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Paper des Monats
- ja (71)
Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs of cations and anions that spontaneously stack in linear columns with high one-dimensional ionic and electronic charge mobility, making them prominent model systems for functional soft matter. Compared to classical nonionic discotic liquid crystals, many liquid crystalline structures with a combination of electronic and ionic conductivity have been reported, which are of interest for separation membranes, artificial ion/proton conducting membranes, and optoelectronics. Unfortunately, a homogeneous alignment of the DILCs on the macroscale is often not achievable, which significantly limits the applicability of DILCs. Infiltration into nanoporous solid scaffolds can, in principle, overcome this drawback. However, due to the experimental challenges to scrutinize liquid crystalline order in extreme spatial confinement, little is known about the structures of DILCs in nanopores. Here, we present temperaturedependent high-resolution optical birefringence measurement and 3D reciprocal space mapping based on synchrotron X-ray scattering to investigate the thermotropic phase behavior of dopamine-based ionic liquid crystals confined in cylindrical channels of 180 nm diameter in macroscopic anodic aluminum oxide membranes. As a function of the membranes’ hydrophilicity and thus the molecular anchoring to the pore walls (edge-on or face-on) and the variation of the hydrophilic−hydrophobic balance between the aromatic cores and the alkyl side chain motifs of the superdiscs by tailored chemical synthesis, we find a particularly rich phase behavior, which is not present in the bulk state. It is governed by a complex interplay of liquid crystalline elastic energies (bending and splay deformations), polar interactions, and pure geometric confinement and includes textural transitions between radial and axial alignment of the columns with respect to the long nanochannel axis. Furthermore, confinement-induced continuous order formation is observed in contrast to discontinuous first-order phase transitions, which can be quantitatively described by Landau-de Gennes free energy models for liquid crystalline order transitions in confinement. Our observations suggest that the infiltration of DILCs into nanoporous solids allows tailoring their nanoscale texture and ion channel formation and thus their electrical and optical functionalities over an even wider range than in the bulk state in a homogeneous manner on the centimeter scale as controlled by the monolithic nanoporous scaffolds.
The ability to controllably move gaseous ions is an essential aspect of ion-based spectrometry (e.g., mass spectrometry and ion mobility spectrometry) as well as materials processing. At higher pressures, ion motion is largely governed by diffusion and multiple collisions with neutral gas molecules. Thus, high-pressure ion optics based on electrostatics require large fields, radio frequency drives, complicated geometries, and/or partially transmissive grids that become contaminated. Here, we demonstrate that low-power standing acoustic waves can be used to guide, block, focus, and separate beams of ions akin to electrostatic ion optics. Ions preferentially travel through the static-pressure regions (“nodes”) while neutral gas does not appear to be impacted by the acoustic field structure and continues along a straight trajectory. This acoustic ion manipulation (AIM) approach has broad implications for ion manipulation techniques at high pressure, while expanding our fundamental understanding of the behavior of ions in gases.
Functional fatigue of shape-memory alloys is a considerable threat to the reliable service of actuation devices. Here, we demonstrate the essentially degradation-free cyclic phase-transformation behavior of Ni-Mn-Ga microcrystals up to one million stress-driven superelastic cycles. Cyclic dissipation amounts to about 1/5 of the bulk counterpart and remains unaffected during cycling, even after the introduction of dislocation structures via plastic straining. Plastic yielding and the transformation stress largely exceed the known bulk values. However, the transformation-stress is found to depend on plastic pre-straining, which suggests that the size-affected transformation stress is sensitive to the initial defect structure and that it can be tuned by a targeted introduction of dislocations. These findings demonstrate the high suitability of Ni-Mn-Ga as a robust shape-memory alloy in small-scale functional device engineering.
Additive manufacturing of metals – and in particular building with laser-based powder bed fusion – is highly flexible and allows high-resolution features and feedstock savings. Meanwhile, though space stations in low Earth orbit are established, a set of visits to the Moon have been performed, and humankind can send out rovers to explore Venus and Mars, none of these milestone missions is equipped with technology to manufacture functional metallic parts or tools in space. In order to advance space exploration to long-term missions beyond low Earth orbit, it will be crucial to develop and employ technology for in-space manufacturing (ISM) and in-situ resource utilisation (ISRU). To use the advantages of laser-based powder bed fusion in these endeavours, the challenge of powder handling in microgravity must be met. Here we present a device capable of building parts using metallic powders in microgravity. This was proven on several sounding rocket flights, on which occasions Zr-based metallic glass parts produced by additive manufacturing in space were built. The findings of this work demonstrate that building parts using powder feedstock, which is more compact to transport into space than wire, is possible in microgravity environments. This thus significantly advances ISRU and ISM and paves the way for future tests in prolonged microgravity settings.
Multiphoton lithography (MPL), an emerging truly 3D microfabrication technique, exhibits substantial potential in biomedical applications, including drug delivery and tissue engineering. Fabricated micro-objects are often expected to undergo shape morphing or bending of the entire structure or its parts. Furthermore, ensuring precise property tuning is detrimental to the realization of the functionality of MPL microstructures. Herein, novel MPL materials based on interpenetrating polymer networks (IPNs) are presented that effectively combine the advantages of acrylate and epoxy systems. IPNs with varying component ratios are investigated for their microfabrication performance and structural integrity with respect to thermal and micromechanical properties. A variety of high-resolution techniques is applied to comprehensively evaluate IPN properties at the bulk, micron, and segmental levels. This study shows that the MPL laser scanning velocity and power, photoinitiator content, and multi-step exposure can be used to tune the morphology and properties of the IPN. As a result, a library of 3D MPL IPN microstructures with high 3D structural stability and tailored thermal and micromechanical properties is achieved. New IPN microstructures with Young’s moduli of 3–4 MPa demonstrate high-to-fully elastic responses to deformations, making them promising for applications in morphable microsystems, soft micro-robotics, and cell engineering.
Cellulose nanofibrils (CNFs) with different charge densities were prepared and investigated by a combination of different complementary techniques sensitive to the structure and molecular dynamics of the system. The morphology of the materials was investigated by scanning electron microscopy (SEM) and X-ray scattering (SAXS/WAXS). The latter measurements were quantitatively analyzed yielding to molecular parameters in dependence of the charge density like the diameter of the fibrils, the distance between the fibrils, and the dimension of bundles of nanofibrils, including pores. The influence of water on the properties and the charge density is studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy. The TGA measurements reveal two mass loss processes. The one at lower temperatures was related to the loss of water, and the second process at higher temperatures was related to the chemical decomposition. The resulting char yield could be correlated to the distance between the microfibrils. The DSC investigation for hydrated CNFs revealed three glass transitions due to the cellulose segments surrounded by water molecules in different states. In the second heating scan, only one broad glass transition is observed. The dielectric spectra reveal two relaxation processes. At low temperatures or higher frequencies, the β-relaxation is observed, which is assigned to localized fluctuation of the glycosidic linkage. At higher temperatures and lower frequencies, the α-relaxation takes places. This relaxation is due to cooperative fluctuations in the cellulose segments. Both processes were quantitatively analyzed. The obtained parameters such as the relaxation rates were related to both the morphological data, the charge density, and the content of water for the first time.
Objectives
The aim of the study was to investigate the impact of organic additives (binder, plasticizer, and the cross-linking ink) in the formulation of water-based feedstocks on the properties of a dental feldspathic glass-ceramic material developed for the slurry-based additive manufacturing technology “LSD-print.”
Material and methods
Three water-based feldspathic feedstocks were produced to study the effects of polyvinyl alcohol (AC1) and poly (sodium 4-styrenesulfonate) (AC2) as binder systems. A feedstock without organic additives was tested as the control group (CG). Disc-shaped (n = 15) and bar (n = 7) specimens were slip-cast and characterized in the green and fired states. In the green state, density and flexural strength were measured. In the fired state, density, shrinkage, flexural strength (FS), Weibull modulus, fracture toughness (KIC), Martens parameters, and microstructure were analyzed. Disc-shaped and bar specimens were also cut from commercially available CAD/CAM blocks and used as a target reference (TR) for the fired state.
Results
In the green state, CG showed the highest bulk density but the lowest FS, while the highest FS in the green state was achieved with the addition of a cross-linking ink. After firing, no significant differences in density and a similar microstructure were observed for all slip-cast groups, indicating that almost complete densification could be achieved. The CAD/CAM specimens showed the highest mean FS, Weibull modulus, and KIC, with significant differences between some of the slip-cast groups.
Significance
These results suggest that the investigated feedstocks are promising candidates for the slurry-based additive manufacturing of restorations meeting the class 1a requirements according to DIN EN ISO 6871:2019–01.
In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as “electron beam-induced fragmentation” or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field B = 2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. B = 0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF.
In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as ‘‘electron beam-induced fragmentation’’ or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field 𝐵 = 2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. 𝐵 = 0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF.
Ergot alkaloids (EAs) formed by Claviceps fungi are one of the most common food contaminants worldwide, affecting cereals such as rye, wheat, and barley. To accurately determine the level of contamination and to monitor EAs maximum levels set by the European Union, the six most common EAs (so-called priority EAs) and their corresponding epimers are quantified using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The quantification of EAs in complex food matrices without appropriate internal tandards is challenging but currently carried out in the standard method EN 7425:2021 due to their commercial unavailability. To address the need for isotopically labeled EAs, we focus on two semi-synthetic approaches for the synthesis of these reference standards. Therefore, we investigate the feasibility of the N6-demethylation of native ergotamine to yield norergotamine, which can subsequently be remethylated with an isotopically labeled methylating reagent, such as iodomethane (13CD3-I), to yield isotopically labeled ergotamine and its C8-epimer ergotaminine. Testing the isotopically labeled ergotamine/-inine against native ergotamine/-inine with HPLC coupled to high-resolution HR-MS/MS proved the structure of ergotamine-13CD3 and ergotaminine-13CD3. Thus, for the first time, we can describe their synthesis from unlabeled, native ergotamine. Furthermore, this approach is promising as a universal way to synthesize other isotopically labeled EAs.
Ring-opening polymerizations (ROPs) of l-lactide (LA) were performed with ethyl l-lactate or 11-bromoundecanol as initiators (In) and tin(II) ethyl hexanoate (SnOct2) as catalyst (Cat) using four different LA/In ratios (20/1, 40/1, 60/1, and 100/1). One series of ROPs was conducted in bulk at 120 °C, yielding PLAs with low dispersities (Ð ~ 1.2–1.4), and a second series was conducted in bulk at 160 °C, yielding higher dispersities (Ð ~ 1.3–1.9). Samples from both series were annealed for 1 or 14 days at 140 °C in the presence of SnOct2. Both polycondensation and disproportionation reactions occurred, so that all four samples tended to form the same type of molar mass distribution below 10,000 Da, regardless of their initially different number average molar masses (Mn). Both initiators gave nearly identical results. The thermodynamic control of all reversible transesterification processes favored the formation of crystallites composed of chains with a Mn around 3500–3700, corresponding to a crystal thickness of 10–13 nm.
The number of vehicles using or transporting cryogenic fuels such as Liquefied Hydrogen (LH2) or Liquefied Natural Gas (LNG) increases fast in the land transportation sector. Does this also entail new risks? The storage of cryogenic fuels requires tanks with Thermal Super Insulations (TSI) to keep the fluid cold and limit the formation of boil-off gas. TSI has proven itself in some applications since the middle of the 20th century, but in the land transport sector they are still quite new, where accidents involving fires, collisions, and their combination are to be expected. This work focuses on investigating the behavior of different types of TSI while exposed to a heat source representing a fire. To this aim, a High-Temperature Thermal Vacuum Chamber (HTTVC) was applied, which allows the thermal loading of a thermal insulation material in a vacuum and measuring the heat flow transported through the TSI in parallel. In this study, the results of 6 samples are presented regarding 3 types of MLI, rock wool, perlites, and microspheres. The thermal exposure caused different effects on the samples. In practice, this can be connected to the rapid release of flammable gases as well as to a Boiling Liquid Expanding Vapour Explosion (BLEVE). These results are relevant for reducing the risks to people and infrastructures in the progressive establishment of tanks for cryogenic fluids in our industry and society. The data presented in the study can be used to improve the design of tanks and TSIs, the assessment of accident scenarios, and the development of measures for first responders.
Concretes produced from salt aggregate and hybrid alkaline cements, an alkali-activated slag/fly ash blend, or a Portland cement were exposed to a magnesium chloride-rich saline solution ([Mg2+] = 3.6 m, [Cl−] = 8.3 m), representing a solution formed after contact of surface water with evaporite rock (rock salt) in a nuclear waste repository. The hydration and deterioration of the concretes were studied with X-ray diffraction, thermogravimetric analysis, pH mapping and permeability measurements. The results show that calcium silicate hydrate (C-S-H) or sodium-substituted calcium aluminium silicate hydrate (C-N-A-S-H) and Friedel's salt were the major reaction products in the concretes prior to exposure to the saline solution. During exposure to the saline solution, increasing amounts of C-S-H/C-N-A-S-H dissolved, and gypsum and a secondary AFm phase formed. The durability of the concretes improved with increasing amounts of Portland clinker in the cements, due to the associated differences in permeability and chemical resistance. Nevertheless, a massive increase of permeability occurred for all concretes, likely caused by crack formation due to the formation of gypsum from anhydrite in the salt aggregate. Thus, the behavior of the concretes differed from, and was more complex than, the behavior of plain cement pastes.
Standards play a crucial role in the transition to more sustainable production and consumption models by promoting the development of new markets for innovative products. In the case of the bioeconomy, standards are particularly relevant to ensure the sustainability of products and processes. Hence, standards represent an essential strategic tool to foster sustainable development. Furthermore, the standard-setting process brings together different stakeholders, which encourages research and the transfer of knowledge to industrial practice. In particular, scientific publications assist the standardisation process by providing scientific evidence. This study investigates the role of science and regulation in the bioeconomy standardisation process. It first provides a general analysis of bioeconomy-related standards, followed by an analysis of the regulations and publications referenced in the standards. Our analysis discloses a strong use of scientific knowledge in the bioeconomy standardisation process and demonstrates the readiness to integrate novel academic findings into revised versions of the standards. In addition, it reveals that the interaction between science and regulation is an important driver for standardisation activities around the bioeconomy, needed to support sustainable transitions.
The use of ashes from municipal solid waste incineration as secondary building materials is an important pillar for the circular economy in Germany. However, leaching of potential toxic elements from these materials must be at environmentally acceptable levels. Normally, a three-month ageing period immobilizes most hazardous heavy metals, but antimony (Sb) and vanadium (V) showed previously unusual leaching. In order to clarify the mechanisms, we analyzed the Sb and V species in various bottom and fly ashes from municipal waste incineration by XANES spectroscopy. Antimony oxidizes from Sb(+ III) species used as flame retardants in plastics to Sb(+ V) compounds during waste incineration. However, owing to the similarity of different Sb(+ V) compound in the Sb K- and L-edge XANES spectra, it was not possible to accurately identify an exact Sb(+ V) species. Moreover, V is mainly present as oxidation state + V compound in the analyzed ashes. However, the coarse and magnetic fraction of the bottom ashes contain larger amounts of V(+ III) and V(+ IV) compounds which might enter the waste incineration from vanadium carbide containing steel tools. Thus, Sb and V could be critical potential toxic elements in secondary building materials and long-term monitoring of the release should be taken into account in the future.
AbstractThis study applies Semantic Web technologies to advance Materials Science and Engineering (MSE) through the integration of diverse datasets. Focusing on a 2000 series age-hardenable aluminum alloy, we correlate mechanical and microstructural properties derived from tensile tests and dark-field transmission electron microscopy across varied aging times. An expandable knowledge graph, constructed using the Tensile Test and Precipitate Geometry Ontologies aligned with the PMD Core Ontology, facilitates this integration. This approach adheres to FAIR principles and enables sophisticated analysis via SPARQL queries, revealing correlations consistent with the Orowan mechanism. The study highlights the potential of semantic data integration in MSE, offering a new approach for data-centric research and enhanced analytical capabilities.
Investigation on the Durability of a Polypropylene Geotextile under Artificial Aging Scenarios
(2024)
Geosynthetics are widely used in various civil engineering applications, such as geotextiles in coastal protection, and display a sustainable alternative to natural mineral materials. However, the full benefits of using geosynthetics can only be gained with a long service lifetime of the products. With the use of added stabilizers to the polymers, service lifetimes can be achieved in the range of 100 years. Therefore, accelerated aging methods are needed for the assessment of the long-term performance of geotextiles. In the present study, the behavior of geosynthetic materials made of polypropylene was investigated under artificial aging conditions involving elevated temperatures ranging from 30 to 80 °C, increased oxygen pressures ranging from 10 to 50 bar in water-filled autoclaves, and UV irradiation under atmospheric conditions. ATR-IR spectroscopy was employed to detect the increase in the carbonyl index over various aging durations, indicating the oxidative degradation of the geotextile. The most pronounced increase was observed in the case of aging through UV irradiation, followed by thermal aging. Elevated pressure, on the other hand, had a lower impact on oxidation. High-temperature size exclusion chromatography was utilized to follow the reduction in molar mass under different degradation conditions, and the results were consistent with those obtained from ATR-IR spectroscopy. In polyolefins such as polypropylene, Hindered Amine Stabilizers (HAS) are used to suppress oxidation caused by UV radiation. The quantitative analysis of HAS was carried out using a UV/Vis method and HPLC. The degradation of UV stabilizers during the aging of geotextiles is responsible for the oxidation and the reduction in the molar mass of polypropylene. From the results, it can be concluded that applications of PP geotextile without soil or sand cover might cause the risk of the formation of microplastic particles. Material selection, design, and maintenance of the construction must follow best practices, including the system’s removal or replacement at end-of-life. Otherwise, a sustainable use of geotextiles in civil engineering is not possible.
Multilayer Insulation (MLI) is frequently used in vacuum conditions for the thermal insulation of cryogenic storage tanks. The severe consequences of the degradation of such materials in engulfing fire scenarios were recently evidenced by several large-scale experimental tests. In the present study, an innovative modelling approach was developed to assess the performance of heat transfer in polyester-based MLI materials for cryogenic applications under fire conditions. A specific layer-by-layer approach was integrated with an apparent kinetic thermal degradation model based on thermogravimetric analysis results. The modeling results provided a realistic simulation of the experimental data obtained by High-Temperature Thermal Vacuum Chamber tests reproducing fire exposure conditions. The model was then applied to assess the behavior of MLI systems for liquid hydrogen tanks in realistic fire scenarios. The results show that in intense fire scenarios degradation occurs rapidly, compromising the thermal insulation performances of the system within a few minutes.
Impact of organic phosphates on the structure and composition of short-range ordered iron nanophases
(2024)
Organic phosphates (OP) are important nutrient components for living cells in natural environments, where they readily interact with ubiquitous iron phases such as hydrous ferric oxide, ferrihydrite (FHY). FHY partakes in many key bio(geo)chemical reactions including iron-mediated carbon storage in soils, or iron-storage in living organisms. However, it is still unknown how OP affects the formation, structure and properties of FHY. Here, we document how β-glycerophosphate (GP), a model OP ligand, affects the structure and properties of GP–FHY nanoparticles synthesized by coprecipitation at variable nominal molar P/Fe ratios (0.01 to 0.5). All GP–FHY precipitates were characterized by a maximum solid P/Fe ratio of 0.22, irrespective of the nominal P/Fe ratio. With increasing nominal P/Fe ratio, the specific surface area of the GP–FHY precipitates decreased sharply from 290 to 3 m2 g−1, accompanied by the collapse of their pore structure. The Fe–P local bonding environment gradually transitioned from a bidentate binuclear geometry at low P/Fe ratios to monodentate mononuclear geometry at high P/Fe ratios. This transition was accompanied by a decrease in coordination number of edge-sharing Fe polyhedra, and the loss of the corner-sharing Fe polyhedra. We show that Fe(III) polymerization is impeded by GP, and that the GP–FHY structure is highly dependent on the P/Fe ratio. We discuss the role that natural OP-bearing Fe(III) nanophases have in biogeochemical reactions between Fe–P and C species in aquatic systems.
Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM ‘Chloride transport in alkali-activated materials’ significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS.
This study investigates the room‐ and high‐temperature (650 °C) tensile and low‐cycle‐fatigue behavior of Inconel 718 produced by laser powder bed fusion (PBF‐LB/M) with a four‐step heat treatment and compares the results to the conventional wrought material. The microstructure after heat treatment is characterized on different length scales. Compared to the wrought variant, the elastic and yield properties are comparable at both test temperatures while tensile strength, ductility, and strain hardening capacity are lower. The fatigue life of the PBF‐LB/M variant at room temperature is slightly lower than that of the wrought material, while at 650 °C, it is vice versa. The cyclic stress response for both material variants is characterized by cyclic softening, which is more pronounced at the higher test temperature. High strain amplitudes (≥0.7%) at room temperature and especially a high testing temperature result in the formation of multiple secondary cracks at the transitions of regions comprising predominantly elongated grain morphology and columns of stacked grains with ripple patterns in the PBF‐LB/M material. This observation and pronounced crack branching and deflection indicate that the cracks are controlled by sharp micromechanical gradients and local crystallite clusters.
In this work, the electrochemical behavior of 4-phenylurazole (Ph-Ur) was studied and the latter was used as a molecular anchor for the electrochemical bioconjugation of tyrosine (Y). Cyclic voltammetry (CV) and controlled potential coulometry (CPC) allowed the in-situ generation of the PTAD (4-phenyl-3 H-1,2,4-triazole-3,5(4 H)-dione) species from phenylurazole on demand for tyrosine electrolabeling. The chemoselectivity of the reaction was studied with another amino acid (lysine, Lys) and no changes in Lys were observed. To evaluate the performance of tyrosine electrolabeling, coulometric analyses at controlled potentials were performed on solutions of phenylurazole and the phenylurazole-tyrosine mixture in different proportions (2:1, 1:1, and 1:2). The electrolysis of the phenylurazole-tyrosine mixture in the ratio (1:2) produced a charge of 2.07 C, very close to the theoretical value (1.93 C), with high reaction kinetics, a result obtained here for the first time. The products obtained were identified and characterized by liquid chromatography coupled to high-resolution electrospray ionization mass spectrometry (LC-HRMS and LC- HRMS2). Two products were formed from the click reactions, one of which was the majority. Another part of this work was to study the electrochemical degradation of the molecular anchor 4-phenylazole (Ph-Ur). Four stable degradation products of phenylurazole were identified (C7H9N2O, C6H8N, C6H8NO, C14H13N4O2) based on chromatographic profiles and mass spectrometry results. The charge generated during the electrolysis of phenylurazole (two-electron process) (2.85 C) is inconsistent with the theoretical or calculated charge (1.93 C), indicating that secondary/parasitic reactions occurred during the electrolysis of the latter. In conclusion, the electrochemically promoted click phenylurazole-tyrosine reactions give rise to click products with high reaction kinetics and yields in the (1:2) phenylurazole-tyrosine ratios, and the presence of side reactions is likely to affect the yield of the click phenylurazole-tyrosine reaction.
Exploring the electrochemical and physical stability of lithium-ion cells exposed to liquid nitrogen
(2024)
The transport and storage of lithium-ion (Li-ion) batteries — damaged or in an undefined state — is a major safety concern for regulatory institutions, transportation companies, and manufacturers. Since (electro)chemical reactivity is exponentially temperature-dependent, cooling such batteries is an obvious measure for increasing their safety.
The present study explores the effect of cryogenic freezing on the electrochemical and physical stability of Li-ion cells. For this purpose, three different types of cells were repeatedly exposed to liquid nitrogen (LN2).
Before and after each cooling cycle, electrical and electrochemical measurements were conducted to assess the impact of the individual freezing steps. While the electrochemical behavior of the cells did not change significantly upon exposure to LN2 , it became apparent that a non-negligible number of cells suffered from physical changes (swelling) and functional failures. The latter defect was found to be caused by the current interrupt device of the cylindrical cells. This safety mechanism is triggered by the overpressure of expanding nitrogen which enters the cells at cryogenic temperatures.
This study underlines that the widely accepted reversibility of LN2 -cooling on a material scale does not allow for a direct extrapolation toward the physical integrity of full cells. Since nitrogen enters the cell at cryogenic temperatures and expands upon rethermalization, it can cause an internal overpressure. This can, in turn, lead to mechanical damage to the cell. Consequently, a more appropriate temperature condition — less extreme than direct LN2 exposure — needs to be found
The corrosion behavior of galvanized steels and zinc components under atmospheric exposure depends mostly on the corrosion product‐based cover layer formation under the prevailing conditions. The use of agar‐based gel electrolytes makes it possible to use electrochemical methods to obtain a characteristic value from these cover layers that describe their current and future protective capacity. It is shown here that different states of galvanized steel can be distinguished very well under laboratory conditions and that this method is also suitable for use under practical conditions. Based on the characteristic values and assuming future time of wetness, it is very easy to draw up a forecast for the future corrosion rate, which provides plausible values.
Tests for assessing prestressing steels' susceptibility to hydrogen‐induced stress corrosion cracking are essential for approvals, in‐house monitoring, and third‐party material testing. According to ISO 15630‐3, the time to brittle fracture by constant load under corrosive conditions in thiocyanate test solutions (A or B) at 50°C is measured. In the literature, a high scattering in stress corrosion tests is reported, which questions the integrity of the test procedure. This paper shows the results of studies about the influence of solution composition on hydrogen charging in electrochemical and permeation measurements. Electrochemical experiments show that polished steel surfaces without common drawing layers have more consistent free corrosion currents, polarization resistances, and B‐values in solution A with low scattering compared to the solution B experiments. The influence of temperature at 50°C and an ambient temperature of 22°C was also tested.
In this study, we demonstrate the applicability of nitrogen microwave inductively coupled atmospheric pressure mass spectrometry (MICAP-MS) for Ca, Fe, and Se quantification in human serum using isotope dilution (ID) analysis. The matrix tolerance of MICAP-MS in Na matrix was investigated, uncovering that high Na levels can suppress the signal intensity. This suppression is likely due to the plasma loading and the space charge effect. Moreover, 40Ca and 44Ca isotopic fractionation was noted at elevated Na concentration. Nine certified serum samples were analyzed using both external calibration and ID analysis. Overestimation of Cr, Zn, As, and Se was found in the results of external calibration, which might be resulted from C-induced polyatomic interference and signal enhancement, respectively. Further investigations performed with methanol showed a similar enhancement effect for Zn, As, and Se, potentially supporting this assumption. The mass concentrations determined with ID analysis show metrological compatibility with the reference values, indicating that MICAP-MS combined with ID analysis can be a promising method for precise Ca, Fe, and Se determination. Moreover, this combination reduces the influences of matrix effects, broadening the applicability of MICAP-MS for samples with complex matrix.
This technical note highlights the fact that CF-LIBS algorithms work in mole fractions, while results of spectrochemical analysis are usually reported in mass fractions or mass percent. Ignoring this difference and not converting mole fractions to mass fractions can lead to errors in reported concentrations determined by the CF-LIBS method and inadequate comparison of these concentrations with certified concentrations. Here, the key points of the CF-LIBS algorithm are reproduced and the formulae for converting a mole fraction to a mass fraction and vice versa are given. Several numerical examples are also given, which show that the greater the difference between the molar mass of an individual element in a sample and the average molar mass, the greater the discrepancy between the mole and mass fractions.
Solvent-free sample preparation offers some advantages over solvent-based techniques, such as improved accuracy, reproducibility and sensitivity, for matrix-assisted laser desorption/ionization (MALDI) analysis. However, little or no information is available on the application of solvent-free techniques for the MALDI analysis of polymer blends. Solvent-free sample preparation by ball milling was applied with varying sample-to-matrix ratios for MALDI time-of-flight mass spectrometry analysis of various polymers, including polystyrenes, poly(methyl methacrylate)s and poly(ethylene glycol)s. The peak intensity ratios were compared with those obtained after using the conventional dried droplet sample preparation method. In addition, solvent-assisted milling was also applied to improve sample homogeneities.
Depending on the sample preparation method used, different peak intensity ratios were found, showing varying degrees of suppression of the signal intensities of higher mass polymers. Ball milling for up to 30 min was required to achieve constant intensity ratios indicating homogeneous mixtures. The use of wet-assisted grinding to improve the homogeneity of the blends was found to be disadvantageous as it caused partial degradation and mass-dependent segregation of the polymers in the vials.The results clearly show that solvent-free sample preparation must be carefully considered when applied to synthetic polymer blends, as it may cause additional problems with regard to homogeneity and stability of the blends.
This contribution reports the development of a polymerizable BODIPY-type fluorescent probe targeting small-molecule carboxylates for incorporation into molecularly imprinted polymers (MIPs). The design of the probe crosslinker includes a urea recognition site p-conjugated to the 3-position of the BODIPY core and two methacrylate moieties. Titration experiments with a carboxylate-expressing antibiotic, levofloxacin (LEVO), showed a blue shift of the absorption band as well as a broadening and decrease in emission, attributed to hydrogen bonding between the probe’s urea group and the carboxylate group of the antibiotic. Using this probe crosslinker, core–shell particles with a silica core and a thin MIP shell were prepared for the detection of LEVO. The MIP exhibited highly selective recognition of LEVO, with an imprinting factor of 18.1 compared to the non-imprinted polymer. Transmission electron microscopy confirmed the core–shell structure and spectroscopic studies revealed that the receptor’s positioning leads to a unique perturbation of the polymethinic character of the BODIPY chromophore, entailing the favourable responses. These features are fully preserved in the MIP, whereas no such response was observed for competitors such as ampicillin. The sensory particles allowed to detect LEVO down to submicromolar concentrations in dioxane. We have developed here for the first time a BODIPY probe for organic carboxylates and incorporated it into polymers using the imprinting technique, paving the way for BODIPY-type fluorescent MIP sensors.
AbstractSorbents are promising materials for applications in atmospheric water harvesting, thermal energy storage, and passive cooling, thereby addressing central challenges related to water scarcity and the global energy transition. Recently, hygroscopic hydrogel composites have emerged as high‐performance sorbents. However, many of these systems are fabricated with unsustainable and costly sorbent materials, which hinders their wide deployment. Here, the synthesis of high‐performance, cost‐efficient polyacrylamide hydrogels loaded with unprecedented amounts of calcium chloride is demonstrated. To this end, the swelling procedure of polyacrylamide hydrogels in aqueous calcium chloride solutions is optimized. The achievable salt loading in the hydrogel is characterized as a function of temperature, calcium chloride concentration in the swelling solution, and the hydrogel preparation conditions. The obtained hydrogel‐salt composites are shown to be stable under repeated sorption‐desorption cycling and enable water uptakes of 0.92 and 2.38 grams of water per gram of dry materials at 30% and 70% relative humidity, respectively. The resulting cost‐performance ratio substantially exceeds lithium chloride‐based systems. Further, the mechanistic insights on hydrogel salt interactions can guide the design of sustainable and low‐cost sorbent materials for future applications in water and energy.
Homochirality is an obvious feature of life on Earth. On the other hand, extraterrestrial samples contain largely racemic compounds. The same is true for any common organic synthesis. Therefore, it has been a perplexing puzzle for decades how these racemates could have formed enantiomerically enriched fractions as a basis for the origin of homochiral life forms. Numerous hypotheses have been put forward as to how preferentially homochiral molecules could have formed and accumulated on Earth. In this article, it is shown that homochirality of the abiotic organic pool at the time of formation of the first self-replicating molecules is not necessary and not even probable. It is proposed to abandon the notion of a molecular ensemble and to focus on the level of individual molecules. Although the formation of the first self-replicating, most likely homochiral molecule, is a seemingly improbable event, on a closer look, it is almost inevitable that some homochiral molecules have formed simply on a statistical basis. In this case, the non-selective leap to homochirality would be one of the first steps in chemical evolution directly out of a racemic “ocean”. Moreover, most studies focus on the chirality of the primordial monomers with respect to an asymmetric carbon atom. However, any polymer with a minimal size that allows folding to a secondary structure would spontaneously lead to asymmetric higher structures (conformations). Most of the functions of these polymers would be influenced by this inherently asymmetric folding. Furthermore, a concept of physical compartmentalization based on rock nanopores in analogy to nanocavities of digital immunoassays is introduced to suggest that complex cell walls or membranes were also not required for the first steps of chemical evolution. To summarize, simple and universal mechanisms may have led to homochiral self-replicating systems in the context of chemical evolution. A homochiral monomer pool is deemed unnecessary and probably never existed on primordial Earth.
Processing and cytocompatibility of Cu-doped and undoped fluoride-containing bioactive glasses
(2024)
Sintered or additive-manufactured bioactive glass (BG) scaffolds are highly interesting for bone replacement applications. However, crystallization often limits the high-temperature processability of bioactive glasses (BGs). Thus, the BG composition must combine high bioactivity and processability. In this study, three BGs with nominal molar (%) compositions 54.6SiO2-1.7P2O3-22.1CaO-6.0Na2O-7.9K2O-7.7MgO (13–93), 44.8SiO2-2.5P2O3-36.5CaO-6.6Na2O-6.6K2O-3.0CaF2 (F3) and 44.8SiO2-2.5P2O3-35.5CaO-6.6Na2O-6.6K2O-3.0CaF2-1.0CuO (F3–Cu) were investigated. The dissolution and ion release kinetics were investigated on milled glass powder and crystallized particles (500–600 μm). All glasses showed the precipitation of hydroxyapatite (HAp) crystals after 7 days of immersion in simulated body fluid. No significant differences in ion release from glass and crystalline samples were detected. The influence of surface roughness on cytocompatibility and growth of preosteoblast cells (MC3T3-E1) was investigated on sintered and polished BG pellets. Results showed that sintered BG pellets were cytocompatible, and cells were seen to be well attached and spread on the surface after 5 days of incubation. The results showed an inverse relation of cell viability with the surface roughness of pellets, and cells were seen to attach and spread along the direction of scratches.
Glycolide was polymerized in bulk by means of four different ROPPOC catalysts: tin(II) 2-ethylhexanoate (SnOct2), dibutyltin bis(pentafluoro-phenoxide) (BuSnOPF),zinc biscaproate (ZnCap), and zinc bis(pentafluoro-phenyl sulfide) (ZnSPF). The temperature was varied between 110 and 180°C and the time between 3 h and 7 days. For the few polyglycolides (PGAs) that were soluble extremely high molecular masses were obtained. The MALDI TOF mass spectra had all a low signal-to-noise ration and displayed the peaks of cyclic PGAs with a“saw-tooth pattern ”indicating formation of extended-ring crystallites in the mass range below m/z 2500. The shape of DSC curves varied considerably with catalyst and reaction conditions, whereas the long-distance values measured by SAXS were small and varied little with the polymeriza-tion conditions.
Additive manufacturing of concrete structures is a novel and emerging technology. Freecontouring in civil engineering, which allows for entirely new designs, is a significant advantage. Inthe future, lower construction costs are expected with increased construction speeds and decreasingrequired materials and workers. However, architects and civil engineers rely on a certain quality ofexecution to fulfil construction standards. Although several techniques and approaches demonstratethe advantages, quality control during printing is highly challenging and rarely applied. Due to thecontinuous mixing process commonly used in 3D concrete printing, it is impossible to exclude varia-tions in the dry mixture or water content, and a test sample cannot be taken as a representative samplefor the whole structure. Although mortar properties vary only locally, a defect in one layer duringprinting could affect the entire integrity of the whole structure . Therefore, real-time process monitor-ing is required to record and document the printing process.At the Bundesanstalt für Materialforschung und -prüfung (BAM) a new test rig for the additive man-ufacturing of concrete is built. The primary purpose is measuring and monitoring the properties of amortar during the printing process.The following study investigates an approach for calculating yield stress and plastic viscosity based onexperimentally recorded pressure data. The calculations assume that fresh mortar behaves as a Bing-ham fluid and that the Buckingham-Reiner-equation is applicable. A test setup consisting of rigid pipeswith integrated pressure sensors at different positions is utilized.Monitoring the printing process with different sensors is crucial for the quality control of an ongoingprocess.
Extended X-ray absorption fine structure (EXAFS) conducted on an equiatomic MoNbTaW bcc medium-entropy alloy that was annealed at 2273 K reveals unexpectedly small 1st and 2nd shell element-specific lattice distortions. An experimental size-mismatch parameter, δexp, is determined to be ca. 50% lower than the corresponding calculated value. Around W, short-range order (SRO) preferring 4d elements in the 1st and 2nd shells persists. A Nb-W ordering is found, which is reminiscent of ordering emerging at lower temperatures in the B2(Mo,W;Ta,Nb)- and B32(Nb,W)-phases. With high-temperature ordering preferences in fcc also foreshadowing low-temperature phase, these findings suggest a general feature of high-temperature SRO.
The digitalization of materials science and engineering (MSE) is currently leading to remarkable advancements in materials research, design, and optimization, fueled by computer‐driven simulations, artificial intelligence, and machine learning. While these developments promise to accelerate materials innovation, challenges in quality assurance, data interoperability, and data management have to be addressed. In response, the adoption of semantic web technologies has emerged as a powerful solution in MSE. Ontologies provide structured and machine‐actionable knowledge representations that enable data integration, harmonization, and improved research collaboration. This study focuses on the tensile test ontology (TTO), which semantically represents the mechanical tensile test method and is developed within the project Plattform MaterialDigital (PMD) in connection with the PMD Core Ontology. Based on ISO 6892‐1, the test standard‐compliant TTO offers a structured vocabulary for tensile test data, ensuring data interoperability, transparency, and reproducibility. By categorizing measurement data and metadata, it facilitates comprehensive data analysis, interpretation, and systematic search in databases. The path from developing an ontology in accordance with an associated test standard, converting selected tensile test data into the interoperable resource description framework format, up to connecting the ontology and data is presented. Such a semantic connection using a data mapping procedure leads to an enhanced ability of querying. The TTO provides a valuable resource for materials researchers and engineers, promoting data and metadata standardization and sharing. Its usage ensures the generation of finable, accessible, interoperable, and reusable data while maintaining both human and machine actionability.
The energy demand of private households contributes globally to 36.5% of the total CO2 emissions. To analyze the emissions reduction potential, we conducted a comparative life cycle assessment of a proton exchange membrane fuel cell in a residential application and a conventional system with a stand-alone gas condensing boiler and electricity from a grid mix. The period under review was referred to as the service life of the PEMFC and is assumed to be 10 years (83,038 h of PEMFC). The applicability of this in a single-family house built between 1991 and 2000 under German climatic conditions was investigated. The functional unit is set to the thermal energy demand of 16,244 kWh/a and electricity demand of 4919 kWh/a of a single-family house. The impact assessment method “CML 2001–August 2016” was used in this investigation. The manufacturing phase of the proton exchange membrane fuel cell showed disadvantages, whereby the use phase had significant advantages in most of the environmental impact categories as compared to the conventional energy supply system. Considering the whole life cycle, the advantages from the use phase could outperform the disadvantages from the manufacturing phase in most of the impact categories, except for ADP elements and TETP.
A high precision nail‐penetration (NP) tool for characterizing the mechanically induced thermal‐runaway (TR) of lithium‐ion battery (LIB) cells in a defined range of temperatures down to −140 °C was developed. To understand the cell specific behavior at low temperatures aiming at the determination of safe handling conditions, different scenarios are analyzed. First, accuracy tests of the NP‐tool regarding motion and penetration depth are conducted with cylindrical cells at different temperatures. Thus, postmortem computer tomographic (CT) images are compared to the data measured with the newly integrated 3‐axis force sensor which is further combined with a high‐resolution position sensor. The herein developed setup allows evaluation of the NP‐metrics at an accuracy of ±1 pierced electrode layer without CT‐scans. Further NP examinations at 20 °C of fully charged cylindrical lithium nickel manganese cobalt oxide cells reveal a reproducible minimum damage as a reliable TR‐trigger. Moreover, NP‐tests at low temperature disclose a relation of the short circuit conductivity and TR‐reactions during subsequent rethermalization to room temperature. Finally, the implementation of a novel fixture for a controlled very fast cooling of LIB‐cells during critical damage opens the way to investigate the individual steps during a TR and, thus, to gain important information of the specific TR‐mechanism of different LIB‐cells.
Thermal transient problems, essential for modeling applications like welding and additive metal manufacturing, are characterized by a dynamic evolution of temperature. Accurately simulating these phenomena is often computationally expensive, thus limiting their applications, for example for model parameter estimation or online process control. Model order reduction, a solution to preserve the accuracy while reducing the computation time, is explored. This article addresses challenges in developing reduced order models using the proper generalized decomposition (PGD) for transient thermal problems with a specific treatment of the moving heat source within the reduced model. Factors affecting accuracy, convergence, and computational cost, such as discretization methods (finite element and finite difference), a dimensionless formulation, the size of the heat source, and the inclusion of material parameters as additional PGD variables are examined across progressively complex examples. The results demonstrate the influence of these factors on the PGD model’s performance and emphasize the importance of their consideration when implementing such models. For thermal example, it is demonstrated that a PGD model with a finite difference discretization in time, a dimensionless representation, a mapping for a moving heat source, and a spatial domain non-separation yields the best approximation to the full order model.
In situ chemical analysis of duplex stainless steel weld by laser induced breakdown spectroscopy
(2024)
The high corrosion resistance and good mechanical properties of duplex stainless steel (DSS) are due to its special chemical composition, which is a balanced phase ratio of ferrite (α) and austenite (γ). Many industrial applications require the integration of DSS components. For this, Gas tungsten arc welding (GTAW) is an excellent choice, as it allows an automated operation with high reproducibility. However, when the weld pool solidifies, critical ratios of α- and γ- phases can occur, which lead to solidification cracking, increased susceptibility to corrosion, and a decrease in ductility and critical strength. Previous studies have shown that these defects can be caused by the accumulation of manganese and chromium in the heat affected zone (HAZ), requiring ongoing monitoring of this accumulation. A suitable method for such monitoring is laser-induced breakdown spectroscopy (LIBS), which can be used in two operating modes: calibration using standard reference samples and calibration-free. Unlike conventional quantitative LIBS measurements, which require reference samples to generate a calibration curve, calibration-free LIBS (CF-LIBS) allows chemical compositions to be determined solely from the emission spectrum of the plasma. Numerous publications show that CF-LIBS is a fast and efficient analytical method for the quantitative analysis of metal samples. In this work, CF-LIBS is applied to spectra obtained during GTAW DSS welding and the result is compared with those obtained by PLS analysis. A good correlation was found between both types of analysis, demonstrating the suitability of the CF-LIBS method for this application. The CF-LIBS method has a significant advantage over conventional LIBS due to the rapid in situ measurement of concentrations of major alloying elements without calibration procedure. This, combined with fast feedback and appropriate adjustment of welding parameters, helps prevent welding defects.
A corrosion study is performed on six variations of titanium grade 5 (Ti6Al4V) samples. Samples are prepared in different conditions by variation of preanodization, postanodization, and picosecond-laser (ps-laser) surface treatment, while polished and anodized samples serve as reference. Microcones and nanosized periodic surface features are successfully produced on Ti6Al4V samples. The morphology and topography of the structures are visualized by scanning electron microscopy and white light interference microscopy. Furthermore, the relative electrochemically active surface area (ECSA) is determined for the ps-laser-treated samples. It is determined that the preanodized and laser-treated sample has 3.5 times larger ECSA than a polished sample, and that the laser-treated sample has 4.1 times larger area. Moreover, Tafel analysis is performed to determine the corrosion properties of the samples. It is shown that the corrosion resistance improves for both laser-structured samples after the anodization. To further study the surface of the samples, electrochemical impedance spectroscopy measurements are conducted. The study indicates that the ps-laser-treated and anodized Ti6Al4V is suitable to be used for the fabrication of bone screws and plates due to its improved corrosion resistance as compared to nonanodized samples.
Heterogeneous sandwich immunoassays are widely used for biomarker detection in bioanalysis and medical diagnostics. The high analyte sensitivity of the current “gold standard” enzyme-linked immunosorbent assay (ELISA) originates from the signal-generating enzymatic amplification step, yielding a high number of optically detectable reporter molecules. For future point-of-care testing (POCT) and point-of-need applications, there is an increasing interest in more simple detection strategies that circumvent time-consuming and temperature-dependent enzymatic reactions. A common concept to aim for detection limits comparable to those of enzymatic amplification reactions is the usage of polymer nanoparticles (NP) stained with a large number of chromophores. We explored different simple NP-based signal amplification strategies for heterogeneous sandwich immunoassays
that rely on an extraction-triggered release step of different types of optically detectable reporters. Therefore, streptavidinfunctionalized polystyrene particles (PSP) are utilized as carriers for (i) the fluorescent dye coumarin 153 (C153) and (ii) hemin (hem) molecules catalyzing the luminol reaction enabling chemiluminescence (CL) detection. Additionally, (iii) NP labeling with hemin-based microperoxidase MP11 was assessed. For each amplification approach, the PSP was first systematically optimized regarding size, loading concentration, and surface chemistry. Then, for an immunoassay for the inflammation marker C- eactive protein (CRP), the analyte sensitivity achievable with optimized PSP
ystems was compared with the established ELISA concept for photometric and CL detection. Careful optimization led to a limit of detection (LOD) of 0.1 ng/mL for MP11-labeled PSP and CL detection, performing similarly well to a photometric ELISA (0.13 ng/mL), which demonstrates the huge potential of our novel assay concept.
The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.
Determination of short carbon fiber orientation in zirconium diboride ceramic matrix composites
(2024)
In fiber-reinforced components, the fiber alignment and orientation have paramount influence on the thermomechanical properties of the resulting composite, for both short and continuous fiber. Here we present the case of an ultra-refractory matrix intended for extreme environment applications, ZrB2, reinforced with 20 vol% and 50 vol% short carbon fibers. In both cases, fibers tend to align perpendicular to the uniaxial pressure applied during shaping and sintering of a pellet, although the fiber tilt across the pellet thickness is difficult to determine. Moreover, for high volume fractions of reinforcement, the spatial distribution of the fibers is heterogeneous and tends to have domains of preferential orientations. We compare the information on the fiber distribution as collected by scanning electron microscopy images, X-ray computed tomography and synchrotron X-ray refraction radiography (SXRR). The three techniques prove to be complementary. Importantly, we demonstrate that SXRR yields the most statistically significant information due to the largest field of view, yet with a sensitivity down to the nanometer, and that can be successfully applied also to heavy matrix materials, such as zirconium boride.
Transparent conductive oxides such as indium tin oxide (ITO) are standards for thin film electrodes, providing a synergy of high optical transparency and electrical conductivity. In an electrolytic environment, the determination of an inert electrochemical potential window is crucial to maintain a stable material performance during device operation. We introduce operando ellipsometry, combining cyclic voltammetry (CV) with spectroscopic ellipsometry, as a versatile tool to monitor the evolution of both complete optical (i.e., complex refractive index) and electrical properties under wet electrochemical operational conditions. In particular, we trace the degradation of ITO electrodes caused by electrochemical reduction in a pH-neutral, water-based electrolyte environment during electrochemical cycling. With the onset of hydrogen evolution at negative bias voltages, indium and tin are irreversibly reduced to the metallic state, causing an advancing darkening, i.e., a gradual loss of transparency, with every CV cycle, while the conductivity is mostly conserved over multiple CV cycles. Post-operando analysis reveals the reductive (loss of oxygen) formation of metallic nanodroplets on the surface. The reductive disruption of the ITO electrode happens at the solid–liquid interface and proceeds gradually from the surface to the bottom of the layer, which is evidenced by cross-sectional transmission electron microscopy imaging and complemented by energy-dispersive X-ray spectroscopy mapping. As long as a continuous part of the ITO layer remains at the bottom, the conductivity is largely retained, allowing repeated CV cycling. We consider operando ellipsometry a sensitive and nondestructive tool to monitor early stage material and property changes, either by tracing failure points, controlling intentional processes, or for sensing purposes, making it suitable for various research fields involving solid–liquid interfaces and electrochemical activity.
AbstractIn this study, we compare the residual stress state in a laser powder bed fusion (PBF‐LB/M) AlSi10Mg alloy in the as‐built (AB) condition with that after two different heat treatments (265 °C for 1 h, HT1; and 300 °C for 2 h, HT2). The bulk residual stress (RS) is determined using synchrotron X‐ray diffraction (SXRD), and near‐surface profiles are determined using laboratory energy‐dispersive X‐ray diffraction (EDXRD). The EDXRD results do not reveal any notable difference between the conditions at a depth of 350 μm, suggesting that the machining process yields a comparable residual stress state in the near‐surface regions. On the other hand, the SXRD results show that HT1 is more effective in relieving the bulk RS. It is observed that HT1 reduces the RS state in both the aluminium matrix and the silicon network. In addtion, HT2 does not have a significant impact on relaxing the RS as‐built state of the matrix, although it does induce a reduction in the RS magnitudes of the Si phase. It is concluded that the heat treatment stress relieving is effective as long as the Si‐network is not disaggregated.
There is only sparse empirical data on the settling velocity of small, non-buoyant microplastics thus far, although it is an important parameter governing their vertical transport within aquatic environments. This study reports the settling velocities of 4031 exemplary microplastic particles. Focusing on the environmentally most prevalent particle shapes, irregular microplastic fragments of four different polymer types (9–289 µm) as well as five discrete length fractions (50–600 µm) of common nylon and polyester fibers were investigated, respectively. All settling experiments were carried out in quiescent water using a specialized optical imaging setup. The method has been previously validated in order to minimize disruptive factors, e.g. thermal convection or particle interactions, and thus enable the precise measurements of the velocities of individual microplastic particles (0.003–9.094 mm/s). Based on the obtained data, ten existing models for predicting a particle’s terminal settling velocity were assessed. It is concluded that models, which were specifically deduced from empirical data on larger microplastics, fail to provide accurate predictions for small microplastics. Instead, a different approach is highlighted as a viable option for computing settling velocities across the microplastics continuum in terms of size, density and shape.
The dripping behaviour of polymers is often observed experimentally through the UL94 flammability standard test. In this work, polymeric dripping under fire is investigated numerically using particle finite element method. A parametric analysis was carried out to observe the influence of a single property on overall dripping behaviour via a UL94 vertical test model. Surrogates and property ranges were defined for variation of the following parameters: glass transition temperature (Tg), melting temperature (Tm), decomposition temperature (Td), density (ρ), specific heat capacity (Cp), apparent effective heat of combustion of the volatiles, char yield (μ), thermal conductivity (k), and viscosity (η). Polyamide, poly(ether ether ketone), poly(methyl methacrylate), and polysulfone were used as benchmarks. Simulated results showed that specific heat capacity, thermal conductivity, and char yield allied with viscosity were the properties that most influenced dripping behaviour (starting time and occurrence).
EPDM, HNBR and FKM materials were exposed at 150 ◦C to air under atmospheric pressure and to hydrogen at 50 bar for different ageing times. All measurements after hydrogen exposure were conducted on samples in degassed condition to assess irreversible effects resulting from that exposure and to compare them to those after ageing in air. Density, hardness, tensile properties, compression set, and hydrogen permeability of all samples were analysed. In both ageing environments, HNBR exhibited the most significant changes of material properties.
However, for both EPDM and HNBR, considerably less severe ageing effects were observed under hydrogen in comparison to ageing in air. On the other hand, FKM showed about the same low level of deterioration in both ageing environments but exhibited poor resistance against damage due to rapid gas decompression in hydrogen environment that can lead to seal failure. The obtained results may serve as a guidance toward a better understanding for design and utilisation of elastomeric materials in future hydrogen infrastructure components.