| 1. |
- Anghel, Clara, et al.
(author)
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Gas phase analysis of CO interactions with solid surfaces at high temperatures
- 2004
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 233:1-4, s. 392-401
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Journal article (peer-reviewed)abstract
- An in situ method including mass spectrometry and labeled gases is presented and used to gain information on adsorption of molecules at high temperatures (>300 degreesC). Isotopic exchange rate in H-2 upon exposure to an oxidized zicaloy-2 sample and exchange rate in CO upon exposure to various materials have been measured. From these measurements, molecular dissociation rates in respective system have been calculated. The influence of CO and N-2 on the uptake rate of H-2 in zirconium and oxidized zicaloy-2 is discussed in terms of tendency for adsorption at high temperatures. In the case of oxidized Cr exposed to CO gas With C-12, C-13, O-16 and O-18, the influence of H2O is investigated with respect to dissociation of CO molecules. The presented data supports a view of different tendencies for molecular adsorption of H2O, CO, N-2, and H-2 molecules on surfaces at high temperatures.
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| 2. |
- Belonoshko, Anatoly B., et al.
(author)
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First-principles study of hydrogen diffusion in α-Al 2O3 and liquid alumina
- 2004
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 69:2, s. 243021-243026
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Journal article (peer-reviewed)abstract
- We have studied the energetics and mobility of neutral hydrogen in alumina Al2O3 using ab initio density-functional calculations. The mobility of hydrogen was studied in corundum (α-Al2O 3) as well as in liquid alumina. Using both static as well as molecular-dynamics calculations, and applying classical transition state theory, we derive the temperature-dependent diffusivity of hydrogen in α-Al 2O3 as D(T)=(21.7 × 10-8 m 2/s)exp(-1.24 eV/kT). The corresponding diffusivity of hydrogen in liquid/amorphous alumina, derived directly from ab initio molecular dynamics calculations, is D(T)=(8.71 × 10-7 m2/s)exp(-0.91 eV/kT). The computed diffusivity compares very well to experimental data. We conclude that diffusion of neutral hydrogen through the bulk of alumina is a good approximation of the mechanism for hydrogen mobility in corrosion scales. The representation of grain-boundary structures by amorphous alumina is, probably, realistic at higher temperatures.
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| 3. |
- Guzhova, Irina, et al.
(author)
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Interferon-gamma cooperates with retinoic acid and phorbol ester to induce differentiation and growth inhibition of human neuroblastoma cells
- 2001
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In: International Journal of Cancer. - : Wiley. - 0020-7136 .- 1097-0215. ; 94:1, s. 97-108
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Journal article (peer-reviewed)abstract
- The prognosis of patients with advanced stages of neuroblastoma with N-myc amplification remains poor despite escalated therapy, a situation that has called for alternative therapeutic approaches. Neuroblastoma cells, which represent immature peripheral neuronal cells, treated with certain physiologic and nonphysiologic agents such as retinoic acid (RA), phorbol esters and interferons (IFN) in vitro undergo cellular differentiation and stop to divide, a process that mimics normal neuronal development. Such "differentiation therapy" using RA after autologous bone marrow transplantation has recently given encouraging results in neuroblastoma patients with advanced disease. Considering approaches for improved differentiation therapy, we investigated possible synergistic effects of combining agents known to influence neuroblastoma growth and differentiation in vitro. Our results show that combined treatment with IFN-gamma and RA or the phorbol ester 12-O-tetradecanoyl-phorbol acetate (TPA) had synergistic or enhancing effects on morphologic differentiation and neurite outgrowth in 5 of 5 neuroblastoma cell lines, 3 of which expressed very high levels of N-myc mRNA due to N-myc amplification. The combinations RA+IFN-gamma or TPA+IFN-gamma also enhanced induced growth inhibition in all 5 cell lines, in several cases resulting in complete growth arrest under conditions where cells stimulated with either agent alone continued to grow. The phenotypic effects of the combined RA+IFN-gamma or TPA+IFN-gamma treatments were in most, but not all, investigated cases accompanied by moderate reductions in N-myc expression, suggesting that the cooperative signals may counteract N-Myc activity at several levels. The cooperativity between IFN-gamma and other differentiation signals may be relevant for approaches to improve the therapy for high-risk neuroblastoma with N-myc-amplification.
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| 4. |
- Hornlund, E., et al.
(author)
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Experimental findings in support of atomic transport of hydrogen in silica
- 2003
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:8, s. 4819-4823
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Journal article (peer-reviewed)abstract
- Data supporting a view of both molecular and atomic transport of hydrogen in quartz is presented. By studying isotopic equilibration, it is shown that virtually all of the molecules diffusing through a 1.5 mm thick quartz membrane at 900 degreesC have undergone dissociation. The catalytic properties of platinum for the dissociation of H-2 are used to increase the surface concentration of atomic hydrogen on a quartz membrane. It is found that the high surface concentration increases the total flux of hydrogen through the membrane. It is also found by comparison with literature data that diatomic molecules probably diffuse in two modes in quartz. We suggest that these two modes are one atomic and one molecular.
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| 5. |
- Hultquist, Gunnar, et al.
(author)
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Hydrogen in chromium : Influence on the high-temperature oxidation kinetics in H2O, oxide-growth mechanisms, and scale adherence
- 2000
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In: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 54:02-jan, s. 1-10
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Journal article (peer-reviewed)abstract
- Oxidation of 1-mm thick chromium samples with 7 to < I wt, ppm hydrogen has been studied at 900 degrees C in a closed reaction chamber. The gases used were O-2, H2O, and gas mixtures of Oz; H2O at a total pressure of about 20 mbar. By means of oxygen labeling in two-stage oxidations, H2O followed by (H2O)-O-18, the position of oxide growth within the oxide scale was determined with secondary-ion mass spectrometry (SIMS). The results are consistent with visual observations and scanning electron microscopy (SEM), which shows flat oxides with good adherence when formed in H2O. When replacing O-2 out H2O in the atmosphere, the oxidation rate increases by a factor of two with an increase of oxide growth at both the inner and outer part of the oxide. An increased metal (cation) transport is observed when 5 wt. ppm hydrogen is present in the chromium metal prior to oxidation in both Oz and H2O. This is detrimental for the adherence of the oxide scale. The uptake of hydrogen in H2O exposure for 1600 min was measured to 1.5 wt. ppm. In exposures to O-2 + H2O mixtures, no H-2 is formed and no net water is consumed as long as O-2 is present. A plausible reaction scheme based on an experiment with (H2O)-O-18 is presented to explain this observation.
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| 6. |
- Hultquist, Gunnar, et al.
(author)
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Influence of deuterium and platinum on the thermal oxidation of GaAs
- 2003
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In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 150:10, s. G617-G623
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Journal article (peer-reviewed)abstract
- The thermal oxidation of GaAs at 500 degreesC in O-18 labeled O-2 has been studied with gas phase analysis, Auger electron spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy. The influence of a few hundred atomic parts per million of deuterium in the GaAs substrate and of surface platinum have been evaluated with respect to oxide growth mechanisms and the degree of As buildup. Deuterium increased the transport from the substrate interface of both Ga and As toward the gas interface thereby lowering the degree of preferential Ga oxidation and As buildup at the substrate interface. Platinum, on the other hand, catalyzed the dissociation of the oxygen molecule at the gas interface and thereby facilitated an increased transport of oxygen toward the substrate interface. That results in an increased overall oxidation rate with a high degree of preferential Ga oxidation and concomitant As buildup. When the oxygen pressure was increased from 20 to 720 mbar, a lowered degree of As buildup was observed due to the lower degree of preferential Ga oxidation.
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| 7. |
- Hultquist, Gunnar, et al.
(author)
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Platinum-induced oxidation of chromium in O-2 at 800 °C
- 2003
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In: Corrosion Science. - 0010-938X .- 1879-0496. ; 45:12, s. 2697-2703
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Journal article (peer-reviewed)abstract
- The effects of porous Pt on the oxidation of Cr at 800degreesC have been studied with the (OSIMS)-O-18 technique, gas phase analysis and XPS. In oxide areas with Pt a pronounced inward oxygen transport takes place and a substantial oxide growth near the Cr substrate is observed. In oxide grown on areas without Pt the counts of CrO ions in SIMS and the binding energy of O (1s) in XPS depend on the distance from the area with Pt. The experimental observations are believed to be a consequence of a high dissociation efficiency of O-2 on areas with Pt in combination with a high diffusivity of O in external and internal oxide surfaces on areas both with and without Pt.
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| 8. |
- Hultquist, Gunnar, et al.
(author)
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Self-repairing metal oxides
- 2001
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In: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 56:04-mar, s. 313-346
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Journal article (peer-reviewed)abstract
- The oxidation of Cu, Zr, and alloys forming chromia, alumina, and zirconia was studied in a closed reaction chamber in O-2 gas near 20 mbar. Information on the position of oxide growth has been gained from the O-18/SIMS technique. Rates Of O-2 dissociation on metal oxides, Au, and Pt have been evaluated from measurements in labeled O-2. The experimental results indicate that hydrogen in the metal substrates induces increased metal-ion transport in internal oxide surfaces during oxidation, which leads to increased oxide growth at the oxide-gas interface. Experiments also show that oxides of rare-earth metals (REM) and Pt catalyze the dissociation Of O-2. An increased rate of O-2 dissociation can lead to increased transport of oxygen ions in the oxides and increased oxide growth at the substrate-oxide interface. A balanced transport of metal and oxygen ions in metal oxides that leads to oxide growth at both the metal-oxide and at the oxide-gas interface is found to be favorable for the formation of protective oxides with good adherence to the metal substrate. Depending on the original proporation of metal-to-oxygen ion transport in the oxide, an addition of hydrogen will increase or decrease the oxidation kinetics. In analogy, an addition of REM will increase or decrease the oxidation kinetics, depending on the original proportion of metal-to-oxygen ion transport.
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| 9. |
- Siddle, A., et al.
(author)
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Investigation of the initial reaction of the alloy Co86Cr14 and its constituent metals with oxygen using secondary ion mass spectrometry
- 2002
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In: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 33:11-okt, s. 807-814
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Journal article (peer-reviewed)abstract
- The initial oxidation of Co86Cr14 and its constituent metals is investigated using an in situ dynamic secondary ion mass spectrometry (SIMS) technique. Simultaneous analysis and controlled formation of oxidation products, rather than just analysis, allows the oxidation to be studied at the very early stages of the process, i.e. when the oxidation product is of submonolayer extent. The technique, initiated by Hultquist(5-7) for the study of pure metals in various in situ environments, involves exposing a sputter-cleaned sample to various partial pressures of oxygen in the SIMS chamber and achieving an equilibrium between the formation and removal of the reaction products under the normal dynamic SIMS conditions. Here, the study is extended to give some insight into the interpretation of the SIMS data obtained by this method, and to determine a model for the oxidation of materials. An empirical model is derived for the oxidation of cobalt. A theoretical model is also derived based on the Langmuir model, but allowing for the more energetic nature of ion bombardment and oxide removal. The theoretical and empirical models are indistinguishable at low oxygen pressures. The cobalt component in the alloy Co86Cr14 behaves in a similar way to that of the pure metal, which suggests that the cobalt oxidizes independently of the chromium in the alloy.
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| 10. |
- Tveten, B., et al.
(author)
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Hydrogen and yttria in chromium : Influence on the high-temperature oxidation kinetics in O-2, oxide-growth mechanisms and scale adherence
- 2001
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In: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 55:04-mar, s. 279-289
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Journal article (peer-reviewed)abstract
- The effects of hydrogen and Y2O3 on high-temperature oxidation of Cr in 20 mbar O-2 have been studied at 900 degreesC. Oxidation- and O-2-dissociation rates were determined from gas-phase measurements. Hydrogen in Cr leads to breakdown of the oxide scale. The oxide scale on Cr-1%Y2O3 charged with hydrogen for 4 hr (resulting in Cr-1%Y2O3 with approximately 10 ppm hydrogen) is adherent to the metal substrate. The oxidation rate is similar for Cr with less than or equal to1 ppm hydrogen and Cr-1%Y2O3 with less than or equal to1 ppm hydrogen, but significantly lower for 4-hr H-charged Cr-1%Y2O3.. The oxidation rate of Cr-5%Fe-1%Y2O3-25 ppm H is also lower than the oxidation rate of Cr-5%Fe-1%Y2O3-less than or equal to1 ppm? H. This indicates that unless hydrogen is present, there are virtually no effects of the addition of 1% Y2O3 to Cr. Using labeled oxygen, O-16,16(2) and O-18,18(2), was found that at 900 degreesC the dissociation rate of O-2 is higher on Y2O3 than on Cr2O3 It is suggested that the well-known improvement of the oxidation resistance of Cr as an effect of additions of Y or Y2O3 is related to an increase in the dissociation rate of O-2 and that there is a synergetic effect in combining Y2O3 and hydrogen.
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