JPS6031796B2 - Zirconia sintered body - Google Patents

Description

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

A pure zirconia sintered body transforms from a monoclinic crystal structure to a tetragonal crystal structure around 1100 oo, and further
At around 0000, it transforms into a cubic crystal structure.

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, Then, oxides such as yttria, magnesia, and calcia are dissolved in zirconia to obtain a sintered body made of zirconia with a tetragonal crystal structure (hereinafter referred to as cubic zirconia), that is, a stabilized zirconia competitive body. . However, since cubic zirconia has a large thermal field modulus, the stabilized zirconia aged crystals have a drawback of low thermal shock strength. On the other hand, zirconia aggregates in which cubic zirconia and zirconia with a monoclinic crystal structure (hereinafter referred to as monoclinic zirconia) coexist, that is, partially stabilized zirconia crystal structures, have a tetragonal crystal structure. Zirconia (hereinafter referred to as tetragonal zirconia) with a crystal structure of It is said to have higher thermal shock strength than

However, the degree of improvement was not so significant because it still contained cubic zirconia, which has a large thermal shock coefficient. On the other hand, 82~
A zirconia serpentine body in which 97 (mol %) of tetragonal zirconia and 18 to 3 (mol %) monoclinic zirconia coexist, and ztria is solidly dissolved therein, is able to withstand tension, compression, bending, and shearing. There are reports that it has high mechanical strength, as well as improved hardness and toughness.

However, this burnt striped body had a drawback of low thermal shock strength because the proportion of monoclinic zirconia was extremely small at 18 to 3 (mol %). 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 Since the micro-cracks that occur in the surrounding area mainly absorb the energy, thermal shock energy cannot be absorbed sufficiently depending on the small amount of micro-cracks generated due to the small amount of transformation. The purpose of the present invention is to
It is an object of the present invention to provide a zirconia composite body which solves the above-mentioned drawbacks of the conventional zirconia composite body and has extremely high thermal shock strength.

To achieve the above object, the present invention provides a Akatsuki crystal consisting of zirconia having a substantially monoclinic crystal structure, the Akatsuki solid in parentheses containing 5 to 9 (mol%) of magnesia. 1~
It is characterized by a zirconia sintered body in which 4 (mol %) of calcia is solidly fused.

In the present invention, the term "sintered body made of zirconia with a substantially monoclinic crystal structure" refers to a zirconia competitive body analyzed by X-ray diffraction at a diffraction angle in the range of 20 to 40 (degrees). In this case, cubic zirconia 111 and 20
This means that the diffraction patterns of 111, 002 and 200 crystalline zirconia cannot be detected.

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

Next, the zirconia powder, magnesia powder, and calcia powder are mixed so that the total amount of magnesia powder and calcia powder is 5 to 9 (mol %) and 1 to 4 (mol %), respectively.

Next, the above mixture is calcined at 800 to 1200 (°C) for several hours, and then pulverized with a ball mill. The raw material powder is obtained by repeating such calcining and pulverization. This raw material powder forms a solid melt in which zirconia powder, magnesia powder, and calcia powder are evenly mixed, and its crystal structure is as follows.
It is either monoclinic or a coexistence of monoclinic and cubic systems. 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 a temperature of 1600 to 178
After the temperature is gradually raised to 0 (°C), the temperature is maintained for several hours to several tens of hours to perform firing.

In the process of temperature increase, the crystal structure of the solid solution changes as follows:
Those in the monoclinic system are in the tetragonal system, cubic system, or a coexistence state of both, and those in the coexistence state of the monoclinic system and the cubic system are in the cubic system, or the tetragonal system and the cubic system. Each metamorphoses into a state of coexistence with the system. The temperature and speed of such crystal structure transformation vary depending on the purity of the zirconia, magnesia and calcia powders used and the amount of magnesia and calcia powders mixed.

Therefore, the firing temperature to obtain the crystal structure as described above is determined. As mentioned above, this adjacent product temperature is 1600 to 17
The temperature is 80 (°C). Next, the fired body was heated to 200 to 2100 (
The material is slowly cooled to about 100 picoC at a rate of 100°C/hour) and then further cooled in a furnace to room temperature.The effects of magnesia and calcia during this cooling process will be explained below.

The crystal structure of the fired body is a cubic system or a coexistence state of a tetragonal system and a cubic system. If the amount of magnesia that is missing is between 5 and 9 (mol%) as mentioned above, and the calcia nose is within the range of 1 and 4 (mol%), it is considered to be cubic or tetragonal. From the coexistence state with the cubic system, the coexistence state of the monoclinic system and the cubic system, the coexistence state of the monoclinic system and the cubic system, the coexistence state of the tetragonal system and the cubic system,
The crystal structure gradually transforms into a coexistence state of the regular crystal system and the cubic system, and the microcracks generated by this transformation are uniformly dispersed, so that the fracture energy caused by the generation of microcracks is absorbed. Crack itself absorbs it. Therefore, destruction of the fired body during the cooling process can be prevented. On the other hand, the amounts of magnesia and calcia are at the lower limit described above, that is, 5 mol% each.
If the amount is less than 1 mol%, the fired body has a tetragonal system or a crystal structure in which a tetragonal system and a cubic system coexist, but the amount of magnesia and calcia is too small. With cooling, the crystal structure rapidly transforms from a tetragonal system to a monoclinic system, and microcracks occur throughout the fired body, and the fired body is destroyed by the energy. In addition, if the amounts of magnesia and calcia exceed the above-mentioned upper limits, that is, 9 mol% and 4 mol%, respectively, the fired product will have a cubic crystal structure or a crystal structure in which a tetragonal system and a cubic system coexist. However, during the cooling process, the state changes from a cubic system or a coexistence state of a tetragonal system and a cubic system, to a state of a coexistence state of a monoclinic system and a tetragonal system, and a state of a monoclinic system and a tetragonal system. The transformation to the coexistence state of monoclinic, tetragonal, and cubic systems does not proceed easily, and if an attempt is made to cause the above transformation by making the cooling time extremely long,
The crystals grow and the crystal grains become larger. In particular, when the amount of calcia exceeds 4 mol %, the cooling time becomes even longer, the crystal growth becomes significant, the crystal grains become large, and the fired body becomes brittle after cooling. Next, the temperature of the fired body cooled to room temperature is gradually raised to 1300 to 1430 (00), and then maintained at that temperature for several hours to several tens of hours for aging.

In this process, the crystal structure of the fired body transforms into a tetragonal system or a coexistence state of a monoclinic system and a tetragonal system. The temperature and speed of this transformation vary depending on the crystal structure of the fired body before aging and the amount of dissolved magnesia and calcia, so the aging temperature at which the above-mentioned crystal structure is obtained is determined. The aging temperature is 1,300 to 1,430 mm as described above. Next, the above-mentioned sintered body is slowly cooled from the aging temperature to about 100,000 at a slow rate of 5 to 100° C./hour, and further cooled to room temperature to obtain the sintered body of the present invention.

The effects of magnesia and calcia in this cooling process will be explained below. The crystal structure of the fired body after aging is a tetragonal system or a coexistence state of a monoclinic system and a tetragonal system. If 5 to 9 (mol%) of magnesia is dissolved in solid solution and 1 to 4 (mol%) of calcia is solidly dissolved, the crystal structure changes from the above crystal structure to a monoclinic crystal structure with cooling. The transformation occurs gradually, and the microcracks generated by this transformation are uniformly dispersed, so
The microcracks themselves absorb the fracture 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-mentioned transformation forms a compressive stress field within the sintered body, energy due to the compressive stress is stored within the sintered body, leading to an improvement in mechanical strength. In contrast, the amount of magnesia is less than 5 mol% and the amount of calcia is 1 mol%
If the amount of magnesia and calcia is less than As the crystal structure is cooled, the crystal structure rapidly transforms from a tetragonal system to a monoclinic system, and microcracks are generated throughout the fired body, and the fired body is destroyed by the energy.

In particular, when the amount of calcia is less than 1 mol %, the transformation rate increases significantly. In addition, if the amount of magnesia exceeds 9 mol% and the amount of calcia exceeds 4 mol%, the fired body has a cubic system or a coexistence of a tetragonal system and a cubic system. Although it has a crystal structure of a monoclinic crystal structure, the transformation to a monoclinic system does not proceed easily even with the cooling described above.
Cubic or tetragonal crystal structures may remain within the brickwork. If an attempt is made to force the transformation by taking an extremely long cooling time, the crystals will grow and the crystal grains will become larger. In particular, when the calcia content exceeds 4 mol %, cubic or tetragonal crystal structures tend to remain, resulting in a significant decrease in thermal shock strength. In this way, the Akatsuki crystal of the present invention consisting essentially of monoclinic zirconia is obtained by the above-mentioned cooling, but in order to do so, it is necessary to mix magnesia powder and calcia powder in the mixture before obtaining the raw material powder. The amount should be in the above range, that is, 5 to 9 (mol%) and 1 to 4 (mol%), respectively (of course, this range does not change even if it becomes a sintered body), and the cooling rate after aging should be 5 to 100. (°C/hour). The presence of monoclinic zirconia, magnesia, and calcia dramatically improves the thermal shock strength of Akatsuki crystals. In other words, the fact that the zirconia that makes up the pseudocrystal has a monoclinic crystal structure means that a sufficient amount of microcracks exist near or around the monoclinic zirconia. It is.

Therefore, when a crack occurs in the compact due to thermal shock, the propagation of the crack is obstructed by the micro-cracks, making it difficult to propagate as it follows a winding course, thereby improving the thermal shock strength. In addition, when the Akatsuki crystal is subjected to rapid heating, distortion occurs in the Akatsuki silk body due to the heating process, but the crystal structure transforms from monoclinic to tetragonal as a result of heating. With volumetric contraction of about 3%,
This volumetric contraction acts to alleviate the above strain, so
Thermal shock strength is improved. Magnesia and calcia are dissolved in the crystalline crystals, and the competitive bodies undergo thermal stress and transform into a monoclinic crystal structure, which reverts to a monoclinic crystal structure upon cooling. When metamorphosing, the speed of the metamorphosis is suppressed to prevent the dawn concretion from being destroyed.

Moreover, magnesia and calcia provide good oxygen ion conductivity to the sintered body. In other words, although a pure zirconia lamp body has a monoclinic crystal structure, the transfer number of oxygen ions is small, so in order to increase this, the sintered silk body has a cubic crystal structure. Adjust the knee joint to about 24cm.
It becomes necessary to heat to a high temperature of 0,000 or higher. However, the aggregate of the present invention has 110,000
Even in terms of degree, a fairly large transport number can be obtained. This temperature is about 300° C. lower than that in which magnesia alone is dissolved in a solid solution of about 6 to 11 (mol %). Therefore, in combination with the high thermal shock strength, the anti-stripe material of the present invention is very suitable as a constituent material of a so-called solid electrolyte oxygen sensor, which measures the oxygen concentration in port steel, for example. As mentioned above, in the Akatsuki compact of the present invention, in order to obtain high thermal shock strength, the amount of magnesia is 5 to 9 (
(mol%), and the amount of calcia is 1 to 4 (mol%)
However, magnesia and The sum of the amounts of calcia is 6~
It is preferable to set it to 11 (mol%).

Furthermore, the competitive body of the present invention has a crystal grain size of 10 to 10
It has a size of 0 (Buddha), and inside each crystal grain,
The crystal structure is monoclinic and the average grain size is 0.1 to 1.
It is preferable that fine crystal grains (subgrains) such as (French) are uniformly dispersed, and that the proportion of the fine crystal grains is 2% by weight or more.

In other words, even if the average particle size of the fine crystal grains is 0.1 mm, the thermal shock strength tends to decrease even if it exceeds IA, and even if the content is less than 2% by weight, the thermal shock strength still decreases. Either case is unfavorable since the impact strength tends to decrease. 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, define a section with an arbitrary fixed area on this photo, and increase the area of particles existing in that section from large particles to smaller particles until the total area becomes 1/2 of the area of the above section. to add. 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 size is determined. In other words, ・ a・10a20a30-----+an: Committee SZan
Injury n4. ...d=22 However, d: Average particle size an: Area of each particle (n≠1, 2, 3,...) s: Area of section Also, monoclinic fine particles within the crystal grains The weight content of crystal grains can be determined by cutting the pseudocrystal, optically polishing the cut surface, and then observing it with a scanning electron microscope, or by making an ultra-thin sample of several tens to several white angstroms and examining it. It can be measured by observing with a transmission electron microscope.

As mentioned above, the sintered body of the present invention has a high thermal shock strength, a high oxygen ion conductivity even at relatively low temperatures, and a relatively high mechanical strength. It can be used for various purposes.

An example is shown below. Solid electrolyte oxygen sensors such as metallurgical sensors and combustion control sensors for internal combustion engines, gas stoves, boilers, etc. General industrial machinery, such as crucibles, various dies, tandem nozzles, protective tubes, bolts, nuts, various valves, mechanical seals, various parts such as nozzles and combustion chambers for coal and oil combustion equipment, dovets for internal combustion engines, etc. Parts of the instrument.

C Hot rolls, slag pedestals, insulation boards, etc. in the steel industry.

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

Example Using zirconia powder, magnesia powder, and calcia powder with an average particle diameter of 0.1 mm, a 2-Mg○-Cao-based calcining body of Z of overnight fleas shown in the table was made. , zirconia, magnesia and calcia, the numbers listed at the bottom right are their amounts in mol%).

That is, after mixing zirconia powder, magnesia powder, and calcia powder in the amounts shown in the table, 1
000qo for 3 hours, and further crushed in a pot mill for 2 hours, and this preliminary combustion and crushing were repeated twice to produce a raw material powder.

Next, a 2% polyvinyl alcohol aqueous solution was added as a binder to the raw material powder, mixed well, and after drying, a plate-shaped molded body was produced by a rubber press method.

Next, the above-mentioned molded body is fired and cooled under the conditions shown in the table to make a fired body, and this fired body is cut and polished to form a thickness 3 side.
A sample with a width of 3 ribs and a length of 24 ribs was made.

Next, the thermal shock strength of each of the above samples was measured.

The results are shown in the table. The thermal shock strength was determined by heating a plate-shaped scale body to an arbitrary temperature of Tx°C, then dropping it into water at a temperature of T°C to rapidly cool it, and then measuring its bending strength by a well-known three-point bending test method.

Then, the heating temperature T at which the bending strength begins to decrease
Read x℃ as critical temperature T, and this critical temperature T
c. The difference Tc-T (°C) between 0 and the temperature T°C of the water was used as an index.

Note that the measurement conditions for the three-point bending test method are a span length of 2 yen and a load application acceleration of 1 rib/min. Table (husband) Cool from the firing temperature to 1200°C at a rate of 100°C/hour, and then cool in the furnace to room temperature.

Claims (1)

[Claims] 1 A sintered body made of zirconia with a substantially monoclinic crystal structure, and this sintered body contains 5 to 9 (mol%
A zirconia sintered body comprising magnesia ( ) and 1 to 4 (mol %) calcia in a solid solution.