Amorphous materials membranes stability

General criteria for selection of materials for the processing of hydrogen separation membranes are discussed. Performance and stability standards required for applications in high temperature membrane reactors have been focused. The correlations between pore structure and stability issues of membranes made of amorphous materials, specifically silica membranes are discussed in detail. 

Another approach is to use amorphous inorganic membranes based on silica, which have an intrinsic lower scaling-up costs. Materials based on pure silica have been proven to be unsuitable for this application because of a too low hydrothermal stability. Recent inventions on membranes that... 

This chapter describes some of the properties of solids that affect transport across phases and membranes, with an emphasis on biological membranes. Four aspects are addressed. They include a comparison of crystalline and amorphous forms of the drug, transitions between phases, polymorphism, and hydration. With respect to transport, the major effect of each of these properties is on the apparent solubility, which then affects dissolution and consequently transport. There is often an opposite effect on the stability of the material. Generally, highly crystalline substances are more stable but have lower free energy, solubility, and dissolution characteristics than less crystalline substances. In some situations, this lower solubility and consequent dissolution rate will result in reduced bioavailability. 

New and up to-date materials have been developed in our laboratory to carry out Fenton photo-assisted processes efficient in the decoloration/degradation of organic pollutants that show stability against radical attack, do not allow the leaching of Fe-ions into the solution and intervene with suitable kinetics in the degradation processes. These new materials comprise Fe-ions supported on Nation membranes, Nafion-glass mats composites, alginate beads, amorphous polycrystalline fused copolymers and silica woven fabrics. 

It is worth noting that both Pd-aUoy and sUica-based membranes present some problem about material instability in the WGS environment. The Pd-aUoy membranes can be negatively affected by surface carbonization, sulfur poisoning, and hydrothermal embrittlement, whereas the amorphous silica-based membranes can show some degradation caused by the condensation reaction of sUanol in hydrothermal conditions (Tang et al., 2010). In particular, the siliceous MFI-type zeolite membranes, constituted by a crystalline microporous zeolite membrane, in recent years have been seen as attractive candidates for the WGS reaction because of the high-temperature hydrogen separation and for their intrinsic sulfur tolerance and hydrothermal stability. 

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