Key technologies for preparation of porous metallic membrane

Membrane filtration is a high-tech separation technique which was triumphantly and cosmically applied to food engineering, biotechnological engineering, electronics engineering, petroleum engineering, chemical engineering and environmental protection engineering; however, some theoretical and technical issues still need to be investigated, especially the materials for membrane. The materials that were utilized at present mainly include organic and ceramic membranes. Owning to natural property of material, organic membranes have low flux, selectivity, chemical and thermal stabilities. The limitation of preparation technique for ceramic membranes leads to a wide pore size distribution which results in a low separation precision and a wide molecular weight cut off. Furthermore, ceramic substrates are too frangible; this makes ceramic membranes tend to be broken abruptly during working. Metallic membrane is a new kind of material, which was first developed in USA in 1990s. It was composited with porous 316L stainless steel substrate and TiO₂ ceramic top layer. The 316L substrates endow the membrane high fatigue, tenacity, intensity and high adaptability for liquid fluid. The excellent material properties make it the most powerful material following organic and ceramic membranes. There are two critical procedures when fabricating it－preparing the porous substrate and top layer. The preparation of substrate depends on powder metallurgy and the top layer is based on the sol-gel technique.