JPH06293552A - Production of yttria molding - Google Patents

Abstract

PURPOSE:To produce a large size of yttria molding which is less apt to cause cracking at the time of firing, having high strength and being excellent in corrosion resistance and heat resistance, at a relatively lower temp. and easily for a short time. CONSTITUTION:Yttria cement consisting essentially of yttria powder, an aqueous ammonium nitrate solution and yttria aggregate, if necessary, are kneaded to prepare a kneaded product and the kneaded product is casted in a casting mold to be solidified at a specific shape, and after the solidified body was aged, it is calcined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a yttria compact having corrosion resistance and heat resistance, which is suitable for containing a highly active compound such as molten metal. More specifically, it relates to a method for producing a yttria compact from yttria cement containing yttria (Y ₂ O ₃ ) powder as a main component.

[0002]

2. Description of the Related Art Conventionally, as a container of highly active metal uranium, there has been known a container made of graphite which does not easily react with metal uranium. However, if the container made of this graphite contains metal uranium for a long time, the container graphite and the metal uranium will start to react with each other, and the metal uranium will be contaminated with carbon. On the other hand, the yttria molded body is chemically stable and has better corrosion resistance and heat resistance than graphite, and is suitable for this type of container. This yttria compact is obtained by adding and mixing a sintering aid, a binder, etc. to yttria powder, compression-molding the mixture into a predetermined shape, and firing this compact at a temperature of 1000 ° C. or higher in an inert atmosphere. Made.

[0003]

However, since the conventional yttria compact is a sintered compact obtained by high temperature firing, the size of the compact depends on the size of the firing furnace. Hateful. Further, the high temperature consumes a large amount of heat energy, and it is necessary to create an inert atmosphere during firing. An object of the present invention is to provide a method for easily producing a yttria compact having excellent corrosion resistance and heat resistance and suitable for containing a chemically active substance such as molten metal at a relatively low temperature. Another object of the present invention is to provide a method for producing a large-sized and high-strength yttria compact in a relatively short time. Still another object of the present invention is to provide a method for producing a lightweight yttria compact having a relatively complicated shape and excellent in thermal shock resistance without cracking.

[0004]

In order to achieve the above object, the method for producing a yttria compact of the present invention comprises kneading yttria cement containing yttria powder as a main component, an ammonium nitrate aqueous solution and yttria aggregate if necessary. In this method, a kneaded product is prepared by casting, the kneaded product is cast into a mold to be solidified into a predetermined shape, the solidified body is cured, and then calcined. The yttria cement of the present invention is produced in the form of yttria powder from a liquid phase such as a precipitation method or a solvent evaporation method.
The average particle size of the yttria powder is preferably 1 to 10 μm, more preferably 4 to 6 μm. This is because if it is less than 1 μm, the manufacturing cost for making it into a fine powder becomes extremely high, while if it exceeds 10 μm, it becomes difficult to become a hydrate. Yttria aggregate is used as a kneading material, and by this aggregate, a large-sized and high-strength molded product can be produced in a short time without cracking. The average particle size of yttria aggregate is preferably 100 to 350 mesh, and 1
50-200 mesh is more preferable. When it exceeds the above range, it becomes difficult to fulfill the role as the above aggregate. This aggregate is made, for example, by crushing a yttria sintered body with a ball mill or the like.

As the concentration of the ammonium nitrate aqueous solution,
A 10 to 20 molar concentration is preferred. When the concentration of this aqueous solution is less than 10 mol%, the coagulation reaction of the kneaded product becomes insufficient, while when it exceeds 20 mol%, ammonium nitrate becomes difficult to dissolve, which is not preferable. The mixing weight ratio of the yttria aggregate to the yttria powder (aggregate weight / powder weight) is preferably 1 to 4. When this ratio exceeds 4, it becomes unfavorable because the viscous property is lost and the strength of the molded product is lowered. The yttria aggregate may not be included depending on the shape or size of the molded body. The mixture ratio of yttria powder or yttria powder and yttria aggregate to the ammonium nitrate aqueous solution (aqueous solution volume / powder weight) is 0.6 to 1.0 mL.
/ G is preferred. If the mixing ratio is less than 0.6 mL / g, it will be difficult to form a kneaded product due to insufficient water content, while if it exceeds 1.0 mL / g, the water content will be too large and the solid and liquid will be easily separated.
Each is not preferable. The curing of the solidified body cast in the mold is preferably 80 to 100% relative humidity, and 90 to 100%.
% Is more preferable. This is because if the relative humidity is less than 80%, the hydration action does not proceed sufficiently, whereas if it exceeds 100%, the water content becomes excessive. This curing is preferably carried out for at least 14 days depending on the curing temperature. For example, hydration is completed within 28 days at room temperature and 14 days at 40 ° C. The calcination of the solidified body is performed in an air atmosphere or an inert gas atmosphere at a temperature rising rate of 6 to 20 ° C./hour for 600 to 9
It is preferable to carry out the treatment at a temperature of 00 ° C. for 30 to 60 minutes. If the rate of temperature increase is less than 6 ° C./hour, the effect of preventing cracks by slowing the rate of temperature increase cannot be expected any further. On the other hand, if it exceeds 20 ° C./hour, cracking is likely to occur. The calcination temperature is preferably in the above range in order to remove excess water after curing and obtain a predetermined strength. 9
If the temperature exceeds 00 ° C, the heating furnace is limited, and it becomes difficult to calcine a large molded body. The yttria compact of the present invention manufactured through a series of manufacturing steps becomes a ceramic product which is porous, lightweight and impact resistant without cracks in the final calcination step.

[0006]

When the kneaded product is cast into the mold, the yttria powder causes the reaction of the following formula (1) to become a binder and solidify.
Ammonium nitrate functions as an auxiliary agent for making the kneaded product into a slurry. Hydration is complete after 14 days of age. The surplus water is removed by the calcination, the surplus ammonium nitrate is decomposed, and the binder Y ₂ (O
H) ₅ NO ₃ · H ₂ O is also decomposed and returns to yttria. As a result, the yttria particles are united more firmly. Y ₂ 0 ₃ + NH ₄ NO ₃ + 2H ₂ O → Y ₂ (OH) ₅ NO ₃ · H ₂ O + NH ₃ (1)

[0007]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. 20 g of yttria powder having an average particle size of about 4 μm, 80 g of yttria aggregate having an average particle size of about 200 mesh, and 20 mL of an ammonium nitrate aqueous solution having an 18 molal concentration were uniformly kneaded to prepare a kneaded product. This kneaded product was cast into a mold having the shape of a container and solidified, and then the solidified body was cured in the mold at 20 ° C. and a relative humidity of about 80% for about one month. After curing, the solidified body was taken out of the mold and heated to 600 ° C. in a heating furnace in an air atmosphere at a heating rate of 6.25 ° C./hour,
I kept it there for 30 minutes. After heating, the molded body was taken out of the heating furnace and left in the air to be cooled. The density of the obtained molded body is about 2.8 g / cm ³ , and the compressive strength is 200 to 300 kg.
Was / cm ² .

[0008]

As described above, according to the present invention, it is possible to manufacture a yttria compact having excellent corrosion resistance and heat resistance. Therefore, the obtained molded body can be used as a reaction vessel or a storage vessel for a chemically active substance such as molten metal. In addition, since calcination is performed at a relatively low temperature, energy can be saved and a large yttria compact can be manufactured by using a large heating furnace instead of a firing furnace. In particular,
By using the yttria aggregate, a high-strength yttria compact can be easily manufactured in a relatively short time, and a yttria compact having a relatively complicated shape can be manufactured without cracking.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location C04B 14:02) Z 2102-4G (72) Inventor Yasushi Hoshino Ozamu, Naka-machi, Naka-gun, Ibaraki Prefecture 14 at 1002 Rokujinka Mitsubishi Materials Co., Ltd. Naka Power Development Center (72) Inventor Isao Kanaya Large-sized Mukaiyama, Nakamachi, Naka-gun, Ibaraki Prefecture 14 Mitsubishi Materials Corporation Nakahara Kyodo Development In the Center (72) Hiroyuki Yagi Inventor Hiroyuki Yagi 14 Nakamura-ko Development Center, Mitsubishi Materials Co., Ltd.

Claims (5)

[Claims] 1. A kneaded material is prepared by kneading yttria cement containing yttria powder as a main component and an ammonium nitrate aqueous solution, and the kneaded material is cast into a mold and solidified into a predetermined shape to cure the solidified body. A method for manufacturing a yttria compact that is then calcined. 2. The kneaded material contains yttria aggregate.
A method for producing the yttria molded body described. 3. A yttria powder having an average particle size of 1 to 10 μm, a yttria aggregate having an average particle size of 100 to 350 mesh, and an ammonium nitrate aqueous solution having a molar concentration of 10 to 20 are kneaded to mix the yttria aggregate with the yttria powder. The weight ratio is 1 to 4, and the mixing ratio of the ammonium nitrate aqueous solution to the yttria powder is 0.6.
It is-1.0 mL / g, The manufacturing method of the yttria molded object of Claim 1 or 2. 4. The method for producing a yttria compact according to claim 1, wherein the curing of the solidified body is carried out at a relative humidity of at least 80% and at least at room temperature for at least 14 days. 5. The calcination of the solidified body is performed in an air atmosphere or an inert gas atmosphere at a temperature rising rate of 6 to 20 ° C./hour for 600 to 9
The method for producing a yttria compact according to claim 1, which is carried out at a temperature of 00 ° C for 30 to 60 minutes.