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  • 251. Zanonato, P.L.
    et al.
    Szabó, Zoltan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Vallet, V.
    Di Bernardo, P.
    Grenthe, Ingmar
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Alkali-metal ion coordination in uranyl(VI) poly-peroxo complexes in solution, inorganic analogues to crown-ethers. Part 2. Complex formation in the tetramethyl ammonium-, Li+-, Na+- and K+-uranyl(VI)-peroxide-carbonate systems2015Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, nr 37, s. 16565-16572Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The constitution and equilibrium constants of ternary uranyl(VI) peroxide carbonate complexes [(UO2)(p)(O-2)(q)(CO3)(r)](2(p-q-r)) have been determined at 0 degrees C in 0.50 M MNO3, M = Li, K, and TMA (tetramethyl ammonium), ionic media using potentiometric and spectrophotometric data; O-17 NMR data were used to determine the number of complexes present. The formation of cyclic oligomers, "[(UO2)(O-2)(CO3)](n)", n = 4, 5, 6, with different stoichiometries depending on the ionic medium used, suggests that Li+, Na+, K+ and TMA ions act as templates for the formation of uranyl peroxide rings where the uranyl-units are linked by mu-eta(2)-eta(2) bridged peroxide-ions. The templating effect is due to the coordination of the M+-ions to the uranyl oxygen atoms, where the coordination of Li+ results in the formation of Li[(UO2)(O-2)(CO3)](4)(7-), Na+ and K+ in the formation of Na/K[(UO2)(O-2)(CO3)](5)(9-) complexes, while the large tetramethyl ammonium ion promotes the formation of two oligomers, TMA[(UO2)(O-2)(CO3)] 5 9-and TMA[(UO2)(O-2)(CO3)](6)(11-). The NMR spectra demonstrate that the coordination of Na+ in the five-and six-membered oligomers is significantly stronger than that of TMA(+); these observations suggest that the templating effect is similar to the one observed in the synthesis of crown-ethers. The NMR experiments also demonstrate that the exchange between TMA[(UO2)(O-2)(CO3)](5)(9-) and TMA[(UO2)(O-2)(CO3)](6)(11-) is slow on the O-17 chemical shift time-scale, while the exchange between TMA[(UO2)(O-2)(CO3)](6)(11-)and Na[(UO2)(O-2)(CO3)](6)(11-) is fast. There was no indication of the presence of large clusters of the type identified by Burns and Nyman (M. Nyman and P. C. Burns, Chem. Soc. Rev., 2012, 41, 7314-7367) and possible reasons for this and the implications for the synthesis of large clusters are briefly discussed.

  • 252.
    Zhang, Biaobiao
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi.
    Why nature chose the Mn4CaO5 cluster as water-splitting catalyst in photosystem II: a new hypothesis for the mechanism of O-O bond formation2018Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, nr 41, s. 14381-14387Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Resolving the questions, namely, the selection of Mn by nature to build the oxygen-evolving complex (OEC) and the presence of a cubic Mn3CaO4 structure in OEC coupled with an additional dangling Mn (Mn4) via mu-O atom are not only important to uncover the secret of water oxidation in nature, but also essential to achieve a blueprint for developing advanced water-oxidation catalysts for artificial photosynthesis. Based on the important experimental results reported so far in the literature and on our own findings, we propose a new hypothesis for the water oxidation mechanism in OEC. In this new hypothesis, we propose for the first time, a complete catalytic cycle involving a charge-rearrangement-induced Mn-VII-dioxo species on the dangling Mn4 during the S-3 -> S-4 transition. Moreover, the O-O bond is formed within this Mn-VII-dioxo site, which is totally different from that discussed in other existing proposals.

  • 253.
    Zhang, Linlin
    et al.
    Dalian University of Technology, China.
    Gao, Y.
    Dalian University of Technology, China.
    Liu, Z.
    Dalian University of Technology, China.
    Ding, X.
    Dalian University of Technology, China.
    Yu, Z.
    Dalian University of Technology, China.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. Dalian University of Technology, China.
    A trinuclear ruthenium complex as a highly efficient molecular catalyst for water oxidation2016Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, nr 9, s. 3814-3819Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A trinuclear ruthenium complex, 3, was designed and synthesized with the ligand 2,2'-bipyridine-6,6'-dicarboxylic acid (bda) and we found that this complex could function as a highly efficient molecular catalyst for water oxidation in homogeneous systems. This trinuclear molecular water oxidation catalyst, 3, displayed much higher efficiencies in terms of turnover numbers and initial oxygen evolution rate than its counterparts, a binuclear catalyst, 2, and a mononuclear catalyst, 1, in both chemically driven and photochemically driven water oxidation based on either the whole catalytic molecules or just the active Ru centers. The reasons for the superior performance of catalyst 3 were discussed and we believe that multiple Ru centers in a single molecule are indeed beneficial for increasing the probability of the formation of O-O bonds through an intramolecular radical coupling pathway.

  • 254. Zhang, Pan
    et al.
    Wang, Mei
    Na, Yong
    Li, Xueqiang
    Jiang, Yi
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Homogeneous photocatalytic production of hydrogen from water by a bioinspired Fe2S2 catalyst with high turnover numbers2010Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, nr 5, s. 1204-1206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three-component homogeneous catalyst system, composed of a cyclometalated iridium(III) photosensitizer, a bioinspired diiron complex, and TEA in aqueous acetone, proved to be catalytically active for photoinduced H-2 production, with up to 660 turnovers over 8 h of irradiation.

  • 255.
    Zhang, Wei
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Sadollahkhani, Azar
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Li, Yuanyuan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Leandri, Valentina
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Gardner, James M.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Mechanistic Insights from Functional Group Exchange Surface Passivation: A Combined Theoretical and Experimental Study2019Inngår i: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, nr 4, s. 2723-2733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Four different functional groups including amino (-NH2), phosphine (-PH2), hydroxyl (-OH), and thiol (-SH) were combined with POSS (polyhedral oligomeric silsesquioxane) molecules to investigate how functional groups affect the surface passivation of POSS systems. Results from density-functional theory (DFT) calculations indicate that functional group amino (-NH2) with adsorption energy 86 (56) kJ mol(-1) is consistently better than that of thiol (-SH) with adsorption energy 68 (43) kJ mor(-1) for different passivation mechanisms. Theoretical studies on the analogous POSS-OH and POSS-PH2 systems show similar adsorption energies. Two of the systems were also investigated experimentally; aminopropyl isobutyl POSS (POSS-NH2) and mercaptopropyl isobutyl POSS (POSS-SH) were applied as passivation materials for MAPbI(3) (MA = methylammonium) perovskite and (FA)(0.85)(MA)(0.15)Pb(I-3)(0.85)(Br-3)(0)(.15)(FA = formamidinium) perovskite films. The same conclusion was drawn based on the results from contact angle studies, X-ray diffraction (XRD), and the stability of solar cells in ambient atmosphere, indicating the vital importance of choice of functional groups for passivation of the perovskite materials.

  • 256.
    Zhang, Wenhua
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    First Principles Studies on Chemical and Electronic Structures of Adsorbates2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, we focus on theoretical study of adsorbates on metal and oxide surfaces that are important for surface chemistry and catalysis. Based on first principles calculations, the adsorption ofCO, NO, NO2, C4H6S2, C22H27SH and other molecules or radicals on nobel metal surfaces (gold and silver) are investigated. Also, NO oxidation on oxygen pre-covered Au(111)surface and CO oxidation on water-oxygen covered Au(111)surface aretheoretically studied. A new mechanism of water-enhanced COoxidation is proposed. As for oxide surfaces, we first investigatethe geometric, electronic and magnetic structures of FeO ultrathin film on Pt(111) surface. The experimentally observed scanning tunneling microscopy images are well reproduced for the first timewith our model. The adsorption and dissociation of water on rutileTiO2(110) surface are investigated by quantum molecular dynamics.By theoretical X-ray photoemission spectroscopy (XPS) calculations,the surface species are properly assigned. The same strategy has applied to the study of the phase transition of water covered reconstructed anatase TiO2(001) surface, from which two different phases are theoretically identified. The structure of graphene oxideis also studied by comparing experimental and theoretical XPS spectra. Based on the novel structures identified, a new cutmechanism of graphene oxide is proposed.

  • 257.
    Zhao, Zhe
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Öijerholm, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Pan, Jinshan
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Microstructure and electrical conductivity of yttria stabilized zirconia ceramics sintered by spark plasma sintering: Part I. 3Y-TZPInngår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689Artikkel i tidsskrift (Annet vitenskapelig)
  • 258. Zheng, D.
    et al.
    Wang, M.
    Chen, L.
    Wang, N.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Redox reactions of [FeFe]-hydrogenase models containing an internal amine and a pendant phosphine2014Inngår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, nr 3, s. 1555-1561Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A diiron dithiolate complex with a pendant phosphine coordinated to one of the iron centers, [(μ-SCH2)2N(CH2C 6H4-o-PPh2){Fe2(CO)5}] (1), was prepared and structurally characterized. The pendant phosphine is dissociated together with a CO ligand in the presence of excess PMe3, to afford [(μ-SCH2)2N(CH2C 6H4-o-PPh2){Fe(CO)2(PMe 3)}2] (2). Redox reactions of 2 and related complexes were studied in detail by in situ IR spectroscopy. A series of new Fe IIFeI ([3]+ and [6]+), Fe IIFeII ([4]2+), and FeIFe I (5) complexes relevant to Hox, Hox CO, and Hred states of the [FeFe]-hydrogenase active site were detected. Among these complexes, the molecular structures of the diferrous complex [4]2+ with the internal amine and the pendant phosphine co-coordinated to the same iron center and the triphosphine diiron complex 5 were determined by X-ray crystallography. To make a comparison, the redox reactions of an analogous complex, [(μ-SCH2)2N(CH 2C6H5){Fe(CO)2(PMe 3)}2] (7), were also investigated by in situ IR spectroscopy in the absence or presence of extrinsic PPh3, which has no influence on the oxidation reaction of 7. The pendant phosphine in the second coordination sphere makes the redox reaction of 2 different from that of its analogue 7.

  • 259.
    Zhou, Ying
    et al.
    Shanghai Jiao Tong Univ, Minist Educ, Key Lab Thin Film & Microfabricat, Sch Chem & Chem Engn, Shanghai 200240, Peoples R China..
    Zhang, Zhao-Yang
    Shanghai Jiao Tong Univ, Minist Educ, Key Lab Thin Film & Microfabricat, Sch Chem & Chem Engn, Shanghai 200240, Peoples R China..
    Huang, Xianhui
    Shanghai Jiao Tong Univ, Minist Educ, Key Lab Thin Film & Microfabricat, Sch Chem & Chem Engn, Shanghai 200240, Peoples R China..
    Li, Jiantong
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Li, Tao
    Shanghai Jiao Tong Univ, Minist Educ, Key Lab Thin Film & Microfabricat, Sch Chem & Chem Engn, Shanghai 200240, Peoples R China..
    Versatile Functionalization of Carbon Nanomaterials by Ferrate(VI)2020Inngår i: NANO-MICRO LETTERS, ISSN 2311-6706, Vol. 12, nr 1, artikkel-id 32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As a high-valent iron compound with Fe in the highest accessible oxidation state, ferrate(VI) brings unique opportunities for a number of areas where chemical oxidation is essential. Recently, it is emerging as a novel oxidizing agent for materials chemistry, especially for the oxidation of carbon materials. However, the reported reactivity in liquid phase (H2SO4 medium) is confusing, which ranges from aggressive to moderate, and even incompetent. Meanwhile, the solid-state reactivity underlying the “dry” chemistry of ferrate(VI) remains poorly understood. Herein, we scrutinize the reactivity of K2FeO4 using fullerene C60 and various nanocarbons as substrates. The results unravel a modest reactivity in liquid phase that only oxidizes the active defects on carbon surface and a powerful oxidizing ability in solid state that can open the inert C=C bonds in carbon lattice. We also discuss respective benefit and limitation of the wet and dry approaches. Our work provides a rational understanding on the oxidizing ability of ferrate(VI) and can guide its application in functionalization/transformation of carbons and also other kinds of materials.

  • 260.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Qin, Haiying
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Single-component and three-component fuel cells2011Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, nr 15, s. 6362-6365Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Single-component and three-component fuel cell devices have been studied using mixed ionic and electronic conductor. The three-component fuel cell means a conventional fuel cell which is the configuration consists of anode, electrolyte and cathode; while the single-component fuel cell uses only one component that can function as the electrodes and electrolyte simultaneously. The single-component fuel cell showed the same or even better performance compared to conventional three-component fuel cell. A maximum power density of 700 mW cm(-2) has been achieved by the single-component fuel cell at 550 degrees C.

  • 261.
    Åkerstedt, Josefin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Subvalent Cluster Compounds and Synthesis in Alternative Reaction Media2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    With the aim of finding alternative reaction media for the synthesis of subvalent main group and transition metal cluster compounds, traditionally made through solid state reactions or in superacidic media, different alternative reaction media have been explored in this work. Room-temperature ionic liquids are amongst the more unconventional reaction media used. The syntheses performed have been aimed at both anionic and cationic cluster and the main tools used for characterization have been different X-ray diffraction and spectroscopic techniques.

    Selected ionic liquids have along with dichloromethane been shown to work as alternative reaction media for room temperature synthesis of the Bi5[GaCl4]3 salt. The salt containing the subvalent naked bismuth polycation Bi5 3+ was isolated from reduction reactions of BiCl3 in Ga/GaCl3-dichloromethane respectively Ga/GaCl3-ioinc liquid media. Three different classes of ionic liquids based on phosphonium-, imidazolium- and pyrrolidinium- salts have been used in synthesis. Homopolyatomic clusters from the lighter Group 15 element arsenic have also been studied. Solutions from the oxidative and reductive reaction routes of arsenic and AsCl3 in Lewis acidic toluene media were studied by EXAFS spectroscopy. The results were evaluated using molecular dynamics simulations of arsenic clusters. A discussion on how the calculated As4 cluster model relates to the experimental data resulted from this study.

    In terms of homopolyatomic anionic clusters the [K+(2,2,2-crypt)]2Ge9 2- compound containing the naked Ge9 2- anionic cluster has been isolated. The crystallographic investigation of [K+(2,2,2-crypt)]2Ge9 2- shows Zintl cluster anion Ge9 2- to be tricapped trigonal-prismatic with a symmetry very close to D3h. A chemical bonding analysis reveals two local minima of D3h symmetry and the cluster interaction scheme to be based on highly delocalised bonding.

    Ligand supported transition metal clusters from tungsten and palladium have also been prepared. Reduction of WCl6 in a reaction mixture of ionic liquid and co-solvent toluene resulted in tritungsten decachloride; W3Cl10(MeCN)3, being formed. Furthermore, palladium sandwich compounds; [Pd2(Ga2Cl7)(C7H8)2], [Pd2(GaCl4)(C9H12)2]∙C9H12 and [Pd2(Ga2Cl7)(C6H5Cl)2] have been prepared using GaCl3-arene reaction media.

  • 262.
    Åkerstedt, Josefin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Gorlov, Mikhail
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Fischer, Andreas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630).
    Synthesis and characterization of binuclear palladium(I) compounds and the influence of competing arenes2010Inngår i: Journal of Organometallic Chemistry, ISSN 0022-328X, E-ISSN 1872-8561, Vol. 695, nr 10-11, s. 1513-1517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The binuclear palladium(I) compounds, [Pd-2(Ga2Cl7)(2)(C7H8)(2)] (1), [Pd-2(GaCl4)(2)(C9H12)(2)]center dot C9H12 (2) and [Pd-2(Ga2Cl7)(2)(C6H5Cl)(2)] (3), have been prepared from palladium(II) chloride in gallium(III) chloride-arene reaction media. All isolated crystalline solids (1, 2 and 3) have been structurally characterized by single crystal X-ray diffraction and Raman spectroscopy. The results form quantum chemical calculations on the interaction energies of the arenes and the dipalladium unit of these compounds is also presented.

  • 263.
    Åkerstedt, Josefin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Zaffaroni, Riccardo
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Dichloromethane as solvent for the synthesis of polycationic clusters at room temperature: a link to standard organometallic chemistry2010Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, nr 35, s. 8132-8134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dichloromethane (DCM), CH2Cl2 has been identified as an alternative reaction medium for room-temperature synthesis of subvalent homopolyatomic clusters of the group 15 element bismuth.

  • 264.
    Öijerholm, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Ionic Transport in Metal Oxides Studied in situ by Impedance Spectroscopy and Cyclic Voltammetry2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Ionic transport in metal oxides is crucial for the functioning of a broad range of different components, such as heat resistant alloys designed for high temperature applications and oxide electrolytes in solid oxide fuel cells. This thesis presents results from in situ electrochemical studies of properties related to ionic transport in metal oxides that are important for their applications as protective oxides and ionic conductors.

    Heat resistant alloys of alumina-former type are known to form an adherent, slowly growing and protective aluminium oxide (Al2O3) scale that protects metals from chemical degradation at high temperature. In situ impedance spectroscopy was used to study highly pure and dense samples of a-alumina in the temperature range 400 – 1000 °C. It was shown that surface conduction on the sample could severely distort the measurement below 700 °C. The magnitude of the distortions appeared to be sensitive to the type of electrodes used. The use of a so-called guard electrode was shown to effectively block the surface conduction in the measurements. By varying the grain size of the sintered alpha-alumina samples, the influence of grain size on the overall conductivity of the a-alumina was studied. It was shown that the activation energy for conductivity increased as the grain size decreased. Molecular dynamics calculations were performed in order to elucidate whether Al- or O ions are dominant in the ionic conductivity of the alpha-alumina. Comparing the calculation and experimental results, the dominating charge carrier was suggested to be oxygen ions.

    Moreover, the ionic transport in thermally grown alumina-like oxide scales formed on a FeCrAl alloy was studied in situ by impedance spectroscopy between 600 and 1000 °C. It was shown that the properties of these scales differ largely from those of pure and dense alpha-alumina. Furthermore, the conductivity is mainly electronic, due to the multiphase/multilayer microstructure and substantial incorporation of species from the base metal. However, the diffusivity obtained from the ionic conductivity was in line with diffusion data in literature obtained by other methods such as thermogravimetry. Besides, the initial stage of oxidation of a number of Fe-, Ni- and Co-based alloys at temperatures between 500 and 800 °C was studied in situ by high temperature cyclic voltammetry, in which the oxygen activity was changed over a wide range. From the resulting voltammograms the redox reactions occurring on the alloy surface could be identified. It was concluded that the base metal oxidized readily on these alloys before a protective chromia- or alumina-like scale is formed. The base metal oxide is most likely incorporated into the more protective oxide.

    Further, the oxygen ionic conductivity of highly pure and fully dense yttria-stabilized zirconia produced by spark plasma sintering was studied by impedance spectroscopy. The aim was to evaluate intrinsic blocking effects on the ionic conduction associated with the space charge layer in the grain boundary region. It was observed that the ionic conductivity of the spark plasma sintered oxides is equal or slightly higher than what has been achieved by conventional sintering methods. In addition, it was shown that the specific grain boundary conductivity increases with decreasing grain size, which can be explained by a decreasing Schottky barrier height (i.e., decreasing blocking effect). The quantitative results from this work verify the space charge model describing the influence of grain size on the ionic conductivity of yttria-stabilized zirconia through dopant segregation and oxygen vacancy depletion along the grain boundaries.

  • 265.
    Öijerholm, Johan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Fafilek, Günter
    Pan, Jinshan
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Cyclic Voltammetry Study of the Early Stage of High Temperature Oxidation of Fe-, Co- and Ni-based alloysInngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111Artikkel i tidsskrift (Annet vitenskapelig)
  • 266.
    Öijerholm, Johan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    Fafilek, Günter
    Institute of Chemical Technology and Analytics, University of Technology of Vienna.
    Pan, Jinshan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    Study of Initial Oxidation of Engineering Alloys by High Temperature Cyclic Voltammetry2007Inngår i: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 10, nr 6, s. 47-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial oxidation of Fe-, Co-, and Ni-based engineering alloys was studied in situ by high-temperature cyclic voltammetry. Measurements were performed at constant temperatures between 500 and 800 degrees C in an electrochemical cell utilizing oxygen ion-conducting yttria-stabilized zirconia as electrolyte and a reference electrode whose potential is determined by the oxygen activity in the ambient gas. The recorded voltammograms show clear current peaks that are associated with the oxidation of the base metal in the investigated alloys. For the Fe- based alloy, multiple peaks are observed, showing oxidation of Fe into different valence oxides. The results indicate that the base metal oxide is formed in the initial oxidation process of these engineering alloys, which may influence long-term high-temperature oxidation resistance of the alloys.

  • 267.
    Öijerholm, Johan
    et al.
    KTH, Tidigare Institutioner, Materialvetenskap.
    Pan, Jinshan
    KTH, Tidigare Institutioner, Materialvetenskap.
    Jönsson, Bo
    Kanthal AB, Hallstahammar.
    Influence of Grain Size on Ionic Conductivity of Pure and Dense alpha-Al2O3 in the Temperature Range 400-1000 degrees C2004Inngår i: High Temperature Corrosion And Protection Of Materials 6, Prt 1 And 2, Proceedings, 2004, Vol. 461-464, nr II, s. 865-872Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ionic transport in alpha-Al2O3 at high temperatures is important for oxidation/corrosion resistance of Al2O3-forming heat resistant alloys. Whereas most of previous studies were performed at temperatures above 1000degreesC, this work concerns the temperature range 400 to 1000degreesC. Electrical proper-ties of polycrystalline and single crystal alpha-Al2O3 were measured in air by using impedance spectroscopy in order to study the ionic transport in Al2O3. The influence of grain size was investigated by measurements on a series of highly pure and dense samples with well-defined grain size ranging from 0.5 to 15 mum, produced by the spark plasma sintering technique. The results show that the grain size has a certain influence on the conductivity in the temperature range between 650 and 1000degreesC, where the activation energy for conductivity decrease from 2.4 to 1.6 eV with increasing grain size. At lower temperatures the activation energy is about 1.0 eV and independent of the grain size, indicating a different conduction mechanism.

  • 268.
    Öijerholm, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Pan, Jinshan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Leygraf, Christofer
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    In-situ measurements by impedance spectroscopy of highly resistive alpha-alumina2006Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, nr 1, s. 243-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In-situ impedance spectroscopy has been used for characterisation of oxides at elevated temperatures. However, for highly resistive oxides, the influence of electrode contact and leakage currents due to gas phase and surface conduction needs to be taken into account. In this study, IS measurements of pure and dense alpha-alumina (alpha-Al2O3) samples were performed in the temperature range 400-1000 degrees C with different types of electrode contact, in air and in nitrogen. The results show that above 700 degrees C the influence is negligible, whereas at lower temperatures the surface leakage current was substantial, and a so-called guard electrode recommendable.

  • 269.
    Öijerholm, Johan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära (stängd 20081231).
    Pan, Jinshan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära (stängd 20081231).
    Lu, Q.
    Kanthal AB, Hallstahammar.
    Leygraf, Christofer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära (stängd 20081231).
    In-situ impedence spectroscopy study of electrical conductivity and ionic transport in thermally grown oxide scales on a commercial FeCrA1 alloy2007Inngår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 68, nr 5-6, s. 253-269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000 degrees C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000 degrees C in air. The impedance spectra of the oxide formed at 1,000 degrees C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.

3456 251 - 269 of 269
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