Thermal Stability of Type II Modifications Inscribed by Femtosecond Laser in a Fiber Drawn from a 3D Printed Preform

Fiber drawing from a 3D printed perform was recently discussed to go beyond the limitations of conventional optical fiber manufacturing in terms of structure and materials. In this work, the photosensitivity of silica optical fibers to femtosecond laser light, and fabricated by 3D printing a preform, is investigated. The writing kinetics and the thermal performance of Type II modifications are studied by varying the laser pulse energy and investigating the birefringence response of the femtosecond (fs)-laser written structures. Compared with a conventional telecom single mode fiber (SMF28), the fiber made by 3D printing is found to have similar writing kinetics and thermal performance. Additionally, the thermal stability of the imprinted fs-laser induced nanostructures is investigated based on the Rayleigh–Plesset equation, describing a model of nanopores dissolution underpinning Type II modifications with thermal annealing

Premieres hybridations experimentales dans le genre Macrothorax Desmarest (Col., Carabidae)

National audienc

Catalyseurs acides hétérogènes pour la transestérification des huiles végétales par l'éthanol en conditions douces

nationa

Les hétéropolyacides : catalyseurs de transesterification des huiles végétales par l'éthanol en conditions douces

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Transesterification of rapeseed oil with ethanol. I. Catalysis with homogeneous Keggin heteropolyacids

International audienceHeteropolyacids (HPA) with Keggin structure were evaluated as homogeneous Brnsted acid catalysts in the reaction of rapeseed oil transesterification with methanol and ethanol at 358 K and atmospheric pressure. Rapeseed oil transesterification with ethanol over anhydrous Keggin HPAs leads to higher conversion level than H2SO4 compared at equivalent H+ concentration and H2O/H+ molar ratio. By contrast, Phosphoric acid, a quite weaker mineral acid, structurally close to H3PW12O40, is not operative under similar conditions. This demonstrates the advantages of strong Brnsted acids in vegetable oil transesterification with ethanol in mild conditions. It is worth noticing that differences in acid strength between anhydrous Keggin heteropolyacids, H3PW12O40, H4SiW12O40, H3PMo12O40, H4SiMo12O40, measured by calorimetry, did not correlate simply the catalytic activity. Indeed, the proton solvation with water molecule was shown to be a crucial parameter. Then, Mo samples exhibited higher activities due to their ability to lose crystallization water at lower temperatures compared to W samples. Finally, it was shown that higher transesterification rates were obtained with ethanol than methanol in presence of HPA

Transesterification of rapeseed oil with ethanol over heterogeneous heteropolyacids

Hamad, B. Lopes de Souza, R. O. Sapaly, G. Carneiro Rocha, M. G. Pries de Oliveira, P. G. Gonzalez, W. A. Sales, E. Andrade Essayem, N.Heterogeneized heteropolyacids, H3PW12O40/SiO2 and Cs2HPW12O40 were shown to catalyze rapeseed oil transesterification with ethanol in mild conditions. The number and the strength of the acid sites were evaluated by calorimetry. Over anhydrous H3PW12O40 and Cs2HPW12O40, acid sites of homogeneous strength with heat of ammonia adsorption near 200 kJ mol(-1) were measured. By contrast, H3PW12O40/SiO2 showed sites of lower strength with a heterogeneous distribution. The catalytic activity did not correlate the acid strength of solid catalysts. Indeed, equivalent TOF were determined on H3PW12O40 and silica supported H3PW12O40 while lower TOF were measured on microporous Cs2HPW12O40. The TOF values were interpreted in terms of leaching of the active phase in the case of H3PW12O40/SiO2 while reduced acid sites accessibility might explain the lower TOF measured on Cs2HPW12O40. (C) 2008 Elsevier B.V. All rights reserved