Lower-energy process for preparing passivated inorganic nanoparticles
View Patent ↗The disclosure is directed to a method for reducing the chemical activity and photo activity of titanium dioxide nanoparticles comprising adding an amorphous alumina-stabilizing agent, specifically an anion, such as citric acid, to an aqueous slurry of the titanium dioxide nanoparticles; treating the aqueous slurry with a source of alumina, such as a solution of sodium aluminate, to form alumina-treated titanium dioxide nanoparticles; recovering the alumina-treated inorganic nanoparticles, wherein the nanoparticles have a particle size of about 50 to about 300 nm; and milling the nanoparticles to form nanoparticles having a particle size about 15% smaller than silica-treated inorganic nanoparticles milled under similar conditions. The titanium dioxide nanoparticles described herein are useful in cosmetic, coating and thermoplastic compositions.
1. A process for making alumina-treated inorganic nanoparticles comprising:
(a) forming a slurry of inorganic nanoparticles by mixing the nanoparticles with water;
(b) contacting the slurry of inorganic nanoparticles with an amorphous alumina-stabilizing agent;
(c) contacting the slurry with a source of alumina to form alumina-treated inorganic nanoparticles;
(d) recovering the alumina-treated inorganic nanoparticles by filtering the slurry to form a wet cake;
(e) liquefying the wet cake and media milling the liquefied wet cake to form a milled slurry;
(f) drying the milled slurry to form a powder; and
(g) micronizing the powder to form alumina-treated inorganic nanoparticles in which 5% or less of the particles, based on the volume particle size distribution within a range of 6 nm to 6000 nm, have a diameter greater than 220 nm.
2. The process of claim 1 wherein the inorganic nanoparticle is selected from the group consisting of metal oxide, mixed metal oxides, metal hydroxide, metal sulfide, metal carbonate, metal sulfate, silica, and mixtures thereof.
3. The process of claim 2 wherein the metal is selected from the group consisting of Ca, Mg, Ti, Ba, Zn, Zr, Mo, Ce, and Al.
4. The process of claim 2 wherein the inorganic nanoparticle comprises titanium dioxide.
5. The process of claim 1 wherein the amorphous alumina-stabilizing agent has an anion.
6. The process of claim 5 wherein the anion is selected from the group consisting of citrate ions, phosphate ions, sulfate ions, and fluoride ions.
7. The process of claim 1 further comprising contacting the slurry of inorganic nanoparticles with sodium aluminate prior to step (b).
8. The process of claim 1 wherein the source of alumina is sodium aluminate.
9. The process of claim 1 further comprising contacting the treated inorganic nanoparticle with an organic composition.
10. The process of claim 1 wherein the treated inorganic nanoparticles are silanized.
11. The process of claim 10 wherein the organic composition comprises at least one of octyltriethoxysilane, aminopropyltriethoxysilane, polyhydroxystearic acid, and polyhydroxy siloxide.
12. The process of claim 5 wherein the source of the anion comprises citric acid.
13. The process of claim 5 wherein the source of the anion comprises phosphoric acid.
14. The process of claim 5 wherein the source of the anion comprises sodium sulfate.
15. The process of claim 5 wherein the source of the anion comprises potassium fluoride.
16. The process of claim 1 wherein less than 5% of the alumina-treated inorganic nanoparticles formed in step (g), based on the volume particle size distribution within a range of from 6 nm to 6000 nm, have a diameter greater than 220 nm.
17. The process of claim 1 further comprising dispersing the inorganic nanoparticles in an organic or aqueous medium.
18. The process of claim 1 further comprising the step of dispersing the inorganic nanoparticles in a thermoplastic material.
19. The process of claim 1 in which the step of micronizing is carried out in a 20 cm micronizer apparatus.
20. The process of claim 1 in which the liquefied wet cake is media milled in a Netzch mill.