A New Phase formed by High-Pressure Treatment : Face-centred Cubic Molybdenum Monocarbide

Clougherty, Edward V.; Lothrop, K. H.; Kafalas, J. A.

doi:10.1038/1911194a0

Cited by 84 publications

(34 citation statements)

References 4 publications

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“…The more negative ΔHr implies more stable phase to be formed. Our calculated results of the relative binary carbides are presented in Table 1, together with available theoretical and experimental data [15,20,[33][34][35][36][37][38][39]. Form Table 1, the lattice parameters and formation energies of relative binary carbides show a good agreement with other theoretical and experimental values in Refs.…”

Section: Advances In Engineering Research Volume 121supporting

confidence: 72%

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Effects of Alloying Elements M (M = Fe, Mo) on Phase Stability of Cr23C6 Carbides from First-principles

Yi¹,

Xu²,

Xia³

et al. 2017

Proceedings of the 2017 2nd International Conference on Advances in Materials, Mechatronics and Civil Engineering (ICAMMCE 2017

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Abstract. The structural and electronic properties of (Cr, M)23C6 (M = Fe, Mo) with a full composition range of Cr/M ratio were carried out by first-principles calculations. The phase stability was investigated by calculating the reaction energy. Results reveal that Cr22FeC6, Cr21Fe2C6, Cr20Fe3C6, Cr21Mo2C6 and Cr20Mo3C6 are the stable phases. Alloying element Fe and Mo prefer to occupy the 4a and 8c sites of Cr23C6 carbides, respectively. Then the stabilized mechanism by alloying elements in Cr23C6 carbides was explored by employing the charge density difference. It provides the explanation that the high stability of Cr22FeC6 and Cr21Mo2C6 is mainly attributed to the strengthening of covalent bonds between the 8c and 32f sites. IntroductionNi-based superalloys are widely used in hot section parts of aircraft engines because of their superior creep strength and thermo mechanical fatigue properties [1,2]. At high temperatures, owing to alternating stress, fatigue related failure becomes one of the primary failure modes for Ni-based superalloys in the hot section structures [3]. According to experimental observations, M23C6-type carbides are principle sites for fatigue crack initiations [4][5][6]. The previous study proposed that the precipitation of M23C6 carbides result in the formation of grain bound serrations [5]. It was also found by scanning electron microscopy that the fatigue cracks followed the continuous film of M23C6 carbides at the grain boundaries [6]. These facts indicate that M23C6 carbides have crucial effects on the formation of fatigue crack. Therefore, the information on the stability and structure of M23C6 carbides, as well as the corresponding mechanical and thermodynamic properties, is very helpful to deeply understand the mechanism of fatigue crack initiation. Since the observation of γ-M23C6 carbides [7], the properties of γ-M23C6 binary phases had been systemically studied [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The structural, mechanical and electronic properties of Cr23C6 were reported by Jiang [10]. The phase stability of M23C6(M = V, Cr, Mn, Fe, Co, Ni) was discussed by Medvedeva [22]. However, M23C6-type carbides in multi-component alloys contain more than one metallic element. Generally, Cr23C6 can dissolve Fe, Mo, or W atoms and form complex γ-(Cr, M)23C6 phases [23]. Xie et al. [8,9] explored several compounds of γ-(Cr, M)23C6 (M = Fe, W, Ni) phases and found that Fe atoms preferred to substitute for Cr at 4a site and then 8c site of Cr23C6 phase. To simulate more substitution situations, Han et al.[24] studied γ-Cr23C6 compounds with each of the four metal Wyckoff sites being occupied in turns by Fe atoms. The obtained substitution sequence was 4a, 8c, 48h and 32f. Recently, the site preference of γ-(Cr, M)23C6 (M = Mo, W; x = 0-3) phases was investigated and Cr21M2C6 (M = Mo, W) was found to be the most stable phase [23]. However, the affecting status of higher concentration of typical alloying elements in Cr23C6 carbides (e.g., Fe, Mo.) is still scarcely studied...

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Section: Advances In Engineering Research Volume 121supporting

confidence: 72%

“…Form Table 1, the lattice parameters and formation energies of relative binary carbides show a good agreement with other theoretical and experimental values in Refs. [15,20,[33][34][35][36][37][38][39], indicating the reliability of this work. Note that the subscripts a-m represent the data from Refs.…”

Section: Advances In Engineering Research Volume 121mentioning

confidence: 66%

Effects of Alloying Elements M (M = Fe, Mo) on Phase Stability of Cr23C6 Carbides from First-principles

Yi¹,

Xu²,

Xia³

et al. 2017

Proceedings of the 2017 2nd International Conference on Advances in Materials, Mechatronics and Civil Engineering (ICAMMCE 2017

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“…The conditions in PEMFCs are oxidizing, especially in the cathode. [7][8][9] These conditions are detrimental to the carbon and the catalysts which interact with it and shorten the lifetime of PEMFCs. 10,11 For these reasons, alternative supports have been developed, mainly electronically conductive ceramic supports such as titanium oxides, 12,13 molybdenum nitride, 14 and tungsten oxide.…”

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confidence: 99%

Evidence of High Electrocatalytic Activity of Molybdenum Carbide Supported Platinum Nanorafts

Elbaz

Phillips

Artyushkova

et al. 2015

J. Electrochem. Soc.

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A remarkable new supported metal catalyst structure on Mo 2 C substrates, 'rafts' of platinum consisting of less than 6 atoms, was synthesized and found to be catalytically active electrocatalyst for oxygen reduction. A novel catalytic synthesis method: Reduction-Expansion-Synthesis of Catalysts (RES-C), from rapid heating of dry mixture of solid precursors of molybdenum, platinum and urea in an inert gas environment, led to the creation of unique platinum Nanorafts on Mo 2 C. The Pt Nanorafts offer a complete utilization of the Pt atoms for electrocatalysis with no "hidden" atoms. This structure is strongly affected by its interaction with the substrate as was observed by XPS. In this work, we show for the first time, evidence of electrocatalytic activity with such small clusters of non-crystalline Pt atoms as catalysts for oxygen reduction. Electrochemical half-cell characterization shows that this structure permit more efficient utilization of platinum, with mass activity conservatively measured to be 50% that of platinum particles generated using traditional approaches. Moreover, as cathode fuel cell catalysts, these novel material may dramatically enhance stability, relative to the commercial Pt/carbon catalysts.

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“…The conditions in PEMFCs and AFCs are oxidizing, especially at the cathode [4][5][6]. As discussed above, these conditions are detrimental to the carbon electrodes and can significantly shorten the lifetime of the fuel cell [7,8].…”

Section: Introductionmentioning

confidence: 99%

Advances in Ceramic Supports for Polymer Electrolyte Fuel Cells

Lori

Elbaz

2015

Catalysts

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Durability of catalyst supports is a technical barrier for both stationary and transportation applications of polymer-electrolyte-membrane fuel cells. New classes of non-carbon-based materials were developed in order to overcome the current limitations of the state-of-the-art carbon supports. Some of these materials are designed and tested to exceed the US DOE lifetime goals of 5000 or 40,000 hrs for transportation and stationary applications, respectively. In addition to their increased durability, the interactions between some new support materials and metal catalysts such as Pt result in increased catalyst activity. In this review, we will cover the latest studies conducted with ceramic supports based on carbides, oxides, nitrides, borides, and some composite materials.

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A New Phase formed by High-Pressure Treatment : Face-centred Cubic Molybdenum Monocarbide

Cited by 84 publications

References 4 publications

Effects of Alloying Elements M (M = Fe, Mo) on Phase Stability of Cr23C6 Carbides from First-principles

Effects of Alloying Elements M (M = Fe, Mo) on Phase Stability of Cr23C6 Carbides from First-principles

Evidence of High Electrocatalytic Activity of Molybdenum Carbide Supported Platinum Nanorafts

Advances in Ceramic Supports for Polymer Electrolyte Fuel Cells

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