【作者】 陆春海；

【导师】 倪师军； 张成江；

【作者基本信息】 成都理工大学 ， 地球化学， 2009， 博士

【摘要】 由于自然因素所致的风化作用和人为因素所致的破坏,许多文物的表面劣化现象严重。工业化进程中产生了酸沉降等环境问题,这些因素加速了文物的破坏。如不采取有效措施延缓文物风化速度,今后许多珍贵的实物记录将不复存在。但是,迄今没有找到一种文物保护材料能完全满足文物保护工作者的要求。因此,研制性能良好的文物保护功能材料,特别是发展文物保护材料的设计方法己成为文物保护研究领域的迫切任务之一。文物的保护涉及到物理、化学、材料学、矿物学、地质学、环境科学、考古学、历史学及艺术研究等多个学科。本论文首先尽可能全面地对石质文物和金属文物的相关保护材料、文物保护方法、国内酸沉降现状及其对文物的危害进行了综述。其次,对把当前先进的数值模拟和理论研究方法用于文物保护材料设计的可行性进行了分析。考虑到聚氯代对二甲苯的特点及该材料已在国外文物保护中得以初步应用的现实,论文以聚氯代对二甲苯为设计方法的检验对象,分别采用量子化学、定量构型关系、分子动力学和蒙特卡洛等方法,对其构型、物理性质、化学性质,特别是关系到其文物保护性质的气体和水的输运特性进行了数值模拟,以验证这些方法得出的结论的可靠性。同时,作者参照相关的高分子材料的评价标准,对聚氯代对二甲苯进行了严格的测评,以验证设计方法的可靠性和聚氯代对二甲苯适用性。另外,在研究中还应用了先进的同步辐射小角X射线散射装置。通过上述实验和理论研究,获得了以下的结果:⑴结合地球化学知识和文献数据分析,可以得出:近几十年来文物风化和锈蚀加速的主要原因是工业废物排放导致环境气氛和沉降物中有害物质增加所致。⑵根据实验考评、数值模拟和基于地球化学反应动力学的合理推断,聚氯代对二甲苯保护文物免受有害气体和酸沉降的影响,从而延缓文物风化和锈蚀速度,使文物得到长期保护。初步实验证实,聚氯代对二甲苯能够满足透明、不破坏原貌和结构的要求。⑶根据聚氯代对二甲苯和聚对二甲苯的分子结构,按照分子拓扑学指数的定义得出高聚物单体中每个非氢原子的成键原子指数和键指数。利用一些高聚物物性的实验值,将链指数与各种物理和化学性质(如高聚物的密度、介电常数、折射指数、杨氏模量、透气率等)通过多元线性回归,分别拟合出各自的定量构性关系(QSPR)方程。利用这些定量构性关系方程,来预报高聚物的物理和化学性质。本文用QSPR方法预报了聚对二甲苯、聚氯代对二甲苯的物性,与已收集到的实验数据相比,除了体电阻和两个力学性质外,QSPR预报的其它物性较实验值的最大误差小于7%。可以认为采用QSPR方法预测物性的方法推广到高聚物类文物保护材料是有价值的。特别是高聚物密度的准确预报为分子动力学模拟模型的建立提供基础数据。⑷用分子动力学方法模拟了不同链长的聚氯代对二甲苯的分子构象。发现在不同链长和不同的温度范围内,分子动力学的模拟均能达到平衡状态。模拟所得到的高分子链的构型均是线型的,这与实验所得的结论一致。在分子动力学模拟中,成键能对平衡趋向的影响要超过范德华能和静电能组成的非键能。⑸通过第一原理计算也证实聚对二甲苯为线性聚合物,而且发现零点能、热容、熵、焓和自由能与聚合度呈线性关系,前沿轨道能隙提示其为绝缘材料。这些既符合实验事实,也验证了分子动力学数值模拟所得的结论。⑹基于蒙特卡洛自避随机行走方法和聚氯代对二甲苯的实际密度,构造了玻璃态的聚氯代对二甲苯膜模型。以此为分子动力学数值模拟的输入模型,然后借用分子动力学数值模拟过程中记录的原子运动轨迹,结合爱因斯坦流体公式,导出了氦原子及小分子气体在聚氯代对二甲苯膜中的扩散系数。又由不同温度下的扩散系数结合阿仑乌斯公式导出了扩散系数方程和扩散活化能,其结果与实验值非常吻合。此外,还利用所构造的模型进行了等温吸附模拟,并与实验值而进行了比对,其结果令人满意。由此可见,该方法可以用于高聚物类文物保护材料的设计和其它应用领域的高聚物材料的设计。⑺考察了聚氯代对二甲苯膜试样在50℃干燥空气、有机试剂、不同浓度的酸碱溶液中长时间浸蚀的变化情况。除了浓硝酸和丙酮浸蚀使聚氯代对二甲苯膜的质量有很小的变化外,其余各组均无明显质量变化。经过热处理和化学试剂浸蚀的聚氯代对二甲苯膜试样,不仅在常规XRD和RAMAN光谱谱图上变化很小外,即使用高灵敏的同步辐射小角X射线散射也没有发现明显的变化。这些实验结果说明聚氯代对二甲苯确实是一种极其耐化学物质侵蚀的材料,即使对浓硫酸也可以长期抗其浸蚀。考虑到该膜是由气相沉积制备,结合地球化学动力学方程,可以推断聚氯代对二甲苯膜可以用于文物保护,使其在室内环境不受气氛和水的侵蚀。因而,特别适于金属文物、小型石质文物的保护和纸质、纺织类文物的修复。总之,经过研究证实,论文所采用的数值模拟方法有望用于延缓文物风化、锈蚀的高聚物类文物保护材料的设计。文献检索表明,目前尚未发现有类似的研究报道。本工作还证实了聚氯代对二甲苯具有极强的耐化学侵蚀作用,这些成果对于发展新型延缓文物风化文物的保护材料具有重要的现实意义,同时也拓宽了文物保护材料的研究领域。更多还原

【Abstract】 A number of historic cultural relics are badly damaged; their weathering and corrosion state is badly serious due to natural and human factors. Modern environmental issue such as acid deposition is speeding up corrosion for cultural relics. If effective measures should not be taken to minimize damage from circumstances and slow down the ageing process of relics, a mass of unique and rare historic cultural relics will be fading way. However, hardly any protective materials satisfy all requirements now. Consequently, it is a matter of great urgency to explore novel method for material design and find new protective materials with a good performance.The historical relic protection relates to many science disciplines such as physics, chemistry, material science, mineralogy, geology, environmental science, archeology, history, art. Firstly, weathering, protective materials and measurement for the historic stone and metal relics, and state and issue for acid deposition are summarized in this dissertation. Secondly, the feasibility analysis is discussed, which the current international advanced numerical modeling and theoretical methods is used to materials design on historical relic protection. The author takes into account the characteristic and applications of paraxylene in heritage preservation. Targeting on poly (chloro-p-xylylene), quantum chemistry, quantitative relationship between structures (QSPR), molecular dynamics and Monte Carlo are used to predict molecular structure, physical and chemical prosperities of poly (chloro-p-xylylene). The author is interesting in its nature of transport gas. Poly (chloro-p-xylylene) is evaluated whether can be used in historical relics. In accordance with the evaluation criteria for polymer and plastic, poly (chloro-p-xylylene) is strictly evaluated. Meanwhile, advanced synchrotron radiation small angle X-ray scattering device was employed to explore information for ageing poly (chloro-p-xylylene). The results obtained from experiments and theoretical studies are as follows:1. Combining knowledge of geochemistry with analysis of data in literature, we found that the main reason is environmental pollution such as acid deposition, which speed up weathering and corrosion for historical relics in recent decades. With the development of industry, harmful chemical from emission of industrial waste increases.2. Basing on experimental and simulation results, and geochemical kinetic, the author concluded that poly (chloro-p-xylylene) film can separate historic relic from harmful active matter such as acid deposition and harmful gas so that the film can protect historic relic and decelerate weathering and corrosion for relic. The experimental results show that poly (chloro-p-xylylene) film satisfies transparency and keeping original appearance and structure.3. Atomic index and bonding index for poly (chloro-p-xylylene) and poly (para-xylylene) are calculated on the basis of the definition of the molecular topology index. These indices are used to calculate the chain index of polymer unit. The equations which describe polymeric quantitative structure property relationship (QSPR) between the chain index and density, dielectric constant, refractive index, the Young′s modulus and permeability, etc. can be fitted by the multiple linear regressions, respectively. These QSPR equations can be used to predict physical and chemical properties of polymer. Comparing with the experimental data in literature, predicting values of the properties are smaller than the experimental values. Apart from mechanical properties and bulk resistance, the maximum error for the other prediction properties of is less than 7%. Therefore, QSPR is valuable for prediction properties of polymeric materials for protection relics. Accurate density is basis for building polymeric membrane model in molecular simulation.4. Molecular dynamics was used to explore molecular conformation of poly (chloro-p-xylylene) with different chain length. Molecular dynamics simulations are able to achieve equilibrium with various chain lengths under different temperature. All polymeric chains are linear in simulation results. The chain in simulation is consistent with the experimental conclusion in the literature. In molecular dynamics simulation, bonding energy more than non-bonding energy consisting of van der waals energy and electrostatic energy affects achieving equilibrium.5. The linear chain structure of poly (para-xylylene) also is confirmed by the first principle calculation. We found there are the linear relationship between degree of polymerization and the zero point energy, heat capacity, entropy, enthalpy and free energy. The energy gap between the frontier orbits implied that poly (para-xylylene) is insulator. These results are consistent with the experimental facts and confirm conclusion obtained from molecular dynamics simulation.6. The model of poly (chloro-p-xylylene) membrane was built on the basis of self-avoiding walk Monte Carlo method. The model was used in molecular dynamics simulation. The diffusion coefficient of Helium and small molecules in poly (chloro-p-xylylene) membrane was calculated by using the trajectory data and Einstein’s fluid equation. The activation energy and prefactor of diffusion coefficient was obtained on the basis of diffusion coefficients under different temperature. These values are in agreement with the experimental data. The membrane model also was used to simulate isothermal adsorption. The results for adsorption are satisfactory, too. The author thought the methods can be used in design new polymeric materials for protection relics.7. The organic and inorganic chemicals were utilized to etch poly (chloro-p-xylylene). And specimen of poly (chloro-p-xylylene) was heated over 15 months under 323K. Only specimens etched by HNO3 and acetone showed few mass changes. Comparing with the original specimen and the specimen heated and etched by chemicals, difference of XRD and RAMAN spectroscopy is slight. Difference in synchrotron radiation small angel X-ray scatter is little, too. These results implied that poly (chloro-p-xylylene) is very stable for chemicals. Poly (chloro-p-xylylene) is made by chemical vapor deposition. The author inferred that poly (chloro-p-xylylene) can be used for long-term protection of cultural relics, especially in indoor environment. Therefore, poly (chloro-p-xylylene) can be used to protect metal, stone relics and to repair paper and silk relics.In short, the study confirms that poly (chloro-p-xylylene) has prefect charactistic for preventing corrosion from chemical. The modeling methods in the paper are expected to design polymeric materials for protection relics. The author has not found similar study during literature search. These achievements have important practical significance for developing new materials to protect cultural relics. The study broadens the field of materials for protection.更多还原