Gas-filled polymers. III. Mechanical behavior of polycarbonate and poly(vinyl chloride)

Gasification behavior and its effects on mechanical properties were determined for amorphous polycarbonate (PC) and poly(vinyl chloride) (PVC). Nitrogen-gasified PC and PVC exhibit interior regions containing gas bubbles surrounded by surface layers of void-free polymer, while in the helium-gasified polymers no gas bubbles could be observed. Scanning electron microscope (SEM) observations of the bubbles in nitrogengasified PC indicate that the bubble walls are smooth and featureless (in contrast to the diffuse walls with fibrils of polymer extending into the bubbles observed previously in gasified polyethylene). For both PC and PVC, neither the yield stress nor the elongation to fracture showed any appreciable variation between gasified and ungasified material. The lack of a significant effect of gas bubbles on the drawing behavior in these glassy polymers stands in contrast with the pronounced effect noted with semicrystalline polyethylene. The origin of this difference in behavior and its relation to the crystallization process in polyethylene are discussed.     

Bücherschau

Ohne Zusammenfassung VDI     

The National Ignition Facility neutron time-of-flight system and its initial performance (invited)

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.     

Influence of Irradiation Temperature on Grafting of Styrene into Poly(tetrafluoroethylene‐co‐hexafluoropropylene) Films

This study concerns with the investigation of the effect of irradiation conditions on grafting of styrene into FEP films by the pre‐irradiation method. EPR spectroscopy was used to characterize the base polymer material regarding the trapped radical species and their concentration. Radiation‐induced changes in the chemical structure were studied by IR spectroscopy. Tensile strength and elongation at break as well as yield of grafting were found to be strongly influenced by irradiation temperature. Main‐chain scissions were identified to be the reason for the deterioration of the mechanical properties after radiation treatment at temperatures below glass transition temperature.

     

Investigation of micromilled tool steel H13 using tungsten carbide micro-end mills

Micromilling allows for the high precision machining of different types of materials and thus promotes the manufacturing of micro-components for various te     

A comparative materials study of magnetron ion etched GaAs using Freon-12, SiCl4 and BCl3

Etch characteristics and residual damage incurred via magnetron ion etching of GaAs using three different etch gases, namely, freon-12, SiCl₄ and BCl₃, at two different power levels has been studied. Transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, and Schottky diode measurements were employed to determine the suitability of the processed surfaces for device fabrication. Lattice damage was incurred in all processing situations in the form of small dislocation loops. Samples etched in freon-12 at the highest power density exhibited the roughest surface morphology, while those etched in SiCl₄ and BCl₃ resulted in planar surfaces. The Schottky barrier diode characteristics, for all etch gases, degraded with increasing power density. The electrical quality of the BCl₃-etched GaAs at the lowest power density was superior to that of the other etch gases at all power levels. The etched profiles of SiCl₄ and BCl₃ yielded vertical sidewalls, whereas freon-12 yielded a negative undercut. The BCl₃-etched GaAs surfaces were residue-free, while those of freon-12 and SiCl₄ exhibited surface or sidewall contamination. Our results have demonstrated that magnetron ion etching with BCl₃ yields planar residue-free surfaces with minimum material surface damage and superior electrical integrity compared with GaAs etched with freon-12 or SiCl₄.     

Fabrication of Flexible Superconducting Wiring with High Current-Carrying Capacity Indium Interconnects

The X-ray integral field unit (X-IFU) is a cryogenic spectrometer for the Advanced Telescope for High ENergy Astrophysics (ATHENA). ATHENA is a planned next-generation space-based X-ray observatory with capabilities that surpass the spectral resolution of prior missions. Proposed device designs contain up to 3840 transition edge sensors, each acting as an individual pixel on the detector, presenting a unique challenge for wiring superconducting leads in the focal plane assembly. In prototypes that require direct wiring, the edges of X-IFU focal plane have hosted aluminum wirebonding pads; however, indium (In) ‘bumps’ deposited on an interface layer such as molybdenum nitride (MoN) can instead be used as an array of superconducting interconnects. We investigated bumped MoN:In structures with different process cleans and layer thicknesses. Measurements of the resistive transitions showed variation of transition temperature T_c as a function of bias and generally differed from the expected bulk T_c of In (3.41 K). Observed resistance of the In bump structures at temperatures below the MoN transition (at 8.0 K) also depended on the varied parameters. For our proposed X-IFU geometry (10 µm of In mated to a 1-µm In bump), we measured a minimum T_c of 3.14 K at a bias current of 3 mA and a normal resistance of 0.59 mΩ per interconnect. We also investigated the design and fabrication of superconducting niobium (Nb) microstrip atop flexible polyimide. We present a process for integrating In bumps with the flexible Nb leads to enable high-density wiring for the ATHENA X-IFU focal plane.     

Evaluation of MR-induced hot spots for different temporal SAR modes using a time-dependent finite difference method with explicit temperature gradient treatment

An investigation of magnetic resonance (MR)-induced hot spots in a high-resolution human model is performed, motivated by safety aspects for the use of MR tomographs. The human model is placed in an MR whole body resonator that is driven in a quadrature excitation mode. The MR-induced hot spots are studied by varying the following: (1) the temporal specific absorption rate (SAR) mode ("steady imaging", "intermittent imaging"), (2) the simulation procedure (related to given power levels or to limiting temperatures), and (3) different thermal tissue properties including temperature-independent and temperature-dependent perfusion models. Both electromagnetic and thermodynamic simulations have been performed. For the electromagnetic modeling, a commercial finite-integration theory (FIT) code is applied. For the thermodynamic modeling, a time-domain finite-difference (FD) scheme is formulated that uses an explicit treatment of temperature gradient components. This allows a flux-vector-based implementation of heat transfer boundary conditions on cubical faces. It is shown that this FD scheme significantly reduces the staircase errors at thermal boundaries that are locally sloped or curved with respect to the cubical grid elements.