PROCESS FOR PRODUCING OXIDE CRYSTAL FINE PARTICLES
To provide a process for producing fine particles of crystalline oxide which have high crystallinity, are excellent in uniformity of the composition and particle diameter, and have a small particle diameter, and such fine particles of crystalline oxide. A process for producing fine particles of crystalline oxide, which comprises: a step of obtaining a melt containing an oxide of M (M is at least one member selected from the group consisting of Ce, Ti, Zr, Al, Fe, Zn, Mn, Cu, Co, Ni, Bi, Pb, In, Sn and rare earth elements (excluding Ce)) and B 2 O 3 , a step of rapidly cooling the melt to form an amorphous material, a step of pulverizing the amorphous material to obtain a pulverized material having a volume-based particle size distribution within a range of from 0.1 to 40 μm, a step of heating the pulverized material to precipitate an oxide crystal containing M in the pulverized particles, and a step of separating components other than the oxide crystal containing M from the crystal-precipitated particles to obtain fine particles of crystalline oxide containing M, in this order.
1 . A process for producing fine particles of crystalline oxide, which comprises:
a step of obtaining a melt containing an oxide of M (M is at least one member selected from the group consisting of Ce,Ti, Zr, Al, Fe, Zn, Mn, Cu, Co, Ni, Bi, Pb, In, Sn and rare earth elements (excluding Ce)) and B 2 O 3 ,
a step of rapidly cooling the melt to form an amorphous material,
a step of pulverizing the amorphous material to obtain a pulverized material having a volume-based particle size distribution within a range of from 0.1 to 40 μm,
a step of heating the pulverized material to precipitate a crystalline oxide containing M in the pulverized particles, and
a step of separating components other than the crystalline oxide containing M from the crystal-precipitated particles to obtain fine particles of crystalline oxide containing M, in this order.
2 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein D 90 of the pulverized material is at most 20 μm, where D 90 is a particle diameter when in a volume-based cumulative particle size distribution curve of the pulverized material, the integrated amount as accumulated from the small particle size side, becomes to be 90%.
3 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein the melt is a melt containing, as represented by mol % based on oxide, from 5 to 70% of the oxide of M and from 30 to 95% of B 2 O 3 .
4 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein the melt further contains an oxide of R (R is at least one member selected from the group consisting of Mg, Ca, Sr and Ba).
5 . The process for producing fine particles of crystalline oxide according to claim 4 , wherein the melt is a melt containing, as represented by mol % based on oxide, from 5 to 50% of the oxide of M, from 10 to 50% of the oxide of R and from 30 to 75% of B 2 O 3 .
6 . The process for producing fine particles of crystalline oxide according to claim 4 , wherein the proportion of the oxide of M contained in the melt is from 5 to 50 mol % to the total amount of the oxide of R and B 2 O 3 .
7 . The process for producing fine particles of crystalline oxide according to claim 4 , wherein the proportion of the oxide of R contained in the melt is from 20 to 50 mol % to B 2 O 3 .
8 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein M is Ce.
9 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein the amorphous material is in a flake form or a fiber form.
10 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein the temperature for heating the pulverized material is from 600 to 900° C.
11 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein the components other than the oxide containing M in the crystal-precipitated particles are eluted by an acid and separated from the oxide crystal containing M.
12 . The process for producing fine particles of crystalline oxide according to claim 1 , wherein D 90 of the pulverized material is at most 10 μm, and the volume-based particle size distribution of the pulverized material is within a range of from 0.1 to 20 μm, where D 90 is a particle diameter when in a volume-based cumulative particle size distribution curve of the pulverized material, the integrated amount as accumulated from the small particle size side, becomes to be 90%.
13 . Fine particles of crystalline oxide, wherein the ratio of the crystallite diameter calculated by using Scherrer's method from the X-ray diffraction measurement to the average primary particle diameter calculated by spherical approximation from the specific surface area measurement by BET method is within a range of crystallite diameter:average primary particle diameter=1:0.8 to 1:2.5; the average primary particle diameter is from 5 to 100 nm; and the variation coefficient of the particle diameter is from 0.05 to 0.3, where the variation coefficient of the particle diameter is a value obtained by dividing the standard deviation of the particle size distribution obtained by measurement from the transmission electron microscopic photograph, by the number average particle diameter.
14 . The fine particles of crystalline oxide according to claim 13 , wherein the ratio is within a range of crystallite diameter:average primary particle diameter=1:1.0 to 1:1.8, and the average primary particle diameter is from 10 to 50 nm.