Toshimitsu Hata

Thermal conversion of alkaline lignin and its structured derivatives to porous carbonized materials

Alkaline lignin was thermally converted to microporous carbon in ca. 50% yield by heating up from room temperature to 900°C without activation process under flowing of an argon gas. The carbonized material prepared by heating up conditions of 1°C min(-1) showed 530 m(2)/g of the Brunauer-Emmett-Teller (BET) specific surface area, which increased to 740 m(2)/g after washing with water. Furthermore, alkaline lignin derivatives were structured as micron scale particles by micelle formation and polymer gelation techniques. Carbonization of the structured lignins could afford high porous materials having BET surface areas above 1000 m(2)/g without surface activation processes.

Microstructure of wood charcoal prepared by flash heating

Abstract Carbonized wood prepared by flash heating at 800xa0°C for 1 h shows a different microstructure and surface chemical structure than char formed after slow heating at 4xa0°C/min to 800xa0°C for 1 h. Flash heating produces pores that are surrounded by aggregates of carbon structures 25 to 100 nm in cross section. The carbon structures are built up of clearly visible graphene layers that are often curved and overlap each other in a disordered manner. The layers consist of a considerable number of oxygen-containing functional groups. The results suggest that the formation mechanism of the microstructure in wood carbonized by the flash heating process seems to originate from fragmented and oxygen-containing pyrolysis compounds in contrast to conventional heating.

Characteristics of a bioxalate chelating extraction process for removal of chromium, copper and arsenic from treated wood

The disposal of wood waste treated with chromated copper arsenate (CCA) is a problem in many countries. We have proposed a novel chelating extraction technique for CCA-treated wood using bioxalate, a solution of oxalic acid containing sufficient sodium hydroxide to adjust the pH to 3.2, which is an effective way to obtain an extraction efficiency of 90% for chromium, copper, and arsenic. The purpose of the present study was to investigate the characteristics of bioxalate extraction of CCA-treated wood. Extractions of CCA-treated western hemlock chips with solutions of bioxalate, oxalic acid, and sodium hydroxide were carried out. The use of bioxalate was confirmed as the most effective extraction technique for chromium, copper and arsenic, with an efficiency of 90%. Extraction with simple oxalic acid was ineffective for copper (less than 40% extraction efficiency), but effective for chromium and arsenic, with 90% efficiency. Sodium hydroxide showed a similar tendency, being ineffective for chromium and copper (less than 20% extraction efficiency), but relatively effective for arsenic (around 70-80% efficiency). We also discovered an interesting phenomenon whereby the addition of sodium hydroxide to a simple oxalic acid solution during the oxalic acid extraction progress resulted in dramatically increased extraction efficiency for copper, chromium and arsenic, up to 90%. Although oxalic acid was ineffective for copper extraction, the addition of sodium hydroxide during the oxalic acid extraction process rendered it effective.

Catalytic Graphitization of Wood‐Based Carbons with Alumina by Pulse Current Heating

Abstract Japanese cedar was preheated at 500°C and subsequently mixed with 40 µm Al2O3 particles. A pulse current heating method was used for a 5‐min carbonization step under a pressure of 50 MPa in order to promote the graphitization at temperatures between 2000 and 2200°C. The samples were analyzed in an analytical transmission electron microscope equipped with a GATAN Imaging Filter, in a high resolution transmission electron microscope and in a scanning electron microscope. Transformation into well‐ordered graphite could be enforced by the intermediate reaction of Al2O3 and carbon to plate‐like Al4C3. This latter compound dissociates under the proper CO pressure and temperature into Al vapor and solid graphite. The addition of Al2O3 and the pressurized heating device improve the graphitization in comparison with the effect of temperature alone. The electron microscopic observations are supported by XPS and XRD spectra.

Silicon carbide nanorods and ceramics from wood

Japanese cedar carbonized at 700degreesC was vacuum infiltrated with tetraethylorthosilicate (TEOS), and heated for 30 min at 1400, 1600 and 1800degreesC by electric pulse heating. The microstructure was investigated by X-ray diffraction and electron microscopy. Extra peaks in the XRD scans could be traced back to beta-SiC. Preliminary Auger analysis indicated an increase of the Si signal in pore walls. This was considered together with SEM images in agreement with the concept of a reaction layer covering the pore walls. Moreover, a large number of nanorods were present inside the pores. TEM analysis confirmed them to be SiC nanorods grown along the direction.

Formation of silicon carbide nanorods from wood-based carbons

Abstract Man‐made ceramic wood similar to petrified wood found in nature can be used at high temperature as the high oxidation rate of carbon above 500°C is suppressed by a 1 µm thin SiC coating similar to the shuttles heat shield. Possible applications are in the field of energy production, e.g., gas filters. In this paper, Japanese cedar was carbonized at 700°C, vacuum infiltrated with tetraethylorthosilicate (TEOS), and heated at 1,500°C for 30 min using a pulse current heating device. A FIB–SEM dual beam microscope combination was used to investigate the SiC/C composite micro‐texture. By milling away successive slices of material approximately 20 nm in thickness, it was possible to confirm that a reaction layer of SiC, about 60 nm in thickness, covers uniformly the surface of all cell walls. Furthermore, SiC nanorods were observed, growing more or less randomly in the charcoal pores. Cross‐sectional SEM images of the SiC nanorods showed that either hollow or solid structures could be formed, having diameters ranging from 100 to 500 nm. The SiC nanorod formation is being initiated by a catalytically operating SiC particle in the SiC coating. TEM analysis confirmed that they were grown along the [1 1 1] direction and indicated that an additional carbon layer covers the external surface of the rods making the rods more resistant against electron beam damage.

Effect of aluminum compound addition on graphitization of wood charcoal by direct electric pulse heating method

The catalytic effect of aluminum on graphitization of wood charcoal was examined. Wood charcoal impregnated with aluminum triisopropoxide to various levels was subjected to direct electric pulse heating. Electric conductivity and heat conductivity of the products showed strong, systematic dependence on the amount of aluminum added. X-ray diffractometry indicated that these effects result from a larger degree of graphitization. Because the amount of aluminum in the final product was negligible, aluminum, before being lost by vaporization, apparently catalyzed graphitization at a lower temperature than is used for conventional treatments.

Resistance of Silicon-Containing Carbonized Lignin to Atomic Oxygen Erosion

Spacecraft in low Earth orbit (LEO) are exposed to atomic oxygen (AO). It is thus important to develop an environmentally friendly material that can be applied to the outer surfaces of spacecraft in LEO to protect them against AO. Carbonized material containing electroconductive graphitic microlayers is promising for this purpose. We produced carbonized lignin (CW) by separating wood in L-lactic acid and we investigated the AO erosion resistances of CW and CW containing Si. X-ray photoelectron spectroscopy (XPS) revealed that the O/C ratio increased on AO exposure. The CW sample without Si and CW samples containing 20% and 40% Si exhibited less erosion than CW samples containing 5% and 10% Si. XPS revealed that the presence of Si resulted in the formation of SiO2 on the sample surface. For CW with Si contents of 20% and 40%, the SiO2 coverage may be sufficiently large to prevent attack by AO.