Surface areas and porosities of ices used to simulate stratospheric clouds
Surface areas and porosities of ices used to simulate stratospheric clouds
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用于模拟平流层云的冰的表面积和孔隙率
DOI：
10.1006/jcis.1993.1018
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
M. Leu
中科院分区：
文献类型：
--
作者：
L. F. Keyser;M. Leu
摘要利用气相沉积形成的低温冰作为平流层冰云的实验室模拟。为了获得这些冰的内在反应性，需要得到它们物理结构的详细信息。表面积由气体吸附等温线的BET分析得到。堆积密度和孔隙率是用摄影测量法测定的。扫描电子显微镜被用来获得颗粒大小和研究冰在不同温度下的形态。在低于200 K的温度下由水蒸气沉积的水冰和HNO3-H2O冰膜表现出较大的BET表面积和高度多孔性。当这些冰在200 K以上加热退火时，BET表面积大幅减少，而堆积密度或颗粒大小没有大的变化。对于退火后的冰，由观测到的颗粒尺寸计算的外表面积与BET面积相当吻合。这证明了退火后的冰是由无孔颗粒组成的，这些冰的多孔性是由于颗粒之间的间隙造成的。对于未退火的冰，在200 K时，BET表面积几乎比外部面积大一个数量级；这表明这些冰是由内部有孔隙的颗粒组成的。对未退火冰进行孔径分析，得到内部或孔表面积。在200k时，外表面和内表面面积的总和仅占BET面积的30-40%左右，这表明BET值的一部分可能是由于孔隙填充造成的，因此在这种情况下不能被认为是真正的表面积。
Abstract Low temperature ices formed by deposition from the vapor phase are used as laboratory simulations of stratospheric ice clouds. To obtain intrinsic reactivities of these ices, detailed information on their physical structure is required. Surface areas are obtained from BET analysis of gas adsorption isotherms. Bulk densities and porosities are determined photogrammetrically. Scanning electron microscopy is used to obtain particle sizes and to study the morphology of the ices at several temperatures. Water ice and HNO3-H2O ice films deposited from the vapor at temperatures below 200 K exhibit large BET surface areas and are highly porous. When these ices are annealed by warming above 200 K, a large decrease in BET surface area occurs without any large change in bulk density or particle size. For the annealed ices, external surface areas calculated from the observed particle sizes agree reasonably well with the BET areas. This is evidence that the annealed ices are composed of nonporous particles and that the porosity of these ices is due to interstices among the particles. For unannealed ices at 200 K, the BET surface areas are almost an order of magnitude higher than the external areas; this indicates that these ices are comprised of particles which have internal porosity. Pore size analysis of the unannealed ices yields internal or pore surface areas. At 200 K, the sum of the external and internal surface areas accounts for only about 30-40% of the BET area and suggests that part of the BET value may be due to pore filling and, thus, cannot be considered a true surface area in this case.