JPS589878A - Zirconia sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zirconia sintered body, and more particularly to a zirconia sintered body having zero mechanical strength and high thermal shock strength.

A pure zirconia sintered body transforms from a monoclinic crystal structure to a tetragonal crystal structure at around 1100°C.

Furthermore, it transforms into a cubic crystal structure at around 2400°C. On the other hand, during the cooling process, a transformation opposite to the above occurs, but especially when transforming from a tetragonal system to a monoclinic system, a large volumetric expansion is accompanied, so in order to prevent destruction due to this volumetric expansion, , zirconia, itztoria,
A sintered body made of zirconia having a cubic crystal structure (hereinafter referred to as cubic zirconia), that is, a stabilized zirconia sintered body, is obtained by dissolving oxides such as magnesia and calcia. However, since cubic zirconia has a large coefficient of thermal expansion, the stabilized zirconia sintered body has a drawback of low thermal shock strength.

On the other hand, a zirconia sintered body is made by coexisting cubic zirconia and zirconia with a tetragonal crystal structure (hereinafter referred to as tetragonal zirconia).

That is, the partially stabilized zirconia sintered body contains tetragonal zirconia with a small coefficient of thermal expansion.

Stabilized zirconia sintered bodies are also said to have high thermal shock strength. However, when it comes to the degree of improvement,
If cubic zirconia, which has a large coefficient of thermal expansion, is present, there will be no difference in melody, so it is not so noticeable.

On the other hand, 82 to 97 (mol%) of tetragonal □zirconia and 18 to 5 (mole percent) of monoclinic crystal structure nosilconia (hereinafter referred to as monoclinic zirconia) were made to coexist, and itria was fixed to this. There are reports that the zirconia sintered body produced by melting has high mechanical strength in tension, compression, bending, and shear, and also has improved hardness and toughness. However, this sintered body has a monoclinic zirconia ratio of 18 to 3 (
It had the disadvantage of low thermal shock strength in winter, when the amount (mol%) was extremely low. In other words, a small proportion of monoclinic zirconia means that the amount of transformation from tetragonal zirconia to monoclinic zirconia is small, but the energy due to thermal shock is This is because the microcracks that occur around it mainly absorb it.

Due to the small amount of microcracks generated due to the small amount of transformation, sufficient absorption of thermal shock energy is not achieved.

The object of the present invention is to solve the above points and provide a zirconia sintered body having extremely high mechanical strength and thermal shock strength.

To achieve the above object, the present invention is characterized in that zirconia with a tetragonal crystal structure and zirconia with a monoclinic crystal structure of 2o to 65 (mole eI) coexist, and zirconia with a cubic crystal structure coexists. A zirconia sintered body substantially free of crystalline zirconia, in which at least one oxide selected from yttoria, magnesia, and calcia is solid-dissolved, and the oxidation The amount of material is 1 to 4 (mol%) in Ittria, 2 to 6 (mol%) in Magnesia, and 2 in Calcia.
It is characterized by a zirconia sintered body having a molar coefficient of ~7.

In the present invention, the term "substantially free of zirconia having a cubic crystal structure" means that when a zirconia sintered body is analyzed by X-ray diffraction at a diffraction angle in the range of 20' to 80 (degrees). , cubic zirconia (004)
This means that the diffraction patterns of (222) and (222) cannot be detected. Namely, when X-ray diffraction is performed on the zirconia sintered body of the present invention, diffraction patterns for tetragonal zirconia and monoclinic zirconia are obtained, but even if cubic zirconia coexists, the diffraction patterns of Since the pattern almost overlaps with that of tetragonal zirconia and it is difficult to distinguish between 0 and 0, we focused on the diffraction patterns of cubic zirconia (OO4) and (222), which can be distinguished from each other.

Next, zirconia sintered body of the present invention (hereinafter referred to as sintered body)
will be explained in detail along with its manufacturing method. First, extremely fine zirconia powder and oxide powder, that is, itria, magnesia, or calcia powder, having an average particle size of 1 μm or less, are prepared.

Next, at least one of the zirconia powder and the oxide powder is
Mix with seeds. At this time, the mixed amount of oxide powder is 1
When using seed oxide powder, 1 to 4 (molar) for Puittria powder to the entire mixture,
Preferably 2 to 4 (mol%), for magnesia powder 2 to 6 (mol%), preferably nL<4 to 6- (mol%)
In the case of calcia powder, the amount should be 2 to 7 (mol S), preferably 6 to 7 (mol S). Even when using two or five of the above oxide powders at the same time,
The above range does not change, but the sum of the mixed amounts of each oxide powder,
That is, the total amount of oxide powder is 5 to 10 (mol%)
It is preferable that it is within the range of . For example, when ittria powder and magnesia powder are used simultaneously, ittria powder is preferably 2 to 4 (mol%) and magnesia powder is 3 to 5 (molar percentage)6. Powder 2-6 (molar ratio) -
Calcia powder 6-5 (molar ratio), Ittria powder 1-2
(mol qb) - Magnesia powder 6゛~4 (mol%) -
Calcia powder 2-4 (molar ratio), magnesia powder 5-5
(mol qb>-calcia powder 2 to 4 (mol qb>).

Next, the above mixture is calcined at 800 to 1200 (°C) and then pulverized with a ball mill. Such calcining and pulverization are repeated to obtain a raw material powder. This raw material/powder forms a solid solution in which zirconia powder and oxide powder are uniformly mixed, and the crystal structure of the solid solution is determined by the particle size and purity of the zirconia powder and oxide powder used, and the oxide Powder type and mixing amount.

Although it varies depending on the calcination temperature, etc., it is usually monoclinic.

However, there are cases where a monoclinic crystal structure and a tetragonal or cubic crystal structure coexist; Sometimes they coexist.

Next, the raw material powder is molded into a desired shape by a known molding method such as a rubber press method, an injection molding method, a mold molding method, an extrusion molding method, etc. to obtain a molded body.

Next, the above-mentioned molded body was placed in a heating furnace, and heated to
After gradually raising the temperature to 00C), it is held at that temperature for several hours and fired. In the process of temperature increase, the crystal structure of the solid solution is transformed from a monoclinic system to a tetragonal system or cubic system, or a state in which both of these systems coexist, and a monoclinic system transforms to a state in which both of these systems coexist. The state is a tetragonal system, a cubic system, or a state where both of these coexist, and a state where a monoclinic system and a cubic system coexist, and a state where a monoclinic system, a tetragonal system, or a cubic system coexist. , transform to a coexisting state of tetragonal and cubic systems or to a cubic system, respectively.

The temperature and rate of such crystal structure transformation are:

It varies depending on the type of oxide powder used and the amount mixed.

Therefore, with reference to the phase diagram, the firing temperature at which the crystal structure described above is obtained is determined. What is the firing temperature?

As mentioned above, it is in the range of 1400 to 1800 (°C).

Next, the fired body was heated at a speed of 20 to 180 (°C/hour) to 800
Either slowly cool the product to a temperature similar to that of the original product, and then cool it in a furnace to room temperature.
Alternatively, the sintered body of the present invention is obtained by slowly cooling to room temperature at the above-mentioned rate, but the effect of the oxide in the cooling process will be explained in the case where only one type of oxide is dissolved in the sintered body. This will be explained below.

If only one type of oxide is dissolved in the fired body, the crystal structure of the fired body is tetragonal regardless of which of the above-mentioned oxidations is used.

Or, the tetragonal system and the cubic system coexist. And if the oxide is within the above range,
The crystal structure gradually transforms from a tetragonal system or a coexistence state of a tetragonal system and a cubic system to a state of a coexistence of a tetragonal system and a monoclinic system, and microcracks generated by this transformation occur. Since it is uniformly dispersed, the microcracks themselves absorb the destructive energy caused by the generation of microcracks.

Therefore, destruction of the fired body during the cooling process can be prevented. Further, since the volumetric expansion accompanying the above transformation forms a compressive stress field within the sintered body, energy due to the compressive stress is stored within the sintered body.

On the other hand, if the amount of oxide is less than the above-mentioned lower limit, the fired body has a tetragonal crystal structure, but the amount of -414 is too small, making it difficult to cool. The accompanying crystal structure transformation from the tetragonal system to the monoclinic system occurs rapidly, and microcracks occur throughout the fired body, and the fired body is destroyed due to the energy. In addition, if the content of oxides exceeds the above-mentioned upper limit, the fired product has a cubic system or a crystal structure in which tetragonal and cubic systems coexist, but in the cooling process, From a cubic system or a coexistence state of a tetragonal system and a cubic system.

The transformation to a state in which the tetragonal system and monoclinic system coexist does not proceed easily, and a cubic crystal structure may remain within the sintered body. If an attempt is made to cause the above transformation by making the cooling time extremely long, the crystals will grow and the crystal grains will become larger.

In the above case, only one oxide is dissolved in the fired body.
Although the case where the oxides are seeds has been described, the same applies to the case where two or six types of oxides are dissolved in solid solution. However, in this case, the total amount taken up by the oxide is 5 to 10 (mol II
b) When it is within the range.

In addition to a tetragonal system or a coexistence state of a tetragonal system and a cubic system, a cubic system crystal structure may be adopted.

Now, by the above cooling, the tetragonal zirconia and 20 to 6
5 (mol ts) of monoclinic zirconia coexists,
And to obtain a sintered body substantially free of cubic zirconia.

The mixing amount of the oxide powder in the mixture in the preliminary stage to obtain the raw material powder is within the above range, that is, 1 to 4 for Ittria.
(mol%), 2 to 6 (mol qb) for magnesia
For calcia, it is possible to set the range to 2 to 7 (molti) (of course, this range does not change even if it becomes a sintered body), and to set the cooling rate to 20 to 180 ('o/hour). is necessary.

The presence of monoclinic zirconia and oxides in the above range dramatically improves the mechanical strength and thermal shock strength of the sintered body.

In other words, the coexistence of tetragonal zirconia and monoclinic zirconia of 20 to 65 (molti) means that the volume of monoclinic zirconia is about 6 inches larger than that of tetragonal zirconia, so it is monoclinic. Crystal Ji.

This means that a sufficiently large compressive stress field is formed in Luconia or its vicinity. Therefore, the elastic strain energy when the sintered body is subjected to mechanical force is reduced by the compressive stress field.

Mechanical strength is improved accordingly. Still, the coexistence of tetragonal zirconia and monoclinic zirphere of 20 to 65 (mol qb>) indicates that a sufficient amount of microcracks exist near or around the monoclinic zirconia. There is also a point.

Therefore, when a crack occurs in the sintered body due to thermal shock, the propagation of the crack is obstructed by the microcracks, making it difficult for the crack to propagate along a convoluted path, thereby improving the thermal shock strength. . Furthermore, the fact that the amount of oxides is in the relatively low range mentioned above means that
That oxide.

This means that it is sufficiently dissolved in tetragonal zirconia, which has a more unstable crystal structure than monoclinic zirconia. Therefore, even if the sintered body is subjected to mechanical load or thermal stress, the transformation from tetragonal zirconia to monoclinic zirconia can be prevented, and the crystal structure is stable and the mechanical strength and thermal shock It has little effect on strength.

In the above, the content of monoclinic zirconia is.

The sintered body was analyzed by X-ray diffraction method 5 as it was or in the powdered state, and the diffraction butter/
Calculated from the intensity obtained by integrating the peak, using the following formula,
You can ask for it. Namely.

However, CM: content of monoclinic zirconia (molti) A: strength of tetragonal zirconia (,111) B: strength of monoclinic zirconia (111) C: strength L of monoclinic zirconia (111) 7' c 75E 2 The content CT of tetragonal zirconia is.

(ICM).

The sintered body of the present invention preferably has a porosity of 2 to 8 (chi). Here, the porosity is expressed as P:
It is defined by porosity (chi). When the porosity is less than 2 cm,
When two cracks occur, the propagation speed increases, and when it exceeds 8 seconds, it becomes porous.

In either case, there is a tendency for mechanical strength to decrease, which is undesirable.

Moreover, it is preferable that the sintered body of the present invention has an average particle diameter of 0.4 to 5 (μ). In other words, if the average particle diameter is less than 0.4μ, the porosity is high; if it exceeds 5μ, the propagation speed of cracks increases, and in either case, the mechanical strength decreases. This is not desirable because a downward trend appears.

Here, the average particle diameter is calculated as follows.

That is, first, the sintered body is cut, the cut surface is polished, and if necessary, chemically etched, and then a microscopic photograph of the surface is taken. Then, on this photo, a section of arbitrary fixed area is defined.

The area of particles existing in that section is sequentially calculated from large particles to small particles, and the sum of the areas is 1 of the area of the above section.
Add up to 72. Next, the average area obtained by dividing this added value by the number of particles from which the added value was obtained is assumed to be a circle, and the average particle diameter is determined. Namely.

Σan πd2 4 where d: average particle diameter an: area of each particle (n = 1.2.3...
) S: Area of the compartment The sintered body of the present invention is used for various purposes because it has high mechanical strength and thermal shock strength as described above, and exhibits oxygen ion conductivity at high temperatures. I can have lunch. An example is shown below.

A. Metallurgical sensors, internal combustion engines and gas stoves.

Solid electrolyte oxygen sensors such as combustion control sensors for boilers, etc.

B. Household items such as forks, spoons, knives, kitchen knives, and various scissors.

Medical supplies such as C0 surgical scalpels.

D. Climbing knife, fishing rod thread guide, golf putter,
Sports and leisure goods such as sea knives.

E. Crucibles, cutting tools, various dies, tundish nozzles, protection tubes, bolts, nuts, springs, various pulps,
Grinding ball, grinding mill.

Balls for bearings, mechanical seals, nozzles and combustion chambers for coal- and oil-burning equipment, and textiles.

Scissors and cutters for magnetic tape, film, etc.

Parts for industrial machinery and equipment such as thread guides.

Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 Using zirconia powder, ittria powder, magnesia powder, and calcia powder with an average particle diameter of 0.1μ, five types of ZrO2-Y2O5 series, ZrO2MgO series, and ZrO2-cao series shown in Table 1-1 were prepared. Sintered body and each of the four types of ZrO2-' shown in Table 1-2
120B-111go series, ZrO2-MgO-Ca
An O-based sintered body was made (see Tables 1-1 and 1-2).
2O3 is abbreviated as Y, MgO as M, and CaO as C. Furthermore, the number written on the lower right side indicates the content expressed in molti; for example, Y4 indicates that the content of Y2O5 is 4 molti).

That is, the zirconia powder and each oxide powder are
After mixing the combinations shown in Tables and Tables 1-2 to achieve the gluing content, this was calcined at 1000°C for 3 hours.
Further, the powder was milled in a pot mill for 24 hours, and the calcining and pulverization were repeated twice to produce a raw material powder.

Next, a 2% aqueous polyvinyl alcohol solution as a binder was added to the raw material powder and mixed well.

After drying, a plate-shaped molded body was made using a rubber press method.

Next, the above molded body was fired and cooled under the conditions shown in Tables 1-1 and 1-2 to produce a sintered body.

This sintered body was cut and polished to a thickness of 3 an and a width of 5 m.
m.

A 24-length sample was made.

Next, the content of monoclinic zirconia, bending strength as an index representing mechanical strength, and thermal shock strength were measured for each of the samples. The results are shown in Tables 1-1 and 1-2.

In addition, the measurement of the monoclinic zirconia content was performed using the above-mentioned X
#Based on diffraction method.

Thermal shock strength was measured by heating a plate-shaped sintered body to an arbitrary temperature of Tx°C and then dropping it into water at a temperature of T''0 to rapidly cool it.

The bending strength was then measured by a well-known three-point bending test method. Then, the heating temperature Tx℃ at which the bending strength begins to decrease is read as the critical temperature T0℃, and the difference between this critical temperature T0℃ and the temperature of the water T''Q is T0-T.
("O") was used as an index.The measurement conditions for the 3° point bending test method were a span length of 20 openings.

The load application acceleration was 1 nn/min.

From Tables 1-1 and 1-2, the sintered bodies whose monoclinic zirconia content and oxide content are both within the range of the present invention, namely Samples 2-4°7-9. 12-14,
17.18, 21.22 are sintered bodies that do not meet the above conditions, that is, sample parts 1, 5, 6, 10, 11,
It can be seen that both the mechanical strength and thermal shock strength of 9 are significantly higher than those of 15, 16, 19, 20, and 23.

Example 2 Although the manufacturing method and measurement method were the same as in Example 1, the reference amount of oxide was changed from the actual amount in order to estimate the influence of monoclinic zirconia content on mechanical strength and thermal shock strength. Although within the scope of the invention.

By changing the firing conditions, nine types of samples with different monoclinic zirconia contents were made. The measurement results are shown in Table 2.

From Table 2, even if the amount of oxide is within the range of the present invention, if the content of monoclinic zirconia is within the range of 20 to 65 (molti), mechanical strength and thermal shock strength of 1 It can be seen that neither of these can be expressed.

Example 6 Corresponding to Example 2, in order to investigate the influence of the content of oxides on mechanical strength and thermal shock strength, the content of monoclinic zirconia was within the range of the present invention, but Three types of prototypes were made in which the content of oxides was outside the scope of the present invention. The measurement results are shown in Table 3. From Table 6, it can be seen that even if the monoclinic zirconia content is within the range of the present invention, the six types of samples mentioned above have an oxidized toxic amount that is within the range of the present invention. It can be seen that both mechanical strength and thermal shock strength are extremely low because they are outside the scope of the invention.

Procedural amendment book Showa-mon. , 1o! '14゜ Japan Patent Office Commissioner Shima 1) Haruki Tono1, Indication of the case, 1982 Patent Application No. 1062632, Name of the invention Zirconia sintered body3, Person making the amendment Relationship to the case Patent applicant address 2-2 Nihonbashi Muromachi, Chuo-ku, Tokyo Name
(315) Toshi Co., Ltd. 4, Date of amendment order Voluntary 5, Number of inventions increased by amendment 0 (1) Amended with the formula on page 13, line 2.

(2) Delete "Contains" in the 5th and 6th lines of page 17.

(3) Correct “prototype” in line 6 of page 24 to “sample” O

Claims (1)

[Claims] Zirconia with tetragonal crystal structure and 20-65 (mol I
s) is a zirconia sintered body in which zirconia having a monoclinic crystal structure coexists and substantially does not contain zirconia having a cubic crystal structure; , at least one oxide selected from magnesia and calcia is dissolved in solid solution, and the intended amount of the oxide is 1 to 4 (mol 1) in itria,
A zirconia sintered body characterized by having a magnesia content of 2 to 6 (mol%) and a calcia content of 2 to 7 (mol%).