以不同分散方式進行奈米粉體之逸散研究

Abstract

本研究以微小粉末分散器 (Small-Scale Powder Disperser, SSPD) 和漩渦震盪器(vortex shaker)進行奈米材料的粉體逸散特性之研究，並將得到的實驗結果與呂 (2008) 以修正採樣系統之旋轉腔體試驗機法得到的實驗數據進行比較，以了解粉體經不同分散方法產生的微粒粒徑分佈之間的差異。 二氧化鈦、氧化鋅和二氧化矽粉體為本研究選用的奈米粉體，每種粉體皆分成奈米級和次微米級二種。 粉體逸散出來的微粒使用掃描式電移動度粒徑分析儀 (Scanning Mobility Particle Sizer, SMPS) 和氣動微粒分析儀 (Aerodynamic Particle Sizer, APS) 進行量測，得到的微粒數目濃度數據以單位粉體重量產生的微粒數目濃度來表示。 本研究以粉體的顯在密度 (apparent density) 做為微粒的有效密度，將數目濃度分佈轉成質量濃度分佈之後，並與多微孔均勻沉積衝擊器 (Multiple-Orifice Uniform Deposit Impactor, MOUDI) 得到的數據進行比對後，發現APS經轉換後得到的質量濃度分佈與MOUDI得到的結果相近。 三種奈米粉體以MOUDI量測得到的質量中間氣動直徑 (mass median aerodynamic diameters, MMADs) 皆落在微米的粒徑範圍，大小為1.105-2.117 □m。 實驗結果指出SSPD是三種方法中，粉體分散能量最高的方法。 由SSPD和漩渦震盪法的實驗系統得到的SMPS數目濃度數據結果，可以得知奈米二氧化鈦粉體的分散性最好、逸散量最高，接著為次微米級二氧化鈦、奈米氧化鋅、次微米氧化鋅，奈米二氧化矽或是次微米二氧化矽粉體的分散性最差、逸散量最低。 本研究以靜電微粒採樣器來收集200 nm的微粒，之後再以電子顯微鏡的進行觀測。 結果發現，圓球狀初始微粒的二氧化鈦之微粒聚集型態較接近圓球狀，扁平狀初始微粒氧化鋅之微粒聚集型態則為扁長型，圓球狀初始微粒的二氧化矽之微粒聚集型態則呈現短鍊狀。

In the present work, the SSPD (Small-Scale Powder Disperser) and vortex shaker methods were used to investigate the emission characteristics of nanopowders. The test results were compared with the experimental data obtained using a modified sampling train for standard rotating drum (Leu, 2008), to examine the differences of particle size distributions obtained by using different dispersion methods. Titanic dioxide, zinc oxide and silica of nano- and submicron sizes were used as the test materials. A TSI SMPS (Scanning Mobility Particle Sizer) and a TSI APS (Aerodynamic Particle Sizer) were used to measure particle size distributions of the dispersed powders. Using the apparent density of nanopowders to convert the number distributions of the SMPS and APS into the mass concentration distributions, it was found that the mass distributions agreed with those measured by the MOUDI (Multiple-Orifice Uniform Deposit Impactor). The mass meadian aerodynamic diameters (MMADs) measured by the MOUDI, which ranged from 1.105-2.117 □m for the three nanopowders, were found to fall in the supermicron range. Experiment results indicate that the SSPD is the most energetic powder dispersion method among the three different methods. From the SMPS number distribution data of the SSPD and vortex shaker, titanic dioxide nanopowder was found to have the highest dispersity and the emission concentration than the other materials, followed by titanic dioxide fine powder, zinc oxide nanopowder and zinc oxide fine powder. Silica nano powder or silica fine nanopwder had the least dispersity and the emission concentration. Using an electrostatic particle sampler to collect 200 nm particles for observation under the SEM, it was found that the agglomerates of titanic oxide nanoparticles were isometric and the primary particles were spherical, the agglomerates of zinc oxide nanoparticles were isometric and the primary particles were flake-shaped, while slica nanoparticles were short chain-like shaped and the primary particles were spherical.