JPS6121184B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a ZrO ₂
This relates to Y ₂ O ₃ based zirconia porcelain. Conventionally, as ZrO ₂ −Y ₂ O ₃ system zirconia porcelain, fully stabilized zirconia porcelain consisting only of cubic crystals and partially stabilized zirconia porcelain consisting of cubic crystals and monoclinic crystals are known, both of which are heat resistant. It is used as a material, solid electrolyte, etc. Fully stabilized zirconia porcelain is stable in the temperature range from room temperature to approximately 1500°C, and has almost no deterioration over time due to long-term use. When used as a solid electrolyte for sensors, it has the disadvantage of being extremely susceptible to damage due to thermal shock. On the other hand, partially stabilized zirconia porcelain made of cubic and monoclinic crystals has higher strength and better thermal shock resistance than fully stabilized zirconia porcelain, but its strength over time in a specific temperature range of 200℃ to 300℃ The deterioration is extremely severe, and if it is used for a long time at this temperature, many minute cracks will occur on the porcelain surface, it will become water absorbent, the strength will decrease significantly, and it will eventually break. It was something that existed. This is because in ZrO ₂ −Y ₂ O ₃ system partially stabilized zirconia porcelain, the crystal grains, which are tetragonal at a firing temperature of about 1500°C, are heated to 500°C during cooling from about 1500°C to room temperature.
A phase transformation to monoclinic occurs in the vicinity, and the volume change that occurs at this time applies excessive stress to the porcelain, resulting in many extremely small cracks within the crystal grains, and these cracks occur at a specific temperature of 200°C to 300°C. It is thought that if left in the area for a long time, it will expand and eventually lead to porcelain destruction. The present invention eliminates the drawbacks of partially stabilized zirconia porcelain, has excellent strength, and
Zirconia porcelain is a zirconia porcelain that has significantly improved its strength over time in a specific temperature range of 200℃ to 300℃, and is mainly composed of ZrO ₂ and Y ₂ O ₃ with a molar ratio of Y ₂ O ₃ /ZrO ₂ of 2/98 to 4/ Zirconia porcelain with a temperature range of 96, consisting mainly of tetragonal crystal grains, an average crystal grain size of 2 μ or less, and excellent durability at 200°C to 300°C, and mainly containing ZrO ₂ and Y ₂ O ₃ The molar ratio of Y ₂ O ₃ /ZrO ₂ is in the range of 2/98 to 7/93, the crystal grains are mainly composed of cubic crystal grains and tetragonal crystal grains, and the average crystal grain size is 2 μ or less It is a zirconia porcelain with excellent durability at 200℃ to 300℃. That is, the present invention sets the molar ratio of Y ₂ O ₃ /ZrO ₂ to a specific value in ZrO ₂ -Y ₂ O ₃ system zirconia porcelain, and sets the average crystal grain to a specific value or less, thereby preventing phase transformation at temperatures below about 500°C. The tetragonal crystal, which was unstable due to the oxidation, is made to exist stably without phase transformation to monoclinic crystal within the temperature range from 500℃ to room temperature, and the crystal grains are mainly tetragonal crystal grains. Alternatively, it is a zirconia porcelain that has extremely high strength and extremely little deterioration over time in a specific temperature range due to the fact that it mainly consists of cubic crystal grains and tetragonal crystal grains. To explain the present invention in more detail, in order for the tetragonal crystal to exist stably, the average crystal grain size of the porcelain must be 2 μm.
It is extremely important that the thickness is preferably 1μ or less. In other words, the relationship between the average crystal grain size and the bending strength is as shown in Figure 1. In curve A before the durability test, no rapid decrease in strength is observed even when the average crystal grain size is 2 μ or more, but at 200°C Curve B after a durability test held in a specific temperature range of ~300℃ for 1500 hours shows that when the average crystal grain size exceeds 2μ, the strength sharply increases due to the presence of fine cracks due to the formation of excessive monoclinic crystals. and deterioration over time becomes significant. Furthermore, as described in the Examples below, if the average crystal grain size is 2μ or less, preferably 1μ or less, the crystal phase will hardly change even if left in a specific temperature range of 200℃ to 300℃, and the tetragonal crystal will not change. It remains stable. In this way, in the present invention, the
200 is said to have excellent durability at 300℃.
This means that there is little deterioration over time at any temperature between ℃ and 300℃. As an example of a specific measurement method, as described in the examples, 200℃ or
In order to cover the entire temperature range of 300°C, we conducted an endurance test in which heating and cooling were repeated between 200°C and 300°C at a rate of 10°C/min in the air, and the bending stress was measured before and after durability testing. It is better to measure changes in strength or crystal phase. The longer the durability time, the greater the degree of deterioration, but the difference between the conventional zirconia porcelain and the zirconia porcelain of the present invention becomes clear after about 1500 hours.
The reason why transformation to monoclinic crystals is less likely to occur when crystal grains are made smaller than that of tetragonal crystals is that when crystal grains are small, the crystal grains become more stable than monoclinic crystals due to the surface free energy of the particles. considered to be a thing. Note that the average crystal grains are measured by the following method. Count the number n of particles within a certain area S that contains 50 or more particles in an electron micrograph of a mirror-polished porcelain surface etched with hydrofluoric acid, and calculate the area equal to the average area s per particle. Calculate the diameter d of the circle using the formula d = (4s/π) ^1/2 . Then, d is determined for three or more visual fields of the same sample, and the average value is taken as the average crystal grain size.
The number of particles n is cut by the boundary line between the number of particles completely included in the constant area s and the constant area. 1/2 of the number of particles
be the sum of The relationship between the X-ray diffraction line peak intensity ratio and the bending strength is as shown in Figure 2.
The X-ray diffraction line intensities of the monoclinic (111) plane, and the cubic (200) plane are T(200) and M(11), respectively.
1), C(200), the strength of the zirconia porcelain C mainly made of tetragonal crystal grains of the present invention is the strength before deterioration of the conventional zirconia porcelain made of cubic crystal grains and monoclinic crystal grains. The strength D of zirconia porcelain E, which is larger than the strength D and is mainly composed of cubic crystal grains and tetragonal crystal grains, is greater than the strength D of zirconia porcelain E, which is mainly composed of cubic crystal grains and tetragonal crystal grains. This is greater than the strength F after deterioration. Furthermore, the zirconia porcelains C and E of the present invention have higher strength than the zirconia porcelain G made of only cubic crystals, and the strength increases as the number of tetragonal crystals increases. In the present invention, zirconia porcelain mainly composed of tetragonal crystals refers to zirconia porcelain mainly composed of tetragonal crystals, as well as those whose X-ray diffraction line peak intensity ratio of (M(111)+C(200))/T(200) is 0.4. Also included are monoclinic and/or cubic crystals as shown below. The above X-ray peak intensity ratio range is approximately 20% for monoclinic and/or cubic crystals.
Equivalent to volume percent or less. Also, zirconia porcelain, which is mainly composed of cubic crystal grains and tetragonal crystal grains, is not only composed of only tetragonal crystal grains and cubic crystal grains, but also T(200)/(T(200)). +C(200)) intensity ratio is 0.05 or more, M(111)/T(200) intensity ratio is 1 or less, M(111)/(T(200)+C
(200)) includes monoclinic crystals with an intensity ratio of 0.4 or less. The above range of X-ray peak intensity ratio corresponds to an amount of monoclinic crystals of approximately 20% by volume or less of the total. Also, in the present invention, zirconia porcelain mainly composed of ZrO ₂ and Y ₂ O ₃ means zirconia porcelain mainly using Y ₂ O ₃ as a stabilizer for ZrO ₂ , and about 30 mol of Y ₂ O ₃ . % or less of other rare earth element oxides, such as Yb ₂ O ₃ , Sc ₂ O ₃ , Nb ₂ O ₃ ,
It may be substituted with Sm ₂ O ₃ or the like, or with CaO or MgO. Furthermore, the zirconia porcelain according to the present invention is
Add sintering aids such as SiO ₂ , Al ₂ O ₃ , and clay to 30% of the entire porcelain
It may contain less than % by weight. The crystalline phase constituting the porcelain is identified by X-ray diffraction using a mirror-polished surface of the porcelain. The reasons for limiting the numerical values of the present invention are as follows.
If the molar ratio of Y ₂ O ₃ /ZrO ₂ is less than 2/98, tetragonal zirconia porcelain cannot be obtained, and if it exceeds 7/93, almost no tetragonal crystals are contained, resulting in cubic zirconia porcelain. Furthermore, if the ratio is outside the range of 2/98 to 4/96, mainly tetragonal zirconia porcelain cannot be obtained. In addition, the zirconia porcelain of the present invention is Y ₂ O ₃ /ZrO ₂
Molar ratio is 2/98 to 4/96 or 2/98 to 7/93,
A Y ₂ O ₃ /
Zirconia porcelain has excellent durability at 200°C to 300°C while meeting all three requirements: ZrO ₂ molar ratio, crystal phase of crystal grains, and average crystal grain size. Note that the present invention mainly consists of tetragonal crystal grains, or mainly cubic crystal grains and tetragonal crystal grains, and has an average crystal grain size of not more than a specific value.
Creating zirconia porcelain with excellent durability at 200°C to 300°C can be easily achieved by selecting the composition, raw materials used, raw material particle size, firing conditions, cooling conditions, etc. The zirconia porcelain mainly composed of tetragonal crystal grains and the zirconia porcelain mainly composed of cubic crystal grains and tetragonal crystal grains of the present invention both have an electromotive force according to the theoretical value when an oxygen concentration battery is constructed. Therefore, the zirconia ceramic according to the present invention can be fully used as an oxygen ion conductive solid electrolyte. Next, an example will be described. ZrO ₂ , Y ₂ O ₃ or their compounds were prepared and mixed in a ball mill so as to have the composition shown in Table 1. The mixture was calcined at 800°C, wet-pulverized in a ball mill, dried, and the powder was press-molded.
The zirconia porcelain of the present invention was obtained by firing at a temperature of 1 to 3 hours at a temperature of 1 to 1400 degrees Celsius. The average crystal grain size, X-ray diffraction intensity, bending strength, and volume resistivity of these porcelains were comparatively measured. The X-ray diffraction line intensity ratio was defined as the ratio of the peak heights of the X-ray diffraction lines on the cubic (200) plane, the tetragonal (200) plane, and the monoclinic (111) plane. The bending strength of porcelain is 3.5
A bar shape of ×3.5 × 50 mm was finished using a three-point bending method. Volume resistivity was determined using the 4-terminal method at 400℃ in the atmosphere.
Measured at In addition, in Table 1, 200℃ to 300℃ durability means 200℃.
This is a durability test in which heating and cooling were repeated between ℃ and 300℃ at a rate of temperature rise and fall of 10℃/min. Table 1 shows the measurement results for various compositions. Table 1 shows 200
The X-ray diffraction line intensity ratio after the durability test at ℃ to 300℃ is also described. Furthermore, in Table 1, the "B/A x 100" column shows the ratio of the bending strength after the durability test to the initial bending strength as a percentage, and the "C/D" column shows the ratio of the bending strength after the durability test to the initial bending strength.
The ratio of the initial value to the value after the durability test of the monoclinic (111) plane/tetragonal (200) plane in the line diffraction line intensity ratio, that is, the degree of phase transformation from tetragonal to monoclinic by the durability test, In other words, it means the reduction rate of tetragonal crystals by durability test, and the closer this value is to 1, the more stable the tetragonal crystals are. Table 1 also lists examples outside the numerically limited range of the present invention as reference examples.

【table】

【table】

[Table] Figure 3 shows the value of C/D with respect to the average crystal grain size for the examples listed in Table 1, and Figure 4 shows the value of B/A x 100 with respect to the average crystal grain. Illustrated. The numbers attached to each point in FIGS. 3 and 4 indicate the number of the example. As is clear from Table 1 and Figures 3 and 4, the zirconia porcelain of the present invention has high strength and
Even when left in a specific temperature range of 200°C to 300°C, there is almost no change in crystal phase or bending strength. Furthermore, it has been found that in order to be stable in a specific temperature range, the average crystal grain size of the porcelain must be 2 μ or less, preferably 1 μ or less. Furthermore, it was confirmed that the volume resistivity was also low. As described above, the zirconia porcelain of the present invention is composed of mainly tetragonal crystal grains or mainly tetragonal crystal grains and cubic crystal grains at a specific Y ₂ O ₃ /ZrO ₂ molar ratio, and Because the diameter is below a certain value, it has extremely high strength and has very little deterioration over time in a specific temperature range of 200℃ to 300℃, and is suitable for applications that require high strength and heat resistance, such as solid for oxygen concentration batteries. It is suitable as an industrial material for a wide range of applications such as electrolytes, internal combustion engine mechanical parts, thermistors, cutting tools, etc., and is extremely useful industrially.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between the average crystal grain size and anti-deposition strength of zirconia porcelain before and after the durability test, and Figure 2 shows the X-ray diffraction lines of the cubic (200) and tetragonal (200) planes. FIG. 4 is an explanatory diagram showing the relationship between the intensity ratio and the transverse strength, and the relationship between the intensity ratio of the X-ray diffraction lines of the cubic (200) plane and the monoclinic (111) plane and the transverse strength before and after aging. Figure 3 shows the X of the zirconia porcelain of the present invention.
A characteristic diagram showing the relationship between the ratio (C/D) of the initial value (C) of the line diffraction line intensity ratio and the value (D) after the durability test and the average crystal grain size, and FIG. B/ of the bending strength of porcelain (A) and the bending strength after durability test (B)
FIG. 2 is a characteristic diagram showing the relationship between A×100% and average crystal grain size.

Claims (1)

[Claims] 1. Mainly composed of ZrO ₂ and Y ₂ O ₃ , Y ₂ O ₃ /ZrO ₂
The molar ratio is in the range of 2/98 to 4/96, the crystal grains are mainly composed of tetragonal crystal grains, and the average crystal grain size is 2 μ or less, and has excellent durability at 200 ° C to 300 ° C. Zirconia porcelain is characterized by: 2 Mainly composed of ZrO ₂ and Y ₂ O ₃ , Y ₂ O ₃ /ZrO ₂
The molar ratio of is in the range of 2/98 to 7/93, the crystal grains are mainly composed of cubic crystal grains and tetragonal crystal grains, and the average crystal grain size is 2 μ or less, and the temperature is 200°C to 300°C. Zirconia porcelain is characterized by its excellent durability at ℃.