21 research outputs found
Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation
We report on the UV laser induced fluorescence of hexagonal boron nitride
(h-BN) following nanosecond laser irradiation of the surface under vacuum and
in different environments of nitrogen gas and ambient air. The observed
fluorescence bands are tentatively ascribed to impurity and mono (VN), or
multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence
band between 300 nm and 350 nm is assigned to impurity-band transition and its
complex lineshape is attributed to phonon replicas. An additional band at 340
nm, assigned to VN vacancies on surface, is observed under vacuum and quenched
by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a
broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further
irradiation breaks more B-N bonds enriching the surface with elemental boron.
However, no boron deposit appears under irradiation of samples in ambient
atmosphere. This effect is explained by oxygen healing of radiation-induced
surface defects. Formation of the oxide layer prevents B-N dissociation and
preserves the bulk sample stoichiometry
Femtosecond and Ultraviolet Laser Irradiation of Graphite-Like Hexagonal Boron Nitride
Effect of the femtosecond and nanosecond UV laser irradiation (below the
ablation threshold) of graphite-like hexagonal boron nitride (hBN) has been
studied. Experiments were carried out with the compacted powder under high
vacuum at room temperature using excimer KrF laser (248 nm). In the nanosecond
operation mode, the laser-induced fluorescence spectra are found strongly
modified depending on the integrated doze, which is attributed to a progressive
enrichment of the surface layer by elemental boron. A slow sample recovery
after the laser irradiation has been observed. On the other hand, in the
femtosecond mode the fluorescence spectra depend on the laser fluence, and the
changes are reversible: low energy fluorescence spectra are restored
immediately when the laser energy decreases. This effect can be explained by a
material bleaching, which favors a bulk centers emission. The ablation
threshold has been determined as 78 mJ/cm2 in the femtosecond laser operational
mode
Les mĂ©taux non ferreux â Alliage cuivre-bĂ©ryllium et titane
International audiencePrĂ©face / Dominique Leguillon P. 17. Introduction gĂ©nĂ©rale / Patrick Boissinot, Patrick Langlois, AgĂlio A.H. PĂĄdua P. 21. Introduction au dimensionnement / AgĂlio A.H. PĂĄdua 1  â DĂ©finition du problĂšme 2 â Dimensionnement 3 â Obturateurs 4 â Conclusion P. 31. Frettage et autofrettage / Patrick Langlois 1  â ConsidĂ©rations prĂ©liminaires au frettage 2 â Frettage dâune enceinte bibloc 3 â Frettage dâune enceinte multibloc 4 â Formulation de lâautofrettage 5 â Modes de rĂ©alisation de lâautofrettage 6 â Conclusion P. 55. MĂ©thodes dâĂ©lĂ©ments finis en calcul de structures Ă©lastiques / JoĂ«l Frelat 1  â Introduction 2 â Rappel de la formule thĂ©orique 3 â Formulation variationnelle 4 â Formulation numĂ©rique 5 â Etapes dâune mise en Ćuvre pratique 6 â Conclusion â Extension aux problĂšmes non linĂ©aires P. 65. Les matĂ©riaux sidĂ©rurgiques et les hautes pressions / Jean-Paul Dichtel 1  â CaractĂ©risation mĂ©canique des aciers 2 â MĂ©tallurgie des aciers et superalliages 3 â Commentaires : la Directive EuropĂ©enne Appareils Ă Pression P. 77. Les mĂ©taux non ferreux â Alliage cuivre-bĂ©ryllium et titane / Jean-Pierre Petitet 1  â Introduction 2 â Le cuivre-bĂ©ryllium 3 â Le titane P. 85. Les Carbures cĂ©mentĂ©s WC-Co / Emmanuel Pauty 1  â Les procĂ©dĂ©s de fabrication 2 â Les propriĂ©tĂ©s des carbures cĂ©mentĂ©s 3 â Conclusions P. 99. Choix et usinage des carbures de tungstĂšne / Jacques Calzas 1  â Choix des carbures de tungstĂšne 2 â Usinage du carbure de tungstĂšne P. 111. CĂ©ramiques et matĂ©riaux pour lâoptique / Jean-Claude Chervin 1  â CĂ©ramiques 2 â MatĂ©riaux pour lâoptique P. 141. Types de joints et de montage / Roger Argoud et Jacques Roux 1  â Introduction 2 â GĂ©nĂ©ralitĂ©s 3 â Joints Ă basse pression 4 â Joints cĂŽne sur cĂŽne 5 â Joints Bridgman Champignon 6 â Joints annulaires auto-serrĂ©s 7 â Joints coniques dâAmagat 8 â Autres joints 9 â Conclusion P. 161. Joints hautes pressions pour la compression de gros volumes solides / Sylvie Le Floch 1  â Joints solides utilisĂ©s dans les diffĂ©rents types dâenceintes hautes pressions 2 â MatiĂšres premiĂšres des joints 3 â Assemblages HP-HT P. 173. Le matĂ©riel standard / Jean-Pierre Petitet 1  â Tubes, conduites et raccords 2 â Les vannes 3 â Quelques types dâenceintes commercialisĂ©es 4 â Les gĂ©nĂ©rateurs de pression 5 â Le matĂ©riel moins standard P. 187. Assemblages haute pression / GĂ©rard Hamel 1  â Montage des raccords de pressions 2 â Montage de quelques passages Ă©lectriques 3 â Les passages de thermocouple 4 â Les passages optiques, montage des fenĂȘtres 5 â Montage des joints et des obturateurs sur une cellule haute pression P. 197. Usinage / Jean-Pierre Michel 1  â Introduction 2 â Les joints de faible Ă©paisseur 3 â Les bagues anti-extrusion Ă 45° 4 â Les joints Ă 45° 5 â Les joints « double Bridgman » 6 â Les joints plats en Ă©lastomĂšres 7 â Les joints en indium (Ă©tanchĂ©itĂ© en hĂ©lium et azote liquide 8 â Joints mĂ©tal-mĂ©tal type Lens ring 9 â Les passages du courant 10 â Usinage de matĂ©riaux exotiques P. 211. Les rĂšgles de sĂ©curitĂ© / Patrick Boissinot 1  â Dangers prĂ©sentĂ©s par les appareils Ă pression 2 â Appareils Ă pression rencontrĂ©s dans les laboratoires et facteurs de risques 3 â Principes gĂ©nĂ©raux de prĂ©vention et rĂ©glementation 4 â Moyens de protection 5 â Conclusio
Le matériel standard
International audienceTubes and pipes for the circulation of fluids under pressure are subject to the same type of calculation as the enclosures and use the same materials. Nevertheless, it is necessary to check the compatibility of the coefficients of expansion when working under the simultaneous action of pressure and temperature (e.g. titanium enclosure-standard steel tubes assemblies). The performance of these tubes can reach, depending on the ratio between the internal and external diameters, pressures of 1.3 GPa beyond which there is, in any case, no standard valve. However, it is worth noting a small quirk due to the fact that the Anglo-Saxon suppliers of materials are much older than the others: practically all the dimensions are given in English units. The tubes are thus packaged between 1/16 of an inch (1.59 mm) and 9/16 of an inch (14.3 mm).The most commonly used sizes are 1/8 inch (3.17 mm) and 1/4 inch (6.35 mm).Depending on the operating pressure range, there are two different connection methods in practice.Les tubes et conduites pour la circulation des fluides sous pression sont soumis au meÌme type de calcul que les enceintes et utilisent les meÌmes mateÌriaux. Il est neÌanmoins neÌcessaire de veÌrifier, lors dâun montage travaillant sous lâaction simultaneÌe de la pression et de la tempeÌrature, la compatibiliteÌ des coefficients de dilatation (par exemple des assemblages enceinte de titane-tubes standard dâacier). Les performances de ces tubes peuvent atteindre, suivant le rapport entre le diameÌtre inteÌrieur et le diameÌtre exteÌrieur, des pressions de 1.3 GPa au-delaÌ desquelles il nâexiste pas, de toute façon, de vanne standard. Il faut noter cependant une petite faceÌtie due aÌ la grande anteÌrioriteÌ des fournisseurs anglo-saxons de mateÌriel sur les autres: pratiquement toutes les dimensions sont donneÌes en uniteÌs anglaises. Les tubes sont donc conditionneÌs entre le 1/16 de pouce (1,59 mm) et le 9/16 de pouce (14,3 mm).Les dimensions les plus utiliseÌes sont le 1/8 de pouce (3,17 mm) et le 1/4 de pouce (6,35 mm).Suivant la gamme de pression de service envisageÌe on peut distinguer, en pratique, deux modes de raccordement.Comme il existe des rĂ©fĂ©rences croisĂ©es au sein de l'ouvrage, voici son sommaire:PrĂ©face / Dominique Leguillon P. 17. Introduction gĂ©nĂ©rale / Patrick Boissinot, Patrick Langlois, AgĂlio A.H. PĂĄdua P. 21. Introduction au dimensionnement / AgĂlio A.H. PĂĄdua 1  â DĂ©finition du problĂšme 2 â Dimensionnement 3 â Obturateurs 4 â Conclusion P. 31. Frettage et autofrettage / Patrick Langlois 1  â ConsidĂ©rations prĂ©liminaires au frettage 2 â Frettage dâune enceinte bibloc 3 â Frettage dâune enceinte multibloc 4 â Formulation de lâautofrettage 5 â Modes de rĂ©alisation de lâautofrettage 6 â Conclusion P. 55. MĂ©thodes dâĂ©lĂ©ments finis en calcul de structures Ă©lastiques / JoĂ«l Frelat 1  â Introduction 2 â Rappel de la formule thĂ©orique 3 â Formulation variationnelle 4 â Formulation numĂ©rique 5 â Etapes dâune mise en Ćuvre pratique 6 â Conclusion â Extension aux problĂšmes non linĂ©aires P. 65. Les matĂ©riaux sidĂ©rurgiques et les hautes pressions / Jean-Paul Dichtel 1  â CaractĂ©risation mĂ©canique des aciers 2 â MĂ©tallurgie des aciers et superalliages 3 â Commentaires : la Directive EuropĂ©enne Appareils Ă Pression P. 77. Les mĂ©taux non ferreux â Alliage cuivre-bĂ©ryllium et titane / Jean-Pierre Petitet 1  â Introduction 2 â Le cuivre-bĂ©ryllium 3 â Le titane P. 85. Les Carbures cĂ©mentĂ©s WC-Co / Emmanuel Pauty 1  â Les procĂ©dĂ©s de fabrication 2 â Les propriĂ©tĂ©s des carbures cĂ©mentĂ©s 3 â Conclusions P. 99. Choix et usinage des carbures de tungstĂšne / Jacques Calzas 1  â Choix des carbures de tungstĂšne 2 â Usinage du carbure de tungstĂšne P. 111. CĂ©ramiques et matĂ©riaux pour lâoptique / Jean-Claude Chervin 1  â CĂ©ramiques 2 â MatĂ©riaux pour lâoptique P. 141. Types de joints et de montage / Roger Argoud et Jacques Roux 1  â Introduction 2 â GĂ©nĂ©ralitĂ©s 3 â Joints Ă basse pression 4 â Joints cĂŽne sur cĂŽne 5 â Joints Bridgman Champignon 6 â Joints annulaires auto-serrĂ©s 7 â Joints coniques dâAmagat 8 â Autres joints 9 â Conclusion P. 161. Joints hautes pressions pour la compression de gros volumes solides / Sylvie Le Floch 1  â Joints solides utilisĂ©s dans les diffĂ©rents types dâenceintes hautes pressions 2 â MatiĂšres premiĂšres des joints 3 â Assemblages HP-HT P. 173. Le matĂ©riel standard / Jean-Pierre Petitet 1  â Tubes, conduites et raccords 2 â Les vannes 3 â Quelques types dâenceintes commercialisĂ©es 4 â Les gĂ©nĂ©rateurs de pression 5 â Le matĂ©riel moins standard P. 187. Assemblages haute pression / GĂ©rard Hamel 1  â Montage des raccords de pressions 2 â Montage de quelques passages Ă©lectriques 3 â Les passages de thermocouple 4 â Les passages optiques, montage des fenĂȘtres 5 â Montage des joints et des obturateurs sur une cellule haute pression P. 197. Usinage / Jean-Pierre Michel 1  â Introduction 2 â Les joints de faible Ă©paisseur 3 â Les bagues anti-extrusion Ă 45° 4 â Les joints Ă 45° 5 â Les joints « double Bridgman » 6 â Les joints plats en Ă©lastomĂšres 7 â Les joints en indium (Ă©tanchĂ©itĂ© en hĂ©lium et azote liquide 8 â Joints mĂ©tal-mĂ©tal type Lens ring 9 â Les passages du courant 10 â Usinage de matĂ©riaux exotiques P. 211. Les rĂšgles de sĂ©curitĂ© / Patrick Boissinot 1  â Dangers prĂ©sentĂ©s par les appareils Ă pression 2 â Appareils Ă pression rencontrĂ©s dans les laboratoires et facteurs de risques 3 â Principes gĂ©nĂ©raux de prĂ©vention et rĂ©glementation 4 â Moyens de protection 5 â Conclusio
Etude par spectroscopie des interactions fluide-liquide et conséquences sur la notion d'effet antisolvant (application à l'élaboration de poudre micronique de HNIW)
PARIS13-BU Sciences (930792102) / SudocSudocFranceF
Utilisation Prédictive de l'Equation d'Etat SAFT
PARIS13-BU Sciences (930792102) / SudocSudocFranceF
Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation
International audienceWe report on the UV laser induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation of the surface under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (VN), or multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence band between 300 nm and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to VN vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry
Coesite (SiO2) as an extreme case of superheated crystal: An X-ray diffraction study up to 1776 K
International audienceThe dense SiO2 polymorph coesite has been investigated by X-ray powder diffraction from room temperature up to 1776 K. No phase transition has been detected in this temperature interval. Thermal expansion shows little anisotropy and remains very small since the volume increases by only 1.6% between 300 and 1776 K. As indicated by theoretical simulations, the small dilation results from limited rotations of SiO4 tetrahedra and also from slight expansion of Si-O bonds. In addition, the results demonstrate that coesite can be kept 900° above its metastable congruent temperature of fusion which is about 875 K. Comparisons with measurements made under the same conditions for quartz and cristobalite indicate that, for SiO2 polymorphs with 4-fold coordinated Si, crystal structure exerts a smaller influence than melt viscosity on the extent of superheating
Raman spectroscopy study of nitromethane in a shear diamond anvil cell
International audienceIn addition to pressure and temperature effects, shear strain has been proposed to play an important role in the initiation and decomposition mechanisms of energetic materials. To study the effect of shear strain in more detail, a shear diamond anvil cell has been developed. In this paper, we present a Raman spectroscopy study of the effects of shear strain on the high-pressure behaviour of nitromethane (NM). Two major effects are observed in our experiments. The first one is a lowering of the pressures at which the different structural modifications of NM occur. The second one is observed at 28 GPa, where the sample decomposes suddenly just after shear application. Examination of the black residue showed that it is composed of carbon, as indicated by the Raman spectrum
Phase transitions and chemical transformations of nitromethane up to 350 °C and 35 GPa
International audienceNitromethane has been studied as a model of the energetic nitro compounds. The phase diagram has been determined by Raman scattering in the pressure and temperature ranges of 0â35 GPa and 20â350â°C, respectively. Three new solid phases of nitromethane called III, IV, V, and their domain of stability have been located. A first chemical transformation is observed by the disappearance of nitromethane Raman modes and by the irreversible formation of a transparent solid called compound I (CI). A second chemical transformation [compound Iâcompound II (CII)], at higher temperature than the first one, is observed by the sudden darkening of the sample