| 摘要: | 摘 要 氣相合成法在奈米粉體合成技術中相對優勢較大，本研究利用熱電漿作為奈米粉體氣相合成之熱源，嘗試自行組裝一熱電漿奈米微粒製備機台。在研究過程中，我們總共組裝三套系統，第一套「電弧系統」雖可產生奈米微粒，但由於製程中有大量焊渣產生，且生成的粉體易形成硬團聚結構，因此將系統更改為「非傳輸型熱電漿-管狀反應器」。第二套系統生成粉體的測試中，由於反應器斷面積、容積太小（斷面積9.5 cm2；容積0.95 L），不利冷卻氣體與電漿氣流混合，加上冷卻氣體僅從單一方向注入，使得混合不均勻，造成冷卻效果不佳、微粒成長距離長，因而生成之微粒粒徑分布極廣。為改善冷卻效果，進一步將反應器變更為斷面積、容積較大（斷面積900 cm2；72 L）之水冷不鏽鋼反應器，稱之為APTPR（atmospheric pressure thermal plasma reactor），經測試比較，APTPR確能有效縮短微粒成長區間，生成奈米微粒。 接著探討不同的操作條件如何影響APTPR生成微粒之粒徑與相態，包括進料方式、進料速率、電漿功率、冷卻氣體流量與系統壓力等，此部份是以氯化法生成二氧化鈦為例。實驗發現，從火炬內進料可得晶相（金紅石為主）之二氧化鈦，但其粒徑分布較寬，約10~40 nm；從電漿焰側邊進料可得非晶相之二氧化鈦，其粒徑均一，約9 nm左右。於粒子尺寸操控方面，四氯化鈦進流流量愈大，則生成微粒比表面積愈小，從0.41 lpm之179 m2/g下降到0.59 lpm之93 m2/g。 為進一步提升製程之完整性，研究中亦嘗試以超音波技術分散自行合成的奈米粉體，實驗發現，分散劑DT-760之最佳添加濃度為0.5%，同時因為相對之空穴強度較強，建議以20,000 Hz之超音波作為粒子分散時之機械力來源；而隨著能量密度增加，分散效果愈顯著。 Abstract Generation of nonoparticles via gas-phase reaction has many advantages over other methods. This study utilizes thermal plasma as the energy source for nanoparticles synthesis and aims to develop a thermal plasma system to synthesize nanoparticles. Three devices have been developed for the purpose. Although the first one is capable of producing nanoscale particles, a lot of welding slags are produced during the process and the obtained particles are apt to form hard aggregates. Therefore, another system based on non-transferred thermal plasma is developed. Due to small cross section and volume, corresponding to 9.5 cm2 and 0.95 L, the quenching gas and plasma gas cannot be well mixed. Besides, the fact that the quenching gas is injected in one direction causes the cooling performance is not good enough for obtaining narrow particle size distribution. In order to improve the cooling performance, a water cooling steel reactor with larger cross section (900 cm2) and volume (72 L) is designed and constructed and named as APTPR (atmospheric pressure thermal plasma reactor). Compared with the results obtained with the senond system, APTPR can effectively narrow down particle size distribution. The influences of several operating parameters, including precursor feeding way, feeding rate, plasma power, flow rate of quenching gas and pressure on particle sizes and crystal form are investigated in this study. The experimental results indicate that the TiO2 powder synthesized by TiCl4 fed through plasma torch is mainly rutile. However, the particles size distribution is broader, about 10-40 nm. Amorphous TiO2 particles with uniform size, corresponding to 9 nm, can be obtained while TiCl4 is injected into plasma jet. Moreover, a higher feeding flow rate of TiCl4 results in the smaller specific surface area of the particles. The specific surface area obtained using flow rate of 0.41 and 0.59 lpm are 179 and 93 m2/g, respectively. To overcome particle agglomeration problem, dispersion of the original particles via supersonic technique is conducted in this study as well. Experimental results indicate the optimal concentration of surfactant DT-760 is 0.5%. Due to the higher strength of cavitation, using audio frequency of 20,000 Hz as the mechanical source is suggested. Dispersion of generated particles is better as a higher energy density is applied. |
