JPH04139062A - Zirconia porcelain - Google Patents

Abstract

PURPOSE:To obtain a zirconia porcelain which has high strength and is extremely small in deterioration with the lapse of time at the temp. range of 200-300 deg.C by constituting zirconia porcelain of a specified crystal phase which mainly consists of ZrO2 and Y2O3 and has a range of the specified molar ratio thereof. CONSTITUTION:Zirconia porcelain is mainly constituted of ZrO2 and Y2O3 and has a range within (2/98 to 7/93) as the molar ratio of Y2O3/ZrO2. The crystal particle mainly consists of cubic crystal particle and tetragonal crystal particle. When the peak intensities of the respective X-ray diffraction beams in the face (200) of tetragonal crystal, the face (200) of cubic crystal and the outside face 1 of an monoclinic crystal are regulated to T(200), C(200) and M-outside 2, the following inequalities are formulated and zirconia porcelain is obtained which has >=2mum mean crystal particle diameter. T(200)/{T(200)+C(200)}>=0.05, M-outside 3/T(200)<=1, M-outside 4/{T(200)+C(200)}<=0.4.

Description

[Detailed description of the invention]

[0001]

[Industrial application field]

The present invention relates to Zr02-Y2O3-based zirconia porcelain that has high strength and exhibits extremely little deterioration over time due to long-term use in a specific temperature range. [0002]

[Conventional technology]

Conventionally, as ZrO2-Y2O3-based 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 made of heat-resistant materials and solid electrolytes. It is used as such. [0003]

[Problem to be solved by the invention]

Fully stabilized zirconia porcelain is stable in the temperature range from room temperature to approximately 1,500°C, and does not deteriorate over time due to long-term use. When used as a solid electrolyte for an oxygen sensor that detects oxygen concentration, it has the disadvantage of being extremely susceptible to damage due to thermal shock. On the other hand, partially stabilized zirconia porcelain consisting of cubic and monoclinic crystals has higher strength and better thermal shock resistance than fully stabilized zirconia and conia porcelain, but it is difficult to use in a specific temperature range of 200°C to 300'C. The deterioration of strength over time is extremely large, and when used for a long time at this temperature, many microscopic racks appear on the surface of the porcelain, which becomes water-absorbing, resulting in a significant decrease in strength and eventually breaking. It was something that I had. [0004] This means that in ZrO2-Y203-based partially stabilized zirconia porcelain, the crystal grains, which are tetragonal at a firing temperature of about 1500'C, change from about 1500'C to 500'C during cooling to room temperature.
A phase transformation to monoclinic crystal occurs near 'C, and the volume change caused by the removal of the earth causes excessive stress in the porcelain, resulting in many extremely small racks being generated within the crystal grains, and these cracks occur at temperatures of 200°C to 300°C. It is thought that if left in a specific temperature range for a long time, it will expand and eventually lead to porcelain destruction. [0005]

[Means to solve the problem]

The present invention eliminates the drawbacks of the conventional partially stabilized zirconia porcelain, has excellent strength, and has 200'
It is a zirconia porcelain that has significantly improved the aging deterioration of strength in a specific temperature range of C to 300'C.It is made mainly of ZrO and YO, with a molar ratio of Y2O3/ZrO2 in the range of 2798 to 7/93, and is crystalline. The particles are mainly composed of cubic crystal grains and tetragonal crystal grains, and the (200) face of the tetragonal crystal, the (200) face of the cubic crystal, and the outer five faces of the monoclinic crystal (the following external characters are

It is shown after the [Explanation of symbols] column. ), the following formula T(200) / (T(200) + C(200)
)≧0.05M outside 7/T(200)≦1M outside 8/ (T(200) +C(200) )≦0.
4 holds true, the average crystal grain size is 2 microns or less,
Zirconia porcelain is characterized by extremely little deterioration over time when exposed to a temperature range of 200°C to 300°C. [0006] That is, the present invention sets the molar ratio of Y2O37Zr02 to a specific value in ZrO-YO-based zirconia porcelain, and sets the average crystal grain size to a specific value or less, thereby preventing phase transformation from occurring at temperatures below about 500°C. The tetragonal crystal, which was unstable in the conventional process, is made to exist stably without phase transformation to monoclinic crystal within the temperature range from 500 °C to room temperature, and the crystal grains are mainly tetragonal crystal particles or mainly cubic crystal grains. This zirconia porcelain has extremely high strength due to its mixed phase of crystal and tetragonal crystal, and exhibits extremely little deterioration over time in a certain temperature range. [0007] To explain the present invention in more detail, in order for the tetragonal crystal to exist stably, it is extremely important that the average crystal grain size of the porcelain be 2 μm or less, preferably 1 μm or less. [0008] 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 sudden decrease in strength is observed even when the average crystal grain size is 2μ or more. However, in curve B after an endurance test held in a specific temperature range of 200°C to 300°C for 1500 hours, when the average crystal grain size exceeds 2μ, fine racks are formed due to the formation of excessive monoclinic crystals. As a result, the strength decreases rapidly and deterioration over time becomes significant. Furthermore, as described in the Examples below, if the average crystal grain size is 2 μ or less, preferably 1 μ or less, the crystal phase will hardly change even if left in a specific temperature range of 200°C to 300°C, and the tetragonal crystal will not change. It remains stable. In this way, in the present invention, 200'C to 300'C
It is said to have excellent durability at temperatures up to 200'C.
This means that there is little deterioration over time at any temperature between 300°C and 300°C. As an example of a specific measurement method, as described in the examples, in order to cover the entire temperature range of 200 to 300 degrees Celsius, measurement was performed in the atmosphere at 200 to 3
It is preferable to conduct an endurance test in which heating and cooling are repeated between 00°C and 10°C/min, and to measure changes in bending strength or crystal phase before and after the durability test. Of course, the durability test may also be conducted by exposing it to a certain temperature range. 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 the crystal grain size is reduced is that when the crystal grains are small, tetragonal crystals are more stable than monoclinic crystals due to the surface free energy of the particles. This is considered to be the case. Note that the average crystal grain size is 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''. Then, calculate d for three or more visual fields of the same sample and use the average value as the average crystal grain diameter. The number of particles n is a constant area. Let it be the sum of the number of particles completely included in S and the number of particles cut by the boundary line of a constant area, 172. [0009] The relationship between the X-ray diffraction line peak intensity ratio and the bending intensity is shown in Figure 2. As shown, (200) plane of tetragonal crystal, outer 9 plane of monoclinic crystal
When the X-ray diffraction line intensities of the (200) plane and cubic crystal plane are respectively T (200) M 10 and C (200), the strength of the zirconia porcelain C mainly composed of tetragonal crystal grains of the present invention is , is larger than the strength before deterioration of conventional zirconia porcelain made of cubic crystal grains and monoclinic crystal grains, and zirconia porcelain E mainly composed of cubic crystal grains and tetragonal crystal grains has a cubic The strength F after deterioration over time in a specific temperature range of zirconia porcelain made of monoclinic crystal grains and monoclinic crystal grains is much higher. 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 improves as the number of tetragonal crystals increases. [0010] In the present invention, zirconia porcelain mainly composed of cubic crystal grains and tetragonal crystal grains refers to zirconia porcelain mainly composed of cubic crystal grains and cubic crystal grains, as well as zirconia porcelain composed only of tetragonal crystal grains and cubic crystal grains.
) / (T(200) +C(200)) intensity ratio is 0.05 or more, M outside 11/T (200) intensity ratio is 1 or less, M outside 12/ (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. [0011] Also, in the present invention, zirconia porcelain mainly composed of Zr 02 and Y2O3 means zirconia porcelain mainly using Y2O3 as a stabilizer of ZrO, and about 30 mol% or less of Y203 is composed of other rare earths. Oxides of similar elements, such as Yb203Sc ONb OSm O
, CeO2 etc. or CaO, MgO with 23!23・
23 It may be substituted. Moreover, the zirconia porcelain according to the present invention is Si02. Sintering aids such as Al2O3 and clay account for 30% by weight of the entire porcelain.
It may contain the following: The crystalline phase constituting the porcelain is identified by X-ray diffraction using a mirror-polished surface of the porcelain. [0012] The reasons for the numerical limitations of the present invention are as follows. Y2O3
If the molar ratio of /ZrO2 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. [0013] The zirconia porcelain of the present invention has a Y2O3/ZrO2 molar ratio of 2/98 to 7/93, crystal grains mainly consisting of cubic crystal grains and tetragonal crystal grains, and an average crystal grain size of 2 μ or less. Y2O3/ZrO. Zirconia porcelain has excellent durability at 200° C. to 300° C. while meeting all three requirements of molar ratio, crystal phase of crystal grains, and average crystal grain size. [0014] Note that the present invention mainly consists of cubic crystal grains and tetragonal crystal grains, and has an average crystal grain size of not more than a specific value.
The production of zirconia porcelain with improved durability at 00°C to 300°C can be easily achieved by selecting the composition, raw materials used, raw material particle size, firing conditions, cooling conditions, etc. [0015] When the zirconia porcelain of the present invention mainly consists of cubic crystal grains and tetragonal crystal grains, an electromotive force according to the theoretical value was obtained in both cases when an oxygen concentration battery was constructed. Porcelain can also be used satisfactorily as an oxygen ion conductive solid electrolyte. [0016]

【Example】

Next, an example will be described. Example 1 ZrO3, Y2O were added to have the compositions shown in Tables 1 to 4.
3 or its compound was prepared and mixed in a ball mill. The mixture was calcined at 800°C, wet-pulverized in a ball mill,
After drying, the powder was press-molded and fired at 1000°C to 1400°C for 1 to 3 hours to obtain the zirconia porcelain of the present invention. The average crystal grain size, X-ray diffraction line intensity, bending strength, and volume resistivity of these porcelains were compared and measured. Note that the X-ray diffraction line intensity ratio is (20
0) plane, the (200) plane of the tetragonal crystal, and the X-ray diffraction line peak height of the outer 13 planes of the monoclinic crystal. The bending strength is determined by finishing the porcelain into a bar shape of 3.5 x 3.5 x 50 mm.Three points l
Obtained using the ge method. The volume resistivity was measured in the atmosphere at 400° C. by a four-probe method. [0017] In Tables 1 to 4, 200° C. to 300° C. durability refers to a durability test in which heating and cooling were repeated between 200° C. and 300° C. at a temperature increase/decrease rate of 10° C./min. Measurement results for various compositions are shown in Tables 1 to 4. Tables 1 to 4 show 20
Durability tests from 0°C to 300°C and X-ray diffraction line intensity ratios of test specimens are also described. Furthermore, in Table 1, the [B/AX100J column shows the ratio of the bending strength after the durability test compared to the initial bending strength as a percentage, and the rC/DJ column shows the monoclinic crystallinity in the X-ray diffraction line intensity ratio. The ratio of the initial value to the value after the durability test of the outer 14 faces/tetragonal (200) face, that is, the degree of phase transformation from tetragonal to monoclinic according to the durability test, or in other words, the ratio of the initial value to the value after the durability test. This means the reduction rate of tetragonal crystals, which is 1
The closer to , the more stable the tetragonal crystal is. Tables 1 to 4
Examples outside the numerical limitation range of the present invention are also described as reference examples. [0018]

[Table 1]

[Table 21 Note 1) The amount of sintering aid added is the weight% of the sintering aid to the whole porcelain.Note 2) T, C, and M are respectively tetragonal (
Tetragonal), Cubic
Note 3) C(200) and T(200) indicate monoclinic (monoclinic).
200) plane, indicates the X-ray diffraction line intensity of the (200) plane of the tetragonal crystal Note 4) M outside 15 indicates the X-ray diffraction line intensity of the outer 16 plane of the monoclinic crystal Note 5) Durability test was conducted at 200°C or 1 between 300℃
Repeated heating and cooling at a rate of temperature rise and fall of 0°C/min 150
[0021] [0022] [0023] Figure 3 shows the values of C/D versus average crystal grain size for the examples listed in Tables 1 to 4, and Figure 4 shows the values of C/D for the examples listed in Tables 1 to 4. Figure 2 shows the value of B/AX100 with respect to the average crystal grain size. The numbers attached to each point in FIGS. 3 and 4 are the No. of the example,
shows. [0024] As is clear from Tables 1 to 4 and FIGS. 3 and 4, the zirconia porcelain of the present invention has high strength and a temperature of 200°C to 30°C.
Even if it is left in a specific temperature range of 0°C, there is almost no change in crystal phase or bending strength. [0025] 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. [0026] [Effect of the invention] In terms of ratio, it is mainly composed of tetragonal crystal grains and cubic crystal grains, and the crystal grain size is below a specific value, so it has extremely high strength and has a temperature of 200°C to 300°C.
Deterioration over time in a specific temperature range of ℃ is extremely low, and it is suitable for applications that require high strength and heat resistance, such as solid electrolytes for oxygen concentration batteries, oxygen sensors for automobiles, oxygen meters for steel, fuel cells for power generation, and internal combustion engines. It is suitable as an industrial material for a wide range of related parts, thermistors, cutting tools, cobblestones, kitchen knives, etc., and is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the average crystal grain size and the bending strength of zirconia porcelain before and after the durability test.

FIG. 2 is an explanatory diagram showing the relationship between the intensity ratio of the X-ray diffraction lines of the cubic (200) plane and the tetragonal (200) plane and the transverse intensity.

[Figure 3] Figure 3 shows the relationship between the ratio (C/D) between the initial value (C) and the value (D) of the X-ray diffraction line intensity ratio of the zirconia porcelain of the present invention and the value after the durability test (D) and the average crystal grain size. FIG.

[Figure 4] Figure 4 also shows the bending strength (A) of the zirconia porcelain of the present invention.
and bending strength after durability test

[Outside 11], , [Outside 12]
, [Outside 13L [Outside 14], [Outside 15], [Outside 16]
. [External 17] (All external characters are the same.)

【Document name】

drawing

[Figure 1]

[Figure 2]
r)

[Figure 3]

[Figure 4] θ ! ,0 Ayu item m-7-nin0su

Claims (1)

[Claims] 1. Mainly composed of ZrO_2 and Y_2O_3, Y_
The molar ratio of 2O_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 (200) face of the tetragonal crystal,
X of each of the (200) plane of the cubic crystal and the outer one plane of the monoclinic crystal
When the peak intensities of the line diffraction lines are T(200), C(200) and 2 outside M, the following formula T(200)/(T(200)+C(200))≧0.
05M outside 3/T(200)≦1 M outside 4/(T(200)+C(200))≦0.4 is established, the average crystal grain size is 2 microns or less, and 200
Zirconia porcelain characterized by extremely little deterioration over time when exposed to a temperature range of 300°C to 300°C. [Example 1], [Example 2], [Example 3], [Example 4] (all the same external characters) (111)