Phys. Rev. Lett. 67, 2585–2588 (1991)Surface and bulk tortuosity of porous ceramics near the percolation thresholdReceived 3 June 1991; published in the issue dated 28 October 1991 The surface and bulk tortuosities of sintered Al2O3 ceramic samples have been measured using third- and fourth-sound propagation in superfluid 4He as a probe. Near the pore-space percolation threshold the index of refraction of both sound modes is found to increase rapidly as the porosity is lowered, to much higher values than previously observed. The bulk tortuosity exceeds the surface tortuosity for porosities below 30%, a reversal of the behavior observed at high porosity. © 1991 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.67.2585
DOI:
10.1103/PhysRevLett.67.2585
PACS:
81.35.+k, 67.40.Hf, 67.40.Pm, 81.60.Dq
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