JPS63129017A - Production of fine powdery zirconia - Google Patents

Abstract

PURPOSE:To obtain the titled fine powder which is easy to sinter, and is simply and surely formed into a fine and uniform sintered body of ZrO2 with high quality at low temp., by filtering a solid matter which is obtained by dissolving the powder of stabilizer into the suspension of fine powdery ZrO2 hydrate, then adding aq. NH3, etc., and precipitating, followed by washing with water, calcining, and pulverizing. CONSTITUTION:(A) The fine powder of ZrO2 hydrate is obtained by hydrolyzing an aq. soln. of zirconium salt or by heating and agring zirconium hydroxide and (B) >=one kind among compd. contg. Y<3+>, Ca<2+>, Mg<2+> or C<4+> [e.g. Y(NO3)3] is dissolved as the stabilizer into the suspension of the above-mentioned fine powdery ZrO2 hydrate. Then (C) the aq. NH3 and/or aq. soln. of NH4 salt is added to the soln. and the B component is allowed to precipitate as a hydroxide or an insoluble carbonate. At the same time, the fine powdery ZrO2 hydrate is allowed to coagulate and precipitate as the solid matter. And the obtained solid matter is filtered, washed with water, calcined and pulverized.

Description

[Detailed description of the invention] [Industrial application field] The present invention has characteristics of high strength and high toughness, and is applicable to bearings, mechanical seals, jigs and tools, cutlery, crushing media, lining materials,
The present invention relates to a method for producing raw material powder for zirconia sintered bodies, which are used as structural ceramics for engine parts and the like, and also as functional material ceramics for oxygen sensors, oxygen pumps, etc. by utilizing their oxygen ion conductivity.

[Conventional technology] Conventionally, high-strength, high-toughness zirconia (stabilized zirconia)
In the production method, stabilizers (Y2O2, CaO1M
Generally, a method is adopted in which powder of zirconium oxide (g01CeO2, etc.) is mixed with powder of zirconium oxide, and this is calcined at a temperature of 1000-1200°C, followed by shaping and sintering.

However, since this method involves mixing powders, it is difficult to obtain uniform mixing, sintering requires a high temperature of 1,600°C or higher, and the distribution of the stabilizer in the sintered body is also uneven. There was a problem that the original characteristics could not be fully expressed.

On the other hand, as an alternative to such conventional production methods, synthesis of raw material powders called a coprecipitation method has recently been carried out. In this method, a water-soluble zirconium salt such as oxidized zirconium chloride and a water-soluble salt of a stabilizer such as yttrium chloride are mixed and dissolved in water, and an alkali such as ammonia is added to the mixture to form zirconium hydroxide. A mixture of hydroxide and a stabilizer is co-precipitated, and this coprecipitate is filtered, washed, dried, calcined, and ground to form a powder.

According to this method, an easily sinterable powder with significantly improved sinterability can be obtained compared to the case where powders are mixed together.

[Problems to be Solved by the Invention] However, according to the above coprecipitation method, there is a difference in the rate of precipitation between zirconium hydroxide and the stabilizer hydroxide depending on conditions such as pH during coprecipitation. Therefore, it is practically difficult to produce an ideal homogeneous coprecipitate, and it is undeniable that some heterogeneity remains. In addition, during the drying and calcining stages, the coprecipitated hydroxide tends to form hard agglomerates, making it difficult to form powders of uniform and fine size necessary for easy sintering.

In view of these problems, the present invention aims to obtain a raw material powder with even better sinterability for use in zirconia sintered bodies.
The present invention aims to provide a new method for producing fine zirconia powder that can more uniformly dissolve a stabilizer in solid solution and can be easily refined.

[Means for Solving the Problems] In order to achieve the above object, the present invention takes the following means. That is, stabilizer ions (Y3-) are added to the suspension of hydrated zirconia fine particles.

One or more of Ca2+, Mg2+, Ce") is added and mixed and dissolved. Next, aqueous ammonia or an aqueous solution of ammonium salts is added alone or in combination,
At the same time as the stabilizer is precipitated as a hydroxide or insoluble carbonate, the hydrated zirconia fine particles are soft aggregated. After that, these are mixed uniformly, and the precipitated solids are separated from the suspension by filtration, washing with water, and further drying.
Through the steps of calcining and pulverization, fine zirconia powder in which the stabilizer is uniformly dissolved is obtained.

The suspension of hydrated zirconia fine particles used in the present invention can be obtained by hydrolysis of an aqueous solution of a zirconium salt, heat aging of zirconium hydroxide, or the like.

In addition, methods for adding stabilizer ions such as (Y 3+') to this suspended sol include the addition of water-soluble salts such as chlorides and nitrates, or dissolving these oxides in acids such as nitric acid. This can be done by means such as mixing solutions.

Furthermore, as a means of precipitating the stabilizer, Y3+,
In the case of Ce4+, it is common to solidify it as a hydroxide by adding an alkali such as ammonia, but Ca2+
+, M g "In the case of 10, Ca by addition of a mixed aqueous solution of alkali and carbonate such as ammonium carbonate.
Preferably, this is through the formation of an insoluble carbonate such as C0z.

Note that the subsequent treatment steps such as filtration and water washing are the same as in the case of the conventional coprecipitation method.

[Function] In this way, when a suspension of hydrated zirconia fine particles in which a desired stabilizer ion is dissolved is treated by adding a precipitant such as an alkali, Zr"+ is stabilized. By adding alkali to a mixed solution of stabilizer ions, both hydroxides are co-precipitated.A coprecipitated solid product is obtained in which zirconia and stabilizer are mixed extremely uniformly, which cannot be obtained by conventional coprecipitation methods. The reason for this is that by precipitating the stabilizer while the hydrated zirconia particles are uniformly dispersed in the liquid, an extremely uniform co-precipitate of zirconia and the stabilizer can be created. Furthermore, unlike the case of hydroxide, the coprecipitate thus obtained does not aggregate strongly during drying and calcining, and is extremely easy to loosen and become fine powder.

[Example] As an example, a method for producing fine zirconia powder containing ittria as a stabilizer, and characteristics of this raw material powder and a zirconia sintered body using the powder will be described in detail below.

1 mol of hydrated zirconia fine particles (average particle size = -
Add yttrium nitrate to 1 g of suspension containing 1 μm).
After adding 6 mol and dissolving and mixing, 1:1 ammonia water was added without stirring until the pH of the liquid became 8 to 9 to precipitate the solid, which was washed, filtered and dehydrated.

When this water-containing cake was dried at 150° C. for 24 hours, the dried product became a lump that could be easily loosened with fingertips. Set this to 0
．． Crush it to 1mm or less and heat it in an electric furnace at 800°C for lhr.
After calcining, it was ground in a pot mill.

Table 1 shows the properties of the obtained zirconia fine powder.

Table 1 Next, using this powder, a pellet-like molded body having a diameter of 20×t2+nm was produced using a mold press (pressing pressure of 98 MPa), and fired at 1300 to 1500°C. The density (g/cm3) of the obtained sintered body is shown in Table 2 in comparison with that using powder obtained by a conventional coprecipitation method.

Table 2 [Effects of the Invention] As shown in the following, according to the production method of the present invention, as a raw material powder of stabilized zirconia for fine ceramics, fine, easily sinterable powder with a more uniform solid solution of the stabilizer can be obtained. You can get something that is excellent. Therefore, by using this powder, a high quality zirconia sintered body having a dense and uniform composition can be reliably provided in a cylinder at a lower sintering temperature.

Claims (1)

[Claims] Each of Y^3^+ and C was added to the suspension of hydrated zirconia fine particles.
One or more compounds containing a^2^+, Mg^2^+, and Ce^4^+ are dissolved, and ammonia water or an aqueous solution of ammonium salts is added alone or in combination to form a solid substance. A method for producing fine zirconia powder, which comprises settling, filtering, washing with water, calcining, and pulverizing the solid material.