The electromagnetic (EM) wave absorption properties in the gigahertz region (12–110 GHz) of carbon microcoils (CMCs) with a three-dimensional-helical/spiral chiral structure (1–10 μm coil diameter and 0.1–10 mm coil length) were examined using the open space method. It was found that the target value of reflection loss, over −20 dB (above 99% absorptivity) necessitated for commercial applications, could be obtained for EM absorption composites of only 1–2 wt % addition of CMCs in a polyurethane matrix for the 30–35, 50–55, 75–80, and 95–100 GHz bands. A CMCs addition of more than 3 wt % resulted in a decrease of the EM wave absorptivity, because of the increase in the reflection of the EM waves. Multilayer absorption composites showed a higher EM absorptivity than that of single-layer composites. The longer the coil length, the higher the absorptivity could be obtained. The absorption mechanism of the EM waves by CMCs is discussed.
Carbon nanocoils with a coil diameter of 50±450 nm were prepared by the catalytic pyrolysis of acetylene, and the preparation conditions and morphology were examined. To clarify the growth mechanism, the carbon nanocoils were also heat treated at 2500 C for 8 h in a N 2 atmosphere, then partially oxidized in air at 600 C for 15 min. The carbon nanocoils could be grown at 740±770 C either by applying a magnetic field to the reaction zone or by using sputtered thin films of Au or Au/Ni as a catalyst. Carbon nanocoils are generally single coils, while carbon microcoils are generally double coils. There are two kinds of nanocoils with differing microstructures. One is formed from a carbon fiber with a double microstructure of thin core fiber and clad, while the other is formed from a fiber with a ªherring-boneº structure.
N-Isopropylcholamide afforded three kinds of matters in organic solvents; organogels, inclusion crystals, and guest-free crystals. The gelation occurred in aromatic liquids in the presence of methanol as a good solvent, while the inclusion crystals were formed when adding ethanol, 1-propanol, or acetone as a good solvent. The guest-free crystals were obtained in benzene when using 2-butanone, 2-pentanone, or 3-pentanone. Electron microscopic image of the organogel exhibited that the network was formed by gathering of many colloidal particles of several hundreds nanometers in diameter.
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