Scarpitta S C, Harley N H
U.S. Department of Energy, Environmental Measurements Laboratory, New York, NY 10014.
Health Phys. 1990 Oct;59(4):383-92. doi: 10.1097/00004032-199010000-00001.
Detailed desorption studies using petroleum-based activated charcoals were conducted in monolayers and packed beds. Less extensive studies were conducted on several other types of charcoal. Kinetic studies, using 133Xe, demonstrated the existence of a micropore volume with entrance capillaries that together determined the response characteristics of charcoal to external concentration gradients of tracer gases. This new two-phase model, composed of micropores and entrance capillaries, describes the desorption dynamics of an adsorbed gas in the presence of water vapor. Condensed water vapor in the entrance capillaries of the charcoal reduced the effective pore radius and increased the diffusion half-time. Water could also adversely affect the integrating capability of the charcoal dramatically if the adsorbed water completely blocked the entrance capillaries. The amount of adsorbed water required to block the capillaries varied with the charcoal type and was termed here as the "break-point." The desorption parameters measured in this work can be used to design an improved passive Rn monitor to effectively integrate during a 3-7 d exposure period by eliminating the adverse effects of water vapor. The improved canister design would provide more accurate and reproducible measurements of indoor Rn concentrations than are currently available.
使用石油基活性炭进行了详细的解吸研究，研究在单层和填充床中进行。对其他几种类型的木炭也进行了较少的研究。使用133Xe进行的动力学研究表明，存在具有入口毛细管的微孔体积，它们共同决定了木炭对示踪气体外部浓度梯度的响应特性。这个由微孔和入口毛细管组成的新的两相模型描述了在有水蒸气存在的情况下吸附气体的解吸动力学。木炭入口毛细管中的凝结水蒸气减小了有效孔径并增加了扩散半衰期。如果吸附的水完全堵塞了入口毛细管，水也会对木炭的积分能力产生极大的不利影响。堵塞毛细管所需的吸附水量随木炭类型而异，在此称为“断点”。这项工作中测量的解吸参数可用于设计一种改进的被动式氡监测器，通过消除水蒸气的不利影响，在3至7天的暴露期内有效地进行积分。改进后的滤罐设计将比目前的设计提供更准确、可重复的室内氡浓度测量值。
