Fabrication of nanowires and hierarchically porous materials through supercritical co2 assisted nebulization

Abstract

A processing technique for creating nanowires and hierarchically porous micro/nano structures of ceramic materials is provided. The process includes evaporation of micron-sized water droplets containing dissolved organic salts on heated substrates followed by thermal decomposition of the deposited material. The micron-sized droplets may be generated by supercritical CO 2 assisted nebulization, in which high-pressure streams of aqueous solution and supercritical CO 2 are mixed, followed by controlled depressurization through a fine capillary. Rapid evaporation takes place on the heated substrates and structures are generated due to CO 2 effervescence from the droplets and evaporation of water, along with the pinning of the three phase contact line. Depending on the mass deposited, a mesh of nano-wires or membrane-like structures may result. Sintering of the membrane-like scaffolds above the decomposition temperature of the organic salt creates nanopores within the structures, creating a dual hierarchy of pores.

What is claimed: 
     
         1 . A process comprising:
 mixing a stream of supercritical CO 2  with an aqueous solution of an organic salt in a continuous flow operation;   creating an aerosol from the mixture; and   depositing the aerosol on heated substrates.   
     
     
         2 . The process of  claim 1 , further comprising sintering the deposited aerosol. 
     
     
         3 . The process of  claim 2 , wherein the sintering produces a nanowire mesh or a hierarchically porous structure. 
     
     
         4 . The process of  claim 2 , wherein the sintering is at a temperature of at least about 300° C. for about 6 hours to about 8 hours. 
     
     
         5 . The process of  claim 1 , wherein the supercritical CO 2  is at a pressure of about 0.1 MPa to about 0.3 MPa. 
     
     
         6 . The process of  claim 1 , wherein creating the aerosol comprises rapidly expanding the mixture through a capillary, nozzle, or tube. 
     
     
         7 . The process of  claim 1 , wherein the heated substrate is at a temperature of about 80° C. to about 150° C. 
     
     
         8 . The process according to  claim 1 , wherein the organic salt is described by the formula:
   M x (N) y      wherein M is at least one of Ca, Ag, Cu, Zn, Co, Fe, Mn, and Ni, and N is at least one of acetate (CH 3 COO − ), acetylacetonate (CH 3 COCH 2 COO − ), oxalate (C 2 O 4   2− ), and hydroxide (OH − ).   
     
     
         9 . The process according to  claim 1 , wherein the deposited material comprises nanowires. 
     
     
         10 . The process according to  claim 1 , wherein the deposited material has a thickness of less than about 100 nm. 
     
     
         11 . The process according to  claim 1 , wherein the deposited material comprises microporous inorganic membranes. 
     
     
         12 . The process according to  claim 1 , wherein the deposited material has a thickness of about 1 μm to about 3 μm. 
     
     
         13 . The process according to  claim 1 , wherein the deposited material comprises:
 nanopores with an average diameter of less than about 100 nm, and   pores with an average diameter of greater than about 100 nm.   
     
     
         14 . The process according to  claim 1 , wherein the deposited material comprises CaCO 3 . 
     
     
         15 . The process according to  claim 1 , wherein the substrate comprises titanium. 
     
     
         16 . The process according to  claim 1 , wherein the substrate comprises a medical implant. 
     
     
         17 . A process comprising:
 creating an aerosol from an aqueous solution of an organic salt in a continuous flow operation; and   depositing the aerosol on heated substrates,   wherein creating the aerosol comprises an inkjet process.   
     
     
         18 . A composite medical implant, comprising:
 a medical implant substrate, and   a coating disposed on a surface of the medical implant substrate,   wherein the coating is biocompatible, osseoconductive, and comprises a nanowire mesh or a hierarchically porous structure.   
     
     
         19 . The coated medical implant of  claim 18 , wherein the medical implant substrate comprises titanium. 
     
     
         20 . The coated medical implant of  claim 18 , wherein the coating comprises CaCO 3 .