1. Field of the Invention
The present invention relates to a method for making nanoparticles, and more particularly to a method for making silica nanoparticles by flame spray pyrolysis adopting a two-fluid nozzle, which sprays droplets under high pressure from a silicon alkoxide solution to directly oxidize in a flame thereby producing spherical silica nanoparticles.
2. Description of the Prior Art
In general, nanoparticles refer to particles having a size 100 nm or less, which are mainly used as advanced materials due to high specific area per mass and novel functions.
Silica (SiO2) particles are adopted in various applications such as fillers of Epoxy display and semiconductor Molding Compound (EMC), fillers of cosmetics and copy machine toner, components of paint and ink for improving endurance and inducing diffused reflection, raw materials of optical fibers, ceramic ware and glasses.
Examples of technologies for making such silica particles are known from U.S. Pat. No. 6,322,765, titled “Process for preparing silicon dioxide”, filed Sep. 8, 1998; U.S. Pat. No. 6,386,373, titled “Process for making silica powder and use of such powder in the manufacture of an optical fiber preform”, filed Mar. 10, 2000; U.S. Pat. No. 6,698,247, titled “Method and feedstock for making silica by flame combustion”, filed May 4, 2001; Korean Patent No. 10-0354432, titled “Method for making spherical silica particles by spray pyrolysis”, filed Jul. 12, 2000; Korean Patent No. 10-0468050, titled “Method for making spherical silica powder”, filed Dec. 4, 2001; Korean Patent No. 10-0503675, titled “Method for making high purity silica”, filed Mar. 9, 2002; and Korean Patent No. 10-0477200, titled “Method for making silica particles by supersonic spray pyrolysis”, filed Jun. 5, 2002.
To be used in advanced material fields such as semiconductor fields which require high integration, small size and thickness reduction, silica particles should be produced in nanosize and maintain a spherical geometry to obtain high filling density.
To make silica nanoparticles, many researchers have developed physical/chemical approaches. Examples of such approaches are known from U.S. Pat. No. 5,580,655, titled “Silica nanoparticles”, filed Mar. 3, 1995; U.S. Pat. No. 5,770,022, titled “Method of making silica nanoparticles”, filed Jun. 5, 1997; and Korean Patent No. 10-0330626, filed “Method for making nanosize silica fine particles”, filed Mar. 7, 2000.
U.S. Pat. No. 5,580,655 relates to a method for vaporizing Si metal with a pulse laser to react with oxygen in order to produce silica nanoparticles. However, pulse laser method shows a low yield of silica nanoparticles, and thus is hardly applicable in the industry.
U.S. Pat. No. 5,770,022 relates to a method for synthesizing silica, in which a direct current discharge is performed with an anode of Si and a cathode of Cu or W to generate plasma in an oxygen atmosphere so that Si in the anode is vaporized and oxidized to synthesize silica. Korean Patent No. 10-0330626 relates to a method for synthesizing silica nanoparticles, in which an evaporator vaporizes source material for silica such as silicon alkoxide, which is then supplied to a flame reactor to be synthesized into silica nanoparticles through Chemical Vapor Deposition (CVD).
According to these methods, however, a large amount of energy is consumed and it is difficult to make spherical silica nanoparticles since source material such as Si metal or silicon alkoxide compound is vaporized and oxidized to produce silica nanoparticles.