Dustiness test of fine and nanoscale powders using a standard rotating drum with a modified sampling train
|摘要:||揚塵特性(dustiness)即為粉體在處理過程中會逸散出粉塵的能力。為了評估奈米粉體與細粉體的揚塵特性，本研究使用歐洲標準化委員會公佈的標準粉體揚塵測試方法－旋轉腔試驗機法，測試德國Degussa公司製造的TiO2奈米粉體(型號為P25)與國內慈陽公司生產的A級ZnO細粉體的逸散特性，實驗時間為1分鐘。接著本研究修改了此方法之採樣系統，在微粒採樣區中接上掃描式電移動度粒徑分析儀(Scanning Mobility Particle Sizer, SMPS)、氣動微粒分析儀(Aerodynamic Particle Sizer, APS)以及多微孔均勻沉積衝擊器(Multiple-Orifice Uniform Deposit Impactor, MOUDI)進行30分鐘的量測。在傳統標準方法的測試結果發現奈米粉體的逸散性比次微米粉體高出很多，TiO2奈米粉體逸散時的可吸入性粉塵、胸腔區粉塵和可呼吸性粉塵質量分率分別為6713±546、576±37和15±2 mg/kg，揚塵等級分別為高等、中等以及低等。ZnO細粉體則分別為142±20、72±6和11±0.3 mg/kg，揚塵等級分別為極低等、低等以及低等。SMPS量測結果發現由旋轉腔試驗機產生出小於100 nm以下的微粒數目很少，代入其粉體密度(TiO2為0.13 g/cm3、ZnO為0.60 g/cm3)，換算成每公斤TiO2或ZnO在30分鐘內所逸散出的平均奈米微粒質量分率僅分別為7.84×10-5和3.72×10-4 μg/kg-min。由SMPS和APS在30分鐘內的量測均發現TiO2與ZnO的微粒逸散量會隨著腔體轉動時間的增加而下降，但微粒數目濃度的分佈型態並無太大的改變，SMPS測得的TiO2數目濃度呈正對數分布，由趨勢線計算得到的微粒數目中間粒徑(number median diameter, NMD)和幾何標準偏差(geometric standard deviation, GSD)分別為356~391 nm和1.7~1.88，APS測得的數目濃度分布並不屬於正對數分布，峰值位置(mode) 由898 nm稍微降至835 nm，約減小7 %。由MOUDI採樣得到100 nm以下的奈米微粒質量濃度近乎於零，此與SMPS監測得到的奈米微粒逸散數據相符，證實不論是次微米級的ZnO粉體或奈米級的TiO2粉體，其奈米微粒的逸散量均非常微少。由於TiO2微粒聚集的結構較鬆散且形狀不規則，造成MOUDI量測的質量濃度分布與APS量測的數目濃度分布再利用粉體密度轉成的質量濃度分布有很大的差異。而ZnO微粒聚集的結構較TiO2緊實，所以MOUDI與APS量測得到的質量濃度分布差異較小。|
Dustiness is defined as the propensity of a material to become airborne when handled. In order to quantify and determine the dustiness of fine and nanopowders, the standard rotating drum tester was used to determine the dustiness of two nanopowders: nano-TiO2 and fine ZnO, in the standard 1-min tests. Then the sampling train was modified to determine the number and mass distributions of the generated particles in the respirable size range using a SMPS (Scanning Mobility Particle Sizer), an APS (Aerodynamic Particle Sizer) and a MOUDI (Multi-orifice Uniform Deposit Impactor) in the 30-min tests. In the standard test, it was found that the dustiness of nanopowder was much higher than submicro-powder. The average inhalable, thoracic and respirable dustiness mass fraction in mg/kg and the dustiness level of TiO2 nanopowder were 6713±546 (high), 576±37 (moderate) and 15±2 (low), respectively, and were 142±20 (very low), 73±6 (low) and 11±0.3 (low) for ZnO submicro-powder. In the modified test, it was found that very few particles below 100 nm were generated from both powders as measured by the SMPS. The average total particle concentrations below 100 nm are only 1.87 and 1.74 #/cm3, which correspond to 7.84×10-5 (assuming TiO2 bulk density is 0.13 g/cm3) and 3.72×10-4 (assuming ZnO bulk density is 0.60 g/cm3) μg/kg-min, for TiO2 and ZnO, respectively. The released rate of particles decreased with increasing rotation time for both nanopowders in the 30-min tests as measured by the SMPS and APS. The shape of the distribution function does not change very much with the NMD (number median diameter) of 356-391 nm and the GSD (geometric standard distribution) of 1.7-1.88 for the SMPS data, and the mode changes slightly from 898 to 835 nm, about 7 %, for the APS data during the 30-min test. The MOUDI data show that nanoparticle emission from the nanoscale and fine powders are negligibly low, which confirms the nearly zero nanoparticle mass concentrations converted from SMPS data. Due to the fluffy structure of the released TiO2 agglomerated particles, the mass distributions measured by the MOUDI showed large differences with those determined by the APS assuming the bulk densities of the powders. The differences were small for the ZnO agglomerates which were more compact than the TiO2 agglomerates.