Methods to stabilize a viscosity-unstable aqueous dispersion of carbon

Abstract

A method for preventing a carbon dispersion from increasing in viscosity during use is described. The dispersion comprises graphite particles or carbon black particles or a combination of both dispersed in a fluid. The method involves lowering the susceptibility of the carbon dispersion to an increase in viscosity or ionic strength by lowering its pH or reducing its exposure to reactive components in the ambient atmospheric gas. The pH can be lowered by at least partially removing ammonia from the dispersion, or by adding a material that reduces the pH of the dispersion. The stability of the dispersion can also be improved by isolating the dispersion from reactive atmospheric gas. The stabilized aqueous carbon dispersion can have a viscosity of less than about 20 cps and a conductivity of less than about 3 mS.

What is claimed is:  
     
         1 . A method of stabilizing a carbon dispersion, comprising: 
 A. providing a viscosity-unstable aqueous dispersion of carbon that has a pH of at least 7.5 and is susceptible to a viscosity increase during use; and    B. reducing the alkalinity of the viscosity-unstable aqueous dispersion of carbon by an amount effective to reduce the susceptibility of the carbon dispersion to a viscosity increase.    
     
     
         2 . The method of  claim 1 , wherein the carbon in said dispersion comprises carbon black.  
     
     
         3 . The method of  claim 1 , wherein the carbon in said dispersion comprises graphite.  
     
     
         4 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a pH of at least 8.  
     
     
         5 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a pH of at least 9.  
     
     
         6 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a pH of at least 10.  
     
     
         7 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a viscosity of at least 2 cps before use.  
     
     
         8 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a viscosity of at least 4 cps before use.  
     
     
         9 . The method of  claim 1 , wherein the viscosity-unstable aqueous dispersion of carbon has a viscosity of at least 6 cps before use.  
     
     
         10 . The method of  claim 1 , wherein said viscosity-unstable aqueous dispersion of carbon comprises ammonia in a concentration sufficient to make it susceptible to a viscosity increase when exposed to the atmosphere and wherein said alkalinity reducing step is carried out by reducing the concentration of ammonia in the viscosity-unstable aqueous dispersion of carbon.  
     
     
         11 . A method of stabilizing a viscosity-unstable aqueous dispersion of carbon, comprising: 
 A. providing a viscosity-unstable aqueous dispersion of carbon that is susceptible to a viscosity increase when exposed to the atmosphere;    B. isolating the carbon dispersion from reactive atmospheric gas during use to a degree sufficient to at least reduce its viscosity increase.    
     
     
         12 . The method of  claim 11 , wherein the reactive gas comprises carbon dioxide.  
     
     
         13 . The method of  claim 11 , wherein said isolating step is carried out by at least reducing the headspace above the dispersion in the bath, during use.  
     
     
         14 . The method of  claim 11 , wherein said isolating step is carried out by introducing an inert fluid in the headspace above the dispersion during use.  
     
     
         15 . The method of  claim 11 , wherein said inert fluid is nitrogen.  
     
     
         16 . The method of  claim 11 , wherein said inert fluid is argon.  
     
     
         17 . The method of  claim 11 , wherein said inert fluid comprises air at least partially depleted of carbon dioxide.  
     
     
         18 . A stabilized aqueous dispersion of carbon having a viscosity of less than about 20 cps and a conductivity of less than about 3 mS.