核磁共振成像原位监测冰融化及四氢呋喃水合物分解的微观过程

核磁共振成像(Magnetic Resonance Imaging,MRI)可以通过物质在不同相态之间的亮度差别来识别物质相态的变化,冰、水和水合物之间较大的亮度对比使MRI成为监测水合物生成分解动态过程的有效工具.采用MRI原位监测了冰融化和四氢呋喃(THF)水合物分解的微观过程,从微观角度对比研究了THF水合物分解与冰融化过程的异同.冰融化和THF水合物的分解过程受传热程控,冰的融化和水合物的分解总是沿着固-液界面从外向内推进,消解速度持续加快.固相表面的"结构化水层"是冰和水合物立体结构瓦解的主要原因.THF水合物的分解过程与气体水合物不同,没有明显的"自保护效应".由于温度梯度产生的密度差异,液相产生自然对流,造成了水合物的分解及冰的融化过程中固-液界面运动的随机性.

In Situ Monitoring Ice Melting and Tetrahydrofuran Hydrates Dissociation with Magnetic Resonance Imaging

Due to large intensity contrast between the images of the liquid components and the solid hydrate,as well as water and ice,Magnetic Resonance Imaging(MRI)becomes a very effective tool for monitoring hydrate decomposition and ice melting.In order to perform the comparative studies on the THF hydrate dissociation and ice melting from a microcosmic aspect,MRI was employed in in-situ monitoring tetrahydrofuran(THF)hydrate decomposition and ice melting.The hydrate dissociation and ice melting always occurred at the surface of the solid phase,developing from external to internal and the elimination rate of the solid phase continued to increase.The "structured liquid water" on the hydrate and ice surface is the main cause of destructing the solid clathrate structure and ice crystal structure.Different from the gas hydrates,the THF hydrate self-preservation is not conspicuous during the dissociation processes.Due to the difference of the density resulted in the gradient of the temperature,natural convection take place in the liquid phase,and consequently the moving of the interface between solid phase and liquid phase is random during the hydrate dissociation and ice melting.