Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing same

Abstract

The present invention provides nanoporous α-alumina powders comprising powder comprising interconnected α-alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids. The invention also provides nanosized α-alumina powders comprising α-alumina particles having an average particle size of less than about 100 nm and slurries, particularly aqueous slurries, which comprise nanosized α-alumina powders of the invention. The invention further provides methods of manufacturing nanoporous α-alumina powders and nanosized α-alumina powders of the invention and methods of polishing using slurries of the invention.

What is claimed is:  
     
         1 . A nanoporous α-alumina powder comprising interconnected α-alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids.  
     
     
         2 . The nanoporous α-alumina powder of  claim 1 , wherein the α-alumina primary particles have a size of between about 10 nm and about 100 nm.  
     
     
         3 . The nanoporous α-alumina powder of  claim 1 , wherein the α-alumina primary particles have a size of between about 20 nm and about 90 nm.  
     
     
         4 . The nanoporous α-alumina powder of  claim 1 , wherein the α-alumina primary particles have a size of between about 25 nm and about 80 nm.  
     
     
         5 . The nanoporous α-alumina powder of  claim 1 , wherein the α-alumina primary particles have a size of between about 30 nm and about 70 nm.  
     
     
         6 . The nanoporous α-alumina powder of  claim 1 , wherein at least 99% of the α-alumina primary particles have a size within about a distribution of about 10 nm.  
     
     
         7 . The nanoporous α-alumina powder of  claim 1 , wherein the pores or voids have a minimum dimension of between about 20 nm and about 400 nm.  
     
     
         8 . The nanoporous α-alumina powder of  claim 1 , wherein the pores or voids have a minimum dimension of between about 50 nm and about 300 nm.  
     
     
         9 . The nanoporous α-alumina powder of  claim 1 , wherein the pores or voids have a minimum dimension of between about 100 nm and about 200 nm.  
     
     
         10 . The nanoporous α-alumina powder of  claim 1 , wherein between about 10 to about 75% of the powder volume is α-alumina.  
     
     
         11 . The nanoporous α-alumina powder of  claim 1 , wherein between about 10 to about 50% of the powder volume is α-alumina.  
     
     
         12 . The nanoporous α-alumina powder of  claim 1 , wherein the interpenetrated array of pores or voids have a columnar or tubular structure.  
     
     
         13 . The nanoporous α-alumina powder of  claim 12 , wherein the columnar or tubular structure have a diameter of between about 20 run and about 250 nm.  
     
     
         14 . The nanoporous α-alumina powder of  claim 12 , wherein the columnar or tubular structure have a diameter of between about 50 m and about 150 nm.  
     
     
         15 . The nanoporous α-alumina particles of  claim 1  wherein the interconnected α-alumina primary particles are connected by a neck.  
     
     
         16 . The nanoporous α-alumina particles of  claim 15 , wherein the cross-section of the neck is between about 10% and about 90% of the cross-section of the α-alumina primary particles.  
     
     
         17 . A nanosized α-alumina powder comprising α-alumina particles having an average particle size of less than about 100 n.  
     
     
         18 . The nanosized α-alumina powder of  claim 17 , wherein the nanosized α-alumina powder is prepared by crushing, milling or breaking a nanoporous α-alumina powder.  
     
     
         19 . The nanosized α-alumina powder of  claim 17 , wherein the α-alumina particles have a size of between about 10 nm and about 100 nm.  
     
     
         20 . The nanosized α-alumina powder of  claim 17 , wherein the α-alumina particles have a size of between about 20 nm and about 90 nm.  
     
     
         21 . The nanosized α-alumina powder of  claim 17 , wherein the α-alumina particles have a size of between about 25 nm and about 80 nm.  
     
     
         22 . The nanosized α-alumina powder of  claim 17 , wherein the α-alumina particles have a size of between about 30 nm and about 70 nm.  
     
     
         23 . A slurry comprising a nanosized α-alumina powder comprising α-alumina particles having an average particle size of less than about 100 nm.  
     
     
         24 . The slurry of  claim 23 , wherein the nanosized α-alumina powder is prepared by crushing, milling or breaking a nanoporous α-alumina powder.  
     
     
         25 . The slurry of  claim 23 , wherein the α-alumina particles have a size of between about 10 nm and about 100 nm.  
     
     
         26 . The slurry of  claim 23 , wherein the α-alumina particles have a size of between about 20 nm and about 90 nm.  
     
     
         27 . The slurry of  claim 23 , wherein the α-alumina particles have a size of between about 25 nm and about 80 nm.  
     
     
         28 . The slurry of  claim 23 , wherein the α-alumina particles have a size of between about 30 nm and about 70 nm.  
     
     
         29 . The slurry of  claim 23 , further comprising water.  
     
     
         30 . The slurry of  claim 23 , further comprising deionized water.  
     
     
         31 . The slurry of  claim 23 , further comprising one or more additives.  
     
     
         32 . The slurry of  claim 31 , wherein the additives are chemically inert to α-alumina under storage conditions or polishing conditions.  
     
     
         33 . The slurry of  claim 31 , wherein the additives inhibit aggregation of α-alumina particles under storage conditions or polishing conditions.  
     
     
         34 . The slurry of  claim 23 , wherein the pH of the slurry is between about 2 and about 11.  
     
     
         35 . The slurry of  claim 23 , wherein the pH of the slurry is between about 1 and about 6.  
     
     
         36 . The slurry of  claim 23 , wherein the pH of the slurry is between about 8 and about 10.5.  
     
     
         37 . A process for the production of nanoporous α-alumina powders which comprises the steps of 
 providing an inorganic sol comprising at least one alumina precursor and a plurality of α-alumina seed particles;  
 adding at least one water soluble organic polymer to the inorganic sol to form an organic-inorganic sol;  
 freeze drying the organic-inorganic sol to form a solid gel; and  
 firing the solid gel at a temperature capable of combusting the organic polymer and inducing α-alumina formation of a nanoporous α-alumina powder comprising interconnected α-alumina primary particles.  
 
     
     
         38 . The process of  claim 37 , wherein the alumina precursor is boehmite.  
     
     
         39 . The process of  claim 37 , wherein the alumina precursor is a molecular aluminum compound.  
     
     
         40 . The process of  claim 37 , wherein the molecular alumina precursor is selected from aluminum salts comprising one or more anions selected from alkoxides, aryl oxides, carboxylates, halides, sulfate, nitrate, oxalates, and acetoacetonates.  
     
     
         41 . The process of  claim 37 , wherein the α-alumina seed particles are homogeneously dispersed in the solid gel.  
     
     
         42 . The process of  claim 37 , wherein the freeze drying step comprises: 
 freezing the organic-inorganic sol to a temperature of 0° C. or less; and    subliming water from the frozen sol at a temperature of between 0° C. and about 80° C. under a reduced atmosphere.    
     
     
         43 . The process of  claim 37 , wherein the freeze drying step comprises: 
 freezing the organic-inorganic sol to a temperature of −20° C. or less; and    subliming water from the frozen sol at a temperature of between 20° C. and about 80° C. and a pressure of about 200 Torr or less.    
     
     
         44 . The process of  claim 37 , wherein the freeze drying step comprises: 
 freezing the organic-inorganic sol to a temperature of −30° C. or less; and    subliming water from the frozen sol at a temperature of between 40° C. and about 80° C. and a pressure of about 50 Torr or less.    
     
     
         45 . The process of  claim 37 , wherein the firing is conducted at a temperature of less than about 1200° C.  
     
     
         46 . The process of  claim 37 , wherein the firing is conducted at a temperature of less than about 1100° C.  
     
     
         47 . The process of  claim 37 , wherein the firing is conducted at a temperature of between about 750° C. and about 1050° C.  
     
     
         48 . The process of  claim 37 , wherein the firing is conducted at a temperature of between about 800° C. and about 1000° C.  
     
     
         49 . The process of  claim 37 , wherein the α-alumina seed particles have an average particle size of less than about 125 nm.  
     
     
         50 . The process of  claim 37 , wherein the α-alumina primary particles have a size of between about 10 nm and about 100 mm.  
     
     
         51 . The process of  claim 37 , wherein the α-alumina primary particles have a size of between about 20 mm and about 90 mm.  
     
     
         52 . The process of  claim 37 , wherein the α-alumina primary particles have a size of between about 25 nm and about 80 mm.  
     
     
         53 . The process of  claim 37 , wherein the α-alumina primary particles have a size of between about 30 nm and about 70 nm.  
     
     
         54 . The process of  claim 37 , wherein at least 99% of the α-alumina primary particles have a size within about a distribution of about 10 mm.  
     
     
         55 . The process of  claim 37 , wherein the pores or voids have a minimum dimension of between about 20 nm and about 400 nm.  
     
     
         56 . The process of  claim 37 , wherein the pores or voids have a minimum dimension of between about 50 mm and about 300 nm.  
     
     
         57 . The process of  claim 37 , wherein the pores or voids have a minimum dimension of between about 100 nm and about 200 nm.  
     
     
         58 . The process of  claim 37 , wherein between about 10 to about 75% of the powder volume is α-alumina.  
     
     
         59 . The process of  claim 37 , wherein between about 10 to about 50% of the powder volume is α-alumina.  
     
     
         60 . The process of  claim 37 , wherein the interpenetrated array of pores or voids have a columnar or tubular structure.  
     
     
         61 . The process of  claim 60 , wherein the columnar or tubular structure have a diameter of between about 20 nm and about 250 nm.  
     
     
         62 . The process of  claim 60 , wherein the columnar or tubular structure have a diameter of between about 50 nm and about 150 nm.  
     
     
         63 . The process of  claim 37 , wherein the interconnected α-alumina primary particles are connected by a neck.  
     
     
         64 . The process of  claim 63 , wherein the cross-section of the neck is between about 10% and about 90% of the cross-section of the α-alumina primary particles.  
     
     
         65 . The process of  claim 37 , wherein the nanoporous α-alumina produced comprises between about 0.1 and about 25 weight percent of the α-alumina seed particles.  
     
     
         66 . The process of  claim 65 , wherein the nanoporous α-alumina produced comprises between about 1 and about 15 weight percent of the α-alumina seed particles.  
     
     
         67 . The process of  claim 37 , wherein the water soluble organic polymer is selected from polyols, sugars, polyalkylene oxides, poly(meth)acrylic acid, poly(meth)acrylates, and mixtures thereof.  
     
     
         68 . The process of  claim 67 , wherein the water soluble organic polymer is polyvinyl alcohol, polyethylene glycol or a mixture thereof.  
     
     
         69 . A process for the production of a nanosized α-alumina powder comprising α-alumina particles having an average particle size of less than about 100 nm, the process comprising the steps of: 
 providing a nanoporous α-alumina powder comprising interconnected α-alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids; and  
 breaking the nanoporous α-alumina powder to form a nanosized α-alumina powder comprising the α-alumina primary particles of the nanoporous α-alumina powder.  
 
     
     
         70 . The process of  claim 65 , wherein the nanoporous α-alumina powder is broken by milling to form the nanosized α-alumina powder.  
     
     
         71 . A process for the production of a nanosized α-alumina powder which comprises α-alumina particles having an average particle size of less than about 100 nm, the process comprising the steps of 
 providing an inorganic sol comprising at least one alumina precursor and a plurality of α-alumina seed particles;  
 adding at least one water soluble organic polymer to the inorganic sol to form an organic-inorganic sol;  
 freeze drying the organic-inorganic sol to form a solid gel; and  
 firing the solid gel at a temperature capable of combusting the organic polymer and inducing α-alumina formation of a nanoporous α-alumina powder comprising interconnected α-alumina primary particles; and  
 breaking the nanoporous α-alumina powder to form a nanosized α-alumina powder comprising the α-alumina primary particles of the nanoporous α-alumina powder.  
 
     
     
         72 . A method of polishing a substrate, the method comprising the steps of: 
 providing slurry comprising a nanosized α-alumina powder which comprises α-alumina particles having an average particle size of less than about 100 nm; and    applying the slurry to an interface between the substrate and a polishing pad.