Environment-friendly rust transforming agent and preparation method thereof

Abstract

According to the environment-friendly rust transforming agent and the preparation method thereof, a tea polyphenol-tannic acid-ascorbic acid-sodium gluconate food-grade quaternary synergistic transformation system is constructed, chelate precipitation is inhibited through specific coordination of sodium gluconate and Fe < 3 + >, and the problem that an existing plant extract transforming agent is prone to losing efficacy during storage is solved; the reaction endpoint is quantitatively judged through the pH response of the purple cabbage anthocyanin and the potassium ferrocyanide-Fe < 3 + > chromogenic reaction, and the visualization is good; the device has the advantages of being safe, non-toxic, low in cost, high in stability, high in education adaptability and the like, can be widely applied to household metal appliance maintenance, small metal handicraft protection and teenager chemical experiment teaching, and has remarkable application value.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to an environmentally friendly rust converter and its preparation method. Background Technology

[0002] Metal corrosion (mainly composed of Fe2O3·nH2O) is a major cause of failure in household and small metal products, necessitating a low-cost and safe treatment solution. Existing technologies suffer from the following key deficiencies, and no patents or literature have yet proposed a systematic solution.

[0003] The technical bottlenecks of existing conversion agent systems include: Plant extract-based conversion agents: The tannic acid-based conversion agent disclosed in Chinese patent CN2019102832.5 uses only a single plant extract, resulting in low conversion efficiency (requiring more than 30 minutes to treat rusted cast iron) and the absence of stabilizers. After one week of accelerated aging at 30°C, the chelate precipitation rate reaches 5.2%, which cannot meet the needs of long-term household storage. Although the tannic acid-organic acid system in Japanese patent JP2018052693 improves the conversion rate, it contains trace amounts of corrosive organic acids (such as citric acid derivatives), and skin irritation tests (rabbits) show slight redness and swelling, making it unsuitable for use in adolescent experiments.

[0004] Synthetic chelating agent conversion agents: Commercially available EDTA and DTPA products (such as a certain brand of "environmentally friendly rust remover") have poor biodegradability (BOD5 / COD < 0.3), and their conversion efficiency decreases by 3.1% after one week of accelerated aging at 30℃. Moreover, the raw materials need to be purchased from professional chemical channels (household users do not have the qualifications to purchase them), and the cost of treating a household iron pot once exceeds 0.5 yuan (low cost performance). Acid-based corrosion converters: Phosphoric acid and hydrochloric acid products (such as a certain industrial rust remover) have a corrosion rate of more than 0.1 mm / year on the metal substrate, and the waste liquid has a pH < 2. Random discharge will cause the soil pH value to drop by 0.5-1.0 units (according to research data from Volume 42 of Environmental Chemistry in 2023). They are completely unsuitable for home and educational settings.

[0005] In the field of STEM education (science, technology, engineering, and mathematics) tools for teenagers, the following deficiencies exist: 1) Lack of educational adaptability: Existing conversion agents are not designed for the cognitive characteristics of adolescents—there is a lack of "visual phenomena-basic principles" connection in junior high school (such as no teaching module on the correspondence between color changes and pH), and there is a lack of "quantitative analysis-advanced principles" experimental support in senior high school (such as no scheme for determining the stability constant of chelates), making it impossible to integrate into the STEM curriculum system.

[0006] 2) High barriers to home use: Commercial conversion agents require high temperature and high pressure to prepare (e.g., a certain product requires 120℃, 0.2MPa reaction for 2 hours), and home users do not have professional equipment; some products require precise concentration control (error ±0.1%), and the failure rate of non-professionals exceeds 40% (based on survey data of 100 home users).

[0007] 3) Uncontrollable reaction process: Existing products rely solely on a single pH indicator (such as phenolphthalein or methyl orange), which cannot determine the Fe content. 3+ Whether the transformation is complete or not, problems often arise such as "over-treatment causing the iron pot to become thinner" or "under-treatment causing it to rust again within a month," with only 52% of household users reporting a satisfactory experience.

[0008] In summary, it is necessary to overcome the shortcomings of existing technologies and develop a rust converter that is environmentally friendly, stable, and has a high conversion rate to meet the needs of STEM education tools for teenagers. Summary of the Invention

[0009] Therefore, the purpose of this invention is to provide a rust converter that is environmentally friendly, stable, and has a high conversion rate, so as to promote its use in STEM education tools for teenagers.

[0010] To solve the above problems, the present invention provides the following solution: The first aspect of the present invention is to provide an environmentally friendly rust converter, which, by mass percentage, comprises: 4-6% tea polyphenols, 2-4% tannic acid, 1-3% natural reducing agent, 1-2% sodium gluconate, 0.3-0.7% purple cabbage concentrate, 0.1% potassium ferrocyanide, and the balance being deionized water.

[0011] Furthermore, the natural reducing agents are vitamin C and / or vitamin E.

[0012] Furthermore, the pH value of the environmentally friendly rust converter is 3.8-4.2.

[0013] Preferably, the pH value is adjusted by adding sodium citrate-malate buffer solution.

[0014] Preferably, the mass ratio of sodium citrate to malic acid in the sodium citrate-malic acid buffer solution is 3:2, and the buffer solution concentration is ≥0.05mmol / L.

[0015] Furthermore, the purple cabbage concentrate is obtained by juicing fresh purple cabbage, with a juice extraction rate of ≥80% and an anthocyanin content of ≥0.1%.

[0016] The second aspect of the present invention is to provide a method for preparing the environmentally friendly rust converter described in the first aspect, comprising the following steps: S1. Prepare a pH buffer solution; S2. Add the natural reducing agent and sodium gluconate to the buffer solution and stir well; S3. Add tea polyphenols and tannins in sequence and dissolve them completely; S4. Add purple cabbage concentrate and potassium ferrocyanide; S5. Filter the solution prepared in step S4 to obtain the environmentally friendly rust converter.

[0017] Furthermore, the dissolution process of the tea polyphenols and / or tannins is carried out by heating.

[0018] Furthermore, the filtration uses a 0.4-2μm filter membrane.

[0019] A third aspect of the present invention is to provide an experimental teaching kit for rust conversion, comprising the environmentally friendly rust conversion agent described in the first aspect, and auxiliary tools; the auxiliary tools include at least one of a pH testing tool, a color recognition tool, and a calculation tool.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The environmentally friendly rust converter provided by this invention contains tea polyphenols (catechol) and tannic acid (polyhydroxyl), which react with Fe through phenolic hydroxyl groups. 3+ Forming a six-membered ring chelate, ascorbic acid partially binds Fe. 3+ Reduced to Fe 2+ (Reducing chelation steric hindrance and increasing conversion rate), sodium gluconate reacts with Fe via α-hydroxyl groups. 3+ It forms an auxiliary coordination structure, inhibits chelate aggregation and precipitation, and has high stability; the purple cabbage concentrate exhibits a gradual color change with pH, ​​from red to purplish-red to bluish-purple to blue to blue to blue-green, indicating that potassium ferrocyanide reacts with unreacted Fe... 3+ The formation of Prussian blue precipitate provides dual indications to ensure complete reaction. Furthermore, all components of the rust converter are environmentally friendly, safe, and non-toxic. The solution has a mild pH value that does not cause strong corrosion. Overall, it meets the requirements for environmental protection, stability, and high conversion rate, making it suitable for STEM education tools for teenagers. Detailed Implementation

[0021] The following embodiments are used to illustrate the present invention, but do not limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0022] In one embodiment of the present invention, an environmentally friendly rust converter is proposed, comprising, by mass percentage: 4-6% tea polyphenols, 2-4% tannic acid, 1-3% natural reducing agent, 1-2% sodium gluconate, 0.3-0.7% purple cabbage concentrate, 0.1% potassium ferrocyanide, and the balance being deionized water.

[0023] In the above embodiments, the mechanism of action of the environmentally friendly rust converter is as follows: 1) Tea polyphenols (catechol) and tannic acid (polyhydroxy) react through phenolic hydroxyl groups with Fe. 3+ Formation of a six-membered ring chelate (stability constant K=10) 23-28 The reducing agent will partially reduce Fe 3+ Reduced to Fe 2+ Sodium gluconate reduces steric hindrance and increases conversion rate by reacting with Fe through α-hydroxyl groups. 3+ Formation of auxiliary coordination structure (K=10) 20 This inhibits the aggregation and precipitation of chelates, resulting in high stability. 2) The purple cabbage concentrate exhibits a gradient of color change with pH: "red (pH=3.0) → purplish-red (pH=3.5) → bluish-purple (pH=4.0) → blue (pH=4.5) → blue-green (pH=5.0)" (the linear correlation coefficient R between RGB color values ​​and pH is...). 2 =0.99), potassium ferrocyanide reacts with unreacted Fe 3+ The formation of Prussian blue precipitate (detection limit 0.01 mol / L) provides a dual indication to ensure the completeness of the reaction; 3) All components of the rust converter are environmentally friendly, with a biodegradability (BOD5 / COD) of 0.85 (meeting the first-class standard of GB / T27857-2011), a waste liquid pH of 4.0-6.0, and a direct discharge effect on soil pH of <0.1 unit; the corrosion rate on cast iron is <0.008 mm / year (determined by gravimetric method), which is 20% lower than commercially available EDTA products; it is safe and non-toxic, and showed no redness or swelling reaction in skin irritation tests (rabbit).

[0024] 4) Excellent conversion performance: The protective film thickness is 6.2±0.3μm (0 grade of cross-cut adhesion, GB / T9286-1998), and there is no new rust after 30 days of salt water immersion (3.5% NaCl solution, 25℃). The salt spray resistance time (36h) of the product in CN2019102832.5 is improved by 33%.

[0025] In a preferred embodiment, the natural reducing agent is at least one of common vitamin-based reducing agents such as vitamin C and vitamin E, preferably vitamin C (ascorbic acid), which has strong reducing properties and can partially reduce Fe. 3+ Reduced to Fe 2+ This reduces chelation steric hindrance and increases the conversion rate.

[0026] In the above embodiments, the pH value of the environmentally friendly rust converter is 3.8-4.2, which is specifically adjusted by adding sodium citrate-malate buffer solution; preferably, the mass ratio of sodium citrate to malic acid in the sodium citrate-malate buffer solution is 3:2, and the buffer solution concentration is ≥0.05mmol / L.

[0027] In a preferred embodiment, the purple cabbage concentrate is obtained by juicing fresh purple cabbage, with a juice extraction rate of ≥80% and an anthocyanin content of ≥0.1%.

[0028] In a preferred embodiment, the environmentally friendly rust converter comprises, by mass percentage: 5% tea polyphenols, 3% tannic acid, 2% ascorbic acid, 1.5% sodium gluconate, 3% sodium citrate-malic acid buffer, 0.5% purple cabbage concentrate, 0.1% potassium ferrocyanide, and the balance being deionized water.

[0029] In the above embodiments, the stability results of the environmentally friendly rust converter are as follows: after accelerated aging at 30℃ for one week (test method: GB / T38571-2020, acceleration conditions: constant temperature at 30℃, protected from light, and sealed), the conversion efficiency decreases by ≤1%, the chelate precipitation rate is ≤0.5%, and after refrigerated storage at 4-8℃ for 6 months, the precipitation rate is ≤3%. In comparison, under the same conditions without sodium gluconate, the accelerated aging precipitation rate reaches 5.2%, and the conversion efficiency decreases by 5.1%. Under the same accelerated aging conditions, the precipitation rate of the commercially available EDTA system reaches 3.3%, and the conversion efficiency decreases by 3.1%.

[0030] The environmentally friendly rust converter provided in the above embodiments is suitable for the following application scenarios: 1) Household scenarios: Rust removal from everyday utensils such as iron pots, iron nails, metal furniture, and gardening tools; 2) Cultural and creative scenarios: Rust repair and protection of small metal crafts (such as wrought iron ornaments and retro badges); 3) Educational scenarios: Adaptable to STEM experimental teaching at different grade levels, including junior high school (observation of acid-base reactions) and senior high school (principles of coordination chemistry).

[0031] In the second embodiment, a method for preparing the environmentally friendly rust converter described in the above embodiments is proposed, the steps of which include: S1. Prepare a pH buffer solution; S2. Add the natural reducing agent and sodium gluconate to the buffer solution and stir well; S3. Heat to 50-60℃, add tea polyphenols and tannic acid in sequence until fully dissolved to obtain a brownish-yellow solution; S4. Add concentrated purple cabbage extract and potassium ferrocyanide until dissolved; the solution turns blue-purple. S5. Cool to room temperature (25±2℃), filter with a 0.4-2μm filter membrane, put into a brown glass bottle (light protection rate ≥95%), and store at 4-8℃ to prepare an environmentally friendly rust converter.

[0032] In the above embodiments, the preparation process is simple and convenient. A homogeneous, environmentally friendly rust-converting agent solution can be obtained simply by stirring and heating. Water bath heating and heat preservation can be performed using a common household rice cooker. A glass rod can be used for manual stirring, and coffee filter paper can be used for filtration. These materials are readily available in homes and easy to operate. Through the simultaneous preparation of the buffer and reduction systems, the preparation time is short, and a single household user can complete the process.

[0033] In the third embodiment, a rust conversion experimental teaching kit is proposed, including the environmentally friendly rust conversion agent described in the first embodiment, and auxiliary tools; the auxiliary tools include at least one of a pH testing tool, a color recognition tool, and a calculation tool.

[0034] The above-mentioned rust conversion experimental teaching kit is suitable for the quantitative detection of Fe. 3+ At the same time, it can gradually visualize and observe Fe. 3+ The transformation process can also be used to determine the stability constant of chelates, providing experimental teaching support for "visualized phenomena - quantitative analysis - advanced principles" experiments, which can meet the cognitive acceptance level of teenagers. Through independent experimental verification by a high school student, the experimenter can complete the entire process of "preparing 4 sets of gradient samples - measuring the precipitation rate over one week - analyzing the coordination principle" within 2 hours. The understanding of the knowledge point of "coordination chemistry" is improved from "being able to describe color change phenomena" to "being able to explain the coordination mechanism of sodium gluconate inhibiting precipitation". The operation difficulty is suitable for high school students to complete independently, and the teaching effect is significant.

[0035] In a preferred embodiment, the pH detection tool includes, but is not limited to, portable tools such as pH test strips and pH meters; the color recognition tool includes, but is not limited to, colorimetric cards and recognition software; and the calculation tool is used to calculate indicators such as rust removal rate and sedimentation rate.

[0036] In the following examples, the tea polyphenols were derived from green tea extract with a purity ≥98% and a catechol content ≥85% (HPLC detection, detection method: GB / T31740-2022). Tannins were derived from gallnut extract with a purity ≥95% and gallic acid content ≥60% (titration method, GB / T27903-2011). Ascorbic acid was food grade with a purity ≥99% and an oxidation potential ≤0.34V (25℃, potentiometric titration). Sodium gluconate was food grade with a purity ≥98% and reacted with Fe... 3+ Coordination stability constant K=10 20(Potential titration method, refer to GB / T3049-2006). The sodium citrate-malate buffer pair has a buffer capacity β ≥ 0.05 mol / L·pH (determined by pH meter method within the pH range of 3.8-4.2). The concentrated purple cabbage extract is obtained from fresh purple cabbage juice (juice yield ≥ 80%), with anthocyanin content ≥ 0.1% (spectrophotometric method, GB / T31532-2022). Potassium ferrocyanide is analytical grade and reacts with Fe... 3+ Colorimetric threshold ≤ 0.01 mol / L (25℃, visual colorimetric method). Deionized water conductivity ≤ 10 μS / cm (measured with a conductivity meter, GB / T6682-2022 Grade I water standard). Preparation Example 1: Preparation of an environmentally friendly rust converter 1. Mix sodium citrate (1.5g) and malic acid (1g), add 51.24g of deionized water (60% of the total volume), and place in a 60℃ constant temperature water bath (temperature fluctuation ±2℃); use a polytetrafluoroethylene stirring paddle, first stir at 200rpm for 5min (for initial dissolution to avoid excessively high local concentration), then increase to 300rpm and stir for 7min (for uniform mixing) to form a buffer solution with pH=4.0±0.1 (buffer capacity β=0.06mol / L·pH). 2. Add ascorbic acid (2g) and sodium gluconate (1.5g) to the buffer solution simultaneously, and stir at 300rpm for 8min. 3. First add tea polyphenols (5g), stir at 300rpm for 10min (55℃, to promote the activation of phenolic hydroxyl groups), then add tannic acid (3g), heat to 60℃ and continue stirring for 20min to form a brownish-yellow homogeneous solution; 4. Add 0.5g of concentrated purple cabbage extract and 0.1g of potassium ferrocyanide, stir at 250rpm for 5min, the solution turns blue-purple; 5. After cooling to room temperature, filter through a 0.45μm mixed cellulose ester filter membrane, and store in a brown glass bottle (light protection ≥95%) at 4-8℃.

[0037] Preparation Example 2 Prepare 500 mL of environmentally friendly rust converter according to the components in Preparation Example 1 above, using a home-operable method. Specifically, use a rice cooker for water bath insulation (temperature fluctuation ±2℃, calibrated with a kitchen thermometer), manually stir with a glass rod (100 revolutions / minute, with a timing wristband for prompting), and filter with coffee filter paper (pore size ≈1μm).

[0038] The preparation was carried out according to the preparation steps of Preparation Example 1. The total preparation time was 42 min. The solution clarity was 98% (1.2 NTU measured by turbidity meter, GB / T5750.4-2023), the conversion efficiency was 95% (comparable to the standard process), and the operation failure rate was 3% (only 3 out of 100 repeated experiments resulted in local precipitation due to uneven stirring), which meets the needs of home operation.

[0039] Test case The environmentally friendly rust converter obtained in Example 1 was subjected to accelerated aging for one week under constant temperature, light-proof, and sealed conditions with two existing products (CN2019102832.5 and commercially available EDTA product). The conversion efficiency and chelate precipitation rate were determined according to GB / T38571-2020, and the results are as follows: Test method description: 1. Conversion efficiency: Gravimetric method, take the same rusted cast iron sheet (50mm×50mm×2mm, rusted area 80%), weigh it after treatment, and calculate the rust removal rate (conversion efficiency = (rust mass before treatment - residual mass after treatment) / rust mass before treatment × 100%). 2. Sedimentation rate: Centrifugation method, take 100mL of sample, centrifuge at 3000rpm for 10min, collect the precipitate, dry and weigh it. Sedimentation rate = (precipitate mass / total sample mass) × 100%; 3. Calculation Basis: Referring to the Arrhenius equation (lnk=-Ea / (RT)+lnA), the activation energy Ea is taken as 80kJ / mol (the conventional value for chelates of plant extracts), and the temperature coefficient Q... 10 =2. Accelerated aging at 30℃ for one week is equivalent to approximately 6 months of refrigerated storage at 4℃.

[0040] Conclusion: The accelerated aging stability of this invention is significantly better than that of existing products in one week, and it can be stored for a long time, avoiding the limitations of a 6-month long-term test.

[0041] Application Example 1: Verification of Applications in Cultural and Creative Scenarios A rusted wrought iron badge (50mm in diameter, 60% rust area, made of low-carbon steel) was selected and treated with the environmentally friendly rust converter from Preparation Example 1. The operating steps are as follows: 1) Remove surface rust with a soft-bristled brush; 2) Apply the conversion agent evenly (approximately 0.5 mm thick); 3) Use the "Rust Conversion Assistant" APP to identify the RGB color value in real time. When the color value changes from (80,120,180) to (120,180,80) (18 min), stop the reaction; 4) Rinse with clean water and let it air dry naturally; Results: A dark blue protective film (5.8 μm thick, measured by a coating thickness gauge) formed on the surface of the badge. No new rust appeared after 6 months of storage, and the badge maintained its retro texture.

[0042] Application Example 2: High School STEM Teaching Experiment (Independent Operation by a Single High School Student) A high school student independently completed an inquiry-based experiment on "Coordination Chemistry and Precipitation Control" in a home / laboratory setting: 1) Experimental objective: To analyze the effect of sodium gluconate content on the stability of the converter over one week and to understand the principles of coordination chemistry; 2) Experimental preparation: Teaching aid kit (including safety measuring spoon, anti-splash dropper, electronic scale (accuracy 0.1g), rice cooker, glass rod, 4 brown sample bottles), and experiment manual.

[0043] 3) Experimental steps: a. Prepare four groups of conversion agents with sodium gluconate content of 0%, 1%, 1.5%, and 2% (50 mL per group, with the amount of other components reduced proportionally) independently according to the preferred component ratio, and record the color change of the solution during the preparation process (e.g., the 0% group showed slight turbidity in the early stage, while the 1.5% group was clear throughout the process). b. After sealing the 4 groups of samples, place them in a constant temperature environment of 30℃ (a constant temperature incubator or a warm, dark place can be used, and the temperature should be monitored in real time with a thermometer) and let them stand for one week. During this period, record the RGB color value of the solution every day through the "Rust Conversion Assistant" APP (if there is no obvious change, the influence of pH fluctuation is excluded). c. One week later, take 10 mL of sample from each group, centrifuge at 3000 rpm for 10 min (in a home setting, a manual centrifuge can be used or the supernatant can be collected after standing for 24 hours), dry the precipitate and weigh it, and calculate the precipitation rate (repeat 3 times and take the average value to reduce operational errors). d. Conjugated polyphenol-Fe 3+ Analyze the coordination structure, examine the relationship between sodium gluconate content and precipitation rate, and write an experimental report. 4) Experimental results (data from individual high school students, average of 3 replicates): Teaching effectiveness: 100% of the experimenters completed the experiment independently (without external assistance), and the experiment took about 2 hours (including a week of resting). Their understanding of coordination chemistry progressed from "phenomenal cognition" to "principle application", proving that this conversion agent is suitable for the independent experimental needs of high school students and can be used as a practical carrier for STEM teaching.

[0044] This invention is not limited to the description in the specification and embodiments. Therefore, other advantages and improvements can be readily realized by those skilled in the art. Thus, without departing from the spirit and scope of the general concept defined by the claims and their equivalents, this invention is not limited to the specific details, representative schemes and described embodiments.

Claims

1. An environmentally friendly rust converter, characterized in that, By mass percentage, the components are: 4-6% tea polyphenols, 2-4% tannins, 1-3% natural reducing agent, 1-2% sodium gluconate, 0.3-0.7% purple cabbage concentrate, 0.1% potassium ferrocyanide, and the balance being deionized water.

2. The environmentally friendly rust converter according to claim 1, characterized in that, The natural reducing agents are vitamin C and / or vitamin E.

3. The environmentally friendly rust converter according to claim 1, characterized in that, The environmentally friendly rust converter has a pH value of 3.8-4.

2.

4. The environmentally friendly rust converter according to claim 3, characterized in that, The pH value was adjusted by adding sodium citrate-malate buffer solution.

5. The environmentally friendly rust converter according to claim 4, characterized in that, The sodium citrate-malate buffer solution has a mass ratio of sodium citrate to malic acid of 3:2 and a buffer concentration of ≥0.05mmol / L.

6. The environmentally friendly rust converter according to claim 1, characterized in that, The purple cabbage concentrate is obtained by juicing fresh purple cabbage, with a juice extraction rate of ≥80% and an anthocyanin content of ≥0.1%.

7. The method for preparing the environmentally friendly rust converter according to any one of claims 1-6, characterized in that, step include: S1. Prepare a pH buffer solution; S2. Add the natural reducing agent and sodium gluconate to the buffer solution and stir well; S3. Add tea polyphenols and tannins in sequence and dissolve them completely; S4. Add purple cabbage concentrate and potassium ferrocyanide; S5. Filter the solution prepared in step S4 to obtain the environmentally friendly rust converter.

8. The preparation method according to claim 7, characterized in that, The dissolution process of tea polyphenols and / or tannins involves heating.

9. The preparation method according to claim 7, characterized in that, The filtration uses a 0.4-2μm filter membrane.

10. A rust transformation experimental teaching kit, characterized in that, It includes the environmentally friendly rust converter as described in any one of claims 1-6, and auxiliary tools; the auxiliary tools include at least one of a pH testing tool, a color recognition tool, and a calculation tool.

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