JPH04202014A - Production of multiple oxide containing rare earth element - Google Patents

Abstract

PURPOSE:To increase working efficiency and to control the shape of particles by adding ammonium carbonate to a slurry of the hydroxides of a rare earth element and a group IVa element, carbonating the hydroxides, making precipitated particles coarse and carrying out thermal decomposition. CONSTITUTION:Alkali is added to an acidic soln. contg. ions of a rare earth element and ions of a group IVa element to coprecipitate the ions as hydroxides. Ammonium carbonate or ammonium hydrogencarbonate is added to the resulting hydroxide slurry and brought into a reaction to carbonate the hydroxides and precipitated particles are made coarse. Working efficiency is improved at the time of filtration and washing and the shape of particles of a double oxide obtd. by thermally decomposing the washed particles is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in a method for producing rare earth-containing composite oxides useful as raw materials for phosphors.

(Prior Art) A coprecipitation method is one of the methods for producing rare earth oxides containing different elements such as group IV-a elements. In this method, different elements and rare earth elements are co-precipitated as oxalate, carbonate, or hydroxide, and this is thermally decomposed to produce a rare earth-containing composite oxide.

(Problems to be Solved by the Invention) However, this method is limited to those having poorly soluble oxalate or carbonate as foreign elements, and cannot be used for Ti, Zr, etc. In addition, in the method of co-precipitating Ti, Zr, etc. as hydroxides, it is difficult to filter and wash with water, and this is thermally decomposed and solidified as an oxide, forming a block that needs to be crushed, making it difficult to control the particle size. Since the particle shape is irregular, industrial mass production is difficult.

The present invention aims to solve these problems and provide a method for obtaining a plate-like or spherical composite oxide having a narrow particle size distribution.

(Means for Solving the Problems) In order to solve the problems, the present inventors studied the reaction conditions of the coprecipitation method of hydroxides and carbonates, and completed the present invention.The gist thereof is as follows. An alkali is added to a solution containing rare earth element ions and IV-a group element ions to co-precipitate a hydroxide, and the hydroxide is reacted with ammonium carbonate or ammonium bicarbonate to form a carbonate, which is then thermally decomposed. This is a method for producing a rare earth-containing composite oxide.

The present invention will be explained in detail below.

Usually, in the hydroxide coprecipitation method, rare earth element ions and IV-a
An acidic solution containing Group element ions is dropped into an alkaline solution such as ammonia, and the pH is adjusted to co-precipitate as a hydroxide, which is then separated, dried, and calcined to produce a rare earth-containing composite oxide. However, the precipitated particles of hydroxide obtained by this method are very fine, and filtration and washing are difficult, such as requiring a long time. In addition, it solidifies during the drying and firing process and is difficult to crush. Furthermore, particle size control is difficult, and the particle shape is irregular.

In order to solve such problems, the present invention adds powder or aqueous solution of ammonium carbonate or ammonium bicarbonate to a hydroxide slurry to carbonate part or all of the hydroxide, thereby coarsening the precipitated particles. , improved the workability of filtration and cleaning, and also made it possible to control the particle size and shape of the composite oxide.

The scope of application of the present invention is that for rare earth elements, L including Y
a, Ce, Pr, Nd, Sm, Eu, Gc
, Tb, Dy, Ho, Er, Tm.

One or more elements selected from Yb and Lu, the IV-a group elements are Ti, Zr, and Hf, and the molar ratio of the rare earth element to the TV-a group element is 1:0.01~
A range of 1:2 is good. The reaction conditions were as follows: First, the reaction of hydroxide was carried out using a known method (the raw material rare earth oxide and IV-
Group A element metals, salts, or oxides are mixed in a predetermined ratio, dissolved in an inorganic acid, and dropped into an alkaline aqueous solution such as ammonia, pH 8-12.10-100°C, 0.5-
The reaction is carried out for 24 hours to obtain a precipitate of composite hydroxide. Next, according to the method of the present invention, ammonium carbonate or ammonium bicarbonate is added as a powder or an aqueous solution in an amount of 1 to 20 moles per mole of composite hydroxide, and the mixture is heated at 10 to 100°C and 0.5
React for ~24 hours to obtain carbonate crystals. in this case,
The carbonates produced are partially or completely substituted. The crystals were separated according to a conventional method, washed with water,
A composite oxide is obtained by firing in the air at 0 to 1,200°C for 1 to 5 hours.

The composite carbonate thus obtained has a composite crystal grain size coarser than that of the composite hydroxide, making it easier to filter, separate, and wash with water, contributing to cost reduction. By controlling the crystal grain size of the composite carbonate by changing the crystallization conditions of the salt, it becomes possible to control the average grain size of the composite oxide after firing within the range of 1 to 100 μm.This composite oxide It has become possible to improve the dispersibility during applied processing of phosphors made using phosphors as raw materials.

Hereinafter, embodiments of the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

(Example 1) Lanthanum oxide La2032.7 mol, terbium oxide T
b4O70, 2 mol nitrate solution and titanium oxide Ti02
A 0.1 mol sulfuric acid aqueous solution is mixed, added dropwise to a 20 mol ammonia aqueous solution, and reacted at pH 8 to 12.60'C to obtain a composite hydroxide. 10 moles of ammonium bicarbonate powder was added to this hydroxide slurry, and the resulting crystals were separated and washed with water. The composition of this carbonate is approximately (La
o8aTbo, +2TLo, 02)2 (CO3)
3-w (O old.

-3H20 (where x<0.1). This composite carbonate is calcined at 900° C. for 2 hours in the air. The composite oxide obtained here is (La,, 8sTbo, +□T
io, o2) 203, average particle size 20 μm, dispersibility,
The particles had good fluidity. When this was processed into a green phosphor for televisions and applied to cathode ray tubes, work efficiency was improved, and it had high uniformity and reduced loss.

(Example 2) Lanthanum oxide La2032.7 mol, terbium oxide T
b, 070.2 mol nitrate solution and titanium oxide Ti02
A 0.1 mol sulfuric acid aqueous solution is mixed and added dropwise to a 6 mol ammonia aqueous solution, and the mixture is reacted at pH 8 and lOoC to obtain a composite hydroxide. 3 mol of ammonium bicarbonate aqueous solution was added to this hydroxide slurry, and the resulting crystals were
After time aging, it was separated and washed with water.

The composition of this carbonate is approximately (Lao, 56Tbo, +
zTio, 02)(OH)8(C03)b・H2O(
Here, the composition was close to 0.9≦a4b≧1.1).

This composite carbonate is calcined at 900° C. for 12 hours in the air. The composite oxides obtained here (Lao86Tbo,
+27io, 02) 203, a group of rounded plate-like particles with an average particle size of 20 μm. When we processed this into a green phosphor for televisions and applied it to cathode ray tubes, we found that work efficiency was improved, the uniformity was high, and loss was reduced.

(Effect of the invention) In the conventional method, hydroxide finely precipitated, making it difficult to filter and wash (and the particle size of the composite oxide was also small (and the composite oxide formed into aggregates, making it difficult to manufacture). This makes it easy to manufacture composite oxides, and it becomes possible to control the particle size and shape, so it has extremely high industrial utility value.

Claims (1)

[Claims] Add an alkali to a solution containing rare earth element ions and IV-a group element ions to co-precipitate a hydroxide, react the hydroxide with ammonium carbonate or ammonium bicarbonate to form a carbonate, and decompose it by heating. A method for producing a rare earth-containing composite oxide.