Ceramic slip composition and method for making the same

Abstract

A uniform suspension of ceramic powder and method for making the same. The suspension is prepared by mixing finely divided ceramic powder in an aqueous carrier fluid, combining with a dispersing agent, and alternatively, an organic binder when forming a slip. The ceramic powder has an average particle size of about 0.5 micron or less and is present in the suspension in a loading of up to 30% by volume of the total solids in suspension. A passivating agent is present in the carrier fluid in an amount of 0.5 to 5% by weight of the ceramic powder present for suspension and slip respectively. After the addition of a dispersant, the suspension has a Bingham yield point of less than 230 dynes/cm 2 and an apparent viscosity of less than 3000 cps. A green layer produced from the slip exhibits a pore size of less than 0.5 micron.

what is claimed is:  
     
         1 . A ceramic composition comprising: 
 a quantity of ceramic powder uniformly suspended in an aqueous carrier fluid ranging up to 30% by volume of total solids in said suspension,    said ceramic powder having an average particle size of 0.5 micron or less,    said carrier fluid having a quantity of passivating agent ranging from 0.5 to 5% by weight of said ceramic powder,    a quantity of dispersing agent of at least 1% by weight,    said suspension having an apparent viscosity of less than 3000 cps.    
     
     
         2 . The composition of  claim 1  wherein said ceramic powder is a metal oxide having a metal component solubility in said carrier fluid of between  10   −4  to  10   −1  moles per liter.  
     
     
         3 . The composition of  claim 2  wherein said suspension has a final pH of between about 4 and 11.  
     
     
         4 . The composition of  claim 3  wherein said ceramic powder is a complex metal oxide having the formula of ABO 3 , wherein A is at least one metallic species selected from the group consisting of barium, calcium, magnesium, lead, strontium, and zinc, and wherein B is at least one metallic species selected from the group consisting of hafnium, tin, titanium and zirconium, or mixtures or solid solutions thereof.  
     
     
         5 . The composition of  claim 3  wherein said ceramic powder is aluminum nitride or silicon nitride.  
     
     
         6 . The composition of  claim 3  wherein said ceramic powder is zinc oxide, bismuth oxide, or aluminum oxide.  
     
     
         7 . The composition of  claim 3  wherein said ceramic powder is suspended in said carrier fluid in an amount between 23% and 30% by volume of total solids present in said suspension.  
     
     
         8 . The composition of  claim 4  wherein said complex metal oxide includes one or more dopants.  
     
     
         9 . The composition of  claim 4  wherein said ceramic powder is barium titanate.  
     
     
         10 . The composition of  claim 4  wherein the ceramic powder is a mixture of barium titanate and strontium titanate.  
     
     
         11 . The composition of  claim 4  wherein the ceramic powder is a mixture of lead titanate and zirconium titanate.  
     
     
         12 . The composition of  claim 7  wherein said passivating agent is oxalic acid.  
     
     
         13 . The composition of  claim 12  wherein said dispersing agent uniformly coats said ceramic particles.  
     
     
         14 . The composition of  claim 13  wherein said dispersing agent is polyethyleneimine.  
     
     
         15 . The composition of  claim 14  wherein said ceramic particles, having been passivated and dispersant coated in said carrier fluids have a zeta potential magnitude between 10 millivolts and at least +40 millivolts.  
     
     
         16 . The composition of  claim 14  wherein said suspension has a Bingham yield point of up to 230 dynes/cm 3 .  
     
     
         17 . The composition of  claim 15  wherein said ceramic particles, having been passivated and dispersant coated in said carrier fluid, have a zeta potential magnitude between −10 millivolts and at least −40 millivolts.  
     
     
         18 . A ceramic suspension composition comprising: 
 a quantity of a metal titanate powder uniformly suspended in an aqueous carrier fluid ranging up to 30% by volume of total solids in said suspension and having an average particle size of 0.05 micron to 0.5 micron,    said carrier fluid having a quantity of oxalic acid ranging from about 1 to about 3% by weight of said metal titanate powder,    a quantity of polyethyleneimine of at least 1% by weight of said metal titanate powder,    said suspension having an apparent viscosity of less than 3000 cps.    
     
     
         19 . The composition of  claim 18  wherein said quantity of oxalic acid is about 1% by weight of said metal titanate powder and said quantity of polyethyleneimine is about 0.5% of said metal titanate powder.  
     
     
         20 . The composition of  claim 18  wherein said quantity of oxalic acid is about 5% and said quantity of polyethyleneimine is about 5% by weight of said metal titanate powder.  
     
     
         21 . The composition of  claim 18  wherein said metal titanate powder is a complex metal oxide having the formula of ABO 3 , wherein A is at least one metallic species selected from the group consisting of barium, calcium, magnesium, lead, strontium, and zinc, and wherein B is titanium.  
     
     
         22 . The composition of  claim 18  wherein said complex metal oxide includes one or more dopants selected from the group consisting of aluminum, bismuth, boron, manganese, neodymium, nickel, niobium, praseodymium, samarium, scandium, silver, tantalum, vanadium, and yttrium.  
     
     
         23 . The composition of  claim 18  wherein said complex metal oxides is barium titanate in said carrier fluid.  
     
     
         24 . The composition of  claim 18  wherein said particles of complex metal oxides have a surface zeta potential between +10 millivolts and at least +40 millivolts.  
     
     
         25 . The composition of  claim 18  wherein said particles of complex metal oxides have a surface zeta potential between −10 millivolts and at least −40 millivolts in said carrier fluid.  
     
     
         26 . The composition of  claim 18  wherein said suspension has a Bingham yield point of up to 230 dynes/cm 3 .  
     
     
         27 . A ceramic slip composition comprising: 
 quantity of ceramic powder uniformly suspended in an aqueous carrier fluid ranging up to 30% by volume of total solids in said suspension,    said ceramic powder having a particle size of 0.5 micron or less,    said carrier fluid having a quantity of passivating agent ranging from 0.5 to 5% by weight of said ceramic powder,    a quantity of dispersing agent of at least 1% by weight of said ceramic powder,    a quantity of organic binder of 12% or less by weight of said ceramic powder,    said slip having a Bingham yield point of less than or equal to 210 dynes/cm 2  and an apparent viscosity of less than 3000 cps.    
     
     
         28 . The composition of  claim 27  wherein said ceramic powder is a complex metal oxide having the formula of ABO 3 , wherein A is at least one metallic species selected from the group consisting of barium, calcium, magnesium, lead, strontium, zinc, and wherein B is at least one metallic species selected from the group consisting of hafnium, tin, titanium and zirconium, or mixtures or solid solutions thereof.  
     
     
         29 . The composition of  claim 28  wherein said complex metal oxide includes one or more dopants.  
     
     
         30 . The composition of  claim 28  wherein the complex metal oxide is a mixture of barium titanate and strontium titanate.  
     
     
         31 . The composition of  claim 28  wherein the ceramic powder is a mixture of lead titanate and zirconium titanate.  
     
     
         32 . The composition of  claim 28  wherein said ceramic powder is barium titanate.  
     
     
         31 . The composition of  claim 26  wherein said ceramic powder is zinc oxide, bismuth oxide, or aluminum oxide.  
     
     
         32 . The composition of  claim 30  wherein said passivating agent is oxalic acid.  
     
     
         33 . The composition of  claim 32  wherein said slip has a final pH of between about 7 and 10.  
     
     
         34 . The composition of  claim 33  wherein said dispersing agent is polyethyleneimine.  
     
     
         35 . The composition of  claim 34  wherein said organic binder is polyethylene glycol.  
     
     
         36 . The composition of  claim 34  wherein said organic binder is polyvinylpyrrolidone.  
     
     
         37 . The composition of  claim 34  wherein said organic binder is polyethyleneimine.  
     
     
         38 . The composition of  claim 35  wherein said slip has a Bingham yield point of less than or equal to 210 dynes/cm 2 .  
     
     
         39 . A method for preparing a suspension of ceramic powder comprising: 
 mixing up to 30% by volume of a ceramic powder having an average particle size of 0.05 micron to 0.5 micron in an aqueous carrier fluid containing a quantity of passivating agent ranging from about 0.5 to about 5% by weight of said ceramic powder,    mixing a quantity of a dispersing agent of at least 1% by weight of said ceramic powder with said suspension to achieve a uniformly distributed suspension with improved stability, and    introducing an additional quantity of water to said suspension to achieve said volume percent loading level, and an apparent viscosity of less than 3000 cps.    
     
     
         40 . The method of  claim 39  wherein said ceramic powder is a complex metal oxide having the formula of ABO 3 , wherein A is at least one metallic species selected from the group consisting of barium, calcium, magnesium, lead, strontium, zinc, and wherein B is at least one metallic species selected from the group consisting of hafnium, tin, titanium and zirconium, or mixtures or solid solutions thereof.  
     
     
         41 . The method of  claim 39  wherein said complex metal oxide includes one or more dopants.  
     
     
         42 . The method of  claim 39  wherein said ceramic powder is a mixture of lead titanate and zirconate titanate.  
     
     
         43 . The method of  claim 39  wherein said ceramic powder is a mixture of barium titanate and strontium titanate.  
     
     
         44 . The method of  claim 39  wherein said quantity of ceramic powder is barium titanate.  
     
     
         45 . The method of  claim 39  wherein said ceramic powder is zinc oxide, bismuth oxide, or aluminum oxide.  
     
     
         46 . The method of  claim 39  wherein said passivating agent is a dilute aqueous solution of oxalic acid.  
     
     
         47 . The method of  claim 39  wherein said dispersant is polyethyleneimine.  
     
     
         48 . The method of  claim 39  wherein said suspension has a final pH of between about 7 and 10.  
     
     
         49 . The method of  claim 39  wherein said particles of ceramic material have a surface zeta potential between +10 millivolts and at least +40 millivolts in said carrier fluid.  
     
     
         50 . The method of  claim 39  wherein said particles of ceramic material have a surface zeta potential between −10 millivolts and at least −40 millivolts in said carrier fluid.  
     
     
         51 . The method of  claim 39  wherein a quantity of an organic binder is added to said suspension to form a slip composition.  
     
     
         52 . The method of  claim 39  wherein said suspension achieves a Bingham yield point of less than 230 dynes/cm 2    
     
     
         53 . A method for preparing a suspension of ceramic powder by the steps consisting of: 
 mixing up to 30% by volume of a ceramic powder having an average particle size of 0.05 micron to 0.5 micron in an aqueous carrier fluid containing a quantity of passivating agent ranging from 0.5 to 5% of said ceramic powder,    mixing a quantity of a dispersing agent ranging from at least 1% by weight of said ceramic powder with said suspension to achieve a uniform distribution of said ceramic powder with improved stability, and    introducing an additional quantity of water to achieve said ceramic powder loading level, and obtaining and an apparent viscosity of less than 3000 cps.    
     
     
         54 . The method of  claim 53  having a Bingham yield point of less than or equal to 210 dynes/cm 2 .  
     
     
         55 . A method for preparing a slip of ceramic powder by the steps consisting of: 
 mixing up to 30% by volume of a ceramic powder having an average particle size of 0.05 micron to 0.5 micron in an aqueous carrier fluid containing a quantity of passivating agent ranging from 0.5 to 5% by weight of said ceramic powder,    mixing a quantity of a dispersing agent ranging from at least 1% by weight of said ceramic powder with said suspension to achieve a uniformly distributed suspension with improved stability,    adding a quantity of organic binder to form a slip, and    introducing an additional quantity of water to achieve said volume percent loading level, and an apparent viscosity of less than 3000 cps.    
     
     
         56 . The method of  claim 55  wherein said slip has a Bingham yield point of less than or equal to 210 dynes/cm 2 .  
     
     
         57 . The method of  claim 56  wherein said ceramic powder is a complex metal oxide having the formula of ABO 3 , wherein A is at least one metallic species selected from the group consisting of barium, calcium, magnesium, lead, strontium, zinc, and wherein B is at least one metallic species selected from the group consisting of hafnium, tin, titanium, zirconium, mixtures and solid solutions thereof.  
     
     
         58 . The method of  claim 56  wherein said complex metal oxide includes one or more dopants.  
     
     
         59 . The method of  claim 56  wherein said ceramic powder is a mixture of barium titanate and strontium titanate.  
     
     
         60 . The method of  claim 56  wherein said ceramic powder is a mixture of lead titanate and zirconium titanate.  
     
     
         61 . The method of  claim 56  wherein said ceramic powder is barium titanate.  
     
     
         62 . The method of  claim 56  wherein said ceramic powder is zinc, bismuth, or aluminum oxide.  
     
     
         63 . The method of  claim 56  wherein said passivating agent is oxalic acid.  
     
     
         64 . The method of  claim 63  wherein said dispersant is polyethyleneimine.  
     
     
         65 . The method of  claim 64  wherein said slip has a final pH of between about 7 and 10.  
     
     
         66 . The method of  claim 65  wherein said particles of ceramic material have a surface zeta potential between +10 millivolts and at least +40 millivolts in said carrier fluid.  
     
     
         67 . The method of  claim 65  wherein said particles of ceramic material have a surface zeta potential between −10 millivolts and at least −40 millivolts in said carrier fluid.  
     
     
         68 . The method of  claim 65 , wherein said organic binder is polyethylene glycol.  
     
     
         69 . The method of  claim 65 , wherein said organic binder is polvinylpyrrolidone.  
     
     
         70 . The method of  claim 65  wherein said organic binder is polyethyleneimine.  
     
     
         71 . The method of  claim 68  wherein said binder is present in said slip in a range of from 3% to 6% by weight of the barium titanate suspended in said slip.  
     
     
         72 . The method of  claim 69  wherein said binder is present in said slip in a range of up to 12% by weight of the barium titanate suspended in said slip.  
     
     
         73 . The method of  claim 70  wherein said binder is present in said slip in a range of up to 12% by weight of the barium titanate in said slip.  
     
     
         74 . A method for preparing a slip of ceramic powder by the steps consisting of: 
 mixing up to 30% by volume of a ceramic powder having an average particle size of 0.05 micron to 0.5 micron in an aqueous carrier fluid containing a quantity of oxalic acid ranging from 0.5 to 5% by weight of said ceramic powder,    mixing a quantity of a polyethyleneimine of at least 1% by weight of said ceramic powder with said suspension to achieve a uniform distribution of said ceramic with improved stability,    adding 12% of polyethyleneimine by weight ceramic powder to form a slip, and    introducing an additional quantity of water to achieve said volume percent loading level, and obtaining a Bingham yield point of 8 dynes/cm 2  and an apparent viscosity of 779 cps.    
     
     
         75 . A green layer prepared by the method of  claim 73  comprising applying the slip to a support means to a uniform thickness and subjecting said applied slip to a temperature sufficient to volatilize the aqueous component.