Oxygen-containing Mixtures Research Articles

Pt–Pd/MnOx–Al2O3 Oxidation Catalysts: Prospects of Application for Control of the Soot Emission with Diesel Exhaust Gases

Together with exhaust gases from motor vehicles with diesel engines, soot and toxic nitrogen oxides are released into the environment. In this work, we consider the possibility of removing diesel soot on the surface of the Pt–Pd/MnOx–Al2O3 oxidation catalyst with a low Pt–Pd content. The rate and activation energy of the catalytic oxidation of diesel soot with oxygen and NOx were studied in the isothermal mode and compared with the kinetic characteristics of the oxidation of charcoal soot and two samples of synthetic soot (Printex U, Vulkan XC-72). The physicochemical properties of soot, such as nano- and microstructure, elemental composition, composition of surface functional groups, determine its oxidative reactivity, which is higher in mixtures with NOx than in oxygen-containing mixtures.

Plasma decay in high-voltage nanosecond discharges in oxygen-containing mixtures

Plasma decay in high-voltage nanosecond discharges in CO2: O2 and Ar: O2 mixtures at room gas temperature and a pressure of 10 Torr is studied experimentally and theoretically. The time dependence of the electron density during plasma decay is measured using microwave interferometry. The time evolution of the charged particle density, ion composition, and electron temperature is simulated numerically. It is shown that, under the given conditions, the discharge plasma is dominated for the most time by O2+ ions and plasma decay is determined by dissociative and three-body electron−ion recombination. As in the previous studies performed for air and oxygen plasmas, agreement between measurements and calculations is achieved only under the assumption that the rate of three-body recombination of molecular ions is much greater than that for atomic ions. The values of the rate constant of three-body recombination of electrons with О2+ ions in a wide range of electron temperatures (500–5500 K), as well as for thermal (300 K) electrons, are obtained by processing the experimental results.

Two-step process for improved diamond deposition on titanium alloys at moderate temperature

A simple two-step process is reported here to deposit diamond coatings on titanium alloys at temperatures equal to or lower than 600 °C. The first step allows us to increase the carbon nucleation rate and to deposit a sacrificial layer which contains more than about 25% sp2 carbon. Its thickness is selected both to limit the interaction of titanium element with the plasmas used for diamond growth during all the second step, even when an oxygen-containing mixture is used, and to diffuse completely at the end of the process. After the first step, the formation of titanium carbide is observed by x-ray diffraction and x-ray photoelectron spectroscopy, which does not reveal any oxygen incorporation in the coating-substrate interfacial region. These results are related to the final strong diamond adherence.