Acidic galvanized trivalent chromium black passivator as well as preparation method and application method thereof

Abstract

The invention provides an acidic zinc-plated trivalent chromium black passivator as well as a preparation method and an application method thereof, and relates to the technical field of electrochemical deposition. The acidic zinc-plating trivalent chromium black passivator comprises a component A and a component B with specific composition, the component A comprises a trivalent chromium compound, oxalic acid, sodium hydroxide, nickel sulfate, cobalt sulfate, citric acid and water, and the component B comprises thiosemicarbazide hydrochloride, cystine and water. And the corrosion resistance of the passivation layer is good.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical deposition, and in particular to an acid zinc plating trivalent chromium black passivating agent and a preparation method and an application method thereof. Background Art

[0002] Acid galvanizing itself does not have high corrosion resistance. Since the main component of acid galvanizing is zinc, if it is not passivated, it is easy to corrode in harsh environments, thereby forming white rust of zinc oxide or zinc hydroxide, which affects the protective and decorative effects of acid galvanizing.

[0003] Therefore, the surface of acid galvanizing is usually passivated. After passivation, the appearance and corrosion resistance of the acid galvanizing coating can be improved and enhanced. At present, the common black passivation process uses hexavalent chromium as a passivator, which has superior salt spray resistance and passivation appearance. However, hexavalent chromium is a highly toxic substance. If it is discharged without treatment, it will cause serious pollution to the environment. If the hexavalent chromium is treated, it will increase the production cost of the enterprise. Therefore, trivalent chromium passivation solution has gradually become the main demand of the market. However, the corrosion resistance and appearance of the trivalent chromium passivation layer are not as good as those of hexavalent chromium, and the stability of the trivalent chromium passivator is poor, the solution produces precipitation, and the appearance of the passivation layer is not full enough.

[0004] In view of this, it is necessary to design an improved acid zinc plating trivalent chromium black passivator and its preparation method and application method to solve the above problems. Summary of the invention

[0005] The invention aims to provide an acid zinc plating trivalent chromium black passivating agent and a preparation method and an application method thereof.

[0006] To achieve the above-mentioned purpose, the present invention provides, on the one hand, an acid zinc plating trivalent chromium black passivating agent, comprising component A and component B;

[0007] Taking mass percentage as 100%, the component A comprises:

[0008] Trivalent chromium compounds 14-19%;

[0009] Oxalic acid 4.5-5%;

[0010] Sodium hydroxide 1.5-3%;

[0011] Nickel sulfate 2-3%;

[0012] Cobalt sulfate 2-5%;

[0013] Citric acid 2-3%;

[0014] Deionized water 60-64.5%;

[0015] Taking mass percentage as 100%, the B component comprises:

[0016] Thiosemicarbazide hydrochloride 8-15%;

[0017] Cystine 5-10%;

[0018] Deionized water 75-87%.

[0019] Preferably, the trivalent chromium compound is one of chromium hydroxide, chromium sulfate and chromium chloride.

[0020] Preferably, based on 100% by mass, the agent A comprises:

[0021] Trivalent chromium compounds 19%;

[0022] Oxalic acid 4.5%;

[0023] Sodium hydroxide 2.5%;

[0024] Nickel sulfate 2.5%;

[0025] Cobalt sulfate 4%;

[0026] Citric acid 3%;

[0027] Deionized water 64.5%;

[0028] Taking mass percentage as 100%, the agent B comprises:

[0029] Thiosemicarbazide hydrochloride 8%;

[0030] Cystine 5%;

[0031] Deionized water 87%.

[0032] Furthermore, the present invention also provides a method for preparing the acid zinc plating trivalent chromium black passivating agent, comprising the following steps:

[0033] The trivalent chromium compound, oxalic acid and deionized water are mixed, heated at 85-90°C for 0.5-1h, and cooled to room temperature after the heating to obtain a trivalent chromium compound solution; sodium hydroxide aqueous solution is added dropwise to the trivalent chromium compound solution, mixed evenly, and nickel sulfate, cobalt sulfate and citric acid are added to obtain component A after the addition is completed;

[0034] Thiosemicarbazide hydrochloride, cystine and deionized water are uniformly mixed to obtain component B.

[0035] Preferably, the mass percentage of each raw material in the A component meets the following conditions: trivalent chromium compound 14-19%, oxalic acid 4.5-5%, sodium hydroxide 1.5-3%, nickel sulfate 2-3%, cobalt sulfate 2-5%, citric acid 2-3%.

[0036] Preferably, the mass percentages of the raw materials in the B component meet the following conditions: 8-15% thiosemicarbazide hydrochloride, 5-10% cystine.

[0037] Preferably, the trivalent chromium compound is one or more of chromium hydroxide, chromium sulfate and chromium chloride.

[0038] On the other hand, the present invention provides an application method of an acid zinc plating trivalent chromium black passivating agent, comprising the following steps:

[0039] Inject component A, component B and deionized water into the passivation tank, maintain the temperature of the passivation tank at 20-40°C, stir for 5-10 minutes, and let stand for 2-3 hours;

[0040] Next, the pH of the mixed solution is adjusted to 2.0 to perform a passivation treatment on the acid galvanized workpiece.

[0041] Preferably, the volume ratio of the component A, the component B and the deionized water is (0.08-0.1):(0.08-0.1):1.

[0042] The beneficial effects of the present invention are:

[0043] The acid zinc plating trivalent chromium black passivator provided by the present invention comprises a component A and a component B of specific composition, wherein the component A comprises a trivalent chromium compound, oxalic acid, sodium hydroxide, nickel sulfate, cobalt sulfate, citric acid and water, and the component B comprises thiosemicarbazide hydrochloride, cystine and water. The passivator proposed by the present invention is prepared by using the component A and the component B, and the two can be mixed when needed to avoid the property change of the passivator during storage, thereby improving the stability of the passivator; secondly, the present invention regulates the content of each raw material, and the passivation layer produced by the passivator has better color than the conventional passivator, and the passivation layer has good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The appearance photos of the workpieces of Examples 1-4 before testing;

[0045] Figure 2 This is a photo of the appearance of the workpiece of Example 1-4 after the workpiece was tested for 120 hours;

[0046] Figure 3 This is a photo of the appearance of the workpiece of Example 1-4 after the workpiece was tested for 288 hours;

[0047] Figure 4 This is a photo of the appearance of the workpiece of Example 1-4 after the workpiece was tested for 480 hours;

[0048] Figure 5 These are optical photographs of various acid galvanized workpieces treated with the passivator prepared in Example 4. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0051] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0052] On the one hand, the acid zinc plating trivalent chromium black passivator provided by the present invention includes component A and component B, and the mass percentage is 100% (taking the mass percentage of deionized water as an example, which represents the ratio of the mass of deionized water to the mass sum of all raw materials of the corresponding component), component A includes:

[0053] Trivalent chromium compounds 14-19%;

[0054] Oxalic acid 4.5-5%;

[0055] Sodium hydroxide 1.5-3%;

[0056] Nickel sulfate 2-3%;

[0057] Cobalt sulfate 2-5%;

[0058] Citric acid 2-3%;

[0059] Deionized water 60-64.5%;

[0060] Taking mass percentage as 100%, component B includes:

[0061] Thiosemicarbazide hydrochloride 8-15%;

[0062] Cystine 5-10%;

[0063] Deionized water 75-87%.

[0064] In some embodiments, the trivalent chromium compound is one of chromium hydroxide, chromium sulfate, and chromium chloride.

[0065] Furthermore, the present invention also provides a method for preparing the above-mentioned acid zinc plating trivalent chromium black passivating agent, which specifically comprises the following steps:

[0066] The trivalent chromium compound, oxalic acid and deionized water are mixed, heated at 85-90° C. for 0.5-1h, and cooled to room temperature (20-30° C.) after the heating is completed to obtain a trivalent chromium compound solution; sodium hydroxide aqueous solution is added dropwise to the trivalent chromium compound solution, and after uniform mixing, nickel sulfate, cobalt sulfate and citric acid are added. After the addition is completed, the mass percentage of each raw material in the mixed solution is ensured to meet the following conditions: 14-19% of the trivalent chromium compound, 4.5-5% of oxalic acid, 1.5-3% of sodium hydroxide, 2-3% of nickel sulfate, 2-5% of cobalt sulfate, and 2-3% of citric acid. If the above conditions are not met, additional deionized water needs to be added to ensure that the content of each raw material meets the required conditions, that is, component A is obtained;

[0067] Thiosemicarbazide hydrochloride, cystine and deionized water are uniformly mixed to obtain component B.

[0068] On the other hand, the present invention also provides an application method of the above acid zinc plating trivalent chromium black passivator, comprising the following steps:

[0069] Inject component A, component B and deionized water into the passivation tank, maintain the temperature of the passivation tank at 20-40°C, stir for 5-10 minutes, and let stand for 2-3 hours;

[0070] Next, the pH of the mixed solution is adjusted to 2.0 to perform passivation treatment on the acidic galvanized workpiece. The passivation treatment time is 60 seconds and the temperature is 25° C. The pH of the mixed solution in the above process can be adjusted by sodium hydroxide solution and / or hydrochloric acid solution.

[0071] In some embodiments, the volume ratio of component A, component B, and deionized water is (0.08-0.1):(0.08-0.1):1.

[0072] The acid zinc plating trivalent chromium black passivating agent and its preparation method and application method proposed by the present invention are further described below in conjunction with specific embodiments:

[0073] Example 1

[0074] This embodiment prepares an acid zinc plating trivalent chromium black passivator, which includes component A and component B, and the preparation method is as follows:

[0075] 19g of chromium hydroxide, 4.5g of oxalic acid and 20mL of water were mixed, stirred at 85°C for 0.5h, and after the stirring was completed, the mixture was allowed to stand and cooled to 20°C to obtain a trivalent chromium compound solution; 2.5g of sodium hydroxide and 21mL of water were mixed, and the mixture was stirred until the sodium hydroxide was completely dissolved to obtain a sodium hydroxide solution; the sodium hydroxide solution was added dropwise to the trivalent chromium compound solution and stirred, and after the addition was completed, 2.5g of nickel sulfate, 4g of cobalt sulfate and 3g of citric acid were added to supplement the remaining water to obtain component A;

[0076] 5 g of cystine, 8 g of 3,3'-dithiodialanine and 87 mL of water were mixed and stirred to dissolve to obtain component B.

[0077] Furthermore, this embodiment also explores the passivation ability of the above-mentioned passivator during the application process, and the specific method is as follows: 100mL of component A, 100mL of component B and 800mL of deionized water are added to the passivation tank, mixed and stirred at 30°C for 5min, and allowed to stand for 2h after the stirring is completed. The pH is adjusted to 2, and the acid galvanized workpiece (specifically, a bolt made of carbon steel) is passivated for 60s at a passivation temperature of 25°C.

[0078] Example 2

[0079] This embodiment prepares an acid zinc plating trivalent chromium black passivator, which includes component A and component B, and the preparation method is as follows:

[0080] 19g of chromium chloride, 4.5g of oxalic acid and 20mL of water were mixed, stirred at 85°C for 0.5h, and after the stirring was completed, the mixture was allowed to stand and cooled to 20°C to obtain a trivalent chromium compound solution; 2.5g of sodium hydroxide and 21mL of water were mixed, and the mixture was stirred until the sodium hydroxide was completely dissolved to obtain a sodium hydroxide solution; the sodium hydroxide solution was added dropwise to the trivalent chromium compound solution and stirred, and after the addition was completed, 2.5g of nickel sulfate, 4g of cobalt sulfate and 3g of citric acid were added to supplement the remaining water to obtain component A;

[0081] 5 g of cystine, 8 g of 3,3'-dithiodialanine and 87 mL of water were mixed and stirred to dissolve to obtain component B.

[0082] Furthermore, this embodiment also explores the passivation ability of the above-mentioned passivator during the application process, and the specific method is as follows: 100mL of component A, 100mL of component B and 800mL of deionized water are added to the passivation tank, mixed and stirred at 30°C for 5min, and allowed to stand for 2h after the stirring is completed. The pH is adjusted to 2, and the acid galvanized workpiece (specifically, a bolt made of carbon steel) is passivated for 60s at a passivation temperature of 25°C.

[0083] Example 3

[0084] This embodiment prepares an acid zinc plating trivalent chromium black passivator, which includes component A and component B, and the preparation method is as follows:

[0085] 19 g of chromium sulfate, 4.5 g of oxalic acid and 20 mL of water were mixed, stirred at 85° C. for 0.5 h, and after the stirring was completed, the mixture was allowed to stand and cooled to 20° C. to obtain a trivalent chromium compound solution; 2.5 g of sodium hydroxide and 21 mL of water were mixed, and the mixture was stirred until the sodium hydroxide was completely dissolved to obtain a sodium hydroxide solution; the sodium hydroxide solution was added dropwise to the trivalent chromium compound solution and stirred, and after the addition was completed, 2.5 g of nickel sulfate, 4 g of cobalt sulfate and 3 g of citric acid were added to supplement the remaining water to obtain component A;

[0086] 5 g of cystine, 8 g of 3,3'-dithiodialanine and 87 mL of water were mixed and stirred to dissolve to obtain component B.

[0087] Furthermore, this embodiment also explores the passivation ability of the above-mentioned passivator during the application process, and the specific method is as follows: 100mL of component A, 100mL of component B and 800mL of deionized water are added to the passivation tank, mixed and stirred at 30°C for 5min, and allowed to stand for 2h after the stirring is completed. The pH is adjusted to 2, and the acid galvanized workpiece (specifically, a bolt made of carbon steel) is passivated for 60s at a passivation temperature of 25°C.

[0088] Example 4

[0089] This embodiment prepares an acid zinc plating trivalent chromium black passivator, which includes component A and component B, and the preparation method is as follows:

[0090] 19g of chromium chloride, 4.5g of oxalic acid and 20mL of water were mixed, stirred at 85°C for 0.5h, and after the stirring was completed, the mixture was allowed to stand and cooled to 20°C to obtain a trivalent chromium compound solution; 2.5g of sodium hydroxide and 21mL of water were mixed, and the mixture was stirred until the sodium hydroxide was completely dissolved to obtain a sodium hydroxide solution; the sodium hydroxide solution was added dropwise to the trivalent chromium compound solution and stirred, and after the addition was completed, 2.5g of nickel sulfate, 4g of cobalt sulfate and 3g of citric acid were added to supplement the remaining water to obtain component A;

[0091] 5 g of cystine, 8 g of 3,3'-dithiodialanine and 87 mL of water were mixed and stirred to dissolve to obtain component B.

[0092] Furthermore, this embodiment also explores the passivation ability of the above-mentioned passivator during the application process. The specific method is as follows: 100 mL of component A, 100 mL of component B and 800 mL of deionized water are added to the passivation tank, mixed and stirred at 30°C for 7 minutes, and allowed to stand for 3 hours after the stirring is completed. The pH is adjusted to 2, and the acid zinc plating is passivated. The passivation time is 60 seconds and the passivation temperature is 25°C.

[0093] The acidic galvanized workpieces (specifically bolts made of carbon steel) after passivation in Examples 1-4 were subjected to neutral salt spray accelerated corrosion tests, and the experimental method was ISO9227:2022 (E). The experimental results are shown in Table 1. The appearance changes of the workpieces of Examples 1 to 4 with the test time during the test are shown in the figure Figure 1-4 In particular, the present invention also explores the applicability of the above passivating agent in the passivation treatment of other workpieces. The optical photographs of other workpieces after passivation treatment with the passivating agent prepared in Example 4 are as follows: Figure 5 As shown, the results show that the passivating agent prepared by the present invention can be applied to the surface passivation treatment of various acid galvanized workpieces.

[0094] Table 1 Corrosion test results of Examples 1-4

[0095] Experiment time Example 1 Example 2 Example 3 Example 4 96h No white rust No white rust No white rust No white rust 120h White rust No white rust White rust No white rust 288h No red rust White rust No red rust White rust 480h No red rust No red rust No red rust No red rust

[0096] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A black passivating agent for acid zinc plating trivalent chromium, characterized in that: It includes component A and component B; Taking mass percentage as 100%, the component A comprises: Trivalent chromium compounds 14-19%; Oxalic acid 4.5-5%; Sodium hydroxide 1.5-3%; Nickel sulfate 2-3%; Cobalt sulfate 2-5%; Citric acid 2-3%; Deionized water 60-64.5%; Taking mass percentage as 100%, the B component comprises: Thiosemicarbazide hydrochloride 8-15%; Cystine 5-10%; Deionized water 75-87%.

2. Acid zinc plating trivalent chromium black passivator according to claim 1, characterized in that, The trivalent chromium compound is one of chromium hydroxide, chromium sulfate and chromium chloride.

3. Acid zinc plating trivalent chromium black passivator according to claim 1, characterized in that, Taking mass percentage as 100%, the agent A comprises: Trivalent chromium compounds 19%; Oxalic acid 4.5%; Sodium hydroxide 2.5%; Nickel sulfate 2.5%; Cobalt sulfate 4%; Citric acid 3%; Deionized water 64.5%; Taking mass percentage as 100%, the agent B comprises: Thiosemicarbazide hydrochloride 8%; Cystine 5%; Deionized water 87%.

4. A method for preparing a trivalent chromium black passivating agent for acid zinc plating, characterized in that: The steps include: The trivalent chromium compound, oxalic acid and deionized water are mixed, heated at 85-90°C for 0.5-1h, and cooled to room temperature after the heating to obtain a trivalent chromium compound solution; sodium hydroxide aqueous solution is added dropwise to the trivalent chromium compound solution, mixed evenly, and nickel sulfate, cobalt sulfate and citric acid are added to obtain component A after the addition is completed; Thiosemicarbazide hydrochloride, cystine and deionized water are uniformly mixed to obtain component B.

5. The preparation method according to claim 4, characterized in that: The mass percentage of each raw material in the A component meets the following conditions: 14-19% of trivalent chromium compound, 4.5-5% of oxalic acid, 1.5-3% of sodium hydroxide, 2-3% of nickel sulfate, 2-5% of cobalt sulfate, and 2-3% of citric acid.

6. The preparation method according to claim 4, characterized in that: The mass percentages of the raw materials in the B component meet the following conditions: 8-15% thiosemicarbazide hydrochloride, 5-10% cystine.

7. The preparation method according to claim 4 or 5, characterized in that: The trivalent chromium compound is one or more of chromium hydroxide, chromium sulfate and chromium chloride.

8. An application method of the acid zinc plating trivalent chromium black passivator as described in any one of claims 1-3, characterized in that: The steps include: Inject component A, component B and deionized water into the passivation tank, maintain the temperature of the passivation tank at 20-40°C, stir for 5-10 minutes, and let stand for 2-3 hours; Next, the pH of the mixed solution is adjusted to 2.0 to perform a passivation treatment on the acid galvanized workpiece.

9. The application method according to claim 8, characterized in that: The volume ratio of the component A, the component B and the deionized water is (0.08-0.1):(0.08-0.1):1.

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