6 Materialchemie
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- 2019 (13) (entfernen)
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- Beitrag zu einem Tagungsband (13) (entfernen)
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- Applications (2)
- Laser-induced periodic surface structures (LIPSS) (2)
- Surface functionalization (2)
- ALD-Hybridprozesse (1)
- Abwasserinfrastruktur (1)
- Adhäsion (1)
- Adsorption (1)
- Aktivkohle (1)
- Al2O3-Schichten (1)
- Alkaliaktivierte Bindemittel (1)
Organisationseinheit der BAM
- 6 Materialchemie (13)
- 6.7 Materialsynthese und Design (4)
- 6.1 Oberflächen- und Dünnschichtanalyse (3)
- 6.6 Physik und chemische Analytik der Polymere (3)
- 6.2 Material- und Oberflächentechnologien (2)
- 7 Bauwerkssicherheit (2)
- 7.4 Baustofftechnologie (2)
- 6.3 Strukturanalytik (1)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (1)
Das Fügeverfahren Kleben bietet viele Vorteile wie z.B. das Verbinden schwieriger Materialklassen, geringe thermische Belastung (Strukturveränderung/-schwächung) der Fügepartner und eine Lastverteilung über den gesamten Fügebereich. Die Auswahl an verfügbaren Klebstoffen und Vorbehandlungsoptionen ist dabei ebenfalls vielfältig. Einige Polymere weisen darüber hinaus Eigenschaften auf, die eine Herstellung von festen und dauerhaft beanspruchbaren Klebverbindungen erschweren. Mittels Oberflächenbehandlung, z.B. durch Plasmafeinreinigung bzw. –aktivierung, können die Grenzflächern solcher Polymere - bezogen auf die Eignung als Fügeteilpartner – optimiert werden. Schnelle Prüfverfahren zur Ermittlung von Verbundeigenschaften sind somit erforderlich.
Das Messprinzip Centrifugal Adhesion Testing Technologie verwendet die radial gerichtete Zentrifugalkraft als Belastungsgröße des zu testenden Verbunds, die durch Variation der Drehzahl gesteuert wird. Bei Erreichen der kritischen Beanspruchung trennt sich ein aufgeklebter Prüfstempel vom Substrat. Zeitgleich wird ein positionsbezogenes IR-Signal aus dem drehenden Rotor an das Basisgerät gesendet und zusammen mit der Drehzahl an die PC-Software übertragen. Für jede Probe wird die Bruchkraft berechnet und in Echtzeit angezeigt. Der Adhesion Analyser LUMiFrac® untersucht bis zu acht Prüfkörper unter identischen Bedingungen. Das neue Messprinzip erfüllt die Anforderungen von DIN EN 15870, DIN EN 14869-2, ISO 4624 sowie DIN EN 13144.
Die Multiprobentestung ermöglicht schnelle Charakterisierungen von Klebverbindungen. So kann der Effekt einer Plasmabehandlung von Bauteilen auf die Verbundfestigkeit zeitsparend bestimmt werden. Die gezielte Veränderung unterschiedlicher Plasma-Parameter, wie beispielsweise, die Plasmazusammensetzung, der Abstand vom Plasmabrenner zur Oberfläche oder die Verweildauer unter dem Brenner, beeinflußt die Festigkeit des Klebsystems und ist dem LUMiFrac direkt quantifizierbar.
Neben der Festigkeitsbestimmung von Klebverbindungen ist die Haftung von Schichtsystemen ein wichtiger Anwendungsbereich. Ergebnisse für Zug- und Scherbeanspruchung, realisiert mit unterschiedlichen Prüfkörper-Geometrien, werden vorgestellt. Ferner werden verschiedene festigkeitsbeeinflussende Faktoren, wie Prüfgeschwindigkeit oder Substratverformung bei Beanspruchung untersucht
In recent years, the improved understanding of the formation of laser-induced periodic surface structures (LIPSS) has led to an emerging variety of applications that modify the optical, mechanical and chemical properties of many materials. Such structures strongly depend on the laser beam polarization and are formed usually after irradiation with ultrashort linearly polarized laser pulses. The most accepted explanation for the origin of the structures is based on the interference of the incident laser radiation with electromagnetic surface waves that propagate or scatter at the surface of the irradiated materials. This leads to an intensity modulation that is finally responsible for the selective ablation in the form of parallel structures with periods ranging from hundreds of nanometers up to some micrometers. The versatility when forming such structures is based on the high reproducibility with different wavelength, pulse duration and repetition rate laser sources, customized micro- and nanometric spatial resolutions, and the compatibility with industrially relevant processing speeds when combined with fast scanning devices. In this contribution, we review the latest applications in the rapidly emerging field of surface functionalization through LIPSS, including biomimetic functionalities on fluid transport, control of the wetting properties, specific optical responses in technical materials, improvement of tribological performance on metallic surfaces and bacterial and cell growth for medical devices, among many others.
Titanium dioxide is one of the most studied metal oxides due to its chemical, surface, electronic and (photo)catalytic properties, providing this material of multisectorial applications ranging from healthcare, photocatalysis, smart materials with self cleaning and self sterilizing properties and solar energy harvesting. However it is difficult to correlate the functional properties of TiO2 nanomaterials to the properties at single nanoparticle level due to the high polydispersity in shape, size and surface features of the currently available TiO2 nanoparticles (NPs). Although intensive experimental and theoretical studies have been conducted on the reactivity of different surfaces of metal oxides such as TiO2 much less attention is paid on the dependence of functional properties, like photocatalytic activity, dye adsorption, open circuit potential and fill factor in dye sensitized solar cells, on crystal facets in different orientations. One of the goal of SETNanoMetro project was the development of design rules to tune crystal facets of TiO2 NPs in order to optimize and control functional properties. In the present work we have developed a series of design rules in order to obtain sets of anatase TiO2 NPs with low polydispersity and to tune their shape and size by hydrothermal processing of Ti(IV)-
Triethanolamine complex in presence of different shape controllers. Through a careful experimental design, a predictive soft model was developed. The model is able to predict the synthesis outcome allowing to tune the shape factor from 5 (prisms) to 1.5 (bipyramids) to 0.2 (platelets). This allows to control the main crystal facets exposed ranging from (100) to (001). Due to the dependence of functional properties of nanomaterials on shape distribution and not only size, the availability of NPs sets with uniform and well defined and tunable shapes can be of paramount relevance in order to produce reference nanomaterials for shape measurement.
The European Commission's recommendation on the definition of nanomaterial [2011/696/EU] is broadly applicable across different regulatory sectors and requires the quantitative size Determination of constituent particles in samples down to 1 nm. A material is a nanomaterial if 50 % or more of the particles are in the size range 1-100 nm. The implementation of the definition in a regulatory context challenges measurement methods to reliably identify nanomaterials and ideally also nonnanomaterials as substance or product ingredient as well as in various matrices.
The EU FP7 NanoDefine project [www.nanodefine.eu] addressed these challenges by developing a robust, readily implementable and cost-effective measurement strategy to decide for the widest possible range of materials whether it is a nanomaterial or not. It is based on existing and emerging particle measurement techniques evaluated against harmonized, material-dependent performance criteria and by intra- and inter-lab comparisons. Procedures were established to reliably measure the size of particles within 1-100 nm, and beyond, taking into account different shapes, coatings and chemical compositions in industrial materials and consumer products. Case studies prove their applicability for various sectors, including food, pigments and cosmetics.
A main outcome is the establishment of an integrated tiered approach including rapid screening (Tier 1) and confirmatory methods (tier 2), a decision support flow scheme and a user manual to guide end-users, such as manufacturers, in selecting appropriate methods. Another main product is the “NanoDefiner” e-Tool which implements the flow scheme in a user-friendly software and guides the user in a semi-automated way through the entire decision procedure. It allows a cost-effective selection of appropriate methods for material classification according to the EC's nanomaterial definition and provides a comprehensive report with extensive explanation of all decision steps to arrive at a transparent identification of nanomaterials as well as non-nanomaterials for regulatory
purposes.
Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with Errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs.
An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal, has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. In the TEM micrograph the particles tracked manually according to the measurement protocol. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the femtosecond to picosecond range. During the past years significantly increasing industrial and research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical or chemical surface properties. In this contribution the mechanisms of formation and current trends and applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animals, the tailoring of surface colonization by bacterial biofilms, the advancement of leadless medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
Einkomponentige alkaliaktivierte Bindemittel (AAB), d. h. AAB, bei denen der Aktivator als Feststoff im Bindemittel vorliegt, weisen Vorteile hinsichtlich der praktischen Anwendung im Bauwesen gegenüber konventionellen AAB auf. Einkomponentige AAB lassen sich als Gemische aus reaktiver Silica und Natriumaluminat herstellen, wobei die Reaktionsprodukte von der eingesetzten Silica und den Verhältnissen Na2O/Al2O3/SiO2/H2O abhängen: Während Mikrosilica und ähnliche Reststoffe zu zeolithreichen Produkten führen, erhält man aus Reisschalenasche vollständig amorphe Gele (sog. «Geopolymere »). Mörtel auf Basis solcher Bindemittel entsprechen den Anforderungen von DIN 19573:2016-03 hinsichtlich des Widerstands gegen Schwefelsäureangriff (Prüfung bei pH = 1 für 70 d) und sind damit potentiell als Reparatursysteme für Abwasserinfrastruktur geeignet. Untersuchungen mittels 29Si-MAS-NMR und 1H-29Si-Kreuzpolarisations(CP)-MAS-NMR sowie REM-Aufnahmen von erhärteten und dem Schwefelsäureangriff ausgesetzten AAB zeigen, dass der hohe Säurewiderstand v. a. auf die Fällung von Silicagel an der Grenzfläche Mörtel/Säure zurückzuführen ist, wodurch der Korrosionsfortschritt in darunterliegenden Schichten verlangsamt wird.
3D microstructures with sub-micron resolution can be manufactured in additive manner applying multi-photon laser structuring technique. This paper is focused on the incorporation of superparamagnetic iron oxide nanoparticles into the photoresist in order to manufacture micrometer-sized devices featuring a magnetic moment. The aim of the project is to achieve untethered actuation of the presented objects through externally applied magnetic fields. Future medical application scenarios such as drug delivery and tissue engineering are targeted by this research.
The presence of polycarboxylate ether (PCE) based superplasticizers (SPs) has enormous influence on the early hydration of cement. C3A as the most reactive phase of Portland cement plays a significant role in early hydration reactions and affects the rheological performance. Therefore, this paper presents experimental results about the influence of delayed addition of PCEs on the Hydration of cement and C3A-gypsum pastes investigated by isothermal heat flow calorimetry. Complementary in-situ XRD was carried out on C3A pastes to analyze hydration and phase changes related to the addition of PCE.
Cement pastes with a delayed addition of PCE showed less Retardation compared to simultaneous addition. The alteration caused by PCE is much more pronounced for C3A-gypsum mixes. With a delayed addition of SP, the hydration of C3A is less retarded or even accelerated. It is obvious that there is less retardation the later the addition of SP. Furthermore, the PCE alter the hydration of C3A when added delayed and exhibit changes in kinetics and hydration rates. XRD results showed that more C3A is dissolved in the presence of PCE. Also, the gypsum depletion occurs earlier in the presence of PCE and even faster with delayed addition. Without PCE AFm starts to form just after the gypsum depletion. However, in the presence of PCE AFm already starts to form at the beginning of the hydration. Due to the faster gypsum depletion in the presence of PCE, also the transformation from ettringite into AFm begins earlier, but takes longer as without SP.
In diesem Beitrag wird gezeigt wie mit Thermogravimetrischen Analysen (TGA) Aktivkohleoberflächen charakterisiert werden können. Außerdem wie TGA mit Zersetzungsgasanalyse zur Untersuchung von Adsorbat-Systemen (Carbamazepin an drei verschiedenen Aktivkohlen) zur Aufklärung von Adsorptionszuständen genutzt werden kann.