Papers by Keyword: Oxidation

Abstract: Intermetallics molybdenum dislicied has a great potential as a protective coating in aircraft engines and gas turbines in the elevated temperature. The suit for plasma spraying MoSi₂ powders were prepared by spray drying process and vacuum sintered. The oxidation behaviors of the coating were determined at 1200 °C. The coatings as sprayed and oxidized were characterized by XRD, SEM and EDS. Results show that the flow ability and loose density of MoSi₂ powder by sintered treatment, were 17.1 s/50g and 2.1g/cm³, respectively, ideal for air plasma spraying. During the course of spraying, some of molybdenum disilicide with a tetragonal lattice was converted into molybdenum disilicide with a hexagonal lattice. Also, part of MoSi2 phase oxidized and transformed to Mo₅Si₃ phase. A relative dense molybdenum disilicide coating was prepared by air plasma spraying. A protective SiO₂ layer, seems to be glassy, with a thickness about 10 μm was formed on the surface of MoSi₂ coating during MoSi₂ coating oxidized at 1200°C for 200 h. The results of the oxidation tests show that MoSi₂ coating prepared by air plasma spraying may be provide a protect layer for high temperature structure material.

Abstract: Amorphous alloys, in general, exhibit superior mechanical and chemical properties as compared to their crystalline counterparts, which is attributed to their chemical homogeneity and to the absence of crystal-like structural defects. Nanocrystalline and fully crystallized forms of these alloys can be easily obtained by a suitable thermal annealing treatment. It is important to have the knowledge of corrosion/oxidation behavior of amorphous and nanocrystalline alloys for various possible applications. In contrast to many investigations on corrosion and oxidation behavior of amorphous alloys reported in the literature, only limited studies have been carried out on comparison of corrosion/oxidation behavior of amorphous and nanocrystalline states of the same alloy. With this motivation potentiodynamic polarization studies were carried out on amorphous and nanocrystalline states of the alloy Ti60Ni40 in several aqueous media at room temperature. The oxidation in air was also investigated in the temperature range 2800C-3800C using a thermogravimetric analyzer. It was found from these investigations that nanocrystalline state exhibits the maximum corrosion/oxidation resistance in comparison to amorphous and crystalline states. The better corrosion/oxidation resistance of nanocrystalline state can be explained in terms of the nature of the nanocrystalline phase/phases and the size of the crystallites. The results of the present study are supported by other similar studies reported in the literature. A short review on comparison of corrosion/oxidation behaviour of amorphous and nanocrystalline Ti-based alloy is also presented in the paper.

Abstract: Thermal barrier coating (TBC), which consisted of a NiCoCrAlY bond coat (BC) and a ZrO₂-8 wt.%Y₂O₃ topcoat (TC), was fabricated on the nickel-base superalloy by air plasma spray (APS). The BC and TBC was treated by vacuum heat treatment (VHT). The oxidation of coating with and without VHT has been performed at 1050°C. Oxidation behavior of coatings and thermally grown oxide(TGO) scale were studied by SEM with EDS. As shown in the results, after treating by VHT, a continuous Al₂O₃ layer formed more rapidly on the VHT coating than that formed on the APS coating, which can act as a diffusion barrier to suppress the formation of other detrimental oxides. The pre-oxidation treatments reduced the growth rate and extend the steady-state growth stage. The TGO in VHT TBC was still a single layer Al₂O₃ oxide after 120h. However, after same oxidation time, the TGO in APS TBC produced a dual-layer oxide consisting of an inner Al₂O₃ layer and outer spinel layer. Therefore the VHT improves the oxidation resistance of APS coating.

Abstract: In this paper, the correlations between the cleavage degree of disulfide bonds and soy protein surface activity had been studied in order to show the surface activity of soy protein. The disulfide bonds of soy protein were oxidized to sulfonic groups by performic acid. The distribution of polar and nonpolar groups, and the molecular structure of soy protein were changed because of the oxidation damage of disulfide bonds, and these changes led to changes in surface activity of soy protein. The results showed that the emulsifying property of soy protein was improved by oxidizing the disulfide bonds of protein compared with that of natural soy protein. The change of soy protein emulsifying property is closely related with the degree of the disulfide bond oxidation damage,and that was also an effective way to prepare the protein-based surfactant.

Abstract: Taixi anthracite coal (TXC) was subjected to oxidation with NaOCl aqueous solution under mild conditions. The reaction mixture was extracted with ethoxyethane, followed by esterification with CH₂N₂, affording esterification products, which were analyzed by GC/MS. A large extent of benzene polycarboxylic acids (BPAs) were obtained in the coal oxidation products. The results showed that oxidation of coals with NaOCl aqueous solution is a useful technique for the high value-added utilization of coals.

Abstract: Four Chinese coals were oxidized with NaOCl aqueous solution under mild conditions. The reaction mixture was extracted with diethyl ether, carbon disulfide, petroleum ether, acetic ester and benzene sequentially. A series of organosulfur compounds (OSCs) were identified in the carbon disulfide fraction from the oxidized coals by GC/MS analysis but no OSCs were detected from other fractions except for 3 thiophene polycarboxylic acids found in ether-extraction. Some new types of sulfur function groups were also detected in the coal oxidation products which were not previously reported from coals. The results revealed that macromolecule OSCs in coals can be effectively degraded to water soluble small molecules with NaOCl aqueous solution, which can be enriched by carbon disulfide. Understanding the distribution of OSCs forms in coals matrix is useful in high value-added utilization of coals and coal desulphurization technologies.

Abstract: Oxidative desulfurization of gasoline was conducted in emulsion oxidative system (water –in-oil [W/O]) using hydrogen peroxide as the oxidizing agent, N-methyl-2-pyrrolidone (NMP) and water as extractive solvent, span60 as surfactant. Phosphomolybdic acid / activated semi-coke (30 wt%)were prepared by impregnation. These catalysts were characterized by scanning electron microscope (SEM). The effect of amount of catalysts, on the efficiency of desulfurization was investigated. Under this operation condition, the sulfur level of the desulfurized gasoline can be lowered from 550 ppm to below 80 ppm after oxidation and extraction. In addition, the gasoline after oxidation and extraction were analyzed by GC-FPD for sulfur content.

Abstract: In order to improve the therapeutic efficacy of retinoid carboxylic acids, a novel retinoate was designed and synthesized with 4-aminophenol as a linker from solanesol and 13-cis-retinoic acid. The synthetic procedure and characterization of the retinoate are described.

Abstract: An improved synthetic approach of tenatoprazole, an antiulcerative drug, is reported. The first step in this synthesis involves the coupling of 2-mercapto-5-methoxyimidazo[4,5-b]pyridine with 2-chloromethyl-4-methoxy-3,5-dimethylpyridine hydrochloride to afford sulfide 4, and the subsequent step of oxidation using substoichiomitric amount of hydrogen peroxide to give sulfoxide 1 quantitatively. The overall yield is around 80% for both two-step synthesis. The progress in this process is no purification process and affords the target compound with 99% purity by HPLC.

Abstract: Phthalocyanine catalysts were synthesized and supported matel phthalocyanines were found to be good catalysts for benzene hydroxylation to phenol. Matel phthalocyanines were characterized by N₂ absorption-desorption, FT-IR spectroscopy, and tranmsission electron microscopy. The experimental results suggested that the supported matel phthalocyanines were good catalysts for benzene hydoxylation reaction. Supported vanadium phthalocyanine performed the best catalytic activity, on which 11.6% of phenol yield and 100% of selectivity were obtained. And it was proved to be reusable in this reaction.