Design of a Subscale, Inert Gas Test for Plume-Surface Interactions in a Reduced Pressure Environment

Uranyl(V) species are normally unstable in solutions but are here shown to be stable in high-temperature chloride melts. Reactions leading to the formation of UO2Cl43– ions were studied, including thermal decomposition and chemical reduction of uranyl(VI) chloro-species in various alkali chloride melts (LiCl, 3LiCl–2KCl, NaCl–KCl, and NaCl–2CsCl) at 550–850 °C. Decomposition of UO2Cl42– species under reduced pressure, with inert gas bubbling through the melt or using zirconium getter in the atmosphere results in the formation of UO2Cl43– and UO2. Elemental tellurium, palladium, silver, molybdenum, niobium, zirconium, and hydrogen, as well as niobium and zirconium ions were tested as the reducing agents. The outcome of the reaction depends on the reductant used and its electrochemical properties: uranyl(VI) species can be reduced to uranyl(V) and uranium(IV) ions, and to uranium dioxide.

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The Influence of Natural Convection on Heating Characteristics of Space Furnaces

MRS Proceedings ◽

10.1557/proc-87-313 ◽

1986 ◽

Vol 87 ◽

Cited By ~ 1

Author(s):

H. Lenski ◽

J. Piller

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Power Consumption ◽

Heat Transfer Characteristic ◽

Thermal Inertia ◽

Transfer Characteristic ◽

Inert Gas ◽

Reduced Pressure ◽

Gas Atmosphere ◽

Gradient Furnace

AbstractDuring the Dl-Spacelab mission, several samples of semiconductor and aluminium alloy have been processed in a single ellipsoid mirror furnace (ELLI) and a gradient furnace (GFQ), respectively. Both furnaces operate under inert gas atmosphere at reduced pressure (100 to 200 mbar). In weightlessness, the heat transfer characteristic changed due to absence of convection. For the ELLI, power consumption in space decreased by 15 to 21 %, while the thermal inertia of the system increased by a factor of 2. In contrast to that, the gradient furnace required higher heater temperatures in space, while the influence on the sample thermal profile was rather low.

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Persistent Photoconductivity in ZnO Nanowires in Different Atmospheres

Advances in Condensed Matter Physics ◽

10.1155/2014/184120 ◽

2014 ◽

Vol 2014 ◽

pp. 1-5 ◽

Cited By ~ 20

Author(s):

Davide Cammi ◽

Carsten Ronning

Keyword(s):

Conduction Band ◽

Inert Gas ◽

Persistent Photoconductivity ◽

Zno Nanowire ◽

Reduced Pressure ◽

Band Bending ◽

Proposed Model ◽

Photo Conductivity ◽

Nanowire Device ◽

Uv Excitation

We investigated the photoconductivity of single ZnO nanowire device as a function of the surrounding atmosphere, considering the comparison between reduced pressure, inert gas environments, and air. We show that after UV excitation the photocurrent persists for hours, in particular in vacuum, nitrogen, and argon. In the presence of oxygen, the photodecay rate is initially fast but then becomes considerably slower, resulting in a long persisting photo-conductivity tail. Our proposed model explains the persistence of the photoconductivity (PPC) in terms of band bending at the surface of the nanowires, which is related to the trapping of electrons from the conduction band.

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Fission Gas Bubbles in Fractured UO2

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101177 ◽

1968 ◽

Vol 26 ◽

pp. 286-287

Author(s):

O. M. Katz

Keyword(s):

Electron Microscopy ◽

Thermal Gradient ◽

Gas Bubbles ◽

Inert Gas ◽

Thermal Gradients ◽

Fission Gas ◽

Beam Heating ◽

Limited Application ◽

Bubble Characteristics ◽

Electron Beam Heating

The swelling of irradiated UO2 has been attributed to the migration and agglomeration of fission gas bubbles in a thermal gradient. High temperatures and thermal gradients obtained by electron beam heating simulate reactor behavior and lead to the postulation of swelling mechanisms. Although electron microscopy studies have been reported on UO2, two experimental procedures have limited application of the results: irradiation was achieved either with a stream of inert gas ions without fission or at depletions less than 2 x 1020 fissions/cm3 (∼3/4 at % burnup). This study was not limited either of these conditions and reports on the bubble characteristics observed by transmission and fractographic electron microscopy in high density (96% theoretical) UO2 irradiated between 3.5 and 31.3 x 1020 fissions/cm3 at temperatures below l600°F. Preliminary results from replicas of the as-polished and etched surfaces of these samples were published.

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Study of Tip-Surface Interactions in Scanning Tunneling Microscopy (STM) by Reflection Electron Microscopy (REM)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180355 ◽

1990 ◽

Vol 48 (1) ◽

pp. 320-321

Author(s):

W. Lo ◽

J.C.H. Spence ◽

M. Kuwabara

Keyword(s):

High Resolution ◽

Elastic Strain ◽

Tunneling Current ◽

Surface Damage ◽

Surface Interactions ◽

Graphite Surface ◽

Scanning Tunneling ◽

Large Area ◽

Tunneling Microscopy ◽

High Resolution Tem

Work on the integration of STM with REM has demonstrated the usefulness of this combination. The STM has been designed to replace the side entry holder of a commercial Philips 400T TEM. It allows simultaneous REM imaging of the tip/sample region of the STM (see fig. 1). The REM technique offers nigh sensitivity to strain (<10−4) through diffraction contrast and high resolution (<lnm) along the unforeshortened direction. It is an ideal technique to use for studying tip/surface interactions in STM.The elastic strain associated with tunnelling was first imaged on cleaved, highly doped (S doped, 5 × 1018cm-3) InP(110). The tip and surface damage observed provided strong evidence that the strain was caused by tip/surface contact, most likely through an insulating adsorbate layer. This is consistent with the picture that tunnelling in air, liquid or ordinary vacuum (such as in a TEM) occurs through a layer of contamination. The tip, under servo control, must compress the insulating contamination layer in order to get close enough to the sample to tunnel. The contaminant thereby transmits the stress to the sample. Elastic strain while tunnelling from graphite has been detected by others, but never directly imaged before. Recent results using the STM/REM combination has yielded the first direct evidence of strain while tunnelling from graphite. Figure 2 shows a graphite surface elastically strained by the STM tip while tunnelling (It=3nA, Vtip=−20mV). Video images of other graphite surfaces show a reversible strain feature following the tip as it is scanned. The elastic strain field is sometimes seen to extend hundreds of nanometers from the tip. Also commonly observed while tunnelling from graphite is an increase in the RHEED intensity of the scanned region (see fig.3). Debris is seen on the tip and along the left edges of the brightened scan region of figure 4, suggesting that tip abrasion of the surface has occurred. High resolution TEM images of other tips show what appear to be attached graphite flakes. The removal of contamination, possibly along with the top few layers of graphite, seems a likely explanation for the observed increase in RHEED reflectivity. These results are not inconsistent with the “sliding planes” model of tunnelling on graphite“. Here, it was proposed that the force due to the tunnelling probe acts over a large area, causing shear of the graphite planes when the tip is scanned. The tunneling current is then modulated as the planes of graphite slide in and out of registry. The possiblity of true vacuum tunnelling from the cleaned graphite surface has not been ruled out. STM work function measurements are needed to test this.

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