兩種不同方法產生的奈米銀微粒之特性分析

Abstract

本研究以蒸發/冷凝法與恆定霧化法產生奈米銀，並以高溫爐控制奈米銀團粒的形貌，研究奈米銀團粒的電移動度直徑(dm, mobility diameter)、質量、肺胞區沉積表面積濃度及形貌的關係。由微粒電移動度直徑與有效密度變化的結果顯示，不論是蒸發/冷凝法與恆定霧化法產生的奈米銀微粒經燒結後，微粒的dm與有效密度的變化趨勢都可以分為三個階段：蒸發/冷凝法的第一階段燒結溫度24 -100℃，奈米微粒燒結情況不明顯，dm變小一些但不明顯，微粒有效密度的變化也非常小；第二階段燒結溫度100-200℃時，燒結情況明顯，dm快速變小，微粒形貌漸趨於圓球且微粒有效密度也快速提升；第三階段燒結溫度200-800℃，微粒直徑變化不大，有效密度緩慢升上且接近銀塊材密度。此結果與Weber and Friedlander (1996)和Shin et al. (2010)相同。而噴霧法的結果受到微粒包覆的介面活性劑的影響燒結溫度到達400℃時才開始有明顯的直徑變化。 根據微粒電移動度直徑變化的結果，本研究參考Weber and Friedlander (1996)的方法算出微粒的碎形微度(Df, fractal dimension)，在燒結溫度為24-300℃時，Df由1.98上升至2.87，在高於300℃後，Df已非常接近3且不再變化。由TEM影像分析結果，本研究發現奈米銀團粒的dm與等似投影面積直徑(dproj)會非常接近，並且得知平均最大長度(Lavg)與dproj的關係為Lavg~dproj1.20，與Shin et al. (2009)的實驗結果接近。DMA-APM系統得知微粒的動力形狀因子( dynamic shape factor)，當燒結溫度由室溫提升至300℃時，微粒的動力形狀因子皆明顯降低，平均值由3.65降低至1.08。由AeroTack 9000量測出的肺胞區沉積表面積濃度的測值與理論計算值的比較結果顯示，銀微粒形貌由不規則狀變為圓球狀時，表面積形狀因子(κs)會越來越接近1。

In this work, the nano-silver agglomerates and silver colloid generated using evaporation/condensation method and constant output atomizer, respectively. Here a tubular furnace was used to change the morphology of the nano-silver particles. A scanning mobility particle sizer (SMPS), aerosol particle mass analyzer (AMP), Aerotrak 9000 were used to measure the particulate size distribution, mass, alveolar deposited surface area concentration. Agglomerates with mobility diameter in the range from 30-300 nm was sampled using the microorifice-based concentrated nanoparticle sampler (CNS) and then imaged by transmission electron microscopy (TEM). The results showed that number median diameter (NMD) and effective density of silver agglomerates were affected by the morphology. The NMD reduced significantly at 100-200℃, but varied a little for sintering temperature above 200℃. The effective density increased with the sintering temperature was increased, and approached to bulk density of 10.53 g/cm3 at 800℃. We found that NMD and effective density of silver colloid decreased for sintering temperature above 400℃ due to the evaporation of the surfactants. From these measurements, it was found that the fractal dimension (Df) varied from 1.98 to 3.00 as the sintering temperature was increased from ambient to 300℃. This phenomenon was caused by sintering process, followed by partial and complete coalescence of fractal-like agglomerates into spheres. As the TEM images, it was found that the silver agglomerates generated by evaporation/condensation method were formed with several primary particles and irregular, but silver colloids generated by constant output atomizer were coated with the surfactant and close to spherical. We obtained the relationship between the projected area equivalent diameter (dproj) and maximum length (Lavg) can be expressed as Lavg~dproj1.20. To compare the actual values measured by the TSI Aerotrak 9000 and the calculated particle surface area concentration, the number distribution and the lung deposition curves in the alveolar region for reference worker of ICRP Model was used. The results showed that the average surface area shape factor of the evaporation/condensation and constant output atomizer for all sizes were 1.09±0.15 and 9.83±0.05, respectively.