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Eingeladener Vortrag
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Effects of amorphous nano-silica additions on mechanical and durability performance of SCC mixtures
(2012)
In the recent years the application of nanotechnology in building materials has increased
exponentially. One of the most referred and used nano-materials is amorphous silica with
particles size in the nano-range, even though its application and effect in concrete has not been
fully understood yet. It has been reported that nano-silica (nS) addition increases the
compressive strength and reduces the overall permeability of hardened concrete due to the
pozzolanic properties which are resulting in finer hydrated phases (C-S-H gel) and densified
microstructure (nano-filler and anti leaching effects). These effects enhance the durability of
concrete structures such as bridges, quays or off-shore oil facilities in marine environments.
In this study two different types of nano-silica were applied in self-compacting concrete (SCC),
both having similar particle size distributions (PSD) but produced in two different processes
(fumed powder silica and precipitated silica in colloidal suspension). The influence of nanosilica
on SCC was investigated with respect to the properties of concrete in the fresh state
(workability) and hardened state (mechanical properties and durability). Additionally, the
densification of microstructure of the hardened concrete was verified by SEM and EDS analyses.
The obtained results demonstrate that an efficient use of nano-silica in SCC can improve its
mechanical properties and durability. Considering the reactivity of the two nano-silica studied,
colloidal type shown more reactivity at early age, which influenced all the final SCC properties.
In this work, reactive magnetron-sputtered Pb(Zr,Ti)O3 thin films were used to fabricate well-ordered nanodot arrays by means of nanosphere lithography (NSL). NSL is based on a two-step etch process by means of, firstly adjusting the diameter of polystyrene spheres in the self-assembled polymeric nanosphere mask using reactive ion etching, and secondly transferring the mask to the substrate by ion milling with adjusted heights. Hence, structures with different aspect ratios can be fabricated.
Piezoresponse force microscopy was used as the inspection tool on both non-patterned and patterned films. Both the topography and polarization out of plane and in plane was deduced in this mode. Grains of nanodots with low aspect ratio form domain structures comparable to domains in non-patterned films. In contrast to that, nanodots with a higher aspect ratio form particular structures. The in-plane amplitude images show mostly a bisectioned domain assembly, while the out-of-plane amplitude images show in some cases more complex structures like 'c'-shaped domains or multi-domains around a center domain.
The patterning of the ferroelectric material was shown to affect the formation of ferroelectric domains. The initial polycrystalline, randomly-ordered films are re-oriented and show domain structures depending on nanodisc diameter and aspect ratio. This may enable tailoring of ferroelectric materials in their piezoelectric and pyroelectric properties by patterning.
Technische Oberflächen - im Anlieferungszustand oder modifiziert — werden hinsichtlich topographischer und energetischer Merkmale in der Abweichung von der »idealen « Oberfläche beschrieben. Die Topographie wird dabei durchgehend vom Makro- über den Mikro- bis in den Nano-Bereich mit den Methoden Streifenlichtprojektion (FP), Lichtmikroskopie (LM), mechanischem Tastschnitt (MS), Weißliehtinterferenzraikroskopie (WLIM), Rasterelektronen- (SEM) und Rasterkraftmikroskopie (AFM) erfasst. Replika-Verfahren ermöglichen dabei auch die indirekte Erfassung der Topographie an Bauteilen. Zur makroskopischen Bestimmung der Oberflächenenergie werden Randwinkelmessungen nach der Tropfen- bzw. der Plattenmethode herangezogen. Im Fokus stehen Materialien der Steriltechnik (Edelstahl, Emaille, PTFE), Passivschichten, Beschichtungen (Si02, a-C:H) und mikrostrukturierte Modelloberflächen (Silizium). Neben Standardisierungsaspekten (Mikro- vs, Nano-Rauheit) ist die Wechselwirkung der Oberflächen mit Partikeln (Haftung) von immanenter Bedeutung. Dabei sind Größe, Form und Plastizität der Partikel im Kontext mit der Oberflächentopographie zu betrachten.
Electron magnetic resonance (EMR) spectroscopy, X-ray-fluorescent microscopy (XFM) and thermal analysis (TGA/DTA) are used to characterize the carbon nano-phase obtained in the reaction between fine-dispersed aluminium and dichlorethane in the liquid paraffin medium and its modified with Mn(II), Fe(III), Ni(II), Cu(II) chlorides forms were studied. It was shown that the solid nano-structured functionalized carbon systems containing metals possess specific magnetic and thermal properties. Key parameters of the process, influencing on the size and structure of the formed carbon nano-phase were determined. Results and regularities established in this work create presumably the certain basis for optimization of physical and chemical properties of similar systems.
The microstructures of two samples of a Zr(C,N) coating on steel, which unexpectedly differed in their tribological properties, were investigated by analytical transmission electron microscopy. The samples were produced by a cathodic arc evaporation process in two commercial coating devices under similar coating conditions with the exception of the number of Zr targets.
The source of the differing tribological properties of the samples was detected by analytical transmission electron microscopy (TEM) methods energy-dispersive X-ray spectroscopy (EDX), energy filtering TEM (EFTEM), electron diffraction, high resolution electron microscopy, and high angel annular dark field. The TEM preparation and the results of the TEM investigations are shown in detail. The origin of the unexpected behavior was determined to be a nano-scale multilayer structure that existed only in the tribologically superior specimen. EDX and EFTEM investigations indicated enrichment in oxygen at the interface between coating and steel substrate in the tribologically inferior sample. Findings of the microstructural configuration were obtained by taking a closer look at the structure and comparing the results of the several analytical TEM techniques. This allows the allocation of the concentration fluctuations in N, C, and Zr to the two thickness fractions of the nano multilayers and a local correlation of the identified minority phase Zr3(C,N)4 to the higher N content in the narrower type of the multilayer fraction of the sample with the excellent tribological properties. The minority phase Zr3(C,N)4 is randomly distributed in the sample with the defective tribological properties.
Coating conditions are not topic of this work, but after discussion of the TEM results, the fact that one of the coating devices worked with one Zr target and the other one with two, could be identified as cause for the formation of the nano multilayer structure in the sample with the superior tribological properties.
This paper addresses the characterization of six different amorphous silica samples with respect to their application in cement paste. Different mixes are compared and analyzed using the mini spread-flow test. Also the granular properties, different void fraction states of packing and distribution moduli q are analyzed and compared using a mix design tool. A deformation coefficient is derived from the spread-flow test, which correlates with the value of specific surface area computed from the particle size distribution, and intrinsic density of the samples. Finally, the thickness of a constant water layer of 25 nm around the particles is computed at the onset of flowing. The granular analysis demonstrated that it is possible to decrease the water demand of the cement paste when nanoparticles are added and the resulting grading follows the modified Andreasen and Andersen curve (q = 0.5), and the concentration of nano silica is less than 5% bwoc.