Process for preparing crystalline mixed metal oxides

• US 5,242,674 A
• Filed: 06/07/1991
• Issued: 09/07/1993
• Est. Priority Date: 10/27/1988
• Status: Expired due to Fees

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Monson, William L., Bruno, Salvatore A.
• Primary Examiner(s): Lewis, Michael
• Assistant Examiner(s): BOS, STEVEN J
• Application Number:
  US07/711,969
• Time in Patent Office: 823 Days
• Field of Search: 423/593, 423/598, 423/DIG. 9, 423/DIG. 15, 501/134, 501/135, 501/136, 501/137, 501/152
• US Class Current: 252/519.1
• CPC Class Codes: C01B 13/32 by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process
• CPC Class Codes: C01B 13/363 Mixtures of oxides or hydroxides by precipitation
• CPC Class Codes: C01G 23/006 Alkaline earth titanates
• CPC Class Codes: C01G 25/006 Compounds containing, besides zirconium, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01G 33/006 Compounds containing, besides niobium, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2004/51 Particles with a specific particle size distribution
• CPC Class Codes: C01P 2004/52 highly monodisperse size distribution
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C01P 2006/80 Compositional purity
• CPC Class Codes: C04B 35/462 based on titanates
• CPC Class Codes: C04B 35/4682 based on BaTiO3 perovskite phase
• CPC Class Codes: Y10S 423/15 Comminution

Abstract

An improved process for preparing crystalline mixed metal oxides, such as barium titanate, in which an organometallic compound is reacted simultaneously and continuously with a solution of a divalent metal ion in an alkaline high turbulence energy environment, the reaction product is crystallized, and the crystals are isolated and may be calcined.

Claims

1. A process for preparing crystalline mixed metal oxides having an A/B ratio of from about 0.990 to about 1.029 of the formula:

space="preserve" listing-type="equation">ABO.sub.3

wherein,

A is a metal cation selected from Ba, Sr, Ca, Mg, Pb and Nd and mixtures thereof; and

B is a metal cation selected from Ti, Zr, Nb, Hf, Zn and Sn and mixtures thereof which comprises the steps of;

(a) simultaneously and continuously mixing an organometallic compound, or mixture of organometallic compounds or a hydrolyzable system, of the structure BL_n, where B is as defined above, L is a hydrolyzable group, or a combination of such groups, selected from the group consisting of an alkoxy, aryloxy, aminoalkyl, acetoxy, acetoacetonyl, a chloride, a nitrate and an acetate and n is 2 or 4 with a solution of a compound, or a mixture of compounds, of the general structure AXy, where A is as defined above, X is an anion, or combination of anions, selected from the group consisting of hydroxide, chloride, nitrate and acetate, and y is 2 or 3 in an alkaline, high turbulence energy environment of a coaxial jet mixer;

wherein said environment is characterized by a turbulence intensity of greater than about 14×

10⁶ cm/sec³ ;

(b) crystallizing a reaction product; and

(c) recovering the crystals, wherein 90% of the particles have a particle size between 0.2 and 1.0 micron and have a surface area of less than about 50 m² /g.

2. The process of claim 1, further including,

(d) calcining the crystals up to about 1080°

C.

3. The process of claim 1 wherein the solution of A cations is an aqueous solution.

4. The process of claim 1 wherein the solution of A cations is a non-aqueous solution.

5. The process of claim 1, 2, 3 or 4 in which the organometallic compounds BL_n are premixed with a nonionic surfactant to form a first ingredient stream which is reacted with the solution of compounds AX_y as a second ingredient stream by mixing said streams simultaneously and continuously in a high turbulence energy environment.

6. The process of claim 5 wherein said mixing comprises pumping said ingredient streams simultaneously through a coaxial jet mixer.

7. The process of claim 5 wherein said organometallic compound BL_n is tetrabutyl titanate and said surfactant is an ethoxylated alkylphenol.

8. The process of claim 1 wherein the crystalline mixed metal oxide is a solid solution of barium titanate, barium zirconate and barium zinc niobate;

the hydrolyzable system is a mixture comprising anhydrous zinc chloride, niobium (V) chloride, zirconium-propoxide and tetrabutyl titanate, and the alkaline earth metal hydroxide is barium hydroxide.

9. The process of claim 2 wherein the calcined crystals have a low surface area in the range of about 1.5 to about 2.5 m² /g while maintaining a narrow particle size distribution (D₉₀) of less than about 4.0 μ

m.

10. A process for preparing crystalline barium titanate which comprises the steps of:

(a) reacting tetrabutyl titanate as a first ingredient stream with a solution of barium hydroxide as a second ingredient stream at a temperature of 80°

-85°

C. in a high turbulence energy environment comprising pumping said ingredient streams simultaneously and continuously through a coaxial jet mixer, said environment characterized by a turbulence intensity greater than about 14×

10⁶ cm/sec³ to form a slurry and discharging said slurry into an alkaline heel of water;

(b) crystallizing said slurry by heating under reflux with continuous agitation for at least about 6 hours to no more than 48 hours; and

(c) recovering crystalline barium titanate having 90% of the particles greater than 0.2 um in size up to about 1.0 μ

m in size, and a surface area of less than about 50 m² /g.

11. The process of claim 10, further including,

(d) calcining the crystals at 1050°

C.

12. The process of claim 11 wherein the calcined crystals have a low surface area in the range of about 1.5 to about 2.5 m² /g while maintaining a narrow particle size distribution (D₉₀) of less than about 4.0 μ

m.

13. A chemically homogeneous crystalline mixed metal oxide having an A/B ratio in the range of about 0.990 to about 1.029 of the formula:

space="preserve" listing-type="equation">ABO.sub.3

wherein,

A is a metal cation selected from Ba, Sr, Ca, Mg, Pb, Nd and mixtures thereof; and

B is a metal cation selected from Ti, Zr, Nb, Hf, Zn, Sn and mixtures thereof which comprises the steps of;

(a) simultaneously and continuously mixing an organometallic compound, or mixture of organometallic compounds, of the general structure BL_n where B is as defined above, L is a hydrolyzable group, or combination of such groups, selected from the group consisting of an alkoxy, aryloxy, aminoalkyl, acetoxy, and acetoacetonyl, and n is 2, 4, or 5 as a first ingredient stream with a solution of a compound, or a mixture of compounds, of the general structure AXy, where A is as defined above, X is an anion, or a combination of anions, selected from the group consisting of a hydroxide, chloride, nitrate and an acetate, and y is 2 or 3 in an alkaline, high turbulence energy environment comprising pumping said ingredient streams simultaneously and continuously through a coaxial jet mixer which produces a turbulence intensity greater than about 14×

10⁶ cm/sec³ ;

(b) crystallizing a reaction product for at least 6 hours to no more than 48 hours; and

(c) recovering the crystals, wherein 90% of the crystalline mixed metal oxide is greater than 0.2 μ

m in size up to about 1.0 μ

m in size, and a surface area of less than about 50 m² /g.

14. The crystalline mixed metal oxide of claim 13 which is barium titanate or strontium titanate.

15. The crystalline mixed metal oxide of claim 14 which is doped with one or more ions selected from Nd, Nb, Zn and Zr.

16. The crystalline mixed metal oxide of claim 13 which is a solid solution of barium titanate, barium zirconate and barium zinc niobate.