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When used as secondary refrigerants for cold storage and refrigeration applications, hydrate slurries offer high-energy densities due to their significant latent heat of fusion. In this context, gas hydrates exhibit a feature not yet explored in the literature: vapor is released when hydrate crystals melt in the heat exchanger supplying cold to end users. This novel feature is investigated in this paper. First, the separation of the released vapor from the solid+liquid slurry is described. This is followed by a study of how the design of the storage system can be adapted to the use of gas hydrate slurries as secondary fluid and specifically the consequences on its volume. A model is developed, based on energy and mass balances, to determine the required storage volume. Two types of hydrates involving a gas are considered: the single hydrate of carbon dioxide and the mixed hydrate of tetra-n-butylphosphonium bromide (TBPB) plus CO2 . The results show that adding vapor compression to the process can save up to 75% of the total storage volume.

International audience; Titanium nitride (TiN) films were grown by CVD (Chemical Vapor Deposition) from 11 titanium chlorides generated in situ by direct chlorination of titanium metal, ammonia (NH3) and 12 hydrogen (H2) as carrier gas on single crystal c-plane sapphire (Al2O3), cemented carbides (WC-Co), 13 stainless steel (AFNOR Z150CDV12) and amorphous graphite substrates. Kinetic pathways 14 involving four surface reactions has been proposed to simulate the growth rate. The proposed 15 model has been validated by experiments performed at different temperatures (650-1400 °C), 16 pressures (300-1000 Pa), with different amount of precursors (N/Ti ratio in gas phase) and on 17 different substrates. The study shows that on polycrystalline materials, the crystal orientation 18 depends on supersaturation while (111) preferred orientation is forced by underlying c-plane 19 sapphire whatever the supersaturation. The low N/Ti ratio in gas phase leads to low growth rate 20 and dense TiN film which is the key to obtain golden TiN. The high growth rate corresponds to 21 brown TiN. Globally, the study shows that golden color is independent from texture and is just the 22 natural aspect of a dense stoichiometric TiN layer. 23

International audience; We propose an innovative process coupling powder bed additive manufacturing by Electron Beam Melting (EBM) with Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) to develop 3D Ti-6Al-4V structures covered with AlN coating. Despite of the high reactivity of Ti-6Al-4V with nitrogen, thick (~10 μm) and conformal AlN films are deposited by CVD on Ti-6Al-4V substrates with high surface roughness. An AlN underlayer deposited by ALD is necessary to mitigate the reaction between Ti-6Al-4V and the nitrogen precursor NH 3(g) and to limit the formation of brittle titanium nitride phases. We have thus achieved an adherent coating without any modification of the Ti-6Al-4V microstructure at the core of the substrate. We show that a 7 μm thick AlN coating is efficient in protecting Ti-6Al-4V against cyclic oxidation at 650 • C for at least 650 h. This study opens new opportunities for the design of coated 3D Ti-6Al-4V structures for use in high temperature oxidizing environments.

International audience; The oxidation resistance of receivers is a critical point in the development of plants using solar tower technology. Intermetallics in Mo-Si-Al system present oxidation maximum temperature and creep resistance superior to the ones of the currently used Ni-based alloys. We followed here the oxidation resistance of such intermetallic exposed to different treatments in air: long-term oxidation (up to 700 h) at 1373 K, and for several cycles of 20 minutes in solar furnace. The normal spectral emissivity is measured up to 1640 K in air, and our main positive conclusion is this property is not degraded by the oxidation.

International audience; A comprehensive model to predict the stress evolution in a multilayer coating during its use in solar receivers is proposed. The model takes into account residual stress in the coatings, thermal gradient in the structure and high temperature phenomena like oxide scale growth and creep relaxation. The numerical tool developed in this work can help to understand the complex interplay of these phenomena occurring in all the materials involved. Additionally, the present model can be used to assess high temperature data like creep when it is compared with an experimental case.

International audience; The origin of threading dislocations (TDs) in nitride films is not completely understood but it is well established that they degrade the film properties. This work investigates the assumption that they arise from the interface between the film and sapphire substrate owing to small in-plane rotations between nitride domains. Bollmann’s formalism is first used to determine the characteristics of dislocations at the nitride film/sapphire interface that compensate both for the parametric misfit and a small in-plane rotation of the film as frequently observed. It is shown that the dislocation density and line direction depend on the rotation angle. When islands grow and coalesce in the nucleation layer, some interfacial dislocations orientate along [0001] in the boundaries between domains and transform to so-called TDs. The amount of TDs lying in the boundaries between nitride domains is calculated as a function of the rotation angle. Estimations of TD density in the nucleation layer are deduced for a range of domain sizes and compared with experimental values of the literature.

Processing of Ti1-xAlxN thin films by the reactive chemical vapor deposition (R-CVD) technique has been performed from the reaction between a titanium tetrachloride (TiCl4-H-2) gas mixture and (0001) c-plane monocrystalline aluminium nitride (AlN) films at high temperatures, in the 800-1200 degrees C range. As a typical result, the growth of epitaxial 70 nm thick layers of (111)-fcc Ti1-xAlxN (0.05 = x = 0.65) has been processed. Multicomponent mass transport and diffusion modelling is proposed to assess the experimental results. A good agreement is found between the experimental thickness of the transformed zones and the calculated titanium diffusion length in AlN. Fcc-Ti1-xAlxN phase formation can be regarded as a diffusion-controlled mechanism. The novel experimental methodology developed in this work could help in understanding the complex formation and stability of this technologically important material.

International audience; In its usual definition, exergy cancels out at the ambient temperature which is thus taken both as a constant and as a reference. When the fluctuations of the ambient temperature, obviously real, are considered, the temperature where exergy cancels out can be equated, either to the current ambient temperature (thus variable), or to a constant reference temperature. Thermodynamic consequences of both approaches are mathematically derived. Only the second approach insures that minimizing the exergy loss maximizes performance in terms of energy. Moreover, it extends the notion of reversibility to the presence of an ideal heat storage. When the heat storage is real (non-ideal), the total exergy loss includes a component specifically related to the heat exchanges with variable ambient air. The design of the heat storage can then be incorporated into an optimization procedure for the whole process. That second approach with a constant reference is exemplified in the case study of heat pumping for heating a building in wintertime. The results show that the so-obtained total exergy loss is the lost mechanical energy, a property that is not verified when exergy analysis is conducted following the first approach.

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International audience; There is an increasing interest for tower concentrated solar power (CSP) systems which can work at temperatures higher than 1073 K to optimize the efficiency. One of the challenges is to design the receiver that will be heated at high temperatures in air. On the contrary to coatings in gas turbine engine, the coating/substrate system must have a high thermal conductivity to ensure a good heat transfer to the fluid. Aluminum nitride (AlN) coating, deposited by chemical vapor deposition at 1373 K at a growth rate of 10-50 μm h −1 , is selected for its high thermal conductivity, low thermal expansion coefficient, high temperature stability and its ability to develop stable alumina scales above 1273 K. Cast and ODS (Oxide Dispersion Strengthened) FeCrAl alloys, also alumina-formers, are chosen as model substrates to reduce the influencing parameters in real-life receivers and to study the potential of these coatings. Accelerated cyclic oxidation tests and emissivity measurements allow the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems show low degradation after hundreds of thermal cycles at 1073 K in air and can support higher temperatures (1373 K) for 100 to 500 h depending on the coating thickness. Nevertheless the fast cyclic oxidations in solar furnace generated cracks through the coatings. The measurement of the optical properties also revealed a decrease of the absorptivity after oxidation.

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International audience; Direct liquid injection – metalorganic chemical vapor deposition (DLI-MOCVD) is the most advanced process dedicated to the internal protection of nuclear fuel cladding in accident conditions such as loss of coolant. It allows the deposition of an amorphous, glassy-like chromium carbide CrCx coating which is resistant against high-temperature oxidation in air and steam. Since the above-mentioned material characterizations demonstrated that coatings possessed the appropriate protection properties, the DLI-MOCVD process was scaled-up. First, a joint development between experimental and numerical studies led to a deposition inside a 1 m long cladding segment with a coating of sufficiently large and uniform thickness. Optimized reactor parameters consist in a combination of low temperature (~600 K) and low pressure (~600 Pa) with a high vapor flow rate of reactive species in the reactor ensuring a short residence time. The second phase of the scale-up consisted in coating simultaneously three, then sixteen segments in a single run. 3D computational simulations of the deposition process assisted the development of specific flanges designed to distribute homogeneously the reactive vapor into the three or sixteen cladding tubes. Experimental conditions have been extrapolated from one to three and to sixteen cladding segments, resulting in the deposition of the CrCx coating inside all segments with a relatively uniform partition. Overall, this paper demonstrates the feasibility of the deposition of CrCx coating in a bundle of several, up to sixteen, nuclear fuel cladding segments of 1 m in length (ID 8 mm), in order to protect them during accident conditions. This “batch demonstration” is a first step in the course of DLI-MOCVD technological transfer. Next step will be the deposition in a full-length cladding tube (4 m) that is already supported by numerical predictions.

International audience; The increased need for protecting cutting tools has led to the development of more and more efficient coatings. Ti-Al-N is one of the most studied systems in the hard coating industry due to the high hardness and good oxidation resistance of Ti1−xAlxN coatings. The development of LPCVD processes has led to the discovery of new microstructures and morphologies. In this study, we discuss the microstructural and morphological changes caused by varying the aluminum content in films deposited by low pressure thermal CVD in an industrial reactor at low carrier gas flow and relatively high pressure (>4 kPa). Coatings were characterized using FE-SEM, XRD and TEM analysis, revealing the growth of nanolamellae with modulated Al and Ti contents for the lowest Al containing coatings. The coatings with the highest Al contents were also found to show particular cube-shaped grains with a micromodulation of composition. Experimental Al content values are higher than the calculated one and their evolutions with the AlCl3/(AlCl3 + TiCl4) molar ratio are similar. The hardness and oxidation resistance were characterized and compared with available data in literature. Higher hardness is obtained for coatings having an Al content up to x = 0.65 and a hardness drop is found for higher Al contents. The oxidation resistance of the coatings rises continuously with an increasing Al content.

Boron Nitride is a promising group 13-group 15 compound material that exhibits various interesting properties like wide band gap, chemical stability, attractive mechanical properties and other. The growth behavior of this material has not been investigated in sufficient details to tailor properties of the resulting films. In this work we present the results on the growth of turbostratic boron nitride (t-BN) thin films at a relatively high growth rate of 3 mu m/h with the aim to investigate the potential use of boron trichloride in combination with ammonia as precursors for growth. Deposition experiments were conducted in a vertical cold wall high temperature chemical vapor deposition reactor in the temperature range 1000 degrees C-1700 degrees C depending on the substrate used. Templates of w-AlN (0001), 4 degrees off-cut 4H-SiC (0001), Cr (110) and W (110) were employed as substrates for the BN growth. As-grown BN layers were characterized by Scanning Electron Microscopy, X-Ray Diffraction, Electron Diffraction and Raman Spectroscopy. The results indicate that temperature and N/B ratio have a great influence on the crystallinity of the deposited films. For AlN and SiC substrates, a temperature of 1600 degrees C and N/B ratio in range between 3 and 7.5 were identified as the best parameters for the growth of a 2 mu m thick t-BN layer with a spacing between basal planes of about 3.36 angstrom compare to the 3.33 angstrom spacing between basal planes of hexagonal or rhombohedral BN (h-BN or r-BN). For Cr and W substrates which have a lower mismatch with h-BN (1 and 8.8 %), layers of t-BN were deposited at much lower temperature (1000 degrees C-1150 degrees C) with a spacing between basal planes of 3.5 angstrom and morphology similar to that observed on SiC substrates. We obtained t-BN layers with in plane strong disorder but out of plane orientation (c-axis normal to the surface).

International audience; For nuclear safety issues, there is an international effort to develop innovative “Enhanced Accident Tolerant Fuels” (EATF) materials. EATF cladding tubes are of particular interest because they constitute the first barrier against radioactive fission species dispersal in case of accidental scenario such as LOCA (LOss of Coolant Accident). Actual nuclear fuel claddings are made from Zr-based alloys and to increase safety margins, both mechanical strength and resistance to high-temperature oxidation have to be improved. Several alternatives using high-temperature oxidation resistant coatings for outer-wall protection have been proposed worldwide but there is currently no solution for the inner-wall protection. In order to resist to high temperature steam environment upon LOCA transients, internal Cr-based coatings deposited by DLI-MOCVD (Direct Liquid Injection of MetalOrganic precursors) were investigated. These hard metallurgical coatings could also be used in high-temperature corrosive environments as those encountered in aeronautics and other industries to protect 3D complex components. Thanks to a suitable chemistry of the liquid Cr precursor, bis(ethylbenzene)chromium, different coatings were deposited including: metal Cr, chromium carbides CrxCy and mixed carbides CrxSizCy. The high-temperature behavior of these Cr-based coatings under oxidizing atmospheres has been studied using several techniques and various oxidation tests including pure steam environment followed by water quenching down to room temperature to be representative of LOCA situations. Amorphous CrxCy coatings showed the most promising properties. For instance compared to uncoated substrate, they shift the catastrophic oxidation towards higher temperatures and delay the complete oxidation of the substrate at 1473K of >2h. The results are discussed in terms of oxidation mechanisms and protection of the fuel claddings inner surface deduced from fine characterizations of the samples before and after oxidation tests.

Plasma enhanced atomic layer deposition (PE-ALD) of aluminum nitride (AlN) thin films often utilizes NH3 or a mixture of N2 and H2 as a plasma source. However, the possibility of separating the activation step from the nitridation step by using H2 alone as the plasma source has never been explored. In this paper, we study the deposition of AlN by PE-ALD by using trimethylaluminum, H2 plasma and NH3 for deposition temperatures below 400 °C. The self-limiting ALD growth was achieved between 325 °C and 350 °C. As a comparison, AlN was also deposited by thermal ALD (T-ALD), where surface reactions between TMA and NH3 occurred with reasonable growth rates only at temperatures above 400 °C. The PE-ALD films showed low oxygen (1.5 at.%) and carbon contaminations (1 at.%). The T-ALD films contained carbon (5 at.%) mainly attributed to the presence of C Al bonds that was insignificant in PE-ALD films. The flow rate of H2 used in H2 plasma was found to have a significant impact on the preferred orientation of AlN films, where higher H2 flow rate promoted the (002) preferred orientation. Besides, the electrical resistivities were probed to be 108 Ω cm, as expected in an insulating material. As an example, AlN was used to infiltrate porous sintered silicon carbide (SiC). Both AlN deposited by PE-ALD and by T-ALD operating with exposure mode deposited at 400 °C were attempted. Even though, there is a greater risk for TMA precursor to decompose at 400 °C, infiltration of AlN was more successful by T-ALD operating with exposure mode.

Please cite this article as: Pons M, Delahaye A, Fournaison L, Dalmazzone D, Energy analysis of two-phase secondary refrigeration in steady-state operation, part 2: Exergy analysis and effects of phase change kinetics, Energy (2018),; International audience; A great deal of attention is paid to secondary refrigeration as a means of reducing excessively high emissions of refrigerants (most of which have a potent greenhouse effect) due to leaks in large cooling units. Among the environmentally friendly fluids that can be used in secondary circuits for transporting and storing cold, hydrate slurries offer the advantage of significant latent heats of fusion associated with good fluidity. Research programs have focused attention on hydrate systems, including CO2, TBPB (tetra n butyl-phosphonium-bromide), and mixed CO2-TBPB hydrates. In addition to feasibility concerns, energy efficiency is also a crucial concern requiring an objective analysis of the improvements likely to result from these new materials. A numerical model of secondary refrigeration system was built for slurries ranging from ice-slurry to TBPB-CO2 mixed hydrate slurries. The circuit was designed for maximizing performance under various constraints relating to power rate, heat transfer areas, and flow ability. The effects of phase change kinetics on thermal exchanges were introduced in the model and in the exergy balance. The results, analyzed in terms of exergy losses, demonstrate the couplings through which kinetics influences global performance.

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International audience; A great deal of attention is paid to secondary refrigeration as a means of reducing excessively high emissions of refrigerants (most of which have a potent greenhouse effect) due to leaks in large cooling units. Among the environmentally friendly fluids that can be used in secondary circuits for transporting and storing cold, hydrate slurries offer the advantage of significant latent heats of fusion associated with good fluidity. Research programs have focused attention on hydrate systems, including CO2, TBPB (tetra-n-butyl-phosphonium-bromide), and mixed CO2-TBPB hydrates. In addition to feasibility concerns, energy efficiency is also a crucial concern requiring an objective analysis of the improvements likely to result from these new materials. An impartial framework was thus constructed based on the principles of optimization methods. This approach was applied to these three hydrate slurries as well as to the well-known ice slurry for comparison purposes. A numerical model of secondary refrigeration system in steady state was built, on the basis of which optimized systems subjected to common external constraints can be designed for each slurry according to its thermophysical properties. Global performance can then be compared on a sound basis, which also makes it possible to identify the hydrate property that is most influential on energetic performance. Part 2 of this study is dedicated to exergy analysis and phase change kinetics.

International audience; The effect of direct recycling of effluents on the quality of CrxCy coatings grown by MOCVD using direct liquid injection (DLI) of bis(ethylbenzene)chromium(0) in toluene was investigated. The results are compared with those obtained using non-recycled solutions of precursor. Both types of coatings exhibit the same features. They are amorphous in the temperature range 673–823 K. They exhibit a dense and glassy-like microstructure and a high hardness (> 23 GPa). Analyses at the nanoscale revealed a nanocomposite microstructure consisting of free-C domains embedded in an amorphous Cr7C3 matrix characterized by strong interfaces and leading to an overall composition slightly higher than Cr7C3. The stiffness and strength of these interfaces are mainly due to at least two types of chemical bonds between Cr atoms and free-C: (i) Cr intercalation between graphene sheets and (ii) hexahapto η6-Cr bonding on the external graphene sheets of the free-C domains. The density of these interactions was found increasing by decreasing the concentration of the injected solution, as this occurred using a recycled solution. As a result, “recycled” coatings exhibit a higher nanohardness (29 GPa) than “new” coatings (23 GPa). This work demonstrates that using bis(arene)M(0) precursors, direct recycling of effluents is an efficient route to improve the conversion yield of DLI-MOCVD process making it cost-effective and competitive to produce protective carbide coatings of transition metals which share the same metal zero chemistry.

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A niching genetic algorithm (NGA) was presented to optimize a SiC-bulk crystal growth system by PVT. The NGA based on clearing mechanism and its combination method with heat transfer model for SiC crystal growth were described in details. Then three inverse problems for optimization of growth system were carried out by NGA. Firstly, the radius of blind hole was optimized to decrease the radial temperature gradient along the substrate while the center temperature on the surface of substrate is fixed at 2500 K. Secondly, insulation materials with anisotropic thermal conductivities were selected to obtain much higher growth rate as 600, 800 and 1000 µm/h. Finally, the density of coils was also rearranged to minimize the temperature variation in the SiC powder. All the results were analyzed and discussed.

The different steps of the fabrication of epitaxial AlN films (0.5–20 µm) by high temperature chemical vapor deposition called also HVPE (Hydride Vapor Phase Epitaxy) are reviewed (i) by thermodynamic modeling to analyze reactions in the chlorination chamber, (ii) by multicomponent heat and mass transport for a better knowledge of actual supersaturation of gas species above the substrate, (iii) by simple mechanical modeling to analyze the different source of stress during growth and (iv) by level set methods to represent the interface evolution at the micrometric level on patterned substrates. The evaluation of thin films is discussed in the light of modeling results. The joint use of the different modeling approaches allowed the quantification, for a 2″ substrate, of (i) the optimum temperature for the chlorination chamber (500 °C) to avoid AlCl specie formation, (ii) the transport of the main species AlCl3 diluted in NH3 and H2 and (iii) the actual supersaturation at the growth interface on 2D surfaces or 3D patterned surfaces to promote lateral epitaxial overgrowth and improve crystalline quality. Finally, the upscaling from 2″ to 4″ substrates is computed and validated.

We modeled and simulated the surface reaction of silicon precursor on different surfaces by thermodynamic analysis and density functional theory calculation. We considered SiH2Cl2 and argon as the silicon precursor and the carrier gas without etchant gas. First, the equilibrium composition of both gaseous and solid species was analyzed as a function of process temperature. SiCl4 is the dominant gaseous species at below 750 °C, and SiCl2 and HCl are dominant at higher temperatures, and the yield of silicon decreases with increasing temperature over 700 °C due to the etching of silicon by HCl. The yield of silicon for SiO2 substrate is lower than that for silicon substrate, especially at 1000 °C or higher. Zero deposition yield and the etching of SiO2 substrate at higher temperatures leads to selective growth on silicon substrate. Next, the adsorption and the reaction of silicon precursor was simulated on H-terminated silicon (100) substrate and on OH-terminated β-cristobalite substrate. The adsorption and reaction of a SiH2Cl2 molecule are spontaneous for both Si and SiO2 substrates. However, the energy barrier for reaction is very small (6×10−4 eV) for Si substrate, whereas the energy barrier is high (0.33 eV) for SiO2 substrate. This makes the differences in growth rate, which also supports the experimental results in literature.

International audience; Cr deposits are widely used as protective coatings but multifunctional performances are required in harsh environments motivating research on new processes. MOCVD of Cr metal coatings was carried out by direct liquid injection (DLI) of a unique solution containing bis(ethylbenzene)chromium as metal source and thiophenol as inhibitor of carbide formation. A low amount (

Chemical process modelling and simulation are widely used in process industries to progress in the understanding and in the improvement of many processes. Due to the complexity and variety of these processes, several pieces of software are often needed to model a given process, hence requiring interoperability between software. CAPE-OPEN is an industry standard for interoperability between process simulation software. Compared to proprietary interfaces of software applications, CAPE-OPEN allows for less overhead on programming and maintenance, fast access to market and a common basis for collaboration in joint projects.

International audience; AlN is epitaxially grown on c-plane sapphire by High Temperature Hydride Vapor Phase Epitaxy (HT-HVPE) at constant growth rate and thickness, while varying the N/Al ratio in the gas phase at 1500 °C. The influence of an additional low temperature (1200 °C) protective layer on AlN crystal quality is also assessed. The experiments and thermodynamic calculations show that the sapphire substrate is unstable at high temperature under hydrogen and ammonia while it is stable at low temperature or under a few hundred nanometers of AlN protective layer even at high temperature. In terms of AlN crystal quality, the optimal process developed here consists in depositing a 170 nm low temperature protective AlN layer with N/Al = 3 followed by a high temperature thick AlN layer grown with N/Al = 1.5. In this case, the interface between AlN and sapphire remains continuous (no etching) and the stress in the grown layer at room temperature is minimized by a balance of the growing tensile stress with the cooling compressive stress.

International audience; One mu m-thick (0001) t-BN layers have been grown on w-AlN template by HT-HVPE (High Temperature Hydride Vapor Phase Epitaxy). The experimental set-up consists of a vertical cold-wall quartz reactor working at low pressure with an inductively heated graphite susceptor. The used reactants are ammonia (NH3) and boron trichloride (BCl3). As-grown BN layers have been characterized by XRD and TEM. The influence of the temperature and the N/B ratio of precursors in the gas phase, on the c-lattice parameter of BN layer, have been investigated in order to optimize the crystalline quality. For a deposition at a temperature of 1600 degrees C and a N/B ratio of 7.5, the growth of a 2 mu m-thick t-BN layer with lattice parameters (a and c) of 2.50 and 6.78 angstrom has been achieved.

Pulsed plasmas are promising candidates to go beyond limitations of continuous waves' plasma. However, their interaction with surfaces remains poorly understood. The authors investigated the silicon etching mechanism in inductively coupled plasma (ICP) Cl2 operated either in an ICP-pulsed mode or in a bias-pulsed mode (in which only the bias power is pulsed). The authors observed systematically the development of an important surface roughness at a low duty cycle. By using plasma diagnostics, they show that the roughness is correlated to an anomalously large (Cl atoms flux)/(energetic ion flux) ratio in the pulsed mode. The rational is that the Cl atom flux is not modulated on the timescale of the plasma pulses although the ion fluxes and energy are modulated. As a result, a very strong surface chlorination occurs during the OFF period when the surface is not exposed to energetic ions. Therefore, each energetic ion in the ON period will bombard a heavily chlorinated silicon surface, leading to anomalously...

International audience; Within the TINA (Transient Integrated Network Analysis) research project and in partnership with Total, IFP is developing a new generation of simulation tool for flow assurance studies. This integrated simulation software will be able to perform multiphase simulations from the wellbore to the surface facilities. The purpose of this paper is to define, in a CAPE-OPEN compliant environment, a numerical and computational strategy for solving pressure-driven steady-state simulation problems, i.e. pure simulation and design problems, in the specific context of hydrocarbon production and transport from the wellbore to the surface facilities.

International audience; It is essential to know the actual exergy input of solar radiation in a given location in order to establishthe exergy budget of a solar collector or any other solar-powered process. To do so, the theories on theentropy of attenuated radiation must be re-interpreted before developing a method for evaluating theexergy flux from meteorological data. It then becomes possible to build a generic framework fordescribing the exergy budget of solar collectors. Three main types of exergy losses can be identified inthis way. The first is related only to the type of technology chosen for the collector: flat-type collectorsand highly concentrating collectors do not have same exergy losses. The second type of exergy loss isrelated mainly to heat dissipation, showing that all dissipated heat fluxes can be combined as the overallexergy loss. The third type is related to the utility furnished by the collector. Graphical examples areshown in a diagram that provides more information than the Sankey diagram.

There is a growing interest in producing tantalum nitride (TaN) thin films for various industrial applications. For example, in microelectronics, the development of IC technology is driven by the need to increase both performance and functionality while reducing power and cost. This goal can be achieved by several solutions among which the introduction of architecture enhancements such as 3D integration. The most challenging step is the deposition of a conformal, continuous, and adherent diffusion barrier. In this work, atomic layer deposition (ALD) of TaN thin films is explored using the combination between the thermodynamical behavior of the precursor, mass transfer in the reactor, and the operating conditions. TaN thin film deposition on very complex shape substrates, such as nanodots, TSV, silicon nanowires, and carbon nanotubes, has been evaluated.

AlN epilayers were grown on c-plane Sapphire substrates using High Temperature Halide Chemical Vapor Deposition (HTCVD). Introduction of low temperature nucleation layers (NLs) prior to the high temperature AlN (HT-AlN) layers was investigated. It was found that NLs stabilizes the epitaxial growth. NL deposition conditions were optimized to improve the quality of AlN epilayers. Increasing nucleation layer deposition temperature from 650 to 850 °C as well as the growth temperature of AlN epilayers from 1200 to 1400 °C improves the structural quality and surface morphology. X-ray diffraction of θ/2θ scan confirms that AlN layers deposited on NLs are (0002) oriented and X-ray rocking curve measurement shows FWHM values as low as 864 arcsec for (0002) plane. Surface steps and specular morphology were observed for such AlN epilayers (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; Thick MN layers were grown by high temperature chemical vapor deposition (HTCVD) on 8 degrees off-axis (0 0 0 1) 4H-SiC, on-axis (0 0 0 1) 6H-SiC and on-axis (0 0 0 1) AlN templates between 900 degrees C and 1600 degrees C. The experimental set-up consists of a vertical cold-wall reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH(3)) and aluminum chlorides (AlCl(x)) species in situ formed via Cl(2) reaction with high purity aluminum wire. As-grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Optical Profilometry, Atomic Force Microscopy (AFM) and Raman spectroscopy. In this study, the influence of the deposition temperature and the N/Al ratio in the gas phase is studied in order to stabilize epitaxial growth. The epitaxy on AlN template is favored using a low N/Al ratio in the gas phase and a high temperature above 1400 degrees C. The crystalline quality of epitaxial AlN layers is found to increase with increasing deposition temperature from 1400 to 1500 degrees C. Growth rates up to 14 mu m h(-1) have been reached for epitaxial AlN layers. An important etching phenomenon is also observed at high temperature: apparition of pin holes certainly around threading dislocations at 1400-1500 degrees C and substrate etching at 1600 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

The residual porosity of structural silicon carbide (SiC) composites limits their use in advanced nuclear systems. The use of thick coatings of high-Z materials like tungsten (W) or tungsten alloys (W1−xRex) is a promising solution to overcome such problems. However, solid-state reactions occur between SiC and metals at high temperatures. An intermediate layer is therefore selected, based on thermodynamic computation. It is shown that aluminum nitride (AlN) could limit the interface reactivity at temperatures close to 1000 °C. Duplex AlN/W1−xRex coatings were fabricated in two steps by chemical vapor deposition on bulk silicon carbide to verify experimentally the theoretical material solution approach. Electron probe micro-analyses showed that, at the micrometer level, there was no interface reaction during the growth process. It is the first time that such a material stack has been fabricated, and it seems promising for the high-temperature use of SiC with tungsten alloys.

Chromium carbide layers were deposited using liquid-injection metal-organic chemical vapor deposition inside long (0.3 to 1 m) and narrow (8 to 24 mm in diameter) metallic tubes. The deposition was carried out using a molecular single-source, bis(benzene)chromium (BBC), as representative of the bis(arene)metal family diluted in toluene and injected with N2 as carrier gas. A multicomponent mass transport model for the simulation of the coupled fluid flow, heat transfer and chemistry was built. The kinetic mechanism of the growth of CrCx films was developed with the help of large-scale experiments to study the depletion of the precursors along the inner wall of the tube. The model fits well in the 400&ndash, 550 &deg, C temperature range and in the 1.3 &times, 102 to 7 &times, 103 Pa pressure range. The pressure is shown to have a pronounced effect on the deposition rate and thickness uniformity of the resulting coating. Below 525 &deg, C the structure, composition and morphology of the films are not affected by changes of total pressure or deposition temperature. The coatings are amorphous and their Cr:C ratio is about 2:1, i.e., intermediate between Cr7C3 and Cr3C2. The model was applied to the design of a long reactor (1 m), with a double injection successively and alternatively undertaken at each end to ensure the best uniformity with sufficient thickness. This innovative concept can be used to optimize industrial deposition processes inside long and narrow tubes and channels.

International audience; The Continuous Feed-Physical Vapor Transport Technique (CF-PVT) was optimized by considering the heating, thermal insulation and the geometry of growth cavity. The effects of seeds on the surface morphology of the grown layer have been discussed. We successfully grew 3C-SiC bulk with a diameter of 7.0 mm and 3.3 mm in height with a high growth rate of 0.8 mm/h by the CF-PVT technique

International audience; Despite its real advantages compared to seeded sublimation growth, SiC solution growth has never given convincing results. The difficulty of stabilizing the growth front, and thus avoiding any polycrystal formation results from a poor description and understanding of the coupled phenomena that occur in the crucible. This paper addresses the coupled heat transfer and fluid dynamic modeling of the SiC solution growth process, with special attention being paid to the different convective flows in the liquid. It is demonstrated that both Marangoni and electromagnetic convections have to be avoided. The configuration where the flow patterns in front of the crystal are driven only by crystal rotation, insures the most stable growth front. The correlation between calculated results and experiments is presented and a 3C-SiC wafer grown by the optimized process is shown.

Summary This chapter contains sections titled: Introduction Experiments Results and discussions Spatial distribution of dislocations in SiC Conclusions References

In this paper, AlN synthesis is achieved by High Temperature CVD which consists of a graphite susceptor heated by induction in a home-built vertical cold-wall reactor working at low pressure. The reactants used are ammonia NH3 and aluminium chlorides AlClx species formed in situ via Cl2 reaction with high purity Al wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200{degree sign}C and 1600{degree sign}C. The influence of deposition temperature on growth rate, surface morphology, grain size and crystalline state is presented. Growth rates of up to 230 µm.h-1 were reached. AlN layers were characterized by SEM, X-ray Diffraction, Raman spectroscopy and Optical Profilometry.

The main problem for the development of 3C-SiC electronics is the lack of an adapted bulk growth process. The seeded sublimation method is not very adapted for the 3C polytype because of the solid-state transition from cubic to hexagonal that occurs at high temperature (above 1800°C). In this paper, we propose a new experimental set-up for the development of a solution route for the growth of high quality 3C-SiC crystals. By a coupled approach involving experiments and global process modeling, we have addressed the problems of dissolution and crystallization, elimination of parasitic nucleation and stabilization of the growth front. With an appropriate control of the different convection mechanisms, a stable growth front is demonstrated, with a growth rate of a few tens of µm/h at 1650°C. Further improvements and potentialities of this approach are discussed.

Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD), are sufficiently mature to help building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions.

International audience; We have investigated through birefiringence microscopy, a set of 3C-SiC crystals grown with the CF-PVT process, starting from different seeds and under different growth conditions. Through self nucleation experiments, the stable growth of very high quality 3C-SiC crystals at high temperature (2100 degrees C) and at high rate (roughly 0.2 mm/h) is demonstrated. The possibility to develop bulk growth of 3C-SiC crystals is discussed.

This paper reviews research on advanced bulk crystal growth of SiC. A brief review highlights the benefits of the so called Modified Physical Vapor Transport Technique which uses an additional gas pipe for fine tuning of the growth cell of a conventional Physical Vapor Transport setup with additional gases. Main emphasis, however, will be laid on a systematic dislocation evolution study for various growth parameter sets. Besides doping, growth temperature was considered. Two main results were found: (i) In p-type SiC, irrespective of the incorporation of aluminum or boron acceptors, basal plane dislocations that are harmful for bipolar power devices appear less pronounced or are even absent compared to n-type SiC. (ii) Growth at elevated seed temperature (i.e. 2300 °C and higher) is beneficial for low dislocation densities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The present paper gives an overview of the different routes to grow SiC single crystals. The focus is put on the new emerging processes compared with the well established ones. A review of the process engineering modelling is given. Finally, some selected results are pointed out as they should be considered for the future development of SiC material.

Silicon carbide is interesting for high power, high temperature and high frequency applications but its development is limited by the low quality and high cost of single-crystalline wafers. The transfer by wafer-bonding of single-crystalline SiC thin films to a polycrystalline SiC support is an attractive way for lowering the cost. This transfer requires high quality polycrystalline substrates fabricated with high growth rate, controlled morphology (columnar, dense, well-oriented layers), and very low surface roughness (RMS