Amorphization Dose Research Articles

Temperature dependence of irradiation-induced amorphization in a high-entropy titanate pyrochlore

AbstractThe temperature dependence of amorphization in a high-entropy pyrochlore, (Yb0.2Tm0.2Lu0.2Ho0.2Er0.2)2Ti2O7, under irradiation with 600 keV Xe ions has been studied using in situ transmission electron microscopy (TEM). The critical amorphization dose increases with temperature, and the critical temperature for amorphization is 800 K. At room temperature, the critical amorphization dose is larger than that previously determined for this pyrochlore under bulk-like 4 MeV Au ion irradiation but is similar to the critical doses determined in two other high-entropy titanate pyrochlores under 800 keV Kr ion irradiation using in situ TEM, which is consistent with reported behavior in simple rare-earth titanate pyrochlores. Graphical abstract

Investigation of the damage behavior in SiC without any additives irradiated with Si ions by GIXRD, Raman and TEM

The SPS-prepared SiC without any additives was irradiated with 15.9 MeV Si ions at room temperature and 500 °C. The damage behavior was investigated by grazing incident X-ray diffraction (GIXRD) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM). GIXRD and Raman spectra show that the disorder of SiC increases and the lattice swelling occurs with the increase of irradiation at room temperature. High temperature irradiation was associated with the reduction of swelling and the recovery of disorder. TEM results indicate that at room temperature, with increasing dose, the material transitions from slight amorphization to complete amorphization. The amorphization dose is estimated to be around 1.2 dpa. The combined effects of stacking faults, high-energy ions accompanied by higher electronic energy loss inducing displacement cascades, and cascade-induced annealing delay damage accumulation, leading to an increased critical dose for amorphization. Moreover, the transient thermal spikes due to higher electronic energy loss, leading to defect annealing and the formation of Frank loops at lower irradiation temperatures.

“Invisible” radioactive cesium atoms revealed: Pollucite inclusion in cesium-rich microparticles (CsMPs) from the Fukushima Daiichi Nuclear Power Plant

Understanding radioactive Cs contamination has been a central issue at Fukushima Daiichi and other nuclear legacy sites; however, atomic-scale characterization of radioactive Cs in environmental samples has never been achieved. Here we report, for the first time, the direct imaging of radioactive Cs atoms using high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In Cs-rich microparticles collected from Japan, we document inclusions that contain 27 – 36 wt% of Cs (reported as Cs2O) in a zeolite: pollucite. The compositions of three pollucite inclusions are (Cs1.86K0.11Rb0.19Ba0.22)2.4(Fe0.85Zn0.84X0.31)2.0Si4.1O12, (Cs1.19K0.05Rb0.19Ba0.22)1.7(Fe0.66Zn0.32X0.41)1.4Si4.6O12, and (Cs1.27K0.21Rb0.29Ba0.15)1.9(Fe0.60Zn0.32X0.69)1.6Si4.4O12 (X includes other cations). HAADF-STEM imaging of pollucite, viewed along the [111] zone axis, revealed an array of Cs atoms, which is consistent with a simulated image using the multi-slice method. The occurrence of pollucite indicates that locally enriched Cs reacted with siliceous substances during the Fukushima meltdowns, presumably through volatilization and condensation. Beta radiation doses from the incorporated Cs are estimated to reach 106 – 107 Gy, which is more than three orders of magnitude less than typical amorphization dose of zeolite. The atomic-resolution imaging of radioactive Cs is an important advance for better understanding the fate of radioactive Cs inside and outside of nuclear reactors damaged by meltdown events.

Effects of grain boundary volume fraction on the threshold dose of irradiation-induced SiC amorphization at 30 °C

Effects of grain boundary volume fraction on the threshold dose of irradiation-induced SiC amorphization at 30 °C

Atomic-scale observation and prediction of gallium ion implantation induced amorphization on natural diamond surface

Gallium ion implantation is an important solution to modify the physical properties of diamonds, in which the critical condition of gallium ion implantation-induced amorphization of diamond has a crucial influence on the modification effect. Therefore, this work attempts to establish an analytical prediction model of the critical implantation dose for diamond amorphization considering the acceleration voltage, implantation angle and crystal orientation. The prediction accuracy of the model is validated with the electron backscatter diffraction pattern technology. The results show that the model has a satisfactory prediction accuracy when the acceleration voltage is higher. Moreover, the atomic-scale observation of gallium ion implantation-induced amorphization of natural diamonds is realized on a spherical aberration projection electron microscope. The results presented in this work are significant to modify the natural diamond tool for service life improvement with focused ion beams in the future as well as to guide doping diamonds to manufacture n-type semiconductor diamonds.

Drop-on-powder 3D printing of amorphous high dose oral dosage forms: Process development, opportunities and printing limitations

Drop-on-powder 3D printing is able to produce highly drug loaded solid oral dosage forms. However, this technique is mainly limited to well soluble drugs. The majority of pipeline compounds is poorly soluble, though, and requires solubility enhancement, e.g., via formation of amorphous solid dispersions. This study presents a detailed and systematic development approach for the production of tablets containing high amounts of a poorly soluble, amorphized drug via drop-on-powder 3D printing (also known as binder jetting). Amorphization of the compound was achieved via hot-melt extrusion using the exemplary system of the model compound ketoconazole and copovidone as matrix polymer at drug loadings of 20% and 40%. The milled extrudate was used as powder for printing and the influence of inks and different ink-to-powder ratios on recrystallization of ketoconazole was investigated in a material-saving small-scale screening. Crystallinity assessment was performed using differential scanning calorimetry and polarized light microscopy to identify even small traces of crystallinity. Printing of tablets showed that the performed small-scale screening was capable to identify printing parameters for the development of amorphous and mechanically stable tablets via drop-on-powder printing. A stability study demonstrated physically stable tablets over twelve weeks at accelerated storage conditions.

Enhanced irradiation-resistance of polymer-derived SiC by incorporation of multiwalled carbon nanotubes

In this work, multiwalled carbon nanotubes were introduced into polycarbosilane to fabricate carbon nanotubes reinforced nano-SiC composites (MWCNTs/ PCS-nano-SiC). Radiation effects on MWCNTs/ PCS-nano-SiC were studied by irradiation with 2 MeV Au2+ ions at room temperature and doses ranging from 2 × 1014 to 8 × 1014 ions/cm2. The sample pyrolyzed at 1400 °C and containing 3 wt% carbon nanotubes exhibited excellent overall performances. The multiple graphite layers in the MWCNTs provided "absorption traps" for defects, improving the efficiency of defect recombination. Tightly combined MWCNTs/ PDC interface is required to enable the two phases to protect each other during irradiation. The critical amorphization dose was increased upon structural optimization, and the hardness degradation was significantly reduced. The rise of Young's modulus at a high damage dose was discovered because of the "interface-driven shrinkage" of nano-SiC. The present study provides insight into SiCf/ SiC design for an advanced nuclear system.

Mechanical property and irradiation resistance of high entropy pyrochlore (Sm0.2Eu0.2Gd0.2Y0.2Lu0.2)2Ti2O7

High entropy ceramics have recently attracted a lot of attention due to their superior physical properties. In this work, a novel high entropy pyrochlore (Lu0.2Y0.2Gd0.2Eu0.2Sm0.2)2Ti2O7 (HTP-1) was designed and prepared. Sample was characterized by X-ray diffraction, Raman spectroscopy and transmission electron microscopy coupled with an energy dispersive spectrometry. The results show that single-phase HTP-1 is successfully synthesized and exhibits severe lattice distortion. The Vickers hardness of HTP-1 measured by the microhardness tester is ∼ 922.28 Hv, which is significantly higher than the result calculated with the mixture rule, demonstrating that high entropy pyrochlore has high mechanical hardness. In-situ TEM was performed on HTP-1 irradiated with 800 keV Kr2+ at room temperature to investigate irradiation resistance of sample. The critical amorphization dose of HTP-1 is 0.27 dpa, which indicates the irradiation resistance of HTP-1 is between Sm2Ti2O7 and Y2Ti2O7.

Radiation induced amorphization of carbides in additively manufactured and conventional ferritic-martensitic steels: In-situ experiments on extraction replicas

In-situ irradiations using 1 MeV Kr2+ ions in a transmission electron microscope were performed on extraction replica samples containing M23C6 carbides and MX carbonitrides from two ferritic-martensitic (FM) steels: (i) 9%Cr-1%W-TaV based Eurofer97 and (ii) 9%Cr-1%Mo-VNb (all in wt.%) based additively manufactured (AM) Grade91 steel. The irradiations were performed between 100 and 773 K up to a maximum dose of ∼2.4 displacements per atom (dpa). The M23C6 carbides are highly susceptible to radiation induced amorphization (RIA), while the MX type nanoprecipitates are highly amorphization resistant across the entire irradiation temperature range. Between 100 and 423 K, RIA of M23C6 carbides occurs very rapidly with critical amorphization doses ranging between ∼0.35 and 0.9 dpa, increasing to higher doses at 573 K. Complete amorphization of the M23C6 carbides up to doses of ∼2.4 dpa is not possible at 773 K under the present irradiation conditions. The critical amorphization dose of M23C6 carbides increases nearly exponentially with irradiation temperature. The critical temperature for the crystalline-to-amorphous phase transformation (Tc→a) of M23C6 carbides irradiated as replica samples, i.e. without the surrounding metal matrix, was estimated to be ∼812 K. Comparing the present results with neutron irradiation data on bulk samples reveals a decrease in the critical amorphization dose for M23C6 and an increase of Tc→a, highlighting the effect of dose rate on the amorphization behavior that is qualitatively consistent with literature on other non-metals. Changes in the minor chemistry of M23C6, such as presence or absence of W, V, Nb, Mo, seems to have little effect on the amorphization behavior. In-situ irradiations on extraction replica samples provide a novel pathway to explore radiation tolerance of nanoprecipitates in nuclear structural materials

Radiation stability of nanostructured hydroxyapatite Ca10(PO4)6(OH)2 under ion irradiations

Radiation stability of nanostructured hydroxyapatite with different interfacial structure is studied. Hydroxyapatite nanoparticle (HAp-np) is fabricated by calcination in muffle furnace and densified nanocrystalline hydroxyapatite (HAp-nc) is synthesized by spark plasma sintering . X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations show the hexagonal structure for both HAp-np and HAp-nc. Irradiation responses of HAp-np and HAp-nc are studied via in situ TEM techniques. The samples are irradiated with 1 MeV Kr 2+ ions over the temperature range of 150 K to 523 K. In situ TEM observations reveal a higher critical amorphization dose of HAp-nc (0.075 dpa) compared to 0.05 dpa of HAp-np at room temperature, indicating enhanced amorphization resistance. The radiation tolerance shows a great dependence on temperature, and a higher critical dose can be observed at elevated temperatures. A lower critical amorphization temperature ( T c ) of HAp-nc (∼437 K) than HAp-np (∼545 K) indicates better radiation tolerance since the lower T c shows better defect annealing ability. This better radiation tolerance of HAp-nc is attributed to the higher sink strength and lower interface energy carried by densified grain boundaries as free-standing open surfaces of HAp-np can carry more isolated dangling bonds that results in a higher interface energy. This excess interface energy can lower the energy difference between crystalline phase and amorphous state, leading to HAp-np to be less radiation resistant. Radiation-induced amorphization is attributed to the accumulation of oxygen vacancies and the glass-like structure rearranged by displaced oxygen and phosphorus atoms.

Calculating Silicon-Amorphization Doses under Medium-Energy Light-Ion Irradiation

Based on the previously proposed diffusion-coagulation model of defect formation under the ion irradiation of silicon using the numerical solution of the corresponding kinetic equations, amorphization doses Φam for medium-energy ions with a mass of M1 ≤ 31 amu are calculated. It is assumed that amorphization at a specified depth occurs at a dose corresponding to a certain threshold total concentration Cam of vacancies and divacancies. In the calculation, the variable parameters are the ion energy, ion-current density, temperature, threshold atomic-displacement energy Ed, and Cam. The limits of applicability of the diffusion-coagulation model are determined. Comparison of the results of calculation within these limits with published experimental data shows, with regard to a variation in the experimental data and some freedom in choosing the parameters Ed and Cam, satisfactory agreement between the calculated and experimental Φam values.

Расчет доз аморфизации кремния при облучении легкими ионами средних энергий

Based on the previously proposed diffusion–coagulation model of defect formation under ion irradiation of silicon and numerically solving the corresponding kinetic equations, amorphization doses (Фam) for ions of medium energy with a mass of M1 ≤ 31 a.m.u. were calculated. It is assumed that amorphization at a given depth occurs at a dose at which a certain threshold value of the total concentration of vacancies and divacancies (Cam) is reached. Variable parameters in the calculations were: ion energy, ion current density, temperature, as well as the threshold atomic displacement energy of atom (Ed) and Cam. Limits of the diffusion–coagulation model are determined. Comparison of the results of calculations carried out at these limits with published experimental data showed (taking into account the variation of the experimental data and a certain freedom of choice of the parameters Ed and Cam) a satisfactory agreement between the calculated and experimental values of Фam.

Synthesis of novel hybrid carbon nanomaterials inside silicon carbide nanotubes by ion irradiation

A novel hybrid carbon nanomaterial was synthesized by ion irradiation of a C–SiC coaxial nanotube. The hybrid consisted of one-dimensionally stacked graphene nanodisks with diameters less than 50 nm and cylindrical multiwalled carbon nanotubes inside an amorphous SiC tubular layer. A sudden emergence of new continuous graphitic layers in the microstructure were observed by in situ transmission electron microscopy following ion irradiation, where these layers were perpendicular to the nanotube's length direction. The SiC crystals in the C–SiC coaxial nanotube became amorphous, also due to the ion irradiation, although the critical amorphization dose was higher than that for bulk SiC. Most remarkably, the carbon layer remained crystalline, even after an irradiation dose higher than 20 dpa (displacement per atom). Such results show that these carbon layers possess better resistance against amorphization when subjected to ion irradiation than the SiC layers in the C–SiC coaxial nanotube. The lattice plane spacing of the carbon layer increases up to the point when irradiation damage lead to the complete amorphization of SiC crystals, after which it starts to decrease. This demonstrates that the carbon layer experiences high compression stress during ion irradiation. Thus, the ion irradiation of C–SiC coaxial nanotubes gives rise to a novel development of the microstructure and can be considered as one of the new synthetic processes for making novel carbon nanomaterials.

Electron beam damage of perfluorosulfonic acid studied by soft X-ray spectromicroscopy

Scanning transmission X-ray microscopy (STXM) was used to study chemical changes to perfluorosulfonic acid (PFSA) spun cast thin films as a function of dose imparted by exposure of a 200 kV electron beam in a Transmission Electron Microscope (TEM). The relationship between electron beam fluence and absorbed dose was calibrated using a modified version of a protocol based on the positive to negative lithography transition in PMMA [Leontowich et al, J. Synchrotron Rad. 19 (2012) 976]. STXM was used to characterize and quantify the chemical changes caused by electron irradiation of PFSA under several different conditions. The critical dose for CF2-CF2 amorphization was used to explore the effects of the sample environment on electron beam damage. Use of a silicon nitride substrate was found to increase the CF2-CF2 amorphization critical dose by ∼x2 from that for free-standing PFSA films. Freestanding PFSA and PMMA films were damaged by 200 kV electrons at ∼100 K and then the damage was measured by STXM at 300 K (RT). The lithography cross-over dose for PMMA was found to be ∼2x higher when the PMMA thin film was electron irradiated at 120 K rather than at 300 K. The critical dose for CF2-CF2 amorphization in PFSA irradiated at 120 K followed by warming and delayed measurement by STXM at 300 K was found to be ∼2x larger than at 300 K. To place these results in the context of the use of electron microscopy to study PFSA ionomer in fuel cell systems, an exposure of 300 e−/nm2 at 300 K (which corresponds to an absorbed dose of ∼20 MGy) amorphizes ∼10% of the CF2-CF2 bonds in PFSA. At this dose level, the spatial resolution for TEM imaging of PFSA is limited to 3.5 nm by radiation damage, if one is using a direct electron detector with DQE = 1. This work recommends caution about 2D and 3D morphological information of PFSA materials based on TEM studies which use fluences higher than 300 e−/nm2.

Laser 3D printing of Zr-based bulk metallic glass

Bulk metallic glasses (BMGs) have attracted increasing attention and tremendous interest owing to their extraordinary mechanical and chemical properties. However, the limited dimensions and simple geometries of the BMGs fabricated by traditional techniques severely restrict their widespread applications. In the present study, a large-size Zr50Ti5Cu27Ni10Al8 (Zr50) BMG is successfully fabricated by laser 3D printing technique. The SEM and XRD results reveal that the microstructure of printed Zr50 BMG consists of both amorphous and crystalline phases. The printed Zr50 alloy possessed high percentage of amorphous phase and dose not crystallize more seriously as the deposited sample becomes thicker.

Stored energy release in neutron irradiated silicon carbide

The purpose of this investigation is to experimentally quantify the stored energy release upon thermal annealing of previously irradiated high-purity silicon carbide (SiC.) Samples of highly-faulted polycrystalline CVD β-SiC and single crystal 6HSiC were irradiated in a mixed spectrum fission reactor near 60 °C in a fluence range from 5 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.05–20 dpa, in order to quantify the stored energy release and correlate the release to the observed microscopic swelling, lattice dilation, and microstructure as observed through TEM. Within the fluence of this study the crystalline material was observed to swell to a remarkable extent, achieving 8.13% dilation, and then cross a threshold dose for amorphization at approximately 1 × 1025 n/m2 (E > 0.1 MeV) Once amorphized the material attains an as-amorphized swelling of 11.7% at this irradiation condition. Coincident with the extraordinary swelling obtained for the crystalline SiC, an equally impressive stored energy release of greater than 2500 J/g at the critical threshold for amorphization is inferred. As expected, following amorphization the stored energy in the structure diminishes, measured to be approximately 590 J/g. Generally, the findings of stored energy are consistent with existing theory, though the amount of stored energy given the large observed crystalline strain is remarkable. The overall conclusion of this work finds comparable stored energy in SiC to that of nuclear graphite, and similar to graphite, a stored energy release in excess of its specific heat in some irradiation conditions.

In-situ TEM study of radiation-induced amorphization and recrystallization of hydroxyapatite

The radiation response of hydroxyapatite, a nuclear waste form candidate, was investigated using 1 MeV Kr2+ and 200 keV electron irradiations combined with in-situ TEM observation. The results showed a remarkable difference in the behavior of nano-crystalline hydroxyapatite under the two different radiation conditions. A crystalline-to-amorphous transformation occurred under the 1 MeV Kr2+ irradiation due to the accumulation of displacement damage, with a critical amorphization dose (Dc) of 2 × 1014 ions/cm2 (0.05 dpa) at room temperature. The Dc increased dramatically with temperature due to effective dynamic annealing of radiation-induced defects, such that no amorphization occurred above a critical temperature (Tc) of 545 K. In contrast, under 200 keV electron irradiation, which mainly dissipates its energy through inelastic ionization processes, the pre-amorphized hydroxyapatite exhibited rapid recrystallization, likely due to the bond breaking and reforming at the amorphous-crystalline interface assisted by the ionization. The electron-irradiation induced recrystallization in amorphous hydroxyapatite was extremely sensitive, with a critical electron dose several orders of magnitude lower than most previously reported ceramics. Under concurrent ion and electron irradiations, the materials retained crystalline even at the critical dose of 0.05 dpa, and remained so until the dose reached 0.15 dpa, lending further proof to the enhanced defect recovery by ionizing electrons. The radiation data of hydroxyapatite highlights the material's sensitivity to radiation conditions and its excellent dynamic defect annealing ability.

Murataite: a matrix for immobilizing waste generated in radiochemical reprocessing of spent nuclear fuel

Incorporation of waste from spent nuclear fuel pyrochemical reprocessing and calcines from the decontamination of glove box and hot cell equipment into murataite-based ceramics was studied. The phase and chemical compositions of the ceramics containing precipitates simulating fission products in molten chlorides were examined. The radiation stability of murataite matrices was studied by incorporating 244Cm isotope (1.8 wt%). In the ceramics produced by melting at 1325 and 1350 °C the murataite phases was rendered to be X-ray amorphous at doses of 2.46 × 1018 and 2.53 × 1018 α-decay/g (0.21 dpa), while for the sample sintered at 1250 °C the amorphization dose was found to be 2.73 × 1018 α-decay/g (0.21 dpa). The murataite structure was recovered after the annealing at 1250 °C for 5 h in air. Both the pristine and amorphized samples had very low leachability of Cm and major elements. Production of highly durable murataite-based ceramics containing waste surrogate after spent nuclear fuel (SNF) pyrochemical reprocessing and calcine after the evaporation of decontamination solutions were demonstrated.

In-situ TEM study of the ion irradiation behavior of U3Si2 and U3Si5

U3Si2 and U3Si5 are two important uranium silicide phases currently under extensive investigation as potential fuel forms or components for light water reactors (LWRs) to enhance accident tolerance. In this paper, their irradiation behaviors are studied by ion beam irradiations with various ion mass and energies, and their microstructure evolution is investigated by in-situ transmission electron microscopy (TEM). U3Si2 can easily be amorphized by ion beam irradiations (by 1 MeV Ar2+ or Kr2+) at room temperature with the critical amorphization dose less than 1 dpa. The critical amorphization temperatures of U3Si2 irradiated by 1 MeV Kr2+ and 1 MeV Ar2+ ion are determined as 580 ± 10 K and 540 ± 5 K, respectively. In contrast, U3Si5 remains crystalline up to 8 dpa at room temperature and is stable against ion irradiation-induced amorphization up to ∼50 dpa by either 1 MeV Kr2+ or 150 KeV Kr+ at 623 K. These results provide valuable experimental data to guide future irradiation experiments, support the relevant post irradiation examination, and serve as the experimental basis for the validation of advanced fuel performance models.

Behavior of Host Materials with Surrogates of the Rare Earth–Actinide Fraction under Ion Irradiation

The behavior of rare earth titanate phases of monoclinic and orthorhombic symmetry under ion irradiation was studied. Three samples contain a set of rare earth elements (REE), and in one sample the high-level waste (HLW) is simulated by neodymium. The samples were prepared by sintering at 1400°С or cold crucible induction melting followed by melt crystallization. The samples were irradiated with 1-MeV Kr2+ ions at temperatures in the range 298–1023 K on a tandem installation consisting of an ion accelerator and a transmission electron microscope. The critical amorphization doses for the samples at 298 K were (1.5–2.5) × 1014 ion cm–2. These values correspond to those for monoclinic titanates Nd2Ti2O7 and La2Ti2O7, are close to those for REE–Ti pyrochlores and brannerite, and are lower by an order of magnitude than those for zirconolites at the same irradiation mode. The critical amorphization temperature of the phases studied (900 K) is comparable to that of Nd2Ti2O7 (920 K), but higher than that of La2Ti2O7 (840 K). Close radiation resistance of the REE2Ti2O7 and REE4Ti9O24 phases in which the rare earth elements are represented by a mixture of elements similar in composition to their set in spent nuclear fuel and liquid HLW from its reprocessing or solely by Nd confirms the assumption that Nd is a suitable surrogate for the whole rare earth–actinide fraction.