Gotowe bibliografie tematyczne / Molybdenum carbides

Gotowa bibliografia na temat „Molybdenum carbides”

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Data publikacji: 22 czerwca 2024

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  1. Artykuły w czasopismach
  2. Rozprawy doktorskie
  3. Książki
  4. Części książek
  5. Streszczenia konferencji
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Artykuły w czasopismach na temat "Molybdenum carbides":

1

De Bonis, Angela, Mariangela Curcio, Antonio Santagata, Agostino Galasso i Roberto Teghil. "Transition Metal Carbide Core/Shell Nanoparticles by Ultra-Short Laser Ablation in Liquid". Nanomaterials 10, nr 1 (14.01.2020): 145. http://dx.doi.org/10.3390/nano10010145.

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Transition metal carbide nanoparticles are a class of technological interesting materials with a wide range of applications. Among metal carbides, tantalum carbides have good compatibility with the biological environment while molybdenum carbides are used as catalyst in electrochemical reactions. Laser ablation of bulk transition metal targets in some liquids is here reported and laser ablation in organic solvents is used as simple synthetic strategy for the production of carbide nanostructures. Herein, the nanoparticles produced by ultra-short laser ablation of tantalum and molybdenum in water, acetone, ethanol and toluene have been characterized by TEM, XRD and XPS analysis. The combined effect of metal and solvent chemical and physical properties on the composition of the nanomaterials obtained has been pointed out. In particular, the different reactivity of Ta and Mo with respect to oxidizing species determines the composition of particles obtained in water, on the other hand the organic solvents decomposition allows to obtain transition metal carbide (TMC) nanoparticles. The observed carbonaceous shell formed on TMC allows to protect the particle’s carbidic core and to improve and tailor the applications of these nanomaterials.
2

Gavrilova, Natalia, Maria Myachina, Victor Nazarov i Valery Skudin. "Simple Synthesis of Molybdenum Carbides from Molybdenum Blue Nanoparticles". Nanomaterials 11, nr 4 (30.03.2021): 873. http://dx.doi.org/10.3390/nano11040873.

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In recent years, much attention has been paid to the development of a new flexible and variable method for molybdenum carbide (Mo2C) synthesis. This work reports the applicability of nano-size clusters of molybdenum blue to molybdenum carbide production by thermal treatment of molybdenum blue xerogels in an inert atmosphere. The method developed made it possible to vary the type (glucose, hydroquinone) and content of the organic reducing agent (molar ratio R/Mo). The effect of these parameters on the phase composition and specific surface area of molybdenum carbides and their catalytic activity was investigated. TEM, UV–VIS spectroscopy, DTA, SEM, XRD, and nitrogen adsorption were performed to characterize nanoparticles and molybdenum carbide. The results showed that, depending on the synthesis conditions, variants of molybdenum carbide can be formed: α-Mo2C, η-MoC, or γ-MoC. The synthesized samples had a high specific surface area (7.1–203.0 m2/g) and meso- and microporosity. The samples also showed high catalytic activity during the dry reforming of methane. The proposed synthesis method is simple and variable and can be successfully used to obtain both Mo2C-based powder and supports catalysts.
3

Gavrilova, Natalia, Maria Myachina, Victor Dyakonov, Victor Nazarov i Valery Skudin. "Synthesis of Microporous Mo2C-W2C Binary Carbides by Thermal Decomposition of Molybdenum-Tungsten Blues". Nanomaterials 10, nr 12 (4.12.2020): 2428. http://dx.doi.org/10.3390/nano10122428.

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Molybdenum and tungsten carbides are perspective catalytic systems. Their activity in many reactions is comparable to the activity of platinum group metals. The development of the synthesis method for of highly dispersed binary molybdenum and tungsten carbides is an important task. Dispersions of molybdenum-tungsten blue were used as a precursor for synthesis of binary molybdenum and tungsten carbides. The synthesis of carbides was carried out by thermal decomposition of molybdenum-tungsten blue xerogels in an inert atmosphere. The binary carbides were characterized by XRD, TGA, SEM and nitrogen adsorption. The influence of the molar ratio reducing agent/Me [R]/[ΣMe], molar ratio molybdenum/tungsten [Mo]/[W] on phase composition, and morphology and porous structure of binary carbides was investigated. Samples of binary molybdenum and tungsten carbides with a highly developed porous structure and a specific surface area were synthesized.
4

Tišler, Zdeněk, Romana Velvarská, Lenka Skuhrovcová, Lenka Pelíšková i Uliana Akhmetzyanova. "Key Role of Precursor Nature in Phase Composition of Supported Molybdenum Carbides and Nitrides". Materials 12, nr 3 (29.01.2019): 415. http://dx.doi.org/10.3390/ma12030415.

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In this work, we studied the effect of molybdenum precursors and the synthesis conditions on the final phase composition of bulk and supported molybdenum carbides and nitrides. Ammonium heptamolybdate, its mixture with hexamethylenetetramine, and their complex were used as the precursors at different temperatures. It was investigated that the synthesis of the target molybdenum nitrides strongly depended on the structure of the precursor and temperature conditions, while the synthesis of carbide samples always led to the target phase composition. Unlike the carbide samples, where the α-Mo2C phase was predominant, the mixture of β-Mo2N, MoO2 with a small amount of metal molybdenum was generally formed during the nitridation. All supported samples showed a very good dispersion of the carbide or nitride phases.
5

S. Maksymova, V. Voronov, P. Kovalchuk i A. Larionov. "Structure and Properties of Graphite-Molybdenum Brazed Joints". Metallurgical and Materials Engineering 29, nr 1 (31.03.2023): 115–28. http://dx.doi.org/10.56801/mme989.

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The paper presents the results of X-ray microspectral studies of dissimilar brazed joints of molybdenum with graphite. It is shown that during active brazing of graphite with molybdenum, mutual diffusion processes occur, and the adhesion-active brazing filler metals penetrates into graphite, and interacts with it, which leads to the formation of carbide phases. When using the Ti-Cr-V and Cu-Ti-Ni systems brazing filler metals, titanium carbides are formed. The zirconium carbides are formed, when using the brazing filler metals based on the Zr-Pd(Mo) systems and the CxMey(Mo, Cr) carbides are formed using the brazing filler metals of the Pd-Ni-Cr-Ge system. The results of tests for three-point bending showed that the using of Pd-Ni-Cr-Ge brazing filler metals provides stable strength at the level of 34-37 MPa, destruction occurs along graphite.
6

Thuvander, Mattias, Hans Magnusson i Ulrika Borggren. "Carbide Precipitation in a Low Alloyed Steel during Aging Studied by Atom Probe Tomography and Thermodynamic Modeling". Metals 11, nr 12 (13.12.2021): 2009. http://dx.doi.org/10.3390/met11122009.

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Carbide precipitation in martensitic low alloyed steels contributes to the mechanical properties through precipitation hardening. A high number density of carbides is desired to maximize the hardening effect, which is achieved through the precipitation of carbides on the dislocations in the martensitic structure. In this study, the nucleation, growth, and coarsening of vanadium and molybdenum carbides during aging at 600 °C for periods up to four weeks were investigated. The work covers characterization with atom probe tomography, which showed that the nucleation of V and Mo rich MC/M2C carbides takes place on dislocations. The growth of these carbides proceeds by the diffusion of elements to the dislocations, which has been modeled using Dictra software, confirming the rate of the reaction as well as the depletion of carbide formers in the matrix. For longer aging times, particle coarsening will decrease the number density of particles with a transition from dislocation-based carbides to separate rounded carbides.
7

Papaefthymiou, Spyros, Marianthi Bouzouni i Roumen H. Petrov. "Study of Carbide Dissolution and Austenite Formation during Ultra–Fast Heating in Medium Carbon Chromium Molybdenum Steel". Metals 8, nr 8 (16.08.2018): 646. http://dx.doi.org/10.3390/met8080646.

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In this study, UltraFast Heat Treatment (UFHT) was applied to a soft annealed medium carbon chromium molybdenum steel. The specimens were rapidly heated and subsequently quenched in a dilatometer. The resulting microstructure consists of chromium-enriched cementite and chromium carbides (in sizes between 5–500 nm) within fine (nano-sized) martensitic and bainitic laths. The dissolution of carbides in austenite (γ) during ferrite to austenite phase transformation in conditions of rapid heating were simulated with DICTRA. The results indicate that fine (5 nm) and coarse (200 nm) carbides dissolve only partially, even at peak (austenitization) temperature. Alloying elements, especially chromium (Cr), segregate at austenite/carbide interfaces, retarding the dissolution of carbides and subsequently austenite formation. The sluggish movement of the austenite /carbide interface towards austenite during carbide dissolution was attributed to the partitioning of Cr nearby the interface. Moreover, the undissolved carbides prevent austenite grain growth at peak temperature, resulting in a fine-grained microstructure. Finally, the simulation results suggest that ultrafast heating creates conditions that lead to chemical heterogeneity in austenite and may lead to an extremely refined microstructure consisting of martensite and bainite laths and partially dissolved carbides during quenching.
8

Abdulazizov, Tilebaldy Adilovich, Abduraim Satyvaldievich Satyvaldiev i Kalyskan Imatali kyzy. "Oxidation of cubic complex carbides (Ti xVyMoz)C synthesis by electrospark dispersion method with atmospheric oxygen". E3S Web of Conferences 537 (2024): 05011. http://dx.doi.org/10.1051/e3sconf/202453705011.

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During the joint electrospark dispersion of titanium with VyMoz alloys in hexane, complex carbides (TixVyMoz)C with a cubic lattice are formed. Assuming that complex carbides (TixVyMoz)C as quasi-binary systems, where complex carbide (VyMoz)C with a cubic structure is dissolved in cubic titanium monocarbide, the composition of complex carbides (Ti0,75V0,05Mo0,20)C and (Ti0,65V0,31Mo0,04)C, formed by electrospark dispersion of Ti-V0,2Mo0,8 and Ti-V0,2Mo0,8 pairs. Using the method of differential thermal analysis, it was shown that the thermal stability against oxidation of complex carbides (TixVyMoz)C, synthesized by joint electrospark dispersion of titanium and the VyMoz alloy, depends on the ratio of metals. Thermal stability against oxidation increases with an increase in the content of titanium and molybdenum in the composition of complex carbides; their resistance to oxidation increases. It has been established that intensive oxidation of complex carbide (Ti0,75V0,05Mo0,20)C occurs at 595oC, and complex carbide (Ti0,65V0,31Mo0,04)C oxidizes at the maximum rate at 520oC.
9

Chen, Meng, Yufei Ma, Yanqiang Zhou, Changqing Liu, Yanlin Qin, Yanxiong Fang, Guoqing Guan, Xiumin Li, Zhaoshun Zhang i Tiejun Wang. "Influence of Transition Metal on the Hydrogen Evolution Reaction over Nano-Molybdenum-Carbide Catalyst". Catalysts 8, nr 7 (22.07.2018): 294. http://dx.doi.org/10.3390/catal8070294.

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The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo2C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo2+ species (Mo2C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo2C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo2C). The 2% Pt-Mo2C required a η10 of 79 mV, and outperformed that of pure β-Mo2C (η10 = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H2SO4. Also, the 2% Pt-Mo2C catalyst demonstrated a high stability for the HER in 0.5 M H2SO4. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure.
10

Covington, Leroy, Kamalesh Munirathinam, Akand Islam i Kenneth Roberts. "Synthesis and characterization of nanostructured molybdenum & tungsten carbide materials, and study of diffusion model". Polish Journal of Chemical Technology 14, nr 1 (1.01.2012): 28–34. http://dx.doi.org/10.2478/v10026-012-0055-8.

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Synthesis and characterization of nanostructured molybdenum & tungsten carbide materials, and study of diffusion model Powders of two molybdenum carbides (Mo2C and MoC1-x) and tungsten carbide (WC) were prepared by means of temperature programmed reaction (TPR) method. Mo2C and MoC1-x were synthesized by reacting MoO3 with a preselected molar ratio of methane/hydrogen and carbon monoxide/hydrogen gas mixtures respectively. WC was prepared using tungsten oxide (WO3) and a methane/hydrogen gas mixture. These carbides were ultrasonically dispersed in de-ionized water. Samples were characterized using room temperature x-ray diffraction and scanning microscopy. A kinetic diffusion model is also studied to determine diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentrations. The method involves measuring the flux of the diffusive species into the solid under the influence of a temperature program.
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Artykuły w czasopismach Rozprawy doktorskie

Rozprawy doktorskie na temat "Molybdenum carbides":

1

Clark, Christopher H. "Characterization and investigation of molybdenum carbides on activated carbon as hydrogenation catalysts". Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4281.

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Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains viii, 76 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 54-57).
2

McCauley, Robert Lowry. "The effects of molar flux, pressure, and product gases on the stability of molybdenum carbide during steam methane reforming". Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/r%5Fmccauley%5F120105.pdf.

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Susanto, Benny Laurensius Materials Science &amp Engineering Faculty of Science UNSW. "Kinetics of carbide dissolution in chromium + molybdenum steels during oxidation". Awarded by:University of New South Wales. Materials Science and Engineering, 2004. http://handle.unsw.edu.au/1959.4/19385.

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Iron-based alloys containing 15% chromium, 2-3% molybdenum and 0.02-1.7% carbon, consisting of M23C6 and M6C carbides in an austenitic matrix were oxidised at 8500C to study their oxidation resistance and a precipitate-free zone formation. Alloy design was carried out using a thermodynamic software Thermo-Calc. Carbides in these alloys were expected to dissolve during oxidation, releasing chromium required for the protective oxide formation. Decarburisation of the matrix was expected to trigger the carbide dissolution, and form a precipitate-free zone. Transformation of the austenitic into ferritic matrix in the precipitate-free zone was expected be essential for providing a fast chromium supply to the oxide/alloy interface. Upon exposure to pure oxygen, most of the alloys oxidised non-protectively due to the fast oxidation attack and low chromium content in the matrix, while carbide dissolution was too slow. The alloys were then pre-oxidised in H2+10%H2O to grow a purely chromia scale. In this low oxygen partial pressure environment, carbides in the alloy's sub-surface dissolved and formed a ferritic precipitate-free zone. The precipitate dissolution model developed by previous investigators was then tested and proven to be valid in this iron-based alloy system. The endurance of the pre-formed chromia scale with its underlying precipitate-free zone was then tested in pure oxygen environment. All of the alloys that had successfully developed a ferritic precipitate-free zone in the pre-oxidation stage, survived the subsequent oxidation in pure oxygen up until 3 weeks observation. Although x-ray diffraction found some minor iron oxides, the oxide consisted of mainly Cr2O3. Since iron activity had increased and iron oxides had become stable after the pure oxygen gas was introduced, the growth of the precipitate-free zone had to compete with the rate at which it was consumed by oxidation. It was concluded that the transformation from austenite to ferrite at the subsurface region of the alloy could be achieved provided that the volume fraction of the carbides did not exceed 0.2. Evidence indicated that the chromia scale grew by chromium provided by the dissolving carbides. Pre-oxidation led to a promising use of the alloys at atmospheric oxygen pressure.
4

Perret, Noemie. "New catalyst formulations based on gold and molybdenum nitrides and carbides : application in selective hydrogenation". Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2657.

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The development of selective heterogeneous catalytic systems is of fundamental importance for the realisation of sustainable green chemical processes. In this thesis, the hydrogenation of nitroarene, aldehyde and carboxylic acid compounds is examined in continuous gas phase operation, for the synthesis of a target functionalised aromatic amine and alcohol. Novel catalysts based on Mo nitride, carbide and supported Au have been synthesised and subjected to an array of complementary characterisation measurements that provide catalyst structure/performance correlations with detailed kinetic and mechanistic analysis. The use of Mo2N and Mo2C as catalysts served to promote the selective hydrogenation of nitrobenzene to aniline and p-chloronitrobenzene to p-chloroaniline where the incorporation of nano-scale Au increased reaction rate. Activity has been correlated to hydrogen adsorption/release capacity, which shows a dependence on the degree of nitridation and crystallographic structure. In contrast, hydrogenation of benzaldehyde is limited by C=O activation, which is facilitated by the Mo component. Alumina supported Au has exhibited 100% selectivity in the hydrogenation of benzaldehyde and 4-nitrobenzaldehyde to the target alcohol, where Au particle size and surface Lewis acidity play crucial roles. The hydrogenation of benzoic acid over Au supported on a CeO2-ZrO2 mixed oxide has shown promising results with the possibility of a one step transformation to the alcohol. The results presented in this thesis establish feasible catalytic routes to high value amines and alcohols where critical process optimisation is demonstrated in terms of catalyst composition/surface structure and reaction conditions.
5

Cunha, Adilto Pereira Andrade 1981. "Caracterização mecânica e microestrutural de aços médio carbono microligados ao nióbio e molibdênio". [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265015.

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Orientador: Paulo Roberto Mei
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-23T13:15:12Z (GMT). No. of bitstreams: 1 Cunha_AdiltoPereiraAndrade_D.pdf: 32849719 bytes, checksum: a54b97b2dde32f5f0d6b96ee877e51fb (MD5) Previous issue date: 2013
Resumo: Neste trabalho foi estudada a influência da adição de molibdênio e nióbio na microestrutura e propriedades mecânicas de aços com 0,5 e 0,6 %C, utilizado na fabricação de rodas ferroviárias. A deformação dos aços foi aplicada através da laminação, em escala de laboratório, simulando o forjamento no processo real de fabricação. As amostras foram aquecidas a 1250 °C para solubilização do nióbio, sendo então laminadas em 4 passes, a partir de 1200 °C, sofrendo uma deformação total (redução em altura) de 67%, seguida de resfriamento ao ar. Posteriormente, os aços C5 e C5Nb foram submetidos a um tratamento térmico de têmpera e revenimento. Foram analisadas amostras dos aços por microscopia óptica, eletrônica de varredura e transmissão e também foram realizados ensaios mecânicos em todas as condições. Após a laminação entre 1200 e 1120 °C, observou-se que a adição de molibdênio e nióbio promoveu um aumento da resistência mecânica em 171 e 119 MPa no limite de escoamento e 61 e 66 MPa no limite de resistência à tração, nos aços C5Nb e C6Nb, respectivamente, devido à precipitação de carbonetos de nióbio, mantendo a mesma ductilidade e tenacidade para o aço C5Nb, mas houve uma queda dessas propriedades para os aço C6Nb. Após a laminação com posterior têmpera e revenimento a 500°C, simulando o mesmo tratamento feito na roda ferroviária, o aço C5 apresentou dureza, resistência mecânica e alongamento iguais à do aço da MWL, porém com redução de área e energia absorvida maiores que o aço da MWL. O aço C5Nb apresentou maiores valores de resistência mecânica, ductilidade e tenacidade que o aço da MWL, o que demonstra seu potencial para melhorar a qualidade das rodas ferroviárias atualmente produzidas
Abstract: The influence of molybdenum and niobium addition on the microstructure and mechanical properties of 0,5 and 0,6 %C steels used in railway wheels was studied. The deformation was applied by rolling, in a thermo mechanical processing laboratory, simulating the forging in the real process of manufacture. The samples were heated to 1250 °C to ensure dissolution of niobium and hot rolled in four passes, starting at 1200 °C, undergoing a total reduction of 67%, followed by air cooling. Steels were water quenched and tempered (heat treatment). Steel samples, before and after rolling and heat treated were analyzed by optical and scanning electron microscopy. Mechanical tests were performed on the all conditions. After rolling between 1200 and 1120 ° C, it was found that the addition of molybdenum and niobium resulted in an increase of mechanical strength at 171 and 119 MPa in yield strength and 61 and 66 MPa in tensile strength, respect due to precipitation of niobium carbides, while maintaining the same ductility and toughness for C5Nb steel, but there was a decrease of these properties for C6Nb. After rolling with subsequent quenching and tempering at 500 ° C, simulating the same treatment done in the railway wheel, steel C5 showed the same toughness, strength and elongation in comparison with MWL rail wheels steel, but with reduced area and absorbed energy greater than the MWL steel. C5Nb steel showed higher strength, ductility and toughness than MWL steel, which demonstrates its potential to improve the quality of railway wheels currently produced
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
6

Posada, Pérez Sergio. "Heterogeneous catalysis of green chemistry reactions on molybdenum carbide based catalysts". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/552405.

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Our society has a problem with the use of fossil fuels, due to the vast and exceeding emissions derived from human activities. Two ways could be consider to mitigate these harmful effects. On the one hand, the capture, activation, and conversion of these hazardous gases towards valuable compounds, and on the other hand, the substitution of fossil fuels for renewable energies. This thesis encompasses the study of two different green chemistry reactions to convert the most abundant greenhouse gas in Earth's atmosphere and the production of a new environmental friendly fuel, the hydrogen. In the current search for new catalysts, Transition Metal Carbides (TMCs) have arisen as an appealing alternative, because their exhibit broad and amazing physical and chemical properties and their low cost. In particular, titanium carbide (001) was proposed from experimental and theoretical points of view as active catalyst and support of small metal particles for CO2 hydrogenation to methanol and water gas shift reaction. However, given that titanium carbide is a cumbersome support to be used in applications due to the difficulty of obtaining nanoparticles on working conditions, we have carried out these reactions on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces. The adsorption and activation of a CO2 molecule on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces have been investigated by means of periodic density functional theory based calculations using the Perdew-Burke-Ernzerhof exchange-correlation functional showing that both surface are promising catalyst for CO2 conversion because they are able to activate and bend the CO2 molecule. The β- Mo2C (001) surface is able to dissociate the CO2 molecule easily, with a low energy barrier, whereas δ-MoC (001) surface activates CO2 but it does not promote its direct dissociation. Experiments accomplished by the group of Dr. Jose Rodriguez revealed that CO and methane are the main products of the CO2 hydrogenation using β-Mo2C (001) as catalyst, and the amount of methanol is lower. On the other hand, only CO and methanol are produced using δ-MoC (001). Experiments revealed that the deposition of small copper particles on the carbide surfaces increase drastically the catalysts' activity and selectivity, which was demonstrated by theoretical calculations. On β-Mo2C, the amount of CO and methanol increase whilst the amount of methane decrease, since copper blocks reactive sites on surface. This is a positive fact since copper avoid the excessive oxygen deposition, which deactivated the catalysts. On the other hand, the deposition of copper on δ-MoC (001) increases a lot the amount of CO and methanol. In summary, our combining DFT- experimental study proposed the Cu/δ-MoC as promising catalyst for CO2 hydrogenation due to its activity (the amount of products is superior than other TMCS, metals, and the model of commercial catalysts), selectivity (only CO and methanol are produced), and stability ( this catalysts is not deactivated by the oxygen deposition). The results obtained in the first part of the thesis were used to study the water gas shift reaction. Given that the excellent features, experiments proposed Au supported on δ-MoC (001) as catalysts. Our theoretical calculations demonstrated that clean δ-MoC (001) is not a good catalysts for WGS, due to the fact that the reverse reactions are favorable respect the direct ones, which implies that the amount of products is lower. Nevertheless, the deposition of Au clusters change the reaction mechanism, favoring the direct barriers instead of reverse ones, and increasing the amount of produced H2. In summary, this thesis has displayed the prominent role of molybdenum carbides as support of small metal particles to catalyze green chemistry reactions.
En aquesta tesi es mostra un treball computacional sobre l'ús de catalitzadors econòmics per a la conversió de CO2, un perillós gas d'efecte hivernacle i també per a la producció d'hidrogen, el combustible del futur. En la recerca actual de nous catalitzadors, els carburs de metalls de transició (TMC) han sorgit com una alternativa atractiva pel el seu baix cost i per exhibir excel·lents propietats físiques i químiques. En aquest treball utilitzarem com a catalitzadors les superfícies cúbica δ-MoC (001) i ortoròmbica β-Mo2C (001). L'adsorció de la molècula de CO2 mostra que ambdues superfícies són capaces d'activar i doblegar la molècula. La superfície β-Mo2C (001) és capaç de dissociar fàcilment la molècula de CO2, mentre que la superfície δ-MoC (001) activa CO2 però no la dissocia. Els experiments realitzats pel grup del Dr. Jose Rodriguez van revelar que el CO i el metà són els principals productes de la hidrogenació de CO2 utilitzant β-Mo2C (001) com a catalitzador, i la quantitat de metanol és menor. D'altra banda, només es produeixen CO i metanol utilitzant δ-MoC (001). La deposició de partícules de coure a les superfícies del carbur augmenta dràsticament l'activitat dels catalitzadors, cosa que es va demostrar mitjançant càlculs teòrics. A la superfície β-Mo2C, la quantitat de CO i metanol augmenten mentre que la quantitat de metà disminueix. D'altra banda, la deposició de coure a δ-MoC (001) augmenta molt la quantitat de CO i metanol. En resum, el nostre estudi proposa el Cu/δ-MoC com a prometedor catalitzador de la hidrogenació de CO2 a causa de la seva activitat (la quantitat de productes és superior a la resta de TMCS, metalls i el model de catalitzadors comercials), selectivitat (només el CO i el metanol es produeixen) i l'estabilitat (aquests catalitzadors no es desactiven per la deposició d'oxigen). Tenint en compte els resultats previs, es va proposar la deposició d'or en la superfície δ-MoC per a la producció d'hidrogen. Els càlculs teòrics demostren que la superfície δ-MoC (001) no és un bon catalitzador per WGS, però la deposició dels clústers d'or canvia el mecanisme de reacció i augmenta la quantitat d'H2 produïda.
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Fonseca, Solange Tamara da 1978. "Efeito de adições de vanádio, nióbio e molibdênio na estrutura e propriedades mecânicas de aços com 0,7 % C utilizados na fabricação de rodas ferroviárias". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265830.

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Orientadores: Paulo Roberto Mei , Amilton Sinatora
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-26T20:19:05Z (GMT). No. of bitstreams: 1 Fonseca_SolangeTamarada_D.pdf: 21576321 bytes, checksum: ed8a1cccc8774fff4540b331b49b44b8 (MD5) Previous issue date: 2015
Resumo: Uma das maneiras de se reduzir os custos no transporte de cargas é aumentando a quantidade de carga transportada por vagão, isto eleva a tensão no eixo do vagão e, consequentemente, a roda deve possuir maior dureza sem perda da tenacidade para suportar o desgaste. Para atingir os níveis de dureza necessários estão sendo desenvolvidas rodas ferroviárias com aços microligados que são definidos como aços carbono-manganês contendo pequenos teores (menores que 0,5% em massa) de elementos de liga, que são fortes formadores de carbonetos como o nióbio (Nb), vanádio (V), molibdênio (Mo) e titânio. Em 2008, a MWL do Brasil iniciou o desenvolvimento de rodas ferroviárias fabricadas com aços microligados, e a partir de 2012, com a colaboração da EPUSP foi necessário o desenvolvimento de uma máquina de ensaio de desgaste tipo disco contra disco que atendesse as especificações da norma AAR (Association of American Railroads). Além disso, havia interesse em se conhecer o comportamento desses aços, sendo assim, seria necessário obter as curvas de resfriamento contínuo (CRC) dos mesmos. A análise destas mostrou que a adição dos elementos microligantes refinou o grão austenítico por formação de finos carbonetos de Nb e V, retardou a formação de ferrita e perlita, o que reduziu o espaçamento interlamelar da perlita; e elevou a temperabilidade dos aços. Entretanto, a adição de microligantes não alterou as temperaturas de início de formação de martensita, mas melhorou a temperabilidade. A formação de martensita não foi finalizada até a temperatura ambiente e todos os aços apresentaram austenita retida junto com a martensita. A análise de corpos de prova retirados das pistas de rolamento das rodas ferroviárias prontas para uso, com estrutura ferrítica-perlítica, revelou que o aço ao V apresentou os melhores resultados em todos os ensaios (tração na temperatura ambiente e 540 ºC, energia absorvida no ensaio Charpy e KIC) quando comparado ao aço sem microligantes ou com a adição de Nb+Mo. O melhor desempenho do aço ao V foi atribuído ao seu menor tamanho de grão austenítico e espaçamento interlamelar da perlita mais refinado. No ensaio de desgaste por deslizamento, a perda de massa foi maior no aço Nb. O primeiro protótipo construído da máquina de desgaste tipo disco contra disco forneceu resultados confiáveis até 250.000 ciclos, não atingindo o valor minímo especificado pela AAR. Entretanto a experiência adquirida foi essencial para projetar um novo protótipo que está em comissionamento
Abstract: One of the main strategies to reduce cost in load transportation is through the increase of the load transported a railroad car. This increase of tension in the wagons axes, require wheels with higher hardness but without loss of ductility and toughness. Thus, to achieve the required levels of hardness, the developments are now focusing on railway wheels composed by microalloyed steels that are defined as carbon-manganese steels containing a small amount (less than 0.5% by mass) of strong carbide-forming elements such as niobium (Nb), vanadium (V), molybdenum (Mo) and/or titanium. The MWL Brazil began in 2008, together with Unicamp, a research project on the development of railway wheel made of microalloyed steel and, later on 2012, EPUSP joined to the project reinforcing the importance of the project. During this work, project developed a disk-on-disk wear test machine that would attend the specifications of the standard AAR (Association of American Railroads). Besides, there was also an interest on further knowing the behavior of these steels, that is, it would be necessary to obtain the continuous cooling curves (CCC). In this work, the analysis of CCC showed that the addition of microalloying elements contributed in refining the austenitic grain size due to fine Nb and V carbides formation; delayed the formation of ferrite and pearlite, which reduced the interlamellar spacing of pearlite; and increased the hardenability of steels. However, the addition of microalloying did not change the starting martensite formation temperature, but increased the hardenability. It was also observed that the formation of martensite was not finished at room temperature and all studied steels presented retained austenite. The analysis of samples taken from the tread of railway wheels, with ferritic-pearlitic structure revealed that the vanadium steel showed the best results in all tests of strength (at room temperature and 540 °C), K1C and Charpy test if compared to steels without microalloying or with the addition of Nb+Mo. The superior performance vanadium steel was attributed to the smallest austenite grain size and the finest interlamellar spacing of the pearlite. In the wear test, the weight loss was greater in the niobium microalloyed steel. The developed prototype of the disk-on-disk wear test machine only provided reliable results up to 250,000 cycles; it not reached the minimum value specified by the AAR. However, the experience was essential to enhance a new prototype that is commissioning
Doutorado
Materiais e Processos de Fabricação
Doutora em Engenharia Mecânica
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Sosa, Letícia. "Hydrodésoxygénation du furfural en 2-methylfurane à l’aide de catalyseurs à base de carbures de molybdène". Electronic Thesis or Diss., Centrale Lille Institut, 2023. http://www.theses.fr/2023CLIL0004.

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Des carbures de molybdène ont été synthétisés, caractérisés et évalués pour la réaction d'hydrodésoxygénation du furfural en 2-méthylfurane à 30 bar de H2, 200 °C dans le 2-butanol et le cyclopentyl méthyl éther. Dans cette thèse, plusieurs facteurs concernant la nature des carbures ont été évalués : (i) l'effet des phases cristallographiques (α-MoC et β-Mo2C) ; (ii) l'effet de l'addition des promoteurs Ni et Cu ; (iii) l'effet de la passivation et de la réactivation ; (iv) l'effet du support (SiO2, TiO2, ZrO2, ZSM-5). Les résultats montrent que la phase β-Mo2C est plus active que la phase α-MoC, mais la même distribution des produits est observée en iso-conversion. L'ajout de Ni et de Cu a eu un effet positif et négatif, respectivement, sur l'activité du carbure. Différents degrés d'oxydation ont eu lieu pendant la passivation des carbures, ce qui était lié à leur dispersion et la réactivation ne les a pas régénérés. Les différents supports ont principalement affecté la première étape de la réaction ainsi que l'état final des carbures de Mo
Molybdenum carbides were synthesized, characterized, and evaluated for the hydrodeoxygenation reaction of furfural to 2-methylfuran at 30 bar of H2 and 200 °C in 2-butanol and cyclopentyl methyl ether. In this thesis, several factors concerning the nature of carbides were evaluated: (i) the effect of crystallographic phases (α-MoC and β-Mo2C); (ii) the effect of the addition of Ni and Cu promoters; (iii) the effect of passivation and reactivation; (iv) effect of support (SiO2, TiO2, ZrO2, ZSM-5). The results show that the β-Mo2C phase is more active than the α-MoC phase, but the same distribution of products is observed in iso-conversion. The addition of Ni and Cu had a positive and negative effect, respectively, on the carbide activity. Different degrees of oxidation occurred during the passivation of carbides, which was related to their dispersion and reactivation did not regenerate them. The different supports mainly affected the first step of the reaction, as well as the final state of the Mo carbides
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Murugappan, Karthick. "Molybdenum trioxide and molybdenum carbide as promising hydrodeoxygenation catalysts for biomass conversion". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111404.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 171-176).
Growing concerns due to rising CO2 emissions have made biomass an indispensable source of renewable fuels and chemicals. However, biomass inherently has high oxygen content, which translates to low energy density, thereby necessitating a deoxygenation step before being utilized as fuels. Recently, MoO3 and Mo2C have emerged as promising earth-abundant cheap catalysts that perform hydrodeoxygenation (HDO) at relatively low temperatures ( 673 K) and ambient H2 pressures wherein oxygen is selectively removed as water. However, there exists a significant knowledge gap in understanding the stability and the active phases responsible for HDO of these catalysts. Furthermore, their applicability for real biomass conversions has not been largely demonstrated. In this thesis, first, HDO of m-cresol, a biomass-derived model compound, is investigated over bulk and supported MoO 3 catalysts. Detailed reactivity and characterization studies reveal that Mo5+ species plays a critical role during HDO. Specifically, TiO2 and ZrO2 are identified as ideal supports as they feature superior HDO reactivity and stability over bulk MoO3 by stabilizing intermediate Mo oxidation states (i.e. Mo5+) while bulk MoO 3 over-reduces to inactive metallic Mo. Translating from model compound studies, supported MoO3 catalysts are demonstrated to be effective in converting biomass (pine) pyrolysis vapors to hydrocarbons (ca. 30 % yield). In comparison with MoO 3, Mo2C is significantly more stable and selective for HDO of 4-methylanisole to toluene under identical reaction conditions. Mo2C predominantly breaks the stronger phenolic C-0 bond while MoO 3 also breaks the weaker aliphatic C-0 bond, likely due to the presence of Bronsted acid sites. To gain insights into the surface active sites, operando near-ambient XPS is employed during HDO and this technique revealed that HDO seems to operate via distinct active sites over both these materials. Finally, Mo2C is shown to be effective in upgrading real lignin streams to a single product propylbenzene, a precursor for renewable polymer. Overall, this thesis demonstrates the applicability of MoO3 and Mo2C in real biomass conversions and provides insights on the working nature of these catalysts, which will enable the design of more effective HDO catalysts.
by Karthick Murugappan.
Ph. D.
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Yu, Jenwei Roscoe. "Methane activation over molybdenum disulfide, molybdenum carbide, and silver(110). Molecular orbital theory". Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1059138320.

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Książki na temat "Molybdenum carbides":

1

Singh, M. Reactive melt infiltration of silicon-molybdenum alloys into microporous carbon preforms. [Washington, D.C: National Aeronautics and Space Administration, 1995.

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H, Titran Robert, i United States. National Aeronautics and Space Administration., red. Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten based alloy wires. [Washington, DC]: National Aeronautics and Space Administration, 1993.

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H, Titran Robert, i United States. National Aeronautics and Space Administration., red. Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten based alloy wires. [Washington, DC]: National Aeronautics and Space Administration, 1993.

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Development and characterization of SiC/MoSi₂-Si₃N₄(p) hybrid composites. [Cleveland, Ohio]: National Aeronautics and Space Administration, Lewis Research Center, 1998.

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Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten based alloy wires. [Washington, DC]: National Aeronautics and Space Administration, 1993.

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Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten based alloy wires. [Washington, DC]: National Aeronautics and Space Administration, 1993.

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Aegerter, Paul A. Thiophene hydrodesulfurization over alumina-supported molybdenum carbide nitride catalysts: Adsorption sites, catalytic activities and nature of the active surface. 1996.

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Części książek na temat "Molybdenum carbides":

1

Storms, E. K. "Molybdenum Carbides". W Inorganic Reactions and Methods, 314. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2007. http://dx.doi.org/10.1002/9780470145265.ch121.

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Dolmatov, V. S., S. A. Kuznetsov, E. V. Rebrov i J. C. Schouten. "Electrochemical Synthesis of Double Molybdenum Carbides". W Molten Salts Chemistry and Technology, 329–37. Chichester, UK: John Wiley & Sons, Ltd, 2014. http://dx.doi.org/10.1002/9781118448847.ch4k.

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Nagai, M., A. Miyata, T. Kusagaya i S. Omi. "Surface molybdenum species and acid sites on nitrided molybdena-alumina catalysts". W The Chemistry of Transition Metal Carbides and Nitrides, 327–44. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1565-7_17.

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Wang, J., M. Castonguay, P. H. McBreen, S. Ramanathan i S. T. Oyama. "Chemisorption of CO and NO on molybdenum carbide foils". W The Chemistry of Transition Metal Carbides and Nitrides, 426–38. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1565-7_23.

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Marchand, R., X. Gouin, F. Tessier i Y. Laurent. "New routes to molybdenum nitrides and oxynitrides: preparation and characterization of new phases". W The Chemistry of Transition Metal Carbides and Nitrides, 252–73. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1565-7_13.

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Ledoux, M. J., C. Pham-Huu, A. P. E. York, E. A. Blekkan, P. Delporte i P. Del Gallo. "Study of the isomerization of C6 and C6+ alkanes over molybdenum oxycarbide catalysts". W The Chemistry of Transition Metal Carbides and Nitrides, 373–97. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1565-7_20.

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Lee, J. S., B. J. Song, S. Li i H. C. Woo. "Characterization of oxygen-treated carbides of molybdenum and tungsten for n-hexane-dihydrogen reactions". W The Chemistry of Transition Metal Carbides and Nitrides, 398–413. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1565-7_21.

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Laine, Richard M., i Albert S. Hirschon. "The Pyrolytic Transformation of Organometallic Compounds into Refractory Metals: Tungsten and Molybdenum Carbides". W Transformation of Organometallics into Common and Exotic Materials: Design and Activation, 21–31. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-1393-6_3.

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Malyshev, V., D. Shakhnin, A. Gab, M. Gaune-Escard i I. M. Astrelin. "Galvanic Coatings of Molybdenum and Tungsten Carbides from Oxide Melts: Electrodeposition and Initial Stages of Nucleation". W Molten Salts Chemistry and Technology, 303–17. Chichester, UK: John Wiley & Sons, Ltd, 2014. http://dx.doi.org/10.1002/9781118448847.ch4i.

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Kapoor, R., i S. T. Oyama. "Comparison of the Syntheses of Vanadium, Niobium, and Molybdenum Carbides and Nitrides by Temperature-Programmed Reaction". W Synthesis and Characterization of Advanced Materials, 211–18. Washington, DC: American Chemical Society, 1997. http://dx.doi.org/10.1021/bk-1998-0681.ch018.

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Streszczenia konferencji na temat "Molybdenum carbides":

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Ferguson, B. Lynn, Zhichao Li, Justin Sims i Tianyu Yu. "Vacuum Carburizing Steel Alloys Containing Strong Carbide Formers". W HT 2017. ASM International, 2017. http://dx.doi.org/10.31399/asm.cp.ht2017p0560.

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Abstract Carburizing grades of high strength steels, such as Ferrium C- 64 alloy, contain strong carbide forming elements such as chromium and molybdenum. Alloys with high amounts of strong carbide formers can form stable carbides during carburization that effectively block carbon diffusion and retard the carburization process. This is especially true for low pressure carburization. To achieve the desired case depth, the low pressure carburization process consists of a series of rapid boost and longer time diffusion cycles. One problem is how to determine an acceptable carburization schedule. This paper will discuss a methodology used to develop the data for Ferrium C-64 so that a proper low pressure carburizing schedule could be determined. Integral parts of this methodology are experiments to determine carbon diffusion rates, carbide formation kinetics, and carbide dissolution kinetics, and use of these data in computer software to simulate the process and to determine the proper schedule.
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Tsakalakos, Loucas, Lauraine Denault, Michael Larsen, Mohamed Rahmane, Yan Gao, Joleyn Balch i Paul Wilson. "Mo2C Nanowires and Ribbons on Si via Two-Step Vapor Phase Growth". W ASME 2004 3rd Integrated Nanosystems Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/nano2004-46098.

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Transition metal carbides are an interesting class of electronic materials owing to their high electrical conductivity at room temperature, which is only slightly lower than that of their constituent transition metal elements. For example, the room temperature electrical resistivity of bulk Mo2C is ∼70 μΩ-cm compared to that of Mo (4.85 μΩ-cm), whereas that of NbC is ∼50 μΩ-cm as compared to 15.2 μΩ-cm for Nb. Indeed, the temperature dependent resistivity of many transition metal carbides suggests metallic-like conduction. Furthermore, certain transition metal carbides are known to become superconducting, with transition temperatures ranging from 1.15 °K for TiC1−x to 14 °K for NbC. [1] They are also able to withstand high temperatures and are chemically stable. Initial synthesis of metal carbide nanorods was demonstrated using the carbon nanotube (CNT) confined reaction mechanism by Lieber and co-workers [2] and subsequent superconducting behavior was shown by Fukunaga et al. [3]. Vapor-liquid-solid growth was employed by Johnson et al. [4] to synthesize micron-sized carbide whiskers. Here, we have successfully synthesized Mo2C nanorods and ribbons on Si substrates using a novel two-step catalytic approach, which allows for synthesis of such high temperature nanostructures at manufacturable temperatures (≤ 1000 °C) and time scales (≤ 60 min). In the first step we utilize a catalytic vapor phase process to grow Mo and/or molybdenum oxide nanostructures, which are subsequently carburized in situ to form the desired Mo2C nanostructures. Unlike true VLS growth of carbides, in which high temperature (≤ 1100–1200 °C) is required to adequately dissolve carbon into the catalyst particles, our strategy is to react the nanostructures along their entire length with a carbon vapor source after creating the oxide/metal nanostructures, which for Mo2C can be achieved at relatively low temperatures. (≤ 1000 °C). The nanorods and ribbons are polycrystalline, with a mean grain size of 20–50 nm and 50–150 nm, respectively. We hypothesize that the growth mechanism is a complex mixture of VLS, VSS, and auto-catalytic growth, in which molten catalyst nanoparticles enter a three phase region once the metal precursor is supplied. The growth then presumably continues via a vapor-solid-solid process and is possible assisted by the presence of various molybdenum oxide species on the surface. Initial single nanowire electrical measurements yield a higher resistivity than in the bulk, which is attributed to the fine grain sizes and/or the presence of an oxide layer. A discussion of the growth mechanism will be presented along with issues relating to single nanowire device fabrication and control of nanowire orientation.
3

Agafii, V., V. Mihailov, N. Kazak, G. Volodina i C. Cracan. "INCREASE OF WEAR RESISTANCE OF Сr18Ni10Ti STAINLESS STEEL BY METHOD OF ELECTRIC-SPARK ALLOYING WITH ELECTRODES OF REFRACTORY METALS AND GRAPHITE". W BALTTRIB. Aleksandras Stulginskis University, 2017. http://dx.doi.org/10.15544/balttrib.2017.11.

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The article presents the results of wear testing of stainless steel Cr18Ni10Тi treated with electrodes made of refractory metals and graphite by the method of electric-spark alloying. It was established that all electrospark coatings had a higher wear resistance than the Cr18Ni10Ti uncoated steel. Wear resistance of coatings was increased in the direction Mo + GraphiteTi + Ni W + Graphite Ti + Al + Graphite. X-ray diffraction analysis showed that molybdenum, tungsten, titanium carbides and other solid materials such as titanium nitride and nickel-titanium intermetallide are formed on the doped steel surfaces, which increased microhardness from 4.9 to 8 times and wear resistance from 1.63 to 29 times.
4

Pershin, Yu P., E. A. Bugaev, I. A. Kopilets, S. A. Yulin i I. V. Kozhevnikov. "ATTAINMENT OF PHASE EQUILBRIUM IN MULTILAYERS". W Physics of X-Ray Multilayer Structures. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/pxrayms.1994.wa.4.

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Structural, phase and chemical stabilities of multilayers Mo-Si, MOSi2- Si, W-Si, WSi2-Si, Cr-Sc, W-Sc, Mo-B4C, Mo−(B+C), Mo2B5-B4C, Cr3C2-C, TiC-C, Ti-Be and others were studied in 300-1100°C temperature range by small-angle and large-angle X-ray diffraction scattering and electron microscopy methods. The structural instability (crystallization of amorphous Si, C, MOSi2, WSi2, MoC, MoB2, Mo2B5, B and Cr3 C2 and recrystal-lization of polycrystal Mo, W, Sc, MoSi2, WSi2, Mo2B5 and MoC layers) as well as the phase instability (transformation of MoSi2 lattice from hexagonal to tetragonal modification) are responsible for the degradation of multilayers due to the development of the interface roughness and mechanical stresses. The chemical instability (formation of MoSi2 and WSi2 silicides at interfaces of Mo-Si and W-Si multilayers, Mo2C and MoC carbides and MoB2 and Mo2B5 borides in Mo-(B+C) multilayers, TiBe12 in Ti-Be ones) influences critically chemical composition profile, layer thicknesses and a period of multilayers. Formation of chemical compounds accompanied by an amorphization of polycrystal layers (growth of amorphous Mo2C and MoC carbides instead of polycrystal Mo at about 450 °C and the subsequent substitution of polycrystal molybdenum carbides on amorphous borides MoB2 and Mo2B5 at 700-800 °C in Mo-(B+C) multilayers) promotes the smoothening of interfaces. This effect of the chemical instability can be used for an improving of the X-ray reflectivity of multilayers.
5

Maroli, B., S. Dizdar i S. Bengtsson. "Iron-Based Hardfacing Alloys for Abrasive and Impact Wear". W ITSC2017, redaktorzy A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen i C. A. Widener. DVS Media GmbH, 2017. http://dx.doi.org/10.31399/asm.cp.itsc2017p0394.

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Abstract Iron-based hardfacing alloys are widely used to counteract abrasive and impact wear of industrial components soil in, sand and mineral processing applications. These alloys show a high performance to cost ratio as well as a low environmental impact. The wear resistance of the components hardfaced with these alloys depends on achieved coating microstructure i.e. on the alloys chemical composition, the coating method and process parameters selected. The present work focuses on iron based hardfacing alloys with varying amount of chromium, vanadium, tungsten, molybdenum, boron and carbon deposited by plasma transferred arc (PTA) overlay welding. Weldability, hardness, abrasive and impact wear of the overlays are presented and interpreted through their microstructure. The performance of the iron based overlays is compared with that of nickel-based metal matrix composite coatings with tungsten carbide (MMC) commonly used for hardfacing of parts subjected to severe abrasive wear. The hardness of the iron based overlays investigated ranges between 60 and 65 HRC while abrasive wear is typically below 20 mm3 (ASTM G65, procedure A). Microstructure consists of different primary precipitated carbides or borides, a martensitic matrix and eutectic structures.
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Maran, João Pedro Leal, João Lourenço Castagnari Williman Pimenta i Luiz Mario de Matos Jorge. "Preliminary chemical process for hydrotreating triolein on a pilot scale using airgel catalyst based on NiMo carbides". W V Seven International Multidisciplinary Congress. Seven Congress, 2024. http://dx.doi.org/10.56238/sevenvmulti2024-114.

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One of the challenges of modern society is producing renewable and economically competitive fuels, reducing carbon emissions and dependence on fossil sources such as oil. In this scenario, the hydrotreatment of vegetable oils has been studied using a wide variety of catalysts and chemical processes, and is also capable of producing other green fuels such as naphtha, propane and aviation kerosene. The present work proposes a preliminary chemical process for the hydrotreatment of triacylglycerides using the airgel catalyst based on nickel and molybdenum carbides supported on alumina, using data reported in previous literature (PIMENTA, 2020). The chemical process simulation was conducted using the Aspen Plus software , version 14, on a pilot production scale with triolein as the only liquid phase reagent fed into the system, considering a hydrogen/triolein ratio of 0.037975 and a triolein feed of 1000 kg. /day. Separation steps were proposed with the main objective of producing and separating hydrocarbons into specific ranges and maintaining low amounts of unwanted components (acylglycerides and unreacted fatty acids). A production capacity of 743.05 kg/day of hydrocarbons in the diesel range was observed, followed by 44.72 kg/day of naphtha and 11.72 kg/day of light hydrocarbons (propane), in addition to other streams of exit. Process optimization, energy integration and economic viability were not evaluated in this work.
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Liu, Michael, i Mathew Kuttolamadom. "Nano-Scale Hardness and Abrasion Resistance of Directed Energy Deposited Co-Cr-Mo Biomedical Alloy". W ASME 2020 15th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/msec2020-8455.

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Abstract The objective of this work is to investigate the hardness and abrasion resistance of a cobalt-chromium-molybdenum (Co-Cr-Mo) alloy fabricated via directed energy deposition (DED) additive manufacturing. Being a bio-compatible alloy, Co-Cr-Mo is commonly used in biomedical implants. Hence, its small-scale tribological behavior needs to be characterized, especially when fabricated via a newer process such as DED; thus the focus at nano scale. For this, a design of experiments was utilized to investigate the relevant process parameter design space for the laser engineered net shaping (LENS) process, with an objective to manufacture structurally-integral samples. Further, the effects of these process parameters were correlated with the resulting material properties at the nanoscale (viz., hardness modulus, and abrasion resistance). Results showed certain samples with competitively-high corresponding properties when compared to traditional made Co-Cr-Mo alloys, but with a large spread in properties, as is typical for such manufacturing processes. Also, microstructural characteristics were in line with traits observed when fabricating via traditional methods. Especially worth noting is the formation of metal carbides at the boundaries of cell-shaped grains; this causes a depletion of carbon at the center of the grain and thin carbides at the boundaries, thus significantly affecting the composite properties of the material. Altogether, this work shows the promise of using LENS to fabricate tailored structurally-integral Co-Cr-Mo alloys.
8

Mohr, A., O. Schwabe, K. Ernst, H. Hill i P. Kluge. "Thermal Spraying of a Novel Nickel-Free High Strength and Corrosion Resistant Austenitic Steel". W ITSC2022. DVS Media GmbH, 2022. http://dx.doi.org/10.31399/asm.cp.itsc2022p0631.

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Abstract Stainless austenitic steels like the 316L (1.4404) are widely applied in various applications and were also used for surface protection using thermal spraying. The reason for this is the easy processability and the high corrosion resistance. Stainless austenitic steels typically contain the following alloying elements: The formation of an austenitic microstructure is achieved by nickel (Ni). The addition of chromium (Cr) lead to good corrosion resistance due to formation of an oxide layer. For resistance against pitting corrosion, molybdenum (Mo) can be added. Also, stainless austenites usually exhibit very low carbon and nitrogen contents to prevent chromium carbides and nitrides which reduces the corrosion resistance. However, both alloying elements cannot be classified as being detrimental in stainless austenites in general. In contrast high nitrogen contents can also be used to improve the chemical properties, especially the resistance against pitting corrosion. Finally, carbon and nitrogen lead to an increase in hardness of the thermal sprayed layer. Based on this knowledge, a high-strength austenite for thermal spraying was developed. The new high strength austenite was processed by HVAF spraying with different particle distributions and parameter variations. Resulting coatings were investigated regarding the microstructure, elemental composition, hardness and corrosion properties in comparison to the standard coating material 316L.
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Kim, Yongkyung, Kihun Seong, Jonghyuk Yoon, Donggi Lee, Seungchan Moon, Sung Kyu Jang, Hyun-Mi Kim, Seul-Gi Kim, Jinho Ahn i Hyeongkeun Kim. "Molybdenum carbide pellicle for high-power EUV lithography". W International Conference on Extreme Ultraviolet Lithography 2023, redaktorzy Kurt G. Ronse, Paolo A. Gargini, Patrick P. Naulleau i Toshiro Itani. SPIE, 2023. http://dx.doi.org/10.1117/12.2686314.

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Myachina, Maria, Natalia Gavrilova i Victor Nazarov. "Molybdenum-Tungsten Blue Dispersions: Some Properties of the Colloid System". W Life Science, Materials and Applied Chemistry. Switzerland: Trans Tech Publications Ltd, 2022. http://dx.doi.org/10.4028/p-3e6s59.

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Dispersions of molybdenum-tungsten blues are promising precursors for the preparation of carbide catalysts by the sol-gel method. Stable systems were synthesized using ascorbic acid as a reducing agent at various molar ratios (Mo) :( W) = 100; 95: 5; 90:10; 80:20; 50:50. To study the properties of colloidal systems, UV / Vis spectroscopy, dynamic light scattering and electrophoretic light scattering were used. It was found that molybdenum-tungsten blue particles with different molar ratios of molybdenum and tungsten have a constant hydrodynamic radius equal to 2.0 nm. In the pH range (0.8 - 3.0) molybdenum-tungsten blue particles are negatively charged; the absolute values of the ζ-potential do not exceed 25 mV.

Raporty organizacyjne na temat "Molybdenum carbides":

1

David Moy, Jun Ma, Robert Hoch, Jim Leacock, Jason Willey, Asif Chishti, Fabio RIbeiro i in. New Nanoscale Catalysts Based on Molybdenum and Tungsten Carbides and Oxycarbides. Office of Scientific and Technical Information (OSTI), sierpień 2002. http://dx.doi.org/10.2172/799250.

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