Preparation And Irradiation-resistance Of Polymer-derived SiC Materials Modified By Carbon Nanomaterials

With the development of the nuclear industry,more and more people pay attention to the safety and dependability of nuclear facilities.Particularly,the new Gen.IV nuclear reactor has higher core temperature and higher radiation dose,which poses a severe challenge to the traditional nuclear structural materials.Nanocrystallization and heterogeneous interfaces are the effective ways to realize the“super irradiation-resistant”materials.Based on the excellent property of traditional SiC application potential in extreme nuclear environment material,the nanocrystallization of SiC and the construction of heterogeneous interface by introducing carbon nanomaterials as the second phase is carried out in this paper in order to improve the amorphous phenomenon and obvious volume swelling under room temperature irradiation.The main research contents and results are as follows:（1）The dynamic transformations and damage behavior of free-standing multi-wall carbon nanotubes（CNT）,carbon nano-onions（CNO）,as well as nanodiamonds（ND）are systematically studied by carrying out in-situ transmission electron microscope（in-situ TEM）measurements.Three key factors,including sp²-sp³ hybrid,inherent defects and morphology,are employed in order to deeply explain the irradiation damage mechanism of carbon nanomaterials.Interestingly,the above carbon structures exhibit similar defect types（new graphite planes and vacancy lines）but different structural stability under electron irradiation by HR-TEM.Under the high dose(26.98×10²⁴ e/cm²)and current density（1.66×10³ A/cm² and 3.79×10³A/cm²）,the NDs and CNOs with～10 nm average diameter presented better structural stability than the CNTs with length-diameter ratio 200～2000.By comparing the defective and the perfect CNOs and CNTs,the existence of inherent defects in the material leads to the degeneration of the stability under irradiation of 5.59×10²⁴e/cm².Further comparison between sp³（ND）and sp²（CNO）shows that sp³structure transforms to sp² structure under electron irradiation and sp² structure shows better stability.In addition,the direction of the defect migration can be changed by the empty internal space,which is ultimately imposed by irradiation-induced pressure in the carbon nanostructures.（2）The optimized nanodiamonds and carbon nano-onions were mixed with solid Polycarbosilane to prepare polymer conversion SiC（PDC-SiC）modified by nano carbon materials with different volume fractions.HR-TEM shows that the addition of ND promotes the growth of SiC grains and inhibits the precipitation and growth of carbon structure,while CNO is just the opposite.The room temperature irradiation experiments of 2 Me V Au²⁺at the dose of 0.25 dpa（displacement per atom）and 1 dpa were carried out to study the effects of the type and content of carbon nanomaterials on the irradiation resistance of the obtained materials.The results show that the critical amorphous dose of ND/PDC-SiC and CNO/PDC-SiC is greater than traditional single crystal SiC（0.25 dpa）,and show a greater degree of"interface driven shrinkage"behavior.Raman spectrum and AFM show that the carbon nanostructure improves the crystal structure stability of the carbon structure in PDC-SiC.The irradiation resistance increases with the increase of the content.Compared with ND,the effect of CNO on the irradiation amorphization resistence and volume swelling of PDC-SiC is more obvious.In terms of macroscopic properties,the addition of ND is more conducive to the irradiation mechanical stability of PDC-SiC.After annealing the irradiated samples at 800～1100℃,the thermal repair behavior of SiC and C structures in the materials can be realized with the increase of temperature.And the thermal repair phenomenon of CNO is more obvious.