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Novo Mesto, Slovenia

Dragomir M.,University of Nova Gorica | Arcon I.,University of Nova Gorica | Arcon I.,Jozef Stefan Institute | Arcon I.,CO NOT | And 3 more authors.
Acta Materialia | Year: 2013

Studies performed on the NdVO4-BiVO4 system showed the existence of the BixNd1-xVO4 homogeneity range for x ≤ 0.49(1). Extended X-ray absorption fine structure and X-ray diffraction analyses confirmed that Bi3+ is incorporated onto the Nd site in the NdVO4 crystal structure with some distortion of the local structure. Surprisingly, the unit cell volume decreases with the increase in the content of the larger Bi3+ ion. On the other side of the NdVO4-BiVO4 system, Nd3+ does not enter the BiVO4 structure but forms the NdVO4-based secondary phase. Ultraviolet-visible spectroscopy showed that the band gap of NdVO 4 can be reduced to below 3.1 eV by the Bi doping. New emissions that do not exist for NdVO4 have been found in the 650-675 nm range of BixNd1-xVO4 photoluminescence spectra. The observed chemical and optoelectronic properties were explained on the basis of the hybridization of Bi 6s2 and O 2p orbitals. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Conradi M.,Slovenian Institute of Metals And Technology | Kocijan A.,Slovenian Institute of Metals And Technology | Zorko M.,Slovenian National Institute of Chemistry | Jerman I.,Slovenian National Institute of Chemistry | Jerman I.,CO NOT
Progress in Organic Coatings | Year: 2012

In this paper we focus on the preparation of thin polymer coatings synthetized from 30-nm and 600-nm silica particles dispersed in polyvinyl chloride (PVC) and deposited on two different steel substrates: duplex DSS 2205 and austenitic AISI 316L steel. We show that a silica surface modification with silane IO 7T 7(OH) 3 (trisilanol isooctyl polyhedral oligomeric silsesquioxane, POSS) significantly improves its dispersion properties when mixed with PVC. For comparison, the surface morphology and surface roughness of PVC coatings filled with both silanated and as-received (non-silanated) silica fillers were analyzed with scanning electron microscopy (SEM) and atomic force microscopy (AFM) when sprayed on the steel surface. The effect of the silica silanization is later on reflected in a decreased average surface roughness in the silanated, compared to non-silanated, silica/PVC-coatings. The wetting properties of the silanated and non-silanated silica/PVC-coatings on DSS 2205 and AISI 316L were investigated using contact-angle and surface-energy measurements, indicating an increased surface hydrophilicity in terms of a decreased static water contact angle and an increased total surface energy compared to the uncoated specimens. Finally, the beneficial corrosion resistance of the silica/PVC coatings was confirmed with potentiodynamic polarization spectroscopy in a 3.5% NaCl solution. © 2012 Published by Elsevier B.V. All rights reserved. Source

Gasperin M.,Jozef Stefan Institute | Boskoski P.,Jozef Stefan Institute | Debenjak A.,Jozef Stefan Institute | Petrovcic J.,Jozef Stefan Institute | Petrovcic J.,CO NOT
Fuel Cells | Year: 2014

This paper presents an alternative computational method for on-line estimation and tracking of the impedance of PEM fuel cell systems. The method is developed in order to provide the information to diagnostics and health management system. Proper water management remains the main issue influencing the reliability and durability of PEM fuel cell technology. While literature reviews reveal the thorough understanding of the underlying processes and extensive experimental work, the existing implementations rely on expensive hardware or time consuming computational methods. In this scope, we will show how the characteristic values of the fuel cell impedance, required by the diagnostic system, can be computed by robust and computationally efficient algorithms, which are suitable for implementation in embedded systems. The methods under consideration include continuous-time wavelet transform (CWT) and extended Kalman filter (EKF). The CWT is a time-frequency technique, which is suitable for tracking transient signal components. The EKF is a stochastic signal processing method, which provides confidence measures for the estimates. The paper shows, that both methods provide accurate estimates for diagnostics of FCS and can perform on-line tracking of these features. The performance of the algorithms is validated on experimental data from a commercial fuel cell stack. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Mihelcic M.,Slovenian National Institute of Chemistry | Francetic V.,University of Ljubljana | Pori P.,Chemcolor Sevnica D.o.o. | Gradisar H.,Slovenian National Institute of Chemistry | And 3 more authors.
Applied Surface Science | Year: 2014

Polyhedral oligomeric silsesqioxanes (POSS) compounds consisting of [RSiO3/2]n groups organized in the form of various polyhedra (Tn, n = 3, 6, 8, 10, 12, ....) have not often been used as pigment surface modifiers. Their interactions with pigments are not known in detail and coatings deposited from pigments modified by POSS dispersants are rare. Identification of interactions between a dispersant and the surface of pigments is important from the point of view of obtaining stable pigment dispersions enabling the deposition of optical coatings with high pigment loading, low haze and mechanical integrity. Thin TiO2 (anatase) pigment coatings (70-260 nm) were deposited from pigment dispersions prepared by milling metatitanic acid (mTiA) powder agglomerates with trisilanol heptaisobutyl silsesquioxane dispersant (trisilanol POSS) in butanol and hexane. The results of TEM, EDAX and TG measurements confirmed the influence of trisilanol POSS dispersant on the formation of a dispersion with a uniform distribution of mTiA and rutile (mTiR) nanoparticles with a size of about 30 ± 5.0 nm and 90 ± 5.0 nm, respectively, as determined from dynamic light scattering (DLS) measurements. The mTiA/trisilanol POSS dispersions with added titanium tetraisopropoxide were deposited on fluorine-doped tin oxide (FTO) coated glass (spin-coating) and indium tin oxide coated polymeric substrate (ITO PET) (coil-coating) and thermally treated at 150 °C. UV-vis spectra, AFM and SEM results showed that the pigment coatings exhibited low haze (up to 6%), low surface roughness (up to 20 nm) and uniform morphology. mTiA/trisilanol POSS interactions were assessed from the frequency shifts of the SiOSi stretching modes of trisilanol POSS, while the adsorption of the dispersant was followed from the intensity changes of the Corresponding CH 3 and CH2 stretching modes, confirming the gradual occupation of the mTiA crystalline sites by trisilanol POSS dispersant. Examination of IR vibrational spectra showed that trisilanol POSS interacted with the mTiA surface by establishing hydrogen bonding. The advantage of using trisilanol POSS dispersant was demonstrated by the enhanced electrochromic effect of the mTiA pigment coatings. © 2014 Elsevier B.V. All rights reserved. Source

Pivko M.,Slovenian National Institute of Chemistry | Pivko M.,CO NOT | Arcon I.,CO NOT | Arcon I.,University of Nova Gorica | And 8 more authors.
Journal of Power Sources | Year: 2012

Two stable modifications of A 3V 2(PO 4) 3 (A = Na or Li) were synthesized by citric acid assisted modified sol-gel synthesis. The obtained samples were phase pure Li 3V 2(PO 4) 3 and Na 3V 2(PO 4) 3 materials embedded in a carbon matrix. The samples were tested as half cells against lithium or sodium metal. Both samples delivered about 90 mAh g -1 at a C/10 cycling rate. The change of vanadium oxidation state and changes in the local environment of redox center for both materials were probed by in-situ X-ray absorption spectroscopy. Oxidation state of vanadium was determined by energy shift of the absorption edge. The reversible change of valence from trivalent to tetravalent oxidation state was determined in the potential window used in our experiments. Small reversible changes in the interatomic distances due to the relaxation of the structure in the process of alkali metal extraction and insertion were observed. Local environment (vanadium-oxygen bond distances) after 1st cycle were found to be the same as in the starting material. Both structures have been found very rigid without significant changes during alkali metal extraction. © 2012 Elsevier B.V. Source

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