Time filter

Source Type

Kovacic S.,University of Graz | Matsko N.B.,Graz Center for Electronic Microscopy | Ferk G.,University of Maribor | Slugovc C.,University of Graz
Journal of Materials Chemistry A | Year: 2013

The high internal phase emulsion (HIPE) templating approach to macroporous poly(dicyclopentadiene) γFe2O3/Fe3O 4 nanocomposite foams via ring opening metathesis polymerisation was elaborated and the influence of the formulation of the HIPE on structural and mechanical properties of the magnetic composite foams of 80% nominal porosity was studied. HIPEs solely stabilized with the nanoparticles resulted in considerably shrunken monolithic specimens characterized by an open cellular morphology with cavities bigger than 265 μm. Nanoparticles were situated in the bulk and on the surface of the polymeric foam skeleton. Precise control over the feature sizes could not be obtained in this case. In contrast, HIPE formulations co-stabilized with a surfactant yielded samples of good casting quality characterized by a fully open cellular morphology in all cases. The cavity and the window size could be controlled by the amount of surfactant in the emulsion. A low surfactant loading of 1.5 v% with respect to the monomer yielded diameters of the cavities of the order of 20 μm interconnected with windows with diameters in the order of 4 μm, while 10 v% surfactant resulted in smaller cavities (10 μm) and windows (2 μm). All these feature sizes are hardly affected by the nanoparticle loading which was varied from 1 to 30 wt%. Surfactant stabilized and cured HIPEs featured the nanoparticles predominantly on the surface of the cavities. Mechanical properties of the composite foams were assessed by stress-strain tests and revealed a strengthening of the foams prepared with 10 v% surfactant upon addition of the nanoparticles. Indicative of the strengthening is an increase of the Young's modulus from 13 ± 2 MPa in the case of a sample without nanoparticles to 104 ± 4 MPa in the case of the composite foam with 15 wt% nanoparticles. This trend was accompanied by a decrease of the elongation at break from 21 ± 4 to less than 1%. Specimens prepared with 1.5 v% surfactant are ductile and gave the same high Young's modulus (104 ± 9 MPa) irrespective of the nanoparticle loading and became stronger upon raising the nanoparticle amount reaching an ultimate strength of 3.4 ± 0.4 MPa at an elongation at break of 13 ± 4%. © 2013 The Royal Society of Chemistry.

Kovacic S.,University of Graz | Matsko N.B.,Graz Center for Electronic Microscopy | Jerabek K.,Czech Institute of Chemical Process Fundamentals | Krajnc P.,University of Maribor | Slugovc C.,University of Graz
Journal of Materials Chemistry A | Year: 2013

Reducing the surfactant amount below generally accepted values in polyHIPE chemistry allowed for distinctly improving the mechanical properties of ROMP derived HIPE templated poly(dicyclopentadiene) without compromising the open cellular structure of the scaffold rendering the preparation of a ductile polymer foam with 80% porosity and a Young's modulus of 110 MPa possible. This journal is © 2013 The Royal Society of Chemistry.

Plank H.,University of Graz | Plank H.,Graz Center for Electronic Microscopy
Nanotechnology | Year: 2015

During the last decade, focused ion beam processing has been developed from traditionally used Ga+ liquid ion sources towards higher resolution gas field ion sources (He+ and Ne+). Process simulations not only improve the fundamental understanding of the relevant ion-matter interactions, but also enable a certain predictive power to accelerate advances. The historic 'gold' standard in ion-solid simulations is the SRIM/TRIM Monte Carlo package released by Ziegler, Ziegler and Biersack 2010 Nucl. Instrum. Methods B 268 1818-23. While SRIM/TRIM is very useful for a myriad of applications, it is not applicable for the understanding of the nanoscale evolution associated with ion beam nano-machining as the substrate does not evolve with the sputtering process. As a solution for this problem, a new, adapted simulation code is briefly overviewed and finally addresses these contributions. By that, experimentally observed Ne+ beam sputter profiles can be explained from a fundamental point of view. Due to their very good agreement, these simulations contain the potential for computer aided optimization towards predictable sputter processes for different nanotechnology applications. With these benefits in mind, the discussed simulation approach represents an enormous step towards a computer based master tool for adaptable ion beam applications in the context of industrial applications. © 2015 IOP Publishing Ltd.

Mittal V.,The Petroleum Institute | Luckachan G.E.,The Petroleum Institute | Matsko N.B.,Graz Center for Electronic Microscopy
Macromolecular Chemistry and Physics | Year: 2014

The microstructure of high-density polyethylene (PE) and chlorinated polyethylene (CPE) blends, as well as their composites with graphene oxide (GO) is characterized. The filler dispersion improves as the extent of chlorination is enhanced. The platelets are also observed to be covered with a harder phase by atomic force microscopy (AFM), due to the stronger nucleating action of the graphene clusters, along with the alignment or ordering of the CPE phase at the interface with the filler. The filler and the CPE phases are observed to undergo chemical interaction during solution mixing, which enhances during melt mixing of the CPE-GO masterbatch with the PE matrix. The majority of the Cl atoms in the CPE chains are observed to be depleted during chemical reaction or thermal degradation at the melt compounding temperature, resulting in chlorine-free materials. The microstructure of high-density polyethylene (PE) and chlorinated polyethylene (CPE) blends, as well as their composites with graphene oxide (GO) are characterized. The filler dispersion improves as the extent of chlorination is enhanced. The majority of the Cl atoms in the CPE chains are observed to be depleted during chemical reaction or thermal degradation at the melt compounding temperature, resulting in chlorine-free materials. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Haberfehlner G.,Graz Center for Electronic Microscopy | Orthacker A.,Graz Center for Electronic Microscopy | Albu M.,Graz Center for Electronic Microscopy | Li J.,University of Leoben | And 2 more authors.
Nanoscale | Year: 2014

Extending the capabilities of electron tomography with advanced imaging techniques and novel data processing methods, can augment the information content in three-dimensional (3D) reconstructions from projections taken in the transmission electron microscope (TEM). In this work we present the application of simultaneous electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS) to scanning TEM tomography. Various tools, including refined tilt alignment procedures, multivariate statistical analysis and total-variation minimization enable the 3D reconstruction of analytical tomograms, providing 3D analytical metrics of materials science samples at the nanometer scale. This includes volumetric elemental maps, and reconstructions of EDS, low-loss and core-loss EELS spectra as four-dimensional spectrum volumes containing 3D local voxel spectra. From these spectra, compositional, 3D localized elemental analysis becomes possible opening the pathway to 3D nanoscale elemental quantification. © The Royal Society of Chemistry 2014.

Voitic G.,University of Graz | Nestl S.,University of Graz | Lammer M.,University of Graz | Wagner J.,Graz Center for Electronic Microscopy | And 2 more authors.
Applied Energy | Year: 2015

Fuel cell cars powered by hydrogen enable CO2-emission free mobility. A main requirement for the success of this technology is the availability of an area-wide and affordable hydrogen supply. A significant cost factor in the hydrogen supply chain is the multi-stage gas compression to provide the mandatory filling pressure for the pressurized tanks. One way to address this issue is to perform the hydrogen production process at elevated pressure. In this paper the feasibility of compressed hydrogen production without additional gas compression based on the steam iron process is discussed. Experiments were performed in a lab-scale test rig using fixed bed reactor technology. The focus was to evaluate the influence of pressurized hydrogen production on the cycle stability, on the conversion efficiency and on the structural integrity of a Fe2O3-Al2O3 (90 + 10 wt%) oxygen carrier. The oxidations were performed at different pressure levels of 7-22 bar (g) at a temperature of 750 °C with steam. The steady steam supply was ensured by a HPLC pump which delivered 0.03 g min-1 (at room temperature) of water, which was evaporated in the heated inlet section. The water was introduced for approximately 100 min until the oxygen carrier was fully oxidized. The iron oxide was reduced in the subsequent reaction steps at 750 °C and ambient pressure with 25 Nml min-1 H2 as reducing agent. The reduction reactions were analyzed to evaluate possible influences of its prior oxidations. The results revealed no signs of negative repercussions. The oxygen carrier conversion of initially 84% remained at a steady behavior between the 15 performed cycles. Only small losses of 0.8% per cycle caused by thermal sintering of the contact mass were observed, which was independent from the different pressure levels of the prior oxidations. The evaluation of the pressurized oxidations did not reveal any performance decrease as well. The rise of pressure in each oxidation showed a consistent characteristic throughout the complete test series. Scanning electron microscopy analysis of the oxygen carrier sample after the experiment revealed some structural changes, which are related to thermal sintering but the structural integrity of the sample stayed intact. The oxidations yielded an average of 18 mmol gFe -1 hydrogen with a maximum hydrogen pressure of 22 bar (g). The conducted experiments showed that the steam iron process is very suitable for the production of compressed hydrogen and that the process is not negatively influenced by the elevated system pressure. © 2015 Elsevier Ltd.

Bucher E.,University of Leoben | Gspan C.,University of Graz | Gspan C.,Graz Center for Electronic Microscopy | Hofer F.,University of Graz | And 2 more authors.
Solid State Ionics | Year: 2013

A degraded sample of the solid oxide fuel cell cathode material La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) is investigated by analytical transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). In the present study TEM is applied in order to analyse the relevant surface-near regions of an LSCF sample which was pre-treated for 1000 h in a dry O2-Ar atmosphere and an additional 1000 h in a humidified atmosphere in the vicinity of a silicon source. The results show that Si contamination occurs in an approximately 20 nm thick layer (with local variations from 4 to 35 nm) at the surface of the degraded LSCF sample. In addition, TEM gives evidence of isolated nanocrystals of SrSO4 with diameters in the range of 200-500 nm. A local decomposition of the perovskite phase is found within depths of 500-600 nm from the surface. The decomposition products are ternary oxides which contain either Sr-La-O or Co-Fe-O. © 2012 Elsevier B.V. All rights reserved.

Mittal V.,Graz Center for Electronic Microscopy | Matsko N.B.,The Petroleum Institute
Journal of Polymer Research | Year: 2012

Surface functionalization of the materials to achieve functionalities like thermal responsiveness has found increasing interest. In the current study, such a functionalization with poly(N-isopropylacrylamide) (PNIPAAM) polymer has been reported by controlled grafting from the surface of aggregated particles to form macroporous monoliths. The particles were first modified with a thin polymer shell of a functional monomer 2-(2-bromopropionyloxy) ethyl acrylate, BPOEA (or copolymer with styrene), which also contained a terminal atom transfer radical polymerization (ATRP) moiety. Surfactant free emulsion polymerization was carried out to generate polystyrene seed particles as well as the shell around them. Due to the colloidal unstability of BPOEA polymer chains, stable particles were formed only in presence of excess molar amount of styrene (styrene to BPOEA mole ratio of 3:1) or seed particles. Collapse of the BPOEA polymer chains on the seed particles was also enhanced by the addition of salt in the shell forming monomer batch, which did not allow the formation of stable secondary particles. The surface morphology of the particles was affected both by the kinetic collapse of the BPOEA chains on surface of the particles and subsequent polymerization as well as efficient stirring of the contents. The emulsifier free particles could not be gelated by the addition of salt and were destabilized by shear. The resulting aggregates were stable and porous which allowed simultaneous grafting of PNIPAAM polymer from the surface as well as imparted dimensional stability to the structure during the grafting process. It was also required to optimize the extent of grafting as the excess grafting could reduce the porosity of the structure. © Springer Science+Business Media Dordrecht 2012.

Mittal V.,The Petroleum Institute | Chaudhry A.U.,The Petroleum Institute | Matsko N.B.,Graz Center for Electronic Microscopy
Journal of Applied Polymer Science | Year: 2014

Biopolymers have gained research focus due to enhanced property profiles as well as need to replace the fossil fuel based polymeric materials. The generation of biocomposites with functional biofillers can lead to further enhancement of their potential. In this study, composites of date seed powder with biopolyesters poly(butylene adipate-co-terephthalate) (PBAT) and poly-l-lactide (PLA) have been demonstrated. The composites exhibited individual degradation peaks for the components in the thermogravimetric analysis (TGA), but still had suitable thermal performance confirmed by the dynamic TGA. The filler also modified the crystalline morphology of the polymers differently. The tensile modulus of the PBAT-based composites had enhancement of more than 300% in the composite with 40% filler content. The PLA composites also enhanced the modulus marginally till 20% filler content, however, it was still significant due to the very high modulus of PLA as compared to PBAT. The rheological properties indicated the polymer still had viscous behavior even when high amount of filler was added. The storage and loss modulus of the composites enhanced with filler fraction, the PLA composites with 30 and 40% content, however, exhibited very high values probably due to filler aggregates and low filler-polymer interfacial interactions. The filler particles were observed to be uniformly distributed in the polymer matrices, though some filler aggregates were also observed in the composites with higher filler fractions. After embedding in compost soil, the composites had significantly enhanced extent of biodegradation as compared to pure polymers, thus, confirming the "true" biocomposite nature. © 2014 Wiley Periodicals, Inc.

Winkler R.,Graz Center for Electronic Microscopy | Geier B.,Graz Center for Electronic Microscopy | Plank H.,Graz Center for Electronic Microscopy | Plank H.,University of Graz
Applied Physics A: Materials Science and Processing | Year: 2014

The successful application of functional nanostructures, fabricated via focused electron-beam-induced deposition (FEBID), is known to depend crucially on its chemistry as FEBID tends to strong incorporation of carbon. Hence, it is essential to understand the underlying mechanisms which finally determine the elemental composition after fabrication. In this study we focus on these processes from a fundamental point of view by means of (1) varying electron emission on the deposit surface; and (2) changing replenishment mechanism, both driven by the growing deposit itself. First, we revisit previous results concerning chemical variations in nanopillars (with a quasi-1D footprint) depending on the process parameters. In a second step we expand the investigations to deposits with a 3D footprint which are more relevant in the context of applications. Then, we demonstrate how technical setups and directional gas fluxes influence final chemistries. Finally, we put the findings in a bigger context with respect to functionalities which demonstrates the crucial importance of carefully set up fabrication processes to achieve controllable, predictable and reproducible chemistries for FEBID deposits as a key element for industrially oriented applications. © 2014, Springer-Verlag Berlin Heidelberg.

Loading Graz Center for Electronic Microscopy collaborators
Loading Graz Center for Electronic Microscopy collaborators