| Summary: | 博士 === 國立成功大學 === 資源工程學系 === 87 === The rice hulls production of Taiwan is about 400,000 tons/years, causing substantial environmental pollution as only a small fraction finds industrial application. However, there is a great potential for the resources recycling and the most valuable converted product in the form of SiC ultrafine powder (US$100/Kg) deserves particular attention. The main objectives of this investigation are as follows: (1) to evaluate the laboratory processing of ultrafine SiC powder from carbonized rice hulls, (2) to characterize various properties of the SiC and others products in the cooling zone, (3) to provide a preliminary planning of a pilot plant for product of SiC from rice hulls.
The experimental results are given as:
1. Carbonized rice hulls (CRH), having high carbon and SiO2 contents, high surface area, represent the ideal feedstock materials for SiC production. The optimum conditions are: 1500℃, vacuum condition of 5x10-2torr, maintaining at 1 hour. Conversion of SiO2 into SiC has been noted to be 48 wt%(based on SiO2 in feedstock).
2. The ultrafine SiC product is primarily composed of aggregates of grains with sub-spherical shapes of β-SiC, a surface area of 11-24 m2/g, only a very small fraction of whiskers of SiC crystal are noted. The true density of SiC is 3.17.
3. In terms of reaction kinetics, the activation energy of the CRH conversion to SiC has been calculated to be 20.2 kcal/mole, given a straight-line relationship between temperature (reciprocal) and weight loss/time.
4. In the cooling zone (1490~700℃) of the reactor, the SiO, CO and other gaseous entities may react to form ultra-fine particles of different deposition products: in the form of thin film, whiskers and spherical grains. The series of products from high to low temperature range are: (a)thin film ofβ-SiC and carbon, (b)β-SiC whiskers, (c)prismatic gehlenite (Ca2Al2SiO7) andβ-SiC whiskers, (d)mixture of SiO2 /Si whiskers, (e)mixture of SiO2 /Si spherical grains.
5. Thin film of SiC is formed by the reaction of SiO and C, and SiC whiskers are formed by vapor liquid solid whisker growth mechanism (VLS) and vapor solid whisker growth mechanism (VS).
The preliminary planning of a pilot plant for production of ultrafine SiC from CRH is provided and this is considered to be a feasible proposition. These various ultrafine SiC products and by-products of SiO2 /Si and gehlenite may find different industrial applications, as: composite materials, surface-coating giving high corrosion/erosion resistance and other aspects.
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