Oxidation Behavior of HfB2-SiC and ZrB2-SiC Ultra-High Temperature Ceramics in different air atmospheres

International audienceUltra-High Temperature Ceramics, in particular diborides of the IVb group, are promising materials for extreme environments, more specifically for thermal protection systems of hypersonic vehicles during their atmospheric reentry at temperatures higher than 1800 °C. The main objective of this work is to study the oxidation behavior in air of (Hf or Zr)B2-SiC composites under severe conditions. The first stage consists in elaborating fully-dense (Hf or Zr)B2-SiC ceramics, from 0 to 30 vol.% SiC, with similar and controlled microstructures using Spark Plasma Sintering to obtain materials with fine grains, high relative density (> 99 %) at lower temperatures and shorter dwell times. An optimization of sintering parameters has been carried out for every composition. The second step consists in understanding the oxidation mechanisms of both composites. To this end, these materials have been oxidized at several temperatures using concentrated solar energy, including the oxidation in atomic oxygen. The mechanisms have been highlighted through the study of the oxidized layers by combining XRD, SEM and Raman spectroscopy with imaging and by the monitoring of oxidation kinetics. This work was helped by a first thermodynamic approach of both systems through the modeling of ternary diagrams

A review of the genus Sclerocollum Schmidt & Paperna, 1978 (Acanthocephala: Cavisomidae) from rabbitfishes (Siganidae) in the Indian and Pacific Oceans

Seven of the eleven species of Siganus Richardson (Siganidae) collected off the coasts of Australia, New Caledonia, French Polynesia and Palau were infected with species of Sclerocollum Schmidt & Paperna, 1978 (Acanthocephala: Cavisomidae). A Principal Component Analysis (PCA) and a Discriminant Analysis were performed on a morphometric dataset of specimens of Sclerocollum including borrowed type-specimens of Sc. rubrimaris Schmidt & Paperna, 1978 from the Indian Ocean and of Sc. robustum Edmonds, 1964, the only acanthocephalan species known previously from an Australian siganid. These analyses showed that the lengths of proboscis hooks were useful variables for separating specimens into groups and supported the presence of two known species (Sc. robustum and Sc. rubrimaris) and one new species (Sc. australis n. sp.) in Australian waters. We found Sc. robustum in Siganus lineatus (Valenciennes) from off Queensland and Sc. rubrimaris in S. fuscescens (Houttuyn) from off Western Australia and Queensland, S. punctatissimus Fowler & Bean from off Queensland and S. argenteus (Quoy & Gaimard), S. corallinus (Valenciennes), S. canaliculatus (Park) and S. doliatus Guérin-Méneville from off New Caledonia (all new host and locality records) which we compared with museum specimens of Sc. rubrimaris from S. rivulatus Forsskål & Niebuhr and S. argenteus [as S. rostratus (Valenciennes)] from the Red Sea. The third species, Sclerocollum australis n. sp., was found only in S. corallinus and S. doliatus from off Queensland. Sclerocollum australis n. sp. can be distinguished from its congeners by a unique combination of characters of the proboscis armature, including lengths of hooks 1–7. Specimens of Sclerocollum were also found in Zebrasoma velifer (Bloch) (Acanthuridae) from off Queensland, and Coradion altivelis McCulloch (Chaetodontidae) and Heniochus acuminatus (Linnaeus) (Chaetodontidae) from off New Caledonia. No acanthocephalans were found in siganids collected from Palau (Micronesia) or Moorea (French Polynesia) or Moreton Bay and Noosa (Queensland, Australia). We found no acanthocephalans in S. puellus (Schlegel), S. punctatus (Schneider & Forster), S. spinus (Linnaeus) or S. vulpinus (Schlegel & Müller). Evidence suggests that species of the genus Sclerocollum have travelled with S. argenteus across the Indo-Pacific with Sc. rubrimaris dispersed widely and Sc. robustum and Sc. australis n. sp. restricted to the Queensland coast, Australia

Évaluation des risques professionnels dans une minoterie

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Contribution to the thermodynamic study and oxidation behavior of HfB2-SiC Ultra-High Temperature Ceramics

International audienceUltra-High Temperature Ceramics (UHTCs), more specifically diborides of the IVb group, are potential candidates for a large variety of applications, in particular as structural materials for thermal protection of hypersonic vehicles exposed to high temperatures (> 1800°C) and to oxidation1. The aim of this work consists in elaborating ultra-high temperature HfB2-SiC ceramic composites used as structural materials for several applications, such as aeronautic and aerospace areas and to understand oxidation mechanisms involved during their entry into the atmosphere. The sintering of these materials at different compositions has been carried out by Spark Plasma Sintering (SPS). This process is used to obtain fully dense materials (> 98% relative density) with fine grains, at lower temperatures and shorter dwell times than conventional techniques (natural sintering, hot pressing)2. In order to favor densification and to obtain a homogeneous distribution of both phases in the final material, a study on the raw powders granulometry has been necessary. An optimization of sintering conditions (applied load, temperature and its hold time, heating rate) has been subsequently carried out in order to elaborate fully dense samples by using parameters adapted to their environment. Obtained bulk bodies have been oxidized at several temperatures with a solar furnace to approach conditions to which hypersonic vehicles are subjected. Oxidation mechanisms have been highlighted through the study of the oxidized layers by combining X-ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectrometry (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). This work was helped by the obtaining of kinetic data during oxidation tests. In order to supplement this study, a first thermodynamic approach of the Hf-B-Si-C system has been made through the modeling of ternary diagrams, the aim being to constitute a coherent data base of this quaternary system.References1 F. Monteverde and A. Belosi, “The resistance to oxidation of an HfB2-SiC composite”, J. Eur. Ceram. Soc., 25, pp.1025-1031, 2005.2 D. Sciti, and al. “Spark Plasma Sintering of HfB2 with low additions of silicides of molybdenum and tantalum”, J. Eur. Ceram. Soc., 30, pp.3253-3258, 2010

Contribution à l'étude thermodynamique et comportement à l'oxydation de céramiques ultra-réfractaires à base de diborure d'hafnium et de carbure de silicium

National audienceLes céramiques ultra-réfractaires (UHTCs), plus particulièrement les diborures du groupe IVb, sont des candidats potentiels pour une grande variété d’applications, notamment en tant que matériaux structuraux pour la protection thermique des véhicules hypersoniques exposés à des températures très élevées (>1800°C) ainsi qu’à l’oxydation [1].L’objectif premier de ce travail consiste à élaborer des composites à base de céramiques ultra-réfractaires HfB2-SiC utilisés comme matériaux structuraux dans les domaines de l’aéronautique et l’aérospatial. Le second réside dans la compréhension des mécanismes d’oxydation mis en jeu lors de l’entrée des véhicules spatiaux dans l’atmosphère.Le frittage de ces matériaux, à différentes compositions, a été entrepris par Spark Plasma Sintering (SPS). Ce procédé est généralement utilisé pour l’obtention de matériaux très denses (>98% densité relative) à la microstructure fine, à des températures plus faibles et des temps plus courts qu’avec des techniques de frittage conventionnelles (frittage naturel, pressage à chaud) [2]. Afin de favoriser la densification et d’obtenir une distribution homogène des phases dans le matériau final, une étude sur la granulométrie des poudres de départ a été nécessaire. Une optimisation des conditions de frittage (pression appliquée, température et temps de maintien, vitesse de chauffage) a ensuite été menée dans le but d’élaborer des échantillons très denses en utilisant des paramètres adaptés à leur environnement. Les matériaux obtenus ont été oxydés à plusieurs températures dans un four solaire afin de se rapprocher des conditions auxquelles sont soumis les véhicules hypersoniques.Les mécanismes d’oxydation ont été mis en évidence à travers l’étude des couches oxydées en combinant la diffraction des rayons X (DRX), la microscopie électronique à balayage (MEB), la spectrométrie photoélectronique X (XPS) et la spectrométrie de masse d’ions secondaires à temps de vol (ToF-SIMS). Ce travail a été appuyé par l’obtention de données cinétiques lors des tests d’oxydation.En parallèle, une première approche thermodynamique du système Hf-B-Si-C a été réalisée à travers la modélisation de diagrammes de phases ternaires, le but étant de constituer une base de données cohérente de ce système quaternaire.[1] F. Monteverde, & A. Belosi, « The resistance to oxidation of an HfB2-SiC composite », J. Eur. Ceram. Soc., 25 (2005) 1025-1031.[2] D. Sciti, G. Bonnefont, G. Fantozzi, & L. Silvestroni, « Spark Plasma Sintering of HfB2 with low additions of silicides of molybdenum and tantalum », J. Eur. Ceram. Soc., 30 (2010) 3253-3258

Comportement des composites ultra‐réfractaires (Hf/Zr)B2‐SiC sous atmosphère dissociée (oxygène atomique)

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High temperature oxidation behavior of fully dense ZrB2/SiC and HfB2/SiC composites with various compositions in air plasma conditions

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Influence of alumina on the passive oxidation at low oxygen pressure of hot-pressed alpha-SiC

International audienceThe influence of an alumina content (2 wt.%) on the oxidation behavior of hot-pressed a-SiC is studied. Sintering of a-SiC powder with alumina rests on the formation of a liquid phase corresponding to the eutectic composition in the SiO2–Al2O3 system. The oxidation kinetics of pure a-SiC at 1470 K under helium with an oxygen partial pressure of 0.1 Pa is linear, although silica is produced. The formation of Al-rich crystallized phase could be responsible for the slower oxidation kinetics of alumina-doped SiC

High temperature oxidation behavior of fully dense ZrB2/SiC and HfB2/SiC ceramic composites with various compositions under atomic oxygen plasma

International audienceFully dense ZrB2/SiC and HfB2/SiC ceramic composites with various compositions were obtained by Spark Plasma Sintering without any sintering aid. The high temperature oxidation of these materials was then studied using the MESOX facility (PROMES, Odeillo, France), placed at the focus of the 6 kW solar furnace, for a total air pressure of 1000 Pa. Atomic oxygen was produced into the silica reactor thanks to a 300 W microwave discharge and the created plasma was surrounding the sample. Two compositions of each system were oxidized in air plasma from 1800 to 2200 K: Z80, Z70, H80 and H70. The denomination of our samples was based on the vol.% of the compound, for example H70 corresponds to 70 vol.% HfB2 and 30 vol.% SiC. These compositions were identified as the most promising during oxidation under molecular oxygen (in air) up to 1800 K [1]. Surfaces and cross-sections of the samples were analyzed using XRD, SEM/EDS, XPS and Raman spectroscopy in order to study the oxidation mechanisms for all the temperatures used. Through the combination of these techniques, it was shown that the behavior of the samples for each system was similar between 1800 and 2000 K, with the formation of a modified silica glassy layer in which B2O3 and ZrO2 or HfO2 were identified. The key parameter for the understanding of the oxidation behavior is the diffusion of atomic oxygen into the material, and when formed, through the glassy layer. Hafnon and Zircon formation were reported in the literature, and only ZrSiO4 was identified in this work. The fact is that the formation of this compound has a direct incidence on the oxygen diffusion through the glassy layer. For temperatures higher than 2000 K and up to 2200 K, the behavior of the material was quite different with the formation of ZrO2 or HfO2 and significant mass losses were measured. Oxidation mechanisms based on these experiments and characterizations were proposed.[1] C. Piriou et al., "Sintering and oxidation behavior of HfB2-SiC composites from 0 to 30 vol% SiC between 1450 and 1800 K", Ceram. Int. 45[2]A (2019) 1846-185

Comportement à l'oxydation des composites ultra-réfractaires (Hf/Zr)B2-SiC à très haute température et au cyclage

International audienceLes céramiques ultra-réfractaires (UHTCs), plus particulièrement les diborures du groupe IVb, sont des matériaux prometteurs pour une grande variété d'applications, notamment dans le domaine de l'aéronautique. En effet, ils sont des candidats potentiels pour certains éléments de chambre à combustion des moteurs pouvant atteindre des températures de l'ordre de 1700-1800 K et fonctionnant sous air, à pression atmosphérique. L'objectif principal de ce travail réside dans la compréhension des mécanismes d'oxydation de différentes nuances de composites (Hf/Zr)B2-SiC sous des conditions environnementales et de température très sévères. Pour cela, des matériaux homogènes en termes de microstructure et de densité relative ont été élaborés par Spark Plasma Sintering (SPS). Ce procédé est généralement utilisé pour l'obtention de matériaux ayant une microstructure fine, présentant des taux de densification élevés (> 98 %) à des températures plus faibles et des temps de traitement plus courts qu'avec des techniques de frittage conventionnelles (frittage naturel, pressage à chaud) [1]. Une optimisation des paramètres de frittage a été entreprise pour chacune des compositions des deux systèmes. L'oxydation de ces céramiques a constitué la seconde étape de ce travail. Pour cela, les matériaux ont été placés dans un four solaire et, à l'aide du montage REHPTS (REacteur Haute Pression et Température Solaire) [2] du laboratoire PROMES, ils ont été exposés à des températures élevées (jusqu'à 1900 K) sous air stagnant. Ce dispositif permet de s'approcher des conditions réelles aéronautiques dans la mesure où les températures sont atteintes en quelques dizaines de secondes seulement. L'étude des mécanismes d'oxydation associés a été menée sur les mêmes matériaux par analyse thermogravimétrique (ATG) avec introduction à chaud des échantillons. Ces derniers ont été testés en température jusqu'à 1900 K et leur résistance au cyclage a été suivie par analyse des cinétiques d'oxydation. Cette étude a été appuyée par la caractérisation des surfaces et sections oxydées en combinant la diffraction des rayons X (DRX), la microscopie électronique à balayage (MEB), la spectroscopie photoélectronique X (XPS) et la spectroscopie Raman. Réferences [1] D. Sciti, G. Bonnefont, G. Fantozzi, and L. Silvestroni, "Spark plasma sintering of HfB2 with low additions of silicides of molybdenum and tantalum,