Characterization of partially sintered ceramic powder compacts using fluorinated gas NMR imaging

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.