Department of Chemistry , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
Department of Geology , State University of New York at New Paltz , New Paltz , New York 12561 , United States.
J Phys Chem A. 2019 Mar 28;123(12):2447-2456. doi: 10.1021/acs.jpca.8b12258. Epub 2019 Mar 12.
Determining the factors that constitute an efficient ice nucleus is an ongoing area of research in the atmospheric community. In particular, surface characteristics such as functional groups and surface defects impact the ice nucleation efficiency. Crystal structure has been proposed to be a possible factor that can dictate ice nucleation activity through the templating of water molecules on the surface of the aerosol particle. If the crystal structure of the surface matches that of the crystal structure of ice, it has been shown to increase ice nucleation activity. In this study, alumina was chosen as a model system because crystal structure and crystallinity can be tuned, and the effect on immersion freezing was explored. The nine alumina samples include polymorphs of AlOOH, Al(OH), and AlO, which have a range of crystal structures and crystallinities. The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) analysis. From the immersion freezing experiments, corundum [α-AlO] was shown to have the highest ice nucleation activity likely because of its high lattice match and high degree of crystallinity. Crystal structure alone did not show a strong correlation with ice nucleation activity, but a combination of a hexagonal crystal structure and a highly crystalline surface was seen to nucleate ice at warmer temperatures than the other alumina samples. This study provides experimental results in the study of ice nucleation of a range of alumina samples, which have possible implications for alumina-based mineral dust particles. Our findings suggest that crystallinity and crystal structure are important to consider when evaluating the ice nucleation efficiency of aerosol particles in laboratory and modeling studies.
确定构成高效冰核的因素是大气科学界正在进行的研究领域。特别是，表面特征，如官能团和表面缺陷，会影响冰核化效率。晶体结构被认为是通过气溶胶粒子表面上水分子的模板化来控制冰核化活性的一个可能因素。如果表面的晶体结构与冰的晶体结构相匹配，则表明其冰核化活性增加。在这项研究中，氧化铝被选为模型体系，因为其晶体结构和结晶度可以进行调节，并探索了其对浸没式冻结的影响。九个氧化铝样品包括 AlOOH、Al(OH)和 AlO 的多晶型物，它们具有不同的晶体结构和结晶度。采用 X 射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、能量色散光谱（EDS）和 Brunauer-Emmett-Teller（BET）分析对样品进行了表征。从浸没式冻结实验中可以看出，刚玉[α-AlO]具有最高的冰核化活性，可能是因为其晶格匹配度高且结晶度高。晶体结构本身与冰核化活性没有很强的相关性，但看到具有六方晶体结构和高结晶表面的组合在比其他氧化铝样品更温暖的温度下引发了冰的形成。本研究为一系列氧化铝样品的冰核化研究提供了实验结果，这可能对基于氧化铝的矿物粉尘颗粒具有重要意义。我们的研究结果表明，在评估气溶胶粒子的冰核化效率的实验室和建模研究中，结晶度和晶体结构是需要考虑的重要因素。
