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 al umina 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, thre e types of membrane were prepared where X equalled 0, 0.02 and 0.06. T he membrane coatings were polymerized by drying at 100 degrees C, and the silica and mixed silicon/tantalum oxide membranes prepared by deco mposition of these layers at temperatures between 150 and 300 degrees C. After five coats the active layers were defect free and between 5 a nd 15 mu m thick, depending upon the composition and temperature of pr eparation. Pure silica membranes (X=0) showed no ion exchange properti es. Si/Ta oxide membranes however had excellent ion exchange propertie s. In the pH range 4-10 the Si/Ta oxide layers were purely cation exch angers with no anion exchange function or uptake and cation exchange c apacities 0.6 mequiv/g. Ion exchange capacities per unit area of membr ane surface were in the range 8-10X10(-3) mequiv cm(-2). The static tr ansport number for potassium in all the Si/Ta oxide membranes with fiv e coating of alkoxide was 0.9 (for pure silica layers 0.5.) The ion ex change character of these Si/Ta oxide layers is identical to that of p ure silica, but the capacity was up to 10 times larger.