Filter element with porous nickel-based alloy substrate and metal oxide membrane

Abstract

Powdered nickel-based alloys having substantial amounts of chromium and molybdenum are molded and sintered to form tubular filter supports. Metal oxide particulates, preferably titanium oxide, are impregnated into the interior surfaces of the tubular elements and sintered to create 0.1 micron filter membranes. Hastelloy C-22 is a preferred nickel-based alloy for forming the porous metal support, while rutile is preferred as a starting material for forming the filter membrane. The resultant porous metal/metal oxide filter elements have superior resistance to chemical attack in high chloride, low pH environments.

We claim:  
     
         1 . A method for forming a tubular filter having a nickel-based metal substrate, comprising the steps of: 
 providing a powdered nickel-based alloy containing chromium and molybdenum, the alloy having a particle size no larger about 44 microns;    filling a tubular mold with the powdered alloy;    subjecting the tubular mold to an isostatic pressure of at least 37,000 pounds per square inch to form an unfired workpiece;    firing the unfired workpiece under a reducing atmosphere to a first temperature sufficient to partially fuse the powdered nickel-based alloy;    impregnating a surface of the workpiece with a metal oxide, to create an impregnated workpiece;    firing the impregnated workpiece under a reducing atmosphere at a second temperature substantially below the first temperature to create a metal oxide filter membrane; and    cooling the fired, impregnated workpiece to produce the tubular filter.    
     
     
         2 . The method of  claim 1  and further comprising the steps of: 
 selecting rutile TiO 2  as the metal oxide used to impregnate the surface of the workpiece; and  
 responsive to said step of firing the coated workpiece under a reducing atmosphere, converting the rutile to one or more titanium oxides having the formula Ti x O y , where y is less than 2×.  
 
     
     
         3 . The method of  claim 1 , wherein said step of providing the powdered nickel-based alloy comprises providing an alloy having at least 56 weight percent nickel, at least 16 weight percent chromium, and at least 5 weight percent molybdenum.  
     
     
         4 . The method of  claim 3 , wherein said step of providing the powdered nickel-based alloy comprises providing an alloy having at least 20 weight percent chromium and at least 16 weight percent molybdenum.