| Summary: | 碩士 === 長庚大學 === 化工與材料工程研究所 === 97 === Zinc oxide is a widely used oxide with a wide band gap and high excitation binding energy and can be used as photocatalysts and light-emitting components. Although several methods have been proposed for zinc oxide preparations, we proposed a method to prepare zinc oxide particles in a supercritical carbon dioxide environment in this study. Such a method combines drying, sintering and other procedures in a simple chamber, which improves the traditional wet chemical synthesis method by reducing chemicals usage and is believed to be an energy saving and environment friendly process.
In this work, zinc nitrate dissolved in ethanol was used as the precursor. The precursor was dried in the supercritical carbon dioxide environment and formed particles. The effects of the precursor solution pH value, supercritical fluid flowing conditions and the supercritical fluid states on the powder formation mechanisms in the supercritical carbon dioxide environment were studied.
The results showed that the supercritical fluid dried powders were zinc carbonate powders. The best operating conditions are: the precursor titrated by NH4OH to pH = 9, the drying pressure of 2000 psi, the drying temperature of 60 ºC and 8-hour drying time. The average particle size was 100 nm. Dried powder TGA and FTIR analysis showed no residual unreacted functional groups on the powders. The dried zinc carbonate powders can be completely converted to zinc oxide powder by 2-hour low oxidation temperature 200ºC.
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