Radial Distribution Of Oxygen Research Articles

TRANOX: Model for non-isothermal steam oxidation of zircaloy cladding

• Developed a mechanistic oxygen distribution model in steam-oxidized Zircaloy-4. • Experimental validation conducted for ECR, oxygen distribution, and phase thickness. • Providing accurate oxidation prediction in non-isothermal conditions. • Validate the accuracy of CP correlation and provide an advanced mechanistic model. • Explaining effect of hydrogen on oxygen content in zr for highburnup cladding. TRANOX-1.0 (TRANsient OXidation), a mechanistic model that calculates oxygen distribution for isothermal and non-isothermal transients (1000–1250 °C) has been developed. TRANOX solves radial transient diffusion equation using Finite Difference Method (FDM) with spatial phase changes for each time step. Diffusion coefficients of each resulting phase were obtained by searching a combination that best guarantees Equivalent Cladding Reacted (ECR) and α-Zr(O) thickness simultaneously. The model has been extensively validated by overarching experimental campaigns including isothermal and non-isothermal high temperature steam oxidation, and post-metallurgical characterization. Accounting for α+β equilibrium phase, TRANOX gives accurate predictions for ECR, spatially averaged radial oxygen distribution, and thicknesses of each phase. Mechanistically solving the diffusion equation, TRANOX exhibits unbiased predictability for isothermal and non-isothermal transients. TRANOX was used to understand the oxygen distribution of pre-hydrided high burnup fuel cladding. The diffusion resistance behavior of α-Zr(O) and α+β with respect to hydrogen content counteract, neutralizing the overall hydrogen effect on oxygen distribution. The limited hydrogen effect on diffusion resistance during the early stage of steam oxidation further reduces the hydrogen-sensitivity of oxygen profiles. This finding provides a cogent explanation for the effect of hydrogen on oxygen distribution and oxidation kinetics observed by a number of past studies.

Effect of crucible rotation and crystal rotation on the oxygen distribution at the solid-liquid interface during the growth of Czochralski monocrystalline silicon under superconducting horizontal magnetic field

Abstract This paper presents incorporating superconducting horizontal magnetic field, a very effective way with low power consumption and high field strength. To improve crystal quality of large diameter Czochralski monocrystalline silicon (CZ-Si) when it grows and to accurately describe the influential process parameters of oxygen distribution on the solid-liquid interface, 3D simulation is running on together with 2D/3D hybrid model established for obtaining boundary conditions. Compared with conventional horizontal magnetic field, the superconducting horizontal magnetic field shows that the increasing magnetic induction intensity helps to adjust the shape of solid-liquid interface, to reduce the oxygen content at the interface and to improve the uniformity of radial oxygen distribution. Further, when crucible is large and melt is deep, the low crucible rotation speed or the low crystal rotation speed is favorable for reducing the oxygen content at the interface. Suitable magnetic induction, low crucible and low crystal rotation speed processes are more conducive to improving the uniformity of the radial oxygen distribution at the interface during the growth. Finally, simulation and experiment results show the effectiveness for the proposed method.

Numerical simulation of heat and mass transfer during Czochralski silicon crystal growth under the application of crystal-crucible counter- and iso-rotations

In this study, the effects of different rotational combinations between the crystal and the crucible on the flow, heat and mass transfer in the melt are discussed based on numerical simulations. Both crystal-crucible counter- and iso-rotations are investigated. The simulation results for the growth of crystal 200 mm in length show that the oxygen concentration along the crystal-melt interface is determined by competition between the mechanisms of convection and diffusion. When the differences in rotation between the crystal and crucible are low during iso-rotation, the melt velocity is significantly weakened and the effect of the diffusion process on oxygen transport in the melt becomes stronger than the effect of convection. The melt flow is more sensitive to changes in the crystal rotation rate. The distribution of oxygen atoms and the temperature of the melt are more significantly affected by the flow pattern in cases of counter-rotation than iso-rotation. Moreover, it is found that a flow transition occurs in the silicon melt when the crystal and crucible have the same iso-rotation rate (ReS/ReC = 0.5842). A lower concentration and more uniform radial distribution of oxygen can be obtained by using the iso-rotation conditions. Rotating the crystal and crucible in the same direction also produces a flatter defect transition with lowering and flattening of the growth parameters Vcr/Gc along the crystal-melt interface.

Galactic Planetary Nebulae as Probes of Radial Metallicity Gradients and Other Abundance Patterns

Abstract We use planetary nebulae (PNe) as probes to determine the Galactic radial oxygen gradients and other abundance patterns. We select data homogeneously from recent data sets, including PNe at large Galactocentric distances. The radial oxygen gradient calculated for the general PN population, which probes the region from the Galactic center out to ∼28 kpc, is shallow, with slope ∼−0.02 dex kpc−1, in agreement with previous findings. We looked for time evolution of the metallicity gradient using PNe with different age progenitors as metallicity probes. We identify PNe whose progenitor stars are younger than 1 Gyr (YPPNe) and those whose progenitor stars are older than 7.5 Gyr (OPPNe) based on the comparison between evolutionary yields and elemental abundances of the PNe. By studying OPPNe and YPPNe separately, we found that (i) the OPPNe oxygen gradient is shallower (∼−0.015 dex kpc−1) than that derived from YPPNe (∼−0.027 dex kpc−1); (ii) the OPPNe inner radial distribution of oxygen is compatible with no gradient to the radial extent of the thick disk population (∼10 kpc), similarly to what has been observed in thick disk stars; and (iii) PNe (especially OPPNe) indicate that significant gradient slope is limited to Galactocentric distances between ∼10 and ∼13.5 kpc, as observed for open clusters and field stars. Outside this range, the distribution is almost flat. We found that the radial oxygen gradient is steeper for a PN population closer to the Galactic disk, similar to what is observed in the general stellar population by the SEGUE survey. We use our novel population dating to compare our results with current chemical evolutionary models and gradients from other Galactic populations for insight on galaxy chemical evolution.

On the radial oxygen distribution in the Galactic disc – II. Effects of local streams

On the radial oxygen distribution in the Galactic disc – II. Effects of local streams

On the radial oxygen distribution in the Galactic disc

On the radial oxygen distribution in the Galactic disc

Numerical investigation of dual-stage high velocity oxy-fuel (HVOF) thermal spray process: A study on nozzle geometrical parameters

The present study takes the advantage of computational fluid dynamics (CFD) methods to model steady-state, two-dimensional, axisymmetric, turbulent, compressible and combusting flow in a dual-stage high velocity oxy-fuel (HVOF) thermal spray system. The Eulerian method is used to solve the continuum gas phase and the Lagrangian method is utilized for tracking the particles. The effects of particle loads on the continuous gas phase are included in the simulation. Thus, compared to the previous studies, we investigate the influence of coupling between the particle and gas phases in modeling of the dual-stage HVOF process. It is found that decouple modeling of the particle and the continuous phase causes a significant error in velocity of particle at the impact moment, even for low powder particle loading. We further investigate the effects of four geometrical parameters on the behavior of gas phase and consequently the particle phase. Results also show that the turbulent intensity of flow at different sections of the warm spray process is the most important factor determining the radial distribution of nitrogen and temperature in the barrel. It also determines the radial distribution of oxygen in the free jet outside of the barrel. It is further found that reduction of the first nozzle diameter and increasing the length of the divergent section (for a fixed divergent angle) of the convergent-divergent nozzle reduce the particle temperature while these changes do not affect the particle velocity. In other words, changing these geometrical parameters has a desirable effect on the particle temperature without causing an undesirable change on the particle velocity.

Delving into the gas-phase of the CALIFA galaxies to trace O and N gradients

AbstractWe study the radial distribution of oxygen and nitrogen abundances in H ii regions in 350 galaxies observed in the CALIFA survey using the semi-empirical N-sensitive code Hii-Chi-mistry. A separate analysis of N/O when using [N ii] is justified as the dispersion in the O/H-N/O diagram is very large. In fact different O/H and N/O slope distributions and flattening in the outskirts are obtained.On the other hand there is a tight correlation between O/H and N/O when the values of the fittings at the effective radius are considered as representative of each galaxy.

Precipitation Behaviors of Rapid Thermal Annealing Treated Silicon Wafers under Various Thermal Cycles

For decades, oxygen precipitates in Cz silicon wafers have been a subject of defect engineering to optimize device yields and performance at both current high volume manufacturing and future generation nodes. With the ability of precipitates capturing metallic impurities, a well controlled built-in intrinsic gettering (IG) provides a self-insurance protecting fabs from suffering unexpected yield loss caused by metal contamination outside the control limit [1]. Such IG sinks traditionally are created, either by RTP or conventional furnace heat treatments, quite deep in the bulk, resulting in a wide denuded zone (DZ). This scheme has worked perfect for most devices with monolithic integration as fast diffusing metals travel the distance equal to the DZ depth quite easy. However, the industry is increasingly adopting 3-D integration, stacking multiple chips vertically using through Si via (TSV) techniques. Multichip stacking requires each die to be thinned substantially by back grinding down to 50um or even <30um, depending on the number of stacked dies. This results in either complete or major loss of IG sinks along with the bulk removal of the wafer. In this respect, IG with a shallower DZ is desired so that a sufficient amount of IG sinks are retained even after extensive thinning. On the other hand, the effect of oxygen precipitation on the yield strength is increasingly receiving attention as photolithography overlay is becoming more sensitive to local deformation [2]. A precisely controlled high density of precipitates would be desirable in this regard.In this report, we demonstrate that a 2-step Rapid Thermal Annealing (RTA) treatment in NH3 and Ar gas is capable of producing a high density of precipitates in an extremely uniform profile in the 300mm silicon wafers under CMOS-like thermal cycles. The RTA treatment is a special variant of MDZ® that has been widely adopted in the industry for >10 years [1, 3]. Figure 1 shows typical depth profiles of precipitates in the high oxygen material after through a CMOS thermal simulation and after a subsequent extra growth cycle. Adding the extra growth cycle was necessary for the sake of ensuring all the existing precipitates to be detectable as the metrology tool (laser scattering tomography) would otherwise miss those sub-threshold size in the count, especially in the case of the lower oxygen concentration material. Quite a uniform density of precipitates is formed at the depth of around 7 microns and extended to the entire thickness of the wafers with the maximum density around 8x109/cm3 and 7x109/cm3 in the cases of higher and lower oxygen concentration materials, respectively. It can also be seen that in the case of higher oxygen material the full cycle of the D simulation has effectively grown the precipitates so about 70% of the precipitate distribution was detectable without going through a growth cycle (the D2 curve). These results are pretty consistent with the previous work reported by co-authors, where the uniform density of precipitates is explained as a result of the nitride layer blocking vacancy sinking to the wafer surface [4]. The precipitation sites are created by vacancy aggregation in the course of fast post-RTA cooling. The radial distribution of oxygen precipitates is remarkably uniform, as shown in Fig. 2 (a) and (c). In comparison, the as-grown wafers (b and d) resulted in a large variation, especially in the high oxygen material, which is due to the inhomogeneous distribution of point defects formed during crystal growth. The result clearly demonstrates that the 2-step RTA eliminated the crystal originated variability, very effectively.In summary, adding a 2-step RTA treatment produces a high density precipitates near surface, uniformly both vertically and laterally, guaranteeing a <20um thick layer of IG sinks to be retained even after through wafer thinning to 30um.

A new method of corotation radius evaluation in our Galaxy

Abstract We propose a new method for the determination of the rotation velocity of the Galactic spiral density waves, respectively the corotation radius, rC, in our Galaxy by means of a statistical analysis of the radial distribution of oxygen in the Galactic disc, derived over Cepheids. The corotation resonance happens to be located at rC∼ 7.0–7.6 kpc, depending on the rate of gas infall on to the Galactic disc, the statistical error being ∼0.3–0.4 kpc. Simultaneously, the constant for the rate of oxygen synthesis in the Galactic disc is determined. We also argue in favour of very short time-scale formation of the Galactic disc, namely tf∼ 2 Gyr. This scenario enables us to solve the problem of the lack of intergalactic gas infall.

Corotation resonance and the radial distribution of oxygen in a spiral galaxy

A theory is proposed for the formation of the bimodal radial distribution of oxygen in the Galaxy, which displays a steep abundance gradient in the inner region and becomes flat in the middle and outer regions. The formation of this structure is associated with the following effects. First, type II supernovae, which are sources of oxygen, are concentrated in the spiral arms. Second, the enrichment rate is proportional to the rate at which a chemical element enters the spiral arm, which has the form of a density wave. This implies that the rate of oxygen production is substantially suppressed in most of the corotation circle due to the low relative velocity of the Galactic material with respect to the spiral arms and the low rate at which the arms are crossed by the Galactic material. Third, the corotation radius is near the Sun. The net result of these effects combined with turbulent diffusion is the development of the structure discussed in the paper.

Oxygen concentration in Czochralski silicon crystals depending on silicon monoxide evaporation from boron doped silicon melts

In order to investigate heterogeneity in silicon single crystals depending on silicon monoxide evaporation from the free melt surface, several Czochralski crystals having various diameters were grown from silicon melts heavily doped with boron and its oxygen and boron concentration were examined. In cases of crystal growth from heavily boron doped silicon melts, it was found that the difference in oxygen concentration between the center part and the periphery of the crystals increases with increasing crystal diameter. On the contrary, in a case of non-doping, the radial oxygen distribution was relatively uniform in comparison to the results of crystal growth from heavily boron doped silicon melts, while boron were distributed uniformly in the silicon crystals. It could be concluded that the radial oxygen distribution in the silicon crystals is much influenced by the silicon monoxide evaporation which is activated by means of boron doping into the silicon melts.

Oxygen transport analysis in Czochralski silicon melt by considering the oxygen evaporation from the melt surface

Oxygen transport analysis of silicon melt in a silica crucible by considering the oxygen evaporation from the free surface was performed. The oxygen concentration stays in the region of 10 15–10 16 atoms/cm 3 along the free surface and it strongly depends on the vertical flow under the free surface. It has been found that the oxygen distribution along the free surface affects the oxygen concentration in wafers obtained from grown crystals. The suction and the sweeping out flows at the peripheral region of the crystal are formed beneath the periphery of the crystal, and these oscillatory flows determine the oxygen concentration at the periphery of the crystal. Present results yielded good agreement with the experimental results of the radial oxygen distribution in grown crystals. Thus we established the method for prediction of the oxygen concentration in silicon crystal using the oxygen concentration conditions based on the experimental results for the free surface.

Microelectrode and Modelling Study of Oxygen Distribution in Roots

The use of polarographic microelectrodes to explore the radial distribution of oxygen in maize roots aerated chiefly via the shoot is described. Also given is a brief description of a mathematical model of root aeration which introduces two simultaneous oxygen sources (the shoot and the rooting medium), and mimicks more realistically than hitherto the diffusive characteristics of the non-porous epidermal/hypodermal shell.In keeping with modelling predictions, steep radial diffusion gradients were a characteristic of the non-porous epidermal/hypodermal shell and stele, while shallow profiles generally characterised the cortex. Stelar anoxia, previously forecast by earlier mathematical modelling, was inducible by manipulating the oxygen concentrations around the shoot.The stelar diffusion gradients always indicated an inward diffusion from the cortex. However, two-way gradients were sometimes evident in the epidermal/hypodermal annulus, and were also found in the sheathing extensions of the root cap. These indicated diffusion into these annuli simultaneously from both the cortex and the rooting medium. Elsewhere the gradients in the epidermis/hypodermal cylinder were either solely positive or negative depending upon the oxygen concentrations within the root cortex and surrounding agar. Examples of two-way and one-way diffusion in the epidermal/hypodermal cylinder were created satisfactorily by the model.Finally, the results indicate that with roots in stagnant anaerobic media, the bulk of the root cap proper is likely to be anoxic, and that some anoxia may be the norm within the basipetal extensions of the cap which ensheath the root apex.

The radial distribution of oxygen in disk galaxies

view Abstract Citations (52) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Radial Distribution of Oxygen in Disk Galaxies Zaritsky, Dennis Abstract The shape of the oxygen abundance profile is examined for seven nearby spiral galaxies in which at least 15 H II regions have been observed. The radial abundance profile for three of these galaxies has a distinct change in slope. The others show no deviation from a single scale-length exponential. This behavior is explained within the framework of the star- forming viscous disk model of galaxy evolution. A prediction is made that radial abundance profiles of noninteracting unbarred spiral galaxies change slope at the radius where the rotation curve changes from linearly rising to flat. For barred and interacting galaxies the situation is complicated by additional mixing mechanisms of the interstellar medium. Publication: The Astrophysical Journal Pub Date: May 1992 DOI: 10.1086/186375 Bibcode: 1992ApJ...390L..73Z Keywords: Abundance; Disk Galaxies; Galactic Evolution; H Ii Regions; Oxygen; Radial Distribution; Spiral Galaxies; Star Formation; Viscosity; Astrophysics; ISM: H II REGIONS; GALAXIES: ABUNDANCES; GALAXIES: EVOLUTION full text sources ADS | data products SIMBAD (7) NED (7)

Oxygen transport under an axial magnetic field in Czochralski silicon growth

Oxygen transport in the Si melt is simulated. The magnetic field not only damps the convection in the melt, but also acts to make the flow in the melt axially two-dimensional. There are two flow regimes depending on the convection in the melt: thermal convection dominant regime and forced convection dominant regime. When the thermal convection due to temperature inhomogeneity is dominant in the melt, the oxygen concentration incorporated into the crystal decreases with the increase of the magnetic field. When the forced convection due to counter-rotation between the crystal and the crucible is dominant, the oxygen concentration increases. The forced convection due to a single rotation of the crystal decreases the oxygen concentration. The radial oxygen distribution is also examined.

Impurities in commercial-scale magnetic czochralski silicon: Axial versus transverse magnetic fields

Magnetic Czochralski (MCZ) silicon crystals, 4 inch diameter, were grown in a HAMCO CG-2000 puller, modified to accommodate either a 5000 G superconducting axial field magnet or a 1500 G transverse field electromagnet. The effect of field strength, crystal and crucible rotation rates on the oxygen concentration and distribution are reported for both field configurations. Results for the axial case demonstrate that the oxygen concentration increases in field strength and crystal rotation rate, while crucible rotation rate has only a small effect. In the case of transverse field, it is shown that the oxygen concentration decreases with increase in field strength and decrease in crucible rotation rate. Crystal rotation rate has negligible effect. The macroscopic radial distribution of oxygen using the transverse field is very uniform under most conditions, compared to the axial field and is comparable to the zero field case. While the application of axial field causes a dramatic increase in the effective segregation coefficient of gallium, no such effects were observed (at least for the low fields used) in the segregation behavior of phosphorous in the transverse field. Probable causes for the various observed differences between the two field configurations are discussed.

Interface shape and radial distribution of impurities in 〈111〉 silicon crystals

The solid-liquid interface shape at the shoulder of ingot growth is affected by the taper angle. The interface changes from concave to convex with an increase of taper angle. The interface shape at the main body of ingot growth depends on the crystal length. The interface becomes more concave with increase in the length of a crystal. The radial dopant distribution has been correlated with the interface shape and its radius of curvature. No correlation is found between the interface shape and radial distribution of oxygen or carbon.

Theoretical predictions for the radial distribution of oxygen in spiral galaxies

To the aim of reproducing the oxygen abundances and gradients observed in the disk of our Galaxy and four nearby spirals (M31, M33, M83, and M101), we have computed numerical models of galactic evolution assuming only two free parameters: the infall of gas from outside the disk and the law of star formation (e.g. proportional to some power of the gas density, decreasing with time, constant, etc.).

Plutonium redistribution in fast reactor mixed oxide fuel pins

Some redistribution effects of uranium and plutonium, caused by thermal diffusion and evaporation-condensation processes in mixed oxide fuels, are discussed by means of autoradiographs of sections of fuel pins irradiated in the fast flux of the RAPSODIE reactor. The change in the stoichiometric state as a function of burnup and the radial distribution of oxygen are described and their influence on the redistribution processes is discussed. A model and suitable data are given to calculate redistribution effects on the basis of thermal diffusion in fast reactor fuels. In fuel pins with power ratings of 500 W/cm and 600 W/cm the enrichment of plutonium around the central cavity produces an increase in the central temperature of about 100°C and 250° C, respectively.