Toshihiro Okabe

New porous carbon materials, Woodceramics: Development and fundamental properties

Woodceramics are new porous carbon materials obtained by carbonizing wood or woody material impregnated with thermosetting resin such as phenol resin in a vacuum furnace. During the carbonizing process, thermosetting resin changes into glassy carbon, which has superior corrosion resistance and mechanical strength, reinforces the material and suppresses the fissures and warps (caused by the porous structure specific to wood) that develop during thermoforming. The dimension, weight decrease rate, and electrical characteristics depend on the thermoforming temperature. The manufacturing method of Woodceramics is introduced in this paper and various industrial uses, such as electromagnetic shields, are discussed.

Graphitization behavior of wood ceramics and bamboo ceramics as determined by X-ray diffraction

Wood and bamboo ceramics are newly developed porous carbon materials from wood and bamboo impregnated with resin, and they possess some special properties and can be expected to be used as electromagnetic materials, absorbents, catalyst carrier materials, etc. In this work, the graphitization behavior of wood and bamboo ceramics was investigated by X-ray diffraction. Experimental results show that the d002 spacing of the bamboo carbon, wood and bamboo ceramics decreased and the apparent graphite crystallite size Lc(002) increased with the increase of graphitization temperature. However, even after heat treatment at 3273 K, the d002 and Lc(002) value was only about 0.341 and 9 nm, respectively. These results indicate that all of the bamboo carbon, wood and bamboo ceramics investigated are typical non-graphitizable carbon or hard carbon.

Effect of carbonization temperature on the structural changes of woodceramics impregnated with liquefied wood

Structural inspection of carbonized woodceramics impregnated with liquefied wood was performed by dimensional shrinkage and weight loss, the content of carbon and oxygen with X-ray energy dispersive analysis (EDS), Raman scattering spectroscopy, laser microscope observation and X-ray diffraction. The results showed that with the increasing temperature, the dimensional shrinkage, weight loss and the ratio of carbon to oxygen in woodceramics increased, the (002) interplanar spacing of the crystalline component in woodceramics decreased and the value of R increased above 650°C. Woodceramics have a turbostratic structure with cracks, and internal stresses etc., especially for those carbonized at temperatures over 650°C.

Electromagnetic Shielding Properties of Woodceramics Made from Wastepaper

Woodceramics are new porous carbon materials, which are made by impregnating woody materials with phenol resin and then thermoformed in a vacuum furnace and these have been shown to have electromagnetic shielding properties. In the recycling of wastepaper, ways of using the wastepaper other than for paper pulp are needed to be developed. In this study, we made Woodceramics from handbill advertisement paper and telephone directory paper, and measured their electromagnetic shielding properties in order to find new uses for wastepaper. The results showed that the Woodceramics made from wastepaper had an electric shielding effectiveness of 30 dB for 100 MHz and 40 to 43 dB for 300 MHz or higher, and had a magnetic shielding effectiveness of 30 dB for 100 MHz and 37 dB for about 400 MHz. An electric equivalent circuit of the pore model in the Woodceramics is introduced. In addition, it is proposed that the excellent electromagnetic shielding effectiveness of the Woodceramics is caused by dielectric loss.

Mechanical Properties of Woodceramics: A Porous Carbon Material

The mechanical properties of woodceramics, which are new porous carbon materials utilizing the natural structure of wood, were investigated. The effects of burning temperature and amount of impregnated phenol resin on Youngs modulus, compressive strength and fracture toughness were measured. The fracture morphology was then observed, and simplified mechanical models of the woodceramics were discussed to explain the mechanical properties. The fracture was initiated at the cell walls that were located in vertical direction against the applied stress. The effect of impregnated phenol resin on the Youngs modulus and the compressive strength was reasonably explained by a wall-bending model.

Electrical Properties of Woodceramics

Woodceramics have recently attracted much attention as ecomaterials at low cost. Electrical properties of the woodceramics (WCM hereafter) have been characterized in the range 10–70% relative humidity and for temperatures from −20 to 100°C. The WCM bulk has been prepared by burning MDF board impregnated with phenolic resin at 650 and 750°C. Electrical resistance decreased linearly with increasing temperature, indicating the negative temperature coefficient like semiconductor. Relative humidity dependence of the resistance also indicated excellent linear characteristics between 10 and 70% RH measured here. Activation energies of 0.21, 0.15, 0.05, and 0.01 eV have been revealed from van der Pauw method. The excellent linearity for humidity and temperature is prominent advantages of WCM which may be useful as a new humidity and also temperature sensor.

Surface Area Characteristics of Woodceramics

Woodceramics have interesting and potential applications such as catalytic, moisture absorption, water treatment etc., where the surface area is the main characterization parameter. In the present study, surface area characteristics of woodceramics was investigated. The results showed that the surface area of the woodceramics increased with increasing carbonization temperature, and decreased with increasing phenol resin content added to wood. The structure of raw wood also played an important role on the surface area of woodceramics, and the thermal activation could increase the surface area of the woodceramics. In the present work, a thermal pyrolysis activation mechanism was presented to discuss the relatively high surface area phenomenon for the woodceramics carbonized at high temperatures.

Friction and Wear of Woodceramics under Oil and Water Lubricated Sliding Contacts

Friction and wear properties of woodceramics were evaluated under oil and water lubricated sliding contacts. The experiment was conducted with a block on a ring wear tester. The block material was woodceramics (MDF-800) and and the ring was a forging steel (SF55). The sliding velocity and the load were varied in the ranges 1.0–19.0 m/s and 98–294 N, respectively. The ring temperature was measured using a thermocouple located at 1.0 mm below the frictional surface of the ring.In the oil lubrication, the coefficient of friction was small and constant at ∼0.12, irrespective of the sliding velocity. The specific wear rate of the woodceramics was also small and was in the range 5 × 10−7−2 × 10−6 mm3/Nm. With the increase in the load, the coefficient of friction and the specific wear rate of woodceramics decreased. It was found that low friction and low wear could be maintained at least until a ring temperature of ∼160°C.In the water lubrication, the coefficient of friction was small and constant at 0.16 until the sliding velocity of ∼12 m/s. The specific wear rate was also small and was in the range 3 × 10−7−2 × 10−6 mm3/Nm. As the sliding velocity increased further and the ring temperature became high, friction and wear increased.

Effect of carbonization temperature on the basic properties of woodceramics made from carbonized bamboo fiber and liquefied wood

In this paper, a new woodceramics from carbonized bamboo fiber and liquefied wood was developed and the effects of carbonization temperature on the dimension shrinkage, weight loss, density, compressive strength, and volume electrical resistivity of the woodceramics were investigated. The results show that, with the increase in the carbonization temperature, liquefied wood decompose and then combine with carbonized bamboo fiber, the dimension of sample almost keep constant, but its compressive strength was improved, and its electrical resistivity was reduced.

Effect of carbonizing speed on the property changes of woodceramics impregnated with liquefacient wood

Properties of the woodceramics impregnated with liquefacient wood and carbonized at different heating rate were performed by dimension shrinkage and weight loss, density, compressive, tensile strength and specific surface area. The results showed that the heating rate played an important role upon the properties of the woodceramics; the dimension shrinkage and the weight loss increased with the increase of heating rate, while the compressive and tensile strength decreased. The results also indicated that high heating rate promoted high surface area.