Abstract:
In a method for making nanoparticles, a reaction chamber and at least two reactants are firstly provided. One of the reactants is a liquid reactant, and at least one high-pressure injector is disposed in the reaction. Secondly, the liquid reactant is atomized by the injector, and simultaneously mixes with the other reactants in the reaction chamber. Nanoparticles can be precipitated from the mixture of the reactants thereby. Finally, the nanoparticles are isolated from the mixture. The reactants can mix on the micro-scale via the atomization of the liquid reactant, which efficiently reduces the mixing scale and increase the effective contact area between the reactants. Thus the particle-size distribution of the precipitate can easily be controlled.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to methods for making nanoparticles and, more particularly, to a method for making nanoparticles via reactive precipitation.  
       BACKGROUND  
       [0002]     Nanoparticles, one of many advanced materials in the field of nanotechnology, have tremendous potential applications in many industries.  
         [0003]     In the past decade, significant international research efforts have been directed towards the synthesis of nanoparticles. Many methods for preparing nanoparticles have been developed and reported. The methods can be classified as physical vapor deposition, chemical vapor deposition, sol-gel processing, wet chemical techniques, microemulsion processing, sonochemical processing, supercritical chemical processing, and so forth. However, no current technique can provide a reliable, simple, and low-cost method for production of nanoparticles of a specific size. Some current methods may produce particles of a desirable size, but with high cost. Other techniques suffer from an inability to control the distribution of sizes around a desired nanoparticle size. Still other techniques require specialized equipment, long processing times, or expensive special chemicals.  
         [0004]     One potentially attractive wet chemical technique for synthesis of nanoparticles is reactive precipitation. Typical reactive precipitation processes are often carried out by mixing reactants in a stirred tank. A reactive precipitation process consists of three main steps: mixing reactants, chemical reaction, and crystal growth. However, typical reactive precipitation process can only provide macro-scaled mixing, which may limit the size and the homogeneity of the precipitate.  
         [0005]     What is needed, therefore, is a simple, and low cost reactive precipitation process for making nanoparticles, which can provide nanoparticles with well-controlled particle-size and particle-size distribution.  
       SUMMARY  
       [0006]     In one embodiment thereof, a method for making nanoparticles is provided. Firstly, a reaction chamber and at least two reactants are provided. One of the reactants is a liquid reactant, and at least one high-pressure injector is disposed in the reaction chamber. Secondly, the liquid reactant is atomized by the injector, and simultaneously mixes with the other reactants in the reaction chamber. Thereby, nanoparticles can be precipitated from the mixture of the reactants. Finally, the nanoparticles are isolated from the mixture.  
         [0007]     Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Many aspects of the method for making nanoparticles can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the method for making nanoparticles. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0009]      FIG. 1  is a flow chart of a method for making nanoparticles in accordance with the present invention;  
         [0010]      FIG. 2  is a schematic view of an apparatus in accordance with a first preferred embodiment of the present invention;  
         [0011]      FIG. 3  is a schematic view of an apparatus in accordance with a second preferred embodiment of the present invention,  
         [0012]      FIG. 4  is a schematic view of an apparatus in accordance with a third preferred embodiment of the present invention; and 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]      FIG. 1  shows a method for making nanoparticles, including steps  100  to  400 . In step  100 , several reactants, one of which is a liquid reactant, are prepared. In step  200 , the liquid reactant is atomized and mixed with other reactants. In step  300 , a nano-structured powder is precipitated from the mixture of the reactants. In step  400 , the powder is isolated from the mixture, thus obtaining the nanoparticles.  
         [0014]     Referring to  FIG. 2 , an apparatus  6  for carrying out the above-mentioned method in accordance with a first preferred embodiment of the present invention, includes two solution containers  10 , two injectors  30 , an extra injector  40 , a reaction chamber  50 , a valve  60 , a pump  70 , a tank  80 , a stirrer  90 , and a plurality of pipes  190 . The injectors  30  are disposed on the inside wall  501  of the reaction chamber  50 . Each injector  30  is connected to a corresponding one of the solution containers  10  by the pipe  190 . The tank  80  is connected to the bottom of the reaction chamber  50  by the pipe  190  and the stirrer  90  is disposed in the tank  80 . The tank  80 , the valve  60 , the pump  70 , and the extra injector  40  are connected in series by the pipes  190 .  
         [0015]     The first embodiment of the method for making nanoparticles is carried out by spray atomizing two liquid reactants to mix them together. The liquid reactants may be an aqueous sodium carbonate (Na 2 CO 3 ) solution and an aqueous strontium nitrate (Sr(NO 3 ) 2 ) solution.  
         [0016]     Firstly, the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution are prepared in appropriate molarities and are then each introduced into their respective solution containers  10 .  
         [0017]     Secondly, the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution are each atomized by their respective injectors  30 , and simultaneously sprayed into the reaction chamber  50  at a rate of 2.0 liters per hour to mix together. The injectors  30  may be high-pressure swirl injectors, and the atomization pressure of the solutions may be in the range of 2˜20 Mpa (megapascals). Therefore, micro-droplets of the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution are obtained with a diameter in the range of 20˜60 μm (micrometers), which allows the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution to mix on a molecular scale.  
         [0018]     After spray mixing the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution in the reaction chamber  50 , nucleation, which forms nuclei of strontium carbonate (SrCO 3 ) particles, occurs in the chamber  50  according to the following reaction: 
 
Sr(NO 3 ) 2 (l)+Na 2 CO 3 (l)→SrCO 3 (s)+2NaNO 3 (l) 
 
         [0019]     Thirdly, the mixture of the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution is transported into the tank  80  via the pipe  190 , and agitated by the stirrer  90 . The growth of the nuclei of strontium carbonate (SrCO 3 ) particles may be well controlled with the agitation of the stirrer  90 . Thereby a final mixture consisting of sodium nitrate (NaNO 3 ), strontium carbonate (SrCO 3 ) particles, and a small amount of sodium carbonate (Na 2 CO 3 ) and strontium nitrate (Sr(NO 3 ) 2 ) is obtained. The mixture of the sodium carbonate (Na 2 CO 3 ) solution and the strontium nitrate (Sr(NO 3 ) 2 ) solution may be returned to the reaction chamber  50  via the valve  60 , the pump  70  and the extra injector  40 , and be reacted again to precipitate more strontium carbonate (SrCO 3 ).  
         [0020]     Finally, the strontium carbonate (SrCO 3 ) particles are separated from the final mixture, and the strontium carbonate (SrCO 3 ) particles are dried to obtain an end-product nano-structured powder.  
         [0021]     Referring to  FIG. 3 , an apparatus  7  for carrying out the above-mentioned method in accordance with a second preferred embodiment of the present invention, includes a solution container  11 , an injector  12 , two gas nozzles  13 , two gas pressure controllers  131 , two gas supply apparatuses, a reaction chamber  14 , a valve  15 , a pump  16 , a stirrer  17 , a tank  18  and a plurality of pipes  19 . The injector  12  is disposed on the top of the inside wall  141  of the reaction chamber  14  and connected to the solution container  11  by the pipe  19 . The gas nozzles  13  are disposed on the inside wall  141  of the reaction chamber  14  and connected to the gas supply apparatuses  132  via the gas pressure controllers  131  to provide gases. The tank  18  is connected to the bottom of the reaction chamber  14  by the pipe  19 , and the stirrer  17  is disposed in the tank  18 . The tank  18 , the valve  15 , the pump  16  and the solution container  11  are connected in series by the pipes  19 .  
         [0022]     The second embodiment of the method for making nanoparticles is carried out by spray atomizing a liquid reactant and mixing the liquid reactant with a gas reactant. The liquid reactant may be an aqueous sodium aluminate (NaAlO 2 ) solution, and the gas reactant may be carbon dioxide (CO 2 ).  
         [0023]     Firstly, the aqueous sodium aluminate (NaAlO 2 ) solution is prepared in an appropriate molarity and introduced into the corresponding solution container  11 .  
         [0024]     Secondly, the sodium aluminate (NaAlO 2 ) solution is atomized by the injector  12  and sprayed into the reaction chamber  14  at a rate of 2.0 liters per hour. Simultaneously, a carbon dioxide (CO 2 ) gas provided by the gas supply apparatuses  132  is also injected into the reaction chamber  14  via the gas nozzles  13 , and meets the atomized sodium aluminate (NaAlO 2 ) solution. The injector  12  may be a high-pressure swirl injector and the atomization pressure of the solution may be in the range of 2˜20 Mpa (megapascals). Therefore, micro-droplets of the sodium aluminate (NaAlO 2 ) solution are obtained with a diameter in the range of 20-60 μm (micrometers), which allows the sodium aluminate (NaAlO 2 ) solution to mix with the carbon dioxide (CO 2 ) on a molecular scale.  
         [0025]     After spray mixing the sodium aluminate (NaAlO 2 ) solution and the carbon dioxide (CO 2 ) in the chamber  14 , nucleation, which forms nuclei of aluminum hydroxide (Al(OH) 3 ) particles, occurs in the reaction chamber  14  according to the following reaction: 
 
2NaAlO 2 (l)+3H 2 O(l)+CO 2 (g)→Na 2 CO 3 (l)+2Al(OH) 3 (s) 
 
         [0026]     Thirdly, the mixture of the sodium aluminate (NaAlO 2 ) solution and the carbon dioxide (CO 2 ) is transported into the tank  18  via the pipe  19 , and agitated by the stirrer  17 . The growth of nuclei of the aluminum hydroxide (Al(OH) 3 ) may be well controlled with agitation of the stirrer  17 . Thereby a final mixture consisting of sodium carbonate (Na 2 CO 3 ), aluminum hydroxide (Al(OH) 3 ) particles, and a small amount of aluminate (NaAlO 2 ) that has incompletely reacted with the carbon dioxide (CO 2 ) is obtained. The mixture of the sodium aluminate (NaAlO 2 ) solution and the carbon dioxide (CO 2 ) may be returned into the reaction chamber  14  via the valve  15 , the pump  16 , the solution container  11  and the injector  12 , for reaction with carbon dioxide (CO 2 ) again to precipitate more aluminum hydroxide (Al(OH) 3 ).  
         [0027]     Finally, the aluminum hydroxide (Al(OH) 3 ) particles are separated from the final mixture, and the aluminum hydroxide (Al(OH) 3 ) particles are dried to obtain an end-product nano-structured powder.  
         [0028]     Referring to  FIG. 4 , an apparatus  8  for carrying out the above-mentioned method in accordance with a third preferred embodiment of the present invention, includes a solution container  21 , an injector  22 , two gas nozzles  23 , two gas pressure controllers  231 , two powder nozzles  330 , two powder supply apparatuses  331 , a reaction chamber  24 , a valve  25 , a pump  26 , a stirrer  27 , a tank  28  and a plurality of pipes  29 . The injector  22  is disposed on the top of the inside wall  241  of the reaction chamber  24  and connected to the solution container  21  by the pipe  29 . The gas nozzles  23  are disposed on the inside wall  241  of the reaction chamber  24  and connected to a corresponding one of the gas supply apparatuses  232  via the gas pressure lock  231  to provide gases. The powder nozzles  330  are disposed on the inside wall  241  of the reaction chamber  24  and connected to a corresponding one of the powder supply apparatuses  331 . The tank  28  is connected to the bottom of the reaction chamber  24  by the pipe  29 , and the stirrer  27  is disposed in the tank  28 . The tank  28 , the valve  25 , the pump  26 , and the solution container  21  are connected in series by the pipes  29 .  
         [0029]     The third embodiment of the method for making nanoparticles is carried out by spray atomizing a liquid reactant and mixing the liquid reactant with a gas reactant and a solid reactant. The liquid reactant, the gas reactant, and the solid reactant may be a distilled water, a carbon dioxide (CO 2 ) gas, and a calcium hydroxide (Ca(OH) 2 ) powder respectively.  
         [0030]     Firstly, the distilled water, the carbon dioxide (CO 2 ), and the calcium hydroxide (Ca(OH) 2 ) powder are provided.  
         [0031]     Secondly, the water is atomized by the injector  22  and sprayed into the reaction chamber  24  at a rate of 2.0 liters per hour. Simultaneously, the carbon dioxide (CO 2 ) gas and the calcium hydroxide (Ca(OH) 2 ) powder are also injected into the reaction chamber  24  via the gas nozzles  23  and the powder nozzles  30  respectively, and meet the atomized water to mix with each other. The injector  22  may be a high-pressure swirl injector and the atomization pressure of the solution may be in the range of 2˜20 Mpa (megapascals). Therefore, micro-droplets of the water can be obtained with a diameter in the range of 20-60 μm (micrometers), which allows the distilled water to mix with the calcium hydroxide (Ca(OH) 2 ) powder and the carbon dioxide (CO 2 ) on a molecular scale.  
         [0032]     After the spray mixing of the distilled water, the calcium hydroxide (Ca(OH) 2 ) powder and the carbon dioxide (CO 2 ) in the reaction chamber  24 , nucleation, which forms nuclei of calcium carbonate (CaCO 3 ) particles occurs in the chamber  24  according to the following reaction: 
 
Ca(OH) 2 (l)+H 2 O(l)+CO 2 (g)→CaCO 3 (s)+2H 2 O(l) 
 
         [0033]     Thirdly, the mixture of the water, the calcium hydroxide (Ca(OH) 2 ) powder and the carbon dioxide (CO 2 ) is transported into the tank  28  via the pipe  29 , and agitated by the stirrer  27 . The growth of nuclei of the calcium carbonate (CaCO 3 ) may be well controlled with agitation of the stirrer  17 . Thereby a final mixture consisting of water, calcium carbonate (CaCO 3 ) particles, and a small amount of calcium hydroxide (Ca(OH) 2 ) that has incompletely reacted with the carbon dioxide (CO 2 ) is obtained. The mixture of the distilled water, the calcium hydroxide (Ca(OH) 2 ) powder and the carbon dioxide (CO 2 ) may be returned to the reaction chamber  24  via the valve  25 , the pump  26 , the solution container  21  and the injector  22  in succession, and reacted with carbon dioxide (CO 2 ) again to precipitate more calcium carbonate (CaCO 3 ).  
         [0034]     Finally, the calcium carbonate (CaCO 3 ) particles are separated from the final mixture, and the calcium carbonate (CaCO 3 ) particles are dried to obtain an end-product nano-structured powder.  
         [0035]     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.