Abstract
To study the freezing/melting behavior of a confined N2, CO, and Kr, we performed X-ray diffraction measurements of N2, CO, and Kr confined inside the cylindrical pores of five kinds of siliceous MCM-41 with different pore radii (R = 1.45−2.9 nm) as a function of temperature. Freezing and melting of these three molecules were almost reversible for all the MCM-41 samples used here. Freezing of the CO confined to the mesopores resulted in the appearance of the orientationally ordered α phase, whereas the N2 solidified into the orientationally disordered phase analogous to the bulk β phase. The solid Kr confined to the mesopores contains a considerable amount of random stacking faults. The freezing-point depressions of N2 and CO relative to the bulk melting point were nearly the same and were slightly larger than that of Kr. Upon cooling, both molecular liquids of N2 and CO confined to the cylindrical mesopores of R = 2.1 nm vitrify, whereas liquid Kr crystallizes within the mesopores of R = 1.8 nm and vitri...
Published Version
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