Wet air oxidation of nitrobenzene enhanced by phenol

Simultaneous nitrobenzene and phenol wet air oxidation was investigated in a stainless autoclave at temperature range of 180-220 ° C and 1.0 MPa oxygen partial pressure. Compared with the single oxidation of nitrobenzene under the same conditions, the presence of phenol in the reaction media greatly improved the removal efficiency of nitrobenzene. The effect of temperature on the reaction was studied. Phenol was considered as a type of initiator in the nitrobenzene oxidation. © 2004 Elsevier Ltd. All rights reserved.

Fracture Properties of LPCVD Silicon Nitride and Thermally Grown Silicon Oxide Thin Films From the Load-Deflection of Long Si3N4 and SiO2/Si3N4 Diaphragms

The bulge test is successfully extended to the determination of the fracture properties of silicon nitride and oxide thin films. This is achieved by using long diaphragms made of silicon nitride single layers and oxide/nitride bilayers, and applying comprehensive mechanical model that describes the mechanical response of the diaphragms under uniform differential pressure. The model is valid for thin films with arbitrary z-dependent plane-strain modulus and prestress, where z denotes the coordinate perpendicular to the diaphragm. It takes into account the bending rigidity and stretching stiffness of the layered materials and the compliance of the supporting edges. This enables the accurate computation of the load-deflection response and stress distribution throughout the composite diaphragm as a function of the load, in particular at the critical pressure leading to the fracture of the diaphragms. The method is applied to diaphragms made of single layers of 300-nm-thick silicon nitride deposited by low-pressure chemical vapor deposition and composite diaphragms of silicon nitride grown on top of thermal silicon oxide films produced by wet thermal oxidation at 950 degrees C and 1050 degrees C with target thicknesses of 500, 750, and 1000 mn. All films characterized have an amorphous structure. Plane-strain moduli E-ps and prestress levels sigma(0) of 304.8 +/- 12.2 GPa and 1132.3 +/- 34.4 MPa, respectively, are extracted for Si3N4, whereas E-ps = 49.1 +/- 7.4 GPa and sigma(0) = -258.6 +/- 23.1 MPa are obtained for SiO2 films. The fracture data are analyzed using the standardized form of the Weibull distribution. The Si3N4 films present relatively high values of maximum stress at fracture and Weibull moduli, i.e., sigma(max) = 7.89 +/- 0.23 GPa and m = 50.0 +/- 3.6, respectively, when compared to the thermal oxides (sigma(max) = 0.89 +/- 0.07 GPa and m = 12.1 +/- 0.5 for 507-nm-thick 950 degrees C layers). A marginal decrease of sigma(max) with thickness is observed for SiO2, with no significant differences between the films grown at 950 degrees C and 1050 degrees C. Weibull moduli of oxide thin films are found to lie between 4.5 +/- 1.2 and 19.8 +/- 4.2, depending on the oxidation temperature and film thickness.

A novel catalyst for clean production of diphenols - Ferric trisacetylacetonate MCM-41

Ferric trisacetylacetonate has been deposited within the zeolite MCM-41 and the product characterized by XRD and IR. In water at pH 7 it catalyzes the oxidation of phenol by H2O2, giving 58% conversion in 1 h at 50 degrees C: products are catechol (66%), hydroquinone (27%) and benzoquinone (7%). Other oxidants and solvents are much less effective. UV-VIS spectra suggest a radical substitution mechanism, and a pollution-free process for phenol hydroxylation is now possible.

Superconductor mixed oxides La2-xSrxCuO4+/-lambda for catalytic hydroxylation of phenol in the liquid-solid phase

Superconductor mixed oxides are often used as catalysts at high temperature in gas-solid phase oxidations and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of La2-xSrxCuO4+/-lambda (x = 0, 0.1, 0.7, 1) mixed oxides in phenol hydroxylation at lower temperatures are studied, and we find that the value of x has a significant effect on catalytic activity: the lower its value, the higher the catalytic activity; a mechanism is proposed to explain the experimental phenomena.

Wet Oxidation of AlxGa1-xAs/GaAs Distributed Bragg Reflectors

The wet oxidation of AlGaAs with high Al content in a distributed Bragg reflectors （DBR） is studied by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Some voids distribute along the oxide/GaAs interfaces due to the stress induced by the wet oxidation of the AlGaAs layers. These voids decrease the shrinkage of the Al2O3 layers to 8% instead of the theoretical 20% when compared to the unoxidized AlGaAs layers. With the extension of oxidation time, the reactants are more completely transported to the front interface and the products are more completely transported out along the porous interfaces. As a result,the oxide quality is better.

Selective oxidation of cyclohexane with hydrogen peroxide in the presence of copper pyrophosphate

Liquid phase oxidation of cyclohexane was carried out under mild reaction condition over copper pyrophosphate catalyst in CH3CN using hydrogen peroxide as an oxidant at the temperature between 25 and 80 degrees C. The copper pyrophosphate catalyst was characterized by means of XRD, FT-IR and water contact angle measurement. It was found that appropriate surface hydrophobicity is the key factor for the excellent performance of the catalyst. In addition, a significant improvement for the cyclohexane conversion in the presence of organic acid was observed.

Direct oxidation of benzene to phenol on manganese pyrophosphate with hydrogen peroxide

A solid catalyst manganese pyrophosphate based on non-sieves to oxidize benzene to phenol with oxidant hydrogen peroxide has shown good conversion with good selectivity in CH3CN at 65 degrees C investigating water contact angle data of three manganese salts, it is found manganese pyrophosphate has certain repulsive water character. It is further to be confirmed by benzene and phenol adsorption experiments onto catalyst surface by GC. With benzene/H2O2 ratio of 1, the benzene conversion of 13.8% with phenol selectivity of 85.0% was achieved. It is noteworthy that no any products are obtained using manganese pyrophosphate as catalyst in the oxidation of phenol in CH3CN solvent.

Time dependence of wet oxidized AlGaAs/GaAs distributed Bragg reflectors

The time dependence of wet oxidized AlGaAs/GaAs in a distributed Bragg reflector (DBR) structure has been studied by mean of transmission electron microscopy and Raman spectroscopy. The wet oxidized AlGaAs transforms from an initial amorphous hydroxide phase to the polycrystalline gamma-Al2O3 phase with the extension of oxidation time. The thickness of oxide layers will contract due to the different volume per Al atom in AlGaAs and in the oxides. In the samples oxidized for 10 and 20 min, there are some fissures along the AlGaAs/GaAs interfaces. In the samples oxidized longer, although no such fissures are present along the interfaces, the whole oxidized DBR delaminates from the buffer. (c) 2005 American Vacuum Society.

Interface of wet oxidized AlGaAs/GaAs distributed Bragg reflectors

The interface of wet oxidized Al0.97Ga0.03As/GaAs in a distributed Bragg reflector (DBR) structure has been studied by means of transmission electron microscopy and Raman spectroscopy. With the extension of oxidation time, the oxide/GaAs interfaces are not abrupt any more. There is an amorphous film near the oxide/GaAs interface, which is Ga2O3 related to the prolonged heating. In the samples oxidized for 10 and 20 min, there are some fissures along the oxidized AlGaAs/GaAs interfaces. In the samples oxidized or in situ annealed for long time, no such fissures are present due to the complete removal of the volatile products.

Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

THE OXIDATION-KINETICS OF THIN POLYCRYSTALLINE SILICON FILMS

The oxidation dynamics and morphology of undoped and heavily phosphorus-doped polycrystalline silicon films oxidized at a wide temperature and time range in dry and wet O2 atmosphere have been investigated. It is shown that the oxidation rates of polycrystalline silicon films are different from that of single-crystal silicon when the oxidation temperature is below 1000-degrees-C. There is a characteristic oxidation time, t(c), under which the undoped polysilicon oxide is not only thicker than that of (100)-oriented single-crystal silicon, but also thicker than that of (111)-oriented single-crystal silicon. For phosphorus-doped polycrystalline silicon films, the oxide thickness is thinner not only than that of (111)-oriented, single-crystal silicon, but also thinner than that of (100)-oriented, single-crystal silicon. According to TEM cross-sectional studies, these characteristics are due to the enhanced oxidation at grain boundaries of polycrystalline silicon films. A stress-enhanced oxidation model has been proposed and used to explain successfully the enhanced oxidation at grain boundaries of polycrystalline silicon films. Using this model, the oxidation linear rate constant of polysilicon (B/A)poly has been calculated and used in the modeling of the oxidation dynamics. The model results are in good agreement with the experimental data over the entire temperature and time ranges studied.