Quantitative Characterization Of Deterioration Degree Of Ancient Fragile Bronzes

"Fragile bronze ware" is a concept based on subjective perception in the preservation practice of cultural relics.It emphasizes that bronze ware loses(or does not possess)its original metal toughness and strength,is easy to be broken,damaged and difficult to be handled by conventional methods,such as deep mineralization,powdery rust,brittle powder rust and thin wall.In this study,"fragile bronze ware" refers to the severe corrosion results of bronze ware under the coupling action of multiple factors(external and internal).In view of the subjectivity and fuzziness of the description of the fragile state of bronze ware in the current protection work,this study provides a way to quantify the degree of corrosion degradation of bronze ware by using multivariate statistical method,so as to achieve the demarcation and numerical differentiation of the fragile range.Firstly,68 ancient bronze samples from different regions and types were selected according to certain principles and standards,and the corrosion deterioration degree of the samples was preliminarily classified according to macroscopic standards.Secondly,by summarizing the characterization methods and indexes commonly used in bronze corrosion research,and considering the existing conditions,comprehensiveness and applicability,6characterization indexes including morphology structure,element composition distribution,hardness,density,water absorption and porosity and 4 characterization methods including super depth of field microscopic analysis,scanning electron microscope energy spectrum analysis,micro Vickers hardness test and hydrostatic weighing test were selected from the aspects of chemical composition and physical and mechanical properties.The original quantitative characterization data were obtained by carrying out characterization experiments.Finally,the classification result based on macro criteria were taken as an independent variable,the experimental results were processed into 9 dependent variables including the overall phase factor,average ratio of oxygen element to alloying element,average ratio of chlorine element to alloying element,average ratio of tin element to sum of copper and lead element,total microvickers hardness,microvickers hardness of mineralized part,apparent relative density,water absorption,apparent porosity.Then the corrosion degradation sequence of bronze samples was established by using variable correlation analysis,grey correlation analysis and cluster analysis,and the validity of each index was discussed.The results show that the grey relational degree method has a good effect on evaluating the corrosion deterioration degree of bronze samples,and the relational degree of corrosion deterioration of the classified fragile bronze samples ranges from 0.4525 to 0.6990.The overall phase factor,average ratio of oxygen element to alloying element,water absorption and apparent porosity can reflect the corrosion deterioration degree of samples well.Average ratio of chlorine element to alloying element and average ratio of tin element to sum of copper and lead element has a good correlation of corrosion degradation under specific corrosion type and alloy type.The overall microvickers hardness and the microvickers hardness of the mineralized part are poor in reflecting the degree of corrosion deterioration.In the future,with the expansion of sample size and the improvement of characterization indexes and methods,the established database of physical and chemical characteristics of corrosion degradation of fragile bronze samples is expected to realize the independent serial characterization of different corrosion types and alloy types of samples,and provide a more effective reference tool for the preservation practice of cultural relics.