Experiment And Atomistic Simulation On Macro-properties And Micro-structures Of Borosilicate Glasses

Borosilicate glass has potential application for vitrification of high-level radioactive waste,which attracts extensive interest worldwide in studying its radiation durability.This work simulated the impact of decays induced from radionuclide during geological disposal on the nuclear waste borosilicate glass form via conducting different ions irradiation experiments.Besides,we used several characterization methods to evaluate the variation of macroscopic properties of these irradiated glasses.For further understanding of the mechanism behind the properties'variations of the pristine and irradiated borosilicate glasses,dynamics molecular simulation method was combined with experimental method to investigate the variation of the structures?elastic parameters and other changes of glasses according to irradiation.Besides,we attempted to analyze the relationship between the macroscopic elastic properties and microscopic structures,which meant making the microscopic mechanism which leads to macroscopic properties'variation clear as much as possible.In terms of experiments——First of all,B type borosilicate glass samples were irradiated by Xe and Kr ions with different fluences.For samples irradiated by Xe and Kr ions,the hardness variation dropped with the irradiation dose in displacement per atom.The experimental results are consistent with those of other studies.A rough model was proposed to explain the results of this study and those of others.Then we use Kr ions to irradiate NBS1 and NBS2 glasses.With the increase of the irradiation dose,both the values of hardness and the modulus dropped and then saturated.The trend was consistent with previous studies,but the decay constants for the hardness of NBS1 and NBS2 were less than those in previous studies.After that,the borosilicate glass samples were irradiated with different ions(single energy Kr ions,single energy Xe ions,single energy P ions,multi energy Ne ions,multi energy Xe ions).The dependence of hardness and modulus on irradiation dose was studied.A semi-empirical formulation was proposed.Possible reasons for the change of modulus and hardness were discussed.Besides,we also irradiated borosilicate glasses with?rays to probe the evaluation of defects and energy bands with absorbed dose.In terms of simulation——Based on precious previous experience,we applied a kind of applicable potential model which to our simulation work and that simplified the simulation procedure very much.Refer to the method in experiments,that using irradiation dose to make analyzing the results of borosilicate glasses irradiated with different ions at same time possible,we introduced a simple version of simulated irradiation process.We named it defects accumulation method,which is independent on the species of incident ions.With the above two points,we successfully reproduced the experimental results and made some predictions about several parameters of irradiated glasses with simulation method.With a combination of atomistic modeling and experimental techniques we have investigated the structural and elastic parameters of sodium borosilicate glasses,including irradiation-induced changes.1)Both approaches show that the Young's modulus depends linearly on the density of material.2)The simulated glass density and boron speciation match also the estimates by independent,elemental glass composition-based models,indicating that atomistic simulations could be used in validation of theoretical models and experimental results.This allows us to formulate Young's modulus-density relationships for investigated borosilicate glasses and test the existing empirical model for description of Vickers hardness of these materials.3)The simulation of irradiation reveals a change of B^[4]content under irradiation.4)By applying a simple defects accumulation procedure,we are able to correctly reproduce the measured critical irradiation dose of?0.1 dpa and provide reasonable information on density change and stored internal energy.5)With the obtained agreements between the experimental and simulations results we obtained superior insights into the atomic-scale structural evolution of the irradiated borosilicate glasses.