Effect Of Oxygen Distribution Research Articles

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity ( GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO 2) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.

Ion beam analysis of PZT thin films

We report the recent results on the effect of oxygen distribution in the Pb(Zr 0.53Ti 0.47)O 3 (PZT) ferroelectric thin films on the dielectric constant and P– E hysteresis and also on the crystalline quality. Depth profiling of oxygen content was estimated accurately by a newly developed ion beam technique (3.045 MeV 16 O (α,α) 16 O resonant backscattering), and the crystalline structure of the films was estimated by an X-ray diffraction method. The PZT films were fabricated by a helicon sputtering method. With increasing substrate temperature during deposition, the films were found to have a smaller content of Pb, though the Pb content did not change much for the post-annealing of the films at 750°C. We have changed the parameters of substrate temperature, annealing temperature, composition of target PZT pellets, partial pressure of oxygen gas, and so on, and finally have obtained very good PZT films with the dielectric constant of about 1400. The properties of the high dielectric PZT film has been clarified in terms of the depth profiling of films and crystalline structure.

Titanium silicide formation: Effect of oxygen distribution in the metal film

The oxygen behavior and its influence on Ti silicide formation is systematically studied in the TiO2/Si and Ti/TiO2/Si systems using Rutherford backscattering, nuclear reaction analysis, and x-rays diffraction techniques. After annealing in vacuum ( p<5×10−7 Torr), no reaction was observed up to 900 °C in the TiO2/Si system, whereas in the Ti/TiO2/Si system, metallic titanium reacts with the TiO2 film above 400 °C and at 600 °C a uniform oxygen solid solution is formed. The silicide formation starts at 650 °C and up to 750 °C the only phase formed is Ti5Si3. We found that this phase is kinetically favored as long as the Ti is being supplied by the unreacted film. The growth rate kinetics was found to have parabolic behavior and was therefore controlled by Si volume diffusion. Above 750 °C, TiSi2 forms very rapidly, its growth being nucleation controlled. During the growth of the silicide layer, a diffusion of oxgen toward the surface region was observed. When the oxygen concentration in the surface layer exceeded the solubility limit, Ti oxide precipitated and the silicide growth nearly stopped, even if some silicon reached the surface. At a temperature higher than 850 °C, a marked oxygen loss takes place, most probably via SiO sublimation. The sublimation process is favored by the presence of Si in the surface region and prevents the formation of a stable SiO2 diffusion barrier at the TiSi2/TiOx interface.