Aluminum oxide diffusion coefficient

Yu, G.T. and S.K. Yen, Determination of the diffusion coefficient of proton in CVD gamma aluminum oxide thin films. Surface and Coatings Technology, 166, 195 (2003). 

Scully et al. have reviewed the available data on H solubility and permeability in A1 and some of its alloys. Their review shows tremendous variability in the available data. However, H is very insoluble in A1 at 25°C and 1 atm pressure, with values ranging from 10 to 10 " atom fraction. They also concluded from data for A1 alloys that Li and Mg alloying additions increased the solubility of H in A1 because of their chemical affinity for H. A summary of the H diffusivity in A1 also revealed a wide range in values, but if it is assumed that the presence of aluminum oxide (AI2O3) on the surface is likely under all these tests, the fastest diffusivity is expected to be that closest to bulk diffusivity in Al, because this likely results from material with a defective or thinnest oxide film. There are several studies that resulted in diffusion coefficients at 25°C of about 10 cm /sec for Al. 

A novel one-sided NMR magnet has been developed for self-diffusion measurements in thin samples [7]. Using this technique, researchers have demonstrated measurements in bulk [BMIM][TFSI] and [BMIM][TFSI] confined in nanoporous anodized aluminum oxide membranes, as shown in Fig. 3. This operates at a proton Larmor frequency of 14.08 MFlz, and the expected appHcation is toward in situ measurements in portable energy devices. This method utilizes the fringe field to measure diffusion coefficients instead of conventional PFG-NMR. 

The self-diffusion coefficient of A1 was determined in polycrystalline aluminum oxide at 1670 to 1905C. Diffusion couples were employed which used in oxide form as a radioactive tracer. Within the above temperature range, the experimental data were represented by ... 

Kingery et al. [10a] have collected the experimental results for cation and anion self-diffusion coefficients in various oxides. For instance, the rate of diffusion of copper in CU2O, a modifier, is six orders of magnitude larger than that of aluminum in AI2O3, a network former when the aluminum is four coordinate. This result is for a temperature of approximately 1500°C, but the relative relationship is expected to hold at room temperature. This finding also supports the postulate that network modifiers can recrystallize more easily than network formers. 

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