An original way to investigate the siliconizing of carbon materials

The reaction of liquid silicon with glassy carbon and polycrystalline graphite was investigated according to two siliconizing processes. In the first process, the reactants are progressively heated from room temperature up to 1600 °C. In the second one, the liquid silicon is poured onto the carbon sample once the reactants have reached the required temperature, in order to consider short reaction times. Thus, an original equipment consisting of a graphite reactor, has been specially designed for this purpose. The nature and the growth rate of the resulting silicon carbide has been studied using scanning electron microscopy. The results showed the formation of a thin continuous layer of SiC crystallites at the liquid silicon/carbon interface. The thickness of the layer shortly becomes independent of reaction time (about 10 µm on glassy carbon and 15 µm on polycrystalline graphite after 30 min reaction time) while some isolated SiC particles appear in the solidified silicon phase, as well as a regular and unusual time dependent SiC layer at the silicon melt/atmosphere interface

Spectres de vibration du sulfate d'ammonium dans l'infrarouge lointain, dans les phases para- et ferroélectrique

Far infrared absorption by an ammonium sulphate single crystal is studied with polarized light between 10 and 250 cm-1, both in the paraelectric phase, at 300 and 223 K, and in the ferroelectric phase, at 203 and 80 K. The principal effect of the phase transition is to decrease the vibrational anharmonicity. No new absorption bands appeared and there was no marked increase in transmission. The soft mode predicted in the paraelectric phase by A. Sawada et al. was not observed.L'absorption dans l'infrarouge lointain d'un cristal de sulfate d'ammonium est étudiée en lumière polarisée de 10 à 250 cm-1 dans la phase paraélectrique à 300 et 223 K, et dans la phase ferroélectrique à 203 et 80 K. Le changement de phase se traduit surtout par une diminution de l'anharmonicité des vibrations, mais il n'y a pas apparition nette de nouvelles bandes, ni augmentation brutale de la transmission. Par ailleurs, le mode mou prévu par A. Sawada et al. dans la phase paraélectrique n'a pu être observé

Etude du vieillissement d'éléments chauffants à haut-flux en graphite ou en composite carbone-carbone

Pour réaliser des thermoplongeurs chauffants à haut flux, différents matériaux carbonés ont été mis en oeuvre : graphite polycristallin et composites C/C. Nous avons mis en évidence l'influence de certaines impuretés : silice, fer et calcium (combinées ou non) qui sont à l'origine d'une forte corrosion et qui doivent être éliminées. Pour limiter le transport du carbone dans l'appareillage, il convient d'utiliser une matrice carbonée graphitée à haute température : soit en ex-résine, soit en pyrocarbone.To realize highly efficient heating element operating at 1400°C under nitrogen environment, with a specific power of 500 W/cm2, various carbon materials have been progressively selected : polycrystalline graphite and carbon/carbon composites coated or not. Some drastic corrosion effects, due to impurities : silica, iron and calcium, have been underlined. To limit carbon transport in the reactor, the carbon matrix of the resistance must be graphitized at high temperature (pyrocarbon or carbonized resin)

Does exercise improve sleep for adults with insomnia? A systematic review with quality appraisal

Insomnia is recognised as the most prevalent sleep disorder. Untreated insomnia carries a heavy burden for patients and society. Exercise is proposed as a safe, inexpensive, and accessible non-pharmacological treatment. To the author's knowledge this is the first systematic review to investigate the sleep-enhancing effects of exercise by focusing exclusively on controlled trials comprising poor sleepers only and examining interventions consistent with national guidelines. Using a narrative synthesis, this review aimed to identify whether exercise improves objective and subjective sleep outcomes for people with insomnia. Five papers including participants with insomnia disorder, and six papers including participants with insomnia symptoms were identified through electronic database searches (CINAHL plus, PsycINFO, EMBASE, MEDLINE, SPORTDiscus, CENTRAL) and quality assessed using the Clinical Trial Assessment Measure. We found that exercise interventions led to improvements in subjective sleep quality for people with insomnia disorder and insomnia symptoms. However, exercise only improved objective and subjective measures of sleep continuity (sleep onset latency and sleep efficiency) for people presenting with insomnia symptoms, with a reduction in sleep onset latency being the most consistently observed effect across studies. The reliability of significant findings is reduced by methodological limitations. Recommendations are made to improve the quality of future research.</p