There are many kinds of cultural relics and a wide range. According to the chemical composition, it can be divided into metal cultural relics, inorganic non-metal cultural relics and organic cultural relics. It includes people's clothing, food, housing, transportation, science and technology, culture and many other aspects. Protecting unearthed cultural relics is of great significance for studying the culture, science and technology and life characteristics of working people in various historical periods. Therefore, the protection of cultural relics is essentially the protection of patterns, patterns, shapes, components and recorded historical events, people, technology and culture. , so that cultural relics have high data value, collection value and artistic value. Only by excavating cultural relics, studying their corrosive environment, and properly protecting them, can some "ancestral secret recipes" regain their luster.
I. Corrosion of cultural relics
Unearthed cultural relics, after careful treatment by archaeologists and chemists, can be directly stored in museums for preservation. The corrosion of cultural relics is mainly due to natural erosion and destruction before they are unearthed, which destroys the original appearance of cultural relics. At this time, most cultural relics exist in the atmosphere, soil and seawater (shipwreck remains), and their corrosion is quite complicated. Now briefly introduce the classification.
1. Corrosion of metal cultural relics
Metal cultural relics include gold, silver, copper, iron, tin and lead vessels, and the corrosion of them by the atmosphere is related to the composition of the atmosphere. The main corrosive substances are sulfide, SO2, SO3 and H2S. Nitride, NO, NO2, NH3, HNO3；; Chloride, Cl2, HCl, organic chloride, etc. These factors act on cultural relics, and the speed of corrosion depends on humidity, temperature, rainfall and sunshine in various regions and periods. Generally speaking, the liquid film visible to the naked eye on cultural relics is called wet atmospheric corrosion; The liquid film (actually existing) that is hard to see with naked eyes is called tidal atmospheric corrosion; Corrosion without liquid film is called dry atmospheric corrosion. The essence of atmospheric corrosion is chemical corrosion and micro-battery corrosion, and the most serious is wet atmospheric corrosion.
The corrosion of metal cultural relics buried in soil depends on the characteristics of soil, such as polyphase, capillary porosity, heterogeneity and relative fixity. Cultural relics mainly constitute macro-battery corrosion in soil. Including macro battery corrosion, such as iron buried horizontally in soil: iron | soil (I) | soil (II) | iron; The corrosion of macro batteries with local inhomogeneity is mainly caused by water permeability and air permeability. For example, the composition of bronzes is copper | soil C(O2)| soil C (O2 | copper; Different burial depths and different oxygen concentrations may lead to edge effects, such as metal (Ⅰ) | soil | metal (Ⅱ), and so on.
2. Corrosion of inorganic nonmetallic cultural relics
Stone carvings, stone carvings, cave temples, pottery, porcelain, jade, murals, clay sculptures and earthen sites are all inorganic non-metallic materials. The main corrosion forms are weathering, crevice corrosion, pitting corrosion and intergranular corrosion. Weathering refers to the gradual loss of water, deterioration, decomposition and fragmentation of crystalline substances in the atmosphere; Crack corrosion refers to the corrosion caused by foreign objects or structures that cause cracks in cultural relics, and the ions in the solution in the cracks cannot migrate and spread; Cavitation corrosion is similar to crevice corrosion, and ions in solution in holes or spots cannot migrate. As a result, the small hole continued to advance and the cultural relics were broken; Intergranular corrosion refers to the change of grain boundary area of different nonmetallic materials, which usually shows the change of physical properties caused by different conductivity to humidity and temperature. For example, the climate in the south is warm and humid all the year round, and lichens and mosses are easy to grow on the surface of stone carvings, coupled with the splitting of roots, chemical corrosion and biological weathering occur; Various degrees of acid rain and pore water, capillary water, CO2, SO2, O2 and NO2 are dissolved in condensed water, which makes the surface of stone carving denude, and the lines and figures on the surface are like powder, flake and grain. 1985 In Lianyungang 1 1 acid rain measurement, the pH value of acid rain was less than 5.6 in 8 times. Although the Kongkeshan stone carvings in this city are granite, they are also peeling off.
3. Corrosion of organic cultural relics
Organic cultural relics include paper products, textiles, bamboo lacquerware, leather, bone chips and buildings. Its corrosion includes biological corrosion, chemical corrosion and photolysis corrosion. The main components of organic cultural relics are fiber and protein, which absorb water and get wet to breed bacteria, so that fiber and protein are degraded into small molecular substances by bacteria, thus destroying the lines, colors and materials of cultural relics and presenting rot, which is biological corrosion. Chemical corrosion is closely related to the water absorption of organic matter. Because of the polarity of hydroxyl, carbonyl and peptide bonds in fiber and protein, it swells with water. At the same time, inorganic ions, acids, alkalis and salts are more easily dissolved and absorbed in it, which makes the fiber and protein decompose with time. Such as the water absorption and expansion process of fibers:
Impurities cause fibers and protein to change their structures. For example, acid and alkali can decompose β- 1, 4- glucoside bond in fiber, and can also hydrolyze peptide bond in protein to become brittle, hard and worse. At the same time, the swollen water and its impurities will spread and distort the colored pictures, characters and lines on the cultural relics, because the pigments used in organic cultural relics (such as red and yellow, madder, alizarin, etc.). ) all come from natural plants and are easily influenced by chemical environment and bacteria.
The photodegradation of organic cultural relics is also very serious. Long-term ultraviolet radiation will degrade fibers, protein and organic dyes. The physical and mechanical properties of cultural relics are degraded. For example, genes such as -OH, -SH and -—NH2 in dyes have poor light resistance, and β- 1, 4- glycoside in fibers and peptide bonds in protein are also affected by light. See the relationship between light wave and chemical bond energy in the table.
Under the initiation of photosensitizer (such as FeII, III, MnII, sizing agent, lignin, free chlorine, etc.). ), or directly irradiated with ultraviolet rays, fibers and protein are decomposed. For example:
The molecular chain gradually becomes shorter, the degree of polymerization decreases, or crosslinking occurs. With the increase of amorphous areas, the appearance of spherulite fibers and spherulite proteins fundamentally destroyed cultural relics.
It can be seen that the corrosion of cultural relics is mainly related to the chemical environment and the material of cultural relics. Understand its corrosion mechanism in order to preserve unearthed cultural relics.
Second, the protection of cultural relics
When unearthed, all kinds of cultural relics undergo mud removal, cleaning, rust removal and protection, and then they are put into storage by the museum. Its principle is aimed at the corrosion mechanism of cultural relics of various materials, and on the premise of not affecting the original appearance of cultural relics, the corrosion process is minimized. Its disadvantage is that it cannot fundamentally prevent cultural relics from continuing to corrode, and the protective layer needs to be painted regularly. This paper discusses the chemical problems in the protection of general cultural relics.
1. Metal cultural relics
Gold, silver and copper containers are protected by different methods, and the corrosion degree is different. Generally, only 2%NaOH or 1%HNO3 is used to clean the calcium and deposits on the surface of gold wares, while potassium tartrate solution is used to dissolve the floating rust on the inner layer of gold wares. Serious floating rust must be removed manually under a microscope. Silver rust spots include AgCl, Ag2O and Ag2S. Those with severe black film should be scrubbed with soft cloth dipped in CaCO3—-water slurry or NH3 H2O-C2H5OH and dilute Na2S2O3. Then, the silk soaked in 10%Pb(OAc)2 was isolated from the air and stored in an environment free of H2S and O3 at room temperature. The composition of bronze rust is complex, which often includes Cu2O, CuCl, CuCO3, Cu(OH)2, CuCl2 3cu (OH) 2) 2, Cu2(OH)2CO3 and so on. EDTA consists of NH3·H2O, alkaline glycerin (composed of 12g NaOH, 4mL glycerin and 100mL water), alkaline potassium sodium tartrate (composed of 5g NaOH, 15g potassium sodium tartrate and 100mL water), H2SO4—K2Cr2O7, and hexametaphosphate. You can also use 10%NaOH and proper amount of Zn and Al powder to make a paste and apply it to rusty parts, and then clean it after reduction. Brush benzotriazole on the surface and form it on the copper surface.
"He Zun" bronzes are still intact after this treatment, and the process is as follows:
The corrosion of iron is particularly complicated, and the components of rust are oxide sulfide, sulfate and phosphate. Remove large rust by hand when unearthed, and then use 10%HOAc (adding 0. 1 ~ 1% CrO42-, Cr2O72-, PO43-, pyridine and urotropine as corrosion inhibitors) for further rust removal. For example, a rust remover consisting of 435 parts of H3PO, 5 parts of butanol, 20 parts of ethanol, 1 part of hydroquinone and 39 parts of water also has the function of surface phosphating and rust prevention. Organic complexing agents such as sodium oxalate, sodium EDTA and sodium gluconate can also be used for rust removal. If the ironware is very fragile when unearthed, it should be soaked with 30 ~ 40% polyacrylic resin emulsion at 10 ~ 20mmhg, solidified and reinforced, and surface treated. There are four methods: (1) anticorrosion method: dicyclohexylamine nitrite 10, cyclohexylamine carbonate 10, water. (2) Phosphate protection method: soak with 10%H3PO4. (3) Tannate protection method: 200 copies of tannic acid, ethanol 150mL, water 100mL, repeated brushing for 6 times. (4) Surface sealing: after being treated by any one of the above methods, it is immersed in molten microcrystalline paraffin until it does not bubble. Take it out and wipe off the wax on the surface with a brush dipped in graphite powder.
Tin and lead containers are slightly rusted. Generally, the surface of tin ware is dark gray-white, that is, SnO and SnO2 rust. Zn and Pb were used as anodes and 10%NaOH was used as electrolyte for reduction, which was the same as the previous wax sealing treatment. The oxide film on the surface of lead is fine and also a protective layer. Special treatment: first soak it in 1.2 mol L- 1 HCl until it does not foam, then soak it in distilled water (boiling) for several times, and then soak it in 25 times of 1.2 mol L- 1nh4oac solution lhr. Soak it in distilled water several times after taking it out, then dry it with ethanol and acetone and seal it with wax.
2. Inorganic nonmetallic cultural relics
The protection of non-metallic cultural relics such as stone carvings, stone carvings and murals is mainly to repair damaged lines, characters and paintings in time and restore the original appearance of cultural relics. Then, apply a protective film against ultraviolet rays and use unsaturated polyester resin. Damaged and cracked cultural relics should be bonded and reinforced with resin. Such as polymethacrylic acid resin, polyvinyl acetate emulsion, polyvinyl butyral emulsion, etc. 1986, the Cultural Relics Management Committee of Jiaojiang City, Zhejiang Province dug up the fragments of the broken "Wang Jingwei couple kneeling statue monument" of the Japanese army. Repaired with adhesive, this patriotic textbook was preserved. Ceramic utensils are generally not corroded, and broken fragments can be bonded with epoxy resin.
3. Organic cultural relics
(1) green plant specimen: soak in 10% Cu (OAC) 2-HOAC solution and heat to 85 ~ 90℃. After the specimen turns green, take it out, rinse it, save it with 5% formaldehyde or 70% ethanol, or dry it. For the tender leaves and stems, they were soaked in the mixed solution consisting of ethanol 100 ml, water 100 ml, 36-38% methanol10/ml, glycerol 5.5 ml, acetic acid 5.5 ml and copper chloride 222 g for 3-5 days. The principle is as follows:
The treated green samples were protected by CMC-Na+ membrane.
(2) Paper cultural relics: When unearthed, they must be deacidified, disinfected and coated before they can be collected and preserved. There are many methods of deacidification, which can be divided into wet deacidification and dry deacidification. Wet deacidification is to soak paper products in alkaline solution or spray alkaline solution on paper products. Commonly used alkali liquor includes saturated solutions such as Ba(HCO3)2, Ca(HCO3)2, Sr(HCO3)2 and Mg(HCO3)2. Dry deacidification is fumigation with alkaline substances. Such as NH3, cyclohexylamine carbonate, moline, diethyl zinc, etc. The usual dosage is: NH3: H2O (1: 10), sealed for 24-36 hours, the pH value of the paper is reduced to 6.8-7.2, cyclohexylamine carbonate is immersed in the medicinal paper, inserted into the book every 50 pages and sealed for two weeks. Maureen is fumigated in vacuum 10 minute; Diethylzinc is also widely used in vacuum, but we must pay attention to safety. Deacidification often plays the role of sterilization at the same time. The mechanical properties and light resistance can be improved only by spraying CMC-Na+ liquid film on the surface of paper products.
(3) Bamboo, wood and lacquerware: When unearthed, they will crack and shrink when naturally dried, and must be dehydrated and set by chemical methods. Commonly used methods include alcohol ether method, polyethylene glycol method and silicone polymer method. The alcohol ether method is the simplest. First, cultural relics are constantly soaked in ethanol, and fresh ethanol is constantly replaced, so that the concentration of ethanol increases and the proportion of H2O decreases. Then soaked in ethanol instead of ethanol, ether is volatile and will not cause cell wall collapse. Finally, organic monomers (such as vinyl acetate) infiltrated into the reactor wall, and polymerization was strengthened under the irradiation of 60Co radioactive source. Then fumigate with ethylene oxide, carbon disulfide, etc. Insecticide and sterilization.
(4) Textile cultural relics: protection includes cleaning, rinsing, pest control, deterioration and reinforcement. Clean with boric acid (1%) first, and the process is as follows:
nabo 2·3H2O·H2O 2→nabo 2+3H2O+H2O 2
The released H2O2 does not exceed 0.7%, which will not damage the fabric. Secondly, reducing Na2S2O4, NaHSO2 CH2O 2H2O (sodium formaldehyde thiosulfate) and 5%HOAc were used for bleaching.
Fumigation with ethylene oxide can kill insects and act on the active groups such as —SH, OH, —NH2 and —COOH in bacteria and pest protein, thus achieving the effects of killing insects and sterilizing. The optimum operating conditions are: relative humidity 25 ~ 50%, 54℃. Finally, 5% nylon ethanol solution, 2% polymethylmethacrylate toluene solution and 5% polyvinyl acetal ethanol solution were selected to coat the protective layer for reinforcement. The "clay gold and silver flame printed yarn" unearthed in Mawangdui is reinforced and protected with raw rubber protein, and the effect is very good. The protection methods and steps of leather and bone fragments are similar. 1 ~ 3% trimethyl resin acetone solution was used to fill and bond the ivory fragments unearthed from Fu Hao's tomb 1976.
The protection of ancient buildings and cultural relics mostly adopts the method of repair and reinforcement rather than reconstruction. Generally, unsaturated polyesters are used as reinforcing agents. For example, the reinforcement of Ling 'en Temple in the Ming Tombs is to mix 307# resin and 18 1# resin in a ratio of 3: 1, and then add 2% o.p. (benzoyl peroxide) and 0.2% cobalt naphthalate, which can be used in the whole building component. After curing, it can be used with floor yellow and soil. The treatment also has the functions of moisture prevention, termite prevention and fire prevention.
In a word, the protection of unearthed cultural relics is an arduous task, and many new materials and technologies will be introduced into cultural relics protection soon. For example, silicone resin with good performance, 14C dating, X-ray diffraction phase analysis, scanning electron microscope and electron probe have been gradually applied to the analysis and protection of cultural relics. Better protect and develop the civilization left by our ancestors.
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