Void Size Research Articles

Microstructural analysis of ex-service neutron irradiated stainless steel nuclear fuel cladding by high-speed AFM

Fuel cladding in advanced gas-cooled nuclear reactors is made of an austenitic stainless steel referred to as 20Cr/25NiNb. This material can undergo microstructural changes in these extreme environments through a combination of thermal effects and radiation damage. In this work, the microstructures present in an ex-service irradiated 20Cr/25Ni-Nb sample are studied using correlated high-speed atomic force microscopy (HS-AFM) and electron microscopy techniques for the first time. Correlated topographic, crystallographic, and chemical information from the sample surface enabled identification of secondary phase precipitates (SPPs) including M23C6, sigma phase, NbC, and G phase. These SPPs can have adverse effects on the material properties. HS-AFM analysis showed surface textures unique to each SPP. Voids formed due to irradiation were also identified across the surface by HS-AFM. These voids were found to be larger in size and depth along grain boundaries. Further analysis identified a relationship between void size and frequency and grain boundary misorientation and SPP presence.

Macroporous hydrogel prepared via aqueous polymerization induced phase separation toward in situ immobilization of yeast

AbstractYeast‐loaded open‐cell macroporous poly(acrylamide) (PAM) hydrogels are prepared by polymerization induced phase separation (PIPS) with potassium persulfate (KPS)‐yeast as a redox initiator in a polyethylene glycol (PEG) aqueous solution. The presence of PEG not only allows the sizes of both void and interconnected pores of the hydrogels controllable, but also enlarges the void. Which makes it possible to embed cells in situ and efficiently transport nutrients inside the hydrogels. Yeasts are herein used to form a redox pair with KPS to run the polymerization of acrylamide (AM) at a mild temperature (less than 31°C), avoiding the cell inactivation during the polymerization. The in situ immobilization causes a uniformly distribution and high immobilization rate (~100%) of yeasts in the hydrogels. The hydrogels are then used to ferment glucose to produce ethanol, exhibiting high fermentation efficiency of 68%. After 10 cycles, the yeast can still maintain 86% of the initial fermentation efficiency. The yeasts maintain 87% and 93% of the initial cell activity after 1 week store at 4°C in dry state and in yeast extract peptone dextrose (YPD) medium, respectively. This study demonstrates that an aqueous PIPS initiated by peroxide‐target cells is an effective platform to efficiently in situ immobilize cells in a hydrogel for high performance fermentation.

Osteogenic differentiation by MC3T3-E1 pre-osteoblasts is enhanced more on wet-chemically surface-modified 3D-printed poly-e-caprolactone scaffolds than on plasma-assisted modified scaffolds

3D-Printed poly-є-caprolactone (PCL)-scaffolds are safe for cell support, but their hydrophobicity, bioinertness, and smooth surface limits bioactive/biomimetic performance. This can be overcome by providing biophysicochemical and biomechanical signals using amine (NH2) or carboxyl (COOH)-surface functionalization via wet-chemical treatment or plasma-assisted modification, but the alteration extent and hence bone-cell activity is unknown. We aimed to investigate the influence of NH2 or COOH-surface functionalization via wet-chemical treatment or plasma-assisted modification on biophysicochemical and biomechanical properties of 3D-printed PCL-scaffolds and osteogenic activity. In PCL/NH2 and PCL/COOH scaffolds, only wet-chemical treatment increased void size and surface-roughness, but both treatments reduced water contact angle. Wet-chemical treatment decreased, but plasma-assisted modification increased the elastic modulus. Finite-element modeling revealed that in all scaffolds, maximum von Mises stress under 2% compression-strain did not surpass yield stress for bulk material, indicating excellent mechanical stability and fracture resistance. Wet-chemical treatment and plasma-assisted modification increased pre-osteoblast proliferation, alkaline phosphatase activity, and mineral deposition. Wet-chemical treatment increased Fgf2 mRNA, while both treatments increased Cox2 mRNA. Only wet-chemical treatment increased collagen production. In conclusion, NH2 and COOH-surface functionalization of 3D-printed PCL-scaffolds via wet-chemical treatment was superior to plasma-assisted modification in enhancing osteogenic activity, and is therefore more promising for in vivo bone formation.

Neutrino Mass Constraint from an Implicit Likelihood Analysis of BOSS Voids

Cosmic voids identified in the spatial distribution of galaxies provide complementary information to two-point statistics. In particular, constraints on the neutrino mass sum, ∑m ν , promise to benefit from the inclusion of void statistics. We perform inference on the CMASS Northern Galactic Cap sample of the third-generation Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (BOSS) with the aim of constraining ∑m ν . We utilize the void size function, the void–galaxy cross power spectrum, and the galaxy auto power spectrum. To extract constraints from these summary statistics we use a simulation-based approach, specifically implicit likelihood inference. We populate approximate gravity-only, particle-neutrino cosmological simulations with an expressive halo occupation distribution model. With a conservative scale cut of kmax=0.15hMpc−1 and a Planck-inspired Lambda cold dark matter prior, we find upper bounds on ∑m ν of 0.43 and 0.35 eV from the galaxy auto power spectrum and the full data vector, respectively (95% credible interval). Relaxing the scale cut to kmax=0.2hMpc−1 , we find 0.28 and 0.32 eV. Generally, void statistics appear to add modest but nonzero information beyond the auto power spectrum. We also substantiate the usual assumption that the void size function is Poisson distributed.

A junction temperature model based on heat flow distribution in an IGBT module with solder layer voids

The presence of voids in a solder layer affects the thermal reliability of an insulated-gate bipolar transistor (IGBT). In this work, the effects of the size and fraction of solder layer voids and the power losses of chips on heat flow distribution, junction temperature and thermal resistance were investigated. It was found that it was difficult for the heat to flow through the voids due to the high thermal resistance of air. Therefore, the heat above the voids could only flow horizontally, and then avoid the voids and move downward in the solder layer and the following layers, leading to a temperature difference in the surface chip layer. An improved junction temperature model based on the heat flow distribution (HD) considering the solder layer voids was established, the horizontal thermal resistance and horizontal heat capacity are introduced to characterize the effect of the solder layer voids, and the parameter extraction method was proposed. The temperature difference on the surface of the module increased with the increase of the void fraction, and when the void fraction increased from 0 % to 40 %, the surface temperature difference increased from 9.591 °C to 109.86 °C. The results showed that the proposed model not only had a higher accuracy in the estimation of the junction temperature compared with the traditional Cauer model and the improved Cauer model, but also monitored the horizontal temperature differences in the chip layer precisely.

Detecting Near-Surface Sub-Millimeter Voids in Additively Manufactured Ti-5V-5Al-5Mo-3Cr Alloy Using a Transmit-Receive Eddy Current Probe.

Additive Manufacturing (AM) Direct Laser Fabrication (DLF) of Ti-5Al-5V-5Mo-3Cr (Ti5553) is being developed as a method for producing aircraft components. The additive manufacturing process can produce flaws near the surface, such as porosity and material voids, which act as stress raisers, leading to potential component failure. Eddy current testing was investigated to detect flaws on or near the surface of DLF Ti5553 bar samples. For this application, the objective was to develop an eddy current probe capable of detecting flaws 500 µm in diameter, located 1 mm below the component's surface. Two initial sets of coil parameters were chosen: The first, based on successful experiments that demonstrated detection of a near surface flaw in Ti5553 using a transmit-receive array probe, and the second, derived from simulation by Finite Element Method (FEM). An optimized transmit receive coil design, based on the FEM simulations, was constructed. The probe was evaluated on Ti5553 samples containing sub-surface voids of the target size, as well as samples with side-drilled holes and samples with holes drilled from the opposing inspection surface. The probe was able to effectively detect 80% of the sub-surface voids. Limitations included the probe's inability to detect sub-surface voids near sample edges and a sensitivity to surface roughness, which produces local changes in lift-off. Multifrequency mixing improved signal-to-noise ratio when surface roughness was present on average by 22%. A probe based on that described in this paper could benefit quality assurance of additively manufactured aircraft components.

Cosmological forecast of the void size function measurement from the CSST spectroscopic survey

ABSTRACT Void size function (VSF) contains the information of the cosmic large-scale structure (LSS), and can be used to derive the properties of dark energy and dark matter. We predict the VSFs measured from the spectroscopic galaxy survey operated by China’s Space Survey Telescope (CSST), and study the strength of cosmological constraint. We employ a high-resolution Jiutian simulation to get CSST galaxy mock samples based on an improved semi-analytical model. We identify voids from this galaxy catalogue using the watershed algorithm without assuming a spherical shape, and estimate the VSFs at different redshift bins from $z=0.5$ to 1.1. We propose a void selection method based on the ellipticity, and assume the void linear underdensity threshold $\delta _{\rm v}$ in the theoretical model is redshift-dependent and set it as a free parameter in each redshift bin. The Markov Chain Monte Carlo method is adopted to implement the constraints on the cosmological and void parameters. We find that the CSST VSF measurement can constrain the cosmological parameters to a few per cent level. The best-fitting values of $\delta _{\rm v}$ are ranging from $\sim -0.4$ to $-0.1$ as the redshift increases from 0.5 to 1.1, which has a distinct difference from the theoretical calculation with $\delta _{\rm v}\simeq -2.7$ assuming the spherical evolution and using particles as tracer. Our method can provide a good reference for the void identification and selection in the VSF analysis of the spectroscopic galaxy surveys.

Fabricating porous adsorbent coatings using resin curing method: A comprehensive experimental investigation

This study investigates a novel stereolithography-based technique using ultraviolet (UV) light and photopolymer resin to fabricate porous and robust MIL-101 (Cr) adsorbent layers. A unique acid-base reaction step is integrated to control the void size of the adsorbent layer. To prepare the slurry, ingredients are mixed in specific ratios, comprising photopolymer resin (50–55 %), sodium bicarbonate (20–23 %), and MIL-101 (Cr) (23–30 %). Afterward, the slurry-coated samples are treated with concentrated Hydrochloric acid (HCl, 12 M or 36.5 %) and are cured using UV light after controlled delays, forming a porous adsorbent layer. The adsorbent layers are experimentally characterized as a function of the initial slurry recipe and the time delay between acid treatment and UV curing. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray Spectroscopy (EDS) are used to analyze the coated layers. Water isotherm experiments are performed to test the coated layers performance for both MIL-101 (Cr) powders and coated samples. The void size volume fraction for coated samples is found to vary between 22 % and 42 %, and maximum void size is observed for 27 % adsorbent and 4 seconds time delay. Such a comprehensive characterization provides a rapid and efficient alternative to conventional adsorbent structuring methods for fabricating adsorbent layers.

Atomic-scale three-dimensional irradiation-induced defect kinetics models for bcc Fe-based alloys

The interaction between irradiation defects and dislocations could lead to macroscopic hardening and embrittlement. In this study, molecular dynamics (MD) and machine learning were conducted to study three-dimensional void- and Cu-cluster-induced kinetics models under interaction with dislocations in body-centered cubic Fe-based alloys. MD Results show that dislocation climb and shear are two types of interaction mechanism based on the defect size. Combined MD results and machine learning, it was found that the dislocation length increased linearly with an increase in the size of the defects after the interaction. In addition, the number of atoms in the Cu-rich cluster and the reduced number of vacancies in the voids had a square relationship with the defect size where 0.85D2 is for Cu-rich cluster and 0.50D2 is for void. Furthermore, atomic-scale three-dimensional irradiation-induced defect kinetics models were developed and incorporated into the crystal plasticity finite element model (CPFEM). We also analyzed the contributions of various defects to the increase in the yield stress during CPFEM simulation. Compared with DBH model, the prediction of MD data-driven CPFEM matches better with the experimental data. Cluster contributed the most to hardening with low obstacle strength due to the higher number density compared with dislocation loops and voids. The loops also contributed to hardening; however, their contribution was smaller than that of the clusters. Although the number density and size of voids were minimized, they may have contributed because of the high obstacle strengths. This work can indeed deepen the understanding of irradiation effect in Fe-based alloys.

Effect of loading modes on uniaxial creep-fatigue deformation: A dislocation based viscoplastic constitutive model

A comprehensive investigation was conducted on the stress-strain responses and microstructural evolutions of 9Cr3Co3WCu martensitic steel at 650 ℃ subjected to low cycle fatigue tests, strain-controlled creep-fatigue tests (SNCFTs), and hybrid stress-strain-controlled creep-fatigue tests (HSSCFTs). The creep strain accumulation per cycle in HSSCFTs exhibited three stages: an initial decrease in the early cycles, followed by a prolonged period of steady increase, culminating in a rapid increase prior to fracture. In contrast, the creep strain accumulation in SNCFTs showed a consistent decreasing trend throughout the test. Through the employment of advanced characterization techniques, the evolution of dislocation density exhibited a decreasing rate in all cases, and a fracture morphology characterized by a large size of creep voids was observed in HSSCFTs. Consequently, a dislocation-based viscoplastic constitutive model was developed, incorporating a relaxation parameter, a slip deformation resistance model and a dislocation density evolution model interacting with the grain boundary. The proposed model demonstrated excellent congruences under fatigue, creep, creep-fatigue, and multi-step creep- fatigue tests between experimental and simulated results, thereby confirming its capability to comprehensively capture cyclic deformation under various loading modes.

Study on the influence of void evolution of porous asphalt concrete on acoustic absorption performance under high-temperature loading

This paper investigated the void evolution in porous asphalt concrete (PAC) under high-temperature loading and the resulting decay in acoustic absorption performance. The specimen of PAC-13 with a void content of 20.2 % was designed and loaded with MMLS3 for 0–100,000 cycles at 60℃. Computed tomography techniques were employed to extract the distribution characteristics and structural parameters of voids. Subsequently, the acoustic absorption coefficients were measured at different loading stages. The results indicate that PAC experienced both rapid and gradual reduction phases in air void content under high-temperature loading. After 100,000 cycles of loading, the air void content decreased by 5.44 %, void connectivity decreased by 4.32 %, and the average number of voids in section reduced by 8.30 %. The distribution range of nearly 90 % of void sizes shifted from below 7 mm to below 6 mm after 100,000 cycles. At different loading stages, the void content, average number and average equivalent diameter of connected voids exhibited a positive correlation and similar trends with the absorption capacity of PAC for small vehicle noise. This study provides novel insights and perspectives into the acoustic performance degradation of PAC due to void evolution under high-temperature loading.

MODELING OF A LIGHTWEIGHT FLAT FLOOR WITH VOIDS MADE OF PLASTIC BALLS

Formulation of the problem. Prefabricated monolithic construction in domestic and global practice in recent years has occupied a small share in the field of construction. A fairly large number of designs of prefabricated monolithic lightweight floors, as well as its individual structural elements, have been proposed. The use of lightweight floors in the construction of residential and public buildings can significantly reduce the consumption of materials and the dead weight of structures and increase the size of live loads and overlapping spans. Despite this, it cannot be said that effective design solutions have been found that can maximally satisfy the requirements of consumers, architects and builders. Based on this, a constructive solution for a lightweight prefabricated monolithic floor with voids made of plastic balls, quite effective from the point of view of construction and subsequent operation, was proposed and investigated. The proposed design solution for a lightweight prefabricated monolithic flat floor with voids made of plastic balls has less mass than solid floors and optimal use of material resources, namely the consumption of concrete and reinforcement. Therefore, research to determine the optimal design parameters of a flat lightweight floor with void formers made of plastic balls is relevant. The purpose of the article is to conduct numerous studies of the stress-strain state of the proposed design of a prefabricated monolithic floor with voids made of plastic balls. Conclusion. As a result of the research, it was established that it is rational to use hollow balls made from recycled materials as a material for making voids from balls in flat floors. Moreover, all studied floor options with spans of 6 m, 7 m, 8 m and void sizes made of balls with diameters of 180 mm, 315 mm and 500 mm meet the requirements of the first and second groups of limit states.

SELECTION OF OPTIMAL PARAMETERS OF A LIGHTWEIGHT FLAT FLOOR WITH VOIDS MADE OF PLASTIC BALLS

Formulation of the problem. Architectural and construction design of buildings using reinforced concrete has led to an increase in the number of objects with an individual space-planning structure, a rich variety of facade and volumetric solutions. Today the question of the effectiveness of using flat prefabricated monolithic lightweight floors in the construction of multi-storey buildings with individual space-planning and architectural solutions is relevant. In a market economy interest in the issue of rational use of resources, namely the cost of concrete and reinforcement in construction, has sharply increased, which is directly related to attracting investment. As it is known, when designing buildings from prefabricated monolithic reinforced concrete, in contrast to prefabricated concrete, there is greater freedom in adopting the space-planning parameters of the building, and there may also be simpler design solutions, in particular for floors. The constructive solution of floors depends on numerous requirements for the building as a whole and directly for the floor. One of the requirements that influences the attraction of investments is a small material-intensive floor covering with significant spans of buildings of various structural systems. The effective use of lightweight precast monolithic reinforced concrete floors with voids made of plastic balls in construction requires a comprehensive technical and economic analysis of this innovative solution for the precast monolithic reinforced concrete floor structure. The purpose of the article is to perform a technical and economic comparison of various design options for a flat lightweight prefabricated monolithic floor. The influence of floor parameters on the consumption of concrete and reinforcement is considered. Conclusion. As a result of the research, it was established that it is rational to use hollow balls made from recycled materials as a material for making voids from balls in flat floors. Moreover, all studied floor options with spans of 6 m, 7 m, 8 m and void sizes made of balls with diameters of 180 mm, 315 mm and 50 0mm meet the requirements of the first and second groups of limit states.

Fabrication of 3D printed hydroxyapatite/polymeric bone scaffold

ABSTRACT Reconstruction in cases of osteoporosis or accidents often requires the use of synthetic bones or scaffolds, with hydroxyapatite standing out as a preferred material due to its biocompatibility. This study focuses on the production and characterization of hydroxyapatite-coated 3D-printed bone scaffolds. The 3D-printed structures were fabricated by blending hydroxyapatite powder, synthesized through the solution combustion technique, with a liquid photopolymer, followed by exposure to UV irradiation. The resulting hydroxyapatite/photopolymer scaffolds were characterized by a uniform distribution of fine hydroxyapatite powder on the surface. Subsequently, these scaffolds underwent coating with a hydroxyapatite slurry, experimenting with various coating and sintering conditions. Despite the decomposition of the photopolymer during the sintering process, the coated scaffold displayed an increased thickness of the infill line within the pattern, resulting in reduced void size and enhanced compressive strength. Weibull analysis of the compressive strength indicated a high likelihood of survival at 4 MPa, falling within the acceptable range for cancellous bone strength. This comprehensive study showcased the potential of hydroxyapatite-coated 3D-printed bone scaffolds with a favorable microstructure and mechanical strength, making them promising for applications in bone reconstruction.

Forming limit and failure characterization of as-received and bi-axial prestrained Cu-Cr-Zr-Ti alloy sheets in the context of multistage forming

The characterization of forming limit utilizing Cu-Cr-Zr-Ti alloy sheets during the multistage forming process is imperative for successfully fabricating thrust chamber liners used in satellite launch vehicles. Therefore, the present work studies the effect of prestrain on the forming limit and failure behaviour of this alloy under different deformation paths. A stretch-forming setup was utilized to induce 8% equi-biaxial prestrain (EBP), and subsequently, these prestrained specimens were deformed till the onset of failure using the same setup. After prestraining, a shift in the failure strains was observed in the principal strain space, whereas it was found to be absent in the polar effective plastic strain, principal stress and effective plastic strain-stress triaxiality loci. The cup height along different deformation paths was marginally decreased in the prestrained specimens because of the reduction in failure strains, and the fracture occurred in the prestrained region. Further, failure analysis revealed intergranular cracks in the specimens deformed along plane strain and uniaxial deformation paths due to the presence of micron-size Cr-rich precipitates along grain boundaries. However, intergranular and transgranular cracks were present in the prestrained specimens, which were deformed equi-biaxially similar to the as-received specimens. The presence of nano-size Cr-rich precipitates inside the grains acted as nucleation sites for voids during equi-biaxial stretching, leading to transgranular cracks. It was also observed that failure in the prestrained and as-received specimens occurred at a similar effective plastic strain value due to the combined effect of void density and void size. Based on experimental observations, it was inferred that the forming limit of Cu-Cr-Zr-Ti sheets under a two-stage forming process was primarily affected by the presence of micro and nano-size Cr-rich precipitates.

Effect of solder void on mechanical and thermal properties of flip-chip light-emitting diode: Statistical analysis based on finite element modeling

With the increasing demand for highly efficient lighting in the automotive industry, flip-chip light-emitting diodes (LEDs) have become widely used for both interior and exterior lighting. Solder, serving as a crucial interconnecting material, often develops voids during the reflow process, compromising the integrity and reliability of the connections. Thus, understanding the impact of these voids on the mechanical and thermal properties of the product is vital for improving reliability accuracy. This work employs computational methods alongside experimental approaches to address the challenges of replicating solder voids and controlling the solder void fraction. A comprehensive study investigates the effects of solder voids on shearing properties and thermal conductance. Random voids were introduced into the solder pads of an LED assembly within a finite element model (FEM), leading to predictions of maximum shear stress and LED junction temperature. The findings correlate well with the experimental data, validating the FEM's applicability. Furthermore, a statistical analysis was conducted to explore the relationship between solder void fraction, position, and size, aiming to provide objective guidelines for analyzing soldered assembly tomography in reliability assessments.

In situ growth and shrinkage of coated voids in aluminium

Voids can be detrimental to the mechanical and electrical properties of materials but may also find applications in catalysis and plasmonics. Key to the performance of materials containing voids are the sizes and morphologies of the voids, which can be tuned by heat treatment. The present work investigates the morphological evolution of voids, with solute segregation at their surfaces, in an aluminium‑copper‑tin alloy during in situ heating in a transmission electron microscope (TEM). These voids exhibited complex morphological changes that included growth or shrinkage, in contrast to voids in pure Al, which all shrank and disappeared (as reported in an earlier study). Without electron irradiation, the voids never grew. Nearly one fourth of the voids grew under certain heating and electron irradiation conditions, showing distinct growth stages. Growth and shrinkage of the voids both occurred primarily along the surface of the Sn particles to which they were attached. The voids exhibited faceting as they grew and gained morphological isotropy while they shrank. The growth and shrinkage fronts were both found to be primarily the curved surfaces and not the facets at the void surfaces. Growth followed by shrinkage led to a well-defined rounded triangular shape, in projection, with smooth boundaries. This work is, to the best of our knowledge, the first to characterise the growth of nanoscale voids in aluminium using in situ heating TEM. The dual effect of heating and electron irradiation could be utilised to switch the voids between growth and shrinkage to manipulate the void size and shape. This work provides useful insights into tuning void morphologies in the development of advanced materials such as for applications in engineering, catalysis and plasmonics.

Effects of heat treatment on the mechanical properties of 3D-printed polylactic acid: Study of competition between crystallization and interlayer bonding

Fused deposition modeling (FDM) is a popular additive manufacturing technique because of its flexibility, customization, cost-effectiveness, and eco-friendliness. However, due to the layer-by-layer fabrication process and the formation of voids, the mechanical properties of printed parts are lower than other manufacturing techniques. As a solution, heat treatments can effectively mitigate additive manufacturing limitations and improve the mechanical properties of printed parts. The interlayer bonding and subsequently mechanical properties of 3D-printed PLA were affected by the competition between crystallization and chain diffusion of 3D-printed polylactic acid during the heat treatment process. This competition highlights the importance of optimization of heat treatment. Additionally, crystallite growth could cause a reduction in some mechanical properties, like elongation. The size, distribution, and content of voids are also influenced by heat treatment, playing a crucial role in the mechanical properties of 3D-printed parts. In this research, printed samples were heat-treated at temperatures of 75 ºC, 110 ºC, and 130 ºC for two hours. Furthermore, compression-molded samples were fabricated to inspect a comparison of mechanical properties between the traditional and additive manufacturing methods and investigate the effect of layer-by-layer fabrication on these properties. Sample AM-75 showed a 15.5% improvement in bonding strength compared to the non-annealed printed sample, resulting in an increase of 20.2% in tensile strength and 275% in impact strength. Moreover, annealing the sample at 130 ºC resulted in a 7.6% reduction in porosity and a significant improvement of 220% in crystallinity, heat deflection temperature, flexural modulus, and flexural strength, with improvements of 121%, 29.5%, and 15.2% respectively.

Void swelling in pure iron after sequential self-ion-irradiation at different energies: Effect of injected interstitials and additional damage in regions containing pre-existing voids

The use of ion irradiation to add displacement dose onto previously neutron-irradiated material is becoming popular, especially since ion irradiation precedes on neutron-typical microstructures and microchemical distributions that would not be produced with ion irradiation alone. One issue to be addressed in these “neutron-preconditioned” specimens concerns the consequences of ion-injected interstitials on preexisting neutron-produced voids, especially since voids have been observed to disappear over a significant portion of the ion range in some recent preconditioning experiments. This situation can be explored using innovative ion simulation, thereby avoiding working with radioactive material.Two self-ion irradiation series of pure single-crystal iron were performed at 475 °C. The first series used 5 MeV Fe2+, reaching 50, 100 and 150 peak dpa, producing voids to ∼2 µm depth. The second series used 2.5 MeV Fe2+ to introduce additional 50 peak dpa onto each of the three first-step specimens with the ion range reaching ∼1.2 µm. Importantly, 1.2 × 10−3 peak dpa/s was used for both ions to minimize the influence of dpa rate. The major objective was to measure the influence of injected interstitials from the 2.5 MeV Fe2+ irradiation on previously existing voids. Another objective was to observe the behavior of voids exposed to additional dose and time, focusing not only on injected interstitials, but also on the effects of coalescence, ripening, and aging.There were significant changes in depth distribution of swelling following the second irradiation, especially void density. Whereas injected interstitials are well-known to suppress void nucleation at the end of ion range, it was shown in this study that injected interstitials are important in another manner, reducing growth of previously existing voids, producing a ‘notch” in both the swelling vs. depth profile and void size profile. At depths where the injected atoms for both ion energies are not significant, swelling proceeds at ∼0.2 %/dpa.

Porous Crystalline Organic Cages Made by Design

AbstractShape‐persistent organic cages are an intriguing class of molecular porous materials. Through hierarchical molecular design, size and shape of the intrinsic molecular voids are controlled by dynamic covalent chemistry, while pore structure and topology are governed by noncovalent alignment in the solid state. However, the predictable and reliable crystallization of organic cages is still challenging since long‐range superstructures are solely based on weak and rather unidirectional supramolecular interactions. In this tutorial review, we provide a general classification of porous solid‐state materials and discuss specific design principles regarding the dynamic covalent reactions, the small‐molecule building blocks and solid‐state engineering. Furthermore, we introduce the most important analytical techniques for porous materials with a special focus on organic cages.