JPH0335260B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing zirconia porcelain having excellent mechanical and thermal properties. Conventionally, zirconia porcelain containing MgO as a stabilizer has been produced using _ZrO2 electrofused raw materials containing MgO or MgO
and ZrO ₂ powder, pulverize the calcined synthetic raw materials, and sinter the pulverized powder. However, by the above-mentioned method, it was not possible to obtain zirconia porcelain with excellent mechanical properties and thermal properties. The reasons for this can include the following. () MgO as a stabilizer has been known for a long time, but it has the drawback of lacking stability in the solid solution state in ZrO ₂ . This is due to the incompatibility of the Mg ²⁺ ion radius. For this reason, in manufacturing zirconia porcelain by the above method, it is often difficult to incorporate a predetermined amount of MgO into solid solution, resulting in non-uniform crystal structure of the sintered body. Therefore, when used as a sensor, etc., it is difficult to obtain stable sensor output characteristics, and damage occurs due to thermal shock, etc., and the sensor life is limited. Furthermore, for the reasons mentioned above, it cannot be said that its mechanical strength is very strong, and it has almost never been used as a structural material. () In the above method, since the pulverized powder has poor sinterability, a large amount of sintering aid is added and firing is performed at high temperature. As a result, significant crystal grain growth occurs and the crystal structure is no longer fine, resulting in poor mechanical and thermal properties. In addition, attempts have been made to improve thermal shock resistance by introducing microcracks through partial stabilization, but as the grains grow, the microcracks increase and often become the source of cracks. This may have been a contributing factor. The present invention has been made in view of the above circumstances, and aims to provide a method for producing zirconia porcelain with excellent mechanical and thermal properties by homogenizing and refining the crystal structure. be. The present inventors first investigated various methods for stabilizing the solid solution state of MgO in the ZrO ₂ lattice.
By mixing zirconia compound powder with MgO as a solid solution in ZrO ₂ lattice at a predetermined ratio, MgO as a stabilizer is added, and this mixed powder is molded and fired to achieve almost satisfactory results. It has been found that zirconia porcelain having good mechanical and thermal properties can be obtained. This is considered to be because, according to the method described above, the solid solution state of MgO in the ZrO ₂ lattice is stable and the crystal structure becomes homogeneous. However, even if only the above-mentioned method was adopted, zirconia porcelain with inferior mechanical properties and thermal properties could still be obtained. This is considered to be because the crystal structure of the obtained zirconia porcelain is not fine. Therefore, the present inventors further investigated cases where mechanical properties and thermal properties are poor, and found that the sintering temperature could be lowered by using small particle sizes with good sinterability as starting materials. It can suppress the growth of crystal grains and has a fine crystal structure.
It has been found that zirconia porcelain with excellent mechanical and thermal properties can be obtained. That is, the method for producing zirconia porcelain of the present invention uses zirconia powder with an average particle size of 2 μm or less and a compound with the general formula nMgO (100-n) obtained by a coprecipitation method.
Average particle size expressed in ZrO ₂ (n is 15 to 20 in mol%)
The method is characterized in that it is mixed with a zirconia compound powder of 2 μm or less so that the MgO content becomes 7 to 12 mol %, molded, and then fired. In the present invention, the most important requirement is to mix zirconia powder and zirconia compound powder, but the reason for specifying that they be mixed so that the MgO content is 7 to 12 mol% is because the MgO content is above This is because if it deviates from this range, zirconia porcelain with excellent mechanical and thermal properties cannot be obtained.
In addition, in order to keep the MgO content within the above range, the MgO content (value of n) in the zirconia compound powder should be adjusted.
The mixing ratio of the zirconia compound powder may be about 30 to 70 wt%, although it varies depending on the material. In the present invention, the average particle size of the zirconia powder and the zirconia compound powder is set to 2 μm or less, respectively, because if the average particle size of the starting raw material exceeds these values, sinterability will deteriorate and low-temperature sintering will not be possible.
This is because the mechanical properties and thermal properties of zirconia porcelain deteriorate due to crystal grain growth and the like. Furthermore, it is more preferable that the average particle size of each of the zirconia powder and the zirconia compound powder is 1 μm or less (here, the average particle size refers to the average particle size of secondary particles). In the present invention, a firing temperature of 1500 to 1700°C is appropriate. This is because at temperatures below 1500°C, sufficient sintering cannot be achieved, and at temperatures above 1700°C, the mechanical and thermal properties of zirconia porcelain deteriorate due to crystal grain growth and the like. In the present invention, if a large amount of impurities is contained in the starting material, the reaction with zirconia will cause the formation of a glass layer at the grain boundaries, leading to non-uniformity of the sintered body, and resulting in poor mechanical properties and thermal properties. In order to reduce the properties, it is desirable that the content of impurities in the starting materials is 0.5 wt% or less. Examples of the present invention will be described below. Table 1 consists of Examples 1-13, Reference Examples 1-3, and Comparative Examples 1-7. Zirconia powder with the average particle size shown in Table 1 below and the general formula of the average particle size (0.8 μm) shown in the same table
A mixed powder was obtained by blending with a zirconia compound powder expressed by nMgO.(100-n)ZrO ₂ obtained by a coprecipitation method at the mixing ratio shown in the same table. in mixed powder
The MgO content is calculated in mol%, and the impurity content is calculated in weight%, and these are also listed in the same table. Next, polyvinyl alcohol was mixed as a binder to each of the obtained mixed powders, and after granulation, 2.0ton/cm ²
Pressure molded. Subsequently, each molded body was fired in air at the temperature shown in the table below for 2 hours, and then cooled to obtain zirconia porcelain. The bending strength, fracture toughness value (K _IC ), and thermal shock resistance value (ΔT _C ) of the obtained zirconia porcelain were measured and are also listed in the same table. The bending strength was measured by a three-point bending test on a test piece with dimensions of 5 x 5 x 60 mm obtained by polishing a rectangular sintered body. Furthermore, the fracture toughness value (K _IC ) was calculated by forming an indentation on a test piece using the Vickers method under a load of 30 kg, measuring the crack length extending from the end of the indentation, and using the calculation method proposed by Evans et al. In addition, thermal shock resistance value (ΔT _C ) is determined by the rapid cooling strength measurement method by dropping into water after heat treatment at each predetermined temperature, and the heat treatment temperature at which the bending strength value decreases by 50% is defined as critical thermal shock temperature ΔT _C (℃) did. In addition, Reference Examples 1 to 3 in Table 1 below are MgO and
This is similar data regarding zirconia porcelain obtained by the conventional method of mixing ZrO ₂ powder, pulverizing a calcined synthetic raw material, and firing the pulverized powder.

[Table] As is clear from the table above, Comparative Examples 1, 2,
Both zirconia porcelains No. 6 and 7 contain MgO in the mixed powder of zirconia powder and zirconia compound powder.
Since the content is outside the range of the method of the invention, the mechanical and thermal properties are poor. In addition, the zirconia porcelains of Comparative Examples 3 to 5 have poor mechanical properties and thermal properties because the average particle size of the zirconia powder is outside the range of the method of the present invention. On the other hand, the zirconia porcelains of Examples 1 to 13 all exhibited very superior mechanical and thermal properties compared to the zirconia porcelains produced by conventional methods (Reference Examples 1 to 3). Note that the zirconia porcelains of Examples 3, 6, and 9 had a high content of impurities, so the mechanical properties and thermal properties slightly returned, but they were sufficiently durable for practical use. As detailed above, according to the present invention, it is possible to provide a method for manufacturing zirconia porcelain having excellent mechanical properties and thermal properties.

Claims (1)

[Claims] 1 Zirconia powder mainly composed of monoclinic crystals with an average particle size of 2 μm or less and a general formula nMgO・(100−n)ZrO ₂ (n is 15 to 15% by mole) obtained by coprecipitation method.
20) with an average particle diameter of 2 μm or less so that the MgO content is 7 to 12 mol%, and after molding, the molded body was
A method for producing zirconia porcelain characterized by firing at ~1700°C.