Synthesis of carbonated vegetable oils: Investigation of microwave effect in a pressurized continuous-flow recycle batch reactor

International audienceWith the depletion of fossil resources, it is essential for the chemical industry to find alternative raw materials for polymers. Polyurethanes can be synthesized from vegetable oils and CO2 via an environmentally friendly, non-isocyanate pathway. Carbonation of epoxidized vegetable oil is a key step allowing the feasibility of this method. Because it requires a high temperature, high pressure and long reaction time to achieve complete conversion, microwave technology (MW) is an interesting approach for the intensification of the carbonation process. However, MW-irradiated batch reactor has multiple issues regarding scale-up. A microwave irradiated continuous-flow recycle batch reactor which can operate at high temperature (130 °C) and moderate pressure (8 bar) was used in the present work. The effect of microwave irradiation on the kinetics of carbonation reaction was studied. A kinetic model was developed to compare quantitatively the performance under microwave and conventional heating (CH). It was found that the activation energy of the carbonation reaction was slightly lower with the use of MW irradiation, where the values for CH and MW are respectively 0.385E + 04 J/mol and 0.338E + 04 J/mol

Coil optimization for low-field MRI: a dedicated process for small animal preclinical studies

International audienceWe demonstrate a method for the fast in vivo quantification of small volumes, down to 25 µL, using low-field magnetic resonance imaging (MRI) coils. The coils were designed so as to maximize the signal-to-noise ratio (SNR) in the images. For this we developed an analytical model for describing the variations of the SNR with coil design and with size/shape suited to the object under observation. Based on the conclusions drawn from the model, the coil parameters were chosen in order to reach an SNR close to the maximum. For the validation of the model, coils were finally characterized in terms of quality factor using saline phantoms. The coil design procedure is illustrated here with two examples: first, the quantification of about 200 µL of intradermal injected gel on rabbits with a single loop surface coil and second, the imaging of the intervertebral disks in rat tails using a small volume coil to detect possible lesions. Such studies would not have been feasible for the clinical low-field MRI system at our disposal using any of the commercially available medium-sized manufactured coils. As a result of this simple optimization procedure, a wide range of applications is accessible even at low magnetic fields, leading to new opportunities for low-cost, though efficient, preclinical studies

Fabrication of surface magnetic nanoclusters using low energy ion implantation and electron beam annealing

Magnetic nanoclusters have novel applications as magnetic sensors, spintronic and biomedical devices, as well as applications in more traditional materials such as high-density magnetic storage media and high performance permanent magnets. We describe a new synthesis protocol which combines the advantages of ion implantation and electron beam annealing (EBA) to produce surface iron nanoclusters. We compare the structure, composition and magnetic properties of iron nanoclusters fabricated by low dose 15 keV Fe implantation into Si02 followed by 10000 degrees C EBA or furnace annealing. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images together with superconducting quantum interference device (SQUID) magnetometry measurements show that only EBA leads to the rapid formation of surface crystalline Fe spherical nanoclusters, showing magnetic moments per Fe atom comparable to that of bulk bcc Fe and superparamagnetic properties. We propose a fabrication mechanism which includes e-beam enhanced desorption of Si02. This method has potential for fabricating nanoscale magnetic sensors integrated in microelectronic devices

Nanocrystalline multiferroic BiFeO3 thin films made by room temperature sputtering and thermal annealing, and formation of an iron oxide-induced exchange bias

Multiferroic nanocrystalline BiFeO3films have been successfully made by room temperature sputtering and thermal annealing in oxygen at 500C. Nanocrystalline Bi was seen before annealing as well asb-Bi2O3 and the iron oxide phases, magnetite, maghemite, and FeO. Superparamagnetism was observed that can be attributed to magnetite and maghemite nanoparticles. The thermally annealed film contained BiFeO3 nanoparticles and magnetite, maghemite, and hematite as well as unidentified BiFexOyphases. Superparamagnetism was also seen after annealing and the magnetic properties are predominately due to magnetite and maghemite nanoparticles rather than from multiferroic BiFeO3. The saturation magnetic moment was 60% lower after annealing, which was due to some of the Fe in the iron oxide nanoparticles being incorporated into the BiFeO3nanoparticles. An exchange bias was observed before and after annealing that cannot be attributed to a structure that includes BiFeO3. It is likely to arise from magnetite and maghemite cores with spin-disordered shells

Nanocrystalline multiferroic BiFeO3 thin films made by room temperature sputtering and thermal annealing, and formation of an iron oxide-induced exchange bias

Multiferroic nanocrystalline BiFeO3films have been successfully made by room temperature sputtering and thermal annealing in oxygen at 500�C. Nanocrystalline Bi was seen before annealing as well asb-Bi2O3 and the iron oxide phases, magnetite, maghemite, and FeO. Superparamagnetism was observed that can be attributed to magnetite and maghemite nanoparticles. The thermally annealed film contained BiFeO3 nanoparticles and magnetite, maghemite, and hematite as well as unidentified BiFexOyphases. Superparamagnetism was also seen after annealing and the magnetic properties are predominately due to magnetite and maghemite nanoparticles rather than from multiferroic BiFeO3. The saturation magnetic moment was 60% lower after annealing, which was due to some of the Fe in the iron oxide nanoparticles being incorporated into the BiFeO3nanoparticles. An exchange bias was observed before and after annealing that cannot be attributed to a structure that includes BiFeO3. It is likely to arise from magnetite and maghemite cores with spin-disordered shells

Multiferroic nanocrystalline BiFeO3 and BiCrO3 thin films prepared by ion beam sputtering

BiFeO3 and BiCrO3 films were made by room temperature sputtering followed by thermal annealing in a partial oxygen atmosphere. The annealed films were found to be nanocrystalline, with an average particle size of 11 nm for BiFeO3 and 8 nm for BiCrO3. The saturation moment per formula unit is 0.39 µB for BiFeO3 which is significantly greater than that found in bulk BiFeO3 (0.02 µB). A similar enhancement was also found in previous studies of BiFeO3 nanoparticles where the nanoparticle size was small. However, no large enhancement of the saturation moment per formula unit was identified for the annealed BiCrO3 films. The annealed BiFeO3 films displayed superparamagnetic behaviour and the particle size estimated from the blocking temperature is comparable to that estimated from the X-ray diffraction data. Our results show that sputtering and oxygen annealing is a method that can be used to make nanocrystalline BiFeO3 and BiCrO3 films