Method of producing oxide particles

1. A method of producing oxide particles, which comprises at least two fluids to be processed including a first fluid and a second fluid, wherein one of the first fluid and the second fluid is an oxide raw material liquid obtained by mixing at least an oxide particle raw material with a solvent, and the other of the first fluid and the second fluid is an oxide precipitation solvent obtained by mixing at least a basic substance with a solvent, and

wherein the method comprises mixing the first fluid and the second fluid in a space between processing surfaces which are disposed so as to face each other, being capable of approaching to and separating from each other, at least one of which rotates relative to the other; and discharging a mixed fluid of the first fluid and the second fluid in which the oxide particles are precipitated from the space between the processing surfaces; and

wherein the method controls crystallinity of the oxide particles discharged from the space between the processing surfaces so that 90% or more of the obtained oxide particles are single crystal oxide particles, by changing at least one selected from the group consisting of the temperature of the first fluid at the time of introduction in the space between the processing surfaces, the temperature of the second fluid at the time of introduction in the space between the processing surfaces, and the temperature of the first fluid and the second fluid at the time of mixing of the first fluid and the second fluid, to be 100° C. or higher.

2. The method of producing oxide particles according to claim 1 , wherein the interval between the processing surfaces is set by a pressure balance between the force applied in the direction of approximating the processing surfaces and the pressure of the mixed fluid.

3. The method of producing oxide particles according to claim 1 , wherein the first fluid passes in the space between the processing surfaces while forming a thin film fluid, and

the second fluid is introduced in the space between the processing surfaces from an opening formed in at least one of the processing surfaces through a separate independent introduction path from the flow path through which the first fluid is introduced in the space between the processing surfaces, and the first fluid and the second fluid are mixed in the space between the processing surfaces.

4. The method of producing oxide particles according to claim 1 , wherein the first fluid contains one or a plurality of solvents, and

the temperature of the first fluid at the time of introduction in the space between the processing surfaces is a temperature higher than the standard boiling point of the solvent having the lowest standard boiling point among one or a plurality of solvents contained in the first fluid.

5. The method of producing oxide particles according to claim 1 , wherein the introduction pressure of the first fluid at the time of introduction in the space between the processing surfaces exceeds the standard pressure, and

the temperature of the first fluid at the time of introduction in the space between the processing surfaces is a temperature higher than the standard boiling point of the first fluid, and lower than the boiling point under the introduction pressure.

6. The method of producing oxide particles according to claim 5 , wherein the temperature at the time of mixing is the introduction temperature c (° C.) between the processing surfaces of the mixed fluid which is calculated by the following equation:

c =( a 1× a 2+ b 1× b 2)/( a 2+ b 2)

wherein,

a1: introduction temperature of the oxide raw material liquid (° C.)

a2: introduction flow rate of the oxide raw material liquid (ml/min)

b1: introduction temperature of the oxide precipitation solvent (° C.)

b2: introduction flow rate of the oxide precipitation solvent (ml/min).

7. The method of producing oxide particles according to claim 1 , wherein pH of the mixed fluid is controlled within a predetermined range.

8. The method of producing oxide particles according to claim 1 , wherein the second fluid contains one or a plurality of solvents, and

the temperature of the second fluid to be introduced in the space between the processing surfaces is a temperature higher than the standard boiling point of the solvent having the lowest standard boiling point among one or a plurality of solvents contained in the second fluid.

9. The method of producing oxide particles according to claim 1 , wherein both of the introduction pressure of the first fluid and the introduction pressure of the second fluid at the time of introduction in the space between the processing surfaces exceed the standard pressure, and

the temperature of the first fluid at the time of introduction in the space between the processing surfaces is a temperature higher than the standard boiling point of the first fluid, and lower than the boiling point under the introduction pressure, and

the temperature of the second fluid at the time of introduction in the space between the processing surfaces is a temperature higher than the standard boiling point of the second fluid, and lower than the boiling point under the introduction pressure.

10. The method of producing oxide particles according to claim 1 , wherein the ratio d/D of the average crystal diameter (d) obtained by X-ray diffraction measurement of the oxide particles to the average particle diameter (D) obtained by transmission electron microscope observation of the oxide particles is 0.50 or more.

11. The method of producing oxide particles according to claim 1 , wherein a temperature of either one of the first fluid and the second fluid is 175° C. or lower.

12. The method of producing oxide particles according to claim 1 , wherein the oxide particles have a primary particle diameter of 20 nm or less.

13. The method of producing oxide particles according to claim 1 , wherein the oxide particles are oxide particles which do not require a dry heat treatment.

14. The method of producing oxide particles according to claim 1 , wherein another element is solid soluted in or compounded with the oxide particles.

15. The method of producing oxide particles according to claim 1 , wherein the oxide particle raw material is magnetite particle raw material, and the oxide particles are magnetite particles.

16. The method of producing oxide particles according to claim 1 , wherein the oxide particle raw material is cerium oxide particle raw material, and the oxide particles are cerium oxide particles.

17. The method of producing oxide particles according to claim 15 , wherein pH of the mixed fluid is 9 or more.

18. The method of producing oxide particles according to claim 17 , wherein the shape of the magnetite particles is controlled so as to approach a spherical shape by decreasing pH of the mixed fluid, and the shape of the magnetite particles is controlled so as to approach a square shape by increasing pH of the mixed fluid.

19. The method of producing oxide particles according to claim 15 , wherein a molar ratio of Fe 2+ ion and Fe 3+ ion contained in the oxide raw material liquid, Fe 2+ /Fe 3+ , is 0.500±0.010.

20. The method of producing oxide particles according to claim 15 , wherein pH of the oxide raw material liquid is 4 or less.