PROPERTIES OF NEW INORGANIC MEMBRANES PREPARED BY METAL ALKOXIDE METHODS .1. A NEW PERMSELECTIVE CATION-EXCHANGE MEMBRANE-BASED ON SI/TA OXIDES

Inorganic silicon/tantalum membranes were prepared on a microporous alumina substrate by dip coating with a solution containing Si(OC2H5)(4), C2H5OH, Ta(OC2H5)(5), CH3COOH in molar ratios of 1:6.8:X:0.068, three types of membrane were prepared where X equalled 0, 0.02 and 0.06. The membrane coatings were polymerized by drying at 100 degrees C, and the silica and mixed silicon/tantalum oxide membranes prepared by decomposition of these layers at temperatures between 150 and 300 degrees C. After five coats the active layers were defect free and between 5 and 15 mu m thick, depending upon the composition and temperature of preparation. Pure silica membranes (X=0) showed no ion exchange properties. Si/Ta oxide membranes however had excellent ion exchange properties. In the pH range 4-10 the Si/Ta oxide layers were purely cation exchangers with no anion exchange function or uptake and cation exchange capacities 0.6 mequiv/g. Ion exchange capacities per unit area of membrane surface were in the range 8-10X10(-3) mequiv cm(-2). The static transport number for potassium in all the Si/Ta oxide membranes with five coating of alkoxide was 0.9 (for pure silica layers 0.5.) The ion exchange character of these Si/Ta oxide layers is identical to that of pure silica, but the capacity was up to 10 times larger.