Sintered metal oxide articles and methods of making

Abstract

Methods of making metal oxide articles, preferably iron oxide articles, and articles thereby produced. The method comprises the steps of slightly pressing powder to a compact, the powder consisting essentially of a first oxide of the metal; and subjecting the compact to a heat treatment that causes the powder to sinter into a unitary body and results in the transformation of at least a portion of the first oxide to a second oxide by oxidation or deoxidation during the heat treatment. In disclosed embodiments, the heat treatment is conducted either in air at atmospheric pressure or at a subatmospheric pressure. The method optionally includes more heating/cooling steps resulting in additional oxidation/deoxidation cycles. Sintered iron oxide articles of the invention have high mechanical strengths and interconnected pore structures, providing for efficient filtering of liquids and gases.

We claim:  
     
         1 . A method of making a metal oxide article, comprising the steps of: 
 pressing powder to a compact, said powder consisting essentially of a first oxide of the metal; and    subjecting said compact to a heat treatment, said heat treatment causing said powder to sinter into a unitary body and resulting in the transformation of at least a portion of said first oxide to a second oxide of the metal.    
     
     
         2 . The method of  claim 1 , wherein said step of subjecting said compact to said heat treatment comprises the steps of: 
 subjecting said compact to a first temperature such that at least a portion of said first oxide transforms to said second oxide; and    subjecting said compact to a second temperature after said step of subjecting said compact to said first temperature, said step of subjecting said compact to said second temperature causing at least a portion of said second oxide to transform to said first oxide.    
     
     
         3 . The method of  claim 2 , wherein said second temperature is greater than said first temperature.  
     
     
         4 . The method of  claim 2 , wherein said second temperature is less than said first temperature.  
     
     
         5 . The method of  claim 2 , wherein said heat treatment further comprises the step of subjecting said compact to a third temperature after said step of subjecting said compact to said second temperature, thus causing at least a portion of said first oxide to transform to said second oxide.  
     
     
         6 . The method of  claim 5 , wherein said third temperature is greater than said second temperature.  
     
     
         7 . The method of  claim 5 , wherein said second temperature is less than said second temperature.  
     
     
         8 . The method of  claim 1 , wherein at least a portion of said heat treatment is conducted at a subatmospheric pressure.  
     
     
         9 . The method of  claim 1 , wherein at least a portion of said heat treatment is conducted in air at atmospheric pressure.  
     
     
         10 . A method of making an iron oxide article, comprising the steps of: 
 pressing powder to a compact, said powder consisting essentially of a first iron oxide; and    subjecting said compact to a heat treatment, said heat treatment causing said powder to sinter into a unitary body and resulting in the transformation of at least a portion of said first iron oxide to a second iron oxide.    
     
     
         11 . The method of  claim 10 , wherein 
 said first iron oxide is hematite;    said second iron oxide is magnetite;    said heat treatment includes the step of heating said compact to a temperature up to about 1250° C.; and    said heat treatment is conducted at a subatmospheric pressure.    
     
     
         12 . The method of  claim 11 , wherein said subatmospheric pressure is within the range of about 10 −4  torr to about 10 −5  torr.  
     
     
         13 . The method of  claim 10 , wherein said step of subjecting said compact to said heat treatment comprises the steps of: 
 subjecting said compact to a first temperature such that at least a portion of said first iron oxide transforms to said second iron oxide;    subjecting said compact to a second temperature after said step of subjecting said compact to said first temperature, said step of subjecting said compact to said second temperature causing at least a portion of said second iron oxide to transform to said first iron oxide; and    subjecting said compact to a third temperature after said step of subjecting said compact to said second temperature, said step of subjecting said compact to said third temperature causing at least a portion of said first iron oxide to transform to said second iron oxide.    
     
     
         14 . The method of  claim 13 , wherein 
 said first iron oxide is magnetite;    said second iron oxide is hematite;    said first temperature is up to about 1300° C.;    said second temperature is up to about 1450° C.;    said third temperature is less than about 1300° C.; and    said heat treatment is conducted in air at atmospheric pressure.    
     
     
         15 . The method of  claim 13 , further comprising the step of subjecting said compact to a fourth temperature after said step of subjecting said compact to said third temperature, said step of subjecting said compact to said fourth temperature causing at least a portion of said second iron oxide to transform to said first iron oxide.  
     
     
         16 . The method of  claim 15 , wherein 
 said first iron oxide is hematite;    said second iron oxide is magnetite;    said first temperature is up to about 1450° C.;    said second temperature is up to about 1250° C.;    said third temperature is up to about 1450° C.;    said fourth temperature is less than about 1300° C.; and    said heat treatment is conducted in air at atmospheric pressure.    
     
     
         17 . A sintered metal oxide article made by the process of  claim 1 .  
     
     
         18 . A sintered metal oxide article made by the process of  claim 2 .  
     
     
         19 . A sintered metal oxide article made by the process of  claim 5 .  
     
     
         20 . A sintered iron oxide article made by the process of  claim 10 .  
     
     
         21 . A sintered iron oxide article made by the process of  claim 11 .  
     
     
         22 . The iron oxide article of  claim 21 , wherein said article has an interconnected pore structure having a pore size of up to about 15 microns and a water filter productivity of at least about 150 cm 3 /cm 2  min.  
     
     
         23 . The iron oxide article of  claim 21 , wherein said article has an interconnected pore structure having a pore size of up to about 40 microns and a water filter productivity of at least about 150 cm 3 /cm 2  min.  
     
     
         24 . The iron oxide article of  claim 21 , wherein said article has an interconnected pore structure and a porosity of at least about 35 percent.  
     
     
         25 . A sintered iron oxide article made by the process of  claim 13 .  
     
     
         26 . A sintered iron oxide article made by the process of  claim 14 .  
     
     
         27 . The iron oxide article of  claim 26 , wherein said article has an interconnected pore structure having a pore size of up to about 10 microns and a water filter productivity of at least about 50 cm 3 /cm 2  min.  
     
     
         28 . The iron oxide article of  claim 27 , wherein said article has a crush strength of at least about 260 atmospheres.  
     
     
         29 . The iron oxide article of  claim 26 , wherein said article has an interconnected pore structure having a pore size of up to about 15 microns and a water filter productivity of at least about 175 cm 3 /cm 2  min.  
     
     
         30 . The iron oxide article of  claim 29 , wherein said article has a crush strength of at least about 200 atmospheres.  
     
     
         31 . The iron oxide article of  claim 26 , wherein said article has an interconnected pore structure and a porosity of at least about 35 percent.  
     
     
         32 . The iron oxide article of  claim 26 , wherein said article has an interconnected pore structure having a pore size of up to about 40 microns and a water filter productivity of at least about 800 cm 3 /cm 2  min.  
     
     
         33 . The iron oxide article of  claim 32 , wherein said article has a crush strength of at least about 30 atmospheres.  
     
     
         34 . A sintered iron oxide article made by the process of  claim 15 .  
     
     
         35 . A sintered iron oxide article made by the process of  claim 16 .  
     
     
         36 . The iron oxide article of  claim 35 , wherein said article has an interconnected pore structure having a pore size of up to about 15 microns and a water filter productivity of at least about 40 cm 3 /cm 2  min.  
     
     
         37 . The iron oxide article of  claim 35 , wherein said article has an interconnected pore structure having a pore size of up to about 40 microns and a water filter productivity of at least about 50 cm 3 /cm 2  min.  
     
     
         38 . The iron oxide article of  claim 35 , wherein said article has an interconnected pore structure having a pore size of up to about 100 microns and a water filter productivity of at least about 175 cm 3 /cm 2  min.