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Автор: Grafiati
Опубліковано: 3 червня 2022

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1

Hou, P. Y., Z. R. Shui, and J. Stringer. "Oxidation Behavior of Co-15wt% Cr Alloy Containing Dispersed Oxides Formed by Internal Oxidation." Corrosion 48, no. 12 (December 1, 1992): 990–1000. http://dx.doi.org/10.5006/1.3315911.

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Анотація:
Abstract Internal oxidation pretreatments of Co-15wt%Cr and Co-15wt%Cr-1 wt% Ti were carried out using a Rhines pack in quartz, in mullite, and in alumina. A dispersion of titanium oxide particles formed in the Ti-containing alloy as a result of the internal oxidation. However, silicon also diffused into all treated specimens when the pretreatments were carried out in quartz or in mullite. The effect of various pretreatments on the subsequent oxidation of these alloys was studied at 1,000°C and compared with that of a Co-15wt%Cr-1wt%Si alloy. The main purpose of this study was to determine the relative effectiveness of the dispersed oxide particles and the contaminated silicon on the selective oxidation of chromium. It was found that the oxidation behaviors of both treated alloys were strongly affected by the degree of silicon contamination. Selective oxidation of chromium to form a nearly continuous protective Cr2O3 scale was achieved with greater than 0.4 wt% silicon. The presence of dispersed particles reduced initial oxidation rate but was ineffective in promoting Cr2O3 scale formation.
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2

Zimbitas, Georgina, and Willem G. Sloof. "Modeling Internal Oxidation of Binary Ni Alloys." Materials Science Forum 696 (September 2011): 82–87. http://dx.doi.org/10.4028/www.scientific.net/msf.696.82.

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Анотація:
A numerical model is presented to simulate the diffusional transport of oxygen and that of an alloying element, within a 1-D binary Ni alloy, leading to the selective oxidation of the alloying element and the formation of an internal oxide precipitate. This specific model is written in MATLAB and, with the aid of the Matlab Toolbox, is coupled to the ThermoCalc extensive database. A reaction time is introduced to overcome problems related to the difficulty of formation of the internal oxide. Two cases are considered: Al as the alloying element for which the solubility product of the oxide forming elements is small, and Mn for which it is large.
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3

Kogo, Yasuo, Yoshie Iijima, and Naohiro Igata. "Enhancement of internal friction of carbon–carbon composites by selective oxidation." Journal of Alloys and Compounds 355, no. 1-2 (June 2003): 154–60. http://dx.doi.org/10.1016/s0925-8388(03)00255-x.

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4

Wen, Jiangwei, Longfei Zhang, Xiaoting Yang, Cong Niu, Shuangfeng Wang, Wei Wei, Xuejun Sun, Jianjing Yang, and Hua Wang. "H2O-controlled selective thiocyanation and alkenylation of ketene dithioacetals under electrochemical oxidation." Green Chemistry 21, no. 13 (2019): 3597–601. http://dx.doi.org/10.1039/c9gc01351b.

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Анотація:
Efficient and H2O-controlled selective thiocyanation and alkenylation of internal olefins, to afford tetrasubstituted olefins under electrochemical oxidation, has been successfully developed.
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5

Cho, Lawrence, Geun Su Jung, and Bruno C. De Cooman. "On the Transition of Internal to External Selective Oxidation on CMnSi TRIP Steel." Metallurgical and Materials Transactions A 45, no. 11 (July 18, 2014): 5158–72. http://dx.doi.org/10.1007/s11661-014-2442-7.

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6

Glickstein, James J., Paul A. Salvador, and Gregory S. Rohrer. "Multidomain simulations of coated ferroelectrics exhibiting spatially selective photocatalytic activity with high internal quantum efficiencies." Journal of Materials Chemistry A 4, no. 41 (2016): 16085–93. http://dx.doi.org/10.1039/c6ta07083c.

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7

Wang, Zi Jun, Saman Ghasimi, Katharina Landfester, and Kai A. I. Zhang. "Highly porous conjugated polymers for selective oxidation of organic sulfides under visible light." Chem. Commun. 50, no. 60 (2014): 8177–80. http://dx.doi.org/10.1039/c4cc02861a.

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Анотація:
High surface area porous conjugated polymers were synthesized via the high internal phase emulsion polymerization technique and micropore engineering as efficient heterogeneous photocatalysts for highly selective oxidation of organic sulfides to sulfoxides under visible light.
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8

Teng, Hua Xiang, Hai Quan Wang, Guang Hui Liu, Guang Rui Jiang, Li Bin Liu, and Yong Lin Kang. "Analysis on Alloying Elements of Selective Oxidation of TRIP Steel." Advanced Materials Research 941-944 (June 2014): 206–11. http://dx.doi.org/10.4028/www.scientific.net/amr.941-944.206.

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Анотація:
Two kinds of TRIP steel with different Al and Si content were researched in this article. Different annealing atmosphere in the trial was achieved by the Hot Dip Galvanized Simulator by Iwatani. The segregation of alloying elements after annealing under different atmosphere were investigated and the compounds on the surface were shown. Furhermore, the distribution of oxides was abserved on the surface and the reactive wetting was assessed and the results after galvanizing was provided. We found out the increasing wettability was abserved under more reducing atmosphere with less Si because of a decrease oxide amount and an increase internal oxidation.
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9

Moghe, Keerti, A. K. Sutar, I. K. Kang, and K. C. Gupta. "Poly(vinylbenzyl chloride-co-divinyl benzene) polyHIPE monolith-supported o-hydroxynaphthaldehyde propylenediamine Schiff base ligand complex of copper(ii) ions as a catalyst for the epoxidation of cyclohexene." RSC Advances 9, no. 53 (2019): 30823–34. http://dx.doi.org/10.1039/c9ra05811g.

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Анотація:
High internal phase emulsion of vinyl benzene and divinyl benzene in aqueous calcium chloride produced porous monoliths,which improved the activity of supported HNPn-Cu catalyst in selective oxidation of cyclohexene in presence hydrogen peroxide.
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10

Swaminathan, Srinivasan, and Michael Rohwerder. "Role of Forming Gas Annealing Characteristics on the Selective Surface Oxidation of Fe-Mn-Si-Cr Model Alloy." Defect and Diffusion Forum 312-315 (April 2011): 918–23. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.918.

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Анотація:
To understand the role of annealing conditions on the segregation and selective oxidation phenomena, Fe 2Mn 2Si 0.8Cr (all in wt.%) model alloy was investigated. The samples were annealed at 820°C in N2-5%H2 forming gas atmospheres over a wide range of dew pints (-80 to 0°C) with dwelling time of 1 to 5 minutes. At all dew points, the strong chemical interaction between Mn and Si causes the formation of manganese silicates. External oxidation of Mn, Si and Cr were decreased at the higher dew points. Increasing the dwelling time shows an extended oxidation front i.e. pronounced external/internal oxidation of Mn, Si and Cr. Basically, the present work addresses the two stages of oxidation front.
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11

Yu, Ping, Long Shi, Wen Wang, and Fu Hui Wang. "Oxidation Behavior of K38 Superalloy with Different Amounts of Yttrium Addition at 1173K in Air." Advanced Materials Research 366 (October 2011): 40–44. http://dx.doi.org/10.4028/www.scientific.net/amr.366.40.

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Анотація:
The oxidation behavior of K38 alloy with 0, 0.05, 0.1, 0.5wt% yttrium concentrations has been investigated during exposures in air at 1173K for 100 hours. The results indicated that Cr2O3 and TiO2 scale mainly formed on the surface of the alloy without yttrium. Yttrium addition promoted the selective oxidation of aluminum and reduced the internal oxidation. The alloy with 0.1 wt.% yttrium addition exhibits excellent oxidation behavior among the four types of the alloys for its decreasing the oxidation rate and forming more continuous and compact Al2O3 scales. Yttrium-rich phase formed in the alloy with 0.5wt.% yttrium, result in a negative effect on the oxidation resistance of cast alloys.
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12

Decker, David, Zhihong Wei, Jabor Rabeah, Hans-Joachim Drexler, Angelika Brückner, Haijun Jiao, and Torsten Beweries. "Catalytic and mechanistic studies of a highly active and E-selective Co(ii) PNNH pincer catalyst system for transfer-semihydrogenation of internal alkynes." Inorganic Chemistry Frontiers 9, no. 4 (2022): 761–70. http://dx.doi.org/10.1039/d1qi00998b.

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Анотація:
A Co(II) PNNH pincer catalyst system for the highly E-selective transfer-semihydrogenation of internal alkynes using ammonia borane and MeOH as the hydrogen source is described. The reaction is proposed to occur via the Co(ii) oxidation state.
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13

Krupp, U., and H. J. Christ. "Selective oxidation and internal nitridation during high-temperature exposure of single-crystalline nickel-base superalloys." Metallurgical and Materials Transactions A 31, no. 1 (January 2000): 47–56. http://dx.doi.org/10.1007/s11661-000-0051-0.

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14

Ji, Kegong, Xiang Liu, Bowen Du, Fang Yang та Jinming Gao. "Gold-catalyzed selective oxidation of 4-oxahepta-1,6-diynes to 2H-pyran-3(6H)-ones and chromen-3(4H)-ones via β-gold vinyl cation intermediates". Chemical Communications 51, № 51 (2015): 10318–21. http://dx.doi.org/10.1039/c5cc02952j.

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Анотація:
α-Oxo gold carbenes generated in situ via the gold-catalyzed selective oxidation of 4-oxahepta-1,6-diynes were effectively trapped by internal alkynes, resulting in the formation of 2H-pyran-3(6H)-ones, 3, and chromen-3(4H)-ones, 4, upon facile trapping the vinyl cation intermediates.
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15

Story, Mary E., and Bryan A. Webler. "Evolution of Near-Surface Internal and External Oxide Morphology During High-Temperature Selective Oxidation of Steels." JOM 70, no. 7 (May 7, 2018): 1225–31. http://dx.doi.org/10.1007/s11837-018-2885-1.

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16

Capell, Brent M., and Gary S. Was. "Selective Internal Oxidation as a Mechanism for Intergranular Stress Corrosion Cracking of Ni-Cr-Fe Alloys." Metallurgical and Materials Transactions A 38, no. 6 (June 13, 2007): 1244–59. http://dx.doi.org/10.1007/s11661-007-9124-7.

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17

Święs, Aneta, Małgorzata Rutkowska, Andrzej Kowalczyk, Urbano Díaz, Antonio E. Palomares, and Lucjan Chmielarz. "Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process." Materials 13, no. 21 (October 30, 2020): 4885. http://dx.doi.org/10.3390/ma13214885.

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Анотація:
Ferrierites and their delaminated forms (ITQ-6), containing aluminum or titanium in the zeolite framework, were synthetized and modified with copper by an ion-exchange method. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV-Vis DRS), textural parameters (N2-sorption), surface acidity (NH3-TPD), form and reducibility of deposited copper species (UV-Vis DRS and H2-TPR). Ferrierites and delaminated ITQ-6 zeolites modified with copper were studied as catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). It was shown that aggregated copper oxide species, which were preferentially formed on Ti-zeolites, were catalytically active in direct low-temperature ammonia oxidation to NO, while copper introduced into Al-zeolites was present mainly in the form of monomeric copper cations catalytically active in selective reduction of NO by ammonia to dinitrogen. It was postulated that ammonia oxidation in the presence of the studied catalysts proceeds according to the internal-selective catalytic reduction mechanism (i-SCR) and therefore the suitable ratio between aggregated copper oxide species and monomeric copper cations is necessary to obtain active and selective catalysts for the NH3-SCO process. Cu/Al-ITQ-6 presented the best catalytic properties possibly due to the most optimal ratio of these copper species.
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18

Qin, Zu Zeng, Zi Li Liu, Yan Bin Liu, and Rui Wen Liu. "Preparation and Characterization of Ni-Modified Fe-Mo and Catalytic Selective Oxidation of p-Xylene." Advanced Materials Research 557-559 (July 2012): 1501–4. http://dx.doi.org/10.4028/www.scientific.net/amr.557-559.1501.

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Анотація:
The preparation of the Fe-Mo-Ni catalyst using the sol-gel method was investigated. In addition, the catalytic selective oxidations of p-xylene (PX) to terephthalaldehyde (TPAL) on the Fe-Mo-Ni catalyst were also investigated. The catalysts were characterized using thermal analysis, H2-temperature programmed reduction (H2-TPR), Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectrum (XPS). The additional of Ni improves the catalytic activity of the Fe-Mo catalyst on selective oxidations of PX to TPAL. The optimal additive amount of Ni is 5%. XPS analysis shows that the introduction of Ni changes the internal structure of the Fe-Mo catalyst improves catalytic performance.
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19

Zhang, Hao, Shu Wang Duo, Xiao Yan Fei, Xiang Min Xu, Ting Zhi Liu, and Yu Bin Wang. "Effect of CrTiAlN Coatings on High-Temperature Oxidation Behavior of H13 Steel." Key Engineering Materials 544 (March 2013): 343–46. http://dx.doi.org/10.4028/www.scientific.net/kem.544.343.

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Анотація:
CrTiAlN hard coatings have been deposited on H13 steel for improving the oxidation resistance by Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The phase components, surface and section morphology of H13 steel before and after oxidation were analyzed by XRD and SEM. The results showed that the columnar crystal film possesses three major parts, i.e., the internal Cr bonding layer, the intermediate CrN transition layer, the external CrTiAlN gradient coating. The selective oxidation of Cr element was found on the surface of uncoated H13 steel while oxidation, but a continuous protective layer was not formed because of low Cr content, finally a lot of alpha Fe2O3 particles took place on the surface of H13 steel owing to the oxidation of the matrix element. O element can diffuse much more easily through the coating and oxide scales at 800 °C, and spallation and cracks were not found during the oxidation. These results indicated that the CrTiAlN coating have excellent high-temperature oxidation resistance at 800 °C.
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20

Chuaiphichai, Surawee, Grace Z. Yu, Cheryl M. J. Tan, Christopher Whiteman, Gillian Douglas, Yasmin Dickinson, Edward N. Drydale, et al. "Endothelial GTPCH (GTP Cyclohydrolase 1) and Tetrahydrobiopterin Regulate Gestational Blood Pressure, Uteroplacental Remodeling, and Fetal Growth." Hypertension 78, no. 6 (December 2021): 1871–84. http://dx.doi.org/10.1161/hypertensionaha.120.17646.

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Abnormal uteroplacental remodeling leads to placental hypoperfusion, causing fetal growth restriction and pregnancy-related hypertension, which are associated with endothelial dysfunction and markers of reduced vascular NO bioavailability and oxidative stress. Tetrahydrobiopterin (BH4) is a redox cofactor for eNOS (endothelial NO synthase) with a required role in NO generation. Using mice models and human samples, we investigated the physiological requirement for endothelial cell BH4 in uteroplacental vascular adaptation and blood pressure regulation to pregnancy. In pregnant mice, selective maternal endothelial BH4 deficiency resulting from targeted deletion of Gch1 caused progressive hypertension during pregnancy and fetal growth restriction. Maternal endothelial cell Gch1 deletion caused defective functional and structural remodeling in uterine arteries and in spiral arteries, leading to placental insufficiency. Using primary endothelial cells isolated from either normal or hypertensive pregnancies, we found that hypertensive pregnancies are associated with reduced endothelial cell BH4 levels, impaired eNOS activity, and reduced endothelial cell proliferation, mediated by reduced GTPCH (GTP cyclohydrolase 1) protein. In rescue experiments, high blood pressure and fetal growth restriction in pregnant endothelial cell Gch1 deficient mice was not rescued by oral BH4 supplementation, due to systemic oxidation of BH4 to dihydrobiopterin. However, the fully reduced folate, 5-methyltetrahydrofolate prevented BH4 oxidation, reduced blood pressure to normal levels, and normalized fetal growth. We identify a critical requirement for maternal endothelial cell BH4 biosynthesis in uteroplacental vascular remodeling in pregnancy. Restoration of endothelial cell BH4 with reduced folates identifies a novel therapeutic target for the prevention and treatment of pregnancy-related hypertension such as preeclampsia.
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21

Ran, Qingxuan, Qinghuan Liu, Yulai Xu, Wanjian Xu, Jun Li, Xueshan Xiao, Jincheng Hu, and Laizhu Jiang. "Nitrogen-induced selective high-temperature internal oxidation behavior in duplex stainless steels 19Cr–10Mn–0.3Ni– x N." Corrosion Science 98 (September 2015): 737–47. http://dx.doi.org/10.1016/j.corsci.2015.06.013.

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22

Wang, Zhi-Ming, Xue-Ling Sang, Chi-Ming Che, and Jian Chen. "Ruthenium(IV) porphyrin catalyzed highly selective oxidation of internal alkenes into ketones with Cl2pyNO as terminal oxidant." Tetrahedron Letters 55, no. 10 (March 2014): 1736–39. http://dx.doi.org/10.1016/j.tetlet.2014.01.098.

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23

Xiang, Jun Huai, Wei Wang, Hong Hua Zhang, and Yu Wei Liu. "Grain Size Effects on the Oxidation of Two-Phase Cu-Fe-Al Alloys." Advanced Materials Research 391-392 (December 2011): 611–14. http://dx.doi.org/10.4028/www.scientific.net/amr.391-392.611.

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Анотація:
The oxidation behavior of thin layers of Fe-15Cu-5Al-0.3Y alloy with grain size in nanometer range, prepared by magnetron sputtering deposition on cast alloy of the same composition, was studied at700oC in 0.1MPa O2. The scales grown on the coatings consist of two layers. The outer layer is composed of an external continuous Fe oxides scale free from copper and aluminum oxides. The inner layer is very complicated, with formation of dark oxides of Fe and Al, coupled with light un-oxidized Cu-rich stringers elongated perpendicularly to the alloy surface. Some degree of internal oxidation of Fe and Al is also present within the coating layer. A grain size reduction can effectively promote the selective external oxidation of Fe.
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24

Zhang, Zuo Tai, S. Balaji, Ii Ryoung Sohn, B. E. Ydstie, and S. Sridhar. "Influence of Fast Path Diffusion on the Oxidation of Mn Strengthened IF Steels." Defect and Diffusion Forum 283-286 (March 2009): 432–38. http://dx.doi.org/10.4028/www.scientific.net/ddf.283-286.432.

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Анотація:
During the in-line coating process of Mn-strengthened-Interstitial-Free-steels, selective oxidation under low dew-point atmospheres may result in surface oxides that are not wetted by the coating alloy. In the current study, we investigate the formation of external and internal oxides in the metal in order to characterize the influence of fast path diffusion. The short-time oxidation in the metal was carried out in a gold-image furnace and the resulting external and internal oxides were characterized through scanning-electron microscopy. An IF steel sample containing 1.5wt.% Mn was used and the effects of dew point (DP) ranging from –75 to –15oC on oxidation was investigated at 800oC by varying the PH2/PH2O ratio in the oxidizing gas. Simulations were carried out by considering the combined effect of diffusion and mass transfer represented by a system of partial differential equations. The model equations were solved using finite element method in a Multiphysics modeling software COMSOL. The experimental and simulated results were found to be in agreement, and showed that, for DP up to –30oC, gas phase mass transport of oxidant gas controls the oxidation which results in exclusively external oxide nodules distributed uniformly on the surface. At –15oC > DP > –30oC, the oxidation evolves as ridges along grain boundaries and the simulations indicate that this is due to solid state diffusion control and the controlling mechanism is fast path diffusion through the alloy. At this point, internal oxides also start to appear.
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25

Sharov, Victor S., Elena S. Dremina, Nadezhda A. Galeva, Todd D. Williams, and Christian Schöneich. "Quantitative mapping of oxidation-sensitive cysteine residues in SERCA in vivo and in vitro by HPLC–electrospray-tandem MS: selective protein oxidation during biological aging." Biochemical Journal 394, no. 3 (February 24, 2006): 605–15. http://dx.doi.org/10.1042/bj20051214.

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Анотація:
The selective reversible S-glutathiolation of specific SERCA (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase) cysteine residues represents a novel physiologic pathway of NO (nitric oxide)-dependent arterial smooth muscle relaxation [Adachi, Weisbrod, Pimentel, Ying, Sharov, Schöneich and Cohen (2004) Nat. Med. 10, 1200–1207]. This mechanism may be impaired through the irreversible oxidation of functionally important cysteine residues as a consequence of oxidative stress and aging. To establish whether in vivo aging and in vitro oxidation by peroxynitrite result in the loss of such functionally important cysteine residues of SERCA, we have developed and optimized a quantitative method to monitor the oxidation state of the individual SERCA cysteine residues using a maleimide-based fluorescence dye, TG1 (ThioGlo® 1), as a label for cysteine residues that have not been altered by oxidation and are not involved in disulphide bridges. A high efficiency for TG1 labelling of such residues and the chemical structure of cysteine–TG1 adducts were validated by MS analysis of model peptides, model proteins and rat skeletal muscle SERCA1. Tryptic peptides containing 18 out of a total of 24 cysteine residues were identified by HPLC–ESI (electrospray ionization)–MS/MS (tandem MS). Two cysteine residues, at positions 344 and 349, were detected in the form of an internal disulphide bridge, and another 16 were found to be labelled with TG1. Using HPLC–ESI–MS, we quantitatively mapped peroxynitrite oxidation of eight cysteine residues (positions 364, 417, 420, 498, 525, 674, 675 and 938), some of which are involved in the control of SERCA activity. Biological aging resulted in the partial modification of cysteine residues 377, 498, 525, 561, 614, 636, 674, 675, 774 and 938. Neither peroxynitrite exposure nor biological aging affected the apparent SERCA1 ATP affinity. Our data show an age-dependent loss of cysteine residues (approx. 2.8 mol of cysteine/mol of SERCA1), which may be partially responsible for the age-dependent decrease in the specific Ca2+-ATPase activity (by 40%).
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26

Zhang, Huihui, Lezheng Huang, Zhen Yang, Jie Chen, Yanjia Liu, Chaofei Zan, and Juntao Yuan. "Coupling effect of temperature and Cr content on the steam oxidation of Ni-Fe-Cr alloys." Materials Research Express 8, no. 11 (November 1, 2021): 116513. http://dx.doi.org/10.1088/2053-1591/ac386e.

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Анотація:
Abstract Excellent resistance to steam oxidation is a key required property for heat-resistant alloys used in next-generation fossil power plants. In order to clarify the degradation mechanism of Ni-Fe-Cr alloys in high temperature steam, four kinds of Ni-Fe-Cr model alloys with various Cr content were prepared and their long-term steam oxidation were investigated at 650 °C and 700 °C. The microstructure and composition of oxide scales were characterized by SEM equipped with EDS, and the oxide phases were identified by XRD. The results showed significant dependence of temperature and Cr content in alloys on the oxidation kinetics, cross-section morphology and elemental section-distribution. For Ni-Fe-Cr alloys with low Cr contents (12∼16 wt.%), the increase of temperature made the oxide scale change from breakaway scale morphology (nodule-crater microstructure with external exfoliation) to protective scale morphology (uniform layer and internal oxidation). For Ni-Fe-Cr alloy with 18wt.% Cr, the effect of temperature was greatly reduced. The oxidation mechanism was discussed from the perspectives of selective oxidation and the effect of alloying elements.
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27

Carmo-Gonçalves, Phelippe, Anderson S. Pinheiro, Luciana Romão, Juliana Cortines та Cristian Follmer. "UV-induced selective oxidation of Met5 to Met-sulfoxide leads to the formation of neurotoxic fibril-incompetent α-synuclein oligomers". Amyloid 21, № 3 (30 квітня 2014): 163–74. http://dx.doi.org/10.3109/13506129.2014.912208.

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28

Álvarez, Eleuterio, Margarita Gómez, Margarita Paneque, Cristina M. Posadas, Manuel L. Poveda, Nuria Rendón, Laura L. Santos, et al. "Coupling of Internal Alkynes in TpMe2Ir Derivatives: Selective Oxidation of a Noncoordinated Double Bond of the Resulting Iridacycloheptatrienes." Journal of the American Chemical Society 125, no. 6 (February 2003): 1478–79. http://dx.doi.org/10.1021/ja0290375.

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29

Richelle, M., M. E. Turini, R. Guidoux, I. Tavazzi, S. Métairon та L. B. Fay. "Gas Chromatograhy-Tandem Mass Spectrometry Determination of 8-Iso-PGF2α, a Biomarker of in vivo Lipid Peroxidation, in Human Plasma and Urine". European Journal of Mass Spectrometry 7, № 4-5 (серпень 2001): 427–32. http://dx.doi.org/10.1255/ejms.453.

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Анотація:
The measurement of isoprostanes is a promising assay that is specific and sensitive enough to detect in vivo lipid peroxidation. We present here a gas chromatography-tandem mass spectrometry (GC/MS/MS)method that enables determination of 8-iso-prostaglandin F2α (8-iso-PGF2α)in human plasma and urine. After the addition of [2H4]-PGF2α as the internal standard to acidified plasma or urine, the samples are purified on C18 and silica cartridges, derivatised as pentafluorobenzyl esters, extracted with diethyl ether, purified on silica gel TLC plates and finally silylated. Then, 8-iso-PGF2α and its internal standard are measured by GC/MS/MS in selective-reaction monitoring mode using the transition [M −181]− to [M −181 – (3 × 90)]−. The detection limit of this method is 5 pg mL−1. Its application is presented in two situations of oxidative stress: in vitro low-density lipoprotein oxidation and in smokers. Measurement of urinary 8-iso-PGF2α levels provides a non-invasive in vivo index of free radical generation that appears not to be confounded by changes in diet.
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30

Azzolina Jury, F., I. Polaert, L. B. Pierella, and L. Estel. "Study of Two Catalyst Configurations under Microwave Irradiation for the Selective Benzaldehyde Production over Co-ZSM-11 and Fe-ZSM-11." International Journal of Chemical Reactor Engineering 13, no. 2 (June 1, 2015): 169–75. http://dx.doi.org/10.1515/ijcre-2014-0111.

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Abstract Intensification process by the use of microwave heating was investigated by testing two catalyst configurations on the selective styrene oxidation for benzaldehyde production. The oxidation reaction was studied over Co-ZSM-11 and Fe-ZSM-11 catalysts. Their catalytic activity was evaluated by using these catalysts in two different forms: compacted pellets and fine particles. Thus, two reaction systems were studied under microwave: a batch system with fine particles in suspension (system 1) and a recirculating batch liquid through a fixed bed system comprising the compact catalyst pellets (system 2). Despite a better microwave interaction with the catalyst in the pellet form, the fixed bed configuration did not lead to a significant intensification of the process. At 60°C, the styrene molar conversions by using Co-ZSM-11 catalyst were found to be 33% and 3% for systems 1 and 2, respectively. With fine particles, the catalytic activity was higher since the styrene oxidation was able to occur without significant internal diffusional resistance of the reagents toward the active acid sites of the zeolite structure.
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31

Park, Eungyeul, Boris Hüning, Hans Jürgen Grabke, and Michael Spiegel. "Annealing of Fe-15at.%Cr Alloy in N2-H2 Gas Mixtures: Effect of Hydrogen." Defect and Diffusion Forum 237-240 (April 2005): 928–33. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.928.

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Анотація:
The effect of hydrogen during annealing of Fe-15.at%Cr alloy on the diffusion profile was investigated concerning the enrichment of chromium and the selective oxidation. Samples were exposed to an annealing gas mixture with different hydrogen contents in an infrared heating furnace and heated to 800oC, kept for 60 seconds and then cooled down to room temperature. After the experiments, field emission scanning electron microscopy (FE-SEM) equipped with electron back-scattering diffraction (EBSD) and x-ray photoelectron spectroscopy (XPS) were employed to characterize the morphology, elemental depth profiles and the chemical states of the elements. The annealing increased the Cr content at the surface in all atmospheres. The increase of hydrogen content in the atmosphere further increased the Cr to Fe ratio in near-surface, and the thickness of the layer affected by the heat treatment. The selective oxidation of chromium occurred as internal Cr2O3 formation, as a function of the Cr content, rather than the oxygen partial pressure. Hydrogen facilitated the diffusion of chromium probably by cleaning of fast diffusion paths.
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32

Wang, Zhi-Ming, Xue-Ling Sang, Chi-Ming Che, and Jian Chen. "ChemInform Abstract: Ruthenium(IV) Porphyrin Catalyzed Highly Selective Oxidation of Internal Alkenes into Ketones with Cl2pyNO as Terminal Oxidant." ChemInform 45, no. 33 (July 28, 2014): no. http://dx.doi.org/10.1002/chin.201433082.

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33

Litz, J., A. Rahmel, and M. Schorr. "Selective carbide oxidation and internal nitridation of the Ni-base superalloys IN 738 LC and IN 939 in air." Oxidation of Metals 30, no. 1-2 (August 1988): 95–105. http://dx.doi.org/10.1007/bf00656646.

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34

Banerjee, Subhadeep, Apeksha Phadte, Anjan Chattopadhyay, P. Bhavana, and Keisham Singh. "Synthesis of Push-Pull Phenazines Possessing pH-Responsive Absorption Spectra and their Application in Selective Detection of Fe3+ Ions and Aromatics." Synlett 29, no. 08 (February 27, 2018): 1014–19. http://dx.doi.org/10.1055/s-0036-1591766.

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Анотація:
Phenazines bearing electron-donor and electron-acceptor groups with high pH-sensing behavior were synthesized in moderate to good yields. Theoretical calculations on the frontier molecular orbitals and experimental oxidation potential measurements under variable pH values provide evidence for extensive internal charge transfer at high pH value. The well-known strong affinity of the catecholate moiety present in our phenazines is utilized for spectrophotometric detection of Fe3+ ion. Fluorescence-quenching behavior of the prepared phenazines is utilized for detection and distinction of electron-rich and electron-poor aromatics.
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35

Hahn, Junhee, Xiao Xiao, and Dong Bok Lee. "Oxidation of Ni-Cr-Co-Al-Mo-Ti-Re-Ta-W-Ru Single Crystals at 1000 oC in Air." Korean Journal of Metals and Materials 58, no. 4 (April 5, 2020): 234–46. http://dx.doi.org/10.3365/kjmm.2020.58.4.234.

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Анотація:
Three kinds of Ni-based single crystals with the compositions of 63.8Ni-7.5Cr-5.1Co-4.8Al-1.9Mo- 0.9Ti-3Re-11.8Ta-1.2W, 61.4Ni-7.4Cr-5Co-4.8Al-1.8Mo-0.9Ti-3.1Re-11.6Ta-4W, and 60.9Ni-7.5Cr-5Co-4.8Al- 2Mo-1Ti-2.9Re-10.9Ta-1.2W-3.8Ru, in wt%, were cast in a Bridgman furnace. In the cast alloys, Cr, Co, Re, Mo, W, and Ru became microsegregated in dendrites consisting of γ-Ni, while Ni, Ta, and Al microsegregated in interdendrites consisting of eutectic γ/γ . The cast alloys were oxidized at 1000 oC up to 275 h in air to study the effect of alloying elements on high-temperature oxidation. The oxide scales consisted primarily of CrTaO4, with some NiCr2O4, NiO, and α-Al2O3. The oxidation resistance was dependent on the formation and continuity of the α-Al2O3 scale. Ta and W were beneficial, while Ru was harmful in improving the oxidation resistance. The selective oxidation of Al in dendrites led to the formation of thin, uniform α-Al2O3 scales, i.e., uniform oxidation. The competitive oxidation of active elements such as Al, Ti, and Ta in interdendrites led to the formation of porous, crack-susceptible oxide nodules, i.e., nodular oxidation. Less active elements such as Ru, Re, Ni, Co, Mo, W, and Cr tended to enrich in the vicinity of the oxide nodules. The oxidation progressed through the outward diffusion of cations and the inward diffusion of oxygen. This inward diffusion formed internal alumina islands, beneath the oxide scale.
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36

SUZUKI, Yoshitsugu, and Kazuaki KYONO. "Effect of Internal Oxidation of the Hot-Rolled Sheet Steel, on the Suppression of the Si and Mn Selective Surface Oxidation in Recrystallization Annealing, after Cold Rolling." Journal of The Surface Finishing Society of Japan 55, no. 1 (2004): 48–55. http://dx.doi.org/10.4139/sfj.55.48.

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37

Pietzsch, J., F. J. Pietzsch, M. Laube, R. Bergmann, F. Wuest, J. Steinbach, and T. Kniess. "P279 INFLUENCE OF NOVEL SELECTIVE CYCLOOXYGENASE-2 (COX-2) INHIBITORS ON COPPER-MEDIATED OXIDATION OF HUMAN LDL." Atherosclerosis Supplements 11, no. 2 (June 2010): 76. http://dx.doi.org/10.1016/s1567-5688(10)70346-9.

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38

Prusty, Priyambada, Subramanian Jambu, and Masilamani Jeganmohan. "Rh(III)-Catalyzed Selective Olefination of N-Carboxamide Indoles with Unactivated Olefins at Room Temperature via an Internal Oxidation." Organic Letters 24, no. 5 (January 31, 2022): 1121–26. http://dx.doi.org/10.1021/acs.orglett.1c03905.

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39

He, Fengshuo, Xiumin Yu, Yaodong Du, Zhen Shang, Zezhou Guo, Guanting Li, and Decheng Li. "Inner Selective Non-Catalytic Reduction Strategy for Nitrogen Oxides Abatement: Investigation of Ammonia Aqueous Solution Direct Injection with an SI Engine Model." Energies 12, no. 14 (July 17, 2019): 2742. http://dx.doi.org/10.3390/en12142742.

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Анотація:
This study contributes to a method based on an aqueous solution of ammonia direct injection for NOx emissions control from internal combustion engines. Many previously published studies about deNOx technology are based on selective catalytic reduction (SCR), but only few deal with inner selective non-catalytic reduction (inner SNCR) technology, which is an intensive improvement of selective non-catalytic reduction (SNCR) applied in the in-cylinder purification procedure. Before numerical calculations were carried out, the computational fluid dynamic (CFD) simulation model was validated with steady-state experimental results. The main results revealed that with the increasing concentration of aqueous solution of ammonia, nitrogen oxides gradually decrease, and the largest decline of NOx is 65.1% with little loss of cylinder peak pressure. Unburned hydrocarbon (UHC) and carbon monoxide (CO) may increase using inner SNCR, and soot emissions show a decreased tendency. However, there is little change when ammonia content varies. Ulteriorly, refining the direct injection phase is of great help to inner SNCR technology to enhance the reduction of NOx and reduce NH3 oxidation and NH3 slipping.
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40

Weyer, C., P. A. Tataranni, S. Snitker, E. Danforth, and E. Ravussin. "Increase in insulin action and fat oxidation after treatment with CL 316,243, a highly selective beta3-adrenoceptor agonist in humans." Diabetes 47, no. 10 (October 1, 1998): 1555–61. http://dx.doi.org/10.2337/diabetes.47.10.1555.

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41

Petruzzelli, Domenico, Giovanni Tiravanti, Mario Santori, and Roberto Passino. "CHROMIUM REMOVAL AND RECOVERY FROM TANNERY WASTES: LABORATORY INVESTIGATION AND FIELD EXPERIENCE ON A 10 m3/d DEMONSTRATION PLANT." Water Science and Technology 30, no. 3 (August 1, 1994): 225–33. http://dx.doi.org/10.2166/wst.1994.0108.

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Анотація:
After extensive laboratory investigation of an ion exchange based process for selective removal, separation and recovery of Cr(III), AI(III) and Fe(III) from tannery wastes (spent chrome baths and leather washing waters), a 10 m3/d mobile pilot plant was assembled to demonstrate technical reliability and economic feasibility of the process. The IERECHROM (Ion Exchange REmoval of CHROMium) process is based on a weak electrolyte carboxyl resin, able to remove the metals from the liquid effluent followed by selective separation and recovery during a regeneration step. The resin is regenerated with alkaline hydrogen peroxide brines (0.15 M H2O2, 1M NaCl, O.1M NaOH, pH ≈ 11) through an internal oxidation of chromic species to chromate, whereas aluminium is co-eluted after hydrolysis as aluminate ion. Ferric species are not released by the resin in these conditions and are easily regenerated by subsequent acidic elution (1M H2SO4). Aluminate is thus separated from chromate ion in the alkaline spent regeneration eluate by pH adjustment to 8.5 and precipitation of aluminum hydroxide. In this paper the basic principles of the process are reported and the promising data obtained with a 10 m3/d mobile demonslration plant running at a tannery site in the Naples area.
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42

Supernak-Marczewska, M., A. Ossowska, P. Strąkowska, and A. Zieliński. "Nanotubular Oxide Layers and Hydroxyapatite Coatings on Porous Titanium Alloy Ti13Nb13Zr." Advances in Materials Science 18, no. 4 (December 1, 2018): 17–23. http://dx.doi.org/10.1515/adms-2017-0046.

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AbstractThe surface condition of an implant has a significant impact on response occurring at the implant-biosystem border. The knowledge of physical-chemical and biological processes allows for targeted modification of biomaterials to induce a specified response of a tissue. The present research was aimed at development of technology composing of obtaining the nanotube oxide layers on a porous titanium alloy Ti13Nb13Zr, followed by the deposition of phosphate coating. The porous substrate (porosity about 50%) was prepared by a selective laser melting of the Ti13Nb13Zr powder with the SLM Realizer 100 equipment. The nanotubular oxide layers were fabricated by electrochemical oxidation in H3PO4 + 0.3% HF mixture for 30 min. at a constant voltage of 20V. The calcium phosphate coatings were formed by the electrochemically assisted deposition (ECAD). The presence of nanotubular oxide layers with their internal diameters ranging from 30 to 100 nm was observed by SEM (JEOL JSM-7600F). The nanotubes have dimensions that facilitated the deposition of hydroxyapatite.
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43

Liang, Chongsheng, Siddabasave Gowda B. Gowda, Divyavani Gowda, Toshihiro Sakurai, Iku Sazaki, Hitoshi Chiba, and Shu-Ping Hui. "Simple and Sensitive Method for the Quantitative Determination of Lipid Hydroperoxides by Liquid Chromatography/Mass Spectrometry." Antioxidants 11, no. 2 (January 25, 2022): 229. http://dx.doi.org/10.3390/antiox11020229.

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Lipid hydroperoxides (LOOH) are the initial products of the peroxidation of unsaturated lipids and play a crucial role in lipid oxidation due to their ability to decompose into free radicals and cause adverse effects on human health. Thus, LOOHs are commonly considered biomarkers of oxidative stress-associated pathological conditions. Despite their importance, the sensitive and selective analytical method for determination is limited, due to their low abundance, poor stability, and low ionizing efficiency. To overcome these limitations, in this study, we chemically synthesized eight fatty acid hydroperoxides (FAOOH), including FA 18:1-OOH, FA 18:2-OOH, FA 18:3-OOH, FA 20:4-OOH, FA 20:5-OOH, FA 22:1-OOH, FA 22:6-OOH as analytes, and FA 19:1-OOH as internal standard. Then, they were chemically labeled with 2-methoxypropene (2-MxP) to obtain FAOOMxP by one-step derivatization (for 10 min). A selected reaction monitoring assisted targeted analytical method was developed using liquid chromatography/tandem mass spectrometry (LC-MS/MS). The MxP-labelling improved the stability and enhanced the ionization efficiency in positive mode. Application of reverse-phase chromatography allowed coelution of analytes and internal standards with a short analysis time of 6 min. The limit of detection and quantification for FAOOH ranged from 0.1–1 pmol/µL and 1–2.5 pmol/µL, respectively. The method was applied to profile total FAOOHs in chemically oxidized human serum samples (n = 5) and their fractions of low and high-density lipoproteins (n = 4). The linoleic acid hydroperoxide (FA 18:2-OOH) and oleic acid hydroperoxide (FA 18:1-OOH) were the most abundant FAOOHs in human serum and lipoproteins. Overall, our validated LC-MS/MS methodology features enhanced detection and rapid separation that enables facile quantitation of multiple FAOOHs, therefore providing a valuable tool for determining the level of lipid peroxidation with potential diagnostic applications.
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44

Shabanov, A. V., D. V. Kondratiev, V. K. Vanin, and A. Yu Dunin. "The issue of improving the efficiency of nitrogen oxide neutralization systems in diesel internal combustion engines." Izvestia MGTU MAMI 1, no. 2 (2021): 101–12. http://dx.doi.org/10.31992/2074-0530-2021-48-2-101-112.

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The most effective method of reducing nitrogen oxides in diesel exhaust gas is selective purifica-tion by the SCR-NH3 method. The method uses ammonia released during thermolysis and hydroly-sis of a urea solution when it is injected through a nozzle into a neutralizer. This method has a rela-tively low efficiency of cleaning the exhaust gas from nitrogen oxides. The main factor hindering the achievement of high efficiency of the NOx neutralization system is the insufficiently high tem-perature during the implementation of this process. The article analyzes various ways to increase the efficiency of the neutralization process and proposes a new method for neutralizing NOx by using urea injection into the cylinders of the inter-nal combustion engine at the expansion stroke in a diesel internal combustion engine. Efficiency can be achieved due to a higher exhaust gas temperature in the cylinder of the internal combustion engine and an increase in the time of the process of thermolysis and hydrolysis of urea. The kinetics of the decomposition of nitrogen oxides, the process of NH3 oxidation, and the cal-culation of temperature conditions in the cylinder of a diesel internal combustion engine at the ex-haust cycle are considered. The experience of neutralization of NOx contained in the flue gases of thermal power plants, where NOx purification takes place at high temperatures without the use of a catalyst, is analyzed. It is shown that the modernization of the SCR-NH3 process, due to the injection of urea at the exhaust stroke in a diesel internal combustion engine, will simplify the existing method of NOx neutralization and at the same time obtain additional advantages for a modern high-speed engine
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45

Maderthaner, Magdalena, Alexander Jarosik, Gerhard Angeli, and Roland Haubner. "3rd Generation Hot-Dip Galvanized Steel Sheet for Automobile Manufacturing - Interface Reactions between Zinc and Metal Oxide." Key Engineering Materials 742 (July 2017): 463–70. http://dx.doi.org/10.4028/www.scientific.net/kem.742.463.

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There is a growing demand for Advanced High Strength Steels (AHSS) in the automotive industry owing to their high specific strength and good formability. The mechanical properties satisfy the demands for improved passenger safety and decreased vehicle weight due to thinner cross sections. Hot-dip galvanizing is a common procedure to prevent corrosion of steel, galvanized steel forms the basis for further processing like organic coating. Industrially, the steel strip is annealed at 840 °C in 5 % H2 in N2 at a dew point (DP) of -30 °C. These conditions are reducing for Fe, but oxidizing for oxygen-affine alloying elements as Mn, Si and Cr. These ignoble elements form an external, covering oxide layer on the steel surface, which exhibits poor wettability for the Zn(Al, Fe)-bath. The liquid Zn(Al, Fe) has a temperature of 460 °C and contains 0,2 wt% Al to form a Fe2Al5-xZnx-layer to inhibit the growth of Fe-Zn-intermetallics. Along with the increased amount of alloying elements to improve strength and ductility of AHSS the evolving oxide layer after annealing at the steel surface deteriorates hot-dip galvanizing. The question arises what happens to the surface oxides during immersion in the Zn(Fe, Al)-bath. For this purpose annealed as well as annealed and galvanized 0.8Si-AHSS and 1.5Si-AHSS were compared by glow discharge optical emission spectroscopy (GD-OES) depth profiles. Galvanized specimens show fewer oxides at the steel-zinc-interface as annealed specimens. A possible explanation is an aluminothermic reduction of oxides by 0.2 wt% dissolved Al in the Zn(Al, Fe)-bath. Al is thermodynamically more affine to oxygen than Mn and Si and may reduce Mn- and Si-oxides. An alternative theory is the dissolution of Fe in Zn during reactive wetting, as a side effect the oxides are rinsed off too. Additionally, the influence of DP was investigated. According to Wagner’s theory of selective oxidation, a higher amount of oxygen in the annealing atmosphere leads to internal oxidation of the alloying elements. Experiments were carried out with 0.8Si-AHSS and 1.5Si-AHSS by altering the DP during annealing from -30 °C (380 ppm H2O) to 0 °C (6000 ppm H2O). Oxidation mode changed from external (DP -30 °C) to internal oxidation along grain boundaries (DP 0 °C), as predicted by Wagner. These oxide-free surface provides good reactivity to enhance reactive wetting with the Zn(Fe, Al)-bath and form a dense Fe2Al5-xZnx-layer.
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46

Avagyan, Rozanna, Maya Spasova, and Johan Lindholm. "Determination of Nicotine-Related Impurities in Nicotine Pouches and Tobacco-Containing Products by Liquid Chromatography–Tandem Mass Spectrometry." Separations 8, no. 6 (June 3, 2021): 77. http://dx.doi.org/10.3390/separations8060077.

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Анотація:
Smokeless tobacco products and nicotine-containing tobacco-free oral pouches have increased in popularity in recent years. They are associated with far fewer health hazards compared to cigarettes. Nicotine pouches are filled with non-tobacco filler and nicotine. The nicotine used in nicotine pouches usually comes from the extraction of tobacco; thus, related alkaloids may be found as impurities at low levels. Moreover, nicotine degradation products are formed because of microbial action, flavor oxidation, exposure to high temperatures etc. Currently, there are no published or recommended methods for the analysis of nicotine degradants in nicotine pouches. Here, we present a sensitive and selective liquid chromatography–tandem mass spectrometry method for the simultaneous determination of seven nicotine-related impurities. All seven analytes and corresponding deuterated internal standards were separated within 3.5 min, including 1 min equilibration. The method was fully validated, showing good linearity with correlation coefficients >0.996 for all analytes, good extraction yields ranging from 78% to 110%, limits of detection between 0.08 and 0.56 µg/g and limits of quantification between 0.27 and 2.04 µg/g. Although the method was mainly developed to determine the degradants of nicotine in nicotine pouches, it was validated and performed well on a broader range of tobacco-containing products.
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47

Young, David J. "Diffusion in Internal Oxidation Reactions." Defect and Diffusion Forum 323-325 (April 2012): 283–88. http://dx.doi.org/10.4028/www.scientific.net/ddf.323-325.283.

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Анотація:
When an alloy component is selectively oxidised but cannot reach the surface quickly enough to form a scale, then internal oxidation results. In this process, a gas phase oxidant dissolves in an alloy and diffuses inwards, reacting with a dilute solute metal to precipitate metal oxide or carbide, etc. Penetration kinetics are parabolic, the rate being controlled by oxidant diffusion and the concentration of reacting metal. Rates are predicted from classical oxidation theory on the basis that the reaction product is exceedingly stable, no solute metal remains in the reacted alloy, and oxidant diffusion is via a solvent metal matrix. This paper is concerned with situations where these approximations fail: the development of low stability precipitates and the growth of elongated precipitates which allow interfacial diffusion of the oxidant. Effects on the rates of internal oxidation are discussed.
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48

Modi, J. G., and J. K. Patel. "STABILITY-INDICATING RP-HPLC METHOD FOR THE SIMULTANEOUS DETERMINATION OF AMLODIPINE BESYLATE AND AZILSARTAN MEDOXOMIL IN TABLET DOSAGE FORM." INDIAN DRUGS 53, no. 06 (June 28, 2016): 51–61. http://dx.doi.org/10.53879/id.53.06.10500.

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Анотація:
A novel, simple, rapid, and highly selective stability indicating RP-HPLC method was developed and validated for simultaneous estimation of azilsartan medoxomil (AZL) and amlodipine besylate HCl (AMLO) in tablet dosage form having strength of 20 mg and 2.5 mg, respectively. The effective chromatographic separation was achieved on a Phenomenex luna ODS C18 (15 cm X 4.6 mm internal diameter, 3.5 μm Particle size) with a mobile phase composed of phosphate buffer (pH-2.5) adjusted with ortho phosphoric acid : acetonitrile in the ratio of 60:40 v/v. The mobile phase was pumped using an isocratic HPLC system at a flow rate of 0.7 mL/min with injection volume 20μl and quantification of the analytes was done at detection wavelength 254 nm. The retention times were found to be 5.918 min and 14.901 min for AMLO and AZL, respectively. The proposed HPLC method was validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, LOD, and LOQ as per ICH Q2 (R1) guideline. Calibration plots were linear over the concentration range of 75-125 µg/mL and 600-1000 µg/mL with correlation coefficients 0.9966 and 0.9948 for AMLO and AZL, respectively. Forced degradation studies were performed using hydrolysis, oxidation, photolytic, and thermal degradation conditions with good resolution between the degradants and analytes. Degradation products resulting from the stress studies did not interfere with the detection of AMLO and AZL, thus the proposed method is sensitive and stability-indicating. The validated HPLC method was successfully applied to the analysis of AMLO and AZL in tablet dosage form.
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49

Brobst, Susan W., and Craig A. Townsend. "The potential role of fatty acid initiation in the biosynthesis of the fungal aromatic polyketide aflatoxin B1." Canadian Journal of Chemistry 72, no. 1 (January 1, 1994): 200–207. http://dx.doi.org/10.1139/v94-031.

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Анотація:
Earlier work in this laboratory has shown the intact incorporation of [1-13C]hexanoate into averufin (1), a key intermediate in aflatoxin B1 biosynthesis. Parallel experiments with equimolar amounts of [1-13C]butyrate, [1-13C]-3-oxo-octanoate, and [1-13C]-5-oxo-hexanoate gave no detectable specific incorporation of heavy isotope but low and equivalent background incorporation comparable to [1-13C]acetate. Three of these potential intermediates in polyketide formation were reexamined as their corresponding N-acetylcysteamine (NAC) thioesters. The NAC thioester of [1-13C]hexanoic acid gave a remarkably high 22% intact incorporation while the NAC thioester of [1-13C]-3-oxo-octanoic acid afforded nearly 5% when an equimolar amount was administered to the producing organism Aspergillus parasiticus (ATCC 24551). In contrast, the NAC thioester of [1-13C]butyric acid showed no selective enrichment of averufin. This negative result was tested further in a more sensitive experiment with the NAC thioester of [2,3-13C2]butyric acid. No 1JCC coupling was detectable, indicating an incorporation efficiency of <0.1%. [1-13C,18O2]Hexanoate was prepared and gave a 53% retention of 18O relative to the I3C internal standard in keeping with previous experiments with [1-13C,18O2]acetate. It is concluded from these data that the initial C6 segment of polyketide biosynthesis is unlikely to arise by β-oxidation of a higher fatty acid but more probably is generated by a specialized fatty acid synthase (FAS) that provides this unit either separately to the polyketide synthase (PKS) or as part of a larger FAS/PKS fusion. While these two physical arrangements cannot be distinguished by these experiments, both must accommodate comparatively efficient exchange of the NAC thioesters of both hexanoic and 3-oxo-octanoic acid, but not the NAC thioester of butyric acid.
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50

Meesa, Siddi Ramulu, Praveen Kumar Naikawadi, Kishan Gugulothu, and K. Shiva Kumar. "Catalyst and solvent switched divergent C–H functionalization: oxidative annulation of N-aryl substituted quinazolin-4-amine with alkynes." Organic & Biomolecular Chemistry 18, no. 16 (2020): 3032–37. http://dx.doi.org/10.1039/d0ob00318b.

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