984 resultados para 327.2


Relevância:

30.00% 30.00%

Publicador:

Relevância:

30.00% 30.00%

Publicador:

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Bulk chlorine concentrations and chlorine stable isotope compositions were determined for hydrothermally altered basalt (extrusive lavas and sheeted dikes) and gabbro samples (n = 50) from seven DSDP/ODP/IODP drill sites. These altered oceanic crust (AOC) samples span a range of crustal ages, tectonic settings, alteration type, and crustal depth. Bulk chlorine concentrations range from < 0.01 wt.% to 0.09 wt.%. In general, higher chlorine concentrations coincide with an increase in temperature of alteration and amphibole content. d37Cl values of whole rock AOC samples range from -1.4 to +1.8 per mil. High d37Cl values (>=~0.5 per mil) are associated with areas of higher amphibole content. This observation is consistent with theoretical calculations that estimate amphibole should be enriched in 37Cl compared to co-existing fluid. Negative to near zero d37Cl values are found in areas dominated by clay minerals. Chlorine geochemistry is a rough indicator of metamorphic grade and mineralogy. AOC is a major Cl host in the subducting oceanic lithospheric slab. Here we show that bulk chlorine concentrations are ~3 times higher than previous estimates resulting in a greater contribution of Cl to the mantle.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The major objective of this research project is to investigate how fly ash influences the chemical durability of portland cement based materials. The testing program is evaluating how Iowa fly ashes influence the sulfate durability of portland cement-fly ash pastes, mortars, and concretes. Also, alkali-reactivity studies are being conducted on mortar bar specimens prepared in accordance with ASTM C 311. Prelimary sulfate test results, based only on mortar bar studies, indicate that only the very high-calcium fly ash (29 percent CaO, by weight) consistently reduced the durability of test specimens exposed to a solution containing 5 percent sodium sulfate. The remaining four fly ashes that were used in the study showed negligible to dramatic increases in sulfate resistance. Concrete specimens were only beginning to respond to the sulfate solutions after about one year of exposure; and hence, considerably more time will be needed to assess their performance. Preliminary results from the alkali-reactivity tests have indicated that the Oreopolis aggregate is not sensitive to alkali attack. However, some of the test results have indicated that the testing procedure may be prone to delayed expansion due to the presence of periclase (MgO) in the Class C fly ashes. Research is being planned to: (1) verify if the periclase is influencing test results; and (2) estimating the magnitude of the potential error.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Sammelrezension von: 1. Gerhard Tulodziecki: Medienerziehung in Schule und Unterricht. Bad Heilbrunn: Klinkhardt 2. Aufl. 1992, 205 S. 2. Wolfgang Schill/Gerhard Tulodziecki/Wolf-Rüdiger Wagner (Hrsg.): Medienpädagogisches Handeln in der Schule. Opladen: Leske + Budrich 1992. 327 S.