Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA.
Langmuir. 2010 May 4;26(9):6374-9. doi: 10.1021/la904032p.
Phase behavior of CO(2) confined in porous fractal silica with volume fraction of SiO(2) phi(s) = 0.15 was investigated using small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) techniques. The range of fluid densities (0 < (rho(CO(2)))(bulk) < 0.977 g/cm(3)) and temperatures (T = 22 degrees C, 35 and 60 degrees C) corresponded to gaseous, liquid, near critical and supercritical conditions of the bulk fluid. The results revealed formation of a dense adsorbed phase in small pores with sizes D < 40 A at all temperatures. At low pressure (P < 55 bar, (rho(CO(2)))(bulk) < 0.2 g/cm(3)) the average fluid density in pores may exceed the density of bulk fluid by a factor up to 6.5 at T = 22 degrees C. This "enrichment factor" gradually decreases with temperature, however significant fluid densification in small pores still exists at temperature T = 60 degrees C, i.e., far above the liquid-gas critical temperature of bulk CO(2) (T(C) = 31.1 degrees C). Larger pores are only partially filled with liquid-like adsorbed layer which coexists with unadsorbed fluid in the pore core. With increasing pressure, all pores become uniformly filled with the fluid, showing no measurable enrichment or depletion of the porous matrix with CO(2).
使用小角中子散射（SANS）和超小角中子散射（USANS）技术研究了体积分数为 SiO₂ 的多孔分形二氧化硅中 CO₂ 的相行为，φ（SiO₂）= 0.15。流体密度（0 <（ρ（CO₂））（bulk）< 0.977 g/cm³）和温度（T = 22°C、35°C 和 60°C）的范围对应于本体流体的气态、液态、近临界和超临界条件。结果表明，在所有温度下，尺寸 D < 40 A 的小孔中都会形成致密的吸附相。在低压（P < 55 巴，（ρ（CO₂））（bulk）< 0.2 g/cm³）下，孔中流体的平均密度可能比本体流体的密度高 6.5 倍，在 T = 22°C 时。这个“富集因子”随着温度的升高逐渐降低，但在温度 T = 60°C 时，小孔隙中仍存在显著的流体致密化现象，远高于本体 CO₂的气-液临界温度（T（C）= 31.1°C）。较大的孔仅部分填充具有与孔芯中未吸附流体共存的类液态吸附层。随着压力的增加，所有的孔都被流体均匀地填充，没有可测量的 CO₂对多孔基质的富集或耗尽。
