Efficient And Sensitive X-Ray Imaging Of Metal Element Distribution And Migration

Metal elements are an important part of the natural systems.The researches regarding to exploring varieties of metal elements and their dynamic migration in a natural system are the key steps to understand its internal composition and the principle of the nature.According to the mutual interactions between different components in the natural systems and their different reaction mechanisms,systems can be divided into two fundamental categories: simple systems and complex systems.The simple system refers to a system with simple interaction dependence among components.It is important to find out the composition,content,and distribution of the metal elements in a simple system to evaluate the performance and application range of the materials.For a complex system,there are various complex interactions or interdependencies among the components,and the detection of metal elements’ migration and conversion processes in it,is also a key step to understand the complex system.Compared to chemical profiling and spectroscopic analysis,the natural systems can be detected and analyzed more concretely by imaging characterization methods.X-ray imaging provides high penetration to the sample,delivers pretty high temporal and spatial resolution,and meets the needs for non-invasive characterization of the system at the same time.The researches on quantitative distribution and migration of metal elements play important roles in the fields of investigating alloy material properties,battery chargedischarge performance,the life of integrated circuits,geological exploration,environmental pollution and remediation,and so on.The existing methods are difficult to make high efficiency and high sensitivity measurement of metal element distribution and migration simultaneously.In this paper,via optimizing X-ray KES imaging and move contrast imaging,an efficient and sensitive wide-field imaging scheme is proposed,to explore metal element distribution and ion migration in alloy materials and electrochemical reaction process.Based on the full-field imaging and the expanded field of view technique,a brand new measurement method is demonstrated,significantly improving the efficiency for charactering the element distribution and migration,compared to the existing methods.Referring to the experimental research and theoretical analysis at X-ray imaging beamline(BL13W)in the Shanghai Synchrotron Radiation Facility(SSRF),the main research results of this dissertation are as follows:(1)A calibration method was developed and established for the linear relationship between the contrast to noise ratio of KES and the content of the interesting element,realizing the high-efficiency and high-sensitivity test of element distribution with a large field of view.Noise in test,uneven distribution of the incident light field,and inconsistent absorption of different samples lead to the problems of low measuring precision and sensitivity of elements content.To solve these problems,the linear relationship between image contrast and element content is studied based on the standard sample.High efficient and sensitive measurement of the content of elements is successfully realized by normalizing the image background and introducing the contrast to noise ratio.Aiming at solving the measurement errors caused by inconsistent experimental conditions,an image normalization method based on contrast noise ratio was developed,which successfully expanded the field of view of element distribution measurement.In principle,the method can be applied to samples of any size by sample scanning,which could furtherly improve the efficiency of elemental distribution measurement.The experimental results show that there is a linear relationship between the gray value of the KES-CT slice image and the content of the interesting elements,which can be used to measure the three-dimensional spatial distribution of elements.(2)Based on the linear relationship between the contrast of the KES image and the content of the element,the influence of sample thickness on the measurement results was eliminated by introducing the gray distribution of the absorption image,and the efficient and sensitive imaging of element distribution of alloy samples was successfully realized.The alloy samples have strong X-ray scattering,which can seriously affect the accuracy and sensitivity of the imaging of element content distribution.The experimental results show that the effect of noise on the measurement accuracy can be significantly reduced by introducing the contrast to noise ratio.The uneven thickness distribution of the test sample will directly affect the measurement result,and the influence of sample thickness on the measurement result is successfully eliminated by introducing the single energy absorption contrast image.In principle,this method can be used for samples with any thickness distribution.The field of view is extended by scanning samples and image stitching.Experimental results show that the method can realize the large field of view measurement of element distribution,thus furtherly improving the measurement efficiency.Based on the method developed,the distribution of Ag in lead-free solder was quantitatively analyzed,and the abnormal aggregation distribution of Ag was found.The experimental results show that the KES imaging can be used for high-efficiency and high-sensitivity in-situ non-destructive tests of the distribution of elements in alloy materials,and is especially suitable for high-efficiency and large-field tests.(3)The move contrast X-ray imaging is introduced to observe the metal ion migration process for the first time.Experimental results show that the sensitivity of element migration imaging can be greatly improved by this method,realizing the metal element migration imaging whose effective signals cannot be observed by traditional methods.Move contrast X-ray imaging was introduced to improve the imaging sensitivity.Based on the electrolytic cell model,the ion concentration and electrochemical reaction intensity in the electrolytic cell were adjusted by changing the voltage of the electrolytic cell.Meanwhile,the sensitivity and signal extraction ability of move contrast imaging were intuitively evaluated by comparing with and analyzing the traditional temporal subtraction imaging.The spatial distribution of electrochemical reaction in the initial stage of electrolysis was successfully observed for the first time using the move contrast X-ray imaging.It is found that the electrochemical reactions take place simultaneously throughout the cell at the initial stage of electrification.The reaction near the electrode is stronger,rather than metal ions migrate between electrodes under electric field forces,which is commonly understood.When the voltage of the electrolytic cell decreases to a critical value and the effective ion migration signal cannot be obtained by traditional methods,the clear path of ion migration can still be obtained by move contrast imaging.The experimental results show that the move contrast X-ray imaging can greatly improve the sensitivity of imaging for electrochemical reaction and ion migration in the electrochemical reaction process,and provide a new method for the study of redox reaction and ion migration in the working state of batteries and electrolytes.(4)Based on the advantages of move contrast X-ray imaging in dynamic process observation,the metal ion migration characteristics in the electrochemical reaction process were quantitatively studied,and a series of new phenomena in electrolysis reaction were revealed.The observation and quantitative analysis of electrolyte migration process,redox reaction of electrode materials,and deposition effect of reduced metal atoms in the electrochemical reaction process of battery and electrolytic cell are of great guiding significance to the design of battery structure,the selection of electrode materials,and the optimization of electrolytic efficiency.The results of move contrast X-ray imaging based on the electrochemical reaction process in the electrolytic cell show that metal ions migrate from anode to cathode,and their trajectories change with time under the influence of multiple factors.As a large number of metal ions are reduced to uncharged atoms at the cathode,electromagnetic shielding will occur in the cathode,thus affecting the ion migration trajectory.Restored metal atoms reunite and deposit to the bottom under the influence of gravity.Ions can receive electrons for reduction reaction bypassing the electromagnetic shielding of the electrode,from the outside of the cathode.Using the phase information of move contrast X-ray imaging,the vector field distribution of the motion direction,the velocity of ion migration,and the atomic deposition are furtherly given.The dynamic quantitative analysis of the electrochemical reaction process is realized.Therefore,the large field of view dynamic quantitative characteristics of move contrast X-ray imaging provides an efficient and sensitive observation method for the study of ion migration.