Active to passive transition in the oxidation of silicon carbide at high temperature and low pressure in molecular and atomic oxygen

The active to passive transition in the oxidation of sintered α-SiC has been determined by a thermodynamic approach and then experimentally under flowing air at high temperatures (1673–1973 K) and low pressures (oxygen partial pressure from 200–2100 Pa). Then, the physico-chemical behaviour of samples was compared for two different environments such as air-plasma atmosphere generated by microwaves, and a molecular atmosphere. The thermodynamic calculation does not predict any variation of the oxidation transition when changing the chemical state of oxygen (O₂ or O) but experimentally the domain characterized by the formation of a passive layer of silica is extended to lower pressure under atomic oxygen (for the same temperature range) than in the case of molecular oxygen.     

Electrochemical biosensing platforms using platinum nanoparticles and carbon nanotubes

Platinum nanoparticles with a diameter of 2-3 nm were prepared and used in combination with single-wall carbon nanotubes (SWCNTs) for fabricating electrochemical sensors with remarkably improved sensitivity toward hydrogen peroxide. Nafion, a perfluorosulfonated polymer, was used to solubilize SWCNTs and also displayed strong interactions with Pt nanoparticles to form a network that connected Pt nanoparticles to the electrode surface. TEM and AFM micrographs illustrated the deposition of Pt nanoparticles on carbon nanotubes whereas cyclic voltammetry confirmed an electrical contact through SWCNTs between Pt nanoparticles and the glassy carbon (GC) or carbon fiber backing. With glucose oxidase (GOx) as an enzyme model, we constructed a GC or carbon fiber microelectrode-based biosensor that responds even more sensitively to glucose than the GC/GOx electrode modified by Pt nanoparticles or CNTs alone. The response time and detection limit (S/N = 3) of this biosensor was determined to be 3 s and 0.5 microM, respectively.