Charcoal consists mostly of carbon materials prepared by carbonization, i.e., traditionally by pyrolysis [1,2] of wood pieces in a kiln. At a high enough temperature and an absence of oxygen [3], high-quality charcoal with low resistance can be produced. A possible application of the low-resistivity charcoal is as an electrode material for electrochemical devices. In this research, bamboo waste was used to produce low-resistance bamboo charcoal. During heating, the temperature gradually increased up to 700°C, was kept approximately constant overnight, and was left to cool down to room temperature. Then, the charcoal bamboo pieces were obtained. A rough temperature-resistivity map was constructed. The bamboo charcoals were divided into 3 resistivity ranges, namely, 20, 100 and 1000 ohm.cm-1. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and microEDX (energy dispersive X-ray spectroscopy), were conducted for charcoal morphology and spectroscopic characterization [4-6]. The morphological results from SEM did not show any significant differences among bamboo charcoals with different resistivity. DF-STEM and EDS-STEM mapping revealed impurities inside the bamboo charcoal. Elemental analysis of micro areas showed weight percentage of carbon and other impurities in the bamboo charcoals. The 20 ohm.cm-1 bamboo charcoal was the best among all resistivity studied in terms of purity and main carbon structure. Decreasing the impurity content was found to be one of the essential parameters to obtain low resistivity bamboo charcoal. It was concluded that improving the stability and condition of the burning process in the conventional kiln was necessary in order to get a high yield of low resistance bamboo charcoals.
The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si3N4 was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si3N4. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm3, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si2N2O, and SiC likely resulted from the reactions between O2 and C impurities with Si3N4.
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