Bibliografías temáticas / Cobalt activation

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Literatura académica sobre el tema "Cobalt activation"

Autor: Grafiati
Publicado: 4 de junio de 2021
Última modificación: 20 de febrero de 2023

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Artículos de revistas sobre el tema "Cobalt activation"

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Mao, Po-Hsin, Ta Cong Khiem, Eilhann Kwon, Hou-Chien Chang, Ha Manh Bui, Xiaoguang Duan, Hongta Yang et al. "Ambient-Visible-Light-Mediated Enhanced Degradation of UV Stabilizer Bis(4-hydroxyphenyl)methanone by Nanosheet-Assembled Cobalt Titanium Oxide: A Comparative and DFT-Assisted Investigation". Water 14, n.º 20 (20 de octubre de 2022): 3318. http://dx.doi.org/10.3390/w14203318.

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Bis(4-hydroxyphenyl)methanone (BHPM), a common ultraviolet stabilizer and filter (USF), is extensively added in sunscreens; however, BHPM is proven as an endocrine disruptor, posing a serious threat to aquatic ecology, and BHPM should be then removed. As sulfate radical (SO4•−) could be useful for eliminating emerging contaminants, oxone appears as a favorable source reagent of SO4•− for degrading BHPM. Even though cobalt is a useful catalyst for activating oxone to generate SO4•−, it would be even more promising to utilize ambient-visible-light irradiation to enhance oxone activation using cobaltic catalysts. Therefore, in contrast to the conventional cobalt oxide, cobalt titanium oxide (CTO) was investigated for chemical and photocatalytic activation of oxone to eliminate BHPM from water. Especially, a special morphology of nanosheet-assembled configuration of CTO was designed to maximize active surfaces and sites of CTO. Thus, CTO outperforms Co3O4 and TiO2 in degrading BHPM via oxone activation. Furthermore, the substituent of Ti enabled CTO to enhance absorption of visible light and possessed a much smaller Eg. These photocatalytic properties intensified CTO’s activity for oxone activation. CTO possessed a significantly smaller Ea of degradation of USFs than other catalytic systems. Mechanistic insight for degrading BHPM by CTO + oxone was explicated for identifying contribution of reactive oxygen species to BHPM degradation. The BHPM degradation pathway was also investigated and unveiled in details via the DFT calculation. These results validated that CTO is a superior cobaltic alternative for activating oxone to eliminate BHPM.
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2

Moselage, Marc, Jie Li y Lutz Ackermann. "Cobalt-Catalyzed C–H Activation". ACS Catalysis 6, n.º 2 (21 de diciembre de 2015): 498–525. http://dx.doi.org/10.1021/acscatal.5b02344.

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Volla, Chandra M. R., Rahul K. Shukla y Akshay M. Nair. "Allenes: Versatile Building Blocks in Cobalt-Catalyzed C–H Activation". Synlett 32, n.º 12 (31 de marzo de 2021): 1169–78. http://dx.doi.org/10.1055/a-1471-7307.

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AbstractThe unique reactivity of allenes has led to their emergence as valuable coupling partners in transition-metal-mediated C–H activation reactions. On the other hand, due to its high abundance and high Lewis acidity, cobalt is garnering widespread interest as a useful catalyst for C–H activation. Here, we summarize cobalt-catalyzed C–H activations involving allenes as coupling partners and then describe our studies on Co(III)-catalyzed C-8 dienylation of quinoline N-oxides with allenes bearing a leaving group at the α-position for realizing a dienylation protocol.
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Rytter, Erling, Christian Aaserud, Anne-Mette Hilmen, Edvard Bergene y Anders Holmen. "Activation of Cobalt Foil Catalysts for CO Hydrogenation". Catalysts 12, n.º 1 (8 de enero de 2022): 65. http://dx.doi.org/10.3390/catal12010065.

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CO hydrogenation has been studied on cobalt foils as model catalysts for Fischer–Tropsch (FT) synthesis. The effect of pretreatment (number of calcinations and different reduction times) for cobalt foil catalysts at 220 °C, 1 bar, and H2/CO = 3 has been studied in a microreactor. The foils were examined by scanning electron microscopy (SEM). It was found that the catalytic activity of the cobalt foil increases with the number of pretreatments. The mechanism is likely an increase in the available cobalt surface area from progressively deeper oxidation of the foil, supported by surface roughness detected by SEM. The highest FT activity was obtained using a reduction time of only 5 min (compared to 1 and 30 min). Prolonged reduction caused the sintering of cobalt crystallites, while too short of a reduction time led to incomplete reduction and small crystallites susceptible to low turn-over frequency from structure sensitivity. Larger crystals from longer reduction times gave increased selectivity to heavier components. The paraffin/olefin ratio increased with the increasing number of pretreatments due to olefin hydrogenation favored by enhanced cobalt site density. From the results, it is suggested that olefin hydrogenation is not structure sensitive, and that mass transfer limitations may occur depending on the pretreatment procedure. Produced water did not influence the results for the low conversions experienced in the present study (<6%).
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Santhoshkumar, Rajagopal y Chien-Hong Cheng. "Hydroarylations by cobalt-catalyzed C–H activation". Beilstein Journal of Organic Chemistry 14 (29 de agosto de 2018): 2266–88. http://dx.doi.org/10.3762/bjoc.14.202.

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As an earth-abundant first-row transition metal, cobalt catalysts offer a broad range of economical methods for organic transformations via C–H activation. One of the transformations is the addition of C–H to C–X multiple bonds to afford alkylation, alkenation, amidation, and cyclization products using low- or high-valent cobalt catalysts. This hydroarylation is an efficient approach to build new C–C bonds in a 100% atom-economical manner. In this review, the recent developments of Co-catalyzed hydroarylation reactions and their mechanistic studies are summarized.
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Zirngast, Michaela, Christoph Marschner y Judith Baumgartner. "Cobalt-Assisted Silicon−Silicon Bond Activation". Organometallics 25, n.º 20 (septiembre de 2006): 4897–908. http://dx.doi.org/10.1021/om0604831.

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Sauermann, Nicolas, Tjark H. Meyer y Lutz Ackermann. "Electrochemical Cobalt-Catalyzed C−H Activation". Chemistry - A European Journal 24, n.º 61 (2 de agosto de 2018): 16209–17. http://dx.doi.org/10.1002/chem.201802706.

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du Plessis, Hester, Roy Forbes, Werner Barnard, Alta Ferreira y Axel Steuwer. "In situ reduction study of cobalt model Fischer-Tropsch synthesis catalyst". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 de agosto de 2014): C948. http://dx.doi.org/10.1107/s2053273314090512.

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Fischer-Tropsch (FT) synthesis is an important process to manufacture hydrocarbons and oxygenated hydrocarbons from mixtures of carbon monoxide and hydrogen (syngas). The catalysis process occurs on for example cobalt metal surfaces at elevated temperatures and pressures. A fundamental understanding of the reduction pathway of supported cobalt oxides, and the intermediate species present during the activation, can assist in developing improved industrial supported cobalt catalysts. Measurements were done during in-situ hydrogen activation of a model Co/alumina catalyst using in-situ synchrotron X-ray powder diffraction and pair-distribution function (PDF) analysis. Strong metal-support interactions between the Co and the support1 can make the catalyst more stable towards sintering. The supported cobalt oxide catalyst precursors have to undergo reductive pre-treatments before their use as FT catalysts. During activation the cobalt oxides evolve, resulting in the formation of metallic cobalt depending on temperature, pressure of activation gases, concentration, time of exposure etc. The effect of hydrogen activation treatments on model catalysts were reported previously [1,2], however analysis of the alumina support phases was excluded from the interpretation by subtraction and normalisation. The PDF refinement accounted for all cobalt present in the catalyst sample and after reduction mainly Co(fcc) with a little Co(hcp) was found to be present. This is a novel approach to in situ PDF analysis of catalysts containing a mixture of phases [3].
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Stuchlý, V., H. Zahradníková y L. Beránek. "Activation of a hydrorefining cobalt—molybdenum catalyst". Applied Catalysis 35, n.º 1 (noviembre de 1987): 23–34. http://dx.doi.org/10.1016/s0166-9834(00)82420-3.

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Stuchlý, V. y L. Beránek. "Activation of a hydrorefining cobalt—molybdenum catalyst". Applied Catalysis 35, n.º 1 (noviembre de 1987): 35–45. http://dx.doi.org/10.1016/s0166-9834(00)82421-5.

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Tesis sobre el tema "Cobalt activation"

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Bu, Qingqing. "Ruthenium- and Cobalt-Catalyzed C-H Activation". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E4FC-F.

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Fallon, Brendan. "Cobalt-catalyzed bond activation : C-H functionalization, hydrosilylation and coupling reactions". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066411/document.

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Dans cette thèse, nous nous concentrerons principalement sur l’utilisation de complexes basse-valence de cobalt bien définis de la famille des RCo(PMe3)4 pour l’activation de divers types de liaisons (C–H, Si–H, C–X). Notre but était de développer un système compétitif par rapport au système bimétallique de Yoshikai, mais aussi par rapport aux systèmes onéreux à base de rhodium. Nous avons démontré avec succès que les complexes isolés Co(PMe3)4 et HCo(PMe3)4 étaient des catalyseurs efficaces pour l’hydroarylation de différents alcynes et alcènes via une activation de liaisons C–H. De plus, nous avons fait une étude mécanistique en couplant des marquages au deutérium et des études de chimie théorique. Nous avons déterminé que la fonctionnalisation de liaisons C–H se faisait selon un mécanisme concerté appelé ‘’Ligand-to-Ligand Hydrogen Transfer’’ (LLHT). A partir de ces études, nous avons pu aussi développer une hydrosilylation hautement régio- et stéréosélective d’alcynes permettant d’utiliser un grand nombre de silanes différents. Nous avons pu au cours de cette étude isoler un nouveau complexe de cobalt(III) bis-hydrure jouant un rôle important dans le mécanisme. Enfin, nous décrivons aussi que ces mêmes complexes de cobalt RCo(PMe3)4 sont capables de catalyser l’homocouplage de bromure et chlorure de benzyle en présence de dimethylzinc. Une étude mécanistique préliminaire suggère que la réaction procède par deux transferts mono-électroniques et que le diméthylzinc permet de régénérer le catalyseur
This thesis has focused on the use of well-defined low-valent cobalt complexes of the family RCo(PMe3)4 for a variety of bond activation (C–H, Si–H, C–X). We aimed to develop a catalytic system that could compete with the previously reported bimetallic systems of Yoshikai and expensive rhodium catalysis. To this end, we successful demonstrated that Co(PMe3)4 and HCo(PMe3)4 are efficient catalysts for the hydroarylation of a broad variety of alkynes and alkenes. In addition, we carried out extensive mechanistic investigations using deuterium labelling experiments and theoretical studies namely DFT. The main finding of these studies was that the C–H bond activation proceeded via a ligand-to-ligand hydrogen transfer mechanism. Following on from this study we then showed that it was possible to carry out the regio- and stereoselective hydrosilylation of internal alkynes with a broad variety of hydrosilanes. During this study we successfully isolated an interesting cobalt(III) intermediate which we believe plays a crucial role in the reaction mechanism. Finally, we report on the ability of these catalysts to efficiently catalyze the homocoupling of benzyl halides in the presence of dimethylzinc. Initial mechanistic investigations suggest that the reaction takes via two single electron transfers and that dimethylzinc act to regenerate the catalyst
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Moselage, Marc Philipp. "C-H and C-C Activation by Cobalt and Ruthenium Catalysis". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3FB2-6.

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Mei, Ruhuai. "Ruthenium- and Cobalt-Catalyzed Chelation-Assisted C–H Functionalization". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3EFB-C.

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Wang, Hui. "Cobalt(III)- and Manganese(I)-Catalyzed C-H and C-C Activations". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/11858/00-1735-0000-002E-E5EF-5.

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Dorval, Céline. "Activation d'électrophiles peu communs pour des couplages catalysés au cobalt : réactions et mécanisme". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX089.

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Ces projets de recherche ont permis d’aboutir au développement de nouvelles réactions de couplage catalysées par un métal relativement abondant, le cobalt, en employant des partenaires électrophiles plus disponibles naturellement ou facilement synthétisables à partir de composés issus de la biomasse. Le premier chapitre est consacré à la mise en place de couplages de type Negishi par activation de dérivés amides pour former divers types de cétones dissymétriques à l’aide de protocoles simples et robustes. Le second chapitre dévoile les premiers exemples d’activation catalytique de la liaison C–CN de dérivés benzonitriles par le cobalt avec la mise en place (i) d’une méthodologie de couplage croisé d’électrophiles de type benzonitrile et halogénure d’aryle pour la formation de biaryles dissymétriques et (ii) d’une méthode de cyanation de dérivés halogénés à partir d’un agent de cyanation carboné simple et non toxique. Par ailleurs, la compréhension des processus mis en jeu lors des réactions de couplage catalysées par des métaux de transition est indispensable tant à l’amélioration de celles-ci qu’à la conception de nouvelles méthodologies. Par conséquent, la troisième partie de cette thèse détaille l’étude mécanistique menée pour comprendre le fonctionnement du couplage réducteur précédemment développé et qui suggère, par diverses expériences, entre autres caractérisation d’espèce active et voltampérométrie cyclique, supporté par calculs DFT, un mécanisme faisant intervenir un échange de ligands à partir de deux espèces de cobalt à bas degré d’oxydation différents. Enfin, la volonté déterminer plus précisément une espèce de cobalt active envers le partenaire benzonitrile a alors mené à la découverte de deux nouveaux complexes de cobalt basse valence encore jamais décrits dont la réactivité envers diverses espèces électrophiles, en particulier benzonitrile, a été évaluée
This research project led to the development of new coupling reactions catalysed by relatively abundant metal, cobalt, and involving coupling partners more available or easily synthesised from biomass sources. The first chapter is dedicated to the implementation of Negishi-type couplings through the activation of amide derivatives in order to form diverse asymmetrical ketones with simple and robust setups. The second chapter reveals the first examples of catalytic coupling reactions involving C–CN activation from benzonitrile derivatives with cobalt and includes the setting-up of (i) a cross-electrophile coupling between benzonitriles and aryl halides in order to synthesize various biaryl compounds and (ii) a cyanation method of halogenated arenes thanks to a simple carbonated non-toxic cyanatingagent. Besides, the understanding of the processes involved in metal-catalysed coupling reactions is crucial for both the improvement of known methodologies and the design of new ones. Therefore, the third chapter details the mechanistic study carried outto better understand the aforementioned cross-electrophile coupling. Mechanistic insights obtained includingcharacterisation of active species as well as cyclic voltammetry, and supported by DFT calculations, suggest a mechanism involving a ligand exchange step from two different low-valent cobalt species of different oxidation states. Finally, the desire determine more precisely an active cobalt species towards benzonitrile derivatives led to the discovery of two new low-valent cobalt complexes, which reactivity towards various electrophiles, including benzonitriles, has been evaluated
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Müller, Jörg [Verfasser]. "Synthetic and mechanistic investigations of dioxygen activation on cobalt-Complexes / Jörg Müller". Gießen : Universitätsbibliothek, 2011. http://d-nb.info/1061195732/34.

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Wigzell, Fiona A. "Characterising the activation process for cobalt catalysts used in Fischer-Tropsch synthesis". Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3753/.

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The effects of precursor, support and calcination procedure on the physical and chemical properties of supported cobalt catalysts have been investigated. A multiple characterisation approach of thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction and transmission electron microscopy was employed in order to gain understanding into the calcination and reduction processes. In addition, the catalysts were screened on a purpose built fixed bed reactor, under industrially relevant conditions, to determine effect of catalyst preparation on Fischer-Tropsch activity.
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Zell, Daniel. "C–H Activation by Ruthenium(II), Cobalt(III) and Manganese(I) Catalysis". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3E9C-2.

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Li, Yingze. "Development of New Cobalt Pincer Complexes for Catalytic Reduction Reactions". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1554215914263187.

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Libros sobre el tema "Cobalt activation"

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Murguia, Mark A. Synthesis and oxidation of two tri-metallic compounds and activation volumes for electron transfer by some cobalt clathrochelates in nonaqueous solution. 1989.

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Lukašēvics, Tomass. Kobalta katalizēta C‒H saites funkcionalizēšana/Cobalt Catalyzed C‒H Bond Functionalization. RTU Press, 2022. http://dx.doi.org/10.7250/9789934227806.

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Over the past few decades, transition metal catalyzed C–H activation has been immensely investigated due to the ability to functionalize relatively unreactive C-H bonds whilst simplifying synthetic schemes and making the synthetic pathway more economical. Nowadays, a great emphasis has been placed on substitution of noble metal catalysts (Pd, Rh, Ru, etc.) with more abundant and cheaper alternatives (Cu, Co, Ni). The aim of the Doctoral Thesis is the development of novel cobalt catalyzed C-H bond functionalization methodology. The Doctoral Thesis is prepared as a collection of publications. The main results of the Thesis were summarized in 4 scientific publications, 3 review articles and 2 book chapters.
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Capítulos de libros sobre el tema "Cobalt activation"

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Simándi, László I. "Catalytic oxidations using cobalt(II) complexes". En Advances in Catalytic Activation of Dioxygen by Metal Complexes, 265–328. Boston, MA: Springer US, 2003. http://dx.doi.org/10.1007/0-306-47816-1_6.

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Martell, Arthur E. "Formation and Degradation of Cobalt Dioxygen Complexes". En Oxygen Complexes and Oxygen Activation by Transition Metals, 87–106. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0955-0_7.

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Bakac, Andreja, Susannah L. Scott, Adam Marchaj y James H. Espenson. "Activation of Dioxygen by Chromium and Cobalt Complexes". En The Activation of Dioxygen and Homogeneous Catalytic Oxidation, 445. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-3000-8_36.

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Chen, Dian y A. E. Martell. "Dioxygen Affinities of Some Synthetic Cobalt Schiff Base Complexes". En Oxygen Complexes and Oxygen Activation by Transition Metals, 309. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0955-0_24.

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Terhune, Kyte H. y Arthur E. Martell. "Oxygenation of Tryptophane Catalyzed by Polyamine Cobalt Dioyxgen Complexes". En Oxygen Complexes and Oxygen Activation by Transition Metals, 326. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0955-0_38.

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Adamian, Victor A., Yurii V. Geletii y Igor V. Zakharov. "Cobalt Bromide Catalysis of the Oxidation of Organic Compounds". En The Activation of Dioxygen and Homogeneous Catalytic Oxidation, 441. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-3000-8_32.

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Basak, Arup K. y Arthur E. Martell. "Kinetics and Mechanisms of Degradation of Binuclear Cobalt Dioxygen Complexes". En Oxygen Complexes and Oxygen Activation by Transition Metals, 307. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0955-0_22.

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Martell, Arthur E., Ramunas J. Motekaitis y Dian Chen. "Binuclear Cobalt(II) Complexes of Macrocyclic and Macrobicyclic Ligands as Oxygen Carriers". En The Activation of Dioxygen and Homogeneous Catalytic Oxidation, 469. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4615-3000-8_60.

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Giannotti, C. "Paramagnetic Species in Photoinduced or Photocatalytic Processes Involving some Cobalt, Titanium and Iron Organometallic Complexes". En Paramagnetic Organometallic Species in Activation/Selectivity, Catalysis, 295–309. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0877-2_21.

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Menif, Rached y Arthur E. Martell. "Synthesis and Metal Ion Affinities of a Binucleating Polyamine: Reversible Formation of a Cobalt Dioyxgen Complex". En Oxygen Complexes and Oxygen Activation by Transition Metals, 314. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0955-0_29.

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Actas de conferencias sobre el tema "Cobalt activation"

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Truc, Nguyen Van, Nguyen Thanh Binh, Vo Thi Dieu Hien y Cheng-Di Dong. "ACTIVATION OF PEROXYMONOSULFATE BY COBALT-IMPREGNATED BIOCHAR (CO-SCG) FOR EFFICIENT DEGRADATION OF TETRACYCLINE IN WATER". En NGHIÊN CỨU CƠ BẢN TRONG LĨNH VỰC KHOA HỌC TRÁI ĐẤT VÀ MÔI TRƯỜNG. Publishing House for Science and Technology, 2019. http://dx.doi.org/10.15625/vap.2019.000201.

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Sakata, K., S. Fujita, H. Miyahara y K. Ogi. "Effects of Diffusion Treatment on the Interface Microstructure Between Thermally Sprayed Cobalt-Based Self-Fluxing Alloy Coating and Steel Substrate". En ITSC2008, editado por B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima y G. Montavon. Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH, 2008. http://dx.doi.org/10.31399/asm.cp.itsc2008p0684.

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Abstract Effects of diffusion treatment were investigated on the interface microstructure between a Co-based self-fluxing alloy coating and a mild steel substrate to improve the adhesion strength. Diffusion treatments were carried out at 1373 K to 1418 K for 600 s to 7200 s in an Ar atmosphere. Diffusion treatment improves the metallurgical bonding at the interface due to the diffusion of Co, Cr, W, Ni, and Si from the sprayed coating layer to the substrate and that of Fe and Mn from the substrate to the coating. This mutual diffusion forms a precipitate-free diffusion layer at the interface, and the width of this layer increases in a parabolic manner as temperature and holding time increase. The apparent activation energy for the formation of precipitate-free diffusion layer was evaluated as about 360 kJ/mol. The shearing adhesion strength of the diffusion-treated coating has been remarkably improved to 200 – 400 N/mm2 in proportion to the width of the precipitate-free diffusion layer formed along the interface, although the shearing adhesion strength of the as-sprayed coating was only 30 N/mm2.
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Brinkevich, D. I., S. D. Brinkevich, H. I. Kiyavitskaya y A. N. Kiyko. "SOURCES OF GAMMA-EMITTING RADIONUCLIDES IN THE PRODUCTION OF RADIOPHARMACEUTICALS USING ТНЕ CYCLONE 18/9 HC CYCLOTRON". En SAKHAROV READINGS 2021: ENVIRONMENTAL PROBLEMS OF THE XXI CENTURY. International Sakharov Environmental Institute of Belarusian State University, 2021. http://dx.doi.org/10.46646/sakh-2021-2-245-248.

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The accumulation of secondary radionuclides (PRN) in water [18O]H2O under irradiation on a Cyclone 18/9 HC cyclotron with a niobium target and an entrance window made of Havar alloy was studied. It is shown that the activity of PRN is mainly determined by the accumulated dose of the target. The dominant source of PRN is the entrance window made of Havar alloy. The niobium target is the source of only one radionuclide, 92mNb, whose activity is low. In the process of water activation, radioisotopes 7Be and probably 65Zn are formed. The water [18O] H2O irradiated on the cyclotron is a dispersed system. Up to 30 % of the activity of cobalt and manganese, as well as ~7% of chromium, are in the composition of solid particles >5 microns in size, washed out of the input foil of the cyclotron target due to intergranular corrosion.
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Stender, Michael E., Lauren L. Beghini, Michael G. Veilleux, Samuel R. Subia y Joshua D. Sugar. "Thermal Mechanical Finite Element Simulation of Additive Manufacturing: Process Modeling of the Lens Process". En ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65992.

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Laser engineered net shaping (LENS) is an additive manufacturing process that presents a promising method of creating or repairing metal parts not previously feasible with traditional manufacturing methods. The LENS process involves the directed deposition of metal via a laser power source and a spray of metal powder co-located to create and feed a molten pool (also referred to generically as Directed Energy Deposition, DED). DED technologies are being developed for use in prototyping, repair, and manufacturing across a wide variety of materials including stainless steel, titanium, tungsten carbide-cobalt, aluminum, and nickel based superalloys. However, barriers to the successful production and qualification of LENS produced or repaired parts remain. This work proposes a finite element (FE) analysis methodology capable of simulating the LENS process at the continuum length scale (i.e. part length scale). This method incorporates an element activation scheme wherein only elements that exceed the material melt temperature during laser heating are activated and carried through to subsequent analysis steps. Following the initial element activation calculation, newly deposited, or activated elements and the associated geometry, are carried through to thermal and mechanical analyses to calculate heat flow due to radiation, convection, and conduction as well as stresses and displacements. The final aim of this work is to develop a validated LENS process simulation capability that can accurately predict temperature history, final part shape, distribution of strength, microstructural properties, and residual stresses based on LENS process parameters.
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Toth, PT, HJ Zhang, J. Rehman, Y. Zhang y SL Archer. "HIF-1alpha Activation by Cobalt Results in Hyperpolarization and Fragmentation of the Mitochondrial Network in Pulmonary Artery Smooth Muscle Cells and Thus Mimics a “Pulmonary Arterial Hypertension” Phenotype." En American Thoracic Society 2009 International Conference, May 15-20, 2009 • San Diego, California. American Thoracic Society, 2009. http://dx.doi.org/10.1164/ajrccm-conference.2009.179.1_meetingabstracts.a1859.

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Honjo, Yoshio, Masahiro Furuya, Tomoji Takamasa y Koji Okamoto. "Interfacial Phenomena of Radiation-Induced and Photo-Induced". En 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48320.

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When a metal oxide is irradiated by gamma rays, the irradiated surface becomes hydrophilic. This surface phenomenon is called as radiation induced surface activation (RISA). In order to investigate radiation-induced and photo-induced hydrophilicity, the contact angles of water droplets on a titanium dioxide surface were measured in terms of irradiation intensity and time for gamma rays of cobalt-60 and for ultraviolet rays. Reciprocals of the contact angles increased in proportion to irradiation time before the contact angles reached their super-hydrophilicity state. The reciprocals of contact angles correlate well with integrated intensity by a straight line, regardless of the irradiation intensity and time. Radiation-induced and photo-induced hydrophilicity phenomena are identical to each other in this regard. In addition, an effect of ambient gas was investigated. In pure argon gas, the contact angle remains the same against the irradiation time. This clearly shows that a certain humidity in ambient gas is required to take the place of RISA hydrophilicity. A single crystal titanium dioxide (100) surface was analyzed by X-ray photoelectron spectrometry (XPS). After irradiation with gamma rays, a peak was found in the O 1s spectrum, indicating the adsorption of dissociative water to a surface 5-fold coordinate titanium site, and the formation of a surface hydroxyl group. We conclude that the RISA hydrophilicity is caused by chemisorption of the hydroxyl group on the surface.
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Sulley, John y David Stewart. "HIPed Hard Facings for Nuclear Applications: Materials, Key Potential Defects and Mitigating Quality Control Measures". En 2016 24th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icone24-61106.

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Hard facings are used in a number of different types of components generally to provide improved wear, erosion, and corrosion resistance to the substrate. A typical application is to a valve seat which may be subjected to high wear loads and high flow rates such that a hard wearing surface is required. Traditionally, a common application method has been to weld deposit the hard facing onto a softer substrate, e.g. the main body material of the component. This can result in poor quality micro-structures, e.g. cast/inhomogeneous structures being created that may not provide the required wear/erosion/corrosion resistance. This can be a particular issue for Nuclear applications where the hard facing is cobalt based. If the facing deteriorates and releases cobalt based debris, the debris (crud), if it becomes activated, can contribute significantly to the overall plant radiation activation level. Also, depending upon the geometry, deposition process, the expansion coefficient difference between the facing and substrate, and the cooling rate, a detrimental tensile residual stress can be generated. This can cause cracking of the facing which, depending upon the in-service loading conditions, could lead to crack propagation into the substrate, potentially threatening the structural integrity of the component; a leak or structural failure could result. One application method to address the potential poor micro-structure that may be created from weld deposition methods, is to use a Hot Isostatically Pressed (HIPed) hard facing. This is where a wear surface is created from the solid state, rather than using a localised melting route, by the HIP consolidation of powder produced by a gas atomisation process. Homogenous, isotropic, finer grained, and defect free microstructures can be created via this method which generally exhibit improved resistance to wear/erosion/corrosion. Also, where the HIP consolidated facing is HIP bonded to the substrate, a beneficial compressive residual stress is created that can arrest any crack propagation into the substrate if cracking of the facing was to occur. For Nuclear applications it is imperative the material quality of a hard facing is assured. It is essential that care is taken particularly in the production of the powder to ensure it does not contain undesirable defects/contamination. This paper presents: the benefits that can be achieved with creating component hard facings using the HIP process, the key defects/contamination that may be present, and the quality control measures recommended to assure the material quality.
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8

Lanzini, A., P. Leone, M. Santarelli, P. Asinari y M. Cali`. "Performance and Degradation Effects of Anode-Supported Cells With LSM and LSCF Cathodes". En ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-43421.

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The performance of solid oxide fuel cells is affected by various polarization losses, usually grouped in ohmic, activation and concentration polarization. Under typical operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometry: as an example, the performance of a tubular cell is strongly limited by the ohmic polarization due to the long current path of electrons, while in a planar cell each of these losses has a comparable effect. It is therefore of interest, in case of planar geometry, to investigate the performance limiting factors. In this paper, a performance evaluation of planar circular-shaped seal-less SOFC cells from InDEC® was performed, with an outline of the limiting factors at reduced temperature. Two different designs of planar cells are considered: both have porous NiO-YSZ anode as mechanical support, NiO-YSZ anode active layer, yttria-stabilized zirconia (YSZ) electrolyte, and only differ for the cathode design: (1) strontium doped lanthanum manganate (LSM)-YSZ cathode functional layer (CFL) and LSM cathode current collector layer (CCCL); (2) yttria doped ceria (YDC) blocking layer and lanthanum strontium cobalt ferrite oxide (LSCF) functional layer. The characterization was performed by taking V-I measurements over a range of temperatures between 650°C and 840°C with hydrogen as fuel, and air as oxidant. The dependence of the cell performance on the various polarization contributions was rationalized on the basis of a analytical model, through a parameter estimation on the experimental data, devoted to the determination of the temperature dependence of the area specific resistance (ASR) and of the cathode exchange current density: in particular, the performance limitation at low temperature is due to activation polarization for ASC1 and ohmic polarization for ASC2. Based on the results of the investigation, it is concluded that LSCF cathodes are really effective for decreasing the cathode activation polarization, allowing the reduction of operating temperature. Finally, a microstructural analysis with SEM and optical microscopy has been performed on the ASC2 cell after the polarization testing. The aim of this investigation was in particular to evaluate the degradation phenomena occurring in the anodic structure and over the interfaces between the various active layers. The ASC2 elastic modulus has also been estimated before and after polarization testing in order to evaluate the decreasing of the mechanical strength of the cell after a complete thermal cycle. The results describe a mechanical degradation of the structure and of the distribution of the phases.
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9

Carvalho, L., W. Pacquentin, M. Tabarant, J. Lambert, A. Semerok y H. Maskrot. "Development of Laser Cleaning for Metallic Equipment". En 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-81853.

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Laser cleaning study was performed on prepared samples using a nanosecond pulsed ytterbium fiber laser. To prepare samples, AISI 304L stainless steel samples were oxidized and implemented with non-radioactive contaminants in a controlled manner. In order to validate the cleaning process for metallic equipment polluted in nuclear installations, two types of contamination with europium (Eu) and with cobalt (Co) were studied. Eu was used as a simulator-product resulting from uranium fission, while Co — as an activation-product of nickel, which is a composing element of a primary coolant system of a reactor. The oxide layers have suffered laser scanning which was followed by the furnace treatment to obtain thicknesses in the range of 100 nm to 1 μm depending on the oxidation parameters [1] with a mean weight percentage of 1% of Eu and 1 % of Co in the volume of the oxide layer. Glow Discharge Optical Emission (GD-OES) and Mass Spectrometry (GD-MS) analyses have been performed to assess the efficiency of the cleaning treatment and to follow the distribution of residual contamination with a detection limit of 0.1mg/kg of Eu and Co. Decontamination rates up to 95.5 % were obtained. One of the identified reasons for this limitation is that the radionuclides are trapped in surface defects like micro cracks [2, 3]. Therefore, cleaning treatments have been applied on surface defects with controlled geometry and a micrometric aperture obtained by laser engraving and juxtaposition of polished sheets of AISI 304L stainless steel. The goal of this study is surface decontamination without either welding or inducing penetration of contamination into the cracks. GD-MS analysis and Scanning Electron Microscopy (SEM) were performed to analyze the efficiency of the treatment and the diffusion of contaminants in this complex geometry.
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Zakeri, Zohreh, Azfar Khalid, Ahmet Omurtag, Greg Hilliard y Philip Breedon. "Building Trust and safety Correlates for Autonomous Systems using Physiological, Behavioral, and Subjective Measures". En 13th International Conference on Applied Human Factors and Ergonomics (AHFE 2022). AHFE International, 2022. http://dx.doi.org/10.54941/ahfe1001595.

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The use of collaborative robots (cobots) in the industrial setting has grown and continues to expand globally, especially in the context of the smart factory. Mistrust and stress results, as cobots don’t provide facial, auditory, and visual cues that workers normally use to predict behavior. For quantification of mental stress, physiological, behavioral and subjective measures are integrated, processed and analyzed in a smart factory lab setting. The impact on the human workers as mental stress and fatigue conditions are correlated with the task complexity, speed of work, length of collaborative task and cobot payload etc. Multimodal functional neuroimaging was used to record participants’ neural and cardiac activity, in addition to the standard subjective and behavioral measures as they collaborated with robots in multitasking contexts. Preliminary results show that task complexity is positively correlated with beta and gamma band power, left prefrontal cortex activation, and heart rate, while it is negatively correlated with alpha band power during task performance.
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Informes sobre el tema "Cobalt activation"

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Kerr, G. D., F. F. Dyer, J. F. Emery, J. V. III Pace, R. L. Brodzinski y J. Marcum. Activation of cobalt by neutrons from the Hiroshima bomb. Office of Scientific and Technical Information (OSTI), febrero de 1990. http://dx.doi.org/10.2172/7243377.

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