Dense metal membranes thin films, porous substrates

Perovskite-structured membranes, in the form of thin films supported on porous ceramic or metal substrates, have been studied extensively in the past decade. Thin films offer several advantages including reduced material cost, improved mechanical strength and possibly higher H2 flux. Chemical vapor deposition (CVD) [99], electrochemical vapor deposition (EVD) [100] and sputtering [101] represent typical methods. However, dense films have been difficult to obtain by these methods. It was found that the continuity and gas-tightness of the deposited films were very sensitive to the morphologies and pore size of substrates. 

Porous membranes (low H2 selectivity) are used as substrate onto which a very thin but continuous film of a selective metal, generally Pd-based, is deposited. Dense composite membranes are also fabricated by sintering together powders of highly H2 permeable metals (Pd, Pt, Nb,Ta,1i, V, Zr and their alloys) with powders of a second metal or alloy which is non-permeable to H2 (Mundschau, 2005), having the function of providing the mechanical support. Some fundamental science related to the H2 separation using dense composite membranes is reported by Mundschau (2008). 

A number of novel applications of zeolites depend on the ability to create thin, adhesive films on various substrates. While zeolite films or layers are commonly prepared on dense substrates such as silicon wafers, zeolite membranes are made on porous supports in order to permit permeation through the zeolite layer. Numerous synthetic studies have addressed the goal of obtaining adhesive layers of zeolites on various substrates such as noble and nonnoble metals, glass, ceramics, silicon, and even biological substrates such as cellulose fibers. For a more detailed discussion of zeolite membranes the reader is referred to the article by Julbe in this book. Pertinent reviews to this subject are given in the following references.[57,58]... 

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