Experimental investigation of a Doubly-Excited Flux-Switching Machine for Aircraft DC Power Generation

International audienceThis paper presents an experimental study on a new design of a Doubly-Excited Flux-Switching Machine (DEFSM) proposed for variable speed DC power generation in future aircraft. This machine uses excitation coils associated with permanent magnets to control the flux-linkage. This gives the possibility of using a diode bridge rectifier which is more reliable than an active bridge. After presenting its design and some of its main characteristics, an experimental investigation of the electromagnetic and thermal performances has been performed on a 3 kW prototype. It is shown that the generated power can be easily controlled using the excitation current which is very interesting for wide-speed-range applications. The unique design of the stator makes it possible to have a low remanent back EMF. This characteristic makes this machine inherently safe in case of fault since no flux weakening is needed. The thermal analysis has shown that the permanent magnets can be kept at relatively low temperatures which makes them more resistant to demagnetization. All of this makes the DEFSM a strong candidate for future aircraft power generation

Approche multiphysique pour la simulation du bruit rayonné par un transformateur : prise en compte des effets magnétostrictifs

Ce papier présente une approche multiphysique pour estimer le bruit rayonné par un transformateur en réponse aux excitations électromagnétiques. La méthode compte 3 étapes : il s'agit tout d'abord de calculer l'induction dans le circuit magnétique. Les effets magnétostrictifs sont alors pris en compte grâce à une analogie thermique et les réponses dynamiques de la structure peuvent être calculées. Le rayonnement acoustique est ensuite estimé par éléments finis acoustiques ou par une méthode analytique. Une démarche expérimentale, analyses modales et réponses en fonctionnement, permet de valider la méthode de simulation

Design of Iodonium Salts for UV or Near-UV LEDs for Photoacid Generator and Polymerization Purposes.

MEDLINE:31905900Iodonium salts are well established photoacid generators, cationic photoinitiators, as well as additives commonly used in photoredox catalytic cycles. However, as a strong limitation, iodonium salts are characterized by low light absorption properties for lambda \textgreater 300 nm so that these latter cannot be activated with cheap, safe, and eco-friendly near UV or even visible light emitting diodes (LEDs). To overcome this drawback, the covalent linkage of an iodonium salt to a chromophore absorbing at longer wavelength is actively researched. With aim at red-shifting the absorption spectrum of the iodonium salt, the synthesis of new compounds combining within a unique chemical structure both the chromophore (here the naphthalimide scaffold) and the iodonium salt is presented. By mean of this strategy, a polymerization could be initiated at 365 nm with the modified iodonium salts whereas no polymerization could be induced with the benchmark iodonium salt i.e., Speedcure 938 at this specific wavelength. To examine the effect of the counter-anion on the photoinitiating ability of these different salts, five different counter-anions were used. Comparison between the different anions revealed the bis(trifluoromethane)sulfonimide salt to exhibit the best photoinitiating ability in both the free radical polymerization of acrylates and the cationic polymerization of epoxides. To support the experimental results, molecular orbital calculations have been carried out. By theoretical calculations, the initiating species resulting from the photocleavage of the iodonium salts could be determined. The cleavage selectivity and the photochemical reactivity of the new iodoniums are also discussed

Organic Electronics: an El Dorado in the quest of new photoCatalysts as photoinitiators of polymerization

International audiencePhotoinitiated polymerization has been the subject of continued research efforts due to the numerous applications in which this polymerization technique is involved (coatings, inks, adhesives, optoelectronic, laser imaging, stereolithography, nanotechnology, etc.). More recently, photopolymerization has received renewed interest due to the emergence of 3D-printing technologies. However, despite current academic and industrial interest in photopolymerization methodologies, a major limitation lies in the slow rates of photopolymerization. The development of new photoinitiating systems aimed at addressing this limitation is an active area of research. Photopolymerization occurs through the exposure of a curable formulation to light, generating radical and/or cationic species to initiate polymerization. At present, photopolymerization is facing numerous challenges related to safety, economic and ecological concerns. Furthermore, practical considerations such as the curing depth and the competition for light absorption between the chromophores and other species in the formulation are key parameters drastically affecting the photopolymerization process. To address these issues, photoinitiating systems operating under low intensity visible light irradiation, in the absence of solvents are highly sought after.In this context, the use of photoredox catalysis can be highly advantageous; that is, photoredox catalysts can provide high reactivities with low catalyst loading, permitting access to high performance photoinitiating systems. However, to act as efficient photoredox catalysts, specific criteria have to be fulfilled. A strong absorption over the visible range, an ability to easily oxidize or reduce as well as sufficient photochemical stability are basic prerequisites to make these molecules desirable candidates for photoredox catalysis. Considering the similarity of requirements between organic electronics and photopolymerization, numerous materials initially designed for applications in organic electronics have been revisited in the context of photopolymerization. Organic electronics is a branch of electronics and materials science focusing on the development of semiconductors devoted to three main research fields; organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells (OSCs). The contribution of organic electronics to the field of electronics is important as it paves the way toward cheaper, lighter, and more energy efficient devices. In the present context of photopolymerization, materials that were investigated as photocatalysts were indifferently organic semiconductors used for transistors, charge-transport materials, and light-emitting materials used in electroluminescent devices or conjugated polymers and small molecule dyes for solar cells. In this Account, we summarize our latest developments in elaborating on photocatalytic systems based on these new classes of compounds. Through an in-depth understanding of the parameters governing their reactivities and our efforts to incorporate these materials into photoinitiating systems, we provide new knowledge and a valuable insight for future prospects

On the Favorable Interaction of Metal Centered Radicals with Hydroperoxides for an Enhancement of the Photopolymerization Efficiency Under Air

International audienceFour metal-based photoinitiating systems (benzene?tricarbonylchromium(0), ArCr(CO)3, cyclopentadienylmolybdenum tricarbonyl dimer, Cp2Mo2(CO)6, diiron nonacarbonyl, Fe2(CO)9, and bis(cyclopentadienylruthenium dicarbonyl), Cp2Ru2(CO)4) are investigated by laser flash photolysis (LFP) and ESR?spin trapping (ESR?ST) experiments and checked as photoinitiators for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). New combinations with silanes instead of alkyl halides improve both the polymerization rates and the final conversions upon irradiation with UV/visible or visible light and laser diodes (405, 457, 473, and 532 nm) under air. The enhancement of the photopolymerization reaction under air in the presence of the selected compounds is ascribed to the reuse of the inherently present hydroperoxides through a set of reactions leading to additional initiating species. These systems are particularly attractive for FRPCP with excellent polymerization rates and final conversions

Experimental investigation of a Doubly-Excited Flux-Switching Machine for Aircraft DC Power Generation

International audienceThis paper presents an experimental study on a new design of a Doubly-Excited Flux-Switching Machine (DEFSM) proposed for variable speed DC power generation in future aircraft. This machine uses excitation coils associated with permanent magnets to control the flux-linkage. This gives the possibility of using a diode bridge rectifier which is more reliable than an active bridge. After presenting its design and some of its main characteristics, an experimental investigation of the electromagnetic and thermal performances has been performed on a 3 kW prototype. It is shown that the generated power can be easily controlled using the excitation current which is very interesting for wide-speed-range applications. The unique design of the stator makes it possible to have a low remanent back EMF. This characteristic makes this machine inherently safe in case of fault since no flux weakening is needed. The thermal analysis has shown that the permanent magnets can be kept at relatively low temperatures which makes them more resistant to demagnetization. All of this makes the DEFSM a strong candidate for future aircraft power generation

Combination of Transition Metal Carbonyls and Si lanes: New Photoinitiating Systems

International audienceThe recently developed silyl radical chemistry is used in combination with transition metal carbonyls MC (dimanganese(0) decacarbonyl; dirhenium decacarbonyl; cyclopentadienyl iron(II) dicarbonyl dimer) for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). The newly developed photoinitiating systems (MC/silane and MC/silane/iodonium salt) are highly efficient under air. Photopolymerization profiles obtained upon a visible light irradiation delivered by a xenon lamp show that high conversion can be easily achieved after a 400 s exposure. Sunlight irradiations under air can also lead to tack free coatings. The processes associated with the metal carbonyl radical/silane interactions are investigated by Laser Flash Photolysis (LFP) and ESR-Spin Trapping (ESR-ST) experiments. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1830-1837, 201

Design Optimization of a Hybrid-Excited Flux-Switching Machine for Aircraft safe DC Power Generation using a Diode Bridge Rectifier

International audienceThis paper presents a design optimization methodology of a Hybrid-Excited Flux-Switching Machine (HEFSM) for aircraft DC power generation. Hybrid machines are favored in new aircraft embedded generation systems because of their high power density. Their flux control capability allows the use of the more reliable diode bridge rectifier and makes them suitable for wide-speed-range DC power generation. However, in order to respect aviation safety requirements, these machines must have a limited remanent voltage and therefore an optimal design is needed. At first, the electromagnetic performances of the HEFSM are studied using a transient FE model. In order to perform design optimization, a static method is used instead. This method is shown to be much less time consuming and more suitable for optimization routines. The results have shown very promising performances of the new design. Despite having a very small remanent voltage, high power density has been still achieved

Novel polymer synthesis methodologies using combinations of thermally - and photochemically-induced nitroxide mediated polymerization

The combination of thermally- and photochemically-induced polymerization using light sensitive alkoxyamines was investigated. The thermally driven polymerizations were performed via the cleavage of the alkoxyamine functionality, whereas the photochemically-induced polymerizations were carried out either by nitroxide mediated photo-polymerization (NMP2) or by a classical type II mechanism, depending on the structure of the light-sensitive alkoxyamine employed. Once the potential of the various structures as initiators of thermally- and photo-induced polymerizations was established, their use in combination for block copolymer syntheses was investigated. With each alkoxyamine investigated, block copolymers were successfully obtained and the system was applied to the post-modification of polymer coatings for application in patterning and photografting

Green Chemistry: Sunlight-Induced Cationic Polymerization of Renewable Epoxy Monomers Under Air

International audienceThe recently developed silyl radical chemistry is used here for the free-radical-promoted cationic polymerization process (FRPCP) of two epoxy monomers (epoxidized soybean oil and limonene dioxide) that are representative of green monomers. The new developed photoinitiating systems are highly efficient under air upon a solar irradiation in autumn French weather and, for example, lead to 60% conversion after 25 mn and form a completely tack-free and uncolored coating after 1 h. Polymerization profiles obtained upon a visible light irradiation delivered by a xenon lamp or a 405 nm diode laser under air show that 70% conversion can be easily achieved after 400 s of exposure. Excited-state processes are investigated and discussed