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  • 1.
    Afrasiabi, Roodabeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Shahid, Robina
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Microwave mediated synthesis of semiconductor quantum dots2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1551-1556Article in journal (Refereed)
    Abstract [en]

    Colloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II-VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield.

  • 2. Akman, O.
    et al.
    Kavas, H.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Coruh, Ali
    Aktas, B.
    Magnetic metal nanoparticles coated polyacrylonitrile textiles as microwave absorber2013In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 327, p. 151-158Article in journal (Refereed)
    Abstract [en]

    Polyacrylonitrile (PAN) textiles with 2 mm thickness are coated with magnetic nanoparticles in coating baths with Ni, Co and their alloys via an electroless metal deposition method. The crystal structure, morphology and magnetic nature of composites are investigated by X-ray Powder diffraction, Scanning Electron Microscopy, and dc magnetization measurement techniques. The frequency dependent microwave absorption measurements have been carried out in the frequency range of 12.4-18 GHz (X and P bands). Diamagnetic and ferromagnetic properties are also investigated. Finally, the microwave absorption of composites is found strongly dependent on the coating time. One absorption peak is observed between 14.3 and 15.8 GHz with an efficient absorption bandwidth of 3.3-4.1 GHz (under -20 dB reflection loss limit). The Reflection loss (RL) can be achieved between -30 and -50 dB. It was found that the RL is decreasing and absorption bandwidth is decreasing with increasing coating time. While absorption peak moves to lower frequencies in Ni coated PAN textile, it goes higher frequencies in Co coated ones. The Ni-Co alloy coated composites have fluctuating curve of absorption frequency with respect to coating time. These results encourage further development of magnetic nanoparticle coated textile absorbers for broadband applications.

  • 3. Altincekic, T. G.
    et al.
    Boz, I.
    Baykal, A.
    Kazan, S.
    Topkaya, R.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of CuFe2O4 nanorods synthesized by polyol route2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 493, no 1-2, p. 493-498Article in journal (Refereed)
    Abstract [en]

    Uniform, high quality, CuFe2O4 nanorods with high aspect ratios were synthesized by a surfactant-free single step polyol process at 220 degrees C. The structure of the product was characterized by XRD and FT-IR, and the morphology of the product was analyzed by SEM. The results showed that the as-prepared nanorods have a uniform cross-section and with average diameter of similar to 100 nm and aspect ratio in the range of 13-52. X-ray line profile fitting resulted in crystallite size of 15 nm, which reveals the polycrystalline nature of these nanorods. Magnetic characterization of product was performed by EPR and VSM techniques and the results show that the CuFe2O4 nanorods are ferromagnetic. The line width of the resonance lines in FMR is about 1.8 kOe which may originate from different resonance fields of randomly distributed nanocrystals which have different orientation of magnetic easy axes.

  • 4. Amir, M.
    et al.
    Baykal, A.
    Güner, S.
    Sertkol, M.
    Sözeri, H.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Synthesis and Characterization of CoxZn1−xAlFeO4 Nanoparticles2015In: Journal of Inorganic and Organometallic Polymers and Materials, ISSN 1574-1443, Vol. 25, no 4, p. 747-754Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline powders of cobalt and aluminum co-substituted zinc ferrites with general formula CoxZn1−xAlFeO4 (x = 0.0–1.0) have been synthesized for the first time. Using the citrate-microwave technique and the citric acid as combustion–complexion agent (fuel), materials with spinel mono-phase cubic spinel structure were successfully prepared. The characterization of products was done by XRD, SEM and VSM. The crystallite size estimated by Scherrer formula has been found in the range of 7.7–9.6 nm. The magnetic properties were studied by room temperature (RT) VSM magnetization measurements. The small remanent magnetization (Mr) and coercivity (Hc) values reveal the superparamagnetic nature of nanoparticles (NPs) at RT. The extrapolated saturation magnetization (Ms) is maximum for Co0.8Zn0.2AlFeO4 (17.15 emu/g) and minimum for ZnAlFeO4 particles (4.22 emu/g). This case is attributed to high or low amount of cation distribution change from normal to mixed spinel structure. The average magnetic diameters (Dmag) were calculated from magnetic fit studies of M–H spectra. Dmag values are between 8.17 and 8.46 nm and this range is in great accordance with the obtained diameters from XRD measurements. The small Mr/Ms ratios (maximum, 0.219) specify the uniaxial anisotropy according to Stoner–Wohlfarth model for CoxZn1−xAlFeO4 NPs. RT effective anisotropy constants (Keff) were calculated by using Ms and Hc values. Keff constants increased with increasing Co content in the spinel NPs.

  • 5. Andõn, F. T.
    et al.
    Kapralov, A. A.
    Yanamala, N.
    Feng, W.
    Baygan, Arjang
    Karolinska Institutet.
    Chambers, B. J.
    Hultenby, K.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Brandner, B. D.
    Fornara, Andrea
    Institute for Surface Chemistry, Stockholm.
    Klein-Seetharaman, J.
    Kotchey, G. P.
    Star, A.
    Shvedova, Anna A.
    West Virginia University, USA.
    Fadeel, B.
    Kagan, V. E.
    Biodegradation of Single-Walled Carbon Nanotubes by Eosinophil Peroxidase2013In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 9, no 16, p. 2721-2729Article in journal (Refereed)
    Abstract [en]

    Eosinophil peroxidase (EPO) is one of the major oxidant-producing enzymes during inflammatory states in the human lung. The degradation of single-walled carbon nanotubes (SWCNTs) upon incubation with human EPO and H2O 2 is reported. Biodegradation of SWCNTs is higher in the presence of NaBr, but neither EPO alone nor H2O2 alone caused the degradation of nanotubes. Molecular modeling reveals two binding sites for SWCNTs on EPO, one located at the proximal side (same side as the catalytic site) and the other on the distal side of EPO. The oxidized groups on SWCNTs in both cases are stabilized by electrostatic interactions with positively charged residues. Biodegradation of SWCNTs can also be executed in an ex vivo culture system using primary murine eosinophils stimulated to undergo degranulation. Biodegradation is proven by a range of methods including transmission electron microscopy, UV-visible-NIR spectroscopy, Raman spectroscopy, and confocal Raman imaging. Thus, human EPO (in vitro) and ex vivo activated eosinophils mediate biodegradation of SWCNTs: an observation that is relevant to pulmonary responses to these materials. Human eosinophil peroxidase (EPO) is able to degrade SWCNTs in vitro in the presence of H2O2. EPO is one of the major oxidant-generating enzymes present in human lungs during inflammatory states. The biodegradation of SWCNTs is evidenced also in an ex vivo culture system using primary murine eosinophils stimulated to undergo degranulation. These results are relevant to potential respiratory exposure to carbon nanotubes.

  • 6.
    Avila, Marta
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Burks, Terrance
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Akhtar, F.
    Department of Materials and Environmental Chemistry, Stockholm Universtiy, Stockholm, Sweden.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Lansåker, P. C.
    Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Uheida, Abdusalam
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Surface functionalized nanofibers for the removal of chromium(VI) from aqueous solutions2014In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 245, p. 201-209Article in journal (Refereed)
    Abstract [en]

    Polyacrylonitrile (PAN) nanofibers functionalized with amine groups (PAN-NH2) were prepared using a simple one-step reaction route. The PAN-NH2 nanofibers were investigated for the removal of chromium(VI) from aqueous solutions. The adsorption and the kinetic characteristics were evaluated in batch process. The adsorption process showed pH dependence and the maximum Cr(VI) adsorption occurred at pH = 2. The Langmuir adsorption model described well the experimental adsorption data and estimated a maximum loading capacity of 156 mg/g, which is a markedly high value compared to other adsorbents reported. The kinetics studies indicated that the equilibrium was attained after 90 min and the experimental data followed a pseudo-second order model suggesting a chemisorption process as the rate limiting step. X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) revealed that the adsorption of Cr(VI) species on PAN-NH2 was facilitated through both electrostatic attraction and surface complexation. High desorption efficiency (> 90%) of Cr(VI) was achieved using diluted base solutions that may allow the reuse of PAN-NH2 nanofibers.

  • 7. Aydin, M.
    et al.
    Durmus, Z.
    Kavas, H.
    Esat, B.
    Sozeri, H.
    Baykal, A.
    Yilmaz, F.
    Toprak, Muhammat S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of poly(3-thiophene acetic acid)/Fe3O4 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 6, p. 1120-1126Article in journal (Refereed)
    Abstract [en]

    Poly(3-thiophene acetic acid)/Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of poly(3-thiophene acetic acid) (P3TAA). Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA. and conductivity measurements, respectively. The capping of P3TAA around Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite and particle size were obtained as 9 +/- 2 nm and 11 +/- 1 nm from XRD line profile fitting and TEM image analysis, respectively, which reveal nearly single crystalline nature of Fe3O4 nanoparticles. Magnetization measurements reveal that P3TAA coated magnetite particles do not saturate at higher fields. There is no coercivity and remanence revealing superparamagnetic character. Magnetic particle size calculated from the theoretical fitting as 9.1 nm which coincides the values determined from TEM micrographs and XRD line profile fitting. The comparison to the TEM particle size reveals slightly modified magnetically dead nanoparticle surface.

  • 8. Aydin, M.
    et al.
    Unal, B.
    Esat, B.
    Baykal, A.
    Karaoglu, E.
    Toprak, Muhammet Sadaka
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Synthesis, magnetic and electrical characteristics of poly(2-thiophen-3-yl-malonic acid)/Fe(3)O(4) nanocomposite2012In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 514, p. 45-53Article in journal (Refereed)
    Abstract [en]

    Poly(2-thiophen-3-yl-malonic acid)/Fe(3)O(4) nanocomposite was synthesized by the precipitation of Fe(3)O(4) in the presence of poly(2-thiophen-3-yl-malonic acid) (PT3MA). Characterizations of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, AC/DC conductivity and dielectric measurements. The capping of PT3MA around Fe(3)O(4) nanoparticles was confirmed by FTIR spectroscopy, the interaction being between bridging oxygen of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite particle sizes of 6 +/- 3 nm and 7 +/- 3 nm were obtained from XRD line profile fitting and from TEM image analysis respectively, and they are in good agreement with each other. Magnetization measurements revealed that PT3MA coated magnetite particles do not saturate at higher fields. The material showed superparamagnetic character as revealed by the absence of coercivity and remnant magnetization. Magnetic particle size was calculated as 7.3 +/- 1.0 nm from the mean magnetization term in the Langevin function which is also in conformity with the values determined from TEM micrographs and XRD line profile fitting. The TEM particle size analysis of the nanoparticles revealed the presence of a slightly modified magnetically dead nanoparticle surface. AC and DC conductivity measurements were performed to elucidate the electrical conduction characteristics of the product.

  • 9. Battiston, S.
    et al.
    Boldrini, S.
    Saleemi, Mohsin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Famengo, A.
    Fiameni, S.
    Toprak, Muhammet
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Fabrizio, M.
    Influence of Al and Mg addition on thermoelectric properties of higher manganese silicides obtained by reactive sintering2017In: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 17, no 3, p. 1668-1673Article in journal (Refereed)
    Abstract [en]

    Higher manganese silicides (HMS), represented by MnSix (x = 1.71-1.75), are promising p-type candidates for thermoelectric (TE) energy harvesting systems at intermediate temperature range. The materials are very attractive as they may replace lead based compounds due to their non-toxicity, low cost of starting materials, and high thermal and chemical stability. Dense pellets were obtained through fast reactive sintering by spark plasma sintering (SPS). The addition -or nanoinclusion, of Al and Mg permitted the figure of merit enhancement of the material obtained with this technique, reaching the highest value of 0.40 at 600°C. Morphology, composition and crystal structure of the samples were characterized by electron microscopies, energy dispersive X-ray spectroscopy, and X-ray diffraction analyses, respectively.

  • 10. Battiston, S.
    et al.
    Fiameni, S.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Boldrini, S.
    Famengo, A.
    Agresti, F.
    Stingaciu, M.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fabrizio, M.
    Barison, S.
    Synthesis and Characterization of Al-Doped Mg2Si Thermoelectric Materials2013In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 42, no 7, p. 1956-1959Article in journal (Refereed)
    Abstract [en]

    Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion for the middle to high range of temperature. These materials are very attractive for TE research because of the abundance of their constituent elements in the Earth's crust. Mg2Si could replace lead-based TE materials, due to its low cost, nontoxicity, and low density. In this work, the role of aluminum doping (Mg2Si:Al = 1:x for x = 0.005, 0.01, 0.02, and 0.04 molar ratio) in dense Mg2Si materials was investigated. The synthesis process was performed by planetary milling under inert atmosphere starting from commercial Mg2Si pieces and Al powder. After ball milling, the samples were sintered by means of spark plasma sintering to density > 95%. The morphology, composition, and crystal structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction analyses. Moreover, Seebeck coefficient analyses, as well as electrical and thermal conductivity measurements were performed for all samples up to 600A degrees C. The resultant estimated ZT values are comparable to those reported in the literature for these materials. In particular, the maximum ZT achieved was 0.50 for the x = 0.01 Al-doped sample at 600A degrees C.

  • 11. Baykal, A.
    et al.
    Bitrak, N.
    Ünal, B.
    Kavas, H.
    Durmus, Z.
    Özden, S.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Polyol synthesis of (polyvinylpyrrolidone) PVP-Mn3O4 nanocomposite2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 502, no 1, p. 199-205Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of (polyvinylpyrrolidone) PVP-Mn3O4 nanocomposite via a polyol route. Crystalline phase was identified as Mn3O4 and the crystallite size was obtained as 6 +/- 1 nm from X-ray line profile fitting. Average particle size of 6.1 +/- 0.1 nm obtained from TEM analysis reveals nearly single crystalline nature of these nanoparticles in the composite. The capping of PVP around Mn3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carbonyl (C=O) and the nanoparticle surface. T-C and T-B for PVP-Mn3O4 nanocomposite were observed at 42K and 28.5 K, respectively. The sample has hysteresis with small coercivity and remanent magnetization at 40K, resembling the superparamagnetic state. ac conductivity measurements on PVP-Mn3O4 nanocomposite revealed a conductivity in the order of 10(-7) S cm(-1) at lower frequencies. The conductivity change with respect to frequency can be explained by electronic exchange occurring between Mr(+2) and Mn+3 existing in sublattice of spinel lattice.

  • 12. Baykal, A.
    et al.
    Deligöz, H.
    Sozeri, H.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Triethylene Glycol Stabilized CoFe2O4 Nanoparticles2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 1879-1892Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis and detailed composition, thermal, micro-structural, ac-dc conductivity performance and dielectric permittivity characterization of triethylene glycol (TREG) stabilized CoFe 2O 4 nanoparticles synthesized by polyol method. XRD analysis confirmed the inorganic phase as CoFe 2O 4 with high phase purity. Microstructure analysis with TEM revealed well separated, spherical nanoparticles in the order of 6 nm, which is also confirmed by X-ray line profile fitting. FT-IR analysis confirms that TREG is successfully coated on the surface of nanoparticles. Overall conductivity of nanocomposite is approximately two magnitudes lower than that of TREG with increase in temperature. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies which is an indication of ionic conductivity. The dc conductivity of the nanocomposites and pure TREG are found to obey the Ar- rhenius plot with dc activation energies of 0.258 eV and 0.132 eV, respectively. Analysis of dielectric permittivity functions suggests that ionic and polymer segmental motions are strongly coupled in the nanocomposite. TREG stabilized CoFe 2O 4 nanoparticles has lower ε and ε than that of pure TREG due to the doping of cobalt. As the temperature increases, the frequency at which (ε ) reaches a maximum shifted towards higher frequencies. On the other hand, the activation energy of TREG for relaxation process was found to be 0.952 eV which indicates the predominance of electronic conduction due to the chemical nature of TREG. Contrarily, no maximum peak of tan Ύ was observed for the nanocomposite due to the being out of temperature and frequency range applied in the study.

  • 13. Baykal, A.
    et al.
    Demir, M.
    Unal, B.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Synthesis, Characterization, and Dielectric Properties of BaFe10(Mn2+Zn2+Zn2+)O-19 Hexaferrite2016In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 29, no 1, p. 199-205Article in journal (Refereed)
    Abstract [en]

    Barium hexaferrite with nominal chemical composition BaMnZn2Fe10O19 has been synthesized by sol-gel method, using polymethyl methacrylate (PMMA) as a template. Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD) were used for approving the formation of barium hexaferrites. In addition, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to investigate the structural and morphological properties of BaM. The dielectric properties were studied by impedance measurements as a function of frequency (in the range 0.1 Hz-1 MHz). The XRD patterns confirmed the formation of single-phase magnetoplumbite with crystallite size around 73 nm. The results of dielectric parameters and conductivity measurements showed three regions with different behaviors in electrical conduction mechanism.

  • 14. Baykal, A.
    et al.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Synthesis and characterization of PEG-Sr hexaferrite by sol-gel conversion2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 2003-2008Article in journal (Refereed)
    Abstract [en]

    Sr-M-type hexagonal ferrites have been prepared via a sol-gel route, and the effects of addition of different molecular weight polyethylene glycol (PEG) into the sol solutions on the static magnetic properties and particle morphology have been studied. Crystalline phases of the samples were determined by XRD analysis. FT-IR and TG analyses were used to prove the presence of PEG on SrFe12O19. The results showed that adding PEG with different molecular weight into the sol solutions affected the formation mechanism of SrFe12O19. Sr-M precursors prepared by various PEG types show different magnetic behaviors after precalcination at 150 degrees C. This discrepancy is explained by the formation of a different phase during the synthesis of SrM particles.

  • 15. Baykal, A
    et al.
    Gozel, G
    Kizilyalli, M
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Kniep, R
    X-RAY powder diffraction and IR study of calcium borophosphate, CaBPO52000In: Turkish Journal of Chemistry, ISSN 1010-7614, Vol. 24, no 4, p. 381-388Article in journal (Refereed)
    Abstract [en]

    In this study, CaBPO5 was synthesized by different solid state reactions than reported before and its X-ray powder diffraction and IR data were reported. In one of these solid state reactions BPO4 was used as a phosphating agent. The examination of the X-ray powder diffraction data showed that this compound crystallized in a hexagonal system and the refilled unit cell parameters were a = 6.684, c = 6.616(2) Angstrom, with Z=3 as reported before. From the observed reflections, the space group was determined as P3(1)21, and its density was found to be 3.15 g/cc. The X-ray powder diffraction and IR data, which were in agreement with the reported crystal structure, are given tho first time in this work.

  • 16. Baykal, A.
    et al.
    Günay, M.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sozeri, H.
    Effect of ionic liquids on the electrical and magnetic performance of polyaniline-nickel ferrite nanocomposite2013In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 48, no 2, p. 378-382Article in journal (Refereed)
    Abstract [en]

    Polyaniline-NiFe2O4 nanofiber composites were successfully synthesized at the interface of water and ionic liquid via in situ polymerization using cetyl trimethylammonium bromide (CTAB) as surfactant. Both TG analysis and FT-IR measurements proved the presence of organic layer on the surface of NiFe2O4 nanoparticles. The influence of 1-butyl-3-methyl-imidazolium bromide [BMIM]Br as ionic liquid on the structure, conductivity and magnetic property of polyaniline-NiFe2O 4-CTAB nanocomposite were studied in detail. The results show that imidazolium-based ionic liquids BMIMBr acts as an anchor agent for the formation of morphology in polyaniline-NiFe2O4-CTAB nanocomposite. Introduction of ionic liquids obviously improves the conductivity but weakens the magnetization of polyaniline-NiFe2O4 nanocomposite.

  • 17. Baykal, A
    et al.
    Kizilyalli, M
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Kniep, R
    Hydrothermal and microwave synthesis of boron phosphate, BPO42001In: Turkish Journal of Chemistry, ISSN 1010-7614, Vol. 25, no 4, p. 425-432Article in journal (Refereed)
    Abstract [en]

    BPO4 was previously synthesized by the solid state reactions of (NH4)(2)HPO4 and B2O3 at 1000 degreesC and was characterized by X-ray powder diffraction and IR methods. We have now succeeded in preparing BPO4 from H3BO3 and P2O5 using hydrothermal synthesis by heating at 160 degreesC for 2 days and obtained a single phase product. We observed that a microwave-assisted synthesis takes only 3 to 5 minutes to transform a solid mixture of (NH4)(2)B4O7. 4H(2)O, and solid H3PO4 Or B2O3 + P2O5 into the crystalline title compound. Its X-ray powder diffraction data and IR spectra were in good agreement with the literature values.

  • 18. Baykal, A.
    et al.
    Senel, M.
    Unal, B.
    Karaoglu, E.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Acid Functionalized Multiwall Carbon Nanotube/Magnetite (MWCNT)-COOH/Fe3O4 Hybrid: Synthesis, Characterization and Conductivity Evaluation2013In: Journal of Inorganic and Organometallic Polymers and Materials, ISSN 1574-1443, Vol. 23, no 3, p. 726-735Article in journal (Refereed)
    Abstract [en]

    A functionalized multiwall carbon nanotube (MWCNT)-COOH/Fe3O4 hybrid was fabricated by co-precipitation method. Fe3O4 nanoparticles were stably attached to the surface of carboxyl groups (COOH). The presence of Fe3O4 nanoparticles and their surface conjugation to MWCNT have been confirmed by XRD, TEM and FT-IR techniques. Magnetic evaluation revealed a superparamagnetic character of the hybrid and therefore the attached Fe3O4 nanoparticles. The crystallite size (9 +/- A 3 nm), particle size (9 +/- A 2 nm) and magnetic domain size estimated for Fe3O4 are consistent with each other, which reveal the single crystalline character of the nanoparticles. Electrical conductivity and dielectric behavior have also been characterized by utilizing impedance spectroscopy up to 3 MHz for an isotherm line varying from 293 to 393 K by 10 K steps. Electrical characteristics and its complex dielectric approaches might be elucidated with the existence of a conventional tunneling conduction mechanism of temperature-independency. The AC conductivity of MWCNT-COOH/Fe3O4 hybrid could also be a consequence of the estimations of the universal dynamic response.

  • 19.
    Baykal, A.
    et al.
    Fatih Univ, Istanbul, Turkey.
    Toprak, M. S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Durmus, Z.
    Fatih Univ, Istanbul, Turkey.
    Senel, M.
    Fatih Univ, Istanbul, Turkey.
    Sozeri, H.
    Natl Metrol Inst, Gebze, Kocaeli, Turkey.
    Demir, A.
    Fatih Univ, Istanbul, Turkey.
    Synthesis and Characterization of Dendrimer-Encapsulated Iron and Iron-Oxide Nanoparticles2012In: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, ISSN 1557-1939, Vol. 25, no 5, p. 1541-1549Article in journal (Refereed)
    Abstract [en]

    In this paper, a series of iron (Fe) containing nanoparticles were prepared by employing PAMAM (Poly(amidoamine), dendrimers with different generations (G0-G3) as templates and sodium borohydride as a reducing agent. The products have been characterized by TEM, FT-IR, XRD, VSM, TGA, and XPS. XRD analysis reveal low crystallinity of formed particles within the dendrimers, however, crystallinity of the nanoparticles was observed to increase with increasing generation of dendrimers. Dominant phases were determined as magnetite (Fe3O4 or maghemite, gamma-Fe2O3). XPS analysis revealed the chemical composition of nanoparticles as iron oxide which indicated the oxidation of Fe species subsequent to the reduction process, in agreement with XRD analysis. The magnetization curves have superparamagnetic nonhysteretic characteristic at lower fields and with nonsaturation characteristic at high fields. Magnetic evaluation of samples with the 20:1 molar ratio of Fe:PAMAM showed decreasing superparamagnetic character and decreasing saturation magnetisation with increasing generation of dendrimers.

  • 20. Baykal, A.
    et al.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Durmus, Z.
    Sozeri, H.
    Hydrothermal synthesis of SrFe 12O 19 and its characterization2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 6, p. 2081-2085Article in journal (Refereed)
    Abstract [en]

    We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180°C. Crystalline phase of samples were determined by XRD and spectroscopic, morphological, and magnetic investigation of the sample were FT-IR, SEM, and TG analysis, respectively. XRD analysis revealed few impurity phases in the as-made powder; upon calcinations, the material is converted to desired hexaferrite phase. As synthesized powder exhibits agglomerates with rather smooth facets, in the form of thick platelets. Upon calcination, all these structures were observed to transfer to rod-like structures. The As calcined sample has high specific saturation magnetization (Ms ) values of 65 emu/g that is close to its theoretical value of 74.3 emu/g but the hydrothermally synthesized sample does not. This is in agreement with the observations from XRD analysis where few impurity phases observed in the as-made powder cause a weak magnetic response. Upon calcination, the material is converted to a desired hexaferrite phase with better magnetic properties.

  • 21. Baykal, Abdulhadi
    et al.
    Karaoglu, Ebubekir
    Sozeri, Huseyin
    Uysal, Emre
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Synthesis and Characterization of High Catalytic Activity Magnetic Fe3O4 Supported Pd Nanocatalyst2013In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 26, no 1, p. 165-171Article in journal (Refereed)
    Abstract [en]

    This study reports the fabrication and characterization of magnetically recyclable catalysts of Fe3O4-Pd nanocomposite as highly effective catalysts for reduction reactions in liquid phase. The characterization of Fe3O4-Pd MRCs were done by X-ray powder diffraction, A +/- nfrared spectroscopy, thermal analyzer, transmission electron spectroscopy, A +/- nductively coupled plasma, UV-Vis spectroscopy, vibrating sample magnetometer, respectively. The reduction of Pd2+ was accomplished with polyethylene glycol 400 (PEG-400) and Fe3O4 nanoparticles were prepared by co-precipitation of FeCI(3)a <...6H(2)O and FeCl(2)a <...4H(2)O. Thus formed Fe3O4-Pd MRCs showed a very high activity in reduction reactions of 4-nitro-aniline and 1,3-di-nitrobenzene in liquid phase. Magnetic character of this system allowed recovery and multiple use without significant loss of its catalytic activity.

  • 22. Baykal, Abdulhadi
    et al.
    Kasapoglu, Nermin
    Durmus, Zehra
    Kavas, Hueseyin
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Koeseoglu, Yueksel
    CTAB-Assisted Hydrothermal Synthesis and Magnetic Characterization of NixCo1-xFe2O4 Nanoparticles (x=0.0, 0.6, 1.0)2009In: Turkish journal of chemistry, ISSN 1300-0527, E-ISSN 1303-6130, Vol. 33, no 1, p. 33-45Article in journal (Refereed)
    Abstract [en]

    Nickel ferrite, NixCo1-xFe2O4, NPs (where x = 0.0, 0.6 and 1.0) were successfully synthesized by a rapid and reproducible CTAB-assisted hydrothermal route. The influence of different hydrolyzing agents on the particle size and magnetic behavior of NixCo1-xFe2O4 NPs was investigated. Particles showed very high phase purity and crystallinity in powder XRD analysis. Compositions of Co, Fe, and Ni in fabricated powders were also determined by AAS and results are in very good agreement with the targeted compositions. Samples hydrolyzed using NH3 showed no significant changes in the particle size and morphology. NH3 hydrolyzed samples were much smaller than their NaOH hydrolyzed counterparts, which was attributed to the strength and concentration of the hydrolyzing agents, NH3 being about 6 times more concentrated than NaOH. This in turn influenced the nucleation rate thus the size of each nucleus formed. Strong temperature and Ni concentration dependence of magnetic parameters was observed. These samples are considered as promising materials for high density magnetic recording media.

  • 23. Baykal, Abdulhadi
    et al.
    Kavas, Hueseyin
    Durmus, Zehra
    Demir, Mine
    Kazan, Sinan
    Topkaya, Ramazan
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sonochemical synthesis and chracterization of Mn3O4 nanoparticles2010In: Central European Journal of Chemistry, ISSN 1895-1066, Vol. 8, no 3, p. 633-638Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of Mn3O4 nanoparticles (NPs) using a novel sonochemical method without requiring any pH adjustment. Synthesized material was identified as tetragonal hausmannite crystal structure model of Mn3O4 from XRD analysis. Crystallite size was estimated from x-ray line profile fitting to be 17 +/- 5 nm. FTIR analysis revealed stretching vibrations of metal ions in tetrahedral and octahedral coordination confirming the crystal structure. TEM analysis revealed a dominantly cubic morphology of NPs with an average size of similar to 20 nm. Magnetic evaluation revealed a blocking temperature, T-B of 40 K above which the material behaves paramagnetic. Asymmetric coercive field is attributed to the interaction between ferromagnetic Mn3O4 and antiferromagnetic Mn oxide at the surface of nanoparticles.

  • 24. Bertini, L
    et al.
    Stiewe, C
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Williams, S
    Platzek, D
    Mrotzek, A
    Zhang, Y
    Gatti, C
    Muller, E
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Rowe, M
    Nanostructured Co1-xNixSb3 skutterudites: Synthesis, thermoelectric properties, and theoretical modeling2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 1, p. 438-447Article in journal (Refereed)
    Abstract [en]

    Nanostructured skutterudite Co1-xNixSb3 has been synthesized by chemical alloying with Ni substitution for Co up to 27.5 at. %. High concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials and could thus increase their thermoelectric dimensionless figure-of-merit ZT. Material preparation comprises two key stages, coprecipitation of the precursor, and thermal processing to produce the skutterudite. By modeling the chemistry of the metal ions in aqueous solution, optimum coprecipitation conditions were achieved. The precipitated precursor consists of a solid solution of the different intermediate compounds, and exhibits high reactivity. Calcination and reduction of the precursor resulted in the alloying of these elements and in the formation of skutterudite at a temperature as low as 723-773 K. Unfilled CoSb3 skutterudites were prepared by chemical precipitation from aqueous solutions to achieve powders with a very small grain size (similar to40 nm). Compacted samples were produced from this powder by uniaxial pressing under various conditions. Thermal conductivity, electrical resistivity and Seebeck coefficient of the resulting compacts were measured in a temperature range from 150 to 575 K. Measurement procedures were standardized for absolute accuracy and reproducibility between the DLR, Cologne and NEDO, Cardiff Laboratories. It was found that the thermal conductivity can be decreased by almost an order of magnitude at the highest concentration of grain boundaries compared to highly annealed CoSb3. Scanning Seebeck microthermoprobe examination, facilitated spatially resolved measurement of Seebeck coefficient S, providing information on samples' homogeneity and on its effect on local S. Indications on the formation of an additional Ni containing phase were found. The electronic structure of Ni-doped skutterudites has been investigated by means of fully periodic density functional theory calculations and a topological analysis of the resulting electron densities. Ni substitution for Co doubles the electronic charge transfer from the pnicogen ring to the metal frame and fills the region of the CoSb3 band gap with occupied states, thus explaining the increase of electrical conductivity observed experimentally. The effect of the Ni substitution on the thermal conductivity is analyzed. The computed changes of the cell parameter with rising Ni content differ with those found by x-ray powder diffraction, thereby suggesting that the structural hypothesis of Ni replacing Co in the cubic frame of the skutterudite is only approximate or possibly incorrect.

  • 25. Bhattacharya, K.
    et al.
    El-Sayed, R.
    Andón, F. T.
    Mukherjee, S. P.
    Gregory, J.
    Li, H.
    Zhao, Yinchen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Seo, W.
    Fornara, A.
    Brandner, B.
    Toprak, Muhammet Sadaka
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Leifer, K.
    Star, A.
    Fadeel, B.
    Lactoperoxidase-mediated degradation of single-walled carbon nanotubes in the presence of pulmonary surfactant2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 91, p. 506-517Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes (CNTs) may elicit inflammatory responses following pulmonary exposure. Conversely, enzymatic biodegradation of CNTs by inflammatory cells has also been reported. The aim of this study was to study the degradation of oxidized single-walled CNTs (ox-SWCNTs) by lactoperoxidase (LPO), a secreted peroxidase present in the airways, and whether pulmonary surfactant affects this biodegradation. To this end, ox-SWCNTs were incubated in vitro with recombinant bovine LPO + H<inf>2</inf>O<inf>2</inf> + NaSCN in the presence and absence of porcine lung surfactant (Curosurf®) and biodegradation was monitored using UV-Vis-NIR spectroscopy, Raman spectroscopy, and scanning electron microscopy. The interaction of recombinant LPO with bundles of ox-SWCNTs was confirmed by atomic force microscopy. Cell-free biodegradation of ox-SWCNTs was also observed ex vivo in murine bronchoalveolar lavage fluid in the presence of H<inf>2</inf>O<inf>2</inf> + NaSCN. Our study provides evidence for biodegradation of ox-SWCNTs with a lung surfactant 'bio-corona' and expands the repertoire of mammalian peroxidases capable of biodegradation of ox-SWCNTs. These findings are relevant to inhalation exposure to these materials, as LPO serves as an important component of the airway defense system.

  • 26. Bhattacharya, Kunal
    et al.
    El-Sayed, Ramy
    Andon, Fernando T.
    Mukherjee, Sourav P.
    Gregory, Joshua
    Li, Hu
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Seo, Wanji
    Fornara, Andrea
    Brandner, Birgit
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Leifer, Klaus
    Star, Alexander
    Fadeel, Bengt
    Lactoperoxidase-mediated degradation of single-walled carbon nanotubes in the presence of pulmonary surfactant (vol 91, pg 506, 2015)2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 95, p. 766-766Article in journal (Refereed)
  • 27. Birsoz, B.
    et al.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of polypyrrole-BaFe12O19 nanocomposite2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 493, no 1-2, p. 481-485Article in journal (Refereed)
    Abstract [en]

    Polypyrrole-BaFe12O19 nanocomposite was successfully synthesized by an in situ polymerization of pyyrole in the presence of synthesized BaFe12O19 nanoparticles. Structural, morphological, electrical and magnetic properties of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, VSM and ac conductivity measurements respectively. XRD analysis reveals the inorganic phase as bariumhexaferrite and TGA shows about 22 wt% loading of hexaferrite in the nanocomposite. FT-IR analysis indicates a successful conjugation of hexaferrite particles with polypyrrole. Magnetization measurements show that polypyrrole coating decreases the saturation magnetization of BaFe12O19 significantly. This reduction has been explained by the pinning of the surface spins by the possible adsorption of non-magnetic ions during the polymerization process. Interactions between the hard and impurity phases, determined using the Stoner-Wohlfarth theory, reveal that particles' single domain character and the coating destabilizes the remanence state of the polypyrrole-BaFe12O19 nanocomposite.

  • 28.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Behi, Mohammadreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mirmohammadi, Seyed Aliakbar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Poth, H.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Shelf stability of nanofluids and its effect on thermal conductivity and viscosity2013In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 24, no 10, p. 105301-Article in journal (Refereed)
    Abstract [en]

    This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes' law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.

  • 29.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Anwar, Zahid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lumbreras, Itziar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Behi, Mohammadreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mirmohammadi, Seyed A.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Poth, Heiko
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Cooling performance of nanofluids in a small diameter tube2013In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 49, p. 114-122Article in journal (Refereed)
    Abstract [en]

    This article reports convective single-phase heat transfer performance in laminar flow for some selected nanofluids (NFs) in an open small diameter test section. A 0.50 mm inner diameter, 30 cm long stainless steel test section was used for screening single phase laminar convective heat transfer with water and five different water based NFs. Tested NFs were; Al2O3 (two types), TiO2 (two types) and CeO2 (one type), all 9 wt.% particle concentration. The effective thermal conductivity of the NFs were measured with Transient Plane Source (TPS) method and viscosity were measured with a rotating coaxial cylindrical viscometer. The obtained experimental results for thermal conductivity were in good agreement with the predicted values from Maxwell equation. The local Shah correlation, which is conventionally used for predicting convective heat transfer in laminar flow in Newtonian fluids with constant heat flux boundary condition, was shown to be valid for NFs. Moreover, the Darcy correlation was used to predict the friction factor for the NFs as well as for water. Enhancement in heat transfer for NFs was observed, when compared at equal Reynolds number, as a result of higher velocity or mass flow rate of the NFs at any given Reynolds number due to higher viscosity for NFs. However, when compared at equal pumping power no or only minor enhancement was observed.

  • 30.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ghadamgahi, Mersedeh
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems2013Conference paper (Refereed)
    Abstract [en]

    Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.

  • 31.
    Burks, Terrance
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Avila, Marta
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Akhtar, F.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Götelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Lansåker, P. C.
    Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Uheida, Abdusalam
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Studies on the adsorption of chromium(VI) onto 3-Mercaptopropionic acid coated superparamagnetic iron oxide nanoparticles2014In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 425, p. 36-43Article in journal (Refereed)
    Abstract [en]

    Chromium (Cr) in the form of Cr(VI) is deemed toxic in water due to its mutagenic and carcinogenic properties. For the successful removal of Cr(VI), we demonstrate a novel adsorbent consisting of superparamagnetic iron oxide nanoparticles (SPION) functionalized with 3-Mercaptopropionic acid (3-MPA). Fourier transform infrared spectroscopy (FT-IR) confirmed the functionalization of nanoparticles and presence of sulfonate groups. Batch adsorption experiments showed that the functionalized adsorbent recovered 45 mg of Cr(VI)/g of 3-MPA coated SPION at initial concentration of 50 mg/L aqueous solution at pH 1 with less than 1% of Fe dissolution from SPION. The results from X-ray photoelectron spectroscopy confirmed that Cr(VI) chemisorbed onto the adsorbent. Hence, the XPS spectra did not indicate any reduction of Cr(VI) to Cr(III) upon adsorption. The adsorption data were better fitted for the Freundlich model. Moreover, the Cr(VI) adsorption kinetics on functionalized SPION followed a pseudo-second order rate, revealing chemisorption as the dominant mechanism. The high Cr(VI) removal, rapid adsorption kinetics and stability of adsorbent indicate that 3-MPA coated SPION could be an efficient adsorbent for the removal of Cr(VI).

  • 32.
    Burks, Terrance
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Uheida, Abdusalam
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Eita, Mohamed
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Removal of Chromium(VI) Using Surface Modified Superparamagnetic Iron Oxide Nanoparticles2013In: Separation science and technology (Print), ISSN 0149-6395, E-ISSN 1520-5754, Vol. 48, no 8, p. 1243-1251Article in journal (Refereed)
    Abstract [en]

    This study describes the removal of Chromium(VI) from aqueous solutions using surface tailored superparamagnetic iron oxide nanoparticles (SPION) coated with bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex-301). The synthesized Cyanex-301 coated SPION has been characterized by Transmission Electron Microscopy (TEM), Fourier-Transfer Infrared Spectroscopy (FT-IR), X-ray Photonic Spectroscopy (XPS), and Thermogravimetric Analysis (TGA). The adsorption mechanism was proposed to be via complexation between the thiol group on Cyanex-301 and Cr(VI) ions based on the XPS and FTIR analysis. It has been found that the equilibrium can be attained in less than 2hr. The adsorption behavior of Cr(VI) on the Cyanex-301 coated SPION can be well described by the Langmuir model and the maximum adsorption capacity for Cr(VI) was estimated to be 30.8mg/g. The selectivity of the Cyanex-301 coated SPION adsorbent towards Cr(VI) ions was found to be high and the maximum loading capacity obtained is up to an order of magnitude higher than that of other adsorbents reported in the literature. The desorption studies showed that more than 70% of Cr(VI) can be recovered using HNO3 as eluting solution. Our findings suggest a high potential of the designed adsorbent material for the treatment of industrial wastewater containing Cr(VI).

  • 33. Christensen, M
    et al.
    Iversen, BB
    Bertini, L
    Gatti, C
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Nishibori, E
    Structural study of Fe doped and Ni substituted thermoelectric skutterudites by combined synchrotron and neutron powder diffraction and ab initio theory2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 6, p. 3148-3157Article in journal (Refereed)
    Abstract [en]

    We present neutron and synchrotron powder-diffraction investigations as well as ab initio calculations to elucidate delicate structural features in doped skutterudites. Samples with assumed Fe doping were investigated (FeyCo4Sb12, y=0.4, 0.8, 1.0, and 1.6), as well as samples with formal Ni substitution (Co4-xNixSb12, x=0, 0.4, 0.8, and 1.2). The present study serves as a case story for the determination of fine structural details of thermoelectric skutterudites by diffraction methods in combination with ab initio calculations. We illustrate the problem of fluorescence in the conventional x-ray powder diffraction on the Fe-doped samples by a comparison with the neutron powder-diffraction data. On the series of the Ni-substituted samples, the neutron powder-diffraction data were collected to investigate the exact sitting of the Ni. The sample with the highest Ni substitution (Co2.8Ni1.2Sb12) was also used for high resolution, high-energy synchrotron powder diffraction measurements. These revealed that the sample consists of two skutterudite phases. A complete description of the Ni-substituted samples was obtained in tandem with ab initio calculations, which show that the system contains a Ni-rich (Co0.38Ni3.62Sb12) and a Ni-poor (Co3.76Ni0.24Sb12)) skutterudite phases.

  • 34.
    Darab, Mahdi
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Syvertsen, Guttorm Ernst
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Nanoengineered BSCF Cathode Materials for Intermediate-Temperature Solid-Oxide Fuel Cells2009In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 156, no 8, p. K139-K143Article in journal (Refereed)
    Abstract [en]

    A recently reported promising cathode material for solid-oxide fuel cells (SOFCs), namely, BaxSr1-xCoyFe1-yO3-delta (BSCF) is fabricated in nanocrystalline form by a chemical alloying approach. The approach is comprised of solution chemical synthesis of a precursor and its thermochemical processing toward the desired phase. All the constituent elements, Ba, Sr, Co, and Fe, were coprecipitated from an aqueous solution of their salts to produce a precursor with a well-defined composition, fine particle size, high homogeneity, and high reactivity. After calcining and sintering at 1000 degrees C, the individual oxides were alloyed into nanostructured perovskite (with x=0.5 and y=0.2) Ba0.5Sr0.5Co0.2Fe0.8O3 of high purity. Spark plasma sintering was used for compaction to preserve the material's nanostructure, and sintered compacts demonstrated a significant increase in electrical conductivity values at temperatures up to 900 degrees C, compared to the earlier reports. The measured conductivity values are sufficiently high for cathode applications with a maximum of about 63 S cm(-1) at 430 degrees C in air and 25 S cm(-1) at 375 degrees C in N-2, respectively. These values are about twice as high as conventional BSCF mainly due to the reduction in interfacial resistance, implying a high promise for nanoengineered BSCF as cathode material at low or intermediate-temperature SOFCs.

  • 35. Deligoz, H.
    et al.
    Baykal, A.
    Senel, M.
    Sozeri, H.
    Karaoglu, E.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of poly(1-vinyltriazole)-grafted superparamagnetic iron oxide nanoparticles2012In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 162, no 7-8, p. 590-597Article in journal (Refereed)
    Abstract [en]

    We reported on the synthesis and detailed physicochemical characterization of poly(1-vinyltriazole)-grafted iron oxide nanoparticles. Superparamagnetic iron oxide nanoparticles (SPION) were fabricated by gel-to-crystalline conversion method. Telomerization of poly(1-vinyltriazole) on iron oxide nanoparticles was achieved via silanization process. XRD analysis confirmed the crystalline phase as magnetite, and FT-IR analysis confirmed the presence of PVTri on nanoparticles. Particle morphology was observed to be polygonic, due to the synthesis process, while average size estimated from TEM micrographs is 7 nm. Agreement between crystallite size estimated from XRD and particle size from TEM affirms single crystalline character of these nanoparticles. Dependence of conductivity on temperature showed a strong evidence for thermally activated polarization mechanism. Temperature and frequency dependence of dielectric permittivity revealed interfacial polarization and temperature-assisted-reorganization effects. Magnetic evaluation showed non-saturation and superparamagnetic characteristics of nanoparticles as well as magnetic particles being single domains.

  • 36. Deligoz, H.
    et al.
    Baykal, A.
    Tanriverdi, E. E.
    Durmus, Z.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis, structural and electrical properties of triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs2012In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 47, no 3, p. 537-543Article in journal (Refereed)
    Abstract [en]

    Triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs was synthesized by a glycothermal reaction. XRD analysis identified the product as Mn0.2Co0.8Fe2O4 with a high phase purity. Nano-sized particles with an average size of about 6-8 nm were obtained with nearly single crystalline nature with TEM analysis. Superparamagnetic-like behavior of TREG stabilized Mn0.2Co0.8Fe2O4 NPs was observed by VSM. The binding between TREG and Mn0.2Co0.8Fe2O4 NPs was investigated with FT-IR and found to be via O on the TREG and NP surface. TG analysis indicated that the Mn0.2Co0.8Fe2O4 NP content was about 40%, with a TREG-shell content to be around 60%. Overall conductivity of the nanocomposite is in the range of 10(-10) to 10(-7) S cm(-1) with a strong dependence on temperature and frequency, indicating ionic conductivity. The nanocomposite exhibited lower epsilon' and epsilon '' compared to TREG stabilized Mn0.2Co0.8Fe2O4 NPs due to the doping of co-doping of manganese and cobalt.

  • 37. Deligöz, H.
    et al.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Tanriverdi, E. E.
    Durmus, Z.
    Sözeri, H.
    Synthesis, structural, magnetic and electrical properties of Co 1-xZnxFe2O4 (x = 0.0, 0.2) nanoparticles2013In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 48, no 2, p. 646-654Article in journal (Refereed)
    Abstract [en]

    Co1-xZnxFe2O4 spinel nanoparticles with Zn concentrations of x = 0.0, 0.2 were prepared by a hydrothermal route in the presence of triethylene glycol (TEG). The structural, magnetic, electrical and dielectric properties of the prepared nanoparticles were studied. The XRD results confirmed the formation of single spinel ferrite structure with crystallite size 9 and 10 nm for x = 0.0 and 0.2 compositions respectively. The lattice parameter (a) increased with increasing Zn concentration. Temperature and frequency dependent electrical and dielectric properties of the prepared ferrites have also been investigated. Our findings show that overall conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle is lower than that of CoFe 2O4 and roughly in the range of 10-11-10 -7 S cm-1 depending strongly temperature and frequency owing to the formation of stable electric bonds between the Zn2+ and Fe2+ ions, which localizes Fe2+ charge carriers. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies, which is an indication of ionic conductivity. dc conductivity of Co0.8Zn0.2Fe 2O4 nanoparticle are found to obey the Arrhenius plot and can be classified into two regions over with activation energy of 0.113 and 0.163 eV in the ranges of 20-40 °C and 70-120 °C, respectively when CoFe2O4 has an activation energy of 0.245 eV.

  • 38.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, Rudolf
    EFFECT OF POLYMER BASED NANOCOMPOSITES ON THE ELECTRICAL ARCS IN AIR2015In: 2015 42ND IEEE INTERNATIONAL CONFERENCE ON PLASMA SCIENCES (ICOPS), ISSN 0730-9244Article in journal (Other academic)
  • 39.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gati, Rudolf
    ABB Switzerland.
    Toprak, Muhammet S.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Functional Materials, FNM.
    Engineered PMMA-CuO nanocomposites for improving the electric arc interruption process in electrical switching applicationsManuscript (preprint) (Other academic)
    Abstract [en]

    Polymer-based nanocomposites (PNCs) display fascinating functionalities to be useful in electrical switching applications like circuit breakers, switch gears, etc. These PNCs are fabricated by incorporating nanoparticles (NPs) into a polymer by in-situ polymerization. When the PNCs interrupt the high energetic fault currents generate between the two contacts in a circuit breaker, they outgas (ablation) chemical species and cooling gases, which change the thermodynamic properties of the arcing environment leading to quench the electrical arcs quickly. Two PNCs are fabricated with different wt% of oleic acid modified CuO NPs and a polymer matrix i.e. poly methyl methacrylate (PMMA). These PNCs are tested with the electrical arcs of a prospective current of 1.6 kA generated in the test-setup. The electrical signals (arc current and voltage) and computed dissipated enegy i.e., ∫𝑖(𝑡)𝑉(𝑡)𝑑𝑡 help to understand the effect of PNCs on the electrical arcs. In addition to that, the computed joule integral and mass loss of the PNCs due to outgassing is reported. The re-depositions of the chemical species are analyzed by using Fourier transform infrared spectroscopy (FTIR) and the morphological changes on the surface of outgassed PNCs are analyzed by using scanning electron microscopy (SEM). These results help to understand the effect of PNCs on the arc interruption process in circuit breakers.

  • 40.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bissai, A.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, R.
    Spectroscopic investigations of the ablated species from the polymers exposed to electric arcs in air2015In: 2015 3rd International Conference on Electric Power Equipment - Switching Technology, ICEPE-ST 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 337-340Conference paper (Refereed)
    Abstract [en]

    Polymeric walls have been widely used in the last decades to improve the arc interruption process in electrical switching applications. This improvement is achieved by the evaporation (ablation) of the polymeric walls due to the highly energetic radiation generated by the electrical arcs. This experimental study deals with polymeric walls that are exposed to the electrical arcs generated between a 5 mm air gap with prospective current of 1.4 kA. In this paper, two different techniques are discussed aiming at the identification of the dominant ablated species produced during the arc interruption process, namely Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis coupled with Fourier transform infrared analysis of evolved gases (EGA). In addition, the morphological and chemical changes on the surface of the exposed polymeric walls are analyzed by microscopical techniques.

  • 41.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, R.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    On the electrical arc interruption by using PMMA/iron oxide nanocomposites2016In: Materials Research Express, ISSN 2053-1591, Vol. 3, no 10, article id 105043Article in journal (Refereed)
    Abstract [en]

    An experimental study is undertaken on the fabrication of poly (methyl methacrylate) (PMMA)/iron oxide nanocomposites to determine their potential use for electrical arc interruption in the electrical switching applications such as circuit breakers. Monodisperse iron oxide nanoparticles of average size ¡«11 nmare synthesized via thermal decomposition method and then homogeneously dispersed in the PMMAmatrix by in situ polymerization.PMMA/iron oxide nanocomposites with different nanoparticle loading have been fabricated to study the effect of loading content on the thermal energy absorption. Detailed physicochemical characterizations on synthesized material are performed using X-ray powder diffraction, scanning electron microscopy, TEM, thermogravimetric analysis and differential scanning calorimetry at different processing stages. Atest-setup was designed to evaluate the quality of the nanocomposites for electric arc interruption capability. The results showed that PMMA/iron oxide nanocomposites have a clear impact on the electric arc interruption and therefore should be considered as promising candidates for electrical switching applications.

  • 42.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, R.
    Toprak, Muhammet Sadaka
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Engineered PMMA-ZnO nanocomposites for improving the electric arc interruption capability in electrical switching applications: Unprecedented experimental insights2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 141, p. 113-119Article in journal (Refereed)
    Abstract [en]

    Polymer inorganic nanocomposites (PINCs) have been engineered for controlling the electrical arc and to improve the arc interruption capability of the electrical switching applications, like circuit breakers. Several PINCs are fabricated by formation of ZnO quantum dots (QDs) in a poly (methyl methacrylate) (PMMA) matrix via in-situ polymerization method to avoid agglomeration of QDs, leading to a good spatial distribution of QDs in the polymer matrix. These PINCs have been characterized in detail for the morphology of QDs, interaction between QDs and polymer matrix, and ultraviolet (UV) radiation absorption. ZnO QDs have been assessed to have particle diameter of 3.5 nm, and their presence in the PMMA is revealed by the unique luminescence characteristics of the QDs under UV light. The presence of ZnO QDs broadened the range of UV radiation absorption of PMMA and the absorption edge is gradually shifted from 270 nm to 338 nm with step-wise loading of ZnO QDs. The PINCs are tested to determine their reproducibility and impact on the electrical arcs of current 1.6 kA generated using a specially designed test-setup. Interaction of PINCs with the electrical arcs generates ablation of chemical species towards core of the electrical arc, resulting in increase of voltage leading to cool-down the arc temperature. This experimental study demonstrates for the first time that these PINCs are reproducible, reliable and provides superior arc interruption capability.

  • 43.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, Rudolf
    ABB Switzerland.
    Toprak, Muhammet Sadaka
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    New experimental insights for controlling the electrical arcs in electrical switching applications: a comparative study on PMMA nanocomposites of Au and ZnO2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050Article in journal (Other academic)
    Abstract [en]

    Polymer inorganic nanocomposites (PINCs) are developed, not only due to scientific interest but also improving theelectric arc interruption process in the electrical switching applications like circuit breakers. The novelty of this work isin integrating the current developments in PINCs into electrical switching application in order to extend the limits of thepower switching devices. Several PINCs are fabricated by using pre-synthesized Au nanoparticles (NPs) of size 2.75 ±0.4 nm and poly (methyl methacrylate) (PMMA) matrix via in-situ polymerization method. Six homogeneous PINCsamples with ultra-low wt% of Au NPs varying from 0.0003 to 0.005 wt% have been fabricated. We find that thepresence of Au NPs improved the convective heat transfer and visible optical radiation absorption of PMMA. Thefabricated PINCs are tested for their arc interruption performance and the results are compared with ZnO PINCs in ourearlier work. The results of the experiments insights demonstrate the impact of PINCs on the electrical arcs and theirpotential advantages of having PINCs for the electric arc interruption process in high power switching devices.

  • 44.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Gati, R.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications2015In: Powder metallurgy and metal ceramics, ISSN 1068-1302, E-ISSN 1573-9066, Vol. 54, no 7-8, p. 397-401Article in journal (Refereed)
    Abstract [en]

    Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5-6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

  • 45.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Pinos, Andrea
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Li, Shanghua
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. Helsinki University of Technology, Finland.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Measurement of radiative lifetime in CdSe/CdS core/shell structured quantum dots2009In: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009, 2009, p. 5377385-Conference paper (Refereed)
    Abstract [en]

    Radiative lifetime of chemically synthesized colloidal CdSe/CdS core/shell quantum dots is measured. Influence of the core size on the electron-hole pair separation is analyzed. A long radiative lifetime and the existence of electron-hole pair separation suggest high potential of these dots as gain material to achieve lasing under continuous-wave excitation.

  • 46.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Hu, Jun
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhou, Sicheng
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Shanghua
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 1, p. 105-109Article in journal (Refereed)
    Abstract [en]

    Spherical CdSe-CdS core-shell quantum dots (QDs) are found to be flexible in the transition between the type-I regime and the type-II regime with different core/shell dimensions. The quasi-type-II feature of the colloidal dots is confirmed with time-resolved photoluminescence (PL) measurements. Two recombination paths of the excitons with significantly different decay rates are observed and analyzed. The spherical CdSe-CdS core-shell QDs are numerically simulated to investigate the carrier separation. A relatively long radiative lifetime and high degree of spatial carrier separation provide good potential to achieve lasing under continuous-wave excitation. Amplified spontaneous emission at room temperature is detected from the QDs embedded in the polymer matrix. It is shown that a larger shell thickness results in a lower pumping threshold, while a smaller shell thickness leads to higher PL efficiency.

  • 47. Durmus, Z.
    et al.
    Baykal, A.
    Sozeri, H.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Preparation of PVP (Polyvinyl Pyrrolidone)/Ba-Sr hexaferrites via gel to crystalline method2012In: Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, ISSN 1553-3174, Vol. 42, no 10, p. 1390-1397Article in journal (Refereed)
    Abstract [en]

    Ba-M- and Sr-M-type hexagonal ferrites have been prepared via a sol-gel route, and the effects of adding different amounts of polyvinyl pyrrolidone (PVP) into the sol solutions. The average crystallite, size, D and σ, was obtained as for Z13 = 22 ± 2 nm and Z13-2 = 16 ± 3 nm and for Z16 = 18 ± 7 nm and Z16-2 = 17 ± 5 nm by XRD. FT-IR and TG analysis were used to prove the presence of PVP on BaFe12O19 and SrFe12O19. Based on the TGA curves the mass losses of the samples are assessed as follows: Z13 ̃15%, Z13-2 ̃25%, Z16 ̃5%, and Z16-2 ̃10%.

  • 48. Durmus, Z.
    et al.
    Erdemi, H.
    Aslan, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sozeri, H.
    Baykal, A.
    Synthesis and characterization of poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite2011In: Polyhedron, ISSN 0277-5387, E-ISSN 1873-3719, Vol. 30, no 2, p. 419-426Article in journal (Refereed)
    Abstract [en]

    Poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of PVPA. Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA and conductivity measurements respectively. The capping of PVPA around the Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the phosphate and the nanoparticle surface. The crystallite and particle size were obtained as 6 +/- 2 and 8.7 +/- 0.1 nm from XRD line profile fitting and TEM image analysis respectively, which reveal nearly single crystalline nature of the Fe3O4 nanoparticles. Magnetic characterization of the bulk magnetite and (PVPA)-Fe3O4 nanocomposite reveals that both are in the superparamagnetic state at room temperature. The average magnetic domain size of the nanoparticles has been calculated using the Langevin function, which was fitted to the measured M-H hysteresis curves as 7.6 nm for the nanocomposite. In the nanocomposite, the reduction is due to the adsorption of PVPA onto the magnetite surface, which cancels some of the free spins at the surface causing a magnetically dead layer. Analysis of the conductivity and permittivity measurements revealed the coupling of ionic and polymer segmental motions and strong temperature dependency in the nanocomposite.

  • 49. Durmus, Z.
    et al.
    Kavas, H.
    Baykal, A.
    Sozeri, H.
    Alpsoy, L.
    Celik, S. U.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis and characterization of L-carnosine coated iron oxide nanoparticles2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 5, p. 2555-2561Article in journal (Refereed)
    Abstract [en]

    L-Carnosine coated iron oxide nanoparticles (CCIO NPs) have been prepared via co-precipitation of iron oxide in the presence of L-carnosine. Crystalline phase was identified as magnetite with an average crystallite size of 8 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM by log-normal fitting was similar to 11 nm. FTIR analysis showed that the binding of carnosine onto the surface of iron oxide is through unidentate linkage of carboxyl group. CCIO NPs showed superparamagnetic charactersitic at room temperature. The magnetic core size of superparamagnetic CCIO NPs was found slightly smaller than the size obtained from TEM, due to the presence of magnetically dead layer. Magnetization measurements revealed that L-carnosine iron oxide composite has immeasurable coercivity and remanence with absence of hysteritic behavior, which implies superparamagnetic behavior at room temperature. The low value of saturation magnetization compared to the bulk magnetite has been explained by spin canting. LDH activity tests showed slight cytotoxicity of high dose of CCIO NPs. The ac conductivity of CCIO NPs was found to be greater than that of carnosine and the effective conduction mechanism was found as correlated barrier hopping (CBH). dc activation energy of the product at around room temperature was measured as 0.312 eV which was in good agreement with the earlier reports.

  • 50.
    Durmus, Z.
    et al.
    Fatih Univ, Istanbul, Turkey .
    Kavas, H.
    Gebze Inst Technol, Izmit, Turkey .
    Sozeri, H.
    Natl Metrol Inst, Gebze, Turkey .
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Aslan, A.
    Fatih Univ, Istanbul, Turkey .
    Baykal, A.
    Fatih Univ, Istanbul, Turkey .
    Poly(vinyl phosphonic acid) (PVPA)-BaFe12O19 Nanocomposite2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 4, p. 1185-1193Article in journal (Refereed)
    Abstract [en]

    We present a method for the fabrication of PVPA/BaFe12O19 nanocomposite by in-situ polymerization of vinyl phosphonic acid, VPA in the presence of synthesized BaFe12O19 NPs. Nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, SEM, TEM, VSM, and conductivity techniques for structural and physicochemical characteristics. Nanoparticles, identified as BaFe12O19 from XRD analysis, were successfully coated with PVPA and the linkage was assessed to be via P-O bonds. Electron microscopy analysis revealed aggregation of BaFe12O19 particles and dominantly platelet morphology upon composite formation. TGA analysis revealed the composition of the nanocomposite as 65% BaFe12O19 and 35% polymer. Magnetic evaluation revealed that adsorption of PVPA anions during the preparation of the nanocomposite strongly influenced the magnetic properties resulting in much lower saturation magnetization values. DC conductivity measurements were used to calculate activation energy of PVPA/BaFe12O19 nanocomposite and it was obtained as 0.37 eV.

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