Hugues Vergnes

Chemical vapor deposition of SnO2 coatings on Ti plates for the preparation of electrocatalytic anodes

Abstract SnO2 coatings have been deposited by metal-organic chemical vapor deposition (MOCVD) on Ti plates using SnEt4 and O2 as reactive gas mixture. The thickness, morphology and microstructure of these coatings are controlled by the growth conditions. The deposition process has been used for the preparation of Ti/IrOx/SnO2 electrodes that were tested for the anodic oxidation of organic pollutants in industrial wastewater. These anodes exhibit a high overpotential for oxygen evolution and a good efficiency for the elimination of total organic carbon (TOC) from wastewater. Electrochemical impedance measurements were used to characterize the activity of the interface SnO2/aqueous media as a function of time during the oxidation process. The influence of the grain size, thickness and surface pre-treatment of the Ti substrate on the electrocatalytic properties is discussed.

Effect of the TiO2 phase and loading on oxygen reduction reaction activity of PtCo/C catalysts in proton exchange membrane fuel cells

We investigated the effect of the TiO2 phase, as either pure rutile (TiO2(R)) or a 4 : 1 (w/w) anatase: rutile ratio (TiO2(AR)), and the loading on the activity of PtCo/C catalyst in the oxygen reduction reaction (ORR) in a proton exchange membrane (PEM) fuel cell. The incorporation of the different phases and loading of TiO2 on the PtCo/C catalyst did not affect the alloy properties or the crystalline size of the PtCo/C catalyst, but affected importantly the electrochemical surface area (ESA), conductivity of catalyst layer and the water management ability. The presence of TiO2(AR) at appropriate quantity can decrease the mass transport limitation as well as the ohmic resistance of catalyst layer. As a result, the optimum loading of TiO2(AR) used to incorporated in the layer of PtCo/C catalyst was 0.06mg/cm2. At this content, the TiO2(AR)-PtCo/C catalyst provided the highest current density of 438 mA/cm2 at 0.6V at atmospheric pressure in PEM fuel cell and provided the kinetic current in acid solution of 20.53 mA/cm2. In addition, the presence of TiO2(AR) did not alter the ORR electron pathway of PtCo/C catalyst. The electron pathway of ORR of TiO2(AR)-PtCo/C was still the four-electron pathway.

Mechanical and Surface Properties of Chemical Vapor Deposited Protective Aluminium Oxide Films on TA6V Alloy

Mechanical, barrier and surface properties of aluminium oxide films were investigated by nanoindentation, microscratch and micro tensile tests, by isothermal oxidation and voltammetry, and by contact angle measurement. The films were grown on TA6V substrates by a low pressure MOCVD process from aluminium tri-isopropoxide. Modelling of local gas flow, gas concentration and deposition rate profiles was performed using the CFD code Fluent on the basis of an apparent kinetic law. Films grown at 350 °C are amorphous AlO(OH), the one at 480 °C is amorphous Al2O3 and the one at 700 °C is nanocrystalline -Al2O3. Scratch tests and micro tensile tests resulted in adhesive failure on the two films grown at low temperature whereas cohesive failure was observed for the high temperature growth. Sample processed at 350 °C presents significantly lower oxidation kinetics in dry air than the bare substrate. Contact angle changes approximately from 100 to 50 degrees for films processed at 350-480 °C and 700 °C, respectively. Concerning the electrochemical behavior in NaCl environment, polarization curves revealed that amorphous alumina coatings improved the corrosion resistance by comparison with the others oxide films. These consolidated results reveal promising combination of properties for the films grown at different temperatures with regard to the targeted applications.

Amorphous alumina coatings on glass bottles using direct liquid injection MOCVD for packaging applications

In the field of packaging, coatings are commonly applied on containers to avoid interactions between them and their content. For glass bottles, application of a thin film prevents interactions with the phase in contact and consequently the alteration of surface properties of the latter. In this article, we propose an innovative way to apply amorphous alumina coatings on glass bottles by metalorganic chemical vapor deposition from aluminum tri-isopropoxide. A numerical model, using the Computational Fluid Dynamics code FLUENT, has been developed to calculate local profiles of gas flow, temperature, concentration and deposition rates into the reactor. The sub-micrometric alumina films have been deposited at reduced pressure between 480°C and 670°C. Uniform thickness profiles have been determined on cross sections over the length of the bottle and have been successfully simulated. Strongly improved hydrolytic resistance with regard to the uncoated bottles reveals the excellent performance of the films.

Electrochemical Incineration of Organic Pollutants for Wastewater Treatment: Past, Present and Prospect

Water is a combination of two parts, hydrogen and oxygen as H2O. However, pure water is only produced in a laboratory, water in general is not pure composition of hydrogen and oxygen. Eventhough, distilled water still has measurable quantities of various substances such as ions, mineral or organic compounds (http://www.environmental-center.com). These substances should be considered as the impurities that dissolved into water during flow through hydraulic pathway. Nowadays, there are some increasing on both population and consumption of natural resources to serve endless needs. Water is most important resource and becomes limited of use due to contamination from discharge of both domestic and industry. The discharge of domestic wastewater contains a large amount of organic pollutants. Industry also contributes substantial amounts of organic pollutants. However, some organic substrates discharged from industry contain a high toxicity and refractory organic pollutants. Figure 1 presents the example of a partially closed water cycle. In the cycle the organic pollutants are neither removed by sorption nor biodegradation. Nevertheless, there are some organic pollutants pass all barriers such as wastewater treatment or underground passage and appear in raw waters used for drinking water production. The other group of organic pollutants may originate from consumer products used in household, pesticides applied in agriculture or chemicals used in industry (Reemtsma & Jekel,2006). Wastewater treatment consists of applying known technology to improve or upgrade the quality of a wastewater. Usually wastewater treatment will involve collecting the wastewater in a central, segregated location and subjecting the wastewater to various treatment processes (Hanze et al., 1995). Wastewater treatment can be organized or categorized by the nature of the treatment process operation being used such as physical, chemical or biological treatment. Biological treatment of polluted water is the most economical process and commonly used for the elimination of degradable organic

Modeling of a pyrolysis process for the elimination of epoxy resin from embedded nuclear fuels

This paper presents the modeling of a bench-scale reactor for the pyrolysis of epoxy resin containing nuclear fuel samples. Strict operating conditions must be met to avoid nuclear fuel oxidation and the final hydrogen content in the residual char must be close to zero. By using the finite element method software, COMSOL Multiphysics®, transport phenomena and reaction kinetics can be combined to obtain a representative model of the reactor in terms of the temperature and the concentration distribution of the representative chemical species. The numerical results have been found consistent with the temperature measurements in the reactor. The model is also able to predict the distribution of permanent gases in the reactor over time. The variation in the composition and concentration of the gas near the fuel sample can then be monitored to control the oxygen potential. We have calculated the in-vessel transfers of a representative species of gases, hydrogen. The comparison of simulated and experimental values for hydrogen shows good agreement.

Magneto-transport properties of a random distribution of few-layer graphene patches

In this study, we address the electronic properties of conducting films constituted of an array of randomly distributed few layer graphene patches and investigate on their most salient galvanometric features in the moderate and extreme disordered limit. We demonstrate that, in annealed devices, the ambipolar behaviour and the onset of Landau level quantization in high magnetic field constitute robust hallmarks of few-layer graphene films. In the strong disorder limit, however, the magneto-transport properties are best described by a variable-range hopping behaviour. A large negative magneto-conductance is observed at the charge neutrality point, in consistency with localized transport regime.

Surface Modification of Polymer Powders by a Far Cold Remote Nitrogen Plasma in Fluidized Bed

In this work, nitrogen was grafted on the surface of polyethylene powders in a fluidized bed coupled to a nitrogen microwave post-discharge, under low pressure (10Torr) and low temperature (<90°C). The influences of treatment-duration (1 to 9 h) and nitrogen flow-rate on the XPS (X-ray Photoelectron Spectroscopy) N/C atomic ratio and on the powder wettability have been studied

Modeling of Silicon Nanodots Nucleation and Growth Deposited by LPCVD on SiO2 : From Molecule/Surface Interactions to Reactor Scale Simulations

We present first results combining models at continuum and atomistic (DFT, Density Functional Theory) levels to improve understanding of key mechanisms involved in silicon nanodots (NDs) synthesis on SiO2 silicon dioxide surface, by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH4. In particular, by simulating an industrial LPCVD reactor using the CFD (Computational Fluid Dynamics) code Fluent, we find that deposition time could be increased and then reproducibility and uniformity of NDs deposition could be improved by highly diluting silane in a carrier gas. A consequence of this high dilution seems to be that the contribution to deposition of unsaturated species such as silylene SiH2 highly increases. This result is important since our first DFT calculations have shown that silicon chemisorption on silanol Si-OH or siloxane Si-O-Si bonds present on SiO2 substrates could only proceed from silylene (and probably from other unsaturated species). The silane saturated molecule could only contribute to NDs growth, i.e. silicon chemisorption on already deposited silicon bonds. Increasing silylene contribution to deposition in highly diluting silane could then also exalt silicon nucleation on SiO substrates and then increase NDs density.