JPH0446884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing raw material powder of a compound having a garnet structure. More specifically, easy reactivity,
The present invention relates to a method for producing raw material powder of a compound having a garnet structure that is easily sinterable and has uniformity.

Compounds with a garnet structure have functions such as magnetic substances, laser host materials, and sensors, and are widely used. Recently, manufacturing methods using ceramic manufacturing methods have been developed, and there is therefore a demand for raw material powders that have high reactivity, easy sinterability, and uniformity.

Prior Art Conventionally, dry methods, wet methods, and direct salt decomposition methods are known as methods for producing raw material powders of compounds having a garnet structure.

The dry method is a method in which constituent raw material compounds are mixed in a dry method and this is calcined. However, this method has the disadvantage that it is difficult to obtain a uniform composition or a single compound raw material powder, making it difficult to produce a compound with a garnet structure that has excellent functionality, and that its sinterability is insufficient.

The wet method is a method in which an alkaline precipitant such as aqueous ammonia is added to a mixed acid solution of the constituent components to cause coprecipitation, and this precipitate is dried and calcined. According to this method, the pH changes instantaneously and the reaction occurs, so the degree of supersaturation of the solution becomes large, many nuclei are formed, and they come into contact with each other to form a jelly-like precipitate, in which by-products of ammonium chloride salt are formed. occlude. Since it is a jelly-like precipitate, it is not easy to wash, and it is extremely difficult to completely remove by-products. This by-product promotes the growth of primary particles during the calcination stage, resulting in a disadvantage that the activity of the resulting powder is lost.

Further, the direct salt decomposition method has the disadvantage that a large amount of harmful gas is generated when a compound having a garnet structure is formed by the decomposition.

OBJECTS OF THE INVENTION The present invention provides a method for producing raw material powder of a compound having a garnet structure, which does not have the drawbacks of the conventional methods.

Structure of the Invention As a result of intensive research to achieve the above object, the present inventor prepared a mixed acidic aqueous solution containing the constituent metal elements of a compound having a garnet structure, and added 2 to 10 times the molar amount to the acid. When urea is added and heated, the pH
8, an insoluble metal salt gradually forms.
It was discovered that by drying and then calcining the obtained precipitate, the drawbacks of the conventional wet method could be overcome, and a raw material powder with high reactivity and sinterability could be obtained without generating harmful gases. I was able to do it. The present invention was completed based on this knowledge.

The gist of the present invention is that the general formula A ₃ B ₅ O ₁₂ (wherein A represents one or more metals having an 8-coordinate position of oxygen, and B represents a metal having a 6-coordinate position of oxygen and a 4-coordinate position of oxygen).
Represents one or more metals that form a coordination site. ) In the production of a raw material powder of a compound having a garnet structure shown in (1), a mixed acidic aqueous solution containing both the metal elements of component A and component B is prepared, and urea is added thereto in a molar ratio of 2 to 10 times the amount of acid. After addition and dissolution, it is heated to the decomposition temperature of urea to form a precipitate of insoluble metal while the pH gradually increases, and the resulting precipitate is dried and then calcined at 500℃ to 1300℃. A method for producing a raw material powder of a compound having a characteristic garnet structure.

Examples of metals that occupy the 8-coordination position of oxygen in component A of the general formula include rare earth elements such as Y and La, and Ca and Bi. Also, the B component oxygen 6
Examples of metals that occupy coordination and four-coordination positions include Al, Fe, Ga, and Sc.

In a compound having a garnet structure, an element having an excess charge can compensate for a lack of positive charge in the A component. It is also possible to compensate for defects in cations or anions. The present invention also includes compounds having these garnet structures.

Components A and B of a compound with garnet structure
The salt used in preparing the acidic aqueous solution may be any of sulfate, chloride, and nitrate. Alternatively, components A and B may be dissolved in a mineral acid. Urea is used as a precipitant, and the molar ratio of this to the acid is 2 to 2.
Add 10 times the amount. If the amount is less than twice the amount, the precipitate cannot be quantitatively obtained. Moreover, if the amount exceeds 10 times, urea will be wasted and by-products will start to be mixed in. This solution is heated to the decomposition temperature of urea. Due to this heating, urea gradually decomposes into CO ₂ and NH ₄ OH, producing
NH ₄ OH gradually increases the pH and forms a precipitate. When the pH is set to 7 to 8, all A and B precipitates are formed. Since the precipitate is formed gradually in this way, the degree of supersaturation is low and the number of nuclei can be suppressed, resulting in a large precipitate that does not become jelly-like. Therefore, the amount of by-products stored is small and each precipitated particle is large, so by-products can be easily removed by washing.

The obtained precipitate is dried and calcined at 500°C to 1300°C. As a result, a raw material powder of a compound having a uniform, easily sinterable, and easily reactive garnet structure can be obtained. If the calcination temperature is less than 500℃, the dehydration and thermal decomposition of the precipitate will be insufficient, and if it exceeds 1300℃, the powder will become coarse and the reactivity will decrease.
It is appropriate that the temperature is ℃.

Example 1 Iron oxide 2.793g and ytterbium oxide 4.137g
(0.007 mol as Yb ₃ Fe ₅ O ₁₂ ) was dissolved in 25 c.c. of concentrated hydrochloric acid, and water was further added to make 1. After adding 175g of urea (10 times the amount of acid) and dissolving it,
Heated at approximately 95°C for 30 minutes. Thereafter, water from Step 2 was added to stop the decomposition of urea, and the precipitate was washed and overdried.

The obtained dried product was calcined in air at 1200°C for 4 hours to obtain a raw material powder of a Yb ₃ Fe ₅ O ₁₂ single-phase compound having a garnet structure.

When this is sintered at 1400℃, the sintered density becomes the theoretical value.
Over 95% was obtained.

Example 2 Water was added to a mixed solution of 20 ml of a 1.07 mol yttrium nitrate solution and 37.98 ml of a 0.939 mol aluminum nitrate solution (0.007 mol as Y ₃ Al ₅ O ₁₂ ). Then, after adding 51.4g of urea and dissolving it, approximately 95g of urea was added and dissolved.
℃ and held for 5 hours. Thereafter, water from Step 2 was added to stop the decomposition of urea, and the precipitate was washed, overdried, and calcined in air at 1100°C for 3 hours. According to powder X-ray diffraction, it was a single-phase compound having a Y ₃ Al ₅ O ₁₂ garnet structure.

When this was sintered at 1600°C, a sintered density of 95% or more of the theoretical value was obtained.

Comparative Example 1 Commercially available Y ₂ O ₃ and Al ₂ O ₃ powders were blended to have a composition of Y ₃ Al ₅ O ₁₂ , and after ball mill mixing, 1100
The mixture was calcined in air at ℃ for 24 hours, and mixed again using a ball mill to obtain a powder. This powder contains Al ₂ O ₃ , Y ₂ O ₃ ,
It was a mixture of Y ₃ Al ₅ O ₁₂ , etc. Add this to 1500 more
Although it was heat-treated in air at ℃ for 12 hours, it did not become a single-phase compound having a Y ₃ Al ₅ O ₁₅ garnet structure. The sintered density of this powder at 1600°C was less than 65% of the theoretical value.

Comparative Example 2 Add 200 c.c. of a 0.5 mol aqueous solution of aluminum chloride and yttrium chloride in a molar ratio of 5:3.
0.5 mol ammonia water was added to adjust the pH to 7.
The resulting precipitate instantly became jelly-like and could not be filtered. Therefore, the precipitate was washed by centrifugation and decantation at 6000 rpm to obtain a powder.

The powder that was washed only once contained more than 20% by weight of chlorine compounds, which required more than seven washes to remove. This cleaning time requires one day or more. The product calcined at 1100°C had a single phase compound with a garnet structure, but the primary particle size was as large as 0.8 μm and the activity was lost.

The sintered density of the once-washed powder at 1600°C was less than 70% of the theoretical value.

Effects of the Invention According to the method of the present invention, urea is added as a precipitate forming agent, and ammonium hydroxide produced by gradual decomposition of the urea is used, so the precipitate is gradually formed and becomes a large precipitate, which becomes jelly-like. Never. Therefore, it is easy to wash the precipitate, and a powder containing no by-products can be easily obtained, and there is no growth of primary particles during calcination, and a uniform, easily sinterable, and easily reactive raw material can be obtained. . This eliminates the drawbacks of conventional wet methods. In addition, compared to the solid phase method, a single-phase compound having a garnet structure can be obtained with easy reactivity and sinterability, and there is no generation of harmful gases as in the direct salt decomposition method.

Claims (1)

[Scope of Claims] 1 General formula A ₃ B ₅ O ₁₂ (However, A represents one or more metals having an 8-coordination position of oxygen, and B represents 6-coordination and 4-coordination positions of oxygen.
Represents one or more metals that form a coordination site. ) In the production of a raw material powder of a compound having a garnet structure shown in (1), a mixed acidic aqueous solution containing both the metal elements of component A and component B is prepared, and urea is added thereto in a molar ratio of 2 to 10 times the amount of acid. After addition and dissolution, it is heated to the decomposition temperature of urea to form a precipitate of insoluble metal while the pH gradually increases, and the resulting precipitate is dried and then calcined at 500℃ to 1300℃. A method for producing raw material powder of a compound having a characteristic garnet structure.