bundle was removed from the fabric and embedded in medium if a first order reaction for the ZrO2 deposition resin(G-1 Epoxy, GATAN Inc ) After breaking the is assumed. 8 embedded bundle the thickness of the coatings on the single fibers could be measured by SEM. In each sample j=-g dx dc approx 80 single fibers taken at random in the bundle (3) were measured. The resulting thickness distributions are shown in Fig. 6. It shows that the thickness on the fibers e is the porosity of the fiber bundle produced by the is more constant at lower temperatures. This can be fibers, D is the gas diffusion coefficient of the precursor expected because the depletion in the gas phase crea in the carrier gas, c is the molar concentration of the ses with the temperature. The thickness distribution can precursor in the gas phase, q is the tortuosity, j is the be explained by Fick's law for the diffusion in a porous current diffusion density related to the cross-section of 1,E04 380°c370°c360°c350°C340°c330°c320°c310°c 0EE 1E-05 deposition rate related to the fiber surface 1,50E03 1.55E03 1,60E03 1,70E03 175E03 deposition tempeture 1/T[1/K ◆ Nextel720■A2O3 Fig. 5. Deposition rate of ZrO2 from Zrfacac) vs reciprocal deposition temperature on the Nextel 720 fiber fabric and on Al2O]wafer(P=500 Pa, ow=200 sccm argon) 100% 56cE品 g巽50% layer thickness [ur 士T=310°C一T=330°C一T=340%"T=370°C Fig. 6. Cumulated distribution of layer thickness in a single fiber bundle (80 fibers measured for each bundle)bundle was removed from the fabric and embedded in resin (G-1 Epoxy, GATAN Inc.). After breaking the embedded bundle the thickness of the coatings on the single ®bers could be measured by SEM. In each sample approx. 80 single ®bers taken at random in the bundle were measured. The resulting thickness distributions are shown in Fig. 6. It shows that the thickness on the ®bers is more constant at lower temperatures. This can be expected because the depletion in the gas phase decrea￾ses with the temperature. The thickness distribution can be explained by Fick's law for the di€usion in a porous medium if a ®rst order reaction for the ZrO2 deposition is assumed.8 j ˆ ÿ " q D dc dx …3† " is the porosity of the ®ber bundle produced by the ®bers, D is the gas di€usion coecient of the precursor in the carrier gas, c is the molar concentration of the precursor in the gas phase, q is the tortuosity, j is the current di€usion density related to the cross-section of Fig. 5. Deposition rate of ZrO2 from Zr(acac)4 vs reciprocal deposition temperature on the Nextel 720 ®ber fabric and on Al2O3-wafer (P=500 Pa, ¯ow=200 sccm argon). Fig. 6. Cumulated distribution of layer thickness in a single ®ber bundle (80 ®bers measured for each bundle). K. Nubian et al. / Journal of the European Ceramic Society 20 (2000) 537±544 541