4 Material und Umwelt
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Eingeladener Vortrag
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Laser Powder Bed Fusion (L-PBF) is a promising additive manufacturing (AM) technology for metal part production especially for complex and lightweight structures or functional designs. In L PBF processes several by-products including welding plume and its condensates, spatter and ejected powder are generated during laser exposure. Investigations of micro- and nano-sized by-products have received little attention in literature. This study focuses on the analysis of particle emissions in L PBF of 316L stainless steel using a scattered light aerosol spectrometer and a fast mobility particle sizer spectrometer during the process which allows for in-situ analysis of particle sizes in the range of 6 nm to 100 µm. A distinct correlation of emission signals to part position can be revealed. In addition, a significant influence of laser scanning vector directions on emission signals is presented. Furthermore, differing powder layer thicknesses can be recognised by deviations in emission signals.
Laser Powder Bed Fusion (L-PBF) is a promising additive manufacturing (AM) technology for metal part production especially for complex and lightweight structures or functional designs. In L PBF processes several by-products including welding plume and its condensates, spatter and ejected powder are generated during laser exposure. Investigations of micro- and nano-sized by-products have received little attention in literature. This study focuses on the analysis of particle emissions in L PBF of 316L stainless steel using a scattered light aerosol spectrometer and a fast mobility particle sizer spectrometer during the process which allows for in-situ analysis of particle sizes in the range of 6 nm to 100 µm. A distinct correlation of emission signals to part position can be revealed. In addition, a significant influence of laser scanning vector directions on emission signals is presented. Furthermore, differing powder layer thicknesses can be recognised by deviations in emission signals.
Brazilian farming industry consumed around 2.2 million tons of phosphorus (P) fertilizers in 2016. The agricultural industry depends on imported P fertilizers and over 98% of P fertilizers were used for sugarcane, soybean and maize production.
An alternative is to use P from sugarcane bagasse. Bagasse is the fibrous plant material remaining after extraction of sugarcane juice, and it is combusted for energy production. Remaining ash con-tains up to 0.6 wt% P. The use of bagasse ash (BA) as P fertilizer could decrease the annual import of P fertilizers by 6% of the imported P fertilizer based on 2016 values. Since the bioavailability of P from BA to plants is poorly investigated, this study addresses the effects of (i) gasification tempera-ture (710-849°C), (ii) processing method (gasification vs. combustion), (iii) biomass modifications by co-processing bagasse with chicken manure (BA+CM), and (iv) the soil (Brazilian Oxisol soil vs. nutri-ent poor substrate) on the bioavailability of P from BA to soybeans (Glycine max).
Gasification of BA at 806 °C resulted in significantly highest uptake of P by soybeans and was around 0.33 mmol after 51 days growing. The bioavailability of P significantly increased due to co-gasification of bagasse and chicken manure (BA+CM) and the soybeans took up around 16% more P. Compared to the nutrient-poor substrate, the bioavailability of P in BA+CM ash treated Oxisol soil was signifi-cantly lower by 46% and there was no significant effect of processing method on the bioavailability of P from the BA+CM ash to soybeans. Contrary to the Oxisol soil, the bioavailability of P from co-combusted BA+CM ash was significantly higher compared to co-gasified BA+CM ash. In conclusion, co-processing of bagasse with nutrient rich residues can increase the value of BA as P fertilizer. The bioavailability of P from ash to plants depends on the P forms. Mineralogical analyses of ash P forms by NMR and X-ray diffraction are in progress and will be presented at the conference.
A reliable analysis of aerosol particle is curial for enforcing EU air quality regulations to protect human health, and for research on climate change effects [1]. Although metrics such as PM10 and PM2.5 are currently in use, the level of uncertainty of aerosol metrics is too high and the traceability is insufficient. Within the AEROMET project [2] procedures are developed aiming at reducing the uncertainties of particle mass, size, and number concentration measurements including the characterization of regulated components in airborne particles. Here, we present an approach how to improve the uncertainties of the particle mass by mobile total reflection x-ray fluorescence (TXRF) analysis. The combination of TXRF and aerosols sampling techniques supported by reference-free synchrotron radiation-based XRF enables a quantitative real-time analysis of particle mass. During in-field campaigns, the procedure was tested, monitoring the size dependent mass concentrations of specific elements in ambient aerosols under dynamic conditions. This approach allows a direct time and size-resolved analysis without laborious digestion steps and a reduced risk of contamination.
Aerosol particles were sampled in a 13-stage DLPI impactor on acrylic discs. TXRF analysis was performed on-site with the transportable spectrometer S2 PICOFOX (Bruker Nano GmbH). The TXRF quantification was based on internal standardization. At moderate air pollution levels (PM10 20 µg/m³) sampling times of less than 2 hours were enough to detect elements in different particle size bins. The on-site approach and the high sensitivity of TXRF enables the observation of rather quick changes in the quantity and distribution of elements in an ambient aerosol on the day of sampling. The analysis of the morning and afternoon sampling shifts reveals the occurrence of the elements Fe, Ca and Si in different size bins as well as their temporal change in respective mass concentrations over the day while the distributions of several other elements remain unchanged.
The container of high-level radioactive waste (HLRW) being in deep geological disposal, the backfill material is needed to serve as the second defense for HLRW and the highly compacted bentonite is generally selected. As the time goes, the underground water will infiltrate the backfill, causing the corrosion of materials for the building of containers in the formed electrolyte. Carbon steel, titanium and its alloy are the potential candidate materials for the fabrication of HLRW containers.
The current investigation aims at assessing the safety of HLRW container in deep geological disposal for hundreds of thousands of years and facilitating the material selection for future Container fabrication by estimating their corrosion behavior in compacted bentonite with a series of moisture content at different temperatures through electrochemical methods including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PC) measurements. The corrosion rates were estimated for a carbon steel, a pure titanium and a titanium alloy in compacted Gaomiaozi Bentonite infiltrated with simulated underground water in Beishan area of China over an expected disposal period up to 106 years respectively, showing that titanium and its alloy are more reliable materials for building HLRW containers than carbon steel.
An understanding of the interactions of 2D nanomaterials with pathogens is of vital importance to developing and controlling their antimicrobial properties. In this work, the interaction of functionalized graphene with tunable hydrophobicity and bacteria is investigated. Poly-(ethylene glycol)-block-(poly-N-isopropylacrylamide) copolymer (PEG-b-PNIPAM) with the triazine joint point was attached to the graphene Surface by a nitrene [2 + 1] cycloaddition reaction. By thermally switching between hydrophobic and hydrophilic states, functionalized graphene sheets were able to bind to bacteria. Bacteria were eventually disrupted when the functionality was switched to the hydrophobic state. On the basis of measuring the different microscopy methods and a live/dead viability assay, it was found that Escherichia coli (E. coli) bacteria are more susceptible to hydrophobic interactions than B. cereus bacteria, under the same conditions. Our investigations confirm that hydrophobic interaction is one of the main driving forces at the presented graphene/bacteria interfaces and promotes the antibacterial activity of graphene derivatives significantly.
In this study, femtosecond laser-induced sub-micrometer structures are generated to modify polyethylene (PE) surface topographies. These surfaces were subjected to bacterial colonization studies with Escherichia coli and Staphylococcus aureus as test strains. The results reveal that the nanostructures do not influence S. aureus coverage, while the adhesion of E. coli is reduced.
Bacterial samples are typically freeze dried or cryo-prepared prior to XPS analysis to allow for measurements in ultra-high vacuum (UHV). The sample environment in the near-ambient pressure (NAP) XPS instrument EnviroESCA allows for measurements in up to 15 mbar water vapor, thus, sample preparation is no longer restricted to UHV-compatible techniques. For instance, biofilms grown in medium can be transferred directly from the medium to the measurements chamber, maintaining a humid environment throughout the measurements. Considering the complexity of bacterial samples, sample preparation must be carefully considered in order to obtain meaningful and reproducible results.
In this talk, various strategies for sample preparation of bacteria and biofilms for NAP-XPS measurements will be discussed. Model systems of planktonic bacteria, artificial biofilms resembling the exopolysaccharide matrix and biofilms have been characterised in various conditions. The stability and homogeneity of the samples was assessed by monitoring the C1s core level peak at different sample locations. The quality of the XPS-spectra is also influenced by the gas environment, which will be exemplified by core level spectra of P. Fluorescens acquired in air, water vapor and ultra-high vacuum.
Introduction: Biofilms are regarded as a common cause of chronic infections on medical devices. Preventive and therapeutic strategies against biofilm infections commonly involve applications of multiple antimicrobial substances: antimicrobial coatings on the implanted biomaterials in combination with systemically administered antibiotics. While this practice of combination therapy harbours the risk of developing cross-resistance, it might also provide the possibility to implement specific antimicrobial-antibiotic combinations (AACs) that can slow down the selection of antibiotic resistant strains.
Hypothesis and aims: Specific AACs can exert combinatorial effects on the growth of susceptible and antibiotic-resistant Pseudomonas aeruginosa that either suppress or increase their individual effects.
Our aim is to identify AACs with antagonistic or synergistic effects on pseudomonal biofilms and to understand their impact on selection of resistant strains. Specifically, we want to identify AACs that select for and against antibiotic resistance during biofilm formation.
Methodology: We screened for AACs that cause antagonistic or synergistic effects on planktonic P. aeruginosa.
To study the effect of antimicrobial-antibiotic exposure on resistance selection in bacterial biofilms, we will grow resistant and sensitive strains on PDMS surfaces with and without antimicrobial coatings and expose them to antibiotics.
Results: Several combinations with synergistic or antagonistic interaction on the growth rate of P. aeruginosa were detected. We observed a strong antagonism when combining the antimicrobial substance chlorhexidine with the carbapenem drug meropenem. A meropenem-resistant mutant showed a selection advantage in low concentrations of chlorhexidine combined with a sub-inhibitory concentration of meropenem over the wild-type. No antagonistic effect was observed for the same combination when E. coli was exposed to chlorhexidine and meropenem, suggesting a non-chemical basis for the observed effect on P. aeruginosa.
Conclusion: Gaining a better understanding about resistance selection during biofilm formation on biomedical surfaces will enable us to mitigate against biofilm-associated antimicrobial resistance.
The earliest known recipes for iron gall inks include four basic ingredients: oak galls – pathological growths of oak leaves; metal salts – usually referred to as vitriol; a binder such as gum Arabic; and water. The final product differs in the elemental composition due to the multitude of recipes as well as differences within the composition of the ink’s ingredients. Nowadays, based on the qualitative and semi-quantitative evaluation of X-ray fluorescence data, it is possible to distinguish inks on the basis of the so-called fingerprint model. The first goal of our study was to determine to what extent the type of XRF spectrometer affects the quality of the ink evaluation. We tested two types of spectrometers, semi-stationary machines equipped with polycapillary focusing optics and a handheld spectrometer with a diaphragm collimator and a relatively big interaction spot.
The second goal was to address the issue of whether the ink composition might be affected by storage in a metal container. The presentation will discuss the role of the spectrometer type in the evaluation of a thin layer material such as ink.
We have also learned that the iron-gall ink composition might depend on the type of vessel in which ink was being stored.