| The development of nuclear energy has led to the generation of a large amount of nuclear waste.How to properly store these nuclear waste is an important factor restricting the development of nuclear energy.The solidified material needs to maintain good structural stability in the long-term geological storage and in the irradiated environment of high-level nuclear waste.Apatite structural material(structure general formula A10(MO4)6Z2)has become a very potential solidified body due to its excellent nuclide tolerance,good physical and chemical stability,and rich content.In this paper,the growth and aggregation of He bubbles in apatite Ca10(PO4)6X2(X=F,Cl,OH)structural materials are simulated and studied by irradiation of He ions at room temperature and high temperature.In this paper,a single Ca10(PO4)6X2(X=F,Cl,OH)apatite was prepared by the traditional solid-phase sintering method.Apatite samples were irradiated with He ions at room temperature and high temperature.The irradiated samples were annealed in situ at high temperature to further compare with the high temperature irradiation experiments.The samples before and after irradiation were simulated using SRIM code,and GIXRD,Raman,and TEM were used to characterize the structure changes of the samples before and after irradiation,as well as to observe the micro-morphology and the growth of He bubbles.In the high temperature irradiation experiment(irradiation energy 80 keV,dose 5×1016 ions/cm2),no obvious radiation damage bands appeared in the Ga10(PO4)6X2(X=F,OH)samples,and the distribution of He bubbles exceeded The most important reason for the SRIM simulation is that the mobility of He ions is greatly improved during high temperature irradiation.Secondly,because the grain size of the sample surface is in the micron level,the channel effect may also promote the He ion to a certain depth.In both samples,He bubbles tend to aggregate at grain boundaries,and He bubbles at grain boundaries are denser and larger in diameter.In Ca10(PO4)6(OH)2 samples,He bubbles are uniformly distributed in an oval shape,while in Ca10(PO4)6F2 samples,He bubbles are more likely to gather together.Formation of He bubble chains and larger irregular He bubbles.At room temperature,TEM observed a radiation damage zone in good agreement with the SRIM simulation,which further illustrates that the migration of He bubbles to a deeper place at high temperature is mainly due to the increase in the mobility of He ions during high temperature irradiation.In all the irradiated samples,the lattice constant and unit cell volume of the irradiated samples increased slightly,the GIXRD diffraction peaks remained well,and no amorphous or other substances appeared in the samples.Even if the irradiation dose was increased to 2×1017 ions/cm2,the sample still maintained a good crystal structure,and no He bubble was observed in the sample irradiated at room temperature.Samples with a dose of 5×1016 ions/cm2 were selected for annealing and compared with high temperature annealing experiments.The location of the He bubble band also corresponds to the SRIM simulation.When the temperature is raised to 450 ℃,He bubbles rapidly appear and grow,but the growth and migration of He bubbles are not obvious when the temperature is maintained at 450℃.He bubbles show more obvious aggregate growth.Small He bubbles are gradually absorbed by larger He bubbles and grow into larger He bubbles.Some He bubbles around He bubbles are absorbed by other He bubbles,so they become isolated He.Bubble,it is speculated that if the annealing is continued,the isolated He bubble will eventually be "swallowed".The migration and aggregation of He bubbles at the grain boundaries are also more obvious,corresponding to the previous high temperature irradiated samples. |
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