Didier Stuerga

Microwave flash synthesis of iron and magnetite particles by disproportionation of ferrous alcoholic solutions

This paper reports the microwave-hydrothermal treatment of alcoholic solutions of ferrous chloride (FeCl2) and sodium ethoxide (EtONa) solutions with a microwave autoclave designed by the authors (the RAMO system). Depending on the initial concentrations, hematite (α-Fe2O3), spinel phase (Fe3 − xO4) or iron-magnetite (Fe0-Fe3O4) nanocomposites are obtained with a lower grain size compared to conventional composites. Indeed, X-ray diffraction (XRD) analysis reveals grain sizes close to 20 nm for magnetite and 60 nm for metallic iron. However, the amount of metal is smaller (close to 11%). Furthermore, these particles are inert in the ambient atmosphere. Consequently, the RAMO (French acronym of Reacteur Autoclave MicroOnde) system appears to provide an efficient source of energy in rapidly producing inert powders of iron, magnetite and iron-magnetite composites.

Microstrip Spiral Resonator For Microwave-Based Gas Sensing

This paper presents the design of a new microstrip gas sensor based on a trapezoidal spiral resonator covered by a titanium dioxide nanoparticle layer. Reflection and transmission coefficient measurements between 1 and 8GHz revealed multiple resonances that can be used in the context of gas detection. The sensor response upon ammonia adsorption has been evaluated on the whole frequency span with a simple spectral analysis. Kinetic parameters such as response time, reversibility, and measurement stability have been determined with a monofrequential temporal analysis. The sensor showed at each resonance a good sensitivity to ammonia for concentrations between 50 and 300ppm, with a response time less than 1 min. The maximal response was reported at 7.76GHz with a reflection coefficient variation of 0.45dB after the injection of 300ppm of ammonia, which is 3.5 times higher than previously reported.

Metal Oxide Nanoparticles Obtained by Microwave Synthesis and Application in Gas Sensing by Microwave Transduction

In literature, many papers describe the applications of semiconductor as sensitive material in sensor field. The gas sensor using tin oxide requires a strictly controlled high operating temperature in order to detect both reducing and oxidizing gases. The semiconductor nanoparticles, with their high specific surface area, increase the gas sensing performance. The originality of this work is to valorize the nanoparticle of metal oxide like SnO2, TiO2 obtained by microwave thermohydrolysis synthesis, using a gas sensing microwave transduction. The present synthesis is to prepare metal oxide nanocrystalline powder with a high surface area by microwave-induced thermohydrolysis. We propose to study the influence of the metal oxide nanoparticle, as a sensitive layer, in gas sensing measurement. The pollutant is added into an argon flow (dynamic regim). This work highlights a specific sensor response to each ammonia concentration at room temperature. It shows a quasi-linear relationship between the set of points of the real part of the response and the ammonia concentration. The authors are currently working on these issues as well as the interaction mechanism between adsorbed gas molecules and metal oxide films.