JPH0472772B2 - - Google Patents

Description

Detailed Description of the Invention The present invention consists of crystalline primary particles with a crystallite diameter of 100 Å or less, has a special microstructure, and has a relatively narrow portion in the range of 0.3 to 3 μm, which is the most important for fine ceramics. The present invention relates to a substantially spherical zirconia-based agglomerated particle powder, and a method for producing the zirconia-based agglomerated particle and agglomerated particle powder related thereto. Here, the term zirconia-based includes solid solutions and compounds containing zirconia as a main component.

Recently, along with the improvement in the performance of fine ceramics, there has been a trend toward ultrafine raw materials, and ultrafine raw materials are becoming increasingly important for zirconia ceramics, especially semi-stabilized zirconia ceramics, which are attracting attention as tough ceramics. ,
Submicron particles or ultrafine particles of about 500 Å or less are beginning to be used.

However, fine particles, especially ultrafine particles of about 500 Å or less, pose important obstacles in the production of ceramics in at least the following two points. One of them is a problem in powder production, and the other is a problem in obtaining a molded body from powder.

In other words, in general, ultrafine particles of 500 Å or less form irregular lumps due to strong bonds between particles due to the action of water during the dry calcination stage for powder preparation, and even after being crushed, they become powders with a uniform particle size again. difficult to become,
Almost all of the properties of ultrafine particles are lost. Usually, before drying, it is necessary to replace water with expensive alcohol or the like or freeze-dry to prevent strong and irregular agglomeration, which is complicated and uneconomical.

Another drawback is that when ceramic raw powder becomes fine particles, it is extremely difficult to mold it even if strong and irregular agglomeration can be prevented. In other words, it becomes difficult to uniformly and tightly pack the fine particles, the firing shrinkage rate increases, deformation and cracks are more likely to occur, and the dimensional accuracy after firing deteriorates. The industrial means to improve the uniform tight packing properties in this molding is granulation technology by spray drying, but as mentioned above, the use of water impairs the characteristics of the fine particles.
After being agglomerated by calcination etc., it is then granulated, and in this case the agglomerated particles that make up the agglomerated particles lose the characteristics of ultrafine particles and are non-uniform, resulting in non-uniformity being introduced into the internal structure of the compact. becomes.

The present invention generates active zirconia-based ultrafine particles in liquid as approximately spherical agglomerated particles with a uniform size in the range of 0.3 to 3 μm, which eliminates all of the above-mentioned drawbacks and eliminates the need for spray drying with water. The present invention provides a spherical zirconia-based fine particle powder for use in fine ceramics that does not lose its fine particle properties even when drying is carried out, and does not necessarily require spray drying.

Through detailed research, the present inventors have found that suspended particles produced by thermal hydrolysis of a zirconium salt aqueous solution at 90 to 250°C are monoclinic zirconia microcrystals (solid solutions of impurities such as hafnium) with a crystallite diameter of 100 Å or less. It was found that the secondary particles are twin-like agglomerated secondary particles of (including), and the secondary particle diameter is in the range of 30 to 3000 Å.
However, no matter how you change the conditions, the number of aggregated particles is 3000.
It hardly grew beyond Å. Conventionally, such a powder consisting of agglomerated particles of 3000 Å or more had not been obtained at all, and its characteristics had not been questioned at all. The present invention
The purpose is to easily produce and put into practical use agglomerated particle powder with a size of 3000 Å or more.

That is, a mixed suspended aqueous solution in which a zirconium salt is added to crystalline zirconia-based aggregated particles of approximately 1000 Å or more obtained by heating and hydrolyzing an aqueous zirconium salt solution is made to have a pH of 1 or less, which is strongly acidic, and the aggregated particles are kept in a suspended state. The suspended particles were then used as seed crystals to form 3000Å crystals.
It is characterized by being made to grow more than the above.

According to experiments conducted by the present inventors, if the thermal hydrolysis temperature of zirconium salt is below 90°C, the growth will take too long, and if it is above 250°C, the primary particles will become large and lose their reaction activity, and the secondary agglomerated particles will interact with each other. This is not appropriate as bonding will begin to occur. In addition, the smaller the aggregated particles of 1000 Å or less, the larger the growth surface area per weight, and they tend to float in the liquid and grow, but they themselves do not grow to 3000 Å or more, and the growth of relatively coarse aggregated particles that are easy to settle. It turned out to be a hindrance. It has also been found that isolated fine particles are less likely to be generated under strongly acidic conditions with a pH of 1 or less. The above invention is an application of these experimental results.

After further repeated experiments, the present inventor found that when the pH becomes lower and the hydrochloric acid concentration exceeds 1.5N, the zirconia-based suspended particles begin to coagulate and settle, and that this aggregation is different from that when the pH is high. isolated
They become relatively weakly aggregated particles with a size of approximately 0.5 to 3 μm and are approximately spherical. Furthermore, these temporary sedimentary aggregate particles are heated at 90°C to 250°C in a suspended state or in a suspended state with a zirconium salt added thereto. It was discovered that if heat treated, strong and stable agglomerated particles could be formed. This is probably due to recrystallization in an aggregated state or growth on the surface of aggregated particles.

A part of the present invention is based on the above discovery, and the present invention is based on the temporary sedimentation property produced by adding an amount of acid sufficient to cause suspended particles to coagulate with each other and cause sedimentation to a crystalline zirconia-based fine particle sol. Agglomerated particles 90-250
This method is characterized by carrying out a heat treatment at a temperature of .degree. C. for a necessary period of time to convert the particles into secondary agglomerated particles having a stable shape.

The above aggregated particles obtained by the method of the present invention are
All are produced as aqueous suspensions, and all
Composed of crystalline primary ultrafine particles of 100 Å or less,
It is also remarkable in that it is obtained as isolated, almost spherical agglomerated particles with a diameter of 3000 Å or more. It is easy to classify the particle size by sedimentation or centrifugation, does not lose its properties by ordinary heat drying, and is easily loosened after drying to give a powder consisting of isolated agglomerated particles. This can be truly called a microgranulation method in water, and granulation in such a microscopic range of 0.3 to 3 μm has never been achieved in the past. Particulate powder has never been obtained before. These agglomerated particle powders with controlled aggregation have extremely high industrial value, as will be described later.

Furthermore, the agglomerated particles obtained by the method of the present invention are characterized by ease of calcining treatment. In other words, the above-mentioned aggregated particles classified into a desired size by a sedimentation method or the like are heat-treated or calcined at an appropriate temperature of 1000°C or less, either alone or in combination with other metal compounds. The size of the primary particle,
Crystal form, chemical composition, agglomeration state, etc. can be changed. During calcination at temperatures below 1000°C, the bonds between aggregated particles that normally occur are relatively weak compared to the inside, so they are easily loosened, and the uniformity of the shape and size of the aggregated particles increases.
There is almost no loss of isolation.

As a result of the above, the method of the present invention can finally achieve a diameter of 0.3 microns or less (30000 Å to 3000 Å).
This provides an ideal ceramic powder consisting of nearly spherical isolated particles with arbitrary particle size and distribution, and this powder particle is agglomerated 2 consisting of primary ultrafine particles of 0.05 microns (500 Å) or less. It is a secondary particle that is extremely active and has excellent reactivity and sinterability. Furthermore, the internal microstructure such as the chemical composition, size of the primary particle, and agglomeration state can be adjusted appropriately by calcination, solid phase reaction, etc. depending on the purpose. The particles themselves also have extremely excellent properties.

As described above, the present invention enables the industrial production of ideal zirconia-based agglomerated particle powder with an almost perfect shape by a relatively simple method, and is useful for industrial production of fine ceramics, abrasives, cosmetics, etc. emulsifier,
It has excellent value in other fields as well.

Example 1 Approximately 10 g of reagent zirconyl chloride (ZrOCl _{2.8H 2} O)
Dissolve in about 60 ml of distilled water to make a solution of about 0.5 mol/ml, and stir about 60 ml of this in a closed container.
Hydrolysis was carried out by heating at 150°C for 8 hours. The obtained suspension is secondary particles in which monoclinic ultrafine crystals with a diameter of about 40 Å are aggregated in an oriented manner according to X-rays, but since it contains fine agglomerated particles with a diameter of less than 1000 Å, the part larger than about 1000 Å is separated by a centrifuge. was separated, and part of it was mixed with about 10 g of zirconyl chloride as a seed crystal to make about 60 ml of suspension. The ratio of seed crystals to Zr in the solution was approximately 1/8 in terms of Zr ratio. When this suspension was heated and water-decomposed at 150°C for 8 hours while stirring in a closed container, the X-ray crystallite diameter was approximately 40 Å, which was almost the same as the initial one.
However, according to an electron microscope, it was a relatively uniform, almost spherical agglomerated particle with a diameter of about 4000 Å. Furthermore, the same production was repeated using these aggregated particles as seed crystals, and 4
In the second round, we were able to grow most of the particles to about 10,000 Å in diameter.

Example 2 From the monoclinic zirconia aggregate particle suspension obtained in Example 1 above, approximately 5000±
A portion corresponding to approximately 500 Å was separated, and yttrium nitrate was added in an amount corresponding to 6 mol % based on zirconia, mixed well, and calcined at 800° C. for 1 hour.
The calcined product was slightly coagulated, but was easily loosened in a mortar.
The powder was found to be a tetragonal solid solution with a crystallite diameter of about 150 Å by X-ray examination, and no free Y ₂ O ₂ was observed.
0.3% by weight of cellosol (stearic acid suspension) was added to this powder as a lubricant, and it was press-molded as it was at a pressure of 2t/ ^cm3 without granulation, and baked at 1350℃ for 1 hour. A sintered body with a density of approximately 98% was obtained. In this case, the firing wire shrinkage rate is approximately
At 15%, the shrinkage rate was extremely small for this type of easily sinterable powder, and the filling properties during molding were excellent.

Example 3 Approximately 97 g of zirconyl chloride reagent was dissolved in approximately 500 ml of distilled water, and a sufficient amount of 1:1 aqueous ammonia was added to form a precipitate of zirconium hydroxide. 39 g of the reagent zirconyl chloride is added to the water-containing cake obtained by suctioning it and stirred to form a fluid slurry.
This was kept at 97℃ for about 40 hours, and the X-ray measurement was about 30 Å.
The primary particles are monoclinic zirconia ultrafine crystals (approximately 40 Å even under an electron microscope), which are oriented and agglomerated.
A sol consisting of secondary agglomerated fine particles of 1000 Å was obtained. When 12N hydrochloric acid was added to this sol, the concentration of hydrochloric acid was approx.
Sedimentation separation occurred at a point near 2N. According to an optical microscope, this precipitate is a spherical agglomerated particle of approximately 1 μm (10,000 Å) in size, but the aggregation is weak and will not become dry particles as it is. A small amount of zirconyl chloride (Zr ratio: 1/10) was added to this precipitate, and the mixture was heated to 150°C for 8 hours while stirring in a closed container.
The X-ray crystallite diameter increased only slightly (approximately 35 Å), and the secondary agglomerated particles became strongly stable at approximately 1 μm, and upon drying, a fine powder was obtained in which the aggregated particles did not coagulate with each other.

The reactivity and sinterability of the obtained powder particles were as shown in Example 2.
The results were almost the same as those obtained for powder particles.

Claims (1)

[Scope of Claims] 1 Consisting of secondary particles in which monoclinic primary ultrafine particles with a crystallite diameter of 100 Å or less are aggregated in an oriented manner, approximately spherical, with a size in the range of 0.3 μm to 3 μm, and relatively A zirconia-based agglomerated particle powder characterized by narrow areas. 2. A mixed suspension aqueous solution in which a zirconium salt is added to monoclinic zirconia aggregate particles of approximately 1000 Å or more obtained by heating and hydrolyzing an aqueous zirconium salt solution is made to have a pH of 1 or less, making it a strongly acidic solution, while maintaining the aggregate particles in a suspended state. Perform thermal hydrolysis at a temperature of 90℃ to 250℃,
A method for producing zirconia-based aggregated particles, which comprises growing suspended particles to a size of 3000 Å or more using seed crystals. 3 A sufficient amount of acid is added to the crystalline zirconia-based fine particle sol to cause the suspended particles to coagulate with each other and cause sedimentation, and the resulting temporary sedimentary agglomerated particles are reduced to 90 to 250.
1. A method for producing zirconia-based agglomerated particles, which is characterized by carrying out a heat treatment at a temperature of °C for a required period of time to convert them into secondary agglomerated particles having a stable shape. 4 Temporary sedimentation by adding acid to zirconia-based aggregated particles or crystalline zirconia-based fine particle sol that are grown to 3000 Å or more by further hydrolysis using secondary aggregated particles obtained from heated hydrolysis of a zirconium salt aqueous solution as seed crystals. Separate any part of the particle size range of 3000 Å or more by sedimentation or centrifugation from a cloudy liquid containing any of the zirconia-based aggregated particles that have been converted into secondary particles with a stable shape. , a method for producing a zirconia-based agglomerated particle powder, which is characterized in that the zirconia-based agglomerated particle powder is heat-treated at a temperature of 1000°C or less, either alone or in combination with another metal compound.