the film. At the same time, an iron ion concentration monitoring mechanism is established when the phosphating solution is applied. Real-time detection is achieved through chemical titration or instrumental analysis. When the iron ion concentration reaches the upper limit, a slag remover is added for centralized treatment. Compared with the traditional process, the present invention extends the slag removal frequency from daily / shift to a controllable cycle, solving the problem of surface defects caused by phosphating slag adhering to the workpiece. Attached Figure Description

[0018] Figure 1 This is a phase diagram of the phosphating film. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments. Example

[0020] A slag-free high-temperature manganese-based phosphating solution comprises the following weight percentages, as detailed below: 85% phosphoric acid 25%; Marif salt 6%; Manganese carbonate 6%; Nitric acid 5%; Nickel nitrate 1%; Nickel carbonate 1%; Potassium pyrophosphate 0.5%; Tartaric acid 0.5%; EDTA 0.2%; EDTMP 0.2%; Sodium citrate 0.3% Pure water balance.

[0021] Among them, Marif salt and manganese carbonate, both manganese salts, are the main cations providing manganese-based phosphating. Nitric acid acts as a promoter, providing an oxidizing environment for the solution, promoting phosphating film formation, and reducing the impact of hydrogen gas generated during the workpiece reaction on the uniformity of the phosphating film. Nickel nitrate and nickel carbonate are both catalysts, refining the crystal structure of the phosphating film, increasing the blackness of the phosphating film, and improving the corrosion resistance of the film. Potassium pyrophosphate, tartaric acid, EDTA, EDTMP, and potassium citrate are all complexing agents, capable of complexing excess metal ions in the solution, stabilizing the bath solution and inhibiting sedimentation. Potassium citrate also acts as a stabilizer, buffering the pH of the solution and stabilizing the free acidity of the solution.

[0022] A method for preparing a slag-free high-temperature manganese-based phosphating solution includes the following steps: S1: Potassium pyrophosphate, tartaric acid, sodium citrate and EDTMP were separately pre-dissolved in water to prepare aqueous solutions of potassium pyrophosphate, tartaric acid, sodium citrate and EDTMP, respectively. S2: Add pure water and phosphoric acid to the reactor and start stirring. The stirring speed is about 400 r / min. The stirring speed needs to be adjusted according to the equipment and the total configuration. S3: Add manganese carbonate to the reactor. When adding manganese carbonate, control the feeding rate of manganese carbonate to be slow to cope with the reaction that releases a large amount of carbon dioxide gas when manganese carbonate dissolves. S4: Add nitric acid to the reaction vessel; S5: Add the pre-dissolved EDTMP aqueous solution to the reactor; S6: Add nickel nitrate and nickel carbonate to the reactor; S7: Add the pre-dissolved tartaric acid aqueous solution to the reactor; S8: Add Marzaff salt and EDTA to the reactor; S9: Finally, add potassium pyrophosphate and sodium citrate aqueous solution to the reactor and stir continuously for 12 hours to obtain a residue-free high-temperature manganese phosphating solution.

[0023] During the preparation process, each step of the feeding process requires waiting until the added material is completely dissolved or the reaction is complete before proceeding to the next feeding step.

[0024] The application temperature of the prepared phosphating solution is 93-97℃. The phosphating time is determined by stopping the reaction on the workpiece, and the common phosphating time is 5-15 minutes. Example

[0025] Example 2 is prepared in the same way as Example 1, except that the proportions of the components are different. Specifically, it consists of 22.0% 85% phosphoric acid, 3.0% Marjoff salt, 6.4% manganese carbonate, 4.7% nitric acid, 5.0% nickel nitrate, 0.2% nickel carbonate, 1.0% potassium pyrophosphate, 0.2% tartaric acid, 1.0% EDTA, 0.3% EDTMP, 0.5% sodium citrate, and the balance being pure water. Example

[0026] Example 3 was prepared in the same way as Example 1, except that the proportions of the components were different. Specifically, it consisted of 30.5% 85% phosphoric acid, 5.0% Marjoff salt, 3.5% manganese carbonate, 7.0% nitric acid, 2.0% nickel nitrate, 0.52% nickel carbonate, 0.51% potassium pyrophosphate, 0.4% tartaric acid, 0.2% EDTA, 0.2% EDTMP, 0.6% sodium citrate, and the balance being pure water. Example

[0027] Example 4 was prepared in the same way as Example 1, except that the proportions of the components were different. Specifically, it consisted of 28.5% 85% phosphoric acid, 7.2% Marjoff salt, 8.0% manganese carbonate, 5.5% nitric acid, 2.9% nickel nitrate, 1.5% nickel carbonate, 0.84% ​​potassium pyrophosphate, 0.68% tartaric acid, 0.63% EDTA, 0.75% EDTMP, 1.0% sodium citrate, and the balance being pure water. Example

[0028] Example 5 was prepared in the same way as Example 1, except that the proportions of the components were different. Specifically, it consisted of 25.0% 85% phosphoric acid, 8.5% Marjoff salt, 5.8% manganese carbonate, 6.8% nitric acid, 4.2% nickel nitrate, 0.75% nickel carbonate, 0.2% potassium pyrophosphate, 1.0% tartaric acid, 0.49% EDTA, 1.0% EDTMP, 0.2% sodium citrate, and the balance being pure water.

[0029] When pure manganese-based phosphating solutions are used for surface treatment of metal workpieces, the phosphate ions (PO4) in the phosphating solution... 3- ) and manganese ions (Mn 2+ Fe can dissolve on the surface of metal workpieces. 2+ / Fe 3+ The reaction involves manganese-based phosphate crystallization, resulting in a pure manganese phosphate film. The main component of this film is (Mn,Fe)₅H₂(PO₄)₄·4H₂O, exhibiting high wear resistance. Typically, only oil immersion is required for rust prevention at the downstream end. It can also be used for friction reduction and wear-resistant treatment of moving parts, and as a carrier for rust-preventive oils. However, as the reaction continues, the dissolution of the workpiece surface leads to the accumulation of free iron ions in the solution. When the iron ion concentration exceeds a critical value, it combines with excess phosphate ions to form a precipitate, i.e., phosphate slag. Simultaneously, excess iron ions interfere with the normal growth of manganese-based phosphate crystals, resulting in a decrease in film density.

[0030] However, this invention, by combining complexing agents such as EDTA, EDTMP, potassium pyrophosphate, and tartaric acid, utilizes the amino, carboxyl, and phosphonic acid functional groups in their molecular structure to form stable chelates with free iron ions in the solution, thus reducing the formation of phosphating slag at the source. Simultaneously, it incorporates stabilizers such as potassium citrate to assist the complexing agents in enhancing their complexing ability with iron ions, expanding the stable complexing range, and regulating the activity of phosphate ions in the solution. This prevents excessively high local phosphate concentrations from reacting rapidly with iron ions, while maintaining the dissolution balance of manganese ions, ensuring a stable manganese ion concentration required for film formation.

[0031] This invention primarily achieves its goal by precisely controlling the ratio of complexing agent to stabilizer, enabling the complexation reaction to address excess iron ions (i.e., iron ions exceeding the requirements for film formation). This ensures both the thickness and density of the phosphating film while preventing excessive iron ions from converting into phosphating slag. Ultimately, it constructs a manganese-based phosphating solution system that synergistically achieves film formation efficiency, iron ion control, and system stability. Furthermore, the precisely controlled ratio can offset the influence of the complexing agent on the film color, maintaining the original film's blackness.

[0032] For the above-mentioned pure manganese phosphating solution, an iron ion concentration monitoring mechanism is established when treating the surface of metal workpieces. The specific details of the iron ion concentration monitoring mechanism are as follows: the iron ions in the pure manganese phosphating solution can be monitored by methods such as titration analysis, potentiometric titration, spectrophotometry, ICP spectroscopy, and electron energy dispersive spectroscopy. The optimal control range for iron ions is 2.0-8.0 g / L. The specific details of titration analysis and potentiometric titration are illustrated below.

[0033] For the titration analysis, transfer 10 mL of the phosphating working solution to an Erlenmeyer flask, dilute with 50 mL of distilled water, and then add 10 mL of 50% sulfuric acid solution. Titrate with potassium permanganate standard solution of known calibration concentration until the solution turns pink, and hold for 30 seconds until the color no longer changes; this is the endpoint.

[0034]

[0035] Where ρ: mass concentration of iron (g / L); C: Concentration of potassium permanganate standard solution (mol / L); V: Volume of potassium permanganate consumed (V); M: Molar mass of iron (55.85 g / mol); V0: Sampling volume.

[0036] Potentiometric titration: After the ferric ions in the solution are completely reduced to ferrous ions, the instrument uses potassium dichromate standard solution to plot an EV curve, observes the abrupt change in the curve, reads the volume, and analyzes and calculates the mass concentration of ferric ions in the solution.

[0037] However, as the phosphate reaction of the workpiece continues to increase, when the concentration of ferrous ions exceeds the limit, after the shift of production, a slag remover is added. The metal ions complexed by the complexing agent will then settle. A common and excellent slag remover is hydrogen peroxide, which has strong oxidizing properties and can remove ferrous ions that cause slag from the source without introducing new harmful anions. It will decompose at high temperatures in the solution. After the metal ions settle out, the solution is kept still, the supernatant is retained, and the lower part of the sludge is poured out. A small amount of sludge present in the solution will dissolve back into the solution as the temperature of the solution rises, thus maintaining the sludge-free characteristic of the production process.

[0038] Test Example 1 Taking Example 1 as an example, when the prepared manganese phosphating solution was diluted to a concentration of 6%, the total acid and acid ratio were tested. The test results showed that the total acid was 22-26 and the acid ratio was 5.5-6.5. A working solution with a concentration of 35% was prepared, which can be directly heated and used without the need for additional neutralizing agents or other materials for adjustment. The manganese-based phosphating solution prepared in Example 1 was used in the following process: degreasing-water washing-water washing-pickling-water washing-water washing-surface conditioning-phosphating-water washing-scalding. The phosphating process was as follows: a 35% working solution was prepared, the temperature was 95℃, and the phosphating time was 7 minutes. The surface of the metal workpiece planetary gear was then phosphating treated. After treatment, the workpiece surface was observed, and the phosphating film was tested. Specifically: Observe its crystallization, blackness and phosphate residue: the phosphate crystals of the workpiece are fine and dense, the phosphate film of the workpiece is uniformly covered, the blackness is high, and there is no color difference between the same workpieces of the same material and the same heat treatment state. Salt water resistance test of phosphating film: The phosphating workpiece treated with the phosphating solution prepared in Example 1 can remain rust-free for 3-4 hours after immersion in a 3% sodium chloride solution. The phosphating film showed no copper red corrosion after being exposed to copper sulfate for 3-4 minutes in a copper sulfate drop test. Roughness test of phosphating film: RA value of phosphating film 0.8-1.2; Phosphate film crystal phase diagram as follows Figure 1 As shown, the size of its phosphating crystals is approximately 7µm; Furthermore, the solution produces no residue during use, is clear, and has good stability. It will not adhere to the workpiece surface and affect the appearance of the workpiece due to the formation of phosphating residue.

[0039] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A residue-free high temperature manganese phosphating solution, characterized in that: The phosphating solution comprises the following weight percentage components: Phosphoric acid 22.0%-30.5%; Manganous salt 3.0-8.5%; Manganese carbonate 3.5-8.0%; Nitric acid 4.0-7.0%; Nickel nitrate 2.0-5.0%; Nickel carbonate 0.2-1.5%; Potassium pyrophosphate 0.2-1.0%; Tartaric acid 0.2-1.0%; EDTA 0.2-1.0%; Sodium citrate 0.2-1.0%; EDTMP 0.2-1.0%; 2. The residue-free high temperature manganese phosphating solution according to claim 1, characterized in that Pure water balance. The phosphating solution comprises the following weight percentage components: Phosphoric acid 25.0%; Manganous salt 6.0%; Manganese carbonate 6.0%; Nitric acid 5.0%; Nickel nitrate 3.0%; Nickel carbonate 1.0%; Potassium pyrophosphate 0.5%; Tartaric acid 0.5%; EDTA 0.2%; Sodium citrate 0.3%; EDTMP 0.3%; 3. The residue-free high temperature manganese-based phosphating solution according to claim 2, characterized in that: Pure water balance.

4. A method for preparing the residue-free high-temperature manganese phosphating solution according to any one of claims 1 to 3, characterized in that: The phosphoric acid is 85% phosphoric acid. The method comprises the following steps: S1: separately pre-solubilize potassium pyrophosphate, tartaric acid, sodium citrate and EDTMP in water to obtain potassium pyrophosphate aqueous solution, tartaric acid aqueous solution, sodium citrate aqueous solution and EDTMP aqueous solution; S2: add pure water and phosphoric acid into a reaction kettle and start stirring; S3: add manganese carbonate into the reaction kettle; S4: add nitric acid into the reaction kettle; S5: add the pre-solubilized EDTMP aqueous solution into the reaction kettle; S6: add nickel nitrate and nickel carbonate into the reaction kettle; S7: add the pre-solubilized tartaric acid aqueous solution into the reaction kettle; S8: add manganous salt and EDTA into the reaction kettle; 5. The method for preparing a slag-free high-temperature manganese phosphating solution according to claim 4, characterized in that: S9: finally, add potassium pyrophosphate and sodium citrate aqueous solution into the reaction kettle and continuously stir for a certain period of time to obtain a residue-free high-temperature manganese series phosphating solution.

6. The method for preparing the residue-free high-temperature manganese phosphating solution according to claim 5, characterized in that: Each step in the preparation process needs to wait for the complete dissolution or complete reaction of the added materials before proceeding to the next step.

7. The method for preparing a slag-free high-temperature manganese phosphating solution according to claim 6, characterized in that: The stirring speed in the S2 step is controlled at 350-450 r / min.

8. The method for preparing a slag-free high-temperature manganese phosphating solution according to claim 7, characterized in that: In the S3 step, when manganese carbonate is added into the reaction kettle, the feeding rate of manganese carbonate is controlled to be slow to cope with the reaction of releasing a large amount of carbon dioxide gas when manganese carbonate dissolves.

9. Use of a phosphating solution prepared according to the method of claims 4 to 8, characterized in that: After all the materials are added, continuously stir for 11.5-12.5 h.

10. The use of a residue-free high-temperature manganese phosphating solution according to claim 9, characterized in that The phosphating solution can be used for surface treatment of workpieces, and the application temperature is 93-97°C. When the phosphating solution is used for surface treatment of workpieces, an iron ion concentration monitoring mechanism is established, and the iron ion concentration in the phosphating solution is detected in real time through chemical titration or instrument analysis, and a residue removal agent is added for centralized treatment when the iron ion concentration reaches the upper limit value.

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