【作者】 王伟；

【导师】 郭劲松； 陈杰；

【作者基本信息】 重庆大学 ， 环境工程（专业学位）， 2021， 硕士

【摘要】 大足千手观音佛像自南宋建造至今经历了多次修缮,其表面金箔曾发生翘边脱落、腐蚀开裂等病害,金箔的损坏受到自然环境中诸多因素的影响,此前研究者们多针对如酸雾、湿度等环境因素对金箔腐蚀,金箔的粘贴工艺,以及翘边金箔的回贴等研究。对于金箔表面微生物对金箔腐蚀损坏的影响研究较少,为此本文通过从千手观音造像表面分离纯化得到的两种霉菌,使用测序等手段鉴定其种类后,在实验室内进行为期31d的实验,研究这两种霉菌对千手观音表面金箔腐蚀的影响,使用电化学技术测定金箔在分别接种单一霉菌的环境中的开路电位（Open Circuit Potential,OCP）、交流阻抗（AC Impedance）以及极化曲线（Cathodic Polarization Curve）的变化情况,以此分析探究这两种单一霉菌生长过程对金箔的影响,并对其影响机理进行了简要解析。实验选取了从千手观音佛像表面分离得到的两种霉菌（分别编号A1、A2）并进行种类鉴定,霉菌A1通过ITS序列测序以及形态结构观察鉴别为杂色曲霉,霉菌A2通过ITS序列测序确定为毛霉属的易脆毛霉种。随后本文通过实验探究了这两种霉菌对金箔的腐蚀影响。将金箔试样分别置于无菌、有杂色曲霉以及有易脆毛霉的环境中在25℃条件下实验31d,监测各实验体系的p H值、开路电位、交流阻抗以及极化曲线的变化情况,并对金箔表面形貌进行表征分析,所得到的主要结果如下:（1）金箔浸置在无菌查氏液体培养基和无菌马铃薯液体培养基中,溶液的p H值均为弱酸性,实验期间p H值平均分别为6.89和6.32,并且p H值在实验周期内保持稳定。而接种了杂色曲霉和易脆毛霉的实验体系中,溶液的p H值在31d内均出现了明显下降,前者溶液中的p H值从6.73下降为4.15,后者从6.45下降为3.56,这两种霉菌均发生产酸代谢,为金箔中较活跃的金属成分的腐蚀营造了酸性条件。（2）实验周期内,金箔试样浸置在无菌查氏液体培养基和马铃薯葡萄糖液体培养基中开的路电位分别在-30 m V、-25 m V左右轻微波动,而金箔试样在接种杂色曲霉和接种有易脆毛霉的实验体系中开路电位均出现下降的趋势。在接种杂色曲霉的实验体系中开路电位降低了159.24%,最终值为-77.28 m V;在接种易脆毛霉的实验体系中开路电位降低了178.64%,最终值为-71.08 m V。开路电位的变化,与金箔受到的腐蚀有关。（3）金箔试样在两种无菌液体培养基以及接种杂色曲霉和易脆毛霉的实验体系中的交流阻抗谱均只有一个容抗弧。在无菌液体培养基中容抗弧半径较大,并且在实验周期内保持稳定;而在接种有杂色曲霉和接种有易脆毛霉的实验体系中的容抗弧半径在实验周期内均出现不同程度的下降。模拟电路结果表明,含杂色曲霉的实验体系中金箔的电荷转移电阻R_ct在前期阶段迅速下降,中后期逐渐稳定,最终值为5.12×10⁵A/cm²,下降88.58%;而在含易脆毛霉的实验体系中R_ct最终值为7.63×10⁵Ω·cm²,下降84.77%。（4）金箔在无菌查氏液体培养基和无菌马铃薯葡萄糖液体培养基实验31d后的腐蚀电位E_corr较高以及其腐蚀电流密度i_corr较小,分别为-0.101 V、6.212×10^-7A/cm²和-0.093 V、6.603×10^-7A/cm²。金箔浸置在两种无菌液体培养基中,性质稳定,耐腐蚀性能良好,没有出现析氢腐蚀和吸氧腐蚀等腐蚀现象。而接种有杂色曲霉和易脆毛霉的实验体系中,金箔腐蚀电位负移较大,其值分别为E_corr为-0.32 V、-0.34V,同时对应的腐蚀电流密度i_corr也较大,分别为7.20×10^-6A/cm²、5.956×10^-6A/cm²。（5）使用场发射透射电子显微镜和X射线能谱仪对实验后的金箔试样表面形貌和组成进行分析,无菌液体培养基中的金箔表面纹理清晰可见,均没有出现明显的腐蚀痕迹。而在有霉菌的试验系统中的金箔表面均有霉菌形成的生物膜,金箔出现不同的腐蚀,腐蚀裂隙中均存在霉菌的菌丝。在杂色曲霉实验系统中的腐蚀裂隙较宽,深度也较深;而在易脆毛霉中的裂隙为狭长形,深度较浅。清除霉菌层后测得裂隙边缘腐蚀产物中的氧元素含量和硫元素含量较高,推测二者产物为Cu的氧化物、硫酸盐等。（6）在实验周期内,杂色曲霉与易脆毛霉均促进了金箔试样的腐蚀进程,金箔在接种杂色曲霉实验系统中的腐蚀速率先快后慢,在接种易脆毛霉实验系统中的腐蚀速率较均衡,并且经过一个实验周期杂色曲霉对金箔造成的腐蚀影响要大于杂色曲霉。另外,二者腐蚀机理基本相同,金箔自身的晶体位错等结构缺陷在酸性条件会成为应力腐蚀开裂的源头,容易产生应力腐蚀裂隙,营养菌丝伸入裂隙中,对腐蚀裂隙产生扩张作用,强化金箔腐蚀作用,同时金箔中的较活跃组分在霉菌及其酸性代谢产物的作用下发生反应,进一步引起金箔破坏。更多还原

【Abstract】 The Dazu Thousand-Hand Guanyin Buddha Statue has undergone many repairs since it was built in the Southern Song Dynasty.The gold leaf on its surface has been damaged by edge-off,corrosion and cracking.The damage of the gold leaf is affected by many factors in the natural environment.Research on the corrosion of gold foil by environmental factors such as humidity and humidity,the pasting process of gold foil,and the back pasting of warped gold foil.There are few studies on the influence of microorganisms on the surface of gold foil on the corrosion damage of gold foil.For this reason,this article uses two kinds of molds isolated and purified from the surface of the Qianshou Guanyin statue to identify their species by sequencing and other means,and then conduct a 31-day laboratory in the laboratory.Experiments to study the effects of these two kinds of molds on the corrosion of the gold foil on the surface of Qianshou Guanyin,and use electrochemical techniques to determine the open circuit potential(OCP),AC Impedance(AC Impedance)and polarity of the gold foil in an environment where a single mold was inoculated separately.The changes of the Cathodic Polarization Curve are used to analyze and explore the impact of the growth of these two single molds on the gold foil,and briefly analyze the impact mechanism.Two kinds of molds(numbered A1 and A2,respectively)isolated from the surface of the Thousand-Hand Guanyin Buddha were selected in the experiment.The mold A1was identified as Aspergillus versicolor by ITS sequence sequencing and morphological structure observation,and the mold A2 was confirmed by ITS sequence sequencing.It is a fragile Mucor species of the genus Mucor.Subsequently,this article explored the effects of these two molds on the corrosion of gold foil through experiments.The gold foil samples were placed in a sterile,Aspergillus versicolor and Mucor fragile environment for 31 days at 25°C,and the p H value,open circuit potential,AC impedance and polarization curve of each experimental system were monitored.The changes,and the characterization and analysis of the surface morphology of the gold foil,the main results obtained are as follows:(1)The gold foil is immersed in sterile Chase liquid medium and sterile potato liquid medium.The p H value of the solution is weakly acidic.During the experiment,the average p H value is 6.89 and 6.32 respectively,and the p H value is within the experimental period.keep it steady.In the experimental system inoculated with Aspergillus versicolor and Mucor fragile,the p H of the solution dropped significantly within 31 days.The p H of the solution in the former dropped from 6.73 to 4.15,and the p H in the latter dropped from 6.45 to 3.56.Both molds produce acid metabolism,which creates acidic conditions for the corrosion of the more active metal components in the gold foil.(2)During the experiment period,the open circuit potential of gold foil sample immersed in sterile Chase liquid medium and potato dextrose liquid medium fluctuates slightly around-30 m V and-25 m V,while gold foil sample is inoculated The open circuit potential of Aspergillus versicolor and the experimental system inoculated with Mucor fragile showed a downward trend.In the experimental system inoculated with Aspergillus versicolor,the open circuit potential was reduced by 159.24%,and the final value was-77.28 m V;in the experimental system inoculated with Mucor fragile,the open circuit potential was reduced by 178.64%,and the final value was-71.08 m V.The change of the open circuit potential is related to the corrosion of the gold foil.(3)The AC impedance spectra of the gold foil sample in the two sterile liquid culture media and the experimental system inoculated with Aspergillus versicolor and Mucor fragile have only one capacitive impedance arc.In the sterile liquid medium,the capacitive resistance arc radius is large and remains stable during the experimental period;while the capacitive resistance arc radius in the experimental system inoculated with Aspergillus versicolor and Mucor fragile is both in the experimental cycle.There are varying degrees of decline.The simulation circuit results show that the charge transfer resistance Rct of the gold foil in the experimental system containing Aspergillus versicolor decreases rapidly in the early stage and gradually stabilizes in the middle and late stages.The final value is 5.12×105 A/cm~2,a decrease of 88.58%;The final value of Rct in the mold experiment system was 7.63×105Ω·cm~2,a decrease of 84.77%.(4)The corrosion potential of gold foil in sterile Chase liquid medium and sterile potato dextrose liquid medium after 31 days of experiment is higher and its corrosion current density icorr is higher,respectively-0.101 V,6.212×10-7 A/cm~2 and-0.093 V,6.603×10-7 A/cm~2.The gold foil is immersed in two sterile liquid culture media,which has stable properties,good corrosion resistance,and no corrosion phenomena such as hydrogen evolution corrosion and oxygen absorption corrosion.However,in the experimental system inoculated with Aspergillus versicolor and Mucor fragile,the negative shift of the corrosion potential of gold foil is larger,and the values are-0.32 V and-0.34 V,respectively.At the same time,the corresponding corrosion current density icorr is also larger,respectively.It is 7.20×10-6 A/cm~2,5.956×10-6 A/cm~2.(5)Use field emission transmission electron microscope and X-ray energy spectrometer to analyze the surface morphology and composition of the gold foil sample after the experiment.The surface texture of the gold foil in the sterile liquid culture medium is clearly visible,and there is no obvious corrosion trace..In the test system with mold,the surface of the gold foil has a biofilm formed by mold.The gold foil has different corrosions,and there are mold hyphae in the corrosion cracks.In the Aspergillus versicolor experimental system,the corrosion cracks are wider and deeper;while the cracks in Mucor fragile are long and narrow with shallow depth.After removing the mold layer,the oxygen content and sulfur content in the corrosion products of the crack edge were measured to be relatively high.It is speculated that the two products are Cu oxides,sulfates,etc.(6)During the experiment period,both Aspergillus versicolor and Mucor fragile promote the corrosion process of the gold foil sample.The corrosion rate of gold foil in the Aspergillus versicolor experimental system is first fast and then slow.In the experiment of inoculating Mucor fragile The corrosion rate in the system is relatively balanced,and the corrosion effect of Aspergillus versicolor on the gold foil is greater than that of Aspergillus versicolor after an experimental period.In addition,the corrosion mechanism of the two is basically the same.The structural defects such as crystal dislocations of the gold foil itself will become the source of stress corrosion cracking under acidic conditions,and it is easy to produce stress corrosion cracks.The vegetative mycelium extends into the cracks and has an expansion effect on the corrosion cracks.Strengthen the corrosive effect of the gold foil,and at the same time,the more active components in the gold foil react under the action of the mold and its acidic metabolites,further causing the damage of the gold foil.更多还原