Densification of aerated powders using positive pressure

Abstract

A process for increasing the bulk density of an aerated powder is provided. The powder is placed in a container. The container is then closed and the gas pressure within the container is increased to a level above atmospheric pressure and at a rate sufficient to cause the powder to compact before a substantial portion of said pressurization gas diffuses into said powder. In one embodiment, the process is utilized to increase the bulk density of an aerated, free-flowing titanium dioxide pigment. Apparatus for carrying out the process is also provided.

What is claimed is:  
     
         1 . A process for increasing the bulk density of an aerated powder, comprising: 
 placing said powder in a container; and    increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to cause said powder to compact before a substantial portion of said pressurization gas diffuses into said powder.    
     
     
         2 . The process of  claim 1  further comprising the steps of depressurizing said container and removing said compacted powder from said container.  
     
     
         3 . The process of  claim 1  wherein said gas pressure in the area of said container containing said powder is increased to a level above atmospheric pressure by injecting a gas into said container.  
     
     
         4 . The process of  claim 3  wherein said gas injected into said container is selected from the group consisting of an inert gas, air, nitrogen, oxygen, carbon dioxide and chlorine.  
     
     
         5 . The process of  claim 4  wherein said gas injected into said container is air.  
     
     
         6 . The process of  claim 1  wherein said powder is an inorganic metal oxide.  
     
     
         7 . The process of  claim 6  wherein said powder is a titanium dioxide pigment.  
     
     
         8 . The process of  claim 7  wherein the bulk density of said titanium dioxide pigment is increased to a level greater than about 35 lbs/ft 3 .  
     
     
         9 . The process of  claim 8  wherein the bulk density of said titanium dioxide pigment is increased to a level in the range of from about 40 lbs/ft 3  to about 50 lbs/ft 3 .  
     
     
         10 . The process of  claim 7  wherein said gas pressure in the area of said container containing said powder is increased to a level above atmospheric pressure by injecting chlorine gas into said container.  
     
     
         11 . The process of  claim 6  wherein said powder comprises a battery-active material.  
     
     
         12 . The process of  claim 11  wherein said battery-active material is selected from the group of metal oxides and metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         13 . The process of  claim 11  wherein said battery-active material is selected from the group of lithium metal oxides and lithium metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         14 . The process of  claim 13  wherein said battery-active material is a lithium vanadium oxide.  
     
     
         15 . The process of  claim 13  wherein the bulk density of said battery material is increased by at least about 10 percent.  
     
     
         16 . The process of  claim 15  wherein the bulk density of said battery material is increased by at least about 15 percent.  
     
     
         17 . A process for placing a predetermined volume of a powder into a receptacle, comprising: 
 placing said powder in a container;    increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to increase the bulk density of said powder to a predetermined level; and    removing a predetermined amount of said powder from said container and placing it in said receptacle.    
     
     
         18 . The process of  claim 17  wherein said gas pressure in the area of said container containing said powder is increased to a level above atmospheric pressure by injecting a gas into said container.  
     
     
         19 . The process of  claim 18  wherein said gas injected into said container is selected from the group consisting of an inert gas, air, nitrogen, oxygen, carbon dioxide and chlorine gas.  
     
     
         20 . The process of  claim 17  wherein said powder is an inorganic metal oxide.  
     
     
         21 . The process of  claim 20  wherein said powder is a titanium dioxide pigment.  
     
     
         22 . The process of  claim 20  wherein said powder comprises a battery-active material.  
     
     
         23 . The process of  claim 22  wherein said battery-active material is selected from the group of metal oxides and metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         24 . The process of  claim 22  wherein said battery-active material is selected from the group of lithium metal oxides and lithium metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         25 . The process of  claim 24  wherein said battery-active material is a lithium vanadium oxide.  
     
     
         26 . A process for increasing the bulk density of an aerated powder, comprising: 
 placing said powder in a container; and    injecting a gas into said container at a rate sufficient to increase the gas pressure in the area of said container containing said powder to a level above atmospheric pressure and cause said powder to compact before a substantial portion of said pressurization gas diffuses into said powder.    
     
     
         27 . The process of  claim 26  wherein said gas injected into said container is selected from the group consisting of an inert gas, air, nitrogen, oxygen, carbon dioxide and chlorine gas.  
     
     
         28 . The process of  claim 26  further comprising the steps of depressurizing said container and removing said compacted powder from said container.  
     
     
         29 . The process of  claim 26  wherein said powder is an inorganic metal oxide.  
     
     
         30 . The process of  claim 26  wherein said powder is a titanium dioxide pigment.  
     
     
         31 . The process of  claim 26  wherein said powder comprises a battery-active material.  
     
     
         32 . The process of  claim 31  wherein said battery-active material is selected from the group of metal oxides and metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         33 . The process of  claim 31  wherein said battery-active material is selected from the group of lithium metal oxides and lithium metal phosphates wherein said metal is vanadium, manganese, nickel, cobalt, iron or a combination thereof.  
     
     
         34 . The process of  claim 33  wherein said battery-active material is a lithium vanadium oxide.  
     
     
         35 . A process for increasing the bulk density of an aerated powder, comprising: 
 placing said powder in a container, said container having a first end and a second end opposing said first end;    increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to cause said powder to compact against said second end of said container before a substantial portion of said pressurization gas diffuses into said powder;    opening said second end of said container whereby said container is depressurized and said powder is expelled from said container through said second end of said container.    
     
     
         36 . The process of  claim 35  wherein said gas pressure in the area of said container containing said powder is increased to a level above atmospheric pressure by injecting a gas into said container.  
     
     
         37 . A process for preparing a slurry, comprising: 
 processing a powder;    prior to allowing said powder to fully settle, increasing the bulk density of said powder by deaerating said powder; and    dispersing said densified powder into a liquid medium.    
     
     
         38 . The process of  claim 37  wherein said powder is deaerated by: 
 placing said powder in a container; and  
 increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to cause said powder to compact before a substantial portion of said pressurization gas diffuses into said powder; and  
 removing said compacted powder from said container.  
 
     
     
         39 . The process of  claim 38  wherein said powder is titanium dioxide pigment, and said liquid medium is water.  
     
     
         40 . A process for preparing a concentrated titanium dioxide pigment slurry, comprising: 
 milling a titanium dioxide pigment;    prior to allowing said titanium dioxide pigment to fully settle, increasing the bulk density of said pigment by: 
 placing said powder in a container; and  
 increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to cause said powder to compact before a substantial portion of said pressurization gas diffuses into said powder; and  
   removing said compacted powder from said container; and    dispersing said deaerated pigment in a liquid medium.    
     
     
         41 . The process of  claim 40  wherein said milling step is carried out in a fluid energy mill.  
     
     
         42 . An apparatus for increasing the bulk density of a powder, comprising: 
 a container for containing said powder under pressure, said container having a first end and a second end opposing said first end; and    pressurization means associated with said container for increasing the gas pressure in the area of said container containing said powder to a level above atmospheric pressure at a rate sufficient to cause said powder to compact before a substantial portion of said pressurization gas diffuses into said powder.    
     
     
         43 . The apparatus of  claim 42  wherein said pressurization means comprise: 
 means for injecting a gas into said container; and  
 a source of gas.  
 
     
     
         44 . The apparatus of  claim 42  wherein: 
 said first end of said container includes an inlet for allowing said powder to be added to said container;  
 said second end of said container includes an outlet for allowing said powder to be removed from said container; and  
 said container further comprises a first valve for opening and closing said inlet and a second valve for opening and closing said outlet.  
 
     
     
         45 . The apparatus of  claim 44  wherein said pressurization means causes said powder to compact against said outlet when said outlet is closed and eject from said container when said outlet is opened.  
     
     
         46 . An apparatus for increasing the bulk density of a powder, comprising: 
 a cylinder, said cylinder having a first end and a second end opposing said first end, said first end containing an inlet and said second end containing an outlet;    a rotary containment device positioned within said cylinder, said rotary containment device including: 
 a hub;  
 a pair of opposed blades attached to said hub and creating two powder containment areas within said cylinder, said rotary containment device being capable of turning within said cylinder such that each of said powder containment areas rotate to a first position within said cylinder adjacent said inlet whereby powder can be added to said area, a second position within said cylinder adjacent said wall of said cylinder whereby powder in said area can be compacted, and a third position within said cylinder adjacent said outlet whereby powder in said area can be ejected from said area; and  
 rotating means for turning said rotary containment device within said cylinder; and  
   pressurization means associated with said cylinder for increasing the gas pressure within said each of said powder containment areas of said rotary contaimnent device to a level above atmospheric pressure when said area is in said second position at a rate sufficient to cause the powder within said area to compact before a substantial portion of the pressurization gas diffuses into the powder.    
     
     
         47 . The apparatus of  claim 46  wherein said pressurization means comprises: 
 means for injecting a gas into said powder containment areas; and  
 a source of compressed gas.