Etienne Savary

Fast synthesis of nanocrystalline Mg2Si by microwave heating: a new route to nano-structured thermoelectric materials

The ultra fast synthesis of nanocrystalline Mg(2)Si was carried out using microwave radiation. The elemental precursors were first milled together under dry conditions to get fine particles. The resulting mixture of powders of Mg and Si was cold pressed before being heated by microwave irradiation. Precursors and products were analyzed by X-ray diffraction and scanning electron microscopy. The high energy ball milling parameters utilized to prepare the reactive powders have quite an influence on the behavior of the mixture under irradiation. Moreover, SEM imaging demonstrates that the power and time of irradiation are crucial for the grain growth of the Mg(2)Si and must be adequately controlled in order to avoid the decomposition of the phase. Our results show that we successfully managed to easily and quickly synthesize homogeneous nanocrystalline Mg(2)Si with particle size smaller than 100 nm using a microwave power of only 175 W for two minutes on powders ball milled for two hours.

Sintering of CuO and ZnO in a Single Mode Microwave Cavity with Shrinkage Control

Abstract A specific TE10m microwave cavity has been designed to follow-up the shrinkage during the microwave sintering of ceramics powders using an optical based position sensing device. The basic principle consists in measuring the distance from a laser source to the sample surface by means of a triangulation method. The spatial resolution device is around a few micrometers that enables to accurately measure the shrinkage versus time of a microwave irradiated sample. The shrinkage curves have been recorded during the direct microwave sintering of CuO and ZnO. Sintering kinetics has been found extraordinarily fast as only a few seconds are needed to achieve the maximum shrinkage for both materials. This new method is undoubtedly powerful to increase our understanding of microwave sintering and very useful to control the microstructure of microwave sintered ceramics.

HMGA2, the Architectural Transcription Factor High Mobility Group, Is Expressed in the Developing and Mature Mouse Cochlea

Hmga2 protein belongs to the non-histone chromosomal high-mobility group (HMG) protein family. HMG proteins have been shown to function as architectural transcription regulators, facilitating enhanceosome formation on a variety of mammalian promoters. Hmga2 are expressed at high levels in embryonic and transformed cells. Terminally differentiated cells, however, have been reported to express only minimal, if any, Hmga2. Our previous affymetrix array data showed that Hmga2 is expressed in the developing and adult mammalian cochleas. However, the spatio-temporal expression pattern of Hmga2 in the murine cochlea remained unknown. In this study, we report the expression of Hmga2 in developing and adult cochleas using immunohistochemistry and quantitative real time PCR analysis. Immunolabeling of Hmga2 in the embryonic, postnatal, and mature cochleas showed broad Hmga2 expression in embryonic cochlea (E14.5) at the level of the developing organ of Corti in differentiating hair cells, supporting cells, in addition to immature cells in the GER and LER areas. By postnatal stage (P0–P3), Hmga2 is predominantly expressed in the hair and supporting cells, in addition to cells in the LER area. By P12, Hmga2 immunolabeling is confined to the hair cells and supporting cells. In the adult ear, Hmga2 expression is maintained in the hair and supporting cell subtypes (i.e. Deiters’ cells, Hensen cells, pillar cells, inner phalangeal and border cells) in the cochlear epithelium. Using quantitative real time PCR, we found a decrease in transcript level for Hmga2 comparable to other known inner ear developmental genes (Sox2, Atoh1, Jagged1 and Hes5) in the cochlear epithelium of the adult relative to postnatal ears. These data provide for the first time the tissue-specific expression and transcription level of Hmga2 during inner ear development and suggest its potential dual role in early differentiation and maintenance of both hair and supporting cell phenotypes.

Control of the Shrinkage during Hybrid Microwave Sintering of Nano-Sized ZnO Based Powder for Varistors

The microwave heating allows sintering in a very short time which is useful to keep the materials nanostructure. Up to now the trial error method is commonly used to find the best experimental parameters. This method is time consuming and does not allow getting a high reliability. In this work, a specific optical based position sensing device has been used to record the shrinkage during hybrid microwave sintering. Owing to this particular device, the control of the nano-sized ZnO based powder sintering has been successfully achieved. Very fine microstructures were obtained and electrical properties of those nano-ceramics were determined.