JPH0214822A - Readily sinterable zirconia powder - Google Patents

Abstract

PURPOSE:To obtain readily sinterable zirconia powder capable of providing zirconia ceramics of stable high quality by using fused powder, consisting of ZrO2 containing Y2O3 having a crystal phase consisting of monoclinic ZrO2 and tetragonal ZrO2 in a specific proportion as a component. CONSTITUTION:Zirconia powder which is fused powder, consisting of 3.2-7.5-wt.% Y2O3 and the remainder of ZrO2 and two crystal phases of 20-75vol.% monoclinic zirconia and 25-80vol.% tetragonal zirconia therein by an X-ray analysis and capable of transition into 0-9vol.% monoclinic zirconia, 49-100vol% tetragonal zirconia and 0-51vol.% isometric zirconia in the crystal phases by heating applied during calcining. Since the zirconia powder is in an ultrahigh active state by transformation, a calcined compact having a sufficient density is readily obtained and a calcined compact having a high bending strength can be obtained due to internal stress produced by the transition during the calcining.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is characterized in that by heating applied during sintering, the volume ratio of the crystal phase is monoclinic zirconia of () to 9% and monoclinic zirconia of 49 to 100%.
The present invention relates to an easily sinterable zirconia powder characterized in that it transforms into tetragonal zirconia and 0 to 51% equiaxed zirconia.

[Prior art] Zirconia has traditionally been used as a highly corrosion-resistant, high-temperature material, but in order to prevent or reduce the catastrophic expansion and contraction that accompanies its transformation, so-called stabilization, in which a stabilizing element is dissolved in solid solution, is used. Zirconia or partially stabilized zirconia is commonly used. Stabilized zirconia or partially stabilized zirconia is composed of a composite of equiaxed and monoclinic crystals, which have a thermally stable structure, and has excellent thermal shock properties. Although excellent,
It did not have sufficient strength against mechanical stress.Recently, ceramics made of rapidly stable tetragonal zirconia have been researched and developed, making it a material that is strong against mechanical stress and has high toughness. It is attracting attention as

Ceramics made of this tetragonal zirconia are, for example (
1) Stabilized zirconia ceramics made only of equiaxed crystals in the United States or partially supported zirconia hiramixes made of mixed crystals of monoclinic crystals and equiaxed crystals are used for long periods in the temperature range where the tetragonal crystals are thermally stable. After being subjected to a time aging treatment, the tetragonal crystal is frozen by rapid cooling, or (2) a zirconium compound and a compound of a stabilizing element are neutralized, co-precipitated, hydrolyzed, or created by spray pyrolysis. It can be produced using a so-called wet-processable fine powder without performing the aging or quenching treatment.

However, although the former method is possible to prepare small samples, cracks may occur in samples large enough to be used as industrial materials due to rapid cooling, and in the latter case, In the wet method fine powder produced,
It is difficult to produce a stable, high-quality sintered body due to various reasons, such as the presence of zirconia particles that do not contain stabilizing elements as a solid solution, and the formation of relatively hard secondary particles that are agglomerated fine primary particles. I couldn't get it.

[Problems to be Solved by the Invention] The present invention provides an easily sinterable zirconia powder that does not generate cracks in the production of ceramics made of tetragonal zirconia and allows stable and high-quality zirconia ceramics to be obtained. This is what I am trying to do.

[Means for Solving the Problems] The present invention has been made in view of the above points, and the easily sinterable zirconia powder according to the present invention has Y, 0. 3.2-7
．． It is obtained by melting a composition consisting essentially of ZrOi and the remainder being ZrOi, followed by rapid cooling to produce a solidified body containing tetragonal zirconia, and then crushing and pulverizing this solidified body.

The above-mentioned solidified body contains sufficient tetragonal crystals, and when it is crushed and crushed, the tetragonal crystals transform into qt oblique crystals due to martensitic transformation, and at this time, the volume expansion is ('F-), so the internal The particle size of the powder is such that the resulting powder is easily sinterable and does not form secondary particles that are tightly agglomerated from primary particles like wet powder. It is desirable that the diameter is 3 μm or less.The sintered body produced from powder raw materials, including JP and other products produced by this martensitic transformation, contains metastable tetragonal crystals produced by reverse transformation of monoclinic crystals. It is in a high energy state and therefore its fracture strength is sufficiently large.

When the amount of Y2O added is 3.21 Mm% or less, tetragonal crystals involved in the martensitic transformation are not formed in the rapidly cooled body, the mechanical strength is not sufficient, and the sintering of the pulverized powder is The quality was poor.

When Y wealth 0 = 7.5ffi% or more, the quenched body is approximately 1 ()
It consists of 0% tetragonal crystals, and almost no monoclinic crystals are generated even by the mechanical stress accompanying the crushing, and in the end, most of the tetragonal crystals in the rapidly solidified body cannot contribute to martensitic transformation.

The distinction between tetragonal crystals that contribute to martensitic transformation and tetragonal crystals that do not contribute to martensitic transformation and the mechanism of their formation are not clear. Phenomenologically, when a melt is slowly cooled, parts that should exist as equiaxed gravity become tetragonal crystals due to rapid cooling. When subjected to mechanical stress,
It can be said that this tetragonal crystal does not transform into a lit-clinic crystal through martensitic transformation; on the contrary, the tetragonal crystal that can contribute to martensitic transformation should exist as a monoclinic crystal in a slowly cooled body.

As stated above, the inventors of the present application do not believe that it is sufficient to simply include a large number of tetragonal crystals; It must be capable of converting into monoclinic crystal. (Even if it is 100% tetragonal, it is useless if this transformation is small.) (2) It is desirable that the powder contains a larger amount of mercury produced by martensitic transformation of the tetragonal crystal in the solidified body.

(3) The sintered body preferably contains a large amount of metastable tetragonal crystals produced by reverse transition of the monoclinic crystals in the powder.

Satisfying these three conditions is an essential condition for the present invention; Y, 0. This is the reason why the content type is 3.2 to 7.5i arsenic%.

In the present invention, slow cooling refers to an operation such as casting approximately 18 g of molten material into a graphite mold, removing it from the mold immediately, immersing it in fine alumina powder, and slowly cooling it. This refers to an operation in which the body is poured onto a graphite plate to a thickness of about 1.5 cm, then transferred onto another cooled graphite plate and rapidly cooled.

In the slow cooling operation, the cooling time from the start of solidification of the melt to room temperature is 24 hours or more, and in the rapid cooling operation, the cooling time is less than 24 hours, but preferably 10 hours or less. In addition to methods such as 1I of the melt
It is also possible to cool the material to room temperature within a few seconds (or less) by applying it to a rotating object rotating at high speed or by blowing a jet stream of air onto it.

[Example] Example The zirconia raw material used in the present invention was obtained by chlorinating and refining baddeleyite ore from South Africa (Zr0
□99% or more), an industrial reagent was used for yzos.

A 300KVAt11-phase arc furnace was used for melting.

The slowly cooled body is produced using the above method, and takes 30 hours to reach a temperature that can be touched by hand after casting, and the rapidly cooled body is produced by pouring the molten body onto a graphite plate to a thickness of 2 to 3C11. 5 hours after the start of solidification, it was cooled to a temperature that could be touched by hand. In addition, X-ray diffraction of the slowly cooled body and rapidly cooled body 5 was performed using a polished surface, regardless of the crushed sample. This is due to the fact that phase change occurs due to martensitic transformation when a pulverized sample is subjected to 8-shaping, so we investigated a sample preparation method to avoid this. Polishing was performed using a 1200 mesh diamond grinder. The results of X-ray diffraction show that in the slowly cooled body, Y2O
, If the content is low, it consists of a single product with 10 equiaxed weight, and Y2O
As the 3 content increases, the equiaxed weight increases, and Y,
At 037.9 weight percent or more, the equiaxed weight becomes 100%, and in the quenched body, if the YJs content is low, it consists of 41 diagonal tentagonal crystals, and as the hos content increases, the tetragonal crystals increase,
Y, 0.4.5 fflfft% or more, tetragonal 100
%. Furthermore, each phase was quantified by X-ray diffraction. This quantitative value is for use +Il+1, +1
The integrated intensity of the 111 diffraction line b*(1111°l11(11
11, integrated intensity of tetragonal [+11] diffraction line It! +11
1° equiaxed weight (I + 11 integrated intensity of diffraction line 1c (I
Measure I I), Garvie and N1chols
This was carried out using the following formula shown by on.

slow cooling body × (Volume chi) × (Volume chi) quenched body (body fit) × (Volume chi) The experimental results are shown in Table 1.

(l (2) Table 1 lists both Examples and Experimental Examples.
6 is an example.

The rapidly cooled body was crushed to 3 μm or less using a diku crusher, and then a stamp mill and a ball mill.

When the constituent phases of the obtained powders were identified by X-ray diffraction, all the compositions were composed of monoclinic tetragonal crystals, but Y, 0. There was a tendency for monoclinic m to decrease as the content increased. Phase quantification 1111
(Iarvie-Nicholson equation (3
1,+41 was used. This is shown in Table-2.

Comparing Tables 1 and 2, we can confirm that pulverization caused martensitic transformation and changed from tetragonal to monoclinic! :+I～ is also clearly recognized. Table 2 also lists the monocrystalline forms produced by the martensitic transformation of the tetragonal crystals in this rapidly solidified solid, but Y! 0.3.4
~7.1% by weight (Examples 1 to 6), the production type is 20% by volume or more, and especially Y! 034.0~5 () Maximum ■ in the range of senior minister%.

Next, the Moeki powder was rubber press molded under a pressure of 1 ton/C11" to 5 (IX 50X fuam).
The sintered body was heated at 550°C for 2 hours in the air, and the phase structure, density, and three-point bending strength of zirconia in the sintered body were measured.
Shown in 3.

According to X-ray diffraction, Y, 0. Content 2.0-3.4% by weight
In the range of
At t%, it becomes 100% tetragonal. After that, as YxOs increased, equiaxed weight was generated, and as y and oa increased, its amount also increased. The phase stone is Gar for monoclinic tetragonal crystals.
This was done using the equations (31, (41) of vie and N1cholson, but in the case of a tetragonal 10 equiaxed mass, both (l l
l) Because the diffraction lines are so close that they cannot be separated, Gar
The formulas of vic and N1cholson cannot be used as they are.

Therefore, in the present invention, this two-phase constant
1 When the cholson formula is derived, monoclinic (III)
, +111) It was assumed that the integral intensity of the diffraction line is equal to the integrated intensity of the transition tetragonal or equiaxed crystal when it is heated to high temperature, which is equal to the integrated intensity of the transition tetragonal or equiaxed crystal. Returning to the original idea of
This was done based on the assumptions shown below. That is, tetragonal crystal (3
11), (The diffraction lines of 1131 and equiaxed weight (3rd) are separated and their integrated intensity values can be measured, so the integrated intensity of the 1-piece product (3111, Tl13) diffraction line is Equiaxed mass that transitions from tetragonal to high temperature (
ILf3111 +1t(1+3) Tetragonal m- It(3111+ lNl131 + Ic(311
The equation was used: 1xlooo (volume %) equiaxed weight = 100 - IE square weight (volume %). Here It(311), It(113)Ic
(311) are IE tetragonal 3111 and f11, respectively.
Equiaxed weight of the 31 diffraction line (This is the integrated intensity value of the 3111 diffraction line. The equiaxed weight generated in the sintered body is a tetragonal crystal in the rapidly solidified body, and does not undergo martensitic transformation due to crushing and pulverization, and is converted into powder as it is. It is thought that the tetragonal crystals that remained in the powder were formed by dislocation, but the positive force amount was the result of reverse transition of the monoclinic crystals formed by martensitic transformation in the powder. It is thought that the tetragonal crystals remained as they were, and Table 3 shows the tetragonal crystals produced by the Ill material transfer in this powder. was also written, but Y2O, containing @3
．． A large value is obtained for compositions in the range of 4 to 5%.
This roughly corresponds to the bending strength of the sintered body.The present invention has been described above, but the tetragonal crystal in the rapidly solidified solid, the monoclinic crystal produced by martensitic transformation in the powder, and the sintered A tetragonal crystal formed by reverse transition of the m-oblique crystal in the structure,
Y, 0. The relationship with the content is shown in FIG. 1, and the present invention is shown in 3.
It is shown in the figure that this is achieved in zirconia-based compositions containing YIOs in the range 2-7.5%.

Next, we will discuss what was cooled and solidified at a faster rate than carbon preliminary quenching. A mixture of refined baddellite ore and industrial ittria powder blended so that the content of Y and O is 4.0% by weight is melted in a carbon ionizing arc furnace,
A thin stream of molten material blown away by subsonic compressed air, and a thin stream with a diameter of 300 rpm rotating at 300 rpm.
Two types of coagulated bodies were obtained by applying it to a mm disk. The cooling rate at this time is about several seconds from the start of solidification to room temperature. This solidified material had a hollow spherical shape when blown with air, and a flaky shape when applied to a rotating disk.

The phase composition of these solidified bodies and the powder obtained by crushing the solidified bodies in the same manner as above, and the zirconia ceramics made from this powder as a raw material, as well as the three-point bending strength of the ceramics, were as shown in Table 4. The results were obtained.

This result shows that both compressed air quenching and rotating disk quenching are somewhat more effective at quenching than the carbon plate quenching shown earlier, and although there are more tetragonal crystals in the solidified body, the powder and sintered body obtained from this solidified body are approximately With similar characteristics, a bite tip made from this sintered body in the shape of 5NP432 is less likely to cause chipping than a conventional alumina tip when used for rough cutting of cast iron, and is more suitable for high-speed heavy cutting. Ta.

In this way, the present invention is achieved using a rapidly solidified body, and when a slowly cooled body that requires F for more than 24 hours from the start of solidification of the melt is used, even a composition containing Y2O in the same range can be achieved in the present invention. The effect shown in the invention cannot be obtained, and the strength of the solidified body is weak and does not contain tetragonal crystals, so the powder obtained from this solidified body contains Ill 14 produced by mardensite transformation.
The sintered body produced from this powder does not contain any reverse transition iE particles and has low bending strength because it does not contain any reverse transition iE particles and therefore a high activation state containing a large amount of strain energy cannot be achieved. is also low.

For example, to explain the measured values of bending strength in Table 3, in Example No. 6, the bending strength of the sintered body was 91.
~108 Kg/mm'', whereas in the comparative example, that is, Experimental Examples A, B, and C, it was all 80 Kg/m
m '' to F. Even when sintered in such a dense manner, the raw material powder that yields only a sintered body with low bending strength is not included in the present invention.

[Effects of the Invention] When a sintered body is obtained using the zirconia powder of the present invention, the following effects can be obtained.

Since the powder of the present invention is reduced through transformation and is in a highly active state, a sintered body with sufficient density can be easily obtained, and a sintered body with high bending strength can be obtained due to the internal strain generated by the transformation during sintering. It will be done. A stable sintered body can be obtained because there are no zirconia particles that do not have a solid solution of two stabilizing elements, and there are no relatively hard secondary particles that are agglomerated fine primary particles.

[Brief explanation of the drawing]

Figure 1 shows the phase composition (volume %) of the solidified body, 81 body, and sintered body.
Figure 2 is a graph showing the bending strength. Patent applicant: Toshiba Monoflux Co., Ltd. (Noufou R) Procedure 7 City official document (method) June 14, 1989 Patent application filed in 1988 No. 315780 2. Title of the invention: Easily sinterable zirconia powder 3. Person making the amendment 4. Agent address: 160 Telephone: 03-354-4084 May 30, 1999 (Start) 6. Inventions increased by amendment No number 7,? Iti Positive object A. The detailed description of the invention in the specification is amended as follows. (1) Print Tables 11, 2 and 4 on pages 16 to 19 of the specification as attached. 9. Amend the document certifying the power of attorney as shown in the attached sheet. C. Amend the representative of the patent applicant in the application as shown in the attached sheet. Table - 3゜

Claims (1)

[Claims] The weight ratio of Y_2O_3 is 3.2 to 7.5%, the remainder is substantially composed of ZrO_2, and the volume ratio of the crystal phase according to X-ray analysis is 20 to 75% monoclinic zirconia and 25%.
A molten powder consisting of two crystalline phases of ~80% tetragonal zirconia, which is heated during sintering so that the volume fraction of the crystalline phases is 0-9% monoclinic zirconia and 49-100%. % of tetragonal zirconia and 0 to 51% of equiaxed zirconia.