Synthesis and Characterizations of High Yield a-FeOOH Nanorods and Fe3O4/SiO2 Magnetic Core-Shell Nanorods

高產率α相鐵氫氧化物奈米棒及四氧化三鐵/二氧化矽磁性核瞉奈米棒合成及特性研究

吳嘉偉(Chia-Wei Wu)

指導教授 ： 周立人

國立清華大學/工學院/材料科學工程學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00406

摘要

High yield α-FeOOH nanorods were successfully synthesized by hydrolysis and hydrothermal methods. Results of differential thermal analysis (DTA) showed that the second thermal decomposition temperature of ammonium perchlorate (AP) was decreased by adding α-FeOOH nanorods into AP. Furthermore, the optimum mixing ratio was 25: 1 (AP : α-FeOOH nanorods), which caused the heat release to increase 3.2 times and the second decomposition temperature to decrease about 50 °C compared with pure AP. High surface to volume ratio of one dimensional nanomaterial resulted in high absorptions of NO, NO2 and NH3 in the decomposition process of AP. Hence, α-FeOOH nanorods exhibited a good catalytic property which will enhance the thermal decomposition of AP.
The second part of this thesis is the synthesis of magnetic core-shell nanorods. First, α-FeOOH/SiO2 core-hell nanorods were fabricated by way of StÖber growth, then they were converted to Fe3O4/SiO2 or Fe/SiO2 core-shell nanorods at 500 °C in different reductive environments. The thickness of outer SiO2 shell could be tuned by controlling the amount of tetraethoxysilane (TEOS). To investigate the magnetic properties, we employed vibration sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements to measure the coercivities and magnetizations of Fe3O4/SiO2 and Fe/SiO2 core-shell nanorods. It was observed that Fe3O4/SiO2 and Fe/SiO2 core-shell nanorods exhibited higher coericivities (about 350 Oe and 603 Oe, respectively) than 1-D pure iron-based nanostructures, this was attributed to the reduced inter-particle interaction due to the hindrance of the contact of magnetic nanorods by the outer uniform non-magnetic shells.

關鍵字

氧化鐵 ； 奈米棒

並列摘要

經由混合水解及水熱法成功合成出高產率的α相鐵氫氧化物奈米棒並透過熱差分析(DTA)的結果發現將此奈米棒與過氯酸銨均勻混合之後，能有效地降低過氯酸銨的第二熱分解溫度。由於一維奈米材料具有高表面積比及高深寬比的特性，所以在參與過氯酸銨分解過程中，可以吸附更多的一氧化氮、二氧化氮及氨氣以致α相鐵氫氧化物奈米棒大大地促進過氯酸銨的熱分解效率。再者，當過氯酸銨與α相鐵氫氧化物以重量比為二十五比一混合時，則展現出最好的催化效果，放熱量和熱分解溫度分別增加三點二倍及降低五十度。
第二部分是將α相鐵氫氧化物當做前驅物轉換成二氧化矽包覆四氧化三鐵殼核結構奈米棒。首先使用溶膠凝膠法將二氧化矽均勻的包覆在α相鐵氫氧化物奈米棒外圍，接著昇溫至攝氏五百度然後通氫氣還原，可藉由通入還原氣氛的強弱來控制所生成的相，分別形成使內層發生相轉變成四氧化三鐵或是純鐵及鐵氧化物。經由振動樣品磁儀分析(VSM)得知，此殼核狀奈米棒具有鐵磁的特性，而且矯頑磁場高達三百五十奧斯特(Oe)，這比文獻報導純的鐵磁四氧化三鐵奈米線的矯頑磁場大出七十個奧斯特，二氧化矽包覆純鐵及鐵氧化物其矯頑磁場更是高達六百奧斯特比文獻報導純的鐵奈米線的矯頑磁場大出三百個奧斯特。推論原因是由於外層非磁性的二氧化矽當作內層磁性材料的阻擋物使得磁性粒子間的交互作用因為彼此距離增加而減少，即為所謂的內粒子交互作用。

並列關鍵字

iron oxides ； nanorods

參考文獻

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