Study Of The Hydrogen Behavior In Tungsten And Elemental Distribution In The Corroded Layer Of ISG Glass Using Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS)

The use of nuclear energy has been considered as a promising way to solve a series of the problems including energy crisis.Relevant research with the development of nuclear energy is also carried out,of which mostly focusing on the basic aspects of material properties.In Fission industry,the disposal of large amounts of radioactive waste generated by fission reactions is mainly concerned.Vitrification,which is the most widely used technology for radioactive waste disposal,has the advantages of high disposal efficiency and long-term storage.However,the vitrification products often demand stabilities of million years,and the corrosion resistance of the glass is therefore concerned.On the other hand,fusion energy is considered as the most important source for future energy due to its high productivity and low radioactive pollution.However,further research is still needed for the design of plasma-facing materials?PFMs?in the fusion device.Because of its high melting point,low sputtering rate and low hydrogen isotope?D/T?retention,tungsten has been selected as the main component in the divertor part of the International Thermonuclear Experimental Reactor?ITER?,which will be subject to low energy and high density of hydrogen ions.The degradation of the tungsten properties after ion bombardment is also an important issue.Current studies are often attributed to fundamental questions,such as the distribution of elements and the changes of the surface topography in materials.However,the experimental technology is still insufficient to solve all the scientific problems.The development of new techniques is therefore very necessary.Secondary ion mass spectrometry?SIMS?is a developing analytical technique,which can obtain important information of materials by analyzing the secondary ions and ion clusters generated by ion bombardment.This technique can be used for both depth profiling and elemental imaging with the properties of excellent detection limit?ppm level?,high mass resolution?M/?M>10000?,high depth resolution?1-10 nm?and decent lateral resolution?100 nm?.The sample preparation for SIMS is also simple,which provides obvious convenience for the experiment.All these advantages make SIMS an outstanding one among all the techniques.In the past decades,SIMS has achieved great development in the applications of biology,chemistry and semiconductor materials.However,the use of SIMS in the field of nuclear material is just started.Therefore,it is needed to investigate the basic questions in PFMs and vitrification products using SIMS in this study.This dissertation is divided into two parts,of which one is the study of the hydrogen distribution and the surface topography in ion-irradiated polycrystalline tungsten.The other is the investigation of the elemental imaging of the ISG glass?vitrification products?.The main contents are described as follows:1.Hydrogen distribution in tungsten is affected by different implantation conditions.In this work,the effects of energy and fluence on the surface morphology and H retention of tungsten materials were investigated using H⁺ ions with a fixed beam intensity.The result shows that the critical fluence for bubbling in tungsten was 2×10¹⁷ H⁺/cm² while the critical fluence for blistering caused by 6 keV H⁺ions is¹×10¹⁹ H⁺/cm².On the other hand,40 keV H⁺ions can effectively cause surface blistering when the fluence reaches²×10¹⁷ H⁺/cm².The defects caused by high-energy hydrogen ion irradiation could trap more hydrogen atoms,but also prevent the further diffusion of H into the material.Moreover,H depth distribution indicates that although the fluence of 40 keV H⁺implantation was low,the H concentration was close to that of 6 keV H⁺ions implanting at a higher fluence.The resulting local saturation is the main reason for blistering on the tungsten surface.2.In order to investigate the properties of various defects in tungsten,40keV H⁺ions were implanted into the unannealed polycrystalline tungsten at a fluence of 2×10¹⁷ H⁺/cm².After the implantation,the surface morphology and H depth distribution in tungsten were observed.Moreover,H behavior during isothermal and isochronal annealing was successfully observed with a TOF-SIMS5 instrument.The in-situ analysis shows two release stages at 200-300? and400-500?,which correspond to two different types of defects.Both of them are located at the projected range of implanted H ions.In addition,the same depth analysis and annealing experiments were performed on another sample after 130 days storage at room temperature.In addition to the same two release stages,the slow release of hydrogen at room temperature was found and corresponds to the weaker trapping sites.These defects could extend throughout the implanted area and is caused by inherent defects in the tungsten and interstitial atom defects.3.As the main component of the divertor part in fusion reactor,tungsten is not only bombarded by hydrogen isotopes with low energy and high fluences,but also is irradiated by higher energy He⁺ions and 14.1 MeV neutrons.Therefore,it is necessary to explore the hydrogen behavior in tungsten under different damage conditions.This work compares the hydrogen distribution behavior of He⁺-H⁺ irradiation,Au⁺-H⁺ irradiation and single hydrogen ions irradiation.The results show that hydrogen depth distribution is related to the pre-damaged levels.For higher damage,higher hydrogen retention in tungsten could be found.Further ex-situ observation shows that the binding energy of Au⁺and He⁺ion induced-defects is related to vacancy and vacancy clusters.The retention of H caused by Au⁺ and He⁺ ions is different,which might be caused by the different distribution of pre-implanted ions.Moreover,He also occupies the H position in the tungsten,which may affect the concentration of H in different ways.This work also indicates higher trapping energy related to the defects that may be caused by H⁺ ion implantation,but more experimental evidence is needed.4.Ion exchange and interdiffusion are two important processes in the glass corrosion behavior.Important exchanged ions such as H⁺and B⁺,Na⁺,Al⁺,Ca⁺,and K⁺ are difficult to characterize by most of the currently used methods.The detection limit and image resolution are also not ideal enough.The elemental imaging of H elements is more difficult to achieve.ToF-SIMS can detect light elements and has excellent lateral resolution and is an important method in glass corrosion research.However,it is still needed to investigate the optimized settings during the experimental process.The first part of this work explored the imaging of H⁺and B⁺,Na⁺,Al⁺,Ca⁺,and K⁺ ions in ISG bulk glass.The rise of vacuum and H background during the analysis were discussed,and the ways to solve these problems were also proposed.Finally,the elemental imaging of corrosion layers in the glass was successfully achieved.This method is also very effective for H,which is extremely difficult to image,and the lateral resolution can reach as well as 200 nm.5.In the second part of the glass etching work,we discussed the corrosion behavior of ISG particles.Due to the irregular shape and the large surface area/solution volume ratio?S/V?,the corrosion behavior of ISG glass particles is very complex.This work provides a way for observing the various corrosion behaviors in the ISG particles.It is observed that the ion exchange behavior is not only closely related to the S/V,but also related to the stress change during the corrosion process.In addition,solution molecules will enter the glass through micron-sized defects and cause more serious corrosion,which in turn causes glass fragmentation.This is one of the reasons for its complex corrosion behavior.The main instrument in this dissertation is a time-of-flight secondary ion mass spectrometry?ToF-SIMS 5?.Other experimental instruments were also used as supplemental tools.For example,the study of the behavior of hydrogen in polycrystalline tungsten has been assisted by scanning tunneling microscopy?SEM?,focused ion beam?FIB?,transmission electron microscopy?TEM?and X-ray diffraction?XRD?.The research on the corrosion mechanism of glass also utilizes related techniques such as SEM.This dissertation makes full use of the characteristics and advantages of ToF-SIMS,which provides H distributions with high resolutions and better sensitivities.Moreover,it enables the high-resolution imaging for various elements?including H?of the corrosion layers in the glass.The analytical method and experimental process of this work can also be extended to the analysis of other inorganic materials.This indicates the importance of ToF-SIMS in the interface imaging and depth analysis of nuclear materials.Finally,the development prospects of this technology in the fields of material analysis are also discussed.