JPH0696471B2 - Method for manufacturing zirconia ceramics - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a high-strength zirconia ceramics.

[Conventional technology]

In recent years, various types of high-strength ceramics have been developed and used as mechanical materials. Among them, partially stabilized zirconia ceramics is attracting attention as a high toughness material with improved brittleness of ceramics. As its manufacturing method, (1) neutralization coprecipitation, hydrolysis, or spraying of a zirconium compound and a stabilizing element compound is performed. Method of forming and sintering fine powder by so-called wet method produced by thermal decomposition as raw material (2) Mixing zirconia and fine powder of stabilizing element oxide and firing in a temperature range where equiaxed crystals are stable A tetragonal crystal that contributes to high toughness by consolidating to form an equiaxed single phase, and then subjecting this to a long-term aging treatment at a lower temperature region where the tetragonal crystal becomes a stable phase, and then rapidly cooling to room temperature. Generally, the method of squeezing out and freezing and the methods of doing so are commonly performed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in these methods, in the case of (1), the raw material ends are likely to be composed of firmly bonded secondary particles of primary particles and are likely to contain residual anions. High strength ceramics cannot be obtained unless In the case of (2), there was a drawback that cracks due to thermal shock were likely to occur in the ceramic product during rapid cooling after aging.

The present invention aims to eliminate the above-mentioned drawbacks.

[Means for Solving the Problems] The gist of the first invention of the present application is to melt a composition containing 1.6 to 3.4 mol% of Y ₂ O ₃ and the balance substantially consisting of ZrO ₂ , and then, The melted composition is cooled to contain tetragonal crystals to obtain a solidified body, and the solidified body is crushed and pulverized to have a particle size of 3
A powder having a size of μm or less is produced, and when the powder is crushed and pulverized, the tetragonal crystal is transformed into martensite to generate a monoclinic crystal so that the powder is composed of a tetragonal crystal and a monoclinic crystal. And sintering, and at the time of the sintering, the monoclinic crystal is reversely transformed to generate a metastable tetragonal crystal, and the sintered body is a combination of a tetragonal crystal and a monoclinic crystal, or a tetragonal crystal alone, or A method for producing zirconia ceramics is characterized by comprising a combination of a tetragonal crystal and an equiaxed crystal.

The sintering of the powder compact requires a high temperature of 1500 ° C. or higher, and at a high temperature of 1600 ° C. or higher, grain growth occurs and the strength of the sintered body tends to decrease. On the other hand, when sintered at a low temperature of 1500 ° C. or lower, grain growth does not occur in the sintered body, but the sintered body is in a ware-fired state, and such a sintered body is naturally low in strength. Therefore, in the partially stabilized zirconia sintered body by Itutria that is produced from the melt-solidified body as the raw material, there is no particle growth, or even if it is small, sintering at low temperature → high strength is desired. .

Therefore, the second invention of the present application improves on this point to provide 1.6-
A composition containing 3.4 mol% Y ₂ O ₃ and the balance substantially consisting of ZrO ₂ was melted, and then the melted composition was cooled to contain tetragonal crystals to obtain a solidified body. The solidified material is crushed and crushed to form a powder having a particle size of 3 μm or less, and the crushed and crushed powder is transformed into a monoclinic crystal by the martensite transition of the tetragonal crystal. as consisting of, further having a total of from 0.005 to 6% by mole so as to MgO in the _{powder, Fe 2 O 3, CeO 2} , La 2 O 3, Al 2 O 3, CaO, 1 kind of TiO ₂ or 2 A zirconia ceramic characterized in that a mixture is prepared by adding and mixing one or more species, the mixture is shaped and sintered, and the monoclinic crystal undergoes a reverse transition during the sintering to generate a metastable tetragonal crystal. The manufacturing method is as a gist.

[Examples] The present invention includes various examples and is not limited to the examples described below.

The present invention will be described in detail. Industrial powder (purity ZrO ₂ : 99.0%, Y ₂ O ₃ : 99.9%) was used as the ZrO ₂ , Y ₂ O ₃ raw material, and the content of Y ₂ O ₃ was 1.1, 1.6,1.9,2.2,2.8,3.4,4.0,4.
18 kg of each mixture was prepared by mixing ZrO ₂ and Y ₂ O ₃ so as to be 5,5.1 mol%, and each mixture was melted in a 100 KVA carbon electrode arc furnace and the arc furnace was tilted to melt the melt. About 5 cm thick
On a graphite plate of about 1.5 cm, and then transferred to another graphite plate for rapid cooling, or compressed air was applied to the narrow stream of the melt to blow it off and instantly cool it. . In either case, when 18 kg of the composition is treated as described above, it is cooled from the molten state to room temperature within a few hours.

After roughly crushing these coagulated bodies to 100 mesh with a crusher, 2.5 kg of this coarsely crushed material is crushed with an iron ball mill for 72 hours, dissolved iron content is mixed with hydrochloric acid, washed with water and dried to obtain a central particle size.
A fine powder of 0.5 to 0.8 μm was obtained. Next, these powders were rubber-press molded at a molding pressure of 1 ton / cm ² to a size of 55 × 55 × 6 mm, and fired in the air at 1550 ° C. for 2 hours under normal pressure, and the parts with different Y ₂ O ₃ contents A stabilized zirconia sintered body was obtained.

The phase constitution of the solidified body, the powder, and the sintered body thus obtained was measured by X-ray diffraction using a mirror-polished surface instead of converting the solidified body and the sintered body into powder. For coagulum
Y ₂ In the O ₃ amount is small range consists monoclinic + tetragonal, Y ₂
The composition containing O ₃ 2.8 mol% or more is composed of a tetragonal single phase.
The powders are monoclinic + tetragonal in all compositions.
Regarding the sintered body, Y ₂ O ₃ is composed of monoclinic crystal + tetragonal when it is 1.9 mol% or less, tetragonal single phase when it is 2.2 mol%, and tetragonal + equiaxed crystal when it is 2.8 mol% or more. Quantitative determination of monoclinic and tetragonal amounts was performed using the integrated intensities of monoclinic (111) and (11) diffraction lines Im (111), Im
(11) Proposed by Garvie and Nicholson using integrated intensity It (111) of tetragonal (111) diffraction line and integrated intensity Ic (111) of equiaxed (111) diffraction line. It was done using a formula. The amount is expressed as a volume fraction.

In case of tetragonal + monoclinic In case of tetragonal + equiaxed crystal The quantitative results are shown in Table 1.

Here, the amount of monoclinic crystals in the powder increased compared to the amount of monoclinic crystals in the solidified body (91-92, 78-84, 46-69, 34-75). The orthorhombic crystals are formed by the martensite transformation of tetragonal crystals in the solidified body. Further, in the sintered body, the monoclinic crystals contained in the raw material powder are drastically reduced or disappeared. (92-92, 84-79, 69-9, 75-0) It is considered that this is because the monoclinic crystal produced by the martensite transition contained in the powder was again transformed to the tetragonal reverse transition. Note that Y ₂ O ₃ 2.
Equiaxed crystals are contained in the sintered body of 8 mol% or more, and it is considered that the tetragonal crystals in the powder are transformed into equiaxed crystals. The relationship between the content of tetragonal crystals in the solidified body, the amount of monoclinic crystals formed by the martensite transition in the powder, and the amount of tetragonal crystals formed by the reverse transition in the sintered body and the content of Y ₂ O _{3 are described} below. As shown in Fig. 1, it can be seen from Fig. 1 that in the composition range of Y ₂ O _{3 of} 1.6 to 3.4 mol%, the amount of tetragonal crystals in the solidified body increased as the amount of Y ₂ O ₃ increased, and the solidification The powder contains the most monoclinic crystals that have undergone martensite transformation by crushing and crushing the tetragonal crystals in the body, and the tetragonal crystals formed by the reverse transformation of the monoclinic crystals in the powder in the sintered body. It is clear that it is contained in the largest amount. Tetragonal crystal in solidified body ↓ Martensite transition (by crushing and pulverization) Monoclinic crystal in powder ↓ Inverse transition (due to sintering) Characteristic of tetragonal crystal in sintered body This is the composition range in which it appears most remarkably. In addition, ○ mark is a tetragonal crystal in the rapidly solidified body, △ mark is a monoclinic crystal formed by the martensite transition in the powder obtained by pulverizing the rapidly solidified body, and □ is a tetragonal crystal formed by the reverse transition in the sintered body. Crystals, expressed as a volume%.

In the present invention, the composition range of the ZrO ₂ —Y ₂ O ₃ system that can be used is Y ₂
This is the reason why the O ₃ is limited to 1.6 to 3.4 mol%.

Next, the sintering temperature will be described. The ZrO ₂ -Y ₂ O ₃ -based composition achieves high strength at each of the sintering temperatures of 1500 to 1550 ° C, but the sintered body obtained at a temperature lower than 1500 ° C does not have sufficient densification. It is unglazed with water absorption and its bending strength is not sufficient. On the other hand, when the sintering temperature exceeds 1550 °, the water absorption of the sintered body becomes substantially equal to 0, but the zirconia particles grow and the bending strength also decreases.

Therefore, the present inventors have found that ZrO ₂ —Y ₂ O ₃ having the above-mentioned properties.
In the method for producing melt-solidified body, powder, and sintered body of the system, 15
It is believed that if densification of the sintered body can be achieved by firing at 00 ° C or less, high strength ceramics with little or no grain growth can be obtained, and various studies are repeated, and 0.005 to 3.0 mol% ZrO ₂ −Y ₂ O with MgO added in range
_It was found that the _3- MgO ceramics are dense and have high strength. That is, among the compositions in which the difference in bending strength depending on the firing temperature was examined, the ZrO ₂ —Y ₂ O ₃ composition powder containing 2.2 mol% Y ₂ O ₃ showing a high strength value at each firing temperature was added as a reagent ( (Special grade) MgO is added in the range of 0.005 to 8.0 mol%, alumina balls are put in a polyethylene container, and after wet mixing for 24 hours with methanol as a solvent, the solvent is volatilized,
Rubber press molding was carried out at a molding pressure of 1 ton / cm ² to a size of 55 × 55 × 6 mm, followed by firing in air at 1400 ° C. for 2 hours to obtain a partially stabilized zirconia sintered body containing MgO. These sintered bodies
The ones that did not contain MgO were unglazed, but both had no water absorption and were densified, but the three-point bending strength was measured for the sintered body compositions with different amounts of MgO added. Results were obtained as shown. This is because the strength of the MgO-free sintered body is 38.8 kg / mm ² , while MgO
It shows that the strength increasing effect is observed when added in the range of 0.005 to 3.0 mol%.

Similarly, when Fe ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Al ₂ O ₃ , CaO, and TiO ₂ were tested, high-strength ceramics were obtained. This will be described with reference to FIGS. All of these oxides with added oxides had high strength because they promoted the sintering at low temperature (1400 ℃). (1400 ° C
In about 2 hours calcining) Figure 3 which was examined flexural strength of a material obtained by adding Fe ₂ O _3, those Fe ₂ O ₃ is from 0.08 to 6 mol% C., the fourth figure with the addition of CeO ₂ 0.01 to 4.0 mol% is preferable, Fig. 5 is 0.02 to 2 mol% with La ₂ O ₃ added, and Fig. 6 is 0.05 to 5 with Al ₂ O ₃ added.
The mol% is good, and Fig. 7 shows 0.005 to 3 with CaO added.
Mol% is good, and Fig. 8 shows that TiO ₂ is added and 0.005〜
3 mol% is a good one.

[Brief description of drawings]

FIG. 1 is a graph showing the phase composition (volume%) of a solidified body, a powder and a sintered body, FIG. 2 is a graph showing the bending strength when MgO is added, and FIG. 3 is Fe ₂ O ₃ A graph showing the bending strength when added, FIG. 4 is a graph showing the bending strength when CeO ₂ is added, FIG. 5 is a graph showing the bending strength when La ₂ O ₃ is added, and FIG. 6 is FIG. 7 is a graph showing the bending strength when Al ₂ O ₃ is added, FIG. 7 is a graph showing the bending strength when CaO is added, and FIG. 8 is a graph showing the bending strength when TiO ₂ is added.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Saito 20-8 Hachimantai, Takeda, Kanzaki-cho, Katori-gun, Chiba Prefecture Toshiba Monoflats Co., Ltd. Kanzaki Plant (56) References JP-A-60-65726 (JP, A) Special Kai 56-50169 (JP, A) JP 56-134564 (JP, A) JP 57-140375 (JP, A) JP 58-156577 (JP, A) JP 61-59265 ( JP, B2)

Claims (2)

[Claims] 1. A composition comprising 1.6 to 3.4 mol% Y ₂ O ₃ and the balance being essentially ZrO ₂ is melted, and then the melted composition is cooled to contain tetragonal crystals. A solidified body is obtained by crushing and crushing the solidified body to form a powder having a particle diameter of 3 μm or less, and during the crushing and crushing, the tetragonal crystal is transformed into martensite to generate a monoclinic crystal. Is composed of tetragonal crystals and monoclinic crystals, and the powder is molded and sintered, and during the sintering, the monoclinic crystals are reversely transformed to generate metastable tetragonal crystals. Is a combination of tetragonal crystals and monoclinic crystals, or tetragonal crystals alone, or a combination of tetragonal crystals and equiaxed crystals. 2. A composition containing 1.6 to 3.4 mol% Y ₂ O ₃ and the balance substantially consisting of ZrO ₂ is melted, and then the melted composition is cooled to contain tetragonal crystals. To obtain a solidified body, and the solidified body is crushed and pulverized to prepare a powder having a particle diameter of 3 μm or less. The crushed and pulverized powder is transformed into a monoclinic crystal by martensite transition of the tetragonal crystal. The body is composed of tetragonal and monoclinic crystals, and the powder contains 0.005-6
MgO so that _{mol%, Fe 2 O 3, CeO} 2, La 2 O 3, Al 2 O 3,
One or two or more kinds of CaO and TiO ₂ are added and mixed to form a mixture, and the mixture is molded and sintered, and the monoclinic crystal undergoes a reverse transition during the sintering to form a metastable tetragonal crystal. A method for producing zirconia ceramics, which comprises producing the zirconia ceramics.