PH range for chemical reagent rust removal of iron cultural relics

Abstract

The invention belongs to the technical field of ironware cultural relic repair, and relates to a pH range for iron cultural relic chemical reagent rust removal. The pH value of the phosphoric acid diluted solution ranges from 1 to 2, and a proper amount of ethylenediamine tetraacetic acid (EDTA). The pH range provided by the invention can be easily fixed during chemical reaction based on the pH range of the phosphoric acid solution, and ethylenediamine tetraacetic acid (EDTA) has very strong complexing ability with metal ions under an acidic condition, so that the rust removal reaction rate of the ironware cultural relics is increased, the rust removal is stably carried out, the rust removal time is shortened, the repair efficiency is improved, and the service life of the ironware cultural relics is prolonged. Investment of manpower and material resources is reduced.

Description

Technical Field

[0001] The invention relates to a pH range of a chemical reagent for removing rust from iron artifacts. Background Art

[0002] During the Song, Liao, and Jin dynasties, ironmaking was primarily carried out in blast furnaces, and ironmaking techniques were mature. Two production methods were used: casting and forging. Casting involves melting pig iron into molten iron, pouring it into a mold, and casting it into an object. Objects produced by casting were mostly large, such as pots. Forging involves forging wrought iron into objects, and while it can produce relatively strong steel, it still has some brittleness. The book "The Exploitation of the Works of Nature" describes ironmaking as follows: "To forge iron into an object, one uses wrought iron. First, cast iron forms an anvil, serving as the hammering surface. ... Wrought iron and steel, after being hammered in the furnace, are not yet hardened by the combination of water and fire. While still out of the furnace, they are quenched in clear water. This is called 'Jigang Jitie,' meaning that before being quenched, they are still steel or iron, and their fragility remains..." This describes the ancient ironmaking methods used by humans.

[0003] The smelting process of iron artifacts means they are essentially composed of an alloy of iron and carbon. These artifacts are highly reactive and easily react with air, moisture, sulfides, and chlorides, making them susceptible to corrosion, forming an oxide film primarily composed of ferrous oxide and ferric oxide. These oxides do not cause significant corrosion to iron artifacts, but once exposed to moisture, the ferric oxide immediately reacts with the water, forming a loose, porous rust layer that severely corrodes the artifacts.

[0004] Guo Xing (Protection of Iron Artifacts in Museums [J]. Collection and Investment, 2022, 13(10):140-142.), Meng Dan et al. (A Brief Discussion on the Moderation in the Restoration of Iron Artifacts - Taking the Restoration of Two Iron Artifacts Unearthed from Huludao as an Example [J]. Journal of Liaoning Provincial Museum, 2012, (00):268-274.), Wang Haotian et al. (Protection and Restoration of Iron Artifacts Unearthed from Weijiazhuang Site [J]. Southern Cultural Relics, 2016, (04):258-268.), Wang Cheng (A Brief Discussion on the Restoration and Protection of Metal Artifacts in Museum Collections [J]. Cultural Relics Appraisal and Appreciation, 2020, (02):84-85.) and many other articles have summarized the rust removal methods of iron artifacts into two methods. One is physical rust removal, which uses tools to polish and remove rust. Currently, this method is mostly used for rust removal because it is safer and more controllable, and reduces damage to the iron matrix. The other is chemical rust removal, which uses chemical reagents or electrophoresis to remove rust. Chemical rust removal is used for metal artifacts with heavy pollutants. Guo Xing (Protection of Museum Iron Artifacts [J]. Collection and Investment, 2022, 13 (10): 140-142.) mentioned that acidic solutions, alkaline solutions, etc. can be used to reasonably configure rust removal solution reagents. Zhao Shengwei et al. (Protecting Historical Traces with Metal Artifacts Protection and Restoration Technology [J]. Cultural Industry, 2024, (15): 94-96.) mentioned that commonly used chemical cleaning solutions include weak acids (citric acid, oxalic acid) and strong bases (sodium hydroxide, potassium hydroxide). These solutions can react chemically with pollutants on the metal surface and quickly dissolve the pollutants. Wang Haotian et al. (Protection and Restoration of Iron Artifacts Excavated from the Weijiazhuang Site [J]. Southern Cultural Relics, 2016, (04): 258-268.) mentioned that the chemical rust removal method is to use 0.01 mol / L NaOH aqueous solution to soften the rust, and then continue to remove it mechanically. Wang Cheng (A Brief Discussion on the Restoration and Protection of Metal Cultural Relics in Museums [J]. Cultural Relics Appraisal and Appreciation, 2020, (02): 84-85.) mentioned in his article that the commonly used methods for using solutions to clean rust on the surface of ironware are: (1) organic solvent cleaning, such as ethanol, acetone, etc.; (2) applying 1% EDTA tetrasodium salt or trisodium salt solution to the corroded area on the surface of objects with less corrosion to remove the calcification layer; (3) using 5%-10% citric acid solution, 5%-10% phosphoric acid or 20% phosphorous acid, plus certain preservatives such as 1% sodium nitrite and sodium sulfite, the oxide layer can be softened and then removed. At the same time, phosphoric acid can form a phosphate protective layer on the surface of the object; (4) For the removal of harmful chlorides contained in ironware, 5% sodium sesquicarbonate soaking is generally used. Pan Yusheng et al. (Research on the Restoration and Protection of Han Dynasty Ironware in Guangxi Museum [J]. Cultural Relics Protection and Archaeological Science, 2006, (03): 5-10+67-70.) used a chemical rust removal method of soaking in EDTA disodium solution. The specific operation was to soak the double-ring ear iron cauldron in 7.5% EDTA disodium solution for 22 hours, and most of the dirt and harmful rust had been removed.The chemical reagents mentioned in Bai Jingzhi's article (Protection and Restoration of Metal Cultural Relics in Museum Collections [J]. Cultural Relics Appraisal and Appreciation, 2022, (18): 33-36.) include EDTA, citric acid, thiourea, ammonia water, and formic acid reagents for rust removal. Sun Xiaoqiang (Protection and Restoration of Corroded Ironware [J]. Cultural Relics Restoration and Research, 2003, (00): 61-72.) also mentioned that rust removers include formic acid, oxalic acid, acetic acid, citric acid, sodium citrate, sodium oxalate, ethylenediaminetetraacetic acid and its salts, and emphasized that the concentration of the reagents should be controlled at a low concentration of less than 5%. It also explained that EDTA and its sodium salt with a concentration of 5%-15% at a pH of about 5-6 are more effective in removing rust. Feng Zhaojuan (A Brief Discussion on the Restoration and Protection of Ironware Excavated from the Tomb of the Nanyue King [A]. Proceedings of the Fourth Annual Academic Conference of the China Association for the Protection of Cultural Relics [C]. China Association for the Protection of Cultural Relics: 2005: 51-52.) used the phosphoric acid immersion method to remove rust. The specific operation was to first clean the surface of the iron sword that had been treated with polymer materials with acetone solution, then heat it to 40℃ with 1% dilute phosphoric acid to phosphate the ironware, and use 7% "hexamethylenetetramine" as a neutralization and corrosion inhibitor. Landesheng (On the Protection and Restoration of Ironware Cultural Relics from the Qin Terracotta Warriors Pit [J]. The Museum of the Mausoleum of the First Qin Emperor, 2011, (00): 396-407.) mentioned that the rust removers include aqueous solutions of oxalic acid, acetic acid, citric acid, phosphoric acid, ammonium citrate, etc., and also mentioned that EDTA and its salts are more effective in removing rust under weak acidic conditions.

[0005] The chemical methods in the above articles mentioned the concentration of the reagents during rust removal, but rarely mentioned the pH of the reagents. The present invention proposes the optimal pH value for rust removal using phosphoric acid reagents. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a pH range of a reagent solution suitable for rust removal of ironware with low rust removal cost and good rust removal effect.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is: A rust removal reagent solution: phosphoric acid (analytical grade) is used and diluted with purified water to obtain phosphoric acid solutions with pH ranges of 1-2, 3-4, and 5-6. Ethylenediaminetetraacetic acid (analytical grade) is added and the rust removal ironware is immersed or applied to the solution. Comparative tests are conducted to analyze which pH range is most effective for rust removal.

[0008] Taking into account the varying degrees of rust caused by different casting methods and the excavated preservation environment, the five iron artifacts used in this restoration were forged and cast, respectively. Their surfaces are covered in rust and earthenware, lacking any decorative patterns. A magnet was used to test the core strength, revealing a high attraction, indicating the core is intact. All five iron artifacts were collected from the site, where they reacted with water and oxygen in the soil, resulting in surface rust.

[0009] Phosphoric acid dissolves iron oxides and softens the hard rust on iron artifacts. As a ternary, medium-strong acid, phosphoric acid maintains a stable pH range during the rust removal process for iron artifacts. The removal rate is relatively stable. However, sulfuric acid or hydrochloric acid reacts with large amounts of iron oxide, causing the pH to rise rapidly and the overall reaction rate to become unstable.

[0010] Ethylenediaminetetraacetic acid (EDTA) has a strong complexing ability with metal ions under acidic conditions. The ferric phosphate formed by the reaction of phosphoric acid and iron oxide is insoluble in water. Without EDTA, the rust removal reaction will initially proceed rapidly, but the insoluble ferric phosphate will coat the surface of the object, causing the rust removal rate to drop sharply. EDTA complexes with the iron ions in the solution and dissolves in water, keeping the overall rust removal reaction ongoing.

[0011] First, three phosphoric acid solutions with different pH ranges were added with an appropriate amount of EDTA and then soaked or applied to ironware. Different pH ranges resulted in different rust removal effects. The rust removal effect in the pH ranges of 1-2 and 3-4 was greater than that in the pH range of 5-6. This indicates that the pH range of the solution affects the rust removal effect, with the rust removal effect ranking from pH 1-2 to pH 3-4 and then to pH 5-6.

[0012] The above results are obviously different from the conclusion of Sun Xiaoqiang (Protection and Restoration of Corroded Ironware [J]. Cultural Relic Restoration and Research, 2003, (00): 61-72.) that EDTA and its salts (concentration 5%-15%) are effective in removing rust at a pH of around 5-6. The rust removal method using EDTA in a phosphoric acid solution at pH 1-2 is more efficient and the rust removal reaction is more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a photo of Example 1-2 before rust removal in the invention of phosphoric acid rust removal application.

[0014] Figure 2 、 3 These are photos of Example 1-2 of the present invention after rust removal. DETAILED DESCRIPTION

[0015] Example 1:

[0016] Place the ironware in boiling water for 30 minutes, then take it out and dry it.

[0017] Mix phosphoric acid and purified water in a 1:9 volume ratio to create a diluted phosphoric acid solution. Measure the pH value to 1-2 using pH paper. Add an appropriate amount of EDTA as a chelating agent. Soak the ironware in the solution for 4-5 hours, and the rust will begin to fall off. Prepare a phosphoric acid solution using the same ratio as above and continue soaking until all the rust is gone.

[0018] Weigh 1g of anhydrous sodium carbonate and dissolve it in 500ml of water to make a sodium carbonate solution. Soak the rust-removed ironware in the solution. After soaking, rinse it in purified water. After soaking and rinsing, titrate with silver nitrate to test for the presence of chloride ions. After testing for chloride ions, dry the ironware.

[0019] Take a certain amount of white wax, add it to water and boil it until it melts. Place the ironware in it until no bubbles appear on the surface of the ironware, then take it out.

[0020] After the ironware is dry, apply B72 solution on the surface of the ironware to seal it.

[0021] Example 2:

[0022] Place the ironware in boiling water for 30 minutes, then take it out and dry it.

[0023] Mix phosphoric acid and purified water in a 1:9 volume ratio to create a diluted phosphoric acid solution. Measure the pH value to 1-2 using pH paper. Add an appropriate amount of EDTA as a chelating agent. Soak the iron in the solution for 4-5 hours. The rust will begin to fall off, and eventually all the rust will be removed.

[0024] The ironware after rust removal is soaked in distilled water and the presence of chloride ions is detected by silver nitrate titration.

[0025] Take a certain amount of white wax, add it to water and boil it until it melts. Place the ironware in it until no bubbles appear on the surface of the ironware, then take it out.

[0026] After the ironware is dry, apply B72 solution on the surface of the ironware to seal it.

[0027] Example 3:

[0028] Place the ironware in boiling water for 30 minutes, then take it out and dry it.

[0029] Mix 0.2ml of phosphoric acid with 500ml of purified water to create a diluted phosphoric acid solution. Measure the pH using pH paper to determine if it is 3-4. Add an appropriate amount of EDTA as a chelating agent. Soak the ironware in the solution for 5 hours, and the rust will begin to fall off.

[0030] Adjust the solution pH to 1-2 and continue soaking until the rust is completely removed.

[0031] The ironware after rust removal is soaked in distilled water and the presence of chloride ions is detected by silver nitrate titration.

[0032] Take a certain amount of white wax, add it to water and boil it until it melts. Place the ironware in it until no bubbles appear on the surface of the ironware, then take it out.

[0033] After the ironware is dry, apply B72 solution on the surface of the ironware to seal it.

[0034] Example 4:

[0035] Place the ironware in boiling water for 30 minutes, then take it out and dry it.

[0036] Mix 0.2 ml of phosphoric acid and 1500 ml of pure water to make a diluted phosphoric acid solution. Measure the pH value of the solution to 5-6 using pH test paper. Add an appropriate amount of EDTA as a complexing agent to the phosphoric acid solution. Soak the ironware in the solution.

[0037] After soaking for about a week, the rust was almost gone.

[0038] Example 5:

[0039] According to the above method, phosphoric acid solutions with pH values of 1-2, 3-4, and 5-6 were prepared respectively. After soaking absorbent cotton in the three solutions, the solutions were applied to the surface of the ironware.

[0040] After about 3 to 4 hours, it was found that the amount of rust on the absorbent cotton at pH 1-2 and 3-4 was greater than that on the absorbent cotton at pH 5-6.

Claims

1. A pH range for rust removal of iron artifacts, characterized in that When the pH of the phosphoric acid reagent solution is within the range of 1-2, adding an appropriate amount of ethylenediaminetetraacetic acid (EDTA) can effectively remove rust. When the pH is within the range of 1-2, stubborn rust can be removed, the rust removal time is shortened, and the rust removal rate is relatively stable.

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