X-ray Structures of Aerococcus viridans Lactate Oxidase and Its Complex with d-Lactate at pH 4.5 Show an α-Hydroxyacid Oxidation Mechanism

2008 ◽  
Vol 378 (2) ◽  
pp. 436-446 ◽  
Author(s):  
Makio Furuichi ◽  
Nobuhiro Suzuki ◽  
Balasundaresan Dhakshnamoorhty ◽  
Hirotaka Minagawa ◽  
Ryosuke Yamagishi ◽  
...  
Keyword(s):  
Oxidation Mechanism ◽  
Lactate Oxidase ◽  
X Ray ◽  
Aerococcus Viridans

L-lactate oxidase from Aerococcus viridans crystallized as an octamer. Preliminary X-ray studies

Biochimie ◽  
1998 ◽  
Vol 80 (4) ◽  
pp. 309-312 ◽  
Author(s):  
Y. Morimoto ◽  
K. Yorita ◽  
K. Aki ◽  
H. Misaki ◽  
V. Massey
Keyword(s):  
Lactate Oxidase ◽  
X Ray ◽  
Aerococcus Viridans

The Oxide Scale Growth Mechanism on Fe20Cr5Al+RE Alloy in SO2+O2

2009 ◽  
Vol 289-292 ◽  
pp. 541-550 ◽  
Author(s):  
Jerzy Jedlinski ◽  
Zbigniew Żurek ◽  
Martah Homa ◽  
G. Smoła ◽  
J. Camra
Keyword(s):  
Phase Composition ◽  
Secondary Ion Mass Spectrometry ◽  
Grazing Angle ◽  
Oxidation Mechanism ◽  
Complex Oxide ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thin Foils ◽  
Manufacturing Procedure ◽  
Secondary Ion

The oxidation mechanism of FeCrAl (+RE), RE: reactive elements: Y and Hf) thin foils was studied at temperatures ranging from 1093 K to 1173 K in SO2+1%O2 atmosphere. Materials were subjected to isothermal and thermal cycling exposures as well as to the so-called two-stage-oxidation. In the latter, an oxygen isotope 18O2 was used as a tracer. Starting materials and scales were characterized using Grazing Angle X-Ray Diffraction (GA-XRD), EDX, SEM, XPS and High Spatial Resolution Secondary Ion Mass Spectrometry (HSR-SIMS). The obtained results showed within the studied range of exposure conditions the scales on all the studied alloys grow via outward mechanism typical for transient oxides and not for the -Al2O3 which is consistent with phase composition results and scale morphology and/or microstructure. It was also found that ‘as received’ foils are not bare metals but complex oxide-on-metal systems resulting from their manufacturing procedure. The obtained results are discussed in terms of the diffusion-related transport properties of the scale and of the scale phase composition.

scholarly journals Keggin-Type Heteropoly Salts as Bifunctional Catalysts in Aerobic Baeyer-Villiger Oxidation

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1208 ◽  
Author(s):  
Katarzyna Pamin ◽  
Jan Połtowicz ◽  
Mateusz Prończuk ◽  
Joanna Kryściak-Czerwenka ◽  
Robert Karcz ◽  
...  
Keyword(s):  
Oxidation Mechanism ◽  
Decomposition Reaction ◽  
Redox Properties ◽  
Lewis Acidity ◽  
Bifunctional Catalysts ◽  
X Ray ◽  
Ethanol Decomposition ◽  
Iron Salts ◽  
First Time ◽  
Villiger Oxidation

The cobalt, manganese, and iron salts of tungstophosphoric or molybdophosphoric acid with growing content of metals were applied for the first time as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone with molecular oxygen. The catalysts were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and ethanol decomposition reaction. Introduction of transition metals into the heteropoly structure increases the activity of resulting heteropoly salts in comparison with parent heteropolyacids. It was shown that the most active catalysts are salts of the heteropoly salts with one metal atom introduced and one proton left (HMPX) type, (where M = Co, Fe, Mn, and X = W, Mo) with the metal to proton ratio equal one. Among all of the studied catalysts, the highest catalytic activity was observed for HCoPW. The effect indicates that both the acidic and redox properties are required to achieve the best performance. The Baeyer-Villiger (BV) oxidation mechanism proposed identifies the participation of heteropoly compounds in three steps of the investigated reaction: oxidation of aldehyde to peracid (redox function), activation of carbonyl group (Lewis acidity), and decomposition of the Criegee adduct to ε-caprolactone (Brønsted acidity).

Revealing the mechanism of the early stages of Ni–W RABiTS oxidation

2010 ◽  
Vol 25 (12) ◽  
pp. 2362-2370 ◽  
Author(s):  
Andrey V. Blednov ◽  
Oleg Yu. Gorbenko ◽  
Dmitriy P. Rodionov ◽  
Andrey R. Kaul
Keyword(s):  
Internal Oxidation ◽  
Photoelectron Spectroscopy ◽  
Oxidation Mechanism ◽  
Surface Oxidation ◽  
Surface Region ◽  
Near Surface ◽  
Precise Position ◽  
X Ray ◽  
Early Stages ◽  
Phase And Chemical Composition

The early stages of surface oxidation of biaxially textured Ni–W tapes were studied using thermodynamic calculations along with experimental tape oxidation at low P(O2). Tape phase and chemical composition, surface morphology, and roughness were examined using x-ray diffraction (XRD), energy-dispersive x-ray analysis (EDX), secondary ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). For a Ni0.95W0.05 alloy tape, the precise position of the tape oxidation line in P(O2)–T coordinates was established. This line includes a break at T ≈ 650 °C that originates from the change of the W oxidation mechanism from internal oxidation to oxidation on a free surface accompanied by segregation of the alloy components in the tape near-surface region. The surface roughness of a polished tape increased drastically during internal oxidation of W; further tape oxidation did not affect the integral roughness parameters, but introduced numerous small (˜;100 nm) features on the tape surface comprising NiO precipitates.

Microstructural Evolution during High-Temperature Oxidation of Ti2AlN Ceramics

2010 ◽  
Vol 65 ◽  
pp. 106-111
Author(s):  
Bai Cui ◽  
Rafael Sa ◽  
Daniel Doni Jayaseelan ◽  
Fawad Inam ◽  
Michael J. Reece ◽  
...  
Keyword(s):  
High Temperature ◽  
Microstructural Evolution ◽  
High Temperature Oxidation ◽  
Oxidation Mechanism ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
X Ray ◽  
Oxidation In Air ◽  
Α Al2o3 ◽  
Increasing Temperature

Microstructural evolution of Ti2AlN ceramics during high-temperature oxidation in air has been revealed by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), and energy-dispersive spectroscopy (EDS). After oxidation below 1200 °C, layered microstructures formed on Ti2AlN surfaces containing anatase, rutile, and α-Al2O3. Above 1200 °C, more complex layered microstructures formed containing Al2TiO5, rutile, α-Al2O3, and continuous void layers. With increasing temperature, anatase gradually transformed to rutile, and TiO2 reacted with α-Al2O3 to form Al2TiO5. Based on these microstructural observations, an oxidation mechanism for Ti2AlN ceramics is proposed.

The Oxidation Behaviour of TiC Matrix Ni3Al and Fe40Al Toughened Composites at High Temperatures

2006 ◽  
Vol 514-516 ◽  
pp. 657-661 ◽  
Author(s):  
Ming Xia Gao ◽  
Filipe J. Oliveira ◽  
Yi Pan ◽  
Y. He ◽  
E.B. Jiang ◽  
...  
Keyword(s):  
Oxidation Mechanism ◽  
Ceramic Matrix ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
Oxidation Layer ◽  
X Ray ◽  
Passive Oxidation ◽  
Melt Infiltration ◽  
Oxidation Resistant ◽  
Oxidation Layers

High temperature oxidation of TiC ceramic matrix Fe40Al and Ni3Al toughened composites (Fe40Al/TiC, Ni3Al/TiC) of different TiC contents, made by pressureless melt infiltration, was investigated. Oxidation experiments were conducted in air for up to 65 hours at 700-1100°C. Weight gains of the composites showed that Fe40Al/TiC is more oxidation resistant than Ni3Al/TiC ones. SEM/EDS and X-ray diffraction showed that the dense oxidation layers of the two types of composites are mainly composed of crystalline TiO2. The growth of the oxidation layer follows parabolic passive oxidation kinetics, the calculated values of the activation energy of the oxidation mechanism being 270-280kJ.mol-1 and 240-250kJ.mol-1 for Fe40Al/TiC and Ni3Al/TiC, respectively. Al2O3 and Ni-rich phases were also detected in the oxidation layer of Fe40Al/TiC and Ni3Al/TiC, respectively.

Near-threshold ultraviolet-laser ablation of Kapton film investigated by x-ray photoelectron spectroscopy

2003 ◽  
Vol 18 (1) ◽  
pp. 53-59 ◽  
Author(s):  
D. W. Zeng ◽  
K. C. Yung ◽  
C. S. Xie
Keyword(s):  
Free Radical ◽  
Photoelectron Spectroscopy ◽  
Oxidation Reaction ◽  
Oxidation Mechanism ◽  
Pulse Number ◽  
Ultraviolet Laser ◽  
Thermally Induced ◽  
X Ray ◽  
Induced Decomposition ◽  
Near Threshold

Near-threshold ultraviolet-laser (355 nm) ablation of 125-μm thick Kapton films was investigated in detail using x-ray photoelectron spectroscopy. Different from the irradiation at higher fluences, the contents of the oxygen, amide group, and C–O group on the ablated surface increased with an increase in the pulse number, whereas the carbon contents decreased, although the contents of the nitrogen and the carbonyl group (C = O) decreased slightly. This implied that there was no carbon-rich residue on the ablated surface. Near the ablation threshold, only photolysis of the C–N bond in the imide rings and the diaryl ether group (C–O) took place due to a low surface temperature rise, and the amide structure and many unstable free radical groups were created. Sequentially, the oxidation reaction occurred to stabilize the free radical groups. The decomposition and oxidation mechanism could explain the intriguing changes of the chemical composition and characteristics of the ablated surface. In addition, the content of the C–O group depended on the opposite factors: the thermally induced decomposition of the ether groups and the pyrolysis of the Caryl–C bond. Upon further irradiation, the cumulative heating may induce the breakage of the Caryl–C bond and enhance the oxidation reaction, resulting in an increase of the content of the C–O group.

Oxidation Resistance of Multicomponent CrTiAlN Hard Coatings at Elevated Temperatures

2009 ◽  
Vol 75 ◽  
pp. 37-42
Author(s):  
P.L. Tam ◽  
Zhi Feng Zhou ◽  
P.W. Shum ◽  
K.Y. Li
Keyword(s):  
Oxidation Resistance ◽  
Photoelectron Spectroscopy ◽  
High Speed ◽  
Elevated Temperatures ◽  
Oxidation Mechanism ◽  
Hard Coatings ◽  
Closed Field ◽  
X Ray ◽  
Mechanical And Tribological Properties ◽  
Pin On Disc

Quaternary CrTiAlN hard coatings were deposited by closed field unbalanced magnetron sputtering ion plating technique onto steel substrates, and their structural, mechanical, and tribological properties after heat treatment in air at different temperatures (500-900 oC) were studied and compared by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-indentation, and pin-on-disc (POD) tribometer, etc. The onset temperature of oxidation was determined by thermogravimetric analyser (TGA). The compositional depth profiles before and after the heat treatments were examined by X-ray photoelectron spectroscopy (XPS) in order to study the oxidation mechanism. The experimental results indicate that the CrTiAlN coatings have excellent oxidation resistance and thermal stability, and outperform the traditional hard coatings like TiN and TiAlN in terms of higher oxidation temperature, hardness, adhesion, and wear resistance. It is expected that the CrTiAlN coatings with superior properties should have better performance in dry high speed machining.

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