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- ItemMechanisms of bonding effected by nanoparticles in zirconia coatings applied by spraying of suspensions(Saarbrücke : Leibniz-Institut für Neue Materialien, 2008) Adam, Jens; Aslan, Mesut; Drumm, Robert; Veith, MichaelZirconia coatings consisting of a mixture of coarse and fine grained zirconia powders prepared by spraying of suspensions and subsequent thermal treatment at limited temperatures (up to 500°C) are poor in adherence and in intrinsic mechanical strength. We have shown elsewhere that mechanical properties of these coatings can be improved clearly by adding a small amount of nanoscaled zirconia. Here, the structural and the chemical development of this coating material and of the nanoparticles is examined to gain information about the underlying bonding mechanisms. The applied temperature is relatively low in comparison to the usual onset temperature of accelerated sintering. Nevertheless, the results show that diffusion controlled material transport mechanisms play their role in bonding. The condensation of surface OH groups may participate in bonding, too. These first results confirm the potential of nanoparticles to act as inorganic binder. Additional research effort to clarify the underlying mechanisms in detail is of interest. For the practical side, it can be concluded that the resulting effect of mechanical consolidation of ceramic structures at relatively low temperatures enables new ceramic applications, for example a new type of ceramic coatings on metallic substrates.
- ItemWork on non photocatalytically active titania particles(Saarbrücke : Leibniz-Institut für Neue Materialien, 2009) Müller, Thomas S.; Faller-Schneider, Christine; Moh, Karsten; Shanmugasundaram, Sakthivel; Oliveira, Peter W. de; Veith, MichaelTitanium dioxide has photocatalytic properties, i.e. under UV irradiation it develops an oxidative potential. In photocatalysis this is very desirable, but not when nano particulate titania is embedded into organic polymer matrices in order to increase the refractive index. UV irradiation would in this case destroy the material in the long run. For deactivation in general the titania is coated by e.g. silica or alumina which leads to other undesired effects like growth of the particle size and enhanced light scattering. The current work focuses on the application of techniques for doping during synthesis of crystallization of nano particulate TiO2. The photocatalysis activity was determined by degradation experiments of 4-chlorophenol using dip coated glass plates under artificial sunlight, where decreases of the photocatalytic effect of up to 90 % were found.
- ItemKelvin probe force microscopy of charged indentation-induced dislocation structures in KBr(Saarbrücken : Leibniz-Institut für neue Materialien, 2009) Egberts, Philip; Bennewitz, RolandThe incipient stages of plasticity in KBr single crystals have been examined in ultrahigh vacuum by means of Atomic Force Microscopy and Kelvin Probe Force Microscopy (KPFM). Conducting diamond-coated tips have been used to both indent the crystals and image the resulting plastic deformation. KPFM reveals that edge dislocations intersecting the surface carry a negative charge similar to kinks in surface steps, while screw dislocations show no contrast. Weak topographic features extending in <110> direction from the indentation are identified by atomic-resolution imaging to be pairs of edge dislocations of opposite sign, separated by a distance similar to the indenter radius. They indicate the glide of two parallel {110} planes perpendicular to the surface, a process that allows for a slice of KBr to be pushed away from the indentation site.
- ItemCorrosion inhibiting cerium compounds for chromium-free corrosion protective coatings on AA 2024(Saarbrücke : Leibniz-Institut für Neue Materialien, 2007) Schem, Michael; Schmidt, Thomas; Caparrotti, Hinka; Wittmar, Matthias; Veith, MichaelDue to the upcoming ban of chromium-containing corrosion protection coatings in the near future, there is a worldwide effort to find a replacement for chromium as a corrosion inhibitor that also exhibits self-healing properties in scratches but without the negative efects like health and environmental hazards. In the present study promising results to achieve this goal are shown by using cerium compounds incorporated into an organic-inorganic hybrid material produced by the sol-gel process. Cerium compounds like cerium nitrate, cerium nitrate plus acetylacetonate, cerium acetylacetonate, and cerium sulphate were incorporated in sol-gel coating systems. The corrosion protection properties of these coatings were determined by means of Electrochemical Impedance Spectroscopy (EIS) and in a conventional salt spray test. Furthermore, the leaching behaviour of the coatings was examined via Optical Emission Spectrometry (OES). Significant hints for self healing properties were obtained with a hybrid system doped with cerium nitrate in combination with acetylacetone.
- ItemOne-dimensional oxide nanostructures: growth, applications and devices(Saarbrücke : Leibniz-Institut für Neue Materialien, 2008) Barth, Sven; Mathur, Sanjay; Hernandez-Ramireza, Francisco; Romano-Rodrigueza, AlbertOne dimensional (1D) inorganic materials are gaining high attention due to their structural stability and unique structural fatures. Among them, oxides are widely studied due to their well established application potential and mechanical as well as chemical stability. We have developed a generic approach for size-selective and site-specific growth of oxide nanowires by combination of a catalyst assisted growth mechanism and a molecular precursor approach, which is a viable alternative to other gas phase and solution procedures and produces well-defined (morphology and composition) materials.
- ItemResearch on the synthesis and applicability of surface modified nanoscaled metal oxide particles as curing catalyseres for UV-print-colours and lacquers(Saarbrücke : Leibniz-Institut für Neue Materialien, 2009) Becker-Willinger, Carsten; Schmitz-Stöwe, Sabine; Bentz, DirkIn the BMBF joint research project - NANOCURE - New Curing Methods for Print-Colours, Glues and Lacquers (prom. ref. : 13N9115) - a new class of nanoscaled photo initiators for radical polymerization processes in the printing industry is to be investigated. A possible mechanism for the reaction of TiO2 with acrylates, which is already described in literature is presented. Different methods of manufacturing TiO2 nanoparticles in the lower nanometric size range and their subsequent processing are described, the method is of special interest as it may lead to a possible integrated production process of UV-printing inks. The TEM analysis shows the homogeneous arrangement of TiO2 nanoparticles in an acrylic matrix, which is a necessary requirement for successful polymerization process. IR-spectroscopy is used to show the effect of TiO2-nanoparticles as UV photocatalytic polymerization initiators.
- ItemPlasma-assisted modulation of morphology and composition in Tin oxide nanostructures for sensing applications(Saarbrücke : Leibniz-Institut für Neue Materialien, 2007) Mathur, Sanjay; Ganesan, Rajesh; Ruegamer, Thomas; Shen, Hao; Barth, Sven[no abstract available]
- ItemFast and sensitive screening of transparent composite materials using polarized light image processing(Saarbrücken : Leibniz-Institut für Neue Materialien, 2009) Weiss, Ingrid M.; Heiland, BirgitComposite materials of natural origin have remarkable material properties. In order to mimic the various functions of such materials for technical applications, it is necessary to understand the structure and the mechanisms of their formation, a scientific field which is called structural biology. A milestone in the era of structural biology was the application of the polarized light microscope for investigating biological specimens by W. J. Schmidt in 1924. A recent development in polarization technology is the LC-PolScope (Abrio IM™ Imaging System) that has been developed by R. Oldenbourg and his colleagues during the past 20 years. Like conventional polarization microscopy, it probes the local anisotropy of the specimen’s optical properties, such as birefringence or dichroism. Since there is a close relationship between such properties and molecular order in bulk materials, polarization microscopy can be regarded as a submicroscopic technique. The LC-PolScope is especially suitable for investigating biological materials without the need for using contrasting agents such as fluorescent markers. We demonstrated the applicability of this technique for the fast and sensitive screening of biological composite materials. Implications for the characterization of biomineralization phenomena in a quantitative manner are discussed.
- ItemInvestigation on thermal and chemical stability of polymer based easy-to-clean nanocomposite systems(Saarbrücke : Leibniz-Institut für Neue Materialien, 2007) Gerdes, Ralf; Kalmes, Pamela; Becker-Willinger, CarstenAnti-adhesive coatings are of significant importance for many industrial processes such as pigment and paint production as well as also food processing industry, because they can help to significantly reduce the cleaning effort. For this reason, the amount of cleaning chemicals and waste water can be reduced, which should have a remarkable effect on the process costs. In this investigation abrasion resistant low surface free energy coatings based on fluoroalkyl group and SiC particles containing polyimides have been synthesised which show surface properties comparable to PTFE and can be coated like a paint on surfaces. Expecially in food production processes a high chemical stability is required for coating materials to withstand the cleaning procedures which are used in order to maintain the hygienic situation in the production facilities. The investigations revealed a high abrasion resistance (weight loss approx. 12 mg after 1000 cycles taber abrader test) and a moderate chemical stability of the coating systems. A chemical attack by sodium hydroxide solution as well as by oxidising substances such as nitric acid (HNO3) at elevated temperatures (90°C) led to a fast destruction of the coating performance caused by damage of the organic matrix. Also the exposure with carrot juice and mik at 90°C showed some influence. The contact angles against water decreased by about 20-30% whereas the oleophobic properties remained almost unchanged. On the other hand the polyimide nanocomposites showed a low surface roughness (Ra <= 0.2µm) and adjustable antistatic properties, what enables to use them in dry food processing (e.g. in flour mills). By using a nanocomposite system filled with 10 wt.-% carbon black FW 200 a resistivity of 1.5x103 Ω and a charge decay time of 0 s were obtained.
- ItemThe analysis of arabidopsis nicotianamine synthase mutants reveals functions for nicotianamine in seed iron loading and iron deficiency responses(Rockville, MD : American Society of Plant Biologists, 2009) Fink-Straube, Claudia; Klatte, Marco; Schuler, Mara; Wirtz, Markus; Hell, Rüdiger; Bauer, PetraNicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.