Radiation Damage In Ceramics Research Articles

In situ heating high-resolution TEM observation of structural recovery in metamict titanite

Besides radiation resistance, thermal recovery of radiation damage provides another critical criterion to evaluate the host phase for immobilizing high-level waste (HLW) produced by nuclear plants. Despite the increasing investigations, a comprehensive atomic-scale understanding remains elusive on thermal annealing of radiation damage in ceramics. Here, using in situ heating high-resolution transmission electron microscopy, we investigate the thermal annealing of radiation damage in natural metamict titanite (CaTiSiO5) caused by a high alpha decay dose from the incorporated U and Th during the geologic time. The recovery of the fully amorphous titanite precursor starts at 456 ℃ from the appearances of monoclinic nanoparticles 2–5 nanometers wide, and more nanoparticles form as the temperature gradually increases. At 1000 ℃, the amorphous phase recovers through epitaxial growth with titanite nanoparticles as templates. This study provides information for a unit-cell-scale understanding of the thermal stability of radiation damage in titanite-based ceramics, having significance for immobilizing HLW.

Study of Degradation Mechanisms of Strength and Thermal-Physical Properties of Nitride and Carbide Ceramics-Promising Materials for Nuclear Energy.

The dependences of changes in the strength properties of nitride and carbide ceramics under high temperature irradiation with Kr15+ and Xe22+ heavy ions at irradiation doses of 1012–1015 ions/cm2 are presented in this work. The irradiation was chosen to simulate radiation damage processes that are closest to the real conditions of reactor tests in operating modes of increased temperatures. Polycrystalline ceramics based on AlN, Si3N4 nitrides, and SiC carbides were chosen as objects of research, as they have great prospects for use as a basis for structural materials for high-temperature nuclear reactors, as well as materials for nuclear waste disposal. During these studies the effect of radiation damage caused by irradiation with different fluences on the change in mechanical strength and hardness were determined, and the mechanisms causing these changes depending on the type of irradiated materials were proposed. The novelty of this study is in the results obtained determining the stability of the strength and thermophysical parameters of nitride and carbide ceramics exposed to high-temperature irradiation, which made it possible to determine the main stages and mechanisms for changing these parameters depending on the accumulated radiation damage. The relevance of this study consists not only in obtaining new data on the properties of structural materials exposed to ionizing radiation, but also in the possibility of determining the mechanisms of radiation damage in ceramics.

Effect of irradiation with heavy Xe22+ ions with energies of 165–230 MeV on change in optical characteristics of ZrO2 ceramic

The aim of this work is to study the effect of irradiation with heavy Xe22+ ions with energies of 165 MeV, 200 MeV, and 230 MeV on the change in the optical properties of ZrO2 ceramic. The choice of ion energies, as well as irradiation fluences of 1013-1014 ion/cm2, is primarily due to the possibility of simulating radiation damage in ceramics that occurs when overlapping damaged areas in the material, comparable to damage from fission fragments of uranium nuclei in an atomic reactor. Using UV–Vis spectroscopy methods, changes in the throughput of ceramics were evaluated depending on the irradiation fluence and the energy of incident ions. It was found that a change in the irradiation conditions leads to the formation of irradiation-induced defects with an energy of 2.4–2.45 eV in the structure, the concentration of which increases with the irradiation dose. Changes in the band gap and refractive index depending on irradiation fluence and incident ions energy indicate a change in the electronic and optical density of ceramics, as well as the formation of additional absorbing centers in the structure.

Characterization of radiation damage in ceramics: Old challenge new issues?

Abstract

Novel approaches to multiscale modelling in materials science

Computational modelling techniques are now widely employed in materials science, due to recent advances in computing power and simulation methodologies, since they can enable rapid testing of theoretical predictions or understanding of complex experimental data at relatively low cost. However, many problems at the leading edge of materials science involve collective phenomena that occur over a range of time and length scales which are intrinsically difficult to capture in a single simulation. This review summarises some of the latest developments in multiscale modelling techniques over the past decade, as applied to selected problems in materials science and engineering, thereby motivating the reader to explore how such techniques might be applied in their own area of specialty. Methods for accelerating molecular dynamics by enhancement of kinetic barrier crossing, such as hyperdynamics and metadynamics, are discussed alongside mesoscale simulation techniques, such as dissipative particle dynamics or adaptive coarse graining, for enabling larger and longer simulations. The applications are mainly focused on simulations of microstructure and mechanical properties, and examples of surface diffusion in metals, radiation damage in ceramics, strengthening of nanocrystalline metals and alloys, crack propagation in brittle solids, polymer chain relaxation in nanocomposites and the control of nucleation in biomimetic materials are discussed.

Investigating Radiation Damage in Ceramics: the Role of In Situ Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Identifying and Quantifying Actinide Radiation Damage in Ceramics with Radiological Magic-Angle Spinning Nuclear Magnetic Resonance

AbstractIn the characterisation of amorphisation or local disordering due to actinide radiation damage, nuclear magnetic resonance (NMR) spectroscopy is attractive because it is element specific and equally sensitive to local structure in crystalline and amorphous materials. Here, we have applied high-resolution solid-state NMR spectroscopy (magic-angle spinning) to radiation damaged natural minerals containing 238U/232Th to determine the ‘number fraction’ of amorphous material (fa) through spin-counting techniques. In samples with a known alpha dose, the number of atoms displaced per alpha decay may be determined from an integration of the spectrum. A protocol for performing similar radiological magic-angle spinning experiments on plutonium containing ceramic samples with an activity of > 5 GBq isp described. Results obtained have allowed data from ancient, radiation damaged mineral samples of ZrSiO4 (238U/232Th) to be compared with modern 238/239Pu doped ceramic ZrSiO4 samples. The number of atomic displacements per alpha particle from 239Pu is similar to that for 238U/232Th (4980 ± 300/α). At lower ?-doses there are significant differences in the amorphous volume fraction (observed by density and x-ray diffraction) and the number fraction of displaced atoms (as measured by NMR) as a function of cumulative dose. These differences arise from local density considerations that manifest themselves in the local structure of the amorphous and crystalline phases. Using ab initio simulations of the damaged crystalline and amorphous regions, the magnetic response of these structures and hence the NMR shifts can be compared with experiment to reveal the nature of radiation induced changes occurring at the local scale.

Applications of advanced electron microscopy techniques to the studies of radiation effects in ceramic materials

This paper summarizes some recent results from the application of several advanced transmission electron microscopy (TEM) techniques to the studies of radiation effects in insulators with the main focus on radiation-induced amorphization. These techniques include in situ TEM during ion-beam irradiation at cryogenic and elevated temperatures, cross-sectional TEM, high-resolution TEM, and image simulation on partially damaged materials, as well as digital TEM with image processing and analysis. The combination of these techniques may often provide very detailed information about the microstructure evolution during energetic particle irradiation, especially at the early stages, which is unobtainable with any other analytical methods. These techniques have been successfully applied to the analysis of a large group of ion-beam-irradiated ceramics, including quartz, silicon carbides, uranium oxide, apatite, spinel and other complex mineral phases. The advantages and limitations of each technique, as well as some important technical details for the analysis of radiation damage in ceramics are presented.

Effects of ionizing radiation in ceramics

The evolution of radiation damage in ceramics under highly ionizing conditions has been examined by irradiating a number of oxides with high-energy heavy ions and electrons simultaneously. α-Al 2O 3, MgTiO 3, FeTiO 3 and Ca 2La 8(SiO 4) 6O 2 were irradiated with 1 MeV Kr + or 1.5 MeV Xe + and 1 MeV electrons. The irradiations were performed in a high-voltage electron microscope interfaced to an ion accelerator that enabled the in situ observation of the structural changes. The results indicate that simultaneous electron irradiation can retard or prevent amorphization by heavy ions. Comparison with similar experiments in metals suggests that highly ionizing radiation can anneal damage to the crystal lattice in ceramics by enhancing the mobility of point defects.

Characteristics of microstructural evolution of radiation damage in ceramics under fusion environment

Spinel ceramics with different stoichiometry were synthesized from MgO and Al2O3 powders by means of hot pressing. These were neutron-irradiated up to 2.3×1024n/m2 (E > 0.1 MeV) at about 500°C. For all compositions, changes in macroscopic length, lattice parameter, Vickers hardness and thermal diffusivity were very small. The average macroscopic length change induced by irradiation increased slightly with increasing Al2O3 content, but the standard deviation was large, especially near the stoichiometric composition, and some specimens actually contracted. The correspondence of length change and lattice parameter change was excellent in near stoichiometric specimens, but slightly larger change in length occurred in Al2O3-rich specimens, indicating the presence of excess vacancies.

Characteristics of microstructural evolution of radiation damage in ceramics under fusion environment

Ceramics undergo radiation damage via the processes of direct atomic displacement and electronic excitation. The microstructural evolution of radiation damage has been observed with use of electron microscopy during and/or after electron-, ion- and neutron-irradiation. A review is given of our recent progress in understanding the effects of the atomic bonding, the crystal structure, the structural vacancies and the impurities on the characteristics of the microstructural evolution such as defect clusters and amorphization in ceramics. Candidate ceramics for fusion reactors such as MgO, TiC 1− x , A1 2O 3, MgAl 2O 4, SiC and graphite are classified into four groups in terms of characteristics of dislocation loop kinetics under electron irradiation. Ion- and neutron-induced phenomena in the candidate ceramics as well as non-candidate ceramics are also summarized for the purpose of understanding the microstructural evolution of radiation damage under fusion environment.

Preliminary Model of Radiation Damage in Ceramics

A preliminary model of radiation damage in binary ceramic oxides has been developed. The model described here accounts in an approximate way for some of the major differences between metallic alloys and ceramics that are believed to be responsible for the fact that ceramic materials appear in some cases to behave differently than metallic alloys when exposed to displacive irradiation. The model considers the influence of the existence of a second lattice and the additional constraint of stoichiometric point defects absorption by dislocation loops on the concentrations of point defects that would be observed at steady state in an irradiated ceramic. These point defect concentrations are then used to compute various measures of the sensitivity of these materials to the type of microstructural evolution that is observed in irradiated metals. Initial results indicate that both the lattice and stoichiometry effects can help to mitigate radiation damage in ceramics. However, the effect is not necessarily large. In agreement with recent data, the results indicate that at least some ceramic oxides may exhibit a sensitivity to displacement damage that is similar to metals.

Radiation Damage in Ceramics

1. Introduction. Studies of radiation damage in ceramics are of interest not only from a fundamental point of view but also because it is important to understand the behavior of ceramics in various practical radiation enyironments- fission and fusion reactors, nuclear waste storage media, ion-implantation devices, outer space, etc. A great deal of work has been done on the spectroscopy of point defects and small defect clusters in ceramics, but relatively little has been performed on defect agglomeration using transmission electron microscopy (TEM) in the same kind of detail that has been so successful in metals. This article will assess our present understanding of radiation damage in ceramics with illustrations using results obtained from the authors' work.

Application of Transmission Electron Microscopy to Radiation Damage in Ceramics

Ceramics are becoming increasingly important in many radiation environments. In addition to refractory fissionable fuels, electrical insulators will be needed for instrumentation in breeder reactor systems and will be widely applied in all fusion reactor concepts, including first‐wall coatings, blanket gaps, injectors, divertors, magnet insulation, and windows. These applications require mechanically stable (and in some cases transparent) dielectric solids which must maintain electrical as well as mechanical integrity under severe radiation fields. Refractory ceramic materials of low atomic number will be increasingly useful in structural applications as well because they resist activation and contribute less objectionable sputter contaminants. Ceramic solids are also likely to be increasingly utilized as repository media for active nuclear wastes. The irradiation behavior of these nonmetallic materials is critical and at present poorly understood, but transmission electron microscopy is beginning to reveal significant similarities, as well as substantial differences, in their behavior as compared to that of better‐characterized metallic solids.