DOCSLIB.ORG

(X=Mo, Nb, V, Zr) with Ho.T Gazes. Example of Nitriding.·

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
(X=Mo, Nb, V, Zr) with Ho.T Gazes. Example of Nitriding.· TITANIUM'99: SCIENCE AND TECHNOLOGY A Method for Scanning the Reaction Behaviour of Ti-X alloys (X=Mo, Nb, V, Zr) with Ho.t Gazes. Example of Nitriding.· A. GUILLOU, J.P. BARS, D. ANSEL, J. DEBUIGNE .. INSA Rennes, GRCM,.20 Av. des Buttes de Coesmes, F-35043, Rennes Cedex, France. ANNOTATION The study of the reaction behavior of binary or more complicated alloys with hot gases is difficult and time consuming. The study of reactions of hot gases with diffusion couples is a method for direct scanning the reaction behavior of alloys of various compositions. Sufficient initial knowledge of diffusion properties allows very valuable results to be obtained. This method is applied to the study of the reaction of the Ti-Mo, Ti-Nb, Ti-V and Ti-Zr beta solid-solutions with nitrogen. Keys words : Nitriding, Titanium alloys, Beta-stabilizer elements, Diffusion 1. INTRODUCTION The study of phases grown during diffusion in interdiffusion couples is a well known method for assessing binary phase diagrams. Fast and valuable results can be obtained if: i) the hypothesis of local equilibrium applies, ii) the kinetics of diffusion and growth allow the fonnation of all the phases thennodynamically stable at the interdiffusion temperature. In the reverse, the knowledge of binary phase diagrams allows, for example, the analysis of the oxidation of pure metals and also of dilute alloys to some extent. When systems are no more binary or quasi binary, the study of solid state diffusion and reaction of alloys with hot gases can become very complicated and time consuming. This is a stumbling block as far as the research goal to find an.alloy composition meeting well defined requirements for industrial applications. To overcome these time consuming investigations, we propose an experimental method evolved from our solid state interdiffusion researches : the reaction of hot gases on a cross-section of diffusion couples previously interdiffused. In that way the characteristics of the gas-alloy reactions can be obtained simultaneously over a large composition range. This gives a panoramic view in composition for the reaction of hot gases with alloys. Similar experiments have been carried out by various authors for multicomponent solid state diffusion studies and phase diagram detenninations. In each :case the results · can be graphically represented as diffusion paths in isothermal sections of multicomponent phase diagrams [ 1,2]. Our method is applied to the investigation of the nitriding of binary alloys, at temperatures for which a single solid solution is observed for the whole composition range. As examples we present the nitriding ofTi-X (X = V, Mo, Nb, Zr) beta solid solutions at high temperatures. Studies of the reaction of nitrogen with diffusion couples between other titanium alloys are under development in our laboratory. Other reacting gases can also be used. These studies imply preliminary quantitative interdiffusion detenninations between Ti and X [3,4]. 2. EXPERIMENT AL PROCEDURES Diffusion couples are made of two pellets cut from metals ingots. Faces to be in contact are carefully polished to obtain flat surfaces. The properly diffusion stage is preceded by a short welding stage called prediffusion while the two pellets are mechanically maintained in contact. Only one fast thennal cycle around the a/P transus of titanium is necessary to have a good prediffusion. The diffusion in P phase that gives a large concentration gradient zone is carried out at high temperature in a r.f. furnace (I 0 kHz) in purified argon. The experimental devices have already been described earlier [5]. The diffusion time has been chosen in order to obtain a concentration gradient zone about 4 mm width. Couples are then cut perpendicularly to the diffusion interface and polished. The one part allows the detennination of the diffusion profiles by EPMA and the other is used for the reactions studies with hot gases. Since the Ka N and L! Ti emission lines overlap, we use a deconvolution software. The EPMA determinations are accurate to within 0.5 at.% for the metals and I at.% for N. The 900 TITANIUM'99: SCIENCE AND TECHNOLOGY interdiffusion coefficients are calculated by the Den Broeder method taking into account the molar volume variation. At low concentration the diffusion coefficients are obtained by Hall's method. The other parts of the couples are nitrided in nitrogen (quality N60 supplied by Air Liquide) in a r.f. furnace (500 kHz). 3. INTERDIFFUSION RESULTS Typical diffusion profiles are given on figure I. The shape of the concentration-penetration curve in the diffusion couple shows the variation of the diffusion coefficient with composition : For the beta stabilizer elements (Mo, Nb; Y), these curves show a strong variation of the diffusion coefficients with respect to concentration and specially for the Ti-Mo system. 100 ..------------------.---, 100 ..-----------------~~ 1600 ·c. B1oo s 1600 ·c - 14400 s BO . :c BO ~ z '#- :: 60 .!!!. ! 60 c .§ 0 i! c 40 ~ 40 8 c 5c 8 8 20 20 0 200 400 600 BOO 1000 1200 0 200 400 600 800 1000 1200 1400 1600 penetration (µm) penetration (µm) 100 ------------------------------- 100 -------·--- 1 1550 ·c -21600 s 1450 "C • 3BBO s 80 80 ;G' *! 60 c 0 i E 40 ~ c 8 20 20 I o~~.----.~~::::::::::_____---'"-------~- 0 -1----~--~-~------------l o 500 1000 1500 2000 2500 3000 3500 4000 4500 0 200 400 600 800 1000 1200 1400 1600 penetration (µm) penetration (µm) Figure I : Interdiffusion profiles This strong concentration dependence explains the behaviors of the various alloys during their high temperatures nitriding and the diffusion profiles give immediately infonnations about the quality of the future results of the nitriding reactions. When a sharp decrease of the diffusion coefficient is observed in a range of concentrations, the interdiffusion zone is then not wide enough for a good description of the nitriding reaction. If the phase diagram shows phases with limited single phase fields, the related interdiffusion zones must be wide enough for analysis to be possible. For low concentrations in beta stabilizer element, greatest is the size of the atom, lowest seems to be the diffusion of the element. As illustration Table 1 represents interdiffusion coefficient at I 400°C versus atomic radius of the element (for a composition of 5 at.%). interdiffusion coefficient atomic radius element (5 at.%) 9 2 1 (I 0· cm .s" ) (run) --- ·-· Nb --- 14.1 0.146 Mo - - 19.6 0.139 v 65.7 0.134 Table I : lnterdiffusion coefficients at I 400°C for low contents of beta stabilizer elements. 901 TITANIUM'99: SCIENCE AND TECHNOLOGY 4. NITRIDING OF TITANIUM-X DIFFUSION COUPLES If Xis a beta stabilizer element (as Mo, Nb or V), nitriding of diffusion couples gives similar results. They.are presented for a nitriding temperanire of l 400°C in figures 2, 4 and 6. Zr is. a "neutrai' element" and gives different results. · For the low concentrations of alloying element nitriding gives the same layers as in the case of the nitriding of pure ti_tanium : an external 8 nitride layer_(fcc structure) with an underlying a solid solution layer (hexagm_lal structure). The difference in the grey level indicates the .0/'8 transition, In- these layers the X concentration is always low and this element is repelled in the core of the sample. This ·effect is .lower for Zr. A low. X concentration (Table 2) is sufficient to slow down the kinetics of the a layer development. For higher beta stabilizer element concentrations, the 8 and a phases expand no more in form of a layer but in form of grains separated by beta metallic matrix zones. Above a typical concentration the nitrogen penetration is strongly slowed down for Mo and Nb, but increased for V. · In some samples the innermost part of the external 8-Ti N 1., nitride layer or some precipitates undergo a transformation to E-Ti 2N subnitride (tretragonal structure). The continuity of the titanium profile through this phase shows unambiguously that this phase forms on cooling, because of the too low cooling rate. Its formation ·is a supplementary proofofthe virtually absence of molybdenum, niobium, vanadium or zirconium. · In the core of Ti-Mo or Ti-V samples, the P phase (bee structure) is not transformed during cooling. But in this matrix one can notice very thin precipitates with a thickness lower than 1 µm. X-ray emission images show that they are composed of titanium and nitrogen but the concentrations are not measurable considering their small size. These precipitates probably form during cooling : the P(Ti,X) solid. solution rejects a(Ti) during the monotectold transformatil:m proposed by the Ti-Mo and Ti-V phase diagrams [6]. Temperature of nitriding: - 1400°C Alloying element Mo Nb v Zr Duration of nitriding 6h 3h lhlO 3h 8-(Ti,X)N1., layer mean width (µm) 30 20 20 limits of at.% min 3 8 4 large area* at.% max 10 18 -30 needled area starting composition (at.%) 20 25 cx-(Ti,X)(N) max width (µm) 210 110 86 105 'layer start of width decrease( at.%)· -1 3 4.5 end (at.%) -3 8 9 50 -· ' internal islands higher core cone. (at.%) .-15 20 * correspond with the lower and higher core concentrations where large 8 area is observed. Table 2. Comparative c~aracteristics for the nitrfding of Mo, Nb,V, Zr. I . , ' . 4.1. Nitriding of titanium-molybdenum couple (figure 2). The phases observed and the metallographic features are the same as for nitrided pure titanium if the molybdenum conc.entration is lower than· I at.%. From outside the layers ·observed are 8-TiN 1., and 'a(Ti,N). The molybdenum concentration in these layers is lower ·than 0'.2 at.%. For this reason we have noted 8-TiN 1., rather than 8-(Ti,Mo)N 1., The core of the sample shows a characteristic a microstructure martensitically· transformed from the high temperature p phase during cooling.
Load more

Recommended publications
  • 1 Understanding Continuous Lithium-Mediated Electrochemical Nitrogen Reduction Nikifar Lazouski,1 Zachary J Schiffer,1 Kindle Wi
    © 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ doi: 10.1016/j.joule.2019.02.003 Understanding Continuous Lithium-Mediated Electrochemical Nitrogen Reduction Nikifar Lazouski,1 Zachary J Schiffer,1 Kindle Williams,1 and Karthish Manthiram1* 1Department of Chemical Engineering; Massachusetts Institute of Technology; Cambridge, MA 02139, USA *Corresponding Author: [email protected] 1 © 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ doi: 10.1016/j.joule.2019.02.003 Summary Ammonia is a large-scale commodity chemical that is crucial for producing nitrogen- containing fertilizers. Electrochemical methods have been proposed as renewable and distributed alternatives to the incumbent Haber-Bosch process, which utilizes fossils for ammonia production. Herein, we report a mechanistic study of lithium-mediated electrochemical nitrogen reduction to ammonia in a non-aqueous system. The rate laws of the main reactions in the system were determined. At high current densities, nitrogen transport limitations begin to affect the nitrogen reduction process. Based on these observations, we developed a coupled kinetic-transport model of the process, which we used to optimize operating conditions for ammonia production. The highest Faradaic efficiency observed was 18.5 ± 2.9%, while the highest production rate obtained was (7.9 ± 1.6) × 10-9 mol cm-2 s-1. Our understanding of the reaction network and the influence of transport provides foundational knowledge for future improvements in continuous lithium- mediated ammonia synthesis.
    [Show full text]
  • Gases in Metals: Iii. the Determination of Nitrogen in Metals by Fusion in Vacuum
    S563 GASES IN METALS: III. THE DETERMINATION OF NITROGEN IN METALS BY FUSION IN VACUUM By Louis Jordan and James R. Eckman ABSTRACT A method has been developed for the determination of nitrogen in the gases evolved from metals fused in vacuum. As in a previously described method for the determination of oxygen and hydrogen by vacuum fusion, the metal sample is melted in a graphite crucible in a high-frequency vacuum furnace. The nitrogen, together with the other gases evolved except the noble gases, is absorbed in calcium vapor. The calcium nitride thus formed is dissolved in dilute hydrochloric acid with the formation of an ammonium salt, and the resulting ammonia is determined by distillation into a standard acid. The efficiency of the determination of nitrogen by absorption in calcium vapor was determined by tests with known gas mixtures. The complete vacuum-fusion procedure was applied to the analysis of several synthetic nitrides (silicon, aluminum, titanium, zirconium, chromium, vanadium) and a few irons and steels. The results ob- tained were compared with the nitrogen values given by the usual acid-solution method for nitrogen in metals. The fusion method has a precision equal to that of .the solution method and gives higher values for nitrogen than the solution method in the analysis of nitrides of silicon, titanium, and vanadium and in certain iron and steel samples. The fusion method should determine also any "uncombined" nitrogen present in a metal. CONTENTS Page I. Introduction 468 II. Review of methods for determining nitrogen in gas mixtures 470 III. Calcium as an absorbent for nitrogen 471 IV.
    [Show full text]
  • Graphitic Carbon Nitride “
    Chem Soc Rev View Article Online REVIEW ARTICLE View Journal | View Issue Graphitic carbon nitride ‘‘reloaded’’: emerging applications beyond (photo)catalysis Cite this: Chem. Soc. Rev., 2016, 45,2308 Jian Liu,*ab Hongqiang Wang*cd and Markus Antoniettia Despite being one of the oldest materials described in the chemical literature, graphitic carbon nitride (g-C3N4) has just recently experienced a renaissance as a highly active photocatalyst, and the metal-free polymer was shown to be able to generate hydrogen under visible light. The semiconductor nature of g-C3N4 has triggered tremendous endeavors on its structural manipulation for enhanced photo(electro)chemical performance, aiming at an affordable clean energy future. While pursuing the stem of g-C3N4 related catalysis (photocatalysis, electrocatalysis and photoelectrocatalysis), a number of emerging intrinsic properties of g-C3N4 are certainly interesting, but less well covered, and we believe that these novel applications outside of conventional catalysis can be favorably exploited as well. Thanks to the general efforts devoted to the exploration and enrichment of g-C3N4 based chemistry, the boundaries of this area have Creative Commons Attribution 3.0 Unported Licence. been possibly pushed far beyond what people could imagine in the beginning. This review strives to cover the achievements of g-C3N4 related materials in these unconventional application fields for depicting the broader future of these metal-free and fully stable semiconductors. This review starts with Received 13th October 2015 the general protocols to engineer g-C3N4 micro/nanostructures for practical use, and then discusses the DOI: 10.1039/c5cs00767d newly disclosed applications in sensing, bioimaging, novel solar energy exploitation including photocatalytic coenzyme regeneration, templating, and carbon nitride based devices.
    [Show full text]
  • Nonaqueous Syntheses of Metal Oxide and Metal Nitride Nanoparticles
    Max-Planck Institut für Kolloid and Grenzflächenforschung Nonaqueous Syntheses of Metal Oxide and Metal Nitride Nanoparticles Dissertation zur Erlangung des akademischen Grades “doctor rerum naturalium” (Dr. rer. nat.) in der Wissenschaftsdisziplin “Kolloidchemie” eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät Universität Potsdam von Jelena Buha Potsdam, im Januar 2008 Dieses Werk ist unter einem Creative Commons Lizenzvertrag lizenziert: Namensnennung - Keine kommerzielle Nutzung - Weitergabe unter gleichen Bedingungen 2.0 Deutschland Um die Lizenz anzusehen, gehen Sie bitte zu: http://creativecommons.org/licenses/by-nc-sa/2.0/de/ Elektronisch veröffentlicht auf dem Publikationsserver der Universität Potsdam: http://opus.kobv.de/ubp/volltexte/2008/1836/ urn:nbn:de:kobv:517-opus-18368 [http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18368] С’ вером у Богa Abstract Nanostructured materials are materials consisting of nanoparticulate building blocks on the scale of nanometers (i.e. 10-9 m). Composition, crystallinity and morphology can enhance or even induce new properties of the materials, which are desirable for todays and future technological applications. In this work, we have shown new strategies to synthesise metal oxide and metal nitride nanomaterials. The first part of the work deals with the study of nonaqueous synthesis of metal oxide nanoparticles. We succeeded in the synthesis of In2O3 nanopartcles where we could clearly influence the morphology by varying the type of the precursors and the solvents; of ZnO mesocrystals by using acetonitrile as a solvent; of transition metal oxides (Nb2O5, Ta2O5 and HfO2) that are particularly hard to obtain on the nanoscale and other technologically important materials. Solvothermal synthesis however is not restricted to formation of oxide materials only.
    [Show full text]
  • Solid State Metathesis Preparations of Hard Refractory Ceramics
    S o u p S t a t e M e t a t h e s is P reparations OF H a r d R e f r a c t o r y C e r a m i c s A thesis presented by: Artur Marek Nartowski BSc in partial fulfilment for the award of Ph. D. U n iv e r s it y C o l l e g e Lo n d o n D e p t , o f C h e m is t r y ProQuest Number: 10014877 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10014877 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Acknowledgements This work was supported by EPSRC and was completed under very helpfiil and encouraging supervision of Dr. I. P. Parkin. Grateful acknowledgement is due to members of staff, especially Dr. C. Carmalt, Prof. A. J. Craven, Dr. M. MacKenzie and the departmental microanalyst. I am also indebted to my fellow students, in particular, L.
    [Show full text]
  • Nitridation in the Processing and Preparation of Metals and Ceramics
    Nitridation in the Processing and Preparation of Metals and Ceramics O. Addemir, A. Tekin and C.K. Gupta* Faculty of Chemistry and Metallurgy, Istanbul Technical University, 80286 Maslak, Istanbul, Turkey; *Materials Group, Bhabha Atomic Research Centre, Bombay 400 085, India ABSTRACT 1. INTRODUCTION The formation and separation of metal nitrides from Most of the elements in the periodic table combine a variety of materials including ferroalloys, oxides, with nitrogen to form nitrogen compounds or nitrides. natural materials and minerals is an important com- Based on their structure and bonding characteristics, ponent in current materials processing practice. they have been divided into four groups and among Ferroalloys like ferroniobium and ferrovanadium these the transition metal nitrides and the diamond-like undergo nitridation by ammonia yielding a mixture of nitrides exhibit more readily usable properties. Among iron nitrides and the refractory metal nitride. Acid the many properties of the nitrides, the high melting leaching effectively separates the iron nitride from the point, high hardness and resistance to corrosion are mixture. Niobium nitride thus obtained is used to very attractive. However, nitrides are also brittle, produce niobium metal by pyrovacuum treatment. readily oxidise at high temperatures and many of them Vanadium nitride converts to metal when pyrovacuum thermally decompose. While some of these limitations treatment is followed by electrorefining. Nitride have been partially overcome in novel compositions suitable for decomposition to metal can be obtained like sialon, the extensive use of the majority of nitrides from niobium pentoxide by reacting ammonia or by is restricted by these limitations. In recent times, the reacting a mixture of carbon and nitrogen.
    [Show full text]
  • Nitrides As Ammonia Synthesis Catalysts and As Potential Nitrogen Transfer Reagents
    Appl Petrochem Res (2014) 4:3–10 DOI 10.1007/s13203-014-0049-y KACST FORUM Nitrides as ammonia synthesis catalysts and as potential nitrogen transfer reagents J. S. J. Hargreaves Received: 5 February 2014 / Accepted: 27 February 2014 / Published online: 19 March 2014 Ó The Author(s) 2014. This article is published with open access at Springerlink.com Abstract In this article, an overview of the application of operation is of significant interest. In this context, it is selected metal nitrides as ammonia synthesis catalysts is salient to note that, taken in its entirety, including the presented. The potential development of some systems into provision and purification of reactant feedstreams, on a nitrogen transfer reagents is also described. global scale, the operation of the Haber Process currently consumes 1–2 % of the world’s energy demand, e.g. [2, 3]. Keywords Nitrogen Á Hydrogen Á Catalysis Á Ammonia Á Therefore, any improvements can potentially yield massive Nitrides rewards both in terms of economic and environmental benefits. The identification and application of more active catalysts could lead to lowering of the process temperatures Introduction and/or pressures of operation necessary to achieve a desired space time yield of product. Indeed, lowered The successful development of the Haber–Bosch Process reaction temperatures result in improved obtainable for the production of ammonia was a paramount achieve- equilibrium yields offering the tantalising prospect of a ment of the twentieth Century. Through the provision of an possible win–win situation, providing sufficiently accessible route to synthetic fertiliser, it has been pivotal in favourable kinetics can be achieved.
    [Show full text]
  • Hydrothermal Synthesis of Vanadium Nitride and Modulation of Its Catalytic Performance for Oxygen Reduction Reaction
    Electronic Supplementary Material (ESI) for Nanoscale. This journal is © The Royal Society of Chemistry 2014 Electronic Supplementary Information Hydrothermal Synthesis of Vanadium Nitride and Modulation of Its Catalytic Performance for Oxygen Reduction Reaction Taizhong Huang1,2†*, Shun Mao2†, Guihua Zhou2, Zhenhai Wen2, Xingkang Huang2, Suqin Ci2, and Junhong Chen2* Methods Sample preparation. VN was prepared by a simple hydrothermal method. In a typical procedure, 0.2 g VCl3 was first dissolved into 40 ml DI water and 8 ml ammonia solution (30 wt.%) was added into the VCl3 solution. Then the solution was treated with ultrasonication until the solution reached limpidity. The limpid solution was transferred into an autoclave for a hydrothermal reaction at 200 °C for 20 hours. The obtained black powder was VN. The VN powders were annealed at 750 °C in an ammonia gas flow (0.5 lpm, quarter inch tube) for two hours to improve the VN crystalline structure. The graphene-supported V2O3 was prepared by a hydrothermal method using VCl3 as the precursor. First, 0.2 g VCl3 (97%, Aldrich) and 8.0 ml graphene oxide (GO) (10 mg/ml in DI water, ACS Materials) were mixed with ultrasonication for 30 minutes. Then hydrothermal reaction occurred at 200 °C for eight hours and the obtained precipitation was washed with a large amount of DI water and dried at 80 °C for four hours. The obtained graphene-supported V2O3 was reduced at 1000 °C in a hydrogen and ammonia gas flow (0.5 lpm, quarter inch tube) for two hours to obtain VC and V(C, N), respectively.
    [Show full text]
  • Synthesis of IV-VI Transition Metal Carbide and Nitride Nanoparticles
    Synthesis of IV-VI Transition Metal Carbide and Nitride Nanoparticles Using a Reactive Mesoporous Template for Electrochemical Hydrogen Evolution Reaction Dissertation by Nawal Alhajri In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy King Abdullah University of Science and Technology Thuwal, Kingdom of Saudi Arabia © January 2016 Nawal Alhajri All Rights Reserved 2 EXAMINATION COMMITTEE APPROVALS FORM The dissertation of Nawal Alhajri is approved by the examination committee. Committee Chairperson Kazuhiro Takanabe Committee Member Yu Han Committee Member Jr-Hau He Committee Member Harun Tüysüz 3 ABSTRACT Synthesis of IV-VI Transition Metal Carbide and Nitride Nanoparticles Using a Reactive Mesoporous Template for Electrochemical Hydrogen Evolution Reaction Nawal Alhajri Interstitial carbides and nitrides of early transition metals in Groups IV-VI exhibit platinum-like behavior which makes them a promising candidate to replace noble metals in a wide variety of reactions. Most synthetic methods used to prepare these materials lead to bulk or micron size powder which limits their use in reactions in particular in catalytic applications. Attempts toward the production of transition metal carbide and nitride nanoparticles in a sustainable, simple and cheap manner have been rapidly increasing. In this thesis, a new approach was presented to prepare nano-scale transition metal carbides and nitrides of group IV-VI with a size as small as 3 nm through the reaction of transition metal precursor with mesoporous graphitic carbon nitride (mpg-C3N4) that not only provides confined spaces for nanoparticles formation but also acts as a chemical source of nitrogen and carbon. The produced nanoparticles were characterized by powder X-ray diffraction (XRD), temperature-programmed reaction with mass spectroscopy (MS), CHN elemental analyses, thermogravimetric analyses (TGA), nitrogen sorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM).
    [Show full text]
  • Porous Voxny Nanoribbons Supported on Cnts As Efficient And
    www.nature.com/scientificreports OPEN Porous VOxNy nanoribbons supported on CNTs as efficient and stable non-noble electrocatalysts Received: 24 August 2015 Accepted: 19 October 2015 for the oxygen reduction reaction Published: 30 November 2015 K. Huang1, K. Bi1, Y. K. Lu2, R. Zhang1, J. Liu2, W. J. Wang3, H. L. Tang4, Y. G. Wang1 & M. Lei1 Novel nanocomposites of carbon nanotubes supported porous VOxNy nonoribbons (VOxNy-CNTs) have been synthesized by the annealing of the sol-gel mixture of CNTs and V2O5 under NH3 atmosphere as well as the ageing process in air. Besides the morphological and structural characterizations revealed by TEM, SEAD, EDS, XRD and XPS measurements, typical electrochemical tests including cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry have been employed to determine the oxygen reduction reaction (ORR) performance of VOxNy-CNTs. Inspiringly, the results 2 indicate that VOxNy-CNTs catalyst exhibits a 0.4 mA/cm larger diffusion-limited current density, a 0.10 V smaller onset potential value, a 10.73% less of ORR current decay and an excellent methanol- tolerance compared with commercial Pt/C catalyst. Therefore, we have reasonable grounds to believe that this new VOxNy-CNTs nanocomposites can be regarded as a promising non-precious methanol- tolerant ORR catalyst candidate for alkaline fuel cells. With the highly social development of industrialization and urbanization, the critical energy shortages mainly from the depletion of fossil fuels have motivated and accelerated intensive researches in devel- oping alternative energy conversion and storage devices (ECSDs) with higher power and energy den- sities1–5. Among various potential ECSDs for practical applications, polymer electrolyte membrane fuel cells (PEMFCs) have been extensively regarded as ideal power sources for future mobile and stationary applications due to their high energy efficiency, high power density and low level of emissions6–8.
    [Show full text]
  • A Theoretical Study on Vanadium Nitride
    Materials Advances View Article Online PAPER View Journal | View Issue Surface oxidation for enhancing the hydrogen evolution reaction of metal nitrides: a theoretical Cite this: Mater. Adv., 2021, 2, 3394 study on vanadium nitride† Samira Adimi,ab Weiliang Qi, b Tiju Thomas,c Ralph Gebauer,*d Minghui Yang *b and Shengping Ruan *a The rational design of novel catalysts for energy applications has been an area of immense interest over the past decades. Recent studies have demonstrated that slight surface oxidation of nitrides can boost their catalytic activity, especially towards hydrogen adsorption. In this study, we have considered VN as a simple model nitride to simulate H adsorption on pure and oxygen polluted surfaces. First, we have evaluated the physical characteristics and stability of various facets. Diversity in the VN catalytic activity can originate from a variety of surface characteristics. Our calculations reveal the (112) and (200) surfaces as the most stable ones, while the (101), (111), and (113) surfaces are roughly in the same range Creative Commons Attribution 3.0 Unported Licence. Received 17th March 2021, of energy. The facet-dependent activity of VN toward H adsorption is then carefully discussed. A low Accepted 30th March 2021 level of oxygen contamination appears to make the VN hydrogen adsorption robust and beyond that, a DOI: 10.1039/d1ma00231g thin oxide surface layer can act as an activation layer, playing a positive role in improving the catalytic performance. We anticipate this picture to be an important input for designing enhanced nitride-based rsc.li/materials-advances catalysts with controlled oxidation of surfaces.
    [Show full text]
  • Nitrogen Solubility and Austenitic Fe-V Alloys* of Nitride In
    Nitrogen Solubility and Precipitation of Nitride in Austenitic Fe-V Alloys* By Harue WADA* * Synopsis same method used in the previous investigation.' The equilibriumnitrogen solubility and nitrideformation in austenitic No increases in AI or Si contents were detected in Fe-V alloyswere measured in thetemperature range from 1273 to 1 523 K. the prepared specimens. Specimens0.5 mm thick were equilibratedwith three differentnitrogen- The experimental apparatus and procedure of argon-1% hydrogengases. The nitrogensolubility obeys Sieverts' law. equilibration were described in previous papers."2) The experimentalresults in 1-phasewere analyzedby the centralatoms Five Fe-V alloy specimens and Fe were equilibrated model,and the Wagnerinteraction coefficient was determinedas a function with three different N2-1 %H2-Ar mixed gases; gas of temperatureas: A(99%N2-1 %H2), gas B(63.55%N2-1 %H2-Ar) and eN= (-323 600±10 860)/T+(165±7.8) gas C(34.0%N2-1 %H2-Ar). All five alloys were The weightpercent interaction parameters, 4 and ey, weredetermined as equilibrated except a few runs in which only selected functionsof temperaturefrom this value. The solubilityof nitrogenat alloys were included to obtain sufficient amounts of PNT2=1is expressedas a function of temperatureas: nitride for analysis of nitrogen in the nitride. log (wt%N)r-re-v = [539+1540(wt%V)]/T 2. Analyses -0 .79(wt%V)-0.20. The nitrogen content in an Fe-V specimen which Theprecipitated nitride was identifiedas vanadiummononitride VN, and contains precipitated nitrides can be divided into the solubilityproduct was determinedas a function of temperatureas: two parts: log (wt%N)(wt%V) _ (-6 777±372)/T+(2.07±0.3).
    [Show full text]