Water vapor absorption in porous media polluted by calcium nitrate studied by time domain nuclear magnetic resonance.
Water vapor absorption in porous media polluted by calcium nitrate studied by time domain nuclear magnetic resonance.
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时域核磁共振研究硝酸钙污染多孔介质中的水蒸气吸收。
DOI：
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发表时间：
2009
影响因子：
3.3
通讯作者：
P. Fantazzini
中科院分区：
文献类型：
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作者：
M. Gombia;V. Bortolotti;R. Brown;M. Camaiti;L. Cavallero;P. Fantazzini
采用核磁共振弛豫分析方法，选取具有相似成分（碳酸盐岩）和不同孔隙结构，且受硝酸钙污染的真实多孔介质中液态水(1)H核，研究孔隙空间内水缩合和盐溶解的动力学。这些现象是多孔材料暴露在潮湿大气中受到污染的环境损伤时劣化的原因。该理论在简单孔隙几何结构中得到了很好的描述，但在具有广泛孔隙尺寸和连接分布的实际多孔介质中尚未得到很好的理解。通过T(1)和T(2)弛豫时间分布，在时间上跟踪孔隙空间内液态水的形成。这些分布使人们可以看到盐浓度和孔隙空间结构对水蒸气凝结量及其动力学的影响。结果表明，对于给定的岩型，即使污染物的量不同，速率-平均弛豫时间T（1ra）也随核磁共振信号的增加而单调增加，与液态水的量成正比。T（1ra）常与表面体积比成反比。这表明随着液态水含量的增加，孔隙有增大的趋势，但并不表明孔隙有严格的顺序填充，按大小顺序从最小的开始；事实上，松弛时间分布清楚地表明，情况并非如此。盐量的增加导致吸水率和吸水量的显著增加。对含水量的核磁共振测量，加上弛豫时间分布，提供了暴露在潮湿大气中但不受液态水影响的多孔材料污染影响的信息，甚至在吸收大量水分和随后的破坏之前。这些现象在其他领域也很重要，例如地热能的开发。
Nuclear magnetic resonance relaxation analysis of liquid water (1)H nuclei in real porous media, selected for their similar composition (carbonate rocks) and different pore space architecture, polluted with calcium nitrate, is presented to study the kinetics of water condensation and salt deliquescence inside the pore space. These phenomena are responsible for deterioration of porous materials when exposed to environmental injury by pollution in a humid atmosphere. The theory is well described for simple pore geometries, but it is not yet well understood in real porous media with wide distributions of pore sizes and connections. The experiment is performed by following in time the formation of liquid water inside the pore space by T(1) and T(2) relaxation time distributions. The distributions allow one to see the effects of both the salt concentration and the pore space structure on the amount of water vapor condensed and its kinetics. It is shown that, for a given lithotype, even with different amounts of pollutant, the rate-average relaxation time T(1ra) tends to increase monotonically with NMR signal, proportional to the amount of liquid water. T(1ra) is often inversely associated with surface-to-volume ratio. This suggests a trend toward the filling of larger pores as amounts of liquid water increase, but it does not indicate a strict sequential filling of pores in order of size and starting with the smallest; in fact, relaxation time distributions show clearly that this is not the case. Increased amounts of salt lead to both markedly increased rates and markedly increased amounts of water absorption. NMR measurements of amounts of water, together with relaxation time distributions, give the possibility of information on the effect of pollution in porous materials exposed to humid atmospheres but sheltered from liquid water, even before the absorption of large amounts of moisture and subsequent damage. These phenomena are of importance also in other fields, such as the exploitation of geothermal energy.