标题： 超声波在吸水性碳气凝胶中的传播 显示英文标题

标题： Ultrasound Propagation in Water-Sorbing Carbon Xerogel

摘要： 水蒸气在纳米多孔碳中的吸附相当复杂，这是由于材料的孔结构和表面化学之间的相互作用。 解密吸附机制需要了解吸附水的空间分布和填充分数。 超声波通过纳米多孔样品传播的特性提供了大量信息，例如限制在孔中的流体性质以及吸附质在孔中的空间分布。 在这里，我们研究了水蒸气在碳气凝胶上的吸附，该气凝胶具有双峰孔径分布，包括微孔（1 nm）和介孔（8 nm），总体孔隙率为68%。 相对湿度分步增加，并在每一步测量样品吸附的水量，通过重量法测定，生成了一种V型等温线，这是弱相互作用碳纳米孔吸附水的特征。 同时，在每个饱和步骤中记录了纵向和横向超声波通过样品的波形。 这些测量提供了波幅和速度作为相对湿度的函数，这些数据用于计算气凝胶-水复合材料的弹性模量和超声衰减。 弹性模量演变的分析表明，受限水在介孔中表现出几乎与块体相似的性质，而在微孔中其模量明显不同于块体水，这与理论预测一致。 此外，在微孔填充过程中观察到的超声衰减增加表明了整个样品体积内水填充孔空间的时空异质性。 总体而言，这项研究展示了无损超声检测在探测纳米多孔介质中的流体吸附机制和吸附相性质方面的成功应用。 显示英文摘要

摘要： Adsorption of water vapor in nanoporous carbons is rather complex due to an interplay between the pore structure and surface chemistry of these materials. Deciphering the mechanism of adsorption requires the knowledge of the spatial distribution and the filling fraction of the adsorbed water. Characteristics of ultrasonic wave propagation through a nanoporous sample provides a wealth of information such as properties of fluids confined in the pores and spatial distribution of adsorbate in the pores. Here we studied water vapor adsorption on carbon xerogel, with a bimodal pore size distribution consisting of micropores (1 nm) and mesopores (8 nm) and overall porosity 68%. The relative humidity was increased in steps and the amount of water adsorbed by the sample was measured gravimetrically at each step, producing a type V isotherm, characteristic of water adsorption to weakly interacting carbon nanopores. Concurrently, we recorded the waveforms for longitudinal and transverse ultrasonic waves that passed through the sample at each saturation step. These measurements provided the wave amplitudes and speeds as a function of relative humidity, and these data were used to calculate the elastic moduli and ultrasonic attenuation of the xerogel-water composite. Analysis of the elastic moduli evolution suggested that confined water shows nearly bulk-like properties in mesopores, while in micropores its modulus noticeably differs from that of bulk water, consistent with theoretical predictions. Furthermore, the observed increase in ultrasonic attenuation during micropore filling indicated the spatial heterogeneity of the water-filled pore space within the overall sample volume. Overall, this study demonstrates the successful utilization of nondestructive ultrasonic testing to probe the fluid adsorption mechanism in a nanoporous medium and the properties of adsorbed phase.