Ceramic hydrogen-permeable

It was not equally obvious that dense ceramic hydrogen-permeable membranes would be of similar interest. There are clearly needs for hydrogen purification membranes, but polymers and microporous materials as well as metals such as palladium and its alloys appeared to fill these needs. In addition, possible candidates for dense ceramic hydrogen-permeable materials were not as appealing as the oxygen-permeable ones in terms of performance and stability. 

Uemiya, S., T. Matsuda, and E. Kikuchi, Hydrogen permeable palladium-silver alloy membrane supported on porous ceramics, /. Membr. Sci., 56, 315,1991b. 

Ceramic and semiconductor thin films have been prepared by a number of methods including chemical vapor deposition (CVD), spray-coating, and sol-gel techniques. In the present work, the sol-gel method was chosen to prepare uniform, thin films of titanium oxides on palladium Titanium oxide was chosen because of its versatility as a support material and also because the sol-gel synthesis of titania films has been clearly described by Takahashi and co-workers (22). The procedure utilized herein follows the work of Takahashi, but is modified to take advantage of the hydrogen permeability of the palladium substrate. Our objective was to develop a reliable procedure for the fabrication of thin titania films on palladium, and then to evaluate the performance of the resulting metalloceramic membranes for hydrogen transport and ethylene hydrogenation for comparison to the pure palladium membrane results. 

In this work for the first time magnetron sputtering (technologically effective method) was used for the modification of the tubular a-alumina ceramic support of the composite Pd - membrane. This modification could be realized due to the choice of Ni as hydrogen permeable metal instead of y-Al203 layers. It allows to use total effective cross section of the surface porous structure of the support in high temperature process of hydrogen purification by Pd membrane. 

Roberts, R.M. et al.. Hydrogen permeability of sintered aluminum oxide. Journal of the American Ceramic Society, 62, 495 (1979). 

At 700°C, the permeability of palladium is approximately 3.0 xlO- [mol/(m s Pa )] and the permeability of iron is 5.0x10- [mol/(m s Pa"0] [Buxbaum and Marker, 1993]. Figure 4 illustrates the hydrogen permeability of palladium, iron and the proton conducting ceramic material as a function of inverse temperature. The driving force for hydrogen flux in each membrane material is... 

Dorris, Stephen E, Lee, Tae H, Balachandran, Uthamahngam. Metal/Ceramic Composites with High Hydrogen Permeability. US Patent 6,569,226 Bl, 27 May 2003. 

Figure 9.10a shows a concept for scale-up of cermet (ceramic-metal) type membranes. Ceramic closed-one-ended tubes coated with thin, dense hydrogen permeable materials are envisioned for the cermet-type membranes (Fig. 9.10a) As with the all-metal systems, the closed-one-ended tube arrangement allows free chemical and thermal expansion and minimizes the seal area. CoorsTek has had previous...

This chapter aims to keep these challenges in mind as we review the defect chemistry, transport theory and aspects of characterization of hydrogen permeation in dense ceramics. We will first look at some applications and simple schemes of operation of hydrogen-permeable membranes and then, briefly, at the literature and status of hydrogen-permeable dense ceramics. 

Defect Chemistry of Dense Hydrogen-permeable Ceramics I 5... 

Dense inorganic membranes for hydrogen separation may consist either of a metal or an alloy, a ceramic (oxide), or a mixture of both, a so-called cermet. One may also envisage a mixture of two ceramics ( cercer ). In the following, we discuss literature on hydrogen permeability in some of these classes of dense membranes. 

From the above evaluation, it seems that a good alternative may be a matrix of a metallic phase with high hydrogen permeability strengthened by a dispersion of ceramic particles (alternative ii). For this class of materials, flux densities have been measured to be of the order of 10-30 mL mim cm 2 using 1 atm total pressure with H2 as feed gas and He as sweep gas. In general, the flux in these materials increases with in the feed gas and is inversely proportional to the thick-... 

B. Wang. O. Sakai, H. Sakai, T. Takaha-shi. Changes in hydrogen permeability and surface state of Pd-Ag/ceramic composite membranes after thermal treatment. J. Membr. Sci., 2005, 252, 145-154. 

As discussed elsewhere in this text, there are two types of dense, hydrogen-permeable metal membranes to consider from the perspective of module scale-up and design thin metal foils and permselective metal layers formed on a porous support. Another class of hydrogen-permeable inorganic membranes - dense proton-conducting ceramic membranes - are still under development and are addressed in Chapter 2. 

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