JPH04202012A - Production of oxide of rare earth element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing rare earth oxides, and particularly aims to provide rare earth oxides suitable as phosphors.

(Prior art) Conventional methods for producing rare earth oxides include obtaining oxalate crystals from a nitric acid solution of rare earth raw materials, filtering the crystals, sufficiently dehydrating the crystals, and then calcining them, or passing through filtration and drying. It was to be fired.

However, the oxide obtained by this method has many aggregated particles and columnar particles due to uneven evaporation during the dehydration process and the resulting difference in oxalate decomposition characteristics, making it difficult to use as a raw material for phosphors. There was a desire for improvement.

(Means for Solving the Problems) In view of this, the present inventors have conducted studies and found that the particle size and shape of the oxide obtained by i-formation of rare earth oxalates are We found that there is a close correlation with water volume. The present invention was made based on this, and was able to solve the conventional problems by adjusting the water content of oxalate to an appropriate value and firing.

(Summary of the Invention) The present invention involves adding water to the oxalate in the step of producing a rare earth oxide by firing a rare earth oxalate containing two or three of La, Ce, and Tb. , the total water content including crystal water is 10 to 25 for rare earth elements.
A method for producing rare earth oxides characterized by double the molar amount and then firing.The method of the present invention will be described in detail below.
For example, La-Tb oxalate, La-C
The starting material is crystals such as e-Tb oxalate. That is, in the present invention, water is added to this oxalate crystal, and the total amount of water including crystal water is 10 to 25% of the rare earth element.
The molar amount is doubled and then fired.

Of course, the water used here must be pure water. If the total amount of water added is less than 10 times the molar amount of the rare earth element, the oxide after firing will have many columnar crystals,
If the amount exceeds 5 times the molar amount, angular crystals tend to form, but the fine particles tend to aggregate. Therefore, in the present invention, it is necessary to keep the total amount of water added within the above range, preferably 15 to 20 times the molar amount, to achieve the purpose. be.

Rare earth oxalate crystals with a given water content were heated to 700°C.
By firing at ~1200°C, preferably 900°C for about 2 hours, an angular oxide with few aggregated particles can be obtained.

(Example) Example 1 1.14 g of lanthanum oxide (La203) and 56 g of terbinium oxide (Tb407) were dissolved in 3 moles of nitric acid, and an aqueous oxalic acid solution containing 190 g of oxalic acid was added to the resulting solution and stirred. a-Tb coprecipitated oxalate crystals were obtained. When this oxalate was filtered and washed with water, the water content after washing was 5 moles.

Add water to this and the total water content is 10.15-20.25
．． Four types of samples with 30 times the molar amount were obtained.

Each of these oxalates with different water contents was
The mixture was calcined at ℃ for 2 hours to obtain an oxide. This composition is (La
Tb)O.

0.7 0.323 Table 1 shows the relationship between water content and oxide powder properties in this case.
- When the water content is 25 times the molar amount.

It is clear that the best powder particles are obtained when

Table 1 Notes 1) Water content...Molar amount of rare earth elements 2) Particle size (μm)...Sedimentation balance method D, o value was taken as the representative value.

3) Shape: Evaluated by electron micrograph.

4) Agglomerated particles: Evaluated by electron micrographs and particle size distribution by sedimentation balance method.

Example 2 65.2 g of lanthanum oxide (La203), selim oxide (
CeO2) 34.4 g, terbium oxide (Tb, 07
) was dissolved in 3 moles of nitric acid, and an oxalic acid aqueous solution containing 190 g of oxalic acid was added to the resulting solution and stirred.
La-Ce-Tb coprecipitated oxalate was obtained. After filtering the oxalate and washing with water, water was added to obtain four types of samples with predetermined water contents in the same manner as in Example 1.

Each sample was fired at 900°C for 2 hours at a heating rate of 0°C/min to obtain an oxide. This composition is (La, 4Ce, 4Tb,
2), 0. Met. Table 2 shows the relationship between water content and oxides obtained here.

Table 2 Example 3 65.2 g of lanthanum oxide (La20.), 110.1 g of cerium carbonate [Ce2(Ce3)3.5H20), and 37.4 g of terbium oxide (T b 407) were mixed with nitric acid 3
A rare earth oxide was obtained by dissolving the resulting solution in the same manner as in Example 2.

The results of examining the relationship between water content and powder properties for this material were the same as in Example 2.

(Effects of the Invention) According to the present invention, the non-uniformity of rare earth oxide powder particles, which has been a problem in the past, can be solved, and an excellent phosphor can be obtained.

Claims (1)

[Claims] In the step of producing a rare earth oxide by firing a rare earth oxalate crystal containing two or three of La, Ce, and Tb, water is added to the oxalate crystal to produce water containing crystal water. A method for producing a rare earth oxide, which comprises making the total amount of the rare earth element 10 to 25 times the molar amount of the rare earth element, and then firing.