Rapid characterization of agglomerate aerosols by in situ mass-mobility measurements.
Rapid characterization of agglomerate aerosols by in situ mass-mobility measurements.
复制标题
通过原位质量迁移率测量快速表征附聚物气溶胶。
作者：
J. Scheckman;P. Mcmurry;S. Pratsinis
纳米颗粒团聚体的传输和物理/化学性质取决于初级颗粒尺寸和团聚体结构（尺寸、分形维数和动态形状因子）。本研究报告原位技术测量这些属性。二氧化硅的纳米颗粒团聚体是通过在甲烷/氧气扩散火焰中氧化六甲基二硅氧烷产生的。在离开火焰时，用微分迁移率分析仪（DMA）选择已知电迁移率尺寸的附聚物，并用气溶胶颗粒质量分析仪（APM）测量它们的质量，得到它们的质量分形维数D（f）和动态形状因子chi。扫描和透射电子显微镜（SEM/TEM）图像用于确定初级颗粒直径和定性研究团聚体形态。DMA-APM测量在5%内是可再现的，如通过在相同火焰条件下在不同天的多次测量所确定的。火焰过程变量（氧气流量和大量生产率）对颗粒特性（D（f），和chi）的影响进行了测定。所有生成的颗粒均为分形状团聚体，平均初级颗粒直径为12-93 nm，D（f）= 1.7-2.4。增加氧气流量会降低初级颗粒尺寸和D（f），而增加chi。增加生产速率增加了团聚体和初级颗粒尺寸，并降低了chi而不影响D（f）。氧气流量和颗粒生产率对初级颗粒尺寸的影响，这里报道的是在协议与文献中的非原位测量，而附聚物形状（chi）的工艺变量的影响是第一次证明我们的知识。
Transport and physical/chemical properties of nanoparticle agglomerates depend on primary particle size and agglomerate structure (size, fractal dimension, and dynamic shape factor). This research reports on in situ techniques for measuring such properties. Nanoparticle agglomerates of silica were generated by oxidizing hexamethyldisiloxane in a methane/oxygen diffusion flame. Upon leaving the flame, agglomerates of known electrical mobility size were selected with a differential mobility analyzer (DMA), and their mass was measured with an aerosol particle mass analyzer (APM), resulting in their mass fractal dimension, D(f), and dynamic shape factor, chi. Scanning and transmission electron microscopy (SEM/TEM) images were used to determine primary particle diameter and to qualitatively investigate agglomerate morphology. The DMA-APM measurements were reproducible within 5%, as determined by multiple measurements on different days under the same flame conditions. The effects of flame process variables (oxygen flow rate and mass production rate) on particle characteristics (D(f), and chi) were determined. All generated particles were fractal-like agglomerates with average primary particle diameters of 12-93 nm and D(f) = 1.7-2.4. Increasing the oxygen flow rate decreased primary particle size and D(f), while it increased chi. Increasing the production rate increased the agglomerate and primary particle sizes, and decreased chi without affecting D(f). The effects of oxygen flow rate and particle production rate on primary particle size reported here are in agreement with ex situ measurements in the literature, while the effect of process variables on agglomerate shape (chi) is demonstrated for the first time to our knowledge.