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排序方式: 共有87条查询结果,搜索用时 15 毫秒
1.
Kreins M. Wilkes J. Wesselmecking S. Krupp U. 《Metallurgical and Materials Transactions A》2022,53(11):3906-3917
Metallurgical and Materials Transactions A - The Bauschinger effect in austenitic–ferritic duplex stainless steel 1.4462 was investigated using tension–compression tests combined with... 相似文献
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3.
Rodriguez Martín-Doimeadios RC Krupp E Amouroux D Donard OF 《Analytical chemistry》2002,74(11):2505-2512
An isotope dilution (ID) procedure for the determination of methylmercury (MMHg) in biological samples using an inductively coupled plasma mass spectrometer as detector after the capillary gas chromatographic separation (CGC/ICPMS) has been developed. For the first time, open-focused-microwave pretreatment has been used in conjunction with ID. Optimum conditions for the measurement of isotope ratios on the fast transient chromatographic peaks have been established. Mass bias was found to be about 1.5%/mass unit and was corrected by using the simultaneously measured thallium signals at 203Tl and 205Tl. After mass-bias correction, deviation of the theoretical mercury ratio values was found to be as low as 0.2%. Isotope ratio precisions based on the peak areas measurements were 0.3% RSD for 20 pg injected (as Hg absolute). The absolute detection limits were in the range of 20-30 fg for 202Hg and 201Hg. Methylmercury enriched in 201Hg has been synthesized by direct reaction with methylcobalamine. The concentration of the MMHg spike has been measured by reverse isotope dilution with a natural MMHg standard. The capabilities of CGC/ICPMS to measure isotope ratios were used to optimize sample derivatization by aqueous ethylation with NaBEt4 with respect to MMHg degradation pathways and quantitative recovery. The accuracy of the method developed has been validated with biological certified reference materials (CRM-463, DORM-1). 相似文献
4.
Rodríguez Martín-Doimeadios RC Monperrus M Krupp E Amouroux D Donard OF 《Analytical chemistry》2003,75(13):3202-3211
Speciated isotope-dilution mass spectrometry (SID-MS) is claimed to be an absolute method; however, it has been found to be affected by artifact monomethylmercury (MMHg) formation in sediments. The determination of MMHg in sediments was carried out by SID-MS after open-focused microwave extraction. The extracted mercury species were then ethylated and separated by capillary gas chromatography (CGC). Isotope ratios (peak area ratios at different masses) were measured by on-line ICP-MS detection of the CGC-separated compounds. Reproducibility of 202Hg/201Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for Et2Hg; for 202Hg/199Hg, 0.43 and 0.46%, respectively, were determined. The absolute detection limits for CGC-ICPMS measurements were better than 26 fg for 202Hg, 20 fg for 201Hg, and 24 fg for 199Hg. For the direct determination of MMHg in sediment reference materials (CRM 580, IAEA 356, and IAEA 405), higher values than the certified were always found. Systematic experiments were carried out to localize the sources of the unintentional abiotic methylmercury formation during analysis. Different spiking and derivatization procedures (either ethylation, propylation, or derivatization by Grignard reagents) were tested. In addition, isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be known and carefully controlled. A simple solvent extraction technique involving no critical cleanup steps was applied in order to reduce high Hg2+ amounts. The method was applied to the determination of MMHg in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulfur contents. The results obtained confirmed that available sediment reference materials are adequate to achieve traceable mercury speciation analysis and to detect potential sources of MMHg artifact formation. 相似文献
5.
G Krupp 《Canadian Metallurgical Quarterly》1995,22(2-3):177-180
TransferRNA recognition was used as leit-motiv in the illustration of possible links between a hypothetical primordial RNA world and the contemporary DNA world. In an RNA world, 'proto-tRNA' could have functioned as replication origin and as primitive telomere. Possibly, this primitive structure is preserved in a 'universal substrate' for modern tRNA-specific enzymes. The combination of acceptor stem and T arm (plus a linker) was finally revealed as sufficient for the recognition by prokaryotic and eukaryotic RNase P, as well as other tRNA enzymes. In modern life forms, a tRNA-like element in viral RNAs still serves as replication origin, and furthermore, the recognition of similar structures as cryptic promoters is universally conserved for template-dependent RNA polymerases. Another common property of modern polymerases is their high, but clearly limited and condition-dependent substrate specificity. Very likely, also substrate recognition by primitive polymerases was not more stringent, and this lead to the occurrence of mixed nucleic acids as intermediates in the transition of genomic RNA to contemporary genomic DNA. 相似文献
6.
Volatilization of organotin species from municipal waste deposits: novel species identification and modeling of atmospheric stability 总被引:1,自引:0,他引:1
Krupp EM Merle JK Haas K Foote G Maubec N Feldmann J 《Environmental science & technology》2011,45(3):943-950
Organotin compounds are used as pesticides and fungicides as well as additives in plastics. This study identifies the de novo generation of novel volatile organotins in municipal waste deposits and their release via landfill gas. Besides tetramethyltin (Me(4)Sn), a strong neurotoxin, and 5 previously reported organotins, 13 novel ethylated, propylated, and butylated tetraalkyltin compounds were identified. A concentration of 2-4 μg of Sn m(-3) landfill gas was estimated for two landfill sites in Scotland. The atmospheric stability of Me(4)Sn and methylated tin hydrides was determined empirically in a static atmosphere in the dark and under UV light to simulate night- and daytime conditions. Theoretical calculations were carried out to help predict the experimentally obtained stabilities and to estimate the relative stabilities of other alkylated species. Assuming first-order kinetics, the atmospheric half-life for Me(3)SnH was found to be 33 ± 16 and 1311 ± 111 h during day- and nighttime conditions, respectively. Polyalkylation and larger alkyl substitutes tend to reduce the atmospheric stability. These results show that substantial concentrations of neurotoxic organotin compounds can be released from landfill sites and are sufficiently stable in the atmosphere to travel over large distances in night- and daytime conditions to populated areas. 相似文献
7.
Whereas in Part I of this study the process ofinternal nitridation was described for binary andternary alloys within the Ni-Cr-Al-Ti system, this partfocuses on quaternary Ni-Cr-Al-Ti alloys, which are similar to commercial Ni-base alloys used inhigh-temperature applications regarding their chemicalcompositions. These alloys can simultaneously form twodifferent nitride-precipitation zones consisting of TiN and AlN. In order to quantify thenitridation process, thermogravimetric measurements inan oxygen-free nitrogen atmosphere in the temperaturerange 800-1100°C were carried out and supplemented by extensive microstructural studies. Whilesingle-nitride internal nitridation can easily bedescribed by Wagner's theory of internal oxidation,modeling of the more complex internal-precipitationreactions that involves more than one nitride requires anumerical treatment of both the diffusion and thethermochemical processes in the alloy. For this purpose,a computer simulation was developed in which the commercial thermodynamic software ChemApp iscombined with a finite-difference diffusion calculation.It was shown that this calculation technique can beapplied successfully to quantitatively describe the internal-nitridation process of theNi-Cr-Al-Ti model alloys used in this study. 相似文献
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9.
K. A. Al-Hatab F. S. Alariqi M. A. Al-Bukhaiti U. Krupp M. Kantehm 《Oxidation of Metals》2011,76(5-6):385-398
The oxidation behavior of the IN600 Ni?CCr?CFe superalloy was investigated in air at temperatures ranging from 750 to 950 °C, for up to 12 cycles. Oxidation kinetics and oxide scale morphologies were examined using weight gain measurements, SEM-EDS, and X-ray diffraction. The cyclic oxidation kinetic results suggested that the oxidation behavior of the IN600 alloy approximately followed a sub-parabolic rate and the scaling process was controlled by the formation of a chromia scale. At 850 °C, SEM-EDS observations indicated that the formed oxide scale was primarily composed of Cr2O3, and the internal oxidation of Cr and Ti occurred. At 950 °C, a fast initial stage with high weight gain was observed, followed by a steady-state stage with gradual weight gain. Additionally, a considerable change in the oxidation kinetic occurred. SEM-EDS observations and XRD results indicated that the external scale was relatively thick with a localized porous, preferential adherent, and a complex oxide scale was developed. This complex oxide scale consisted of an outermost thin layer composed of MnCr2O4?CCr2O3 mixed together with a small amount of isolated TiO2, an intermediate relatively thick layer, composed of Cr2O3, and an innermost discrete layer formed at the scale/alloy interface, which enriched by Ni/NiO mixed with Ti-, Al-, and Fe-oxides. Finally, only the Al alloying element was internally oxidized to form Al2O3 fingers, which create a discrete and narrow internal oxidation zone. Al oxide was observed as a dark area and primarily grows along the alloy grain boundaries in the vicinity of the inward chromia pegs. 相似文献
10.
Vicente Braz Trindade Ulrich Krupp Hans-Jürgen Christ 《Journal of Materials Engineering and Performance》2008,17(6):915-919
The oxidation behavior of steels containing low-Cr concentrations (0.5-2.25 wt.%) has been studied in laboratory air in the
temperature range of 400-550 °C. The oxidation rate of the steels was lower than that of pure iron, but higher than that of
pure iron when a small amount of rare earth element cerium (0.03 wt.%) is added to the 2.25Cr1Mo steel. The mass change follows
a nearly parabolic law for the case of pure iron and the steel without Ce addition, while linear behavior describes the oxygen
uptake for the case of the 2.25Cr1Mo+0.03Ce steel. SEM cross-section observations and thermodynamic calculations confirm that
there is no wustite (FeO) formation during oxidation of pure iron and low-Cr steels at 550 °C, whereas FeO might be formed
in the oxide scale of 2.25Cr1Mo+0.03Ce at the same oxidation conditions (temperature, atmosphere, and exposure time). By investigating
the temperature for FeO stability, this study reveals that the temperature for FeO formation on pure iron is 568 °C, for the
2.25Cr1Mo steel 589 °C, and 471 °C for the 2.25Cr1Mo+0.03Ce. This low value for the FeO stability temperature found for the
steel 2.25Cr1Mo+0.03Ce steel explains why this steel oxidizes very fast at 550 °C. 相似文献