【作者】 王锋；

【导师】 魏书亚；

【作者基本信息】 北京科技大学 ， 科学技术史， 2023， 博士

【摘要】 大理岩材质细腻,具有极好的观赏性,兼具良好的机械性能,使其广泛应用于石雕石刻和建筑当中。房山大石窝丰富的大理岩为北京地区大量的石质文物提供了资源,例如故宫和十三陵中的石刻文物、房山石经、进士题名碑等,这些珍贵的石刻文物具有非常高的历史和艺术价值。然而,由于长期受到物理(冻融、温度、风蚀等)、化学(水、酸雨、有害气体等)、生物(微生物、植物、昆虫等)因素的影响,石刻文物出现了粉化、溶蚀、剥落、结壳、开裂等病害,使得其所承载的历史价值、艺术价值和科学价值在不断损坏减少,亟需采取保护措施。本研究首先根据北京地区气候及大气污染特点,选取了东城区、海淀区、石景山区、昌平区、房山区、大兴区中七处文化遗产地的大理岩石刻文物进行调研和检测,发现主要以青白石和方解石质的大理岩为主,其中青白石材质占到75%以上,表面粉化、表面污染、水锈结壳和溶蚀为主要病害。通过研究揭示了这些病害形成的原因,尤其是详细探索了黑色结壳(水锈结壳的一种)的形成机理,与污染物的关系以及污染物的来源,并筛选出合适的方法成功对黑色结壳进行了清洗和盐分评估,为后续保护做好了准备。基于这些调查和研究发现对于风化严重的石刻文物急需加固保护,目的是减少风化后本体的孔隙率,增加胶结物质,减少水分等物质的侵入,增加本体强度;对于容易受到腐蚀的结壳和溶蚀位置,应该增加保护膜,增加石刻文物抵御劣化的能力。经过文献调研,筛选出纳米氢氧化钙材料符合对加固材料性能的要求,而羟基磷灰石(HAP)可以用作保护层。如何制备出粒径小、分散性好、碳酸化速度快的纳米氢氧化钙是解决问题的关键。零维的石墨烯量子点(graphene quantum dots,GQDs)具有较大的比表面积,通过π-π键较易实现化学嫁接,并且因其尺寸通常在10nm以下,因而可以产生显著的量子尺寸效应和边界效应。将石墨烯材料引入到纳米氢氧化钙、保护膜的制备中,有利于改善材料的渗透性、分散性、相容性等。另外,石墨烯本身的优异性质可以在保护材料应用后,帮助提升石质本体的力学性能,以及耐腐蚀能力、自清洁性等。然而目前将石墨烯复合材料应用于石质文物保护的研究还未见报道,对于石墨烯材料与相关保护材料的复合机理,及其在文物中的作用机理尚没有非常明确的解释。本研究首先基于密度泛函理论进行了第一性原理计算,从理论方面揭示了石墨烯与纳米氢氧化钙的复合机理;然后在实验部分,采用络合物为钙的前驱体,引入GQDs与其复合,调节络合比例、反应温度、GQDs加入量,通过反复实验成功制备出了石墨烯增强纳米氢氧化钙这一新型的石质文物加固材料;并且,对于容易受到腐蚀的结壳和溶蚀位置,基于采用溶胶凝胶法制备了石墨烯复合羟基磷灰石(HAP)-正硅酸乙酯(TEOS)保护层,经过疏水性、耐酸性和抗冻融性测试,此保护膜使得石材表面具有更好的防污染耐腐蚀性能。以北京石刻艺术博物馆提供的风化大理岩石刻残块为样本,采用不同条件下得到的纳米氢氧化钙进行加固实验,通过评估形貌、色度、渗透性、吸水率、孔隙率、表面里氏硬度、纵波波速和抗冻融性,筛选出加固性能最佳的材料以及最佳使用量,并从理论方面解释了石墨烯对加固的增强机理。根据模拟实验的结果,将合成的石墨烯增强纳米氢氧化钙在北京石刻艺术博物馆东南库区两座露天石刻海色碑、宝和殿碑上进行加固实验,定期检测其加固效果和加固材料的老化性能,对加固过的部分进行形貌、色度、表面里氏硬度和粉化程度的表征,分别与未复合GQDs的纳米氢氧化钙以及未采用络合前驱体的材料进行对比,验证了模拟实验效果最好的材料在实际环境中依然具有较好的性能。综上所述,本研究在对北京地区典型大理岩石刻文物调研分析的基础上,设计合成了用于加固本体的石墨烯复合纳米氢氧化钙,以及用于防护易腐蚀位置的石墨烯复合HAP-TEOS保护膜。经过实验室模拟实验、理论计算和现场应用评估,效果良好,为大理岩石刻文物保护提供了新的思路和参考。更多还原

【Abstract】 Marble was utilized extensively for sculptures and constructions,owing to its delicate texture,graceful exterior and excellent mechanical properties.Thanks to the abundant marble resources in Dashiwo(Fangshan District),a large number of stone cultural relics in Beijing have been created,such as the stone sculptures in Forbidden City,the Ming Tombs,Fangshan Stone Sutra,as well as the Jin-Shi(Successful Candidate at Imperial Examination)Stelae.These stone cultural relics exposed outdoors suffer from deterioration caused by physical factors(freeze-thaw cycling,temperature difference,wind erosion,et al.),chemical factors(water,acid rain,harmful gases,et al.)and biological factors(microorganism,plant,insect,et al.),leading to sugaring,corrosion,desquamation,crusts,cracks and so on.As a result,the historical value,artistic value and scientific value of the objects are constantly reduced,thus proctective measures need to be taken urgently.In this study,marble carvings from seven cultural heritage sites in Dongcheng district,Haidian district,Shijingshan district,Changping district,Fangshan district and Daxing district were investigated,considering the characteristics of climate and air pollution in Beijing.The host rocks were mainly dolomitic marbles called Qingbaishi(accounted for more than 75%)and white calcitic marbles.Major diseases were sugaring,surface contamination,rust crust and corrosion.Formation mechanisms of these diseases,especially the black crusts(a kind of rust crust),were studied and the resource of pollutants were revealed.A better way was chosen from the existing methods to clean the black crusts and the content of the soluble salts was evaluated,providing scientific information for further conservation.Based on these investigations and studies,the weathered marble sculpture should be reinforced urgently,aiming to reduce the porosity,as well as to increase the cements,anti-corrosion property and mechanical strength.As for the positions susceptible to corrosion,the protective films should be prepared to enhance the ability of resisting degradation.Nano calcium hydroxide(nanolime)was chosen to consolidating the marble,while the hydroxyapatite(HAP)could be used for the protection coating,after the investigation of literatures.The key solution was the preparation of nano calcium hydroxide with smaller particle size,good dispersion and fast carbonation rate.Graphene quantum dots(GQDs)was a kinds of zerodimensional carbon materials,with large specific surface area and tiny size less than 10 nm primarily,which could cause significant quantum size effects and boundary effects,as well as the functionalization through π-π bonds.Therefore,addition of GQDs could be beneficial to improve the permeability,dispersibility and compatibility of the material.Besides,the excellent properties of graphene itself can enhance the host rock,such as mechanical property,corrosion resistance,selfcleaning,etc.However,GQDs composites has not been applied in the conservation of stone cultural,and the mechanism of combination between graphene with related conservation materials,as well as the effects in cultural relics,has not been clearly explained.In this work,first-principle calculations based on spin-polarized density functional theory(DFT)were carried out to study the reaction process firstly.Then GQDs enhanced hexagonal Ca(OH)2 nanoparticles were successfully prepared using ammoniated CaCl2 as precursor in aqueous media.Through adjusting the complexation ratio,reaction temperature and the addition amount of GQDs,the nanocomposite with good consolidation effect was successfully obtained.Aiming to protect the easily corroded positions on marble carving,like the parts of black crust and corrosion,the graphene enhanced hydroxyapatite(HAP)ðyl silicate(TEOS)film was successfully prepared with the sol-gel method,using the Ca(OH)2&GQDs nanoparticles as the precursor.The noteworthy improvement of hydrophobicity,acid resistance and the freeze-thaw resistance property was demonstrated,resulting a new material with better anti-pollution and anti-corrosion performance.The prepared Ca(OH)2&GQDs nanoparticles with different formulas were used for consolidating the naturally weathered marble samples,provided by Beijing Stone Carving Art Museum.By evaluating their morphology,chroma,permeability,water absorption,porosity,surface leeb hardness,P-wave velocity and freeze-thaw resistance,the materials with the best reinforcement performance and the most appropriate usage were screened out.The first principles calculation based on density functional theory was performed to explain the enhancement mechanism theoretically.According to the results of simulation experiments,consolidation experiments were carried out on the stele of Haise and stele of Baohedian in the open air,which were located in the southeast store of Beijing Stone Carving Art Museum.The morphology,chromatic aberration,surface leeb hardness and sugaring condition were monitored regularly to assess the consolidation effect.Compared with the materials without GQDs and without complex precursor,it was verified that the material with the best simulation result still had better performance in the actual environment.In summary,on the basis of investigation and analyses of typical marble stone carvings in Beijing area,graphene-enhanced Ca(OH)2 nanoparticles and graphene-enhanced HAP-TEOS film were successfully synthesized for the consolidation and protection of the marble carvings.The performance of the two materials was satisfactory according to the results of laboratory simulation experiment,theoretical calculation and field application evaluation,providing a new idea and reference for the conservation of marble carvings.更多还原