“…For example, a diffusion method in which the effective diffusivity was measured directly, such as the measurement of diffusion flux, was performed by Kwon et al [2]. Furthermore, the diaphragm method was used by Kawazoe et al [3], Henry et al [4], and Masamune and Smith [5], a separation membrane method by Hamai and Mitani [6] and Gibilaro and Waldram [7], and a method with an yttrium-stabilized zirconia oxygen sensor was used by Mezedur et al [8]. A zirconia-type oxygen sensor is based on the principle that oxygen ion transfer in zirconia produces an electric current; however, this sensor is generally used at temperatures above 300 °C and it is difficult to obtain measurements of microporous materials under wet conditions where liquid water is present in some of the micropores.…”