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Structural changes of CAST soot during a thermal–optical measurement protocol

机译：热光学测量协议过程中铸造煤的结构变化

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摘要

Thermal–optical measurement techniques are widely used to classify carbonaceous material. The results of different methods for total carbon are comparable but can vary by 44 % for elemental carbon. One major cause of variation is the formation of pyrolyzed carbon during the heating process which occurs mainly in samples with a high amount of brown carbon (BrC). In this study the structural changes of two different CAST (combustion aerosol standard) aerosol samples caused by the heating procedure in a thermal–optical instrument were investigated with UV–VIS and Raman spectroscopy, the integrating-sphere technique (IS) and transmission electron microscopy. All analysis techniques showed significant structural changes for BrC-rich samples at the highest temperature level (870 °C) in helium. The structure of the heated BrC-rich sample resembles the structure of an unheated BrC-poor sample. Heating the BrC-rich sample to 870 °C increases the graphitic domain size within the material from 1.6 to 2 nm. Although the Raman spectra unambiguously show this increase in ordering only at the highest temperature step, UV–VIS and IS analyses show a continuous change in the optical properties also at lower temperatures. The sample with a negligible amount of BrC, however, did not show any significant structural changes during the whole heating procedure.
机译：热光学测量技术广泛用于分类碳质材料。对于总碳的不同方法的结果是可比的，但元素碳的含量可以变化> 44％。变异的一个主要原因是在加热过程中形成热解碳，其主要发生在具有大量棕色碳（BRC）的样品中。在这项研究中，用UV-VIS和拉曼光谱研究了由热光学仪器中的加热过程引起的两种不同铸造（燃烧气溶胶标准）气溶胶样品的结构变化，整合 - 球体技术（IS）和透射电子显微镜。所有分析技术均显示出在氦气最高温度（870℃）的BRC富含样品的显着结构变化。加热的BRC的样品的结构类似于未加热的BRC差的样品的结构。将BRC的样品加热至870°C将材料域尺寸从1.6〜2nm增加。尽管拉曼光谱明确地显示在最高温度步骤中的顺序下的这种增加，但是UV-Vis和分析显示在较低温度下也显示光学性质的连续变化。然而，具有可忽略量的BRC的样品在整个加热过程中没有显示出任何显着的结构变化。

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