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Origin of melting point depression for rare gas solids confined in carbon pores
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2015-07-21 11:27:42 , DOI: 10.1063/1.4927143
Kunimitsu Morishige 1 , Takaaki Kataoka 1
Affiliation  

To obtain insights into the mechanism of the melting-point depression of rare gas solids confined in crystalline carbon pores, we examined the freezing and melting behavior of Xe and Ar confined to the crystalline pores of ordered mesoporous carbons as well as compressed exfoliated graphite compared to the amorphous pores of ordered mesoporous silicas, by means of X-ray diffraction. For the Xe and Ar confined to the crystalline carbon pores, there was no appreciable thermal hysteresis between freezing and melting. Furthermore, the position of the main diffraction peak did not change appreciably on freezing and melting. This strongly suggests that the liquids confined in the carbon pores form a multilayered structure parallel to the smooth walls. For the Xe and Ar confined to the amorphous silica pores, on the other hand, the position of the main diffraction peak shifted into higher scattering angle on freezing suggested that the density of the confined solid is distinctly larger than for the confined liquid. Using compressed exfoliated graphite with carbon walls of higher crystallinity, we observed that three-dimensional (3D) microcrystals of Xe confined in the slit-shaped pores melted to leave the unmelted bilayers on the pore walls below the bulk triple point. The lattice spacing of the 3D microcrystals confined is larger by ∼0.7% than that of the bilayer next to the pore walls in the vicinity of the melting point.

中文翻译:

限制在碳孔中的稀有气体固体的熔点降低的起源

为了深入了解封闭在结晶碳孔中的稀有气体固体的熔点降低的机理,我们研究了Xe和Ar的冻结和熔化行为,该行为受限于有序介孔碳以及压缩的脱落石墨的结晶孔。通过X射线衍射,可以观察到有序介孔二氧化硅的无定形孔。对于Xe和Ar局限于结晶碳孔,在冻结和熔化之间没有明显的热滞后。此外,主衍射峰的位置在冷冻和熔化时没有明显变化。这有力地表明,封闭在碳孔中的液体形成了平行于光滑壁的多层结构。另一方面,对于Xe和Ar限制在无定形二氧化硅孔中,冷冻时主衍射峰的位置移到更高的散射角,表明密闭固体的密度明显大于密闭液体的密度。使用具有更高结晶度碳壁的压缩片状石墨,我们观察到Xe的三维(3D)微晶体被限制在狭缝形孔中熔化,从而在未膨胀的三点以下的孔壁上留下未熔融的双层。所约束的3D微晶的晶格间距比熔点附近紧邻孔壁的双层的晶格间距大〜0.7%。我们观察到,局限于狭缝状孔中的Xe三维(3D)微晶融化,从而在孔壁上的三重体以下留下了未熔融的双层。所约束的3D微晶的晶格间距比熔点附近紧邻孔壁的双层的晶格间距大〜0.7%。我们观察到,局限于狭缝状孔中的Xe三维(3D)微晶融化,从而在孔壁上的三重体以下留下了未熔融的双层。所约束的3D微晶的晶格间距比熔点附近紧邻孔壁的双层的晶格间距大〜0.7%。
更新日期:2015-07-22
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