Most of the iron is mainly iron, and carbon combined alloy, China is the world's earliest use of iron countries, so China unearthed a lot of valuable iron relics, has become an important study of China's social and historical evolution . . Because the iron relics have been buried in the ground for a long time and have been seriously corroded, and after excavation, due to the sharp changes in the environment, the degree of corrosion of iron has been aggravated, and if effective protective measures are not taken, it will be completely unrecognizable in a few years. The following lists the main factors for the formation of rust in iron artifacts and the method steps for protecting iron artifacts for reference:
First, the main factors that make iron corrosion
Usually the damage to excavated iron artifacts is rust, expansion, cracking, deformation, etc., and the chemical properties of iron are more active than copper, so in the natural environment, iron is more difficult to preserve than bronze. The influencing factors of iron in different burial sites are complex, and in summary, there are eight factors that make iron rust: structural defects of the iron itself, oxidation atmosphere, humid environment, pH value of the soil, soluble salts in the buried environment, the influence of chloride ions, sulfur dioxide in the industrial atmosphere, the rust layer formed in the soil of the iron and the rust layer formed in the warehouse are out of sync with the drying and shrinkage effect.
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Second, the methods and steps for the protection of iron artifacts
First, surface cleaning and rust removal. The purpose is to remove the outer layer of loose rust, retain the inner layer of rust, and stabilize and strengthen its protective effect on the iron matrix. The tools used are bamboo knives, scalpels, dental drills, etc. If the iron artifacts are well preserved, they can be cleaned with chemical reagents or electrochemical cleaning, and different concentrations of phosphoric acid, phosphorous acid, citric acid, EDTA trisodium salt or tetrasodium salt, sodium hexametaphosphate and so on are commonly used.
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Second, desalting. Ultrasonic cleaning with deionized water or 5% sodium sesquite carbonate, using alternating hot and cold methods to remove soluble salts, and regularly change the solution until the concentration of chloride ions in the solution is detected below 4 mg/L. After desalting, it is repeatedly washed with deionized water and soaked with ethanol solution to allow it to dry naturally.
Third, reinforcement and repair. In order to prevent the cracking part of the artifact from continuing to expand, orthopedic and reinforced repair measures are required for the artifact. Orthopedics is mainly a corrective measure taken for the change in the shape of the utensil due to the squeezing or cracking of the object by external force. Restoration, on the other hand, is mainly aimed at the fragility or mutilation of the utensils. Generally, according to the degree of corrosion and fragility of the utensils, epoxy resins and polyacrylic acid resins are selected to break and stick the iron back to the original place. The missing part can be replaced or not according to the actual situation.
Fourth, corrosion inhibition. In order to slow down the corrosion rate of iron artifacts, it is necessary to choose suitable metal corrosion inhibitors, such as benzotriazole (BTA), tannins, phosphates, and sodium molybdate and sodium silicate.
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Fifth, sealing. Better iron sealing materials are silicone substances, but the price is expensive, and the surface color of the utensils is slightly deepened after treatment, generally using trichloromethane or butyl acetate solution for sealing treatment, the concentration is 1% to 5%. In a fume hood, apply to the surface of the utensils with a soft-bristled brush and remove after natural drying.
Sixth, sealed deaeration preservation. After the above steps of the iron cultural relics, but also need to be sealed and deoxygenated preservation, optional RP protection materials can be used to encapsulate the treated iron cultural relics, put oxygen absorber inside, or seal the utensils and fill them with nitrogen for preservation. When the warehouse is stored, it should also make a capsule box to avoid physical damage and achieve the purpose of long-term safe storage.
The above are the main factors and protection methods and steps of rust of iron artifacts, and it can be seen that providing an effective protection environment for restored iron is the key to consolidating the restoration results, and it is also the basis for its academic research and exhibition. For the collection of iron artifacts, the use of safe and reliable protection facilities is the guarantee for the long-term display of iron relics.