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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 345-346 (Aug. 2007), p. 1345-1348 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A primary water stress corrosion cracking (SCC) and an outside diameter SCC haveoccurred in the steam generator (SG) tubes of nuclear power plants around the world. It is importantto establish the repair criteria for the degraded tubes to assure a reactor integrity, and yet maintainthe plugging ratio within the limits needed for an efficient operation. For assessment andmanagement of the degradation, it became crucial to understand initial leak behaviors under a smallpressure and leak rate evolution under a constant pressure of SCC flaws. Stress corrosion crackedtube specimens were prepared by using a room temperature cracking technique, and leak behaviorsof these tubes were measured at room temperature. Water pressure inside the tube was increasedslowly in a step like manner with a designated holding time. Water leak rates just after a ligamentrupture were measured by collecting the leaked water in a plastic container for a designated time. Aleak rate was calculated by dividing the amount of water by the time. Under 3.45 MPa, a smallwater droplet was formed, but it did not grow after a 10 minute holding period at a constantpressure of 3.45 MPa. A throughwall crack seemed to open at around 8.28 MPa (1200 psi). Sometubes with 100 % through wall cracks did not show a leakage at 10.8 MPa, which is a typicalpressure difference of pressurized water reactors (PWRs) during a normal operation. The higher thepressure was applied, the larger the rates of increase with the time were. Axial cracks showed alower leak pressure than that of the circumferential cracks, which might be from a higher hoopstress than the axial stress. A large open and long axial crack showed an increasing leak rate withthe time at a constant pressure
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 119 (Jan. 2007), p. 87-90 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: Alloy 600 tubing can be repaired by using a Ni electroplating to have an excellent SCCresistance. In order to carry out a successful Ni electrodeposition inside a steam generator tubing,the effects of various parameters on the material properties of the electrodeposit should beelucidated. Hence this work deals with the effects of the applied current density and the dutycycle(Ton / (Ton + Toff)) of the pulse current on the material properties of the Ni electrodepositobtained from a Ni sulphamate bath by analyzing the current efficiency, the potentiodynamic curve,the hardness and the stress-strain curve. Hardness, YS(yield strength) and TS(tensile strength)decreased whereas the elongation increased as the applied current density increased. This was dueto a concentration depletion of the nickel ion at the interface of the electrodeposit/solution, and afractional decrease of the hydrogen reduction reaction. As the duty cycle increased, the hardness,YS and TS decreased while the elongation increased. During an off time at a high duty cycle, theconcentration depletion of the nickel ion could not be sufficiently recovered and the fraction of thehydrogen evolution reaction which is kinetically faster than the nickel ion reduction decreased,which contributed to a coarse grain sized electrodeposit. The experimental results of the hardnessand the stress-strain curves were supplemented by the results of the potentiodynamic curve
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 119 (Jan. 2007), p. 111-114 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: The precipitates in the base metal and the fusion zone of an Alloy 600/182 weld werecharacterized through a transmission electron microscopy. Precipitates in the Alloy 600 base metalwere identified as Cr7C3. On the other hand, (Nb,Ti)C, Al-rich and Ti-rich oxides were found on thedendritic interfaces, and tiny Cr-rich M23C6 were distributed on the grain boundaries in the Alloy182 fusion zone
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 26-28 (Oct. 2007), p. 1213-1216 
    ISSN: 1662-8985
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Steam generators(SG) of the Korean nuclear power plants were replaced with a new oneafter a 20 year operation. A metallographic examination of the defected tubes is needed for settingup a guide line for a safe operation of the other SG. A destructive analysis of 50 tubes wasaddressed, and a relationship between the SCC defect location and defect depth wasobtained. Tubes extracted from the retired SG were transferred to a hot laboratory. Detailednondestructive analysis examinations were taken, then the tubes were destructively examined.Types and sizes of the defects were characterized. A location and depth of the SCC were evaluatedin terms of the location and height of the sludge. Most axial cracks were in the sludge pile, whereasthe circumferential ones were around the top of the tube sheet(TTS) or below the TTS. Cracks werefound with various lengths in a specific zone. Average defect depth of the axial cracks was deeperthan that of the circumferential ones
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 47-50 (June 2008), p. 1466-1469 
    ISSN: 1662-8985
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Corrosion-resistant nickel-based Alloy 600 is susceptible to a lead-induced stresscorrosion cracking (PbSCC) in aqueous solutions. The lead species incorporated into the oxide atthe alloy surface degraded the passivity, and caused the PbSCC. Effects of lead on the properties ofthe surface passive films were investigated. The cross sections of the surface films were examinedby the transmission electron microscopy and the species present in the films were analyzed with theenergy dispersive x-ray spectroscopy and the x-ray photoelectron spectroscopy. In-depthconcentration profiles of the species were analyzed by using an ion sputtering technique. Theelectrochemical impedance spectroscopy technique was used to characterize the electrochemicalbehaviors. Effectiveness of a nickel boride inhibitor was evaluated. The boride inhibitor altered theproperties of the passive film, and significantly reduced the susceptibility to the PbSCC
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 135 (Feb. 2008), p. 103-106 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: Alloy 600(74wt% Ni, 15wt% Cr, 9wt% Fe) is used as a material for steam generatortubing in pressurized water reactors(PWR) due to its high corrosion resistance under a PWRenvironment whose primary side and secondary side are operated under 340oC, 150bar and 290oC,50bar, respectively. However, in spite of its outstanding corrosion resistance, a stress corrosioncracking(SCC) which has been one of the most important degradation issues, has occurredoccasionally owing to the severe high temperature and pressure condition of a PWR. It is expectedthat a SCC is deeply related to an electrochemical property of a passive film formed under a hightemperature and pressure condition. Therefore an understanding of the basic electrochemicalbehaviors regarding an anodic dissolution and a passivation of the bare surface of metals and alloysprovides important information about a SCC mechanism and control. In the present work, thepassive oxide films on Alloy 600 were investigated as a function of the dissolved oxygen contentand the pH by using a potentiodynamic polarization, electrochemical impedance spectroscopy(EIS)and a depth profiling by Auger electron spectroscopy(AES). For this purpose, 0.5M H3BO3, 0.5MNa2SO4 and 0.1M NaOH aqueous solutions with/without dissolved oxygen at 300oC were used asthe test solutions. The resistance of an oxide formed in an aerated solution was smaller than that in adeaerated solution while the oxide film in the aerated solution was thicker than the oxide film in thedeaerated solution
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Microstructural dependence of stress-corrosion cracking behaviour in commercial Al-Zn-Mg-Cu alloy (AA 7075)The stress corrosion cracking (SCC) behaviour of commercial Al-Zn-Mg-Cu alloy (AA 7075) has been investigated by measuring the relative fracture energy under constant strain rate as a function of microstructural parameters such as precipitate free zone (pfz) width, precipitate (ppt) size in the grain boundaries (gbs) and coherency of ppts in the grain. The SCC specimens were so aged that a given variation in one feature could be produced nearly without a concomitant change in the other variables. The respectively obtained change in microstructural variables was identified by transmission electron microscopy (TEM). SCC tests were conducted in an aqueous 3.5 wt.% NaCl solution of pH = 1 at the temperature of 30°C with an applied corrosion potential of the specimen. It is suggested from the present experimental results that the effect of coherency of ppts in the grain on the resistance to SCC is stronger than the influence of ppt size in the gbs, while pfz width scarcely influences any resistance to SCC. The effects of ageing stages on the SCC behaviour have been discussed in terms of change in slip mechanism due to the interaction between the dislocations and the ppts in the grain.
    Notes: Das Spannungsrißkorrosions(SpRK)-Verhalten der handelsüblichen Al-Zn-Mg-Cu-Legierung (AA 7075) wurde durch die Messung der relativen Bruchenergie in Abhängigkeit von den Gefügekenngrößen, wie der Breite der ausscheidungsfreien Säume, der Größe der Korngrenzen (KG)-Ausscheidungen sowie der Ausscheidungen in der Matrix untersucht. Die Versuchsproben wurden so ausgelagert, daß eine der Gefügekenngrößen fast ohne eine Änderung der übrigen Kenngrößen variiert werden konnte. Die jeweilig erzielten Änderungen der Gefügemerkmale wurden durchstrahlungselektronenmikroskopisch (TEM) nachgewiesen. Die Durchführung der SpRK-Versuche erfolgte in einer 3,5%igen Kochsalzlösung von pH = 1, bei einer Temperatur von 30°C und einem potentiostatisch vorgegebenen, festen Korrosionspotential unter langsamer konstanter Dehngeschwindigkeit. Die vorliegenden Versuchsergebnisse deuten darauf hin, daß die Größe der Matrix-Ausscheidung die SpRK-Beständigkeit mehr als die Größe der KG-Ausscheidung beeinflußt, während die Breite der ausscheidungsfreien Säume keinerlei Einfluß auf die SpRK-Beständigkeit ausübt. Der Einfluß der Auslagerungszustände auf das SpRK-Verhalten wurde unter Berücksichtigung der Änderung des Gleitmechanismus durch Wechselwirkung zwischen den Versetzungen und den Ausscheidungen in der Matrix erörtert.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 124-126 (June 2007), p. 1529-1532 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: Growth model of a circumferential outer diameter stress corrosion crack (ODSCC) in a retiredsteam generator tube of the Kori 1 nuclear power plant was proposed based on extensive destructiveexaminations of the pulled tubes of Alloy 600 from the Kori 1 plant. A small ODSCC grows in alateral direction as well as a forward direction until it meets a neighboring ODSCC which alsogrows in a lateral direction as well as a forward direction. And then, the two ODSCCs which meeton the same circumferential plane are consolidated into a single ODSCC. By repeating such aconsolidation process with time, it seems that the apparent growth rate of an ODSCC in the lateraldirection is much faster than that in the forward direction. Growth model of a circumferentialODSCC from a retired steam generator tube of the Kori 1 plant reveals that many ODSCCs areinitiated and grow in both directions independently until they meet and finally they are consolidated
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 124-126 (June 2007), p. 1545-1548 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: Since the PbSCC(Lead stress corrosion cracking) of alloy 600 tubing materials wasreported by Copson and Dean in 1965, the effect of lead on a corrosion film and crackingmorphology have been continually debated. An electrochemical interaction of lead with thealloying elements of SG tubings was studied and the corrosion products were analyzed. It wasfound that lead enhanced the anodic dissolution of alloy 600 and alloy 690 in the electrochemicaltest. The lead preferentially dissolved the Cr from the corrosion film of alloy 600 and alloy 690 inalkaline water. The lead ion seemed to penetrate into the TG crack tip and react with the corrosionfilm. A selective Cr depletion was observed to weaken the stability of the passive film on the alloys.Whereas passivity of Ni became stable in lead containing solution, Cr and Fe passivity becameunstable
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  • 10
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Pharmacology 46 (2006), S. 411-449 
    ISSN: 0362-1642
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Chemistry and Pharmacology
    Notes: Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.
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