Unclassified U.S. Atomic Energy Commission reports on the metallurgy of zirconium and hafnium /

"TID-3508 Metallurgy and Ceramics."

Distillation separation of zirconium and hafnium : summary report for February 14, 1949 to March 31, 1950 /

"Contract No. AT(30-1)-534."

The first spectrum of hafnium (Hf I) /

Mode of access: Internet.

Hafnium cross sections and their temperature dependence,

"Contract W-7 405-Eng. 36 with the U. S. Atomic Energy Commission."

Zirconium and hafnium, a bibliography,

"Work performed under Contract no. AT-(30-1)-534."

(Table 1) Dissolved Hafnium and Neodymium in the South Atlantic measured on water bottle samples during POLARSTERN cruise ANT-XXIV/3

We present the first combined dissolved hafnium (Hf) and neodymium (Nd) concentrations and isotope compositions of deep water masses from the Atlantic sector of the Southern Ocean. Eight full depth profiles were analyzed for Hf and twelve for Nd. Hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0.2 pmol/kg and 0.4 pmol/kg and increase to relatively constant values of around 0.6 pmol/kg in the deeper water column. At the stations north of the Polar Front (PF), Nd concentrations increase linearly from about 10 pmol/kg at depths of ~ 200 m to up to 31 pmol/kg close to the bottom indicating particle scavenging and release. Within the Weddell Gyre (WG), however, Nd concentrations are essentially constant at 25 pmol/kg at depths greater than ~ 1000 m. The distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry. Hafnium essentially shows invariant isotope compositions with values averaging at epsilon-Hf = +4.6, whereas Nd isotopes mark distinct differences between water masses, such as modified North Atlantic Deep Water (NADW, epsilon-Nd = -11 to -10) and Antarctic Bottom Water (AABW, epsilon-Nd = -8.6 to -9.6), but also waters locally advected via the Agulhas Current can be identified by their unradiogenic Nd isotope compositions. Mixing calculations suggest that a small fraction of Nd is removed by particle scavenging during mixing of water masses north of the PF. Nevertheless, the Nd isotope composition has apparently not been significantly affected by uptake and release of Nd from particles, as indicated by mixing calculations. A mixing envelope of an approximated North Pacific and a North Atlantic end-member shows that Nd isotope and concentration patterns in the Lower Circumpolar Deep Water (LCDW) can be fully explained by ~ 30:70 percentage contributions of these respective end-members.

Hafnium and neodymium in surface waters of the Atlantic sector of the Southern Ocean

Radiogenic isotopes of hafnium (Hf) and neodymium (Nd) are powerful tracers for water mass transport and trace metal cycling in the present and past oceans. However, due to the scarcity of available data the processes governing their distribution are not well understood. Here we present the first combined dissolved Hf and Nd isotope and concentration data from surface waters of the Atlantic sector of the Southern Ocean. The samples were collected along the Zero Meridian, in the Weddell Sea and in the Drake Passage during RV Polarstern expeditions ANT-XXIV/3 and ANT-XXIII/3 in the frame of the International Polar Year (IPY) and the GEOTRACES program. The general distribution of Hf and Nd concentrations in the region is similar. However, at the northernmost station located 200 km southwest of Cape Town a pronounced increase of the Nd concentration is observed, whereas the Hf concentration is minimal, suggesting much less Hf than Nd is released by the weathering of the South African Archean cratonic rocks. From the southern part of the Subtropical Front (STF) to the Polar Front (PF) Hf and Nd show the lowest concentrations (<0.12 pmol/kg and 10 pmol/kg, respectively), most probably due to the low terrigenous flux in this area and efficient scavenging of Hf and Nd by biogenic opal. In the vicinity of landmasses the dissolved Hf and Nd isotope compositions are clearly labelled by terrigenous inputs. Near South Africa Nd isotope values as low as epsilon-Nd = -18.9 indicate unradiogenic inputs supplied via the Agulhas Current. Further south the isotopic data show significant increases to epsilon-Hf = 6.1 and epsilon-Nd = -4.0 documenting exchange of seawater Nd and Hf with the Antarctic Peninsula. In the open Southern Ocean the Nd isotope compositions are relatively homogeneous (epsilon-Nd ~ -8 to -8.5) towards the STF, within the Antarctic Circumpolar Current, in the Weddell Gyre, and the Drake Pasage. The Hf isotope compositions in the entire study area only show a small range between epsilon-Hf = +6.1 and +2.8 support Hf to be more readily released from young mafic rocks compared to old continental ones. The Nd isotope composition ranges from epsilon-Nd = -18.9 to -4.0 showing Nd isotopes to be a sensitive tracer for the provenance of weathering inputs into surface waters of the Southern Ocean.

Tailoring polyolefin properties by metallocene catalysis

This doctoral thesis deals with the syntheses of olefin homo- and copolymers using different kind of metallocene catalyst. Ethene, propene, 1-hexene, 1-hexadecene, vinylcyclohexane and phenylnorbornene were homo- or copolymerized with the catalysts. The unbridged benzyl substituted zirconium dichloride catalysts (1-4), ansa- bridged acenaphtyl substituted zirconium dichloride catalysts, ( 5, 6), rac- and meso-ethylene-bis(1-indenyl)zirconium dichlorides, (rac- and meso-8), rac-ethylene-bis(1-indenyl)hafnium dichloride, ( 12), bis(9-fluorenyl)hafnium dichloride (14 ) enantiomerically pure (R)- phenylethyl[(9-fluorenyl-1-indenyl)]ZrCl2, (11), 14 and asymmetric dimethylsilyl[(3-benzylindenyl-(2-methylbenzen[e]indenyl)] zirconium dichloride, (13), were prepared in our laboratory. Dimethylsilyl-bis(1-indenyl)zirconium dichloride, (9), isopropylidene(9-fluorenyl-cyclopentadienyl)zirconium dichloride, (10), and were obtained commercially. The solid-state structures of the catalysts rac- and meso-1 were determined by X-ray crystallography. Computational methods were used for the structure optimization of the catalyst rac- and meso-1 in order to compare the theoretical calculations with the experimental results. Polymerization experiments were conducted in a highly purified autoclave system using low pressures (< 5 bar) of gaseous monomers. The experiments were designed to attain the optimal catalytic activity and a uniform copolymer composition. The prepared homo- and copolymers were characterized by the gel permeation chromatography, GPC, differential scanning calorimetry, DSC, nuclear magnetic resonance, NMR, and Fourier transform infrared spectrometry, FTIR . Molar mass (Mw, Mn), molar mass distribution (Mw/Mn), tacticity, comonomer content, melting temperature, glass transition temperature, and end group structures and content were determined. A special attention was paid on the correlation of the polymer properties with the catalyst structures and polymerization conditions. An intramolecular phenyl coordination was found in phenyl substituted benzyl zirconocenes 1-3 explaining the decreased activity of the catalysts. Novel copolymers poly(propene-co-phenylnorbornene) and poly(propene co-vinylcyclohexane), were synthesized and high molar mass poly(ethene-co-1-hexene) and poly(ethene-co-1-hexadecene) copolymers with elastic properties were prepared. Activation of a hafnocene catalyst was studied with UV-Vis spectrometry and activation process for the synthesis of ultra high molar mass poly(1-hexene) was found out.