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Mechanical and electrical properties of porous composites consisting of spring-shape carbon microcoils (CMCs) and silicone-rubber were investigated. The CMC/rubber porous composites having 71–81% porosity had compressive elastic moduli of 0.04–0.1 MPa which were 2–4% of a composite having the same ingredients without pores. The porous structure gave the composites not only the flexibility but a unique piezoresistivity in a wide compressive strain range. Resistivities of the porous composites increased over 104 times with a compressive strain up to 80%, while those of other porous composites including fibrous or particulate carbon fillers decreased only several tens of percent. CMC/rubber porous composites having such a unique piezoresistivity enabled us to develop a new tactile sensor system.

Spring-shaped carbon microcoils (CMCs) were embedded in silicone–rubber to form CMC/silicone–rubber composites. The electrical and mechanical properties of the composites were examined and compared with those of the composites involving straight carbon nanofibers and carbon blacks as a conductor. The electrical resistivity of the CMC/silicone–rubber composites decreased dramatically by increasing the CMC content and was as low as 100 Ω cm at 10% CMC volume content. With a compressive or tensile strain, the resistivity increased sharply much more than that of the other composites. The high resistive sensitivity of the composites is ascribed to an easy-to-deform configuration of the CMCs in the composites under an applied stress.

Helical TiO2/CMC (carbon microcoils) microtubes and helical TiO2 microtubes were obtained by making TiO2 layer coatings on the surface of CMC templates using a sol-gel and chemical vapor deposition (CVD) processes. The preparation conditions, morphologies and some properties were examined. Uniform TiO2 (anatase) layers were obtained on the CMC templates by a CVD process using vapor phase hydrolysis of titanium tetra-isopropoxide at 300°C followed by heat treatment in N2 or by calcination in air at 500–;650°C. The helical TiO2/CMC microtubes showed good photocatalytic activity. It was considered that the helical structure activated and enhanced the photocatalytic activity of TiO2, probably caused by the generation of inductive microelectric current induced by the irradiation of UV light, resulting in the generation of micromagnetic fields around the tubes.

Hydrogen was adsorbed on carbon coils under 10 MPa hydrogen gas at liquid nitrogen temperature. The equilibrium pressure of hydrogen desorbed from the as-grown carbon coils with an amorphous structure was three to four times greater than those of multiwall carbon nanotubes (MWNT) and active carbons (AC). The heat treatment of the carbon coils at 850 °C contributed to an increase in hydrogen adsorption by 20% compared to the as-grown carbon coils. On the other hand, the adsorption of hydrogen gas on the carbon coils decreased significantly after heat treatment at a temperature higher than 1000 °C due to formation of capsule-like carbon composed of 10–20 layers on the surface of the carbon coils.

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.

Novel TiO 2 microcoils were obtained by coating TiO 2 layers on the carbon microcoil templates by using a sol–gel process. The preparation conditions, morphologies, microstructure, and some properties were examined. It was found that helical TiO 2 fibers, including TiO 2 microcoils (TMCs) or TiO 2 microtubes with negative coiling patterns on the surface (TMCNCs) were obtained, depending on the coating conditions. TMCNCs were formed when used low concentrations of titanium tetra-isopropoxide in ethanol, while TMCs were formed when used high concentrations.

The carbon micro-coils were prepared by the catalytic pyrolysis of acetylene at 770–775 °C using Ni, Nb, Ta and their oxides with the superimposed application of an electromagnetic field (AC, DC) from both the outer and inner sides of the reaction tube as well as with application of a bias voltage to the substrate. The effect of the electromagnetic field on the coil yield and morphology were examined. The coil yield increased by 1.1–1.2 times with the superimposed application of the AC or DC electromagnetic field. It was found that the superimposed application of the outer and inner electric magnetic fields resulted in the strong influence on the morphology of the grown carbon coils. The effect of the non-inductive zero magnetic field obtained with a counter magnetic field on the growth of the carbon coils was also examined. The maximum coil yield of 30–32.5 mg/cm2-substrate was obtained with the application of both the outer and inner DC–EM fields or non-inductive EM field.