Hybrid synthesis of zirconium oxycarbide nanopowders with defined and controlled composition

Hauser, Daniel; Auer, Andrea; Kunze‐Liebhäuser, Julia; Schwarz, Sabine; Bernardi, Johannes; Penner, Simon

doi:10.1039/c8ra09584a

Cited by 17 publications

(21 citation statements)

References 26 publications

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“…Recent studies 8,11,12,20,25 have shown a linear relationship or polynomial relationships between lattice parameter and C/Zr atomic ratio and it is remarkable that the authors presenting this new correlations were working on either ZrC x 8,11,12 or ZrC x O y 20,25 . Zhou et al 26 discuss the difficulties encountered for the determination of carbon and nitrogen inclusions in ZrC x using XRD and they confirmed the expected usefulness of neutron diffraction to determine accurately carbon and oxygen stoichiometries.…”

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confidence: 99%

“…Zhou et al 26 discuss the difficulties encountered for the determination of carbon and nitrogen inclusions in ZrC x using XRD and they confirmed the expected usefulness of neutron diffraction to determine accurately carbon and oxygen stoichiometries. However, neutron diffraction could not or was not used for the characterization of ZrC x specimens in other literature 8,[11][12][13][14]20,25 , obviously because this technique is quite difficult to access (only ~20 facilities worldwide having an external users program 27 ). Other techniques such as Raman spectroscopy that could be used to detect the presence of microcrystalline carbon or amorphous carbon in carbide systems 28,29 , or X-ray photoelectron spectroscopy (XPS) that can also help distinguish the nature of bonds present in the sample, if the metal in the carbide is bonded with carbon, oxygen 30 or nitrogen 31 , are not often used within the ceramic processing community.…”

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On the stoichiometry of zirconium carbide

Gasparrini

Rana

Brun

et al. 2020

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the dependencies of the enhanced thermomechanical properties of zirconium carbide (Zrc x) with sample purity and stoichiometry are still not understood due to discrepancies in the literature. Multiple researchers have recently reported a linear relation between the carbon to zirconium atomic ratio (c/Zr) and the lattice parameter, in contrast with a more established relationship that suggests that the lattice parameter value attains a maximum value at a C/Zr ~ 0.83. In this study, the relationship between C/Zr atomic ratio and the lattice parameter is critically assessed: it is found that recent studies reporting the thermophysical properties of Zrc x have unintentionally produced and characterised samples containing zirconium oxycarbide. to avoid such erroneous characterization of Zrc x thermophysical properties in the future, we propose a method for the accurate measurement of the stoichiometry of ZrC x using three independent experimental techniques, namely: elemental analysis, thermogravimetric analysis and nuclear magnetic resonance spectroscopy. Although a large scatter in the results (Δc/Zr = 0.07) from these different techniques was found when used independently, when combining the techniques together consistent values of x in Zrc x were obtained. Zirconium carbide (ZrC) is a much-promising material, it has received increased interest recently as an alternative material to silicon carbide (SiC) in nuclear fuel applications 1,2 , in next-generation nuclear fusion reactors 3 , and also as an ultra-high-temperature ceramic to be used in ceramic-metal composite heat exchangers in concentrated solar power (CSP) plants 4,5. ZrC (here denoted as ZrC x) is typically non-stoichiometric as it can contain up to 50% of unoccupied carbon sites 6,7 , it has been found that deviations in the stoichiometry of ZrC x can severely affect its thermal and mechanical properties 8,9. Given its potential in high-temperature applications, it is extremely important to define a method that robustly determines its stoichiometry and purity. The purity of ZrC x should always be assessed as the presence of contaminants such as nitrogen or oxygen is detrimental for its performance. For example, if ZrC x is to be used as a nuclear fuel coating in a nuclear reactor, any nitrogen contamination should be avoided due to the production of radioactive 14 C from nitrogen 14 N inside the reactor 10. There are two common methods for defining the stoichiometry of ZrC x. The first one is to evaluate the C/Zr atomic ratio from the lattice parameter measured by X-ray diffraction (XRD) using the correlation published in Jackson & Lee 6. The second one is to quantify through the inert-gas fusion technique the carbon content in ZrC x and calculate the C/Zr atomic ratio assuming that the sample is free from impurities. Both techniques, however, have limitations and when used in standalone approaches can lead to erroneous stoichiometry estimations, as we will proceed to demonstrate later in this paper. The need for an established robust method to measure ...

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On the stoichiometry of zirconium carbide

Gasparrini

Rana

Brun

et al. 2020

Sci Rep

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“…Generally, higher faradaic current densities are measured with carbon Vulcan XC-72R, which is visible after normalization of the current with respect to the geometrical (see Figure 3) and the BET surface areas of Vulcan (250 m 2 g À 1 ) [34] and ZrO 0.31 C 0.69 (350 m 2 g À 1 ) [30] (see Figure S3, supporting information). The differences in the CVs show that the ZrO 0.31 C 0.69 cannot be entirely covered with the excess carbon from the synthesis process.…”

Section: Resultsmentioning

confidence: 91%

“…The differences in the CVs show that the ZrO 0.31 C 0.69 cannot be entirely covered with the excess carbon from the synthesis process. [30] Comparison of the cathodic potential region from À 0.6 V to 0 V for both ZrO 0.31 C 0.69 and carbon shows that the ZrO 0.31 C 0.69 is more active in the potential region where the HER takes place, resulting in an earlier HER onset potential and in higher current densities compared to carbon. At anodic potentials of > 1.8 V carbon shows high anodic currents with an earlier onset compared to that of ZrO 0.31 C 0.69 , suggesting an active dissolution of carbon at these high potentials.…”

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confidence: 97%

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Zirconium Oxycarbide: A Highly Stable Catalyst Material for Electrochemical Energy Conversion

et al. 2019

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Metal carbides and oxycarbides have recently gained considerable interest due to their (electro)catalytic properties that differ from those of transition metals and that have potential to outperform them as well. The stability of zirconium oxycarbide nanopowders (ZrO0.31C0.69), synthesized via a hybrid solid‐liquid route, is investigated in different gas atmospheres from room temperature to 800 °C by using in‐situ X‐ray diffraction and in‐situ electrical impedance spectroscopy. To feature the properties of a structurally stable Zr oxycarbide with high oxygen content, a stoichiometry of ZrO0.31C0.69 has been selected. ZrO0.31C0.69 is stable in reducing gases with only minor amounts of tetragonal ZrO2 being formed at high temperatures, whereas it decomposes in CO2 and O2 gas atmosphere. From online differential electrochemical mass spectrometry measurements, the hydrogen evolution reaction (HER) onset potential is determined at −0.4 VRHE. CO2 formation is detected at potentials as positive as 1.9 VRHE as ZrO0.31C0.69 decomposition product, and oxygen is anodically formed at 2.5 VRHE, which shows the high electrochemical stability of this material in acidic electrolyte. This peopwery makes the material suited for electrocatalytic reactions at anodic potentials, such as CO and alcohol oxidation reactions, in general.

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