Nanoporous oxide ceramic membranes of tubular and hollow fiber shape and method of making the same

Abstract

The present invention is aimed to fabricate nanoporous anodic oxide ceramic membrane tubes with excellent pore characteristics by anodizing metal tubes located in a cylindrical symmetry with respect to a cathode which itself has a cylindrical symmetry. The membrane tubes may have protruded portions acting as supports and joints. The present invention also deals with stacks and bundles consisted of numbers of the anodic oxide ceramic tubes for filter and dialysis applications.

1 . Nanoporous anodic aluminum oxide membranes of tubular and hollow fiber shape with through-hole nanopores on the cylinder wall, fabricated by anodizing aluminum or aluminum alloy tubes and hollow fibers using an anodization apparatus incorporating cylindrical symmetry in arrangement of anode and cathode which themselves have shapes of cylindrical symmetry and/or excellent thermal contact between the tube or the hollow fiber to be anodized and heat sink. 
     
     
         2 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes are fabricated by anodizing aluminum tubes and hollow fibers, respectively, fabricated by performing mechanical work such as machining, drawing, scratching, welding, and riveting. 
     
     
         3 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein outer diameters of the membranes vary from several tens of meters to several tens of microns and thicknesses thereof vary from 50 mm to tens of microns. 
     
     
         4 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes comprise nanopores of 1 to 300 nm in size. 
     
     
         5 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes are fabricated by anodizing either of the inner or the outer wall of aluminum tubes and hollow fibers in an outward or inward direction, respectively, or are fabricated by anodizing both the inner and outer walls simultaneously in outer and inward directions. 
     
     
         6 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes are fabricated by anodizing using an electrolyte selected from the group consisting of phosphoric acid, oxalic acid, malonic acid, tartaric acid and citric acid solution, a mixed solution of sulfuric and oxalic acids, and a mixed solution of organic acids, and applying an electrical voltage in a range of 10 to 250 V. 
     
     
         7 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes are fabricated by using high purity grade aluminum or low purity grade aluminum, or aluminum alloy containing one to four metal elements selected from the group consisting of Cu, Mn, Si, Mg, Cr, Zn, Zr, Ti and Li elements. 
     
     
         8 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes are coated with adsorbent or catalytic materials selected from the group consisting of TiO 2 , V 2 O 3 , WO, SnO 2 , ZnO, etc. by using a coating method which is sputtering, evaporation, electrodeposition, or sol-gel, and wherein the coated layers are also nanoporous. 
     
     
         9 . The tubular and hollow fiber shaped membranes of  claim 1 , wherein the membranes comprise thick protruded parts acting as supports for mechanical strengthening and joints for connecting with another neighboring structure, and thin layers with nanopores of 1 to 300 nm in size. 
     
     
         10 . The tubular and hollow fiber shaped membranes of  claim 9 , wherein protruded supports and thin layers with nanopores are present in any pattern and shape. 
     
     
         11 . The tubular and hollow fiber shaped membranes of  claim 9 , wherein the protruded parts are fabricated by performing either lithography or mechanical working which is machining, drawing, scratching, welding, or riveting, or both lithography and mechanical working, and performing anodization. 
     
     
         12 . The tubular and hollow fiber shaped membranes of  claim 9 , wherein the thick protruded parts are of any shape and are located at any position in the membranes. 
     
     
         13 . A membrane filter fabricated using the tubular or hollow fiber shaped membranes of  claim 1 . 
     
     
         14 . The membrane filter of  claim 13 , wherein the membrane filter comprises filters consisted of a plurality of said tubular or hollow fiber membranes. 
     
     
         15 . The membrane filter of  claim 14 , wherein the membrane filter includes cylinder stacks assembled with a plurality of anodic alumina membrane tubes or hollow fibers with different diameters with respect to a concentric axis. 
     
     
         16 . The membrane filter of  claim 15 , wherein the membrane filter comprises tubes or hollow fibers with pore diameters which increase or decrease with increasing the tube or the hollow fiber diameter. 
     
     
         17 . The membrane filter of  claim 14 , wherein the membrane filter includes a bundle of several to numerous numbers of anodic alumina membrane tubes or hollow fibers. 
     
     
         18 . Nanoporous anodic titanium oxide membranes of tubular and hollow fiber shape with through-hole pores on the cylinder wall, fabricated by anodizing titanium or titanium alloy tubes and hollow fibers using an anodization apparatus incorporating cylindrical symmetry in arrangement of anode and cathode and/or excellent thermal contact between the tube or the hollow fiber to be anodized and heat sink. 
     
     
         19 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes are fabricated by anodizing titanium tubes and hollow fibers, respectively, fabricated by performing mechanical work such as machining, drawing, scratching, welding, and riveting. 
     
     
         20 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein outer diameters of the membranes vary from several tens of meters to several tens of microns and thicknesses thereof vary from 50 mm to tens of microns. 
     
     
         21 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes comprise nanopores of 1 to 300 nm in size. 
     
     
         22 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes are fabricated by anodizing either of the inner or outer wall of the tube and the hollow cylinder in an outward or inward direction, respectively, or are fabricated by anodizing both the inner and outer walls simultaneously in outer and inward directions. 
     
     
         23 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes are fabricated by anodizing using an electrolyte selected from the group consisting of HF, KF, NaF, and a mixed solution of H 2 SO 4  and HF, CrO 3  and HF, (NH 4 ) 2 SO 4  and NH 4 F, and (NH 4 ) 2 SO 4  and NaF, and applying an voltage in a range of 10 to 250 V corresponding to the selected electrolyte. 
     
     
         24 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes are fabricated by using high purity grade titanium or low purity grade titanium, or titanium alloy. 
     
     
         25 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes are coated with adsorbent or catalytic materials selected from the group consisting of TiO 2 , V 2 O 3 , WO, SnO 2 , ZnO, etc. by using a coating method which is sputtering, evaporation, electrodeposition, or sol-gel, and wherein the coated layers are also nanoporous. 
     
     
         26 . The tubular and hollow fiber shaped membranes of  claim 18 , wherein the membranes comprises thick protruded parts acting as supports for mechanical strengthening and joints for connecting with another neighboring structure, and thin layers with nanopores of 1 to 300 nm in size. 
     
     
         27 . The tubular and hollow fiber shaped membranes of  claim 26 , wherein protruded supports and thin layers with nanopores are present in any pattern and shape. 
     
     
         28 . The tubular and hollow fiber shaped membranes of  claim 26 , wherein the protruded parts are fabricated by performing either lithography or mechanical working which is machining, drawing, scratching, welding, or riveting, or both lithography and mechanical working, and performing anodization. 
     
     
         29 . The tubular and hollow fiber shaped membranes of  claim 26 , wherein the thicker protruded parts are of any shape and are located at any position in the membranes. 
     
     
         30 . A membrane filter fabricated using the tubular or hollow fiber shaped membranes of  claim 18 . 
     
     
         31 . The membrane filter of  claim 30 , wherein the membrane filter comprises a plurality of said tubular or hollow fiber membranes. 
     
     
         32 . The membrane filter of  claim 30 , wherein the membrane filter includes a cylinder stack of a plurality of anodic alumina membrane tubes or hollow fibers with different diameters with respect to a concentric line. 
     
     
         33 . The membrane filter of  claim 32 , wherein the membrane filter comprises hollow cylinders of differing pore sizes which increase or decrease with increasing diameter. 
     
     
         34 . The membrane filter of  claim 32 , wherein the membrane filter includes a bundle of several to numerous numbers of anodic alumina membrane tubes or hollow fibers.