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[en] Whiskers phenomenon and their growth on pure tin layers have been known for many years. Whiskers are hair-like, electrically conductive, single-crystal structures that may grow to be several millimetres long. Tin Whiskers was identified in the late 1940s, during WWII due to detrimental short circuits and arcing in electrical devices, eventually causing the failure of devices. Whiskers growth mechanism remains unknown after more than 60 years of research. In recent years, concerns have been escalating, especially in the sector of high-reliability products. The elimination of lead in electronic equipment due to government regulations (RoHS) has increased the risk of failures due to the formation of tin whiskers in electronic devices because the use of pure tin (Sn) presents a high risk of tin whiskers caused failures in electronics, particularly those demanding high level of reliability. Consequently, JEDEC standard No.201 provides general guidelines for electronic products defined as Class 3, i.e. 'Mission/Life critical applications such as military, aerospace and medical applications'. In such products, pure tin and high tin content alloys are not acceptable. However, in commercial electronics segment, which utilizes the majority of electronic components, product life cycles are often measured in months. In contrast, high-performance electronics products typically have product life cycles that are measured in decades and therefore are much more susceptible to potential long-term threat of tin whiskers. Many of electronic failures are attributed to tin whiskers, ranging from space and military applications through medical, industrial applications and applications in nuclear power plants (NPP). Signal transients, parametric deviation or equipment failure can be linked to whiskers shortening. At Krsko Nuclear Power Plant, tin whiskers inspection, cleanliness and other planned maintenance activities on built-in electronic equipment are being performed during outage period. Preventive maintenance of storage equipment is being performed periodically through 'ISM' (In-Storage Maintenance) program. Despite preventive and corrective maintenance, equipment could fail to function. Tin whiskers are almost invisible to human eye and require magnification and lighting to be seen. Inadequate lighting technique and incorrect angle of inspection or magnification could cause tin whiskers to be overseen. In these cases, operator's experience with whiskers and other electronic inspections are crucial factors. At Krsko NPP maintenance department, the goal is to decrease tin whisker failure risk on electronic equipment by planning and performing preventive maintenance actions, applying recommended mitigation technics and monitoring operational experience. (author).
[en] Composites are composed of multiphase materials, where each phase has specific properties that differ from those of the other phases which can effect on the whole properties of composite. Nanocomposites are class of materials that contain at least one phase in the nanometric size range and can be produced by any suitable technique for preparing nanomaterials. Composites are an interesting class of materials that have recently been used in numerous applications, including structural, biomedical, electronics, and environmental applications. In composites, reinforcements might be fibers, particulates, or whiskers. Mechanical alloying (MA) is a promising technique for producing nanocomposite materials that are difficult or impossible to prepare via conventional techniques. In this review, we provide an overview of nanocomposites prepared by the MA process. The mechanism of milling and other milling parameters are overviewed, and insights into sintering categories and parameters are also presented.
[en] A range of micron-sized Hall probe arrays has been used to investigate the Bean-Livingston surface barrier in single crystal whiskers of the type 11 superconductor Bi2Sr2CaCu2O8+δ. It is shown that the magnetic properties of the whiskers are dominated by surface barriers, and hysteresis loops exhibit behaviour entirely consistent with such a system, showing very small magnetisation on the return leg. Measurements of the temperature dependence of the field of first flux penetration indicate that above approximately 5mT the vortex lines decouple into stacks of two-dimensional vortex pancakes, which surmount the surface barrier through thermal activation, in agreement with recent models of giant flux creep over surface barriers. Once inside the whisker, the vortices collect in the centre to produce a dome-shaped magnetic flux profile, which is observed experimentally. Careful measurements of the initial leg of the hysteresis loop show a sawtooth structure, which is interpreted as evidence of a hierarchy of stable vortex states. Field-cooled measurements exhibit a sharp drop in the local magnetic induction, which is interpreted as a boundary between a regime dominated by surface barriers and a regime dominated by the inter-vortex repulsion. Transport measurements have also been carried out, and the results support the idea that the transport properties of the whiskers are strongly affected by surface barriers. (author)
[en] Studies of high aspect ratio structures with widths/thicknesses in the nanometer range - nanowires - have revealed extremely interesting behaviour associated with their reduced dimensionality [Fasol, 1998]. Metal nanowires in particular show interesting magnetic, superconducting and magnetotransport properties, but because it is so difficult to prepare nanowires of the same material with different crystal textures in a controlled fashion, it has been extremely hard to study how the texture affects the physical properties of such nanowires. In this study, an electrochemical system, which allows Pb nanowires to be deposited in nanoporous polycarbonate membranes was fully developed. Superconducting Pb nanowires with diameter ∼50 nm were deposited by pulse electrodeposition. It was shown that the texture of Pb nanowires may be manipulated by varying the pulse potential, either polycrystalline or single-crystal. TEM studies have confirmed that the structure control method is very reproducible and reliable
[en] Phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells (macrophage-like cells) were exposed to the C60 fullerene nanowhiskers (C60 NWs) with an average length of about 6.0 μm and an average diameter of about 660 run and observed with an inverted optical phase-contrast microscope for 48 h. The C60 NWs were well and stably dispersed onto the dishes of culture medium during the observation. The number of cells that internalised C60 NWs gradually increased after the exposure to C60 NWs. But no alteration of cellular morphology was observed compared to the control group without exposure to C60 NWs during this period in this pilot study.
[en] The growth kinetic and size decreasing process of tungsten rod-like crystals by heating in the iodine vapour are studied. Effects of tungsten filament temperature (2400-3500 K), iodine concentration (to 6 mg/cm3) and water contents (0.01-0.05 mg/cm3) are shown. Maximal growth rate of tungsten whiskers to 30 μm/min. Stopping of the growth and following removing by iodine reactions take place after heating to 3500 K. (author)
[en] Since the discovery of C60 nanowhiskers in a colloidal solution of PZT in 2001, various low-dimensional fullerene nanomaterials such as fullerene nanotubes and fullerene nanosheets have been synthesized by the liquid-liquid interfacial precipitation method (LLIP method) as well as the C60 and C70 nanowhiskers. The LLIP method is an excellent process to synthesize the quasi one-dimensional fullerene nanomaterials. This paper first reviews the typical fullerene nano and micro materials that have been prepared by the LLIP method and then show that the LLIP method is also applicable to the synthesis of composite C60 nano and micro whiskers containing wide compositions of C60 derivative molecules.
[en] Formation and structure of toughened C60 nanowhiskers (C60NWs) were investigated. C60NWs are modified when pristine ones grown by a liquid-liquid interfacial precipitation method are kept in the growth solution for more than 3 years. The modified ones have a hexagonal solvated structure not only in the solution but also in air or a vacuum. The modified ones exhibit high strength and large elastic deformation in air, quite differing from the brittle in pristine ones in air.
[en] In situ TiB whiskers have a hexagonal shape in the transverse section and grow along the TiB direction. The crystallographic planes of the TiB whiskers in the transverse section are always (100) (101) and (101-bar ). The stacking faults in TiB are typically with a stacking fault plane of (100)TiB. The locations of boron atoms and the lattice mismatch energy between TiB and Ti matrix play key roles in the formation of stacking faults