JPH0511063B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a zirconia sintered molded body, and more specifically, a zirconia sintered molded body suitable for solid electrolytes such as gas sensors, fuel cells, oxygen pumps, daily necessities such as cutlery, and mechanical parts such as engines. Relating to a manufacturing method. (Prior Art) Ceramics containing clay can be easily shaped by plastic deformation. Furthermore, non-plastic ceramics containing zirconia or the like as a main component can also be molded by adding and blending an organic binder. However, since the molded bodies manufactured by these methods deform during firing, it is necessary to carry out post-processing and modification if dimensions and precision are required. Furthermore, there is a method that uses pressure forming, which is widely used in the production of electronic and mechanical parts, but while this pressure forming method allows mass production and high-speed molding, it is difficult to uniformly fill the raw materials. If it is difficult and requires high precision, it is necessary to correct it by post-processing as in the existing method. Furthermore, there is a slurry casting method as a method for easily obtaining a complicated molded body without distortion with a simple operation. However, this casting method has a slow working speed and is poor in mass production. Furthermore, there is the problem that it is difficult to produce a sintered body with high strength and high density. On the other hand, the hot press method and hot isostatic press method, which perform molding and firing at the same time, can adjust the microstructure of the sintered body and promote densification.
Compared to other methods, sintering can be completed in a relatively short time and at a lower temperature, so it is an extremely effective method.
However, it is difficult to produce products with complex shapes and thinness, and there is a tendency that mass production is not possible and product costs are high. As mentioned above, when attempting to manufacture dense sintered bodies at high speed using zirconia as a raw material using existing methods, it has been difficult to manufacture complex shapes and thin bodies. On the other hand, if the purpose is to produce complex-shaped or thin products in large quantities, it is not possible to produce dense sintered bodies at high speed. In this way, there was an antinomic relationship between mechanical strength and densification and the production of complex shapes and thin objects. (Problems to be Solved by the Invention) In view of the above-mentioned problems of existing methods, the present inventors have completed the present invention as a result of extensive research, and the purpose thereof is to: It is an object of the present invention to provide a method for producing a zirconia sintered body having excellent mechanical strength and compactness. Another object of the present invention is to provide a method for manufacturing a zirconia sintered body having a complex shape or a thin shape, in addition to the above characteristics. Further objects and advantages will become apparent from the description below. (Means for solving the problem) The main ingredients are zirconium oxide (A) and at least one stabilizer (B) selected from the group of yttrium oxide, cerium oxide, calcium oxide and magnesium oxide. At normal pressure made of ceramic raw material that
Temperature t (℃) and load stress P (Kg
This is achieved by a method for producing a zirconia sintered body, which is characterized by plastic working under conditions of f/mm ² ). P≧3×10 ^-37 ×(1600−t) ¹⁴ +0.1 P≦5, t≦1600 The ceramic raw material according to the present invention contains zirconium oxide (ZrO ₂ ), yttrium oxide (Y ₂ O ₃ ), and calcium oxide ( CaO), magnesium oxide (MgO)
The main component is a stabilizer (B) selected from the group of cerium oxide (CeO ₂ ), which is typically added to aluminum oxide, silicon oxide, and bismuth oxide, which are usually added to ceramic raw materials. additives such as sintering aids, or Sc, La, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
It goes without saying that rare earth oxides such as Tm, Yb, and Lu may be added and blended in small amounts as appropriate.
The amount of stabilizer (B) to be blended with zirconium oxide (A) varies depending on the properties required of the target zirconia sintered body, the type of stabilizer (B) to be blended, etc., and cannot be absolutely specified. It is preferable to limit the amount to about 15 mol% at most. The preferred range of the stabilizer (B) to be added to zirconium oxide is 2.0 to 10.0 mol% for yttrium oxide, 5.0 to 15.0 mol% for calcium oxide, and 5.0 to 5.0 mol% for magnesium oxide.
15.0 mol%, and about 7.0 to 15.0 mol% of cerium oxide. These ceramic raw materials may be prepared by appropriately selecting from known methods, and these methods can be broadly classified into dry methods and wet methods. As a dry method, there is a method in which, for example, a predetermined amount of powder of a stabilizer such as zirconium oxide and yttrium oxide is mixed using a ball mill, pulverized, heat treated, and then mechanically pulverized. Furthermore, examples of the wet method include the following methods. (1) A precipitating agent such as ammonia is added to a mixed aqueous solution of a water-soluble zirconium salt such as zirconium oxychloride and a water-soluble salt of a metal that serves as a stabilizer such as yttrium chloride, and a stabilizer such as zirconium and yttrium is added. A method in which a hydroxide sol is generated, followed by filtration, washing, drying, and subsequent heat treatment. (Co-precipitation method) (2) A method in which a mixed aqueous solution similar to the above-mentioned coprecipitation method is heated to produce a sol of hydroxide, etc., which is then filtered, washed, dried, and subsequently heat-treated.
(Hydrolysis method) (3) Mix and dissolve an alkoxide of zirconium such as zirconium isopropoxide and an alkoxide of a metal element constituting a stabilizer such as yttrium isopropoxide in an organic solvent, and add to the solution. A method in which a sol is generated by adding water to hydrolyze an alkoxide, followed by filtering, washing, drying, and subsequent heat treatment. (Alkoxide method) The ceramic raw material applied to the present invention preferably has a particle size of 1 μm or less and is preferably as fine as possible. From this point of view, a wet method is suitable as a method for preparing the ceramic raw material, since it produces fine particles, a narrow particle size distribution, and a uniform composition. Next, the ceramic raw material prepared in this way is
It is used to manufacture calcined molded products for plastic working. Ceramic raw material is 100-200μm with excellent fluidity.
It is preferable to use it in the form of granules. The granules can be prepared by using a spray dryer or the like from a slurry of ceramic raw materials containing water-soluble resins such as polyvinyl alcohol and hydroxyethyl cellulose. Next, a pressure molding method of pressing the granules,
A casting method involves injecting a slurry of ceramic raw materials into a mold made of gypsum, etc.; an extrusion molding method in which a plastic mixture consisting of an organic binder, ceramic raw materials, and water is extruded from a die; ceramic raw materials are filled as they are or granules are filled into a rubber mold, and pressure is applied. isostatic press molding method in which the mixture of thermoplastic resin and ceramic raw material is isotropically pressed, injection molding method in which the mixture of thermoplastic resin and ceramic raw material is extruded into a mold under heating, and the mixture of resin binder and ceramic raw material is made into a thin film using a doctor blade, etc. A powder compact is prepared by selecting an appropriate method from known methods such as sheet molding. Subsequently, the powder compact was heated at normal pressure to 600~
A calcined molded product as a precursor is prepared by heat treatment at a temperature of 1200°C. Heat treatment is usually carried out in an oxidizing atmosphere such as the air, an inert atmosphere such as a nitrogen atmosphere, or a vacuum atmosphere, but an oxidizing atmosphere in which the organic substances contained are removed by incineration is advantageous. The heat treatment is carried out using a commonly used high-temperature furnace such as an electric furnace, gas furnace, or heavy oil furnace. Ordinary sintered bodies are molded using an organic binder such as paraffin and then fired at a high temperature of about 1500°C, so they have large plastic resistance and are extremely difficult to cut using a lathe. However, in the case of the above-mentioned pre-fired product, cutting with a lathe is easy, so
It has the advantage of being able to efficiently manufacture products with complex shapes with simple operations by cutting the calcined product, shaping it into an approximate shape, and expanding the necessary parts in the subsequent plastic working. Furthermore, if a sintered compact is used as a precursor, the particles will grow in the subsequent plastic working process, making it easier for tetragonal to monoclinic transition to occur, increasing the monoclinic content;
When the calcined product is used as a precursor as in the present invention, grain growth is small and the increase in monoclinic crystals accompanying the transition from tetragonal crystals to monoclinic crystals is slight. It is thought that this phenomenon promotes the increase in strength due to plastic working. During plastic working, the temperature t shown by the following formula is
(°C) and pressure P (Kgf/mm ² ). P≧3×10 ⁻³⁷ ×(1600−t) ¹⁴ +0.1 P≦5, t≦1600 The range represented by this formula is illustrated in FIG. 1. If it deviates from the above range, the plastic working resistance will be extremely high, making it impossible to obtain industrially dense sintered bodies. Furthermore, complicated operations and expensive and complicated equipment are required. Plastic working is a process that utilizes plastic deformation, such as rolling, extrusion, drawing, and forging, using a jig made of alumina, silicon carbide, carbon, or the like.
For example, in a high-temperature furnace using electrical heating, gas combustion heating, dielectric heating, etc., in an oxidizing atmosphere such as atmospheric atmosphere,
This is carried out by applying tensile or compressive force using a hydraulic mechanism or the like in various atmospheres such as an inert atmosphere such as a nitrogen atmosphere or a vacuum atmosphere. The heating method, atmosphere, etc. may be appropriately selected from known methods. (Effects of the invention) The method for producing a zirconia sintered body of the present invention includes:
The zirconia sintered body has a small porosity, is dense, and has high strength, and it is possible to easily obtain a zirconia sintered body that is dense and has a complicated shape or an extremely thin shape and has excellent dimensional accuracy without any post-processing. Therefore, mechanical parts such as automobile engines that require complex shapes, gas sensors that need to reduce their electrical resistance by thinning,
It is suitable for manufacturing solid electrolytes used in fuel cells, oxygen pumps, etc., and cutlery such as scissors and knives that are extremely thin and require dimensional accuracy. The present invention will be specifically described below with reference to Examples. In addition, in the examples, the average particle diameter, bending strength, and monoclinic crystal content were measured by the following methods. (1) Average particle size This is a value calculated from the average value of 10 particle sizes measured by breaking the sample and observing the broken surface with an electron microscope. (2) Bending strength In accordance with JISR1601, the value was determined by cutting the sample into 3 x 4 x 40 mm pieces, polishing the sample surface, and using a 4-point bending test method. (3) Monoclinic content A given sample is analyzed by X-ray diffraction, and from the integrated intensity obtained from the peak area of the diffraction pattern,
The content of monoclinic zirconium oxide was calculated based on the following formula. Content of monoclinic zirconium oxide = M
/M+T+C×100 (mol%) where M is monoclinic zirconium oxide (111)
Sum of integrated intensities of plane and (111) plane T is integrated intensity of (111) plane of tetragonal zirconium oxide C is integrated intensity of (111) plane of cubic zirconium oxide Example 1 Manufactured by coprecipitation method Approximately 40g of the ceramic raw materials made of zirconium oxide and yttrium oxide listed in Table 1 below was placed in a mold and heated to 2.5 (Kgf/mm ² ) at 20°C.
After being press-formed at a pressure of For calcining, the temperature is raised to 1100℃ at a rate of 15℃/min, held at 1100℃ for 30 minutes, and then heated to 15℃/min.
Cooled at a cooling rate of min. The bending strength, grain size, monoclinic content, and porosity of the calcined molded product were each 4.
(Kgf/mm ² ), 0.15 μm, 19 mol%, and 41%. Next, the calcined molded product was placed in a silicon carbide mold and heated at 20°C/min from 1200°C to 1200°C in an electric furnace.
After increasing the temperature to the specified temperature listed in the table at a rate of 15°C/min, the stress specified in the table was applied and pressure was applied from both sides. Rapid contraction occurred at the beginning of pressurization, and after densification progressed, plastic deformation gradually occurred. After pressurizing for 60 minutes, the pressure was removed and the mixture was cooled at a cooling rate of 15° C./min. The effects are shown in Table 1. As is clear from Table 1 below, plastic working improved the strength of all items, but
In particular, an improvement in strength was observed in Run No. 13.
In Run No. 13, a high intensity change of approximately 30 times was observed.
Plastic deformation was noticeable at temperatures above 1300°C, resulting in the lateral spread of the pressurized surface and the desired shape.

【table】

[Table] Example 2 In Example 1, predetermined amounts of magnesium oxide, calcium oxide, and cerium oxide listed in Table 2 below were used in place of yttrium oxide, and the second
A zirconia sintered body was produced in the same manner as in Example 1, except that the plastic working was carried out under the plastic working temperature and pressure conditions listed in the table. The results are shown in Table 2.

[Table] From the above table, it was found that even when magnesium oxide, calcium oxide, and cerium oxide were used as stabilizers instead of yttrium oxide, they showed the same tendency as yttrium oxide. Comparative Example 1 In Run No. 13 of Example 1, the precursor was fired at normal pressure under the conditions shown in Table 3 below instead of the pre-calcination conditions, and the other conditions were the same as in Example 1. A zirconia sintered body was manufactured. The results are shown in Table 3.

[Table] From the above table, when a sintered molded product is used as a precursor, particles grow in the plastic working process described later, transition from tetragonal to monoclinic tends to occur, and the monoclinic content increases. However, when a calcined product is used as a precursor as in the present invention, grain growth is small and the monoclinic content decreases, contrary to the comparative example. Example 3 A zirconia sintered body was produced in the same manner as in Example 1 Run No. 13, except that a ceramic raw material with an average particle size of 1.8 μm was used in Example 1. In addition, in the above comparative example, an attempt was made to produce a zirconia sintered body in the same manner as in the above comparative example except that a ceramic raw material having an average particle size of 1.8 μm was used. The results are also shown in Table 4 below.

[Table] From the table above, in the comparative example using pressureless sintered material as a precursor, the plastic working resistance was significantly large.
However, in the present invention, which uses a pre-sintered material as a precursor, plastic processing is possible with only a slight increase in the monoclinic content even if a ceramic raw material with a large particle size is used. As a result, it is clear that the strength is significantly improved. Example 4 According to Example 1, a calcined molded product with a thickness of 0.5 mm was produced. The calcined product was placed on a silicon carbide die with a diameter of 12 mm and a depth of 15 mm, and was pressurized using a silicon carbide punch with a diameter of 10 mm to perform deep tightening by plastic working. As a result, a bag tubular product having the same dimensions and shape as inside the die was obtained. Here, the ceramic raw material and plastic working conditions are Run No. 13 listed in Table 1 of Example 1.
According to. The obtained tubular bag was a good sintered compact with no cracks. Comparative Example 2 Normal hot press sintering was carried out in the same manner as in Example 4 except that the ceramic raw material was directly filled into the die without using a calcined product. It was observed that there were no cracks and that there were many cracks. Example 5 According to Example 4, deep drawing by plastic working was performed to produce a bag tubular article. However, for calcining, the temperature is increased at 15℃/min to the specified heating temperature shown in Table 4, and after being held at the specified temperature for 30 minutes, the heating temperature is increased to 15℃/min.
It was cooled at a cooling temperature of .

[Table] In addition, sample No. 1 had low handling strength of the calcined product and broke at the initial stage of plastic working.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the range of preferable conditions during plastic working in the present invention, and the horizontal axis is the temperature t.
(°C) and the vertical axis represents the applied stress P (Kgf/mm ² ).

Claims (1)

[Claims] 1. Zirconium oxide (A) and yttrium oxide,
At least one stabilizer selected from the group of cerium oxide, calcium oxide and magnesium oxide (B)
At normal pressure, it is made of ceramic raw material whose main ingredients are
Temperature t (℃) and load stress P (Kg
This is achieved by a method for producing a zirconia sintered body, which is characterized by plastic working under conditions of f/mm ² ). P≧3×10 ^-37 ×(1600−t) ¹⁴ +0.1 P≦5, t≦1600 2. Claim 1 contains at most 15 mol% of the stabilizer (B). A method for producing the described zirconia sintered body. 3. The method for producing a zirconia sintered body according to any one of claims 1 to 2, wherein the ceramic raw material has an average particle diameter of μm or less.