Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Solar glass in arid and semi-arid regions is exposed to sand storms which can affect the durability of PV modules. Related erosion processes have been extensively studied but the results given are difficult to compare due to being obtained by different variables like particle speed and sand mass. This study correlates the damage of solar panels to the cumulative impact energy as a global parameter.
Experimental study on M23C6 nucleation and growth mechanisms in Ni-base superalloy single crystals
(2017)
The addition of carbon to Ni-base superalloy single crystals has been increasingly carried out to improve low angle grain boundary (LAGB) resistance and castability. Consequently, the precipitation of carbides is highly probable during long-term application of components subjected to higher temperatures (> 1000 °C). While the view on the role of carbides as strengthening or detrimental is polemical, their inevitable increased presence in carbon-doped alloys must be addressed. In the present work, the evolution of M23C6 carbides forming in the commercial grade Ni-base superalloy LEK 94 during high-temperature and low-stress creep exposure is assessed. Although carbon is not intentionally added to the LEK 94 alloy, it admits up to 0.1 at. %, which together with the high content of M23C6-forming transition metals, leads to their precipitation. The precipitation is induced here during creep experiments at 1020 °C and a nominal applied stress of 160 MPa along [001]. The correlation of precipitation and external load is carried out by evaluating the carbides in the gage section of parallel and circularly notched cylindrical samples, as well as in their heads. Characterization is made by transmission electron microscopy (TEM). Although primary MC carbides form mostly in interdendritic regions during casting, high temperature exposure induces M23C6 carbide nucleation especially in the γ phase of dendritic regions, where a stronger partitioning of refractory elements is present. The carbides have a needle shape with their main axis on 〈100〉 and a cube-on-cube orientation relationship. They present incoherent {100} facets along their elongated region and semi-coherent {111} facets at their ends. Their nucleation and growth mechanisms are discussed based on microstructural observation under different experimental conditions.
Oxidation of a Fe-13Cr alloy under water vapor at 600 °C produced a zone of nano-sized precipitation underneath the outside scale formed by iron oxides and Fe‒Cr spinel. The majority of the spinel layer shows a mixed orientation relationship to the ferritic matrix {100}α || {100}sp & <011>α || <001>sp. However, also the discovered precipitated particles are characterized by the same crystallographic orientation relationship to the respective ferritic parent grain. The habit of the precipitates is best described by a lath morphology with their main axis parallel to <100> of ferrite.
Energy dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD) in an scanning electron microscope (SEM) have been applied to characterize the oxide layer in the micrometer scale. The clearly smaller precipitates were subsequently investigated by transmission electron microscopy (TEM). Specimens have been prepared by focused ion-beam (FIB) milling at an area previously characterized by EBSD. They cover the ferritic base material, but mainly the precipitation zone and the Fe‒Cr spinel layer. Energy filtered selected area diffraction (SAD) in the conventional (C)TEM and high-angle annular darkfield (HAADF) imaging in the scanning (S)TEM mode were employed in the characterization of the specimens.
We report on the in situ investigation of mechanochemical syntheses of metal phosphonates. The metal phosphonates are formed in milling reactions starting from a metal acetate and a phosphonic acid. The conversions are observed by synchrotron PXRD and Raman spectroscopy to shed light on the reaction mechanisms including possible intermediates.
The exploration of metal phosphonates chemistry has gained great interest during the last decades, because of their structural diversity. Transition metal phosphonates are promising candidates for an application as electrocatalysts in oxygen evolution reactions (OER).
Here, we present the in situ investigation of mechanochemical syntheses of different manganese phosphonates by synchrotron X-ray diffraction. Nitrilotri(methylenephosphonic acid) and N,N-Bis(phosphonomethyl)glycine were chosen as ligands. The liquid-assisted milling process can be divided into three steps, including an amorphous stage. One of the products has not been obtained by classical solution chemistry before.
These metal phosphonates and/or their derivatives are considered to be active in electrochemical energy conversion. The verification of their applicability is one of the topics of our resent research.
Mechanochemistry is a versatile approach for green and fast synthesis of pure substances. By milling the reactants, various organic, inorganic, and metal-organic compounds can be obtained in high yields. Although mechanochemistry is widely used, the underlying mechanisms are not fully understood making mechanochemical reactions difficult to predict. Metal phosphonates are metal-organic compounds accessible by grinding. Because of their structural diversity, the exploration of the chemistry of metal phosphonates has gained considerable interest during the last decades. Transition metal phosphonates are promising candidates for an application as electrocatalysts in oxygen evolution reaction (OER). Here, we present the in situ investigation of the mechanochemical synthesis of a manganese(II)-phosphonate by synchrotron X-ray diffraction and thermography. The product has not been obtained by classical solution chemistry before and its crystal structure was determined from PXRD data. The milling process can be divided into different steps, with the product crystallization corresponding with the highest temperature rise. The activity of this metal phosphonate towards OER was measured and is presented here.
Mechanochemistry is a versatile approach for green and fast synthesis of pure substances. The exploration of the chemistry of metal phosphonates has gained considerable interest during the last decades due to their structural diversity. We synthesized manganese phosphonates in milling reactions. The mechanochemical reactions were investigated in situ to reveal the underlying mechanisms.
Additive manufacturing (AM) offers a range of novel applications. However, the manufacturing process is complex and the production of defect-free parts with a high reliability is still a challenge. Thermography is a valuable tool for process surveillance, especially in metal AM processes. The high process temperatures allow one to use cameras usually operating in the visible spectral range. Here, we compare the results of first measurements during the manufacturing process of a commercial laser metal deposition (LMD) setup using a MWIR camera with those from a VIS high-speed camera with band pass filter in the NIR range.
Additive manufacturing (AM) opens the route to a range of novel applications.However, the complexity of the manufacturing process poses a challenge for the production of defect-free parts with a high reliability. Since process dynamics and resulting microstructures of AM parts are strongly influenced by the involved temperature fields, thermography is a valuable tool for process surveillance. The high process temperatures in metal AM processes allow one to use cameras usually operating in the visible spectral range to detect the thermally emitted radiation from the process. In our work, we compare the results of first measurements during the manufacturing processes of a commercial laser metal deposition (LMD) setup and a laser beam melting (LBM) setup using a MWIR camera with those from a VIS high-speed camera with band pass filter in the NIR range.
Additive manufacturing (AM) opens the route to a range of novel applications. However, the complexity of the manufacturing process poses a challenge to produce defect-free parts with a high reliability. Since process dynamics and resulting microstructures of AM parts are strongly influenced by the involved temperature fields and cooling rates, thermography is a valuable tool for process monitoring. Another approach to monitor the energy input into the part during process is the use of optical tomography.
Common visual camera systems reach much higher spatial resolution than infrared thermography cameras, whereas infrared thermography provides a much higher temperature dynamic. Therefore, the combined application increases the depth of information. Here, we present first measurement results using a laser beam melting setup that allows simultaneous acquisition of thermography and optical tomography from the same point of view using a beam splitter. A high-resolution CMOS camera operating in the visible spectral range is equipped with a near infrared bandpass filter and images of the build plate are recorded with long-term exposure during the whole layer exposing time. Thus, areas that reach higher maximum temperature or are at elevated temperature for an extended period of time appear brighter in the images. The used thermography camera is sensitive to the mid wavelength infrared range and records thermal videos of each layer exposure at an acquisition rate close to 1 kHz.
As a next step, we will use computer tomographic data of the built part as a reference for defect detection.
This research was funded by BAM within the focus area Materials.
Material Selection Strategy
(2023)
In the pursuit of discovering materials with desirable properties, extending the available material libraries is crucial. High-throughput simulations have become an integral part in designing new materials in the past decades. However, there is no straightforward way of distinguishing synthesizable materials from all the proposed candidates. This project focuses on employing AI-driven methods to estimate synthesizability of materials.
Up to now, material scientists and engineers have relied on domain knowledge as well as empirical heuristics to guess the stability and synthesizability of molecules and crystals. The famous Pauling rules of crystal stability are an example of such heuristics. However, after the accelerating material discovery in all the years since Pauling, these rules now fail to account for the stability of most known crystals. A new predictive set of heuristics for crystal stability/synthesizability is unlikely to be uncovered by human perception, given the magnitude and dimensionality of crystallographic data. Hence, a data-driven approach should be proposed to find a predictive model or set of heuristics which differentiate synthesizable crystal structures from the rest. The main challenge of this research problem is the lack of a negative set for classification. Here, there are two classes of data: the positive class which contains synthesizable materials and the negative class which contains materials which are not synthesizable. While the data from the positive class is simply the data of crystals which have been experimentally synthesized, we do not have access to data points which are certainly unsynthesizable. Strictly speaking, if an attempt of synthesizing a crystal fails, it does not necessarily follow that the crystal is not synthesizable. Also, there is no database available which contains the intended crystal structures of unsuccessful synthesis attempts.
This project proposes a semi-supervised learning scheme to predict crystal synthesizability. The ML model is trained on experimental and theoretical crystal data. The initial featurization focuses on local environments which is inspired by the Pauling Rules. The experimental data points are downloaded through the Pymatgen API from the Materials Project database which contains relaxed structures recorded in Inorganic Crystal Structure Database – ICSD. The theoretical data is queried from select databases accessible through the Optimade project’s API.
Microbial modelling of sulfate-reducing bacteria (SRB) and methanogenic archaea (ME) using iron
(2019)
Sulfate reducing bacteria (SRB) and methanogenic archaea (MA) are commonly found in the oil and gas environments. The formation of hydrogen sulfide (HS-) is particularly concerning for the petroleum industry due to its corrosiveness. However, the activities of SRB are limited to the concentration of sulfate present in the environment, whereas methanogens can utilize substrates such as H¬2 for methanogenesis. MA is commonly found in sulfate-free environments, such as deep sediments, and are known to form interspecies electron transfer relationships with SRB. Recently, SRB and MA capable of microbiologically influenced corrosion (MIC) by using elemental iron as a direct electron source (EMIC) have gained increased attention. On the iron surface, EMIC-SRB can outcompete EMIC-MA in the presence of sulfate, but this changes as sulfate depletes. The formation of FeS on the metal surface can be further utilized by MA for methanogenesis as it provides a conductive path. However, the possible kinetics involved of the overall process are currently unknown.
We obtained a co-culture of EMIC-SRB and EMIC-MA to investigate the growth rates and electrical potential changes under different environmental conditions, including changes in pH, temperature and salinity. Results indicate that under neutral conditions and using iron as the sole substrate, methane production (up to 5 mM) starts after sulfate was depleted. Electrochemical measurements will be conducted on the co-culture under different conditions to determine the changes in the electrical potential in correlation with the sulfate and methane concentration. Fluorescence and electron microscope images of the biofilm structure will be used to visualize cell distribution and morphology. This study embarks the first step of understanding the relationship between EMIC-SRB and EMIC-MA. Such knowledge is important for the field of microbial electrophysiology and can be further explored for industrial applications.
Microbiologically influenced corrosion (MIC) is the deterioration of metals due to the metabolic activities of microorganisms. Microorganisms can take electrons directly from the metal surface (EMIC) thereby causing corrosion. Well known culprits of EMIC are: sulfate-reducing bacteria (SRB), acetogens and methanogens.
Our aims
- Develop a novel flow system to study MIC by methanogens to mimic industrial Environments
- Investigate the inhibitory concentrations of biocides targeting SRB on corrosive methanogenic strains
- Investigate the inhibitory effects of corrosion inhibitors on methanogens
- Compare the inhibitory concentrations to SRB
Electrochemical study of polyaniline/silicon dioxide containing coatings in geothermal solution
(2018)
Polyaniline/Silicon Dioxide containing coatings were electrochemically investigated in a saline geothermal solution.
With the increase of exposure time, impedance values of coated specimens decreased at low frequency, which could be caused by the decrease of pore resistance due to electrolyte or water uptake.
Coating system needs further optimization work.
Geothermal brine is considered to be an aggressive environment as it contains various dissolved salts. Even though carbon steel is commonly used as a construction material due to its machinability and economical reason, it is susceptible to uniform and localized corrosion in a high temperature and high pressure system. Therefore, a coating system is introduced to protect the carbon steel against corrosion in such environment.
-It is necessary to find the optimum composition of SiO2 addition in the organic coatings to enhance the material performance, i.e. coatings adhesion, thickness optimization, thermal resistance.
Current project aims at the addition of Polyaniline (PANi) as the active agent to improve the corrosion resistance of materials against a high saline medium at elevated temperatures.
One of the alternative renewable fuels is biomass but it is a difficult fuel because of its diversity and complexity. It can contain high percentages of K and Cl responsible for corrosion together with sand that have additionally an abrasive effect during combustion. Because of permanently extending the surface reaction due to abrasion the corrosion of the materials increases. In particular in power plants, the superheater tubes are exposed to a corrosive abrasive attack that is one of the main sources of concern. The development of new alloys for multilayer surface, which combines corrosive and abrasive resistance is therefore of high importance. Those new technical approaches must be at the same time cost-effective to be an alternative to conventional materials. The aim of the presented investigation methods is to test and develop suitable alloys for coatings for the super heater tubes of biomass power plants. First results of abrasion investigations show improved abrasion resistance compared to the multi-component reference material Alloy 625.
The main solidification parameters, namely the crystal axis, the growth rate, and the cross-sectional area of the columnar crystal control the primary microstructure and thus the final weld seam properties.
Limited understanding of solidification parameters due to complexities in experimental and theoretical weld pool boundary determination and
its mathematical description.
Application of local Lamé curves for efficient weld pool boundary reconstruction Derivation of general analytical solutions for the main solidification parameters of a two-dimensional columnar crystal growth during laser beam welding of thin steel sheets.
The Lamé curves approximation technique was successfully applied for the reconstruction of the rear part of the two-dimensional steady-state weld pool boundary. General analytical expressions for the main solidification parameters, namely the crystal axis, the growth rate and the cross-sectional area of the crystal were derived.
The derived expressions and herewith obtained results were verified and validated by comparing them to known theoretical solutions and experimental measurements. Dimensionless analysis of the influence of the size and shape of the rear weld pool boundary on the solidification parameters was provided.
The derived general solutions and the analysis provided allow for critical welding parameters to be estimated and adapted accordingly to improve the welding process.
Despite of the significant advances in additive manufacturing (AM) process optimization there is still a lack of experimental results and understanding regarding the mechanical behavior and its relationship with the microstructural features of AM-parts, especially in loading conditions typical for safety-relevant applications. Within the scope of the presented ongoing investigations, a basic microstructural characterization, tensile tests at room and elevated temperature (400°C) as well as a characterization of the fatigue behavior of additively manufactured Ti-6Al-4V in the low cycle fatigue regime are carried out in the as-built state. After failure, different techniques are used to describe the failure mechanisms of the specimens. The AM-Specimens are provided by the Fraunhofer institute for production systems and design technology and investigated at the BAM following the philosophy of the TF-Project AGIL.
In the presentation different zinc coatings are presented and investigated. Their naturally formed protective layers are electrochemically characterized and corrosion relevant values are determined by using a gel pad based on polysaccharide. The corrosion relevant values allow the differentiation of various zinc coating systems and can describe the current protective effect provided by the coating. It is shown that gel-type electrolytes influence protective layers and coatings considerably less than corresponding bulk electrolytes. From the results it is evident that gel-type electrolytes represent a viable and promising field in corrosion research.zeige mehr
Influence of corundum grinding processes on the corrosion behaviour of austenitic stainless steels
(2017)
The scientific poster shows by means of corrosion testing in combination with surface analytical methods to which degree corundum grinding influences the corrosion behaviour of stainless steel surfaces. The austenitic stainless steel AISI 304 from a consistent heat was used for all investigations to guarantee the same chemical composition and thus no additional influences caused by the material itself. A wide range of different grinding parameters such as pressure, cooling medium and grain size of the abrasive was varied. Thus, comparison of the corrosion behaviour of different surface states and the evaluation of an optimum grinding process using corundum abrasives were possible. The results will contribute to present discussions and give novel impulses for companies in the metalworking industry.
The motivation and the measurement setup for large fast-scanning piezoresistive cantilevers are presented. The theory behind the measurements of mechanical properties through contact resonance is explained. Results of such measurements on two kinds of polymer are compared to results from force distance curves. Noise, time-dependency and dependency of the results on the vibration mode are identified as challenges of contact resonance.
Within the perspective of increasing reliability of AM processes, real-time monitoring allows part inspection while it is built and simultaneous defect detection. Further developments of real-time monitoring can also bring to self-regulating process controls. Key points to reach such a goal are the extensive research and knowledge of correlations between sensor signals and their causes in the process.
The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 20 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry in the partial penetration mode by means of a high-speed camera. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the weld pool root. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model considers the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
One of the biggest problems in high-voltage silicone rubber insulation cable accessories is the damage on electrical treeing, initiated by partial discharges. The electrical treeing starts at unavoidable imperfections inside the material or at interfaces. The damage is usually irreversible and leads around the starting points to a partial destruction of the material. To prolong the lifetime and thereby to increase the assurance of the structural component commonly, for mechanical improvement constituted filler is modified to obtain a self-healing silicone rubber. Damage mechanism is analysed to address the filler to the damage mode.
To avoid a catastrophic failure of insulation in high-voltage (HV) applications, a monitoring of partial discharges (PD) is necessary. Fluorescently labelled polymer optical fibres (F-POF) offer an electrically passive method for PD detection in HV facilities. F-POF could be embedded into HV cable insulation material, which are usually made of silicone rubber. Due to the difficult accessibility of HV cable accessories, a self-healing silicone rubber, based on incorporated capsules, with prolonged service life after PD detection represents an attractive material design for HV electrical insulation.
Multifunctional Graphene in Flame Retarded Polybutadiene/ Chloroprene/ Carbon Black Composites
(2021)
Multilayer graphene is investigated as a multifunctional nanofiller to polybutadiene/ chloroprene rubbers (BR/CR) that partially substitutes carbon black (CB) and aluminum trihydroxide (ATH). Loadings of only 3 parts per hundred rubber (phr) MLG replaced 15 phr of CB and/or 3 phr of ATH in BR/CR nanocomposites. Mechanical and fire behavior were investigated, and results point to improved rheological, curing and mechanical properties of MLG-containing rubber composites.
In dentistry it is of great interest to achieve good sealing interzones between tooth tissue and restoration materials to avoid, e. g. secondary caries. μXRF and CμXRF are suitable to investigate the elemental composition at these interzones in respect to diffusion of elements. Synchrotron X-ray refraction radiography (SXRR) and μCT measurements deliver highly resolved structural information and make structural changes such as micro cracks within the filling and the tooth tissue visible. The presented measurements are part of the DFG funded project IXdent (Integrative X-ray techniques for chemical and structural characterizations of dental interzones.)
The depth-resolved CμXRF measurements are affected by absorption effects, making a quantitative investigation of the interzone in depth difficult. Full 3D quantification of heterogenous samples requires a complete model including dark matrix and density for each voxel. The combination of different techniques paves the way for a quantitative analysis of dental interzones.
Within the DFG project ‘IXdent’, first results have been achieved on 2D µXRF and X-ray refraction radiography measurements as well as combined 3D confocal µXRF and µXCT investigations at the interface between filling and bovine tooth tissue. The benefit of multiple analytical techniques and the combination of structural and elemental analysis will be demonstrated.
Nowadays, teeth are not directly extracted when tooth decay occurs. Whenever treatment of the affected tooth is possible, the carious region is replaced with a suitable filling. The filling material differs according to the position and size of the cavity. Since the restoration will remain in the tooth for many years, a well adhering and sealing interface between filling and healthy tooth tissue is needed. There is continuous development of new materials, but intensive studies of this complex interface between filling and healthy tooth are still lacking. Little is known about possible diffusion of elements from dental materials into healthy tooth tissue forming a socalled interzone with specific chemical and structural properties.
The combination of different analytical X-ray methods at synchrotron radiation facilities and in the laboratory enables an extensive structural and elemental investigation of such interzones. While X-ray fluorescence techniques and X-ray absorption spectroscopy yield elemental distributions and localized chemical speciation, X-ray diffraction, refraction and computed tomography add structural information to the full 3D analysis of model and real life tooth
samples. Within two DFG funded projects, we develop adapted methodologies and investigate
micro-chemical changes in interzones which we hypothesize may lead to sclerotic dentine.
This poster presents the focused ion beam preparation methodologies developed within the framework of the EU funded EURAMET project ADVENT (Advanced Energy-Saving Technology).
It summarises the key breakthroughs achieved for various in situ investigation techniques, e.g. in situ experiments at the Synchrotron facility BESSY II (IR-SNOM and XRS), TEM and SMM instrumentation.
The created experimental devices from diverse thin-film semiconductor materials paved the way to dynamic structural studies bearing the potential to determine nanoscale correlations between strain and electric fields and, moreover, for the fundamental development of new in situ capabilities.
The PMD Core Ontology (PMDco) is a comprehensive set of building blocks produced via consensus building. The ontological building blocks provide a framework representing knowledge about fundamental concepts used in Materials Science and Engineering (MSE) today. The PMDco is a mid-level ontology that establishes connections between narrower MSE application ontologies and domain neutral concepts used in already established broader (top-level) ontologies. The primary goal of the PMDco design is to enable interoperability between various other MSE-related ontologies and other common ontologies.
PMDco’s class structure is both comprehensive and extensible, rendering it an efficient tool to structure MSE knowledge. The PMDco serves as a semantic middle-layer unifying common MSE concepts via semantic mapping to other semantic representations using well-known key terms used in the MSE domain. The PMDco enables straight-forward documentation and tracking of science data generation and in consequence enables high-quality FAIR data that allows for precise reproducibility of scientific experiments.
The design of PMDco is based on the W3C Provenance Ontology (PROV-O), which provides a standard framework for capturing the production, derivation, and attribution of resources. Via this foundation, the PMDco enables the integration of data from various data origins and the representation of complex workflows.
In summary, the PMDco is a valuable advancement for researchers and practitioners in MSE domains. It provides a common MSE vocabulary to represent and share knowledge, allowing for efficient collaboration and promoting interoperability between diverse domains. Its design allows for the systematic integration of data and metadata, enabling seamless tracing of science data. Overall, the PMDco is a crucial step towards a unified and comprehensive understanding of the MSE domain in general.
THz and mid IR spectroscopy of high-molecular PE (HMW) and ultra high-molecular PE (UHMW) reveals modifications of the molecular structure. Characteristic absorption bands are changed if the two materials are exposed by γ-Co60 radiation up to 600 kGy and subsequently stored at an annealing temperature of 398 K until for 729 days. UHMW-PE and HMW-PE behave differently during the ageing process because of their molecular weight and inherent structure distinctions. The spectroscopic data offer characteristic absorption bands, which have been used to describe the complete ageing process in more detail. For instance, the integral absorption in the B1u THz-region can be used to describe quantitatively the reduction of crystallinity. The formation of trans vinylene unsaturation and the decay of vinyl during ageing can be observed in detail in the mid IR range.
Novel Technique for On-Line Monitoring of the Curing Process of Fiber Reinforced Polymer Composites
(2020)
A specially designed experimental set up has been integrated into a commercially available FT IR Spectrometer for ATR experiments on Epoxy Systems. Representative data of far infrared spectra measured during the curing process at different temperatures of an epoxy system will be presented in dependency of the curing situation. The experiments and the selected set up are discussed to demonstrate its potential for future monitoring and ageing control applications during a manufacturing process of polymer composites.
Casks for storage and transportation of used fuel rods of radioactive material are equipped with polyethylene (PE) for improved neutron flux shielding. The embedded PE structures are additionally exposed to gamma radiation and heat flow due to the specific high activity of the fission products. 60Co γ-radiation and heat load experiments at 125°C has been performed to evaluate PE degradation during the ageing process. FAR-FTIR-experiments were subsequently performed at differently aged PE test samples to characterize the oxidation process and morphological changes in the samples during the ageing at 125°C.
THz and mid IR spectroscopy of high-molecular PE (HMW) and ultra high-molecular PE (UHMW) reveals modifications of the molecular structure. Characteristic absorption bands are changed if the two materials are exposed by -Co60 radiation up to 600 kGy and subsequently stored at an annealing temperature of 398 K until for 729 days. UHMW-PE and HMW-PE behave differently during the ageing process because of their molecular weight and inherent structure distinctions. The spectroscopic data offer characteristic absorption bands, which have been used to describe the complete ageing process in more detail. For instance, the integral absorption in the B1u THz-region can be used to describe quantitatively the reduction of crystallinity. The formation of trans vinylene unsaturation and the decay of vinyl during ageing can be observed in detail in the mid IR range.
aRTist is an easy-to-use and practical simulation tool to generate realistic radiographic images from CAD objects. A dedicated add-on module makes CT simulation easy (virtual computer tomography). Just choose the number of projections.
Unlike in the practice, simulation can separately image the primary and scatter radiation. This allows studying the scattering artefacts in CT (gray-level variations in regions of homogeneous material).
A series of different nanoparticle suspensions (Gold, Latex, and SiO2 in varying concentrations) were microprinted onto TEM grids in a 4 x 4 array in the concentration range 7x10^8 to 1x10^11 NP/mL and imaged with SEM and TSEM. Concentrations and printing conditions (temperature, relative humidity) were varied in order to minimize the coffee ring effect.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media with applications in the field of drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and/or 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
UCST-type thermoresponsive polymers that phase separate from solution upon cooling present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol. In this context, acrylamide-based monomers can be very useful building blocks for designing novel UCST-type polymers because of their hydrophilic nature (with the right side chain) and propensity to form hydrogen bonds.
We want to present our latest results on the copolymer poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) that present a UCST in water as well as on two homopolymers based on an acrylamide derivative of 2,6-diaminopyridine, namely poly(N-(6-aminopyridin-2-yl)acrylamide) (PNAPAAm) and poly(N-(6-acetamidopyridin-2-yl)acrylamide) (PNAcAPAAm) that show UCST-type thermoresponsiveness in water/alcohol mixtures.
Our focus for P(AAm-co-AN)) is its aggregation behaviour above and below its phase transition temperature as the size of thermoresponsive polymeric systems is of prime importance for biomedical applications (as size dependent processes take place in the body) and is linked to the optical properties of a material that matter in materials science.
In the case of PNAPAAm and PNAcAPAAm, we focused on the co-solvency/co-non solvency effect on the phase transition temperature in water/alcohol mixture. Indeed, polymers with UCST behavior below 60°C in water/alcohol mixtures are extremely promising for the preparation of “smart” materials for sensing.
Proton exchange membrane fuel cells (PEMFCs) are one of the most promising alternative green energy technologies that deliver high energy density without CO2 emissions. The proton conductivity of proton exchange membranes (PEM) contributes to the overall efficiency of a PEMFC. Materials being used as PEMs must exhibit high proton conductivity at the working conditions of the targeted PEMFC. To date, Nafion and Nafion-like polymers with acidic functionality are widely used as membrane materials due to their high proton conductivity in the range of 10-1 to 10-2 Scm-1 at higher relative humidity. However, these materials suffer from high costs, hazardous production process, and poor performance at high temperatures, limiting their versatility.
In this context, crystalline porous materials are recognized as promising proton conductors for the proton exchange membrane (PEM) in fuel cell technology, owing to their tunable framework structure. However, it is still challenging bulk synthesis for real-world applications of these materials. Herein, we present mechanochemical gram-scale synthesis of series of mixed ligand metal organic frameworks (MOFs) and metal hydrogen‐bonded organic frameworks (MHOFs) using phenylene diphosphonic acid and 1-hydroxyethylidene-1,1-diphosphonic acid with different bipyridyl type of ligands, respectively. In all cases, the existence of extensive hydrogen bonds with amphiprotic uncoordinated phosphonate hydroxyl and oxygen atoms, the frameworks exhibited high proton conductivity. The study demonstrates the potential of green mechanosynthesis for preparations of framework-based proton conducting materials in bulk scale for green energy generation.
Bioglass® 45S5 is mainly used clinically as powders, granules or pastes instead of sintered compacts. This is due to the inherent problem of crystallization during the sintering, which results in poor mechanical properties and reduced bioactivity. Recently, new bioactive glasses with improved crystallization stability have been developed as promising candidates for manufacturing of sintered powder compacts for bone regeneration, which combine improved sintering behavior with bioactivity. Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkali oxide ratio was increased, sodium oxide was partially replaced by potassium oxide and up to 3 mol% calcium fluoride were added, in order to stabilize the glass against crystallization. The aim of this study was to investigate the sintering and crystallization behavior of these new bioactive glasses.
Sintering and crystallization were characterized by heating microscopy, XRD, FTIR, SEM, and DTA. The results show that a sintered density of 88-99 % is achieved in contrast to only 57-67% for Bioglass® 45S5. In addition, FTIR and XRD analyses show that Bioglass® 45S5 crystallized during sintering while for the new glasses no crystalline phases are detected. The thermal properties of all glasses were studied by DTA measurements, and the influence of grain size was characterized. These studies showed that full densification can be attained for particle size < 32 µm, whereas coarser particles progressively increase residual porosity. Observed foaming phenomena, are strongly retarded by crystallization of beta-HAp.
Nowadays, the use of bioactive glasses is established for bone regeneration; however glasses are used mostly as powders, granules or in a paste. Sintered scaffolds are not used clinically, because of the in inherent problem of crystallization during the sintering process, resulting in poor mechanical properties and reduced bioactivity. The aim of this study was therefore to design new bioactive glasses, which combine improved processing and sintering with bioactivity.
Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkalioxide ratio was increased, sodiumoxide was partially replaced by potassiumoxide and up to 8 mol% calciumflorid were added, in order to stabilize the glass against crystallization.
The sintering behavior of the new glasses was characterized by heating microscopy and compared to Bioglass® 45S5. The results showed that the new glasses achieved a sintered density of 88-99 % in contrast to only 57-67% for Bioglass® 45S5. In addition FTIR and XRD analyses showed that Bioglass® 45S5 crystallized during sintering while for the new glasses no crystalline phases were detected. The thermal properties of all glasses were studied by DTA and DSC measures, and the influence of grain size and heating rate were characterized. These studies showed a shift of start and end temperature of sintering process as well as the final density. The structure of sintered specimens during and after sintering was examined using light and electron microscopy (REM).
Bioglass® 45S5 is mainly used clinically as powders, granules or pastes instead of sintered compacts. This is due to the inherent problem of crystallization during sintering. Recently, new bioactive glasses with improved crys-tallization stability have been developed as promising candidates for manufacturing of sintered powder compacts for bone regeneration, which combine improved sintering behavior with bioactivity. Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkali oxide ratio was increased, sodium oxide was partially replaced by potassium oxide and up to 3 mol% calcium fluoride were added, in order to stabilize the glass against crystallization. Sintering and crystallization were characterized by heating microscopy, XRD, FTIR, SEM, and DTA. The results show that a sintered density of 88-99 % is achieved in contrast to only 57-67% for Bioglass® 45S5. Whereas Bioglass® 45S5 powder compacts crystallize during sintering, for the new glasses no crystalline phases were detected. Additionally the influence of grain size was characterized. These studies showed that full densification can be attained for particle size < 32 µm, whereas coarser particles pro-gressively increase residual porosity. Observed foaming phenomena, are strongly retarded by crystallization.