TEM study of the reaction mechanisms involved in the carbothermal reduction of zirconia

David, Jérémy; Trolliard, Gilles; Gendre, Mathieu; Maı̂tre, Alexandre

doi:10.1016/j.jeurceramsoc.2012.07.024

Cited by 56 publications

(56 citation statements)

References 31 publications

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“…The increase in the number of these spherical particles observed in the SEI micrograph ( figure 6) and the BF-TEM images (figure 9a-c) suggest the ZrN particles form at the surface of the larger ZrC particles. This again agrees with observations by David et al [27] that the nucleation of Zr (g) and C occurs at a point separate to the particles surface. In the case that a nitrogen-rich Zr phase grows at the surface of the bulk ZrC particles so that two mechanisms of growth may be possible, either evaporation-condensation of Zr (g) and HCN (g) , or the migration of Zr at the particles interface which then reacts with HCN (g) .…”

Section: Discussion Of Synthesissupporting

confidence: 93%

“…From this bonding order it can be seen that during dissolution the removal of a crystal at the kinked face will be easier than crystals at the stepped face, with the most difficult to remove being crystal at the flat face, this gives rise to the structures observed in the SEI micrographs of nitrided powders (figure 4). Similar observations of crystal defect formation resulting in ledge formation of particles were made by David et al [27] with regards to the carbothermic reduction of ZrO 2 to ZrC, whereby the reaction of ZrO 2 with free carbon results in removal of oxygen from the lattice. The resulting ZrO 2−x is reduced continually until Zr (g) forms at the particles surface which then combines with free carbon to nucleate ZrC.…”

Section: Discussion Of Synthesissupporting

confidence: 78%

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On the fabrication of ZrC x N y from ZrO 2 via two-step carbothermic reduction–nitridation

Harrison

Rapaud

Pradeilles

et al. 2015

Journal of the European Ceramic Society

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This study examined the processing parameters of a two-step carbothermal reduction-nitridation of ZrO 2 as a UO 2 /PuO 2 simulant to fabricate ZrN. Variables studied were the reaction time, reaction temperature and the starting powder composition Higher temperatures, longer reaction times and higher initial amounts of carbon in the starting material lead to increased nitridation similar to previous work with uranium oxide but that reaction rate decreases with time. SEM and TEM of the reacted powders reveal regions of ZrC with ledges indicative of crystal defects with small particles of ZrN growing on the ZrC bulk material suggesting a reaction that occurs via Zr transport to the reaction site either through mass diffusion or evaporation-condensation of Zr (g) and with N 2(g) forming the nitride. Annealing experiments on these mixed phases shows formation of a solid solution is rapid compared to the nitridation, where there is no formation of a mixed phase.

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Section: Discussion Of Synthesissupporting

confidence: 93%

Section: Discussion Of Synthesissupporting

confidence: 78%

On the fabrication of ZrC x N y from ZrO 2 via two-step carbothermic reduction–nitridation

Harrison

Rapaud

Pradeilles

et al. 2015

Journal of the European Ceramic Society

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“…It has been previously shown that slight substitution of carbon atoms by oxygen atoms leads to a significant decrease in the cell parameter, the covalent radius of oxygen (rO = 0.64 Å) being lower than that of carbon (rC = 0.74 Å) [2][3][4]23,24]. A small change of the cell parameter induces in turn peak shifts in the XRD patterns, the peaks typically shifting towards high 2 angles as the oxygen content increases within the oxycarbide.…”

Section: Shaping Of Pellet-type Bulk Materials and Comparison With Pomentioning

confidence: 99%

“…Indeed, as the most used route to elaborate carbides, the carbothermal reduction reaction which consists in the progressive reduction of dioxides with carbon generally leads to an oxycarbide final product [2][3][4] whose composition is largely dependent on the synthesis conditions. Besides, these ultrarefractory carbides are ideally suited for ultra-high temperature applications [5], thanks to their favorable properties: high hardness, good wear resistance and high decomposition temperature [6].…”

Section: Introductionmentioning

confidence: 99%

Novel insight into the chemical analysis of light elements in oxycarbides

et al. 2018

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Pure powders of TiCxO(1-x) solid solution were synthesized through the carbothermal route. The chemical analysis of the light elements in the as-obtained TiCxO(1-x) oxycarbides powders were performed by Instrumented Gas Analysis (IGA). The cell parameters of the samples were determined with an accuracy of about 2% by means of X-ray powder diffraction and the internal standard method. As a result, a model correlating the cell parameters to the chemical composition was established. These reference TiCxO(1-x) oxycarbides powders were then sintered in order to obtain pellets of dense ceramics. After having determined that the sintering process does not change the chemical composition of the starting powder, chemical analysis of the different samples of the solid solution were successfully undertaken by Ion Beam Analysis techniques (IBA). The Nuclear Reaction Analysis (NRA) method -that was used to analyse light elements with very high sensitivity -was coupled with Rutherford Back Scattering (RBS) analysis in order to accurately determine the metallic over light elements ratio and to determine the stoichiometry of the phase on massive samples. Exhaustive simulations of the NRA spectra were performed and demonstrated that discrete compositions of the TiCxO(1-x) can be efficiently measured locally for bulk samples. Compared to IGA results, the relative amounts of carbon and oxygen of bulk materials were determined with a bias lower than 5%. This protocol being implemented for the TiCxO(1-x) system was then tested on HfCxO(1-x)with the same success.3

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“…According to the Boltzmann distribution, the distribution of atoms that populate higher energy states decreases exponentially and so is proportional to exp(2DE/kT), where DE (J) is the energy difference between two states, k is the Boltzmann constant (1.381610 223 J K 21 ) and T is the temperature (K). The diffusion coefficient, D (m 2 s 21 ) is related to this activation energy by equation (12), where D 0 is a constant for that system and corresponds to the y intercept on a plot of lnD versus 1/T (T ¼ '). the reaction is driven by this large decrease in enthalpy.…”

Section: Oxidation Behaviourmentioning

confidence: 99%

Processing and properties of ZrC, ZrN and ZrCN ceramics: a review

Harrison

Lee

2016

Advances in Applied Ceramics

174

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ZrC and ZrN ceramics are of interest in the application of materials in extreme high temperature environments, particularly for nuclear applications in generation IV reactors. These materials demonstrate desirable characteristics such as high thermal and electrical conductivities along with high hardness and melting temperatures. Data reported in the literature often suffer from scatter due to differences in processing techniques and difficulty determining stoichiometry, which will significantly affect thermophysical properties. This article reviews the current available data for the properties of ZrC, ZrN and mixed carbonitrides phases and identifies causes of scatter in the literature and areas requiring further research.

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TEM study of the reaction mechanisms involved in the carbothermal reduction of zirconia

Cited by 56 publications

References 31 publications

On the fabrication of ZrC x N y from ZrO 2 via two-step carbothermic reduction–nitridation

On the fabrication of ZrC x N y from ZrO 2 via two-step carbothermic reduction–nitridation

Novel insight into the chemical analysis of light elements in oxycarbides

Processing and properties of ZrC, ZrN and ZrCN ceramics: a review

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