Process for preparing nanostructured materials of controlled surface chemistry

Abstract

A process to prepare stoichiometric-nanostructured materials comprising generating a plasma, forming an “active volume” through introduction of an oxidizing gas into the plasma, before the plasma is expanded into a field-free zone, either (1) in a region in close proximity to a zone of charge carrier generation, or (2) in a region of current conduction between field generating elements, including the surface of the field generation elements, and transferring energy from the plasma to a precursor material to form in the “active volume” at least one stoichiometric-nanostructured material and a vapor that may be condensed to form a stoichiometric-nanostructured material. The surface chemistry of the resulting nanostructured materials is substantially enhanced to yield dispersion stable materials with large zeta-potentials.

We claim:  
     
         1 . A process to prepare stoichiometric-nanostructured materials comprising: 
 generating a plasma;    forming an “active volume” through introduction of an oxidizing gas into the plasma, before the plasma is expanded into a field-free zone, either (1) in a region in close proximity to a zone of charge carrier generation, or (2) in a region of current conduction between field generating elements, including the surface of the field generation elements; and    transferring energy from the plasma to a precursor material or materials and forming in the “active volume” at least one of stoichiometric-nanostructured materials and a vapor that may be condensed to form a stoichiometric-nanostructured material.    
     
     
         2 . The process of  claim 1 , wherein the step of generating comprises utilizing a radio-frequency field to generate the plasma.  
     
     
         3 . The process of  claim 1 , wherein the step of generating comprises utilizing a microwave discharge to generate the plasma.  
     
     
         4 . The process of  claim 1 , wherein the step of generating comprises utilizing a free-burning electric arc to generate the plasma.  
     
     
         5 . The process of  claim 1 , wherein the step of generating comprises utilizing a transferred electric arc to generate the plasma.  
     
     
         6 . The process of  claim 1 , wherein the step of generating comprises utilizing a high-intensity laser to generate the plasma.  
     
     
         7 . The process of  claim 1 , wherein the step of generating comprises utilizing a capacitively coupled electro-thermal igniter to generate the plasma.  
     
     
         8 . The process of  claim 1 , wherein the step of generating comprises utilizing a DC glow discharge to generate the plasma.  
     
     
         9 . The process of  claim 1 , wherein the step of generating comprises utilizing a DC cold cathode discharge to generate the plasma.  
     
     
         10 . The process of  claim 1 , wherein the step of forming comprises selecting the oxidizing gas from one of a gas containing oxygen atoms or a gas mixture containing oxygen atoms.  
     
     
         11 . The process of  claim 1 , wherein the step of forming comprises selecting non-oxygen components of the oxidizing gas from a group comprising He, Ne, Ar, Kr, Xe, N2, and H2, or mixtures thereof.  
     
     
         12 . The process of  claim 1 , wherein the step of forming comprises selecting N2O as the oxidizing gas.  
     
     
         13 . The process of  claim 1 , wherein the step of forming comprises selecting O2 as the oxidizing gas.  
     
     
         14 . The process of  claim 1 , wherein the step of forming comprises selecting CO2 as the oxidizing gas.  
     
     
         15 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas into a anodic column of a transferred electric arc.  
     
     
         16 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas into a cathodic column of a transferred electric arc.  
     
     
         17 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas into a anodic column of a free-burning electric arc.  
     
     
         18 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas into a cathodic column of a free-burning electric arc.  
     
     
         19 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas to the plasma by natural convection.  
     
     
         20 . The process of  claim 1 , wherein the step of forming comprises introducing the oxidizing gas to the plasma by forced convection.  
     
     
         21 . The process of  claim 1 , wherein the step of forming comprises allowing the oxidizing gas to atomize a liquid nanoparticle precursor and introduce it into the “active volume”.  
     
     
         22 . The process of  claim 1 , wherein the step of forming comprises allowing the oxidizing gas to fluidize and transport a solid nanoparticle precursor into the “active volume”.  
     
     
         23 . The process of  claim 1 , further comprising: 
 Injecting at least one of a quench and dilution stream just beyond the “active volume.” The injection point beyond the “active volume” is from one mean free path of a plasma species to a larger distance deemed to be appropriate to quench the vapor and is generally determined by process equipment configuration.    
     
     
         24 . The process of  claim 23 , wherein the step of injecting comprises creating a nanoparticle aerosol of controlled particle size.  
     
     
         25 . Stoichiometric-nanostructured materials produced through steps comprising: 
 generating a plasma;    forming an “active volume” through introduction of an oxidizing gas into the plasma, before the plasma is expanded into a field free zone, in a region in close proximity to either (1) a zone of charge carrier generation, or (2) a region of current conduction between field generating elements, including the surface of the field generating electrodes; and    transferring energy from the plasma to a precursor material or materials and forming in the “active volume” at least one of stoichiometric-nanostructured materials and a vapor that may be condensed to form a stoichiometric-nanostructured material.    
     
     
         26 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials are metal oxides.  
     
     
         27 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials are substantially spherical nanocrystalline metal oxides.  
     
     
         28 . The stoichiometric-nanostructured materials of  claim 26 , wherein the metal oxides are selected from a group comprising aluminum oxide, zinc oxide, iron oxide, cerium oxide, chromium oxide, antimony tin oxide, mixed rare earth oxides, and indium tin oxide.  
     
     
         29 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials generally have a size distribution and range in mean diameter from about 1 nm to about 900 nm.  
     
     
         30 . The stoichiometric-nanostructured materials of  claim 29 , wherein the stoichiometric-nanostructured materials generally have a size distribution and range in mean diameter from about 2 nm to about 100 nm.  
     
     
         31 . The stoichiometric-nanostructured materials of  claim 30 , wherein the stoichiometric-nanostructured materials generally have a size distribution and range in mean diameter from about 5 nm to about 40 nm.  
     
     
         32 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials have a surface chemistry having a high aqueous dispersion stability.  
     
     
         33 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials have a surface chemistry having a low rate of hydrolysis.  
     
     
         34 . The stoichiometric-nanostructured materials of  claim 25 , wherein the stoichiometric-nanostructured materials have a surface chemistry with the absolute value of the zeta potential greater than 20 mV.  
     
     
         35 . The stoichiometric-nanostructured materials of  claim 34 , wherein the stoichiometric-nanostructured materials have a surface chemistry with the absolute value of the zeta potential greater than 30 mV.  
     
     
         36 . The stoichiometric-nanostructured materials of  claim 35 , wherein the stoichiometric-nanostructured materials have a surface chemistry with the absolute value of the zeta potential greater than 35 mV.