Synthesis of Biomorphic Silicon Carbide from Wood
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1094-DD07-20
Synthesis of Biomorphic Silicon Carbide from Wood Kwok Cheung Li, and Dickon H. L. Ng Department of Physics, The Chinese University of Hong Kong, Room 107, 1st Floor, Science Centre North Block, The Chinese University of Hong Kong, Hong Kong, China, People's Republic of ABSTRACT We have successfully produced biomorphic SiC ceramics from silica-infiltrated wood samples of balsa (Ochroma pyramidale) and flame tree (Delonix regia). This conversion of wood samples to SiC structures was performed by a sol-gel technique and a carbothermal reduction process. The biomorphic products were confirmed containing β-SiC and their structures were replica of the original structures of the raw wood samples. The biomorphic C-SiC from the denser flame tree had higher specific strength than that of the SiC produced from soft balsa. INTRODUCTION Wood is naturally structural optimized material [1]. Due to their unique cellular structure and potential applications in filters [2], catalysts [3] and light weight structural materials, the conversion of wood into biomorphic SiC is a focus of research interest. Many conversion techniques, such as sol-gel processing [4, 5, 6, 7], sol infiltration [8], reaction melt infiltration [9, 10], chemical vapor infiltration [11, 12], and their respective reaction mechanisms have been studied. In this work, wood samples of balsa and flame tree were converted to structures of SiC by a sol-gel process and a carbothermal reduction process. Both types of wood are common. Balsa has a low density which allows us to identify the key factor that affects the infiltration process. Flame tree has higher density and its biomorphic products would have a much better mechanical strength. From previous work [4], the infiltration of silica into pine and poplar wood samples could be up to 20 wt%. In order to produce a biomorphic SiC with high integrity of cellular structure, the amount of infiltration material must be increased, but without sacrificing the homogeneity of infiltration. In this experiment, a modified sol gel process was applied and infiltration behavior in different conditions was examined. EXPERIMENTS Balsa is commonly used to made toys. Samples of balsa were cut from wooden toys, while samples of flame tree were collected from the hillside of the Chinese University campus. Both types of samples were cut into 2 × 1.5 × 1.5 cm3 rectangular blocks. The samples were pretreated by etching in a 2M HCl solution at 60 oC for 48h to increase their porosity for effective infiltration. The samples were then washed and soaked in water at 60 oC for 24h before dried at 60 oC for 24h in air. The samples received the infiltration in a beaker containing the sol of TEOS/HCl/ethanol/H2O (molar ratio = 1:0.01:2:8). To assist the infiltration process, the beaker was placed in a low pressure desiccator for 15 minutes. The beaker was then placed in an open thermal bath of different thermal conditions and time durations ranged between 40oC and 60 oC, and 48h and 72h, respectively. Thereafter, the samples were dried
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