Study On Erosion Diseases Of Plaster Of The Statues Or Murals By Water Vapor And Microorganisms In The Air

Statues or murals,as treasures in ancient Chinese art palaces,have extremely high historical,cultural,and scientific value.However,due to long-term natural factors and human factors,diseases such as disruption,crater eruption,flaking,color alteration,mildew,and diseases by microbiological corrosion are commonly found in statues/murals,which seriously threaten the preservation of cultural relics and are major problems in the protection of cultural relics.In order to scientifically and effectively maintain the preservation of statues or murals,this study takes plaster of the statue or mural as the research object,and conducts the research on the moisture absorption and desorption characteristics of the water vapor in the air to plaster and the simulation research on the corrosion of plaster by microorganisms in dustfall,In-depth discussion of the occurrence mechanism and influence mechanism of diseases in plaster,to provide references for the preservation,restoration and daily maintenance of statues or murals.（1）The research on the absorption-desorption characteristics of water vapor in the air to plaster shows that:1)The moisture absorption-desorption kinetics test of plaster shows that when the temperature is 15℃,the moisture absorption rates per unit area of the coarse mud block and the fine mud block have double exponential growth relationship with time.When humidifying,the amount of absorbing moisture is less than the amount of absorbing moisture,and part of the water will be trapped between the particles of plaster.When the conditions are suitable,water and salt migration can be carried out,which is easy to cause water and salt diseases.2)The isothermal moisture absorption test of plaster shows that at 15℃,the isothermal hygroscopic curves of the coarse mud block,fine mud block,fine+coarse mud block,white ash+fine+coarse mud block belong to the typeⅡadsorption isotherm.As porous mediums,they can perform single-layer or multi-layer isothermal adsorption.3)Research on the factors influencing the moisture absorption of plaster shows:（1）The greater the relative humidity of the preservation environment,the more water molecules are filled in the space,and the easier block is to absorb moisture.The experimental results show that the critical relative humidity of the block is about 80%at a temperature of15°C,indicating that a humidity environment with a relative humidity lower than 80%is relatively suitable for the preservation of statues/murals.（2）When RH=75%,when the temperature is 5,15℃,the moisture absorption capacity of plaster is stronger.And when the temperature is 25,35℃,the moisture absorption capacity of plaster is weaker.It shows that the higher the ambient temperature,the more unfavorable the moisture absorption of plaster.（3）Due to the compact structure and small porosity,the fine mud layer has weaker hygroscopic capacity than the coarse mud layer;the main component of the white lime layer is calcium carbonate,which is insoluble in water and plays a role in moisture isolation.The above reasons lead to the hygroscopic capacity of test blocks is:coarse mud block>fine+coarse mud block>white ash+fine+coarse mud block>fine mud block.This shows that plaster of the statue/mural is easy to absorb moisture,and cause water and salt diseases,which is not conducive to the preservation of the statue/mural.（4）Due to the hygroscopic effect,water and salt migration will occur in plaster.The soluble salts Na Cl,Na₂SO₄,etc.migrate fastest,followed by the moderately soluble salts Ca SO₄,etc.,and the insoluble salts Ca CO₃,etc.,hardly move;Cl^-,SO₄^2-,Na⁺are the most active migration.And the migration of soluble salts is mainly Na Cl and Na₂SO₄,which has a significant effect on the destruction of herpes and sodium hydroxide;The higher the salt content of plaster,the stronger the hygroscopic capacity,indicating that plasters with salt damage are more hygroscopic than the ones without salt damage,which will aggravate the salt damage and cause irreversible damage;Due to the compatibility problem between different materials,the migration of soluble salts can accumulate between the plaster and the pigment layer,between the coarse mud layer and the fine mud layer,which easily leads to peeling and fracture at the contact surface of different materials.（2）The research of microbial characteristics and corrosion mechanism in dustfall shows:1)Research on the characteristics of microorganisms in dustfall:The concentration of microorganisms separated in dustfall is mainly bacteria,followed by fungi,less actinomycetes,and the least halophilic archaea.There are mainly five kinds of bacteria isolated,among which are Bacillus,Arthrobacter and Aureobacillus,with a small amount of Micrococcus and Corynebacterium;There are four main types of fungi,mainly Penicillium,Aspergillus,and Mucor,with a small amount of Trichoderma;Actinomycetes are mainly separated into two types:Propionibacterium and Streptomyces;The halophilic archaea are mainly divided into two types:Haloferax Torreblanca and Halococcus Schoop.Most of these microorganisms can metabolize secreted enzymes,and can also decompose organic matter to produce acid,which is easy to cause ground corrosion.2)Research on microbial corrosion mechanism shows:（1）Microorganisms in dustfall grow well in a humid environment.In the range of RH=68～97%,with the increase of environmental humidity,the microbial activity and respiration in dustfall are enhanced.At RH=97%,the microbial growth and metabolism are the strongest.It shows that the greater the humidity of the environment,the easier the microorganisms on the surface of plaster will multiply.（2）The ambient temperature range is 5～35℃,the higher the temperature,the faster the biochemical reaction in the cell,so that the metabolism of microorganisms in the dust is more vigorous,and the enzyme activity and respiration are stronger.At 35°C,microorganisms grow most vigorously.This shows that the higher the ambient temperature,the easier it is to cause the growth of microorganisms,thereby causing the occurrence of microbial diseases in plaster.（3）When the salt content is 2%and 3%,it can inhibit the growth of bacteria,fungi and actinomycetes in the dust,while the salt content of 1%grows well,indicating that the bacteria,fungi and actinomycetes separated from the dust are resistant salt,an appropriate amount of salt can stimulate its growth and metabolism.However,the halophilic archaea can grow well with the increase of the amount of salt,because the halophilic archaea can survive in a high-salt environment.This shows that salt damage can form a high-salt environment,which gradually leads to the enrichment of salt-tolerant microorganism and corrosion affects cultural relics.（4）In the pigment layer,the presence of heavy metals in pigments such as lead red（Pb₃O₄）,scarlet（Fe₂O₃）,cinnabar（Hg S）,azurite（Cu₃（CO₃）₂（OH）₂）will affect the growth of microorganisms on the surface of the statue/mural.When the concentration of Hg²⁺,Pb²⁺,Cu²⁺and Fe³⁺on the surface of plaster is 1 mg/L,the toxic effect on the microorganisms in dustfall is Hg²⁺>Pb²⁺>Cu²⁺>Fe³⁺.The results show that cinnabar has the strongest toxic effect on microorganisms,followed by lead red and azurite,and earth red has little effect,indicating that the pigment layer has a certain antibacterial effect.（5）The coarse mud layer in plaster has a higher proportion of reinforced fibers and higher organic content than the fine mud layer.Calcium carbonate,the main component of white ash,can react with carbonic acid or organic acids secreted by microorganisms to form soluble calcium bicarbonate,which causes the white ash layer to fade and the structure to be destroyed,which weakens its resistance to weathering.（6）The four types of microorganisms in the dust,such as bacteria,fungi,actinomycetes,and halophilic archaea,grow on the surface of the white ash+fine+coarse mud block with a salt content of 0.1%.As the time increases,the microorganisms slowly start to multiply.Due to the large number of bacteria,short growth cycle,and diverse types of metabolism,the proliferation is the first to take advantage,and fungi and actinomycetes grow accordingly,which can produce penicillin and streptomycin to inhibit bacterial growth and produce antagonistic effects.Due to the small number,the halophilic archaea has a slow growth and a slight disadvantage.Various types of microorganisms restrict each other to maintain the stability of the entire microbial community on the surface of plaster,which can reduce the degree of corrosion of the microorganisms.The main conclusion of this study shows that the changes in the environment caused by water vapor in the air can cause the salt in plaster to repeatedly dissolve and crystallize,causing salt damage and destroying the stability of plaster;the microorganisms in the air can contact plaster,Proliferate and metabolize under appropriate conditions to corrode the battlefield of pollution;The damage and pollution produced by the two factors are quite serious,and these factors cannot be ignored for the long-term preservation of the statue/mural.Therefore,in the daily maintenance of statues/murals,more attention should be paid to the temperature and humidity,ventilation conditions,and air pollution conditions of the preservation environment.Based on the comprehensive research results,it is recommended that the preservation environment of statues/murals should be ventilated in a timely manner.The temperature should be maintained at 15～25℃,and the relative humidity RH should be maintained at 60%or below;When treating microbial diseases,bacteriostatic agents should be used with caution to prevent breaking the overall balance of the microbial community and preserving the relative stability of the ecosystem in the environment,thereby slowing the impact of microbial corrosion on plaster.