High-temperature oxidation kinetics of NiAl single crystal and oxide spallation as a function of crystallographic orientation

Isothermal and cyclic high-temperature oxidation of NiAl single crystal samples are presented. Oxidations have been carried out at 900, 1050, 1100 and 1150 ◦C on (1 0 0) and (1 1 0) oriented surface. Continuous thermogravimetry in cyclic conditions allows isothermal oxidation kinetics and spalling at each cycle to be followed. Oxidation kinetics are compared between (1 0 0) surface and (1 1 0) surface. (1 0 0) oriented surfaces appeared to oxidize slightly faster than (1 1 0) oriented surfaces. Experimental results of cyclic oxidation are compared to simulated results using a previously published statistical model. Spalling increases when the average oxide scale thickness increases with the number of cycles. Longer tests are necessary to study this evolution during the ’steady-state’ but no critical oxide thickness was found

Iron Thin Films from Fe„CO…5 and FeCp2/H2O under Atmospheric Pressure

Iron layers were first obtained from iron pentacarbonyl in metallorganic chemical vapor deposition MOCVD process under atmospheric pressure, in the temperature range 473–773 K, in a vertical cold wall reactor. Films of good purity were obtained with or without hydrogen as co-reactant, no chemical additives being used. The experiments showed that the velocity of the gas stream and, to a lower extent, the precursor molar fraction are the key parameters to be controlled, in order to monitor film growth rate and purity. In a second step, Fe thin layers were obtained by atmospheric pressure MOCVD starting from the reactive gas mixture FeCp2 and H2O in the temperature range 973–1073 K. A thermochemical simulation of the Fe-C-H-O system allowed optimum processing conditions to be approached. X-ray diffraction and microprobe analysis showed that the highest iron content in the layer was obtained for H2O/FeCp2 ratios between 4 and 6. Film growth occurs in two steps: the initial formation of a black, powdered, and porous layer that becomes densified as a result of the grain growth on increasing the deposition time in order to form compact gray metal films. This two-step mechanism was confirmed by kinetic and in situ IR pyrometric observations

Optimization of the Vaporization of Liquid and Solid CVD Precursors: Experimental and Modeling Approaches.

Two representative examples of the vapor phase transport of liquid and solid molecular precursors from a bubbler and a saturator, respectively, are presented. The influence of the vaporization conditions on the amount of vaporized precursor makes it possible to propose a model suitable for delivering high flow rates for, for instance, large-scale reactors or continuous deposition in conveyor-belt reactors. For the liquid compound Ti(OiPr)4 (TTIP) used in atmospheric pressure CVD of TiO2 thin films, the vapor flow rate increases linearly with the carrier gas flow rate up to a critical value, and also exponentially with the bubbler temperature. A numerical model is developed to simulate the experimental data. To illustrate the case of solid precursor, the sublimation of Fe(C5H5)2, used in the MOCVD of iron thin films, is studied. In this case, the amount of vaporized ferrocene is not proportional to the carrier gas flow rate. A model is developed for a powdery precursor, taking into account the gas/solid exchange surface and therefore the initial amount of precursor in the saturator. It can be used to predict the best vaporization conditions required to maximize and keep constant the precursor flow rate delivered to the CVD reactor

Large temperature range model for theatmospheric pressure chemical vapor deposition ofsilicon dioxide films on thermosensitive substrates

tCoating complex surfaces by functional amorphous silica films for new applications includ-ing energy harvesting and health depends on the operating range and robustness of theirdeposition process. In this paper, we propose a new kinetic model for the atmosphericpressure chemical vapor deposition of SiO2films from TEOS/O2/O3valid in the 150−520◦C temperature range, thus allowing for treating thermally sensitive substrates. For this,we revisit reported chemical schemes in Computational Fluid Dynamics simulations con-sidering original experimental data on the deposition rate of SiO2films from a hot-wallreactor. The new model takes into account for the first time a thermal dependency of thedirect formation of SiO2from TEOS and O3and yields excellent agreement in both shapeand value between experimental and calculated local deposition rate profiles. The modelprovides non-measurable information such as local distributions of species concentrationand reaction rates, which are valuable for developing optimized CVD reactor designs. Origi-nal solutions for the introduction of the reactants are proposed, to uniformly coat complexand/or large parts at a wide temperature range

Tunable SiO2 to SiOxCyH films by ozone assisted chemical vapor deposition from tetraethylorthosilicate and hexamethyldisilazane mixtures

Silica and silica-based materials with tunable functionalities are frequently encountered in low-k material applications, porous membranes, and microelectonic devices. In the present study, an innovative O2/O3 assisted CVD process for the deposition of such films at moderate temperature is presented, based on a dual precursor chemistry from hexamethyldisilazane (HMDS) and tetraethyl orthosilicate (TEOS). Films with tunable carbon content were obtained through variation of the HMDS flow ratio. A comprehensive FT-IR study reveals the transition of the material from a SiOxCyH type film containing -CH3 moieties, to a methyl-free SiOx film with the increase of the temperature. At the same time the water contact angle of 81.0° at 400°C is decreased to 52.8° at 550°C, related to the absence of methyl moieties in the latter. Ion beam analysis (IBA) confirms the lack of carbon in the films when deposition temperatures are equal to or exceed 500°C. The resistance to liquid corrosion is investigated as a function of the deposition temperature; SiOx type films present a low Pliskin etching rate of 15 Å.s-1, with this value increasing to 60 Å.s-1 for the SiOxCy:CH3 films produced at the lower temperatures. It is found that the addition of HMDS to a TEOS chemistry can be utilized to modulate the film composition from SiOx to SiOxCyH and by such, tune the film functional properties, in particular its etching rate, opening the way to the development of new sacrificial films

Etude immunochimique de la protéolyse de la caséine b (ciblage des sites préférentiels de coupure par la plasmine)

La qualité des fromages se construit progressivement durant leur affinage par la protéolyse du réseau de para-caséines. L'hydrolyse successive par des protéases et des peptidases variées libère de nombreux peptides qui contribuent directement ou indirectement à la flaveur. La contribution de la plasmine (EC 3.4.21.7) du lait à l'hydrolyse initiale, et surtout à celle de la caséine b, est reconnue mais mal comprise, car les méthodes analytiques sont inadaptées à la complexité du processus protéolytique. L'objectif de ce travail était donc de développer une méthode quantitative de suivi immunochimique, en mesurant l'intégrité des sites spécifiquement protéolysés dans la caséine b. Ce travail est rapporté dans quatre articles. Un variant silencieux inconnu de la caséine b, nommé H, et la plasmine bovine ont été isolés, et leur interaction analysée in vitro. Des anticorps de spécificité étroite dirigés contre la caséine b, dont 21 anticorps monoclonaux reconnaissant six déterminants, et 14 anticorps anti-peptide dirigés contre cinq déterminants ont été ensuite testés, en ELISA, en immuno-blotting et sur BIAcore, pour ne retenir que quatre anticorps anti-peptide détectant l'hydrolyse in vitro de deux liaisons majeures et deux mineures.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Heat treatment effect on polyphosphate chain length in aqueous and calcium solutions

International audienc

Heat treatment effect on polyphosphate chain length in aqueous and calcium solutions

International audienc

A new bovine beta-casein genetic variant characterized by a Met93 --> Leu93 substitution in the sequence A2

International audienc