Zirconium oxide nanoparticles

Abstract

An object of the present invention is to provide zirconium oxide nanoparticles that have excellent dispersibility in a polar solvent and are capable of increasing a core concentration in a dispersion liquid. Zirconium oxide nanoparticles according to the present invention are coated with at least one compound selected from the group consisting of R.sup.1—COOH, (R.sup.1O).sub.3-n—P(O)—(OH).sub.n, (R.sup.1).sub.3-n—P(O)—(OH).sub.n, (R.sup.1O)—S(O)(O)—(OH), R.sup.1—S(O)(O)—(OH), and (R.sup.1).sub.4-m—Si(R.sup.4).sub.m, wherein R.sup.1 represents a group comprising a carbon atom and at least one element selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and having the total number of carbon atoms, oxygen atoms, nitrogen atoms, and sulfur atoms of 8 or less; R.sup.4 represents a halogen atom or —OR.sup.2, and R.sup.2 represents a hydrogen atom or an alkyl group; and n represents 1 or 2, and m represents an integer of 1 to 3.

Claims

1. Zirconium oxide nanoparticles coated with a secondary carboxylic acid and at least one compound selected from the group consisting of R.sup.1—COOH, (R.sup.1O).sub.3-n—P(O)—(OH).sub.n, (R.sup.1).sub.3-n—P(O)—(OH).sub.n, (R.sup.1O)—S(O)(O)—(OH), R.sup.1—S(O)(O)—(OH), and (R.sup.1).sub.4-m—Si(R.sup.4).sub.m, wherein R.sup.1 represents a group comprising a carbon atom and at least one element selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom, and having the total number of carbon atoms, oxygen atoms, nitrogen atoms, and sulfur atoms of 4 or less; R.sup.4 represents a halogen atom or —OR.sup.2, and R.sup.2 represents a hydrogen atom or an alkyl group; n represents 1 or 2, and m represents an integer of 1 to 3; and the secondary carboxylic acid has 4 or more carbon atoms.

2. The zirconium oxide nanoparticles according to claim 1, wherein R.sup.1 has a ratio of a sum of the number of oxygen atoms, nitrogen atoms, and sulfur atoms to the number of carbon atoms (sum of the number of oxygen atoms, nitrogen atoms, and sulfur atoms/number of carbon atoms) of 1/7 or more and 1/1 or less.

3. The zirconium oxide nanoparticles according to claim 1, wherein the compound has a ratio of the number of oxygen atoms to the number of carbon atoms (number of oxygen atoms/number of carbon atoms) of more than 1/6 and 1/0.2 or less.

4. The zirconium oxide nanoparticles according to claim 1, wherein the zirconium oxide nanoparticles have a crystal structure, and a total of a tetragonal crystal and a cubic crystal is 60% or more of entire crystal structures.

5. The zirconium oxide nanoparticles according to claim 1, having an average particle diameter of 1 to 100 nm.

6. The zirconium oxide nanoparticles according to claim 1, wherein R.sup.1 has a Hansen solubility parameter (HSP) distance to ethanol of 0 (MPa).sup.1/2 or more and 20 (MPa).sup.1/2 or less.

7. The zirconium oxide nanoparticles according to claim 1, wherein R.sup.1 has a Hansen solubility parameter (HSP) distance to water of 20 (MPa).sup.1/2 or more and 41 (MPa).sup.1/2 or less.

8. The zirconium oxide nanoparticles according to claim 1, wherein the secondary carboxylic acid is at least one selected from the group consisting of isobutyric acid, 2-methylbutyric acid, 2-ethylbutyric acid, 2-ethylhexanoic acid, 2-methylvaleric acid, 2-methylhexanoic acid, 2-methylheptanoic acid, 2-propylbutyric acid, 2-hexylvaleric acid, 2-hexyldecanoic acid, 2-heptylundecanoic acid, 2-methylhexadecanoic acid, and 4-methylcyclohexanecarboxylic acid.

9. A dispersion liquid comprising the zirconium oxide nanoparticles according to claim 1.

10. The dispersion liquid according to claim 9, comprising a solvent having a Hansen solubility parameter (HSP) distance to water of 0 (MPa).sup.1/2 or more and 40 (MPa).sup.1/2 or less.

11. A resin composition comprising the zirconium oxide nanoparticles according to claim 1.

12. The resin composition according to claim 11, comprising at least one resin component selected from a monomer, an oligomer, and a polymer.

13. The resin composition according to claim 11, comprising a solvent having a Hansen solubility parameter (HSP) distance to water of 0 (MPa).sup.1/2 or more and 40 (MPa).sup.1/2 or less.

14. A molded material comprising the zirconium oxide nanoparticles according to claim 1.

15. A ceramic material comprising the zirconium oxide nanoparticles according to claim 1.

16. A process for producing a ceramic material, comprising firing the zirconium oxide nanoparticles according to claim 1 at 500° C. or higher.

17. A process for producing a ceramic material, comprising firing a composition comprising the zirconium oxide nanoparticles according to claim 1 at 500° C. or higher.

Description

EXAMPLES

(1) Hereinafter, the present invention is more specifically described with reference to examples. The present invention, however, is not limited by the following examples but can also be absolutely carried out with appropriate changes to the examples within a scope in compliance with the intent described above and later, and all the changes are to be encompassed within a technical scope of the present invention.

(2) Physical properties and characteristics that are disclosed in the examples were measured by following methods.

(3) (1) Analysis of crystal structure

(4) Crystal structures of zirconium oxide nanoparticles were analyzed using an X-ray diffractometer (RINT-TTRIII manufactured by Rigaku Corporation). Measurement conditions are as follows.

(5) X-ray source: CuKα (0.154 nm)

(6) X-ray output setting: 50 kV, 300 mA

(7) Sampling width: 0.0200°

(8) Scanning speed: 10.0000°/min

(9) Measurement range: 10 to 75°

(10) Measurement temperature: 25° C.

(11) (2) Quantitative Determination of Ratio of Tetragonal Crystal and Monoclinic Crystal

(12) On the basis of a value calculated using the X-ray diffractometer (RINT-TTRIII manufactured by Rigaku Corporation), a tetragonal crystal and a monoclinic crystal were quantitatively determined by reference intensity ratio method (RIP method) using computational software (PDXL manufactured by Rigaku Corporation) (Peaks were assigned according to directions of the computational software).

(13) (3) Calculation of Crystallite Diameter by X-Ray Diffraction Analysis

(14) A crystallite diameter of zirconium oxide nanoparticles was calculated using the computational software (PDXL manufactured by Rigaku Corporation) on the basis of width at half maximum of a peak at 30° that is analyzed and calculated by the X-ray diffractometer (RINT-TTRIII manufactured by Rigaku Corporation).

(15) In the X-ray diffraction measurement, it is difficult to distinguish a cubic crystal of zirconium oxide nanoparticles from the tetragonal crystal. Therefore, even with the cubic crystal present in the nanoparticles, ratio of the cubic crystal is counted as ratio of the tetragonal crystal.

(16) (4) Measurement of Weight (Mass) Decrease Rate

(17) Zirconium oxide nanoparticles were heated from room temperature to 800° C. at 10° C./min in an air atmosphere, and a weight (mass) decrease rate of the particles was measured by TG-DTA (thermogravimetric-differential thermal analysis) apparatus. This weight (mass) decrease rate can provide a ratio of a coating agent that coats the zirconium oxide nanoparticles.

(18) (5) Measurement of Average Primary Particle Diameter with Electron Microscope

(19) An average primary particle diameter of coated type zirconium oxide particles was measured by observing the nanoparticles with an ultra-high resolution field-emission scanning electron microscope (S-4800 manufactured by Hitachi High-Technologies Corporation). Being observed at 150000-fold magnification, any 100 particles of the coated type zirconium oxide particles was measured for length along a major axis of the particles, and an average value of the length was defined as the average primary particle diameter.

(20) (6) Calculation of Core Concentration

(21) Core concentration was calculated on the basis of a formula (A). In the examples, “total weight of a metal oxide contained in nanoparticles in a dispersion liquid” is calculated as “(weight of nanoparticles blended×(1−weight decrease rate measured in (4))).”
Core concentration=total weight of metal oxide contained in nanoparticles in dispersion liquid/weight of dispersion liquid  (A)

Comparative Example 1

Production of Zirconium Oxide Nanoparticles Coated with 2-Ethylhexanoic Acid (R.SUP.1 .has a Hansen Solubility Parameter (HSP) Distance to Ethanol of 21 (MPa).SUP.1/2.) and/or A Carboxylate Derived from 2-Ethylhexanoic Acid

(22) A mineral spirit solution of zirconium 2-ethylhexanoate (90.4 g, content rate of zirconium 2-ethylhexanoate: 44% by mass, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) was mixed with pure water (15.5 g) and charged into a 200-mL hydrothermal synthesis vessel. This vessel was heated to 190° C. and kept at the same temperature for 16 hours for reaction. Pressure during hydrothermal synthesis was 1.3 MPaG (gauge pressure). After the reaction, water was removed through separation from the hydrothermal synthesis reaction solution.

(23) An upper layer of the hydrothermal synthesis reaction liquid from which water had been removed was heated at 180° C. to remove the organic solvent and thus give zirconium oxide nanoparticles whose crystal structures were confirmed. In the confirmation, diffraction lines attributed to a tetragonal crystal and a monoclinic crystal were detected, intensity of which provided a ratio between the tetragonal crystal and the monoclinic crystal of 74/26, and the particle diameter (crystallite diameter of the tetragonal crystal and/or a cubic crystal) was 5 nm. The average primary particle diameter was measured with the electron microscope to be 11 nm. The weight (mass) decrease rate of the zirconium oxide nanoparticles was 14% by mass. Accordingly, the coating 2-ethylhexanoic acid and/or carboxylate derived from 2-ethylhexanoic acid was determined to be 14% by mass of the entire zirconium oxide nanoparticles.

(24) Ethanol (0.5 g, Hansen solubility parameter (HSP) distance to water: 24 (MPa).sup.1/2) was added to these particles (1 g) obtained by removing the organic solvent, but the mixture became cloudy and the particles were not capable of being dispersed in the mixture.

Example 1

Production of Zirconium Oxide Nanoparticles Coated with Methoxyacetic Acid

(25) The upper layer (50 g) of the hydrothermal synthesis reaction liquid of Comparative Example 1 from which water had been removed was mixed under stirring with 5 g of methoxyacetic acid (R.sup.1 has a Hansen solubility parameter (HSP) distance to ethanol of 14 (MPa).sup.1/2) at 60° C. for 30 minutes. Next, n-hexane was added and then aggregation particles were separated through filtration. Subsequently, the separated aggregation particles were added to n-hexane and stirred for 10 minutes and then the aggregation particles were separated through filtration. The resultant particles were vacuum-dried at room temperature to give zirconium oxide nanoparticles coated with methoxyacetic acid.

(26) In confirmation of the crystal structures of these particles, diffraction lines attributed to a tetragonal crystal and a monoclinic crystal were detected, intensity of which provided a ratio between the tetragonal crystal and the monoclinic crystal as 74/26, and the particle diameter (crystallite diameter of the tetragonal crystal and/or a cubic crystal) was 5 nm. The weight (mass) decrease rate of the zirconium oxide nanoparticles was 11% by mass. Accordingly, the mass of the coating 2-ethylhexanoic acid, carboxylate derived from 2-ethylhexanoic acid, and methoxyacetic acid was determined to be 11% by mass of the entire zirconium oxide nanoparticles.

Example 2

Production of Inorganic Oxide Fine Particle-Containing Solution 1

(27) The zirconium oxide nanoparticles (1 g) obtained in Example 1 was blended with ethanol (0.5 g) and stirred until the mixture became uniform, to give an inorganic oxide fine particle-containing solution 1. In the dispersion liquid, the concentration (core concentration) of the metal oxide contained in the resultant nanoparticles was 59% (=(1 g×(1−0.11))/(1 g+0.5 g)).

Comparative Example 2

Production of Yttria-Stabilized Zirconium Oxide Nanoparticles Coated with 2-Ethylhexanoic Add and/or Carboxylate Derived from 2-Ethylhexanoic Acid

(28) Nanoparticles were synthesized in the same manner as in Example 1 except for changing to 86.7 g the amount of the mineral spirit solution of zirconium 2-ethylhexanoate (content rate of zirconium 2-ethylhexanoate: 44% by mass, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) in Example 1 and using 10.1 g the amount of NIKKA OCTHIX YTTRIUM (content of yttrium: 6.2%, manufactured by Nihon Kagaku Sangyo Co., Ltd.).

(29) In confirmation of the crystal structures of the resultant yttria-stabilized zirconium oxide nanoparticles, diffraction lines attributed to a tetragonal crystal and a monoclinic crystal were detected, intensity of which provided a ratio between the tetragonal crystal and the monoclinic crystal of 97/3, and the particle diameter (crystallite diameter of the tetragonal crystal and/or a cubic crystal) was 4 nm. The average primary particle diameter was measured with the electron microscope to be 6 nm. The weight (mass) decrease rate of the yttria-stabilized zirconium oxide nanoparticles was 25% by mass. Accordingly, the coating 2-ethylhexanoic acid and/or carboxylate derived from 2-ethylhexanoic acid was determined to be 25% by mass of the entire yttria-stabilized zirconium oxide nanoparticles. Yttria-stabilized zirconium oxide nanoparticles (1 g) obtained by removing the organic solvent was mixed with ethanol (0.5 g) and stirred but the white powder was never dispersed.

Example 3

Production of Coated Type Yttria-Stabilized Zirconium Oxide Nanoparticles Coated with Methoxyacetic Acid

(30) Nanoparticles were synthesized in the same manner as in Example 1 except for using the upper layer synthesized in Comparative Example 2 as the upper layer of the hydrothermal synthesis reaction liquid from which used water had been removed. The weight (mass) decrease rate of the yttria-stabilized zirconium oxide nanoparticles was 15% by mass. Accordingly, the mass of the coating 2-ethylhexanoic acid, carboxylate derived from 2-ethylhexanoic acid, and methoxyacetic acid was determined to be 15% by mass of the entire yttria-stabilized zirconium oxide nanoparticles.

Example 4

Production of Inorganic Oxide Fine Particle-Containing Solution 2

(31) The yttria-stabilized zirconium oxide nanoparticles (1 g) obtained in Example 3 was blended with ethanol (0.5 g) and stirred until the mixture became uniform, to give an inorganic oxide fine particle-containing solution 2. In the dispersion liquid, the concentration (core concentration) of the metal oxide contained in the resultant nanoparticles was 57% (=(1 g×(1−0.15))/(1 g+0.5 g)).

Example 5

Production of Inorganic Oxide Fine Particle-Containing Resin Composition 1

(32) The zirconium oxide nanoparticles (1 g) obtained in Example 1 were blended with 1 g of 2-hydroxyethyl acrylate (manufactured by NIPPON SHOKUBAI CO., LTD.) and 4 g of methanol and stirred at room temperature for 1 hour to give a uniform inorganic oxide fine particle-containing resin composition 1.

Example 6

Production of Inorganic Oxide Fine Particle-Containing Resin Composition 2

(33) The zirconium oxide nanoparticles (1 g) obtained in Example 1 were blended with 1 g of pentaerythritol triacrylate (manufactured by SARTOMER JAPAN INC. “SR444 NS”) and 4 g of methanol and stirred at room temperature for 1 hour to give a uniform inorganic oxide fine particle-containing resin composition 2.

Example 7

Production of Inorganic Oxide Fine Particle-Containing Resin Composition 3

(34) The zirconium oxide nanoparticles (1 g) obtained in Example 1 were blended with 1 g of dipentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd. “KAYARAD DPHA”) and 4 g of methanol and heated and stirred at 80° C. for 1 hour to give a uniform inorganic oxide fine particle-containing resin composition 3.

Example 8

Production of Inorganic Oxide Fine Particle-Containing Resin Composition 4

(35) The zirconium oxide nanoparticles (1 g) obtained in Example 1 were blended with 1 g of polyvinyl alcohol (manufactured by KURARAY CO., LTD. “CP-1210”) and 4 g of ion-exchanged water and heated and stirred at 80° C. for 1 hour to give a uniform inorganic oxide fine particle-containing resin composition 4.

INDUSTRIAL APPLICABILITY

(36) Zirconium oxide nanoparticles according to the present invention has excellent dispersibility in a polar solvent such as alcohol and are capable of increasing a core concentration in a dispersion liquid. The zirconium oxide nanoparticles are useful because they can be widely used for, for example, optical materials and electronic component materials.