Kouji Saito

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.

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.

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.

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.

Friction properties of new porous carbon materials: Woodceramics

Woodceramics are new porous carbon materials obtained from wood or woody materials impregnated with phenol resin, and carbonized in a vacuum furnace at high temperature. Woodceramics have several superior characteristics from the viewpoints of engineering materials and ecological materials: they are hard and strong, have porous structure and low density, are made from natural resources, do not cause environmental pollution, and are cheap to manufacture. This paper describes the fundamental friction properties of Woodceramics in sliding contact with several materials. Woodceramics made of medium density fiberboard (MDF) and beech impregnated with phenol resin and carbonized in a vacuum furnace at 800°C and 2000°C were rubbed against alumina, silicon nitride, bearing steel and diamond by using a reciprocating friction apparatus. Experiments were carried out unlubricated in air, impregnated with base oil and in water, at several normal loads and sliding velocities. The following principal results were obtained: (1) The friction coefficient is around 0.15, under all three lubrication conditions; (2) The friction coefficient slightly decreases and then stays constant with increasing normal load; (3) The friction coefficient is not affected by sliding velocity; (4) Woodceramics have a good self-lubricity.

Specific heat capacity of new porous carbon materials: Woodceramics

Abstract New porous carbon materials, ‘Woodceramics’, have been developed by carbonizing wood or woody materials impregnated with thermosetting resin, such as phenol resin, in a vacuum furnace at high temperatures. Woodceramics have superior characteristics from the viewpoint of engineering and ecological materials: they are hard and strong, have porous structure and low density, are made from natural resources, do not cause environmental pollution, and are cheap to manufacture. We have carried out differential scanning calorimetry in order to determine the heat capacity at high temperatures.

The effect of burning temperature on the structural changes of Woodceramics

Woodceramics are new porous carbon materials obtained by burning wood or woody material impregnated with thermosetting resin in a vacuum furnace. In this paper, the effect of burning temperature on the structural changes of Woodceramics is analyzed experimentally.Woodceramics were prepared using medium density fiberboard which was burned at temperatures less than 1000°C in a charcoal kiln. A drastic decrease in dimensions and weight was observed at temperatures lower than 600°C but they decreased gradually at temperatures higher than 600°C. Reproducibility of dimensions and weight by burning is possible.When Woodceramics were prepared by burning at higher than 1600°C by high frequency induction furnace, dimensions and weight decreased due to transformation of amorphous carbon to graphite, but the porous structure of wood remains unchanged.The distribution of glassy carbon and amorphous carbon was difficult to decipher after graphitization by observation with SEM and X-ray diffraction analysis.

Mechanical properties of porous carbon material: Woodceramics

The mechanical properties of Woodceramics which were made from medium-density fiberboard have been investigated with special reference to the effect of burning temperature on their bending Youngs modulus and bending strength. Woodceramics made from beech wood have also been tested to clarify the compressive strength anisotropy, and the role of phenol resin impregnation in strengthening the beech based charcoal.The bending Youngs modulus hardly varies for burning temperatures between 300 and 500°C, but it improves remarkably for burning temperatures between 500 and 800°C. The bending strength degrades with temperature for burning temperatures between 300 and 500°C, but it improves remarkably with increasing temperature of burning between 500 and 800°C. The bending Youngs modulus and bending strength gradually degrade with temperature for burning temperatures at and above 2000°C.The compressive strength of beech wood burned at 800°C in the longitudinal direction is greater than that in the radial direction, which in turn is greater than that in the tangential direction; this reflects the anisotropy of wood. Woodceramics made from beech wood have a compressive strength superior to beech charcoal in any of the following three directions: 4.5 times in the longitudinal direction, 3.4 times in the radial direction, and 2.0 times in the tangential direction. Both for beech charcoal and beech Woodceramics, brittle fracture is brought about by the buckling of cell wall in compression along the longitudinal direction but by the bending of cell wall in the compression along radial and tangential direction.

Influence of Laser Beam Irradiation Conditions on the Machinability of Medium Density Fiberboard Impregnated with Phenolic Resin

The applicability of CO2 laser beam machining (cutting) to resin impregnated woody products has been investigated with special reference to the effect of laser beam machining parameters such as laser power, feed speed of workpiece, pulse duty, frequency, assist gas pressure and defocus distance. The optimum laser beam machining conditions are as follows: Laser power: 1500 W; output wave form: pulse oscillation wave (pulse duty: 40%); frequency: optional (0 to 1000 Hz); feed speed of workpiece: 900 mm/min; assist gas: nitrogen gas; assist gas pressure: optional (0.1 to 0.5 MPa); and defocus distance: (0 to 1 mm).A carbonized layer of 1 to 2 mm thickness is always formed near the cut surface. In other words, materials not thermoformed after impregnation with phenol resin are influenced by heat to some extent while being machined by the laser beam.