Alumina membrane chemical stability

The advantage of sol-gel technology is the ability to produce a highly pure y-alumina and zirconia membrane at medium temperatures, about 700 °C, with a uniform pore size distribution in a thin film. However, the membrane is sensitive to heat treatment, resulting in cracking on the film layer. A successful crack-free product was produced, but it needed special care and time for suitable heat curing. Only y-alumina membrane have the disadvantage of poor chemical and thermal stability. 

Alumina membranes. It has been established that several phases of alumina exist and a particular phase of alumina is determined not only by the temperature it has experienced but also by the chemical path it has taken. For commercial membrane applications, the alpha- and gamma-phases of alumina are the most common. Alpha-alumina membranes are well known for their thermal and hydrothermal stabilities beyond 1,000 C. In fact, other transitional forms of alumina will undergo transformation towards the thermodynamically stable alpha-alumina at elevated tcmjxratures beyond 900 C. On the contrary, commercial gamma-alumina membranes are typically calcined at 400-600 C during production and are, therefore, subject to potential structural changes beyond 600°C. Moreover, alumina chemistry reveals that phase transition also occurs beyond that temperature [Wefers and Misra, 1987]. 

Molecularly bonded silver membranes have also been used to purify aggressive HPLC solvents [Minneci and Paulson, 1988]. Similar to the anodic alumina membranes, silver membranes are preferred for this application due to the following reasons high chemical and thermal stabilities leading to no or negligible amount of dissolved or leached membrane constituents in the solvents. 

Alumina occupies the dominant position in the research and development of ceramic membranes due to its high chemical and mechanical stability as well as low cost. Anodic alumina membranes are ideally suited... 

Van Gestel, T., Vandecasteele, C., Buekenhoudt, A. et al. (2002) Alumina and titania multilayer membranes for nanofiltration Preparation, characterization and chemical stability. Journal of Membrane Science, 207, 73-89. 

Properties of alumina manbranes and polymer membranes, like chanical/thermal stabilities and pore density, are often quite different, and selection of the proper material for desired applications is important Chanical modification has proven useful to impart functionality to nanoporous membranes. For alumina manbranes in particular, growth of thin sol-gel films on the walls of the membrane provides an opportunity to functionalize membranes with organosilanes (e.g., triethoxy-or trichlorosilanes). Deposition of gold films also provides a method for chemical modification... 

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