γ预辐照对管流冲刷条件下铍在EDM-1中腐蚀性能的影响

Corrosion of beryllium in EDM-1 fluid after γ pre-irradiation

构建管流式冲刷腐蚀实验装置研究γ预辐照对铍在一号电火花加工油(EDM-1)中腐蚀性能的影响,研究铍试样质量变化,进行表面形貌及成分分析.结果表明,铍在EDM-1管流冲刷条件下受冲刷腐蚀和化学腐蚀的共同作用,前者主要受试样表面形态影响,后者主要受γ预辐照剂量、杂质元素、EDM-1中含硫有机物等的影响.辐照前后,试样质量均呈现先减小、后增大、再减小趋势,腐蚀速率基本随辐照剂量的升高而增大.γ预辐照促进了铍试样在EDM-1中点蚀核和蚀孔的产生,腐蚀2880 h后,未接受预辐照试样仅产生较为明显点蚀核,而接受200和100 k Gy预辐照试样中的部分点蚀核发展成为蚀孔,前者直径约为后者2倍.点蚀核和蚀孔区域出现Al、Si、Fe、Cr、Ti等杂质元素及S元素,杂质元素为诱导产生点蚀的重要因素,含S有机物发生化学反应分别生成物理吸附和化学吸附于蚀孔内部的SO2和SOx,促进蚀孔的形成及扩展.

Beryllium is one of the most important materials in particle physics and nuclear physics experiments.Among these applications,it is used as the material in particle collision tubes,such as the beam pipe in the operational Beijing Electron and Positron Collider (BEPC II)and in the Circular Electron Positron Collider (CEPC)currently in the planning stage.High-speed particles produce large amounts of γ irradiation and impose a heat load on the beam pipe.The beam pipe must be cooled by the scouring fluid to maintain a stable temperature for particle detection;this cooling process will induce fluid erosion of the beam pipe.The corrosion prop- erties of materials in contact with the oil No.1 for electric discharge machining (EDM-1)fluid under irradiation are not yet known.A device for testing pipeline corrosion was built to study the corrosion of beryllium in EDM-1 fluid after γ pre-irradiation.The mass of the sample was measured by an electronic balance,and the surface morphologies and composition were examined by scanning electron microscopy (SEM),X-ray energy dispersive spectroscopy (EDS),X-ray photoelectron spectroscopy (XPS),and X-ray diffraction (XRD).The results show that the corrosion of beryllium in EDM-1 is affected by two corrosion mechanisms:erosion and chemical corrosion.Erosion is mainly influenced by the surface morphology of the sample,whereas the chemical corrosion is mainly influenced by the dose of γ irradiation,impurity elements in the sample,and organic sulfides in EDM-1.Measurements of the sample before and after irradiation reveal that the mass decreases,then increases,and then decreases again under the combined effects of the two kinds of corrosion.The corrosion rate increases substantially with increasing radiation dose,and γ pre-irradiation promotes pitting nucleation and the formation of pitting holes in beryllium in EDM-1.After 2880 h of corrosion,the sample not subjected to pre-irradiation exhibits only obvious pitting nuclei,whereas some of the pitting nuclei on the sample subjected to 200 and 100 kGy of pre-irradiation develop pitting holes ;the diameter of the pitting holes in the former case is approximately twice that of the pitting holes in the latter case.The larger the radiation dose,the earlier the pitting occurs and the larger the diameter of the corrosion holes.Impurity elements (e.g.,Al, Si,Fe,Cr,and Ti)and S appear in the pitting nuclei and pitting holes.The impurity elements in the beryllium samples are important factors to induce pitting.The chemical reactions of organo-sulfur compounds produce SO2 and SOx (SO2,SO3 ,and SO4)in the pitting holes by physical and chemical adsorption,which promotes the formation and expansion of pitting.