Capillary condensation of nitrogen in MCM-41 and SBA-15

被引:138
作者
Morishige, K [1 ]
Ito, M [1 ]
机构
[1] Okayama Univ Sci, Dept Chem, Okayama 7000005, Japan
关键词
D O I
10.1063/1.1510440
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We performed measurements of a series of adsorption-desorption isotherms of nitrogen into MCM-41 and SBA-15 mesoporous molecular sieves with different pore sizes in a wide temperature range between a bulk triple point (T-t) and a bulk critical point (T-c). The hysteresis loop shrinks with increasing temperature and eventually disappears at the hysteresis critical temperature (T-ch), in accord with the appearance of metastable states in a single pore. We estimated the exact pore sizes of our samples from comparing the experimental equilibrium pressure at 77 K with the NLDFT isotherms, where the condensation pressures at 77 K were determined by extrapolating a plot of the equilibrium pressure versus temperature measured above T-ch. The pore critical temperature (T-cp) was also determined from the inflection point in a plot of the inverse slope of the adsorption step against temperature. T-ch is always lower than T-cp. Both plots of (T-c-T-ch)/T-c versus d/r(p) and (T-c-T-cp)/T-c versus d/r(p) form straight lines passing through the origin, where d is the molecular diameter, although the former plot deviate from the linear relationship at large pores; T-ch approaches T-cp in large pores. This strongly suggests that in large pores the energy barrier from the metastable state to the stable state is too large to be overcome within the period of observations even at the high temperatures just below T-cp. (C) 2002 American Institute of Physics.
引用
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页码:8036 / 8041
页数:6
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