A. Caprihan et al., Characterization of partially sintered ceramic powder compacts using fluorinated gas NMR imaging, MAGN RES IM, 19(3-4), 2001, pp. 311-317
We use nuclear magnetic resonance (NMR) imaging of C2F6 gas to characterize
porosity, mean pore size, and permeability of partially sintered ceramic (
Y-TZP Yttria-stabilized tetragonal-zirconia polycrystal) samples. Conventio
nal measurements of these parameters gave porosity values from 0.18 to 0.4,
mean pore sizes from 10 nm to 40 nm, and permeability from 4 nm(2) to 25 n
m(2). The NMR methods are based on relaxation time measurements (T-1) and t
he time dependent diffusion coefficient D(Delta). The relaxation time of C2
F6 gas is longer in pores than in bulk gas and it increases as the pore siz
es decrease. NMR yielded accurate porosity values after correcting for surf
ace adsorption effects. A model for T-1 dependence on pore size that accoun
ts for collisions between gas molecules and walls as well as surface adsorp
tion effects is proposed. The model fits the experimental data well. Finall
y, the long time limit of D(Delta)/D-o, where D-o is the hulk gas diffusion
coefficient is useful for measuring tortuosity, while the short time limit
was not achieved experimentally and could not be used for calculating surf
ace-area to volume (S/V) ratios. (C) 2001 Elsevier Science Inc. All rights
reserved.