Christina Kr
Abstract
Recently, a new approach was developed and published which focuses on the preparation of inorganic foams and their application in foam concrete production. Through the incorporation of nanostructured pozzolans in the foam structure, so-called three-phase-foams show a higher stability than foams only ...
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Recently, a new approach was developed and published which focuses on the preparation of inorganic foams and their application in foam concrete production. Through the incorporation of nanostructured pozzolans in the foam structure, so-called three-phase-foams show a higher stability than foams only based on surfactants. Due to pozzolanic hardening, shrinkage cracks were healed and reaction products can be observed. By implementation of nanotubes in the foam structure as nanoreinforcement, a further stabilization was reached. After incorporation of wet three-phase-foams in cement paste, foam concretes with improved mechanical properties were achieved. It was also shown that the pore size distribution was similar to the introduced three-phase-foams and also smaller pore sizes can be observed compared to foam concretes based on surfactant foams. Additionally, a specific shell-like pore structure was obtained and a theoretical model developed. This could be confirmed by investigations of the influence of the surfactant used on the formation and carbonation of calcium hydroxide. To further enhance the mechanical properties of foam concretes based on three-phase-foams, an UHPC (Ultra-high Performance Concrete) formulation has been applied. Resultant UHPC foam concretes showed dense packed borders, improved homogeneity related to the pore size distribution and enhanced mechanical properties. Furthermore, the UHPC approach was combined with nanoreinforcement.
A. Dussan; Heiddy P. Quiroz
Abstract
In this work, we fabricated samples of titanium dioxide nanotube arrays via electrochemical anodization by using titanium foils as anode and cathode. A solution of water, ethyleneglycol, and ammonium fluoride (NH4F) at room temperature was used for the samples synthesis process. Different times and anodizing ...
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In this work, we fabricated samples of titanium dioxide nanotube arrays via electrochemical anodization by using titanium foils as anode and cathode. A solution of water, ethyleneglycol, and ammonium fluoride (NH4F) at room temperature was used for the samples synthesis process. Different times and anodizing voltages were used during reaction. From X-ray diffraction (XRD) and micro-diffraction (mXRD) measurements, rutile and anatase phases were identified as function of deposition parameters. The Ti3O5 phase was observed by deconvolution of Debye-Scherrer rings of the microdiffraction spectra. Annealing processes were performed for all samples in the range between 273 and 723 K, without changes in the material’s morphological properties, while the crystalline structure was affected. Nanotube diameters varying between 30 and 42 nm were observed from SEM micrographs, when NH4F concentration was changed from 0.25 to 0.50 wt%. An alternating anodizing voltage generates the formation of nanotubes evenly spaced on the surface with nodes in bamboo-type form, while a smooth form for nanotubes was observed with constant applied voltage. From stereoscopic 3D micrographs, a reconstruction of the topographic surface of the TiO2 nanotubes was conducted. A correlation between synthesis parameters and morphological properties is presented.
C. P. Barrera-Pati
Abstract
In this work we present a theoretical-experimental study of optics effects in nanostructures formed during the growth of titania nanotubes. Titania nanotubes were fabricated via electrochemical anodization method using Ethylene glycol. Traces or prints left by the nanotubes on the titanium surface are ...
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In this work we present a theoretical-experimental study of optics effects in nanostructures formed during the growth of titania nanotubes. Titania nanotubes were fabricated via electrochemical anodization method using Ethylene glycol. Traces or prints left by the nanotubes on the titanium surface are observed thought X-ray diffraction measurements. The pattern shows a polycrystalline structure with the presence of Anatase and titanium phases. The reflectance and absorbance spectra reveal in the traces optical phenomena similar to iridescence. The iridescence behavior is commonly found in nature and is traditionally associated to photonic properties. Using the plane wave method and modelling the nanostructures observed on the interphase like two-dimensional photonic crystals, the photonic dispersion relation was calculated in function of geometrical parameters. Enlargement of the photonic band gap was found as spatial contrast is increased. These results suggest that these types of nanostructures can be promissory candidates to develop photonic devices.