920 resultados para ALUMINA POWDER


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Fossil corals are unique archives of past seasonal climate variability, providing vital information about seasonal climate phenomena such as ENSO and monsoons. However, submarine diagenetic processes can potentially obscure the original climate signals and lead to false interpretations. Here we demonstrate the potential of laser ablation ICP-MS to rapidly detect secondary aragonite precipitates in fossil Porites colonies recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 from submerged deglacial reefs off Tahiti. High resolution (100 µm) measurements of coralline B/Ca, Mg/Ca, S/Ca, and U/Ca ratios are used to distinguish areas of pristine skeleton from those afflicted with secondary aragonite. Measurements of coralline Sr/Ca, U/Ca and oxygen isotope ratios, from areas identified as pristine, reveal that the seasonal range of sea surface temperature in the tropical south Pacific during the last deglaciation (14.7 and 11 ka) was similar to that of today.

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Mode of access: Internet.

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Advertising matter: p. 663-696.

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Uranium is a ductile metal and cannot be comminuted to a fine powder by any mechanical means such as crushing, milling or grinding. Uranium, however, reacts readily with hydrogen and forms UH3, which is a fine powder of less than 400 mesh screen size. The factors controlling the rats of the hydride formation are: (a) The surface area of the metal; (b) the temperature at which the reaction takes place; (c) the pressure of hydrogen. In order to increase the reaction area, one has to hydride small metal pieces rather than a single mass. The hydrogen reacts with uranium metal at temperatures as low as 100 deg to 1500 deg, and the reaction rate becomes quite rapid at approximately 225 deg C. The hydrogen for this purpose has to be of high purity and any small amount of oxygen in hydrogen delays the start of the reaction.

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Pages 505-560, advertising matter.

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Federal Highway Administration, Washington, D.C.

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"Contract AT-30-1 GEN 366."

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"Contract AT-30-1-GEN-366."

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"Work performed under Contract No. AT-30-1-gen-366"--Page 2 of cover.

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Three samples of thorium powder as supplied by Horizons, Inc. of Cleveland, Ohio were compared. The powder was processed entirely without the use of protective atmospheres with the exception of the sintering which was performed in a tank argon atmosphere with a dew point of approximately -80°C and the hot-pressing which was carried out in vacuum. The equipment and procedures used for cold-pressing and sintering were identical to those used in the evaluation of Sylvania produced thorium powders. The hot-pressing was done with standard uranium hot-pressing equipment.