Abstract:

Nano self-assembled γ-Al₂O₃, having two kinds of nano-scale pore structures, which can be used as a catalyst carrier suitable for large molecule diffusion and shale gas reservoir models. Characterization of the pore structures in nanomaterials are scanning electron microscopy, nitrogen adsorption method, mercury injection method, etc. These characterization techniques have their own limitations. This paper utilized nuclear magnetic resonance (NMR) relaxation measurements to study and quantitatively characterize the pore structures of nano self-assembled γ-Al₂O₃. Random walker simulation and error function analysis were used to explore the surface relaxation strength and pore size distribution of nano self-assembled γ-Al₂O₃. The random walker simulation results show that the main apertures of nano self-assembled γ-Al₂O₃ are 5-7 nm and 30-42 nm; NMR experiments through error function analysis show that the main apertures of the nano self-assembled material are 5-9 nm and 29-47 nm. Nitrogen adsorption only characterized the microporous, mesoporous, and part of the macroporous structures. The pore diameters greater than 100 nm cannot be detected by the nitrogen adsorption method. The mercury injection method characterizes apertures of size less than 10 nm relatively inaccurately. Nuclear magnetic relaxation can comprehensively characterize bimodal pore system of nano self-assembled γ-Al₂O₃ of size 2.8-315 nm. As one of the NMR measurements, the T₂ spectrum signal amplitude ratio of three samples, S-1, S-2 and S-3 are 0.603, 1.15, 1.84, directly reflect the variety of their micropores and mesopores chemical Al₂O₃ material ratio 0.85, 1.38, 1.7 respectively. The suggested method can be applied to the investigation for shale gas pore structure and associated mechanisms.

Key words: Pore distribution, Nuclear magnetic relaxation, Radom walker, Error function analysis, Nano self-assambly