JP2005187219A - Zirconium oxide mixed powder and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconium oxide raw material powder for producing a sintered compact excellent in thermal shock resistance and in capability of stabilizing electromotive force value while preventing cracking of the sintered compact even when the sintering temperature varies; especially a raw material powder suitable for an MSZ (MgO-solid solubilized Zirconia) sintered compact used for a solid electrolyte element. <P>SOLUTION: The zirconium oxide mixed powder contains 6-12 mol% magnesium oxide and 0.1-2 mol% calcium oxide. In the mixed powder, a part of the magnesium oxide and a part of the calcium oxide form a solid solution, and the monoclinic crystal ratio is 70-99%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a raw material powder for obtaining a partially stabilized zirconium oxide sintered body in which magnesium oxide and calcium oxide are dissolved, and particularly a solid having excellent electromotive force characteristics and thermal shock resistance as an oxygen sensor for molten metal It is an invention relating to a raw material powder for obtaining an electrolyte sintered body.

  As a zirconium oxide sintered body used as an oxygen sensor, a sintered body in which 5 to 10 mol% of yttrium oxide is dissolved (hereinafter referred to as YSZ), and a sintered body in which 7 to 10 mol% of magnesium oxide is dissolved (hereinafter referred to as MSZ). ), And a sintered body (hereinafter referred to as CSZ) in which 10 to 15 mol% of calcium oxide is dissolved.

  YSZ has good electromotive force characteristics at low temperatures, but has low thermal shock resistance, and is therefore used as an oxygen sensor for automobiles used at relatively low temperatures. MSZ is excellent in corrosion resistance and thermal shock resistance, and is used as an oxygen sensor for molten metal. Moreover, CSZ is excellent in temperature stability and is used for general gas measurement.

In particular, MSZ used for measuring the oxygen concentration of molten metal is resistant to thermal shock caused by a rapid temperature rise when immersed in molten metal at 1400 ° C. or higher. In the sintered body containing zirconium oxide and silicon oxide in a solid solution of 7 to 10 mol% of magnesium oxide as a structure and 0.1 to 0.5 wt%, the total amount of monoclinic crystals is changed from 60 mol% depending on the high temperature sintering conditions. It is known that the amount is controlled to 80 mol% and volume shrinkage in the transformation from monoclinic to cubic is utilized. As a raw material powder for obtaining the sintered body, a powder obtained by wet mixing a raw material having an average particle diameter of 1 μm or less with a ball mill and calcining at 800 ° C. to 1200 ° C. has been used (for example, see Patent Document 1). )
Japanese Patent Publication No. 3-64468

  In general, in a large-scale furnace for mass production, it is very difficult to reduce the dispersion of the sintering temperature in the furnace within 10 ° C. under a high temperature condition of 1000 ° C. or more. Therefore, from the powder obtained by the conventional method, However, it is difficult to control the ratio of monoclinic crystals and cubic crystals of the zirconium oxide sintered body to a certain range due to the variation in temperature, resulting in large variations in quality such as thermal shock resistance and electromotive force stability of the product. In addition, when sintering is performed in a state where an extreme change in temperature is observed, the sintered body may be broken and may not be a product.

  Therefore, the present invention provides a zirconium oxide raw material for producing a sintered body that prevents cracking of the sintered body even when the sintering temperature varies, and has excellent thermal shock resistance and stable electromotive force performance. It is to obtain a powder. It is another object of the present invention to provide a suitable material powder for an MSZ sintered body used for a solid electrolyte element.

  In view of the above problems, the present invention employs the following means. That is, a zirconium oxide mixed powder containing 6 to 12 mol% of magnesium oxide and 0.1 to 2 mol% of calcium oxide, wherein a part of the magnesium oxide and a part of the calcium oxide are in solid solution, and It is a zirconium oxide mixed powder having an oblique crystal ratio of 70 to 99%.

  Moreover, it is a manufacturing method of the zirconium oxide mixed powder which mixes the zirconium oxide powder, the magnesium oxide powder, and the calcium oxide powder in which 0.04 to 2 mol% of calcium oxide is solid solution and heat-treats at 900 to 1100 ° C. in the atmosphere. .

  By using the zirconium oxide mixed powder of the present invention as a raw material powder, even when the sintering temperature varies, the occurrence of cracking of the sintered body in the manufacturing process of the sintered body is improved compared to the prior art, It becomes possible to manufacture a sintered body having excellent performance in which the electromotive force value is stable. In addition, by using the zirconium oxide mixed powder of the present invention, mass production of a sintered body is possible, which helps to reduce costs. Moreover, the manufacturing method of the zirconium oxide mixed powder of this invention can provide the zirconium oxide powder which has the said effect by the method which can be industrially produced.

  Embodiments of the present invention will be described below.

  In the zirconium oxide mixed powder of the present invention, the most important factor is that magnesium oxide and a part of calcium oxide are dissolved in the zirconium oxide. Here, the determination of whether calcium oxide and magnesium oxide are dissolved in the present powder includes an EDX (energy dispersive X-ray) element point analysis method using FESTEM (high resolution transmission electron microscope). This method is a method in which each element is detected by performing point analysis on the primary particles observed by FESTEM using characteristic X-rays. By measuring the composition of the primary particles in the zirconium oxide mixed powder using this method, it is confirmed that calcium element and magnesium element are present in the primary particles of zirconium oxide, and solid solution is confirmed. . Since such elements are dissolved in advance, it is possible to suppress variations in the solid solution state of the obtained sintered body even when the sintering temperature varies to some extent when the raw material powder of the present invention is used. There is an effect. The smaller the mixing amount of the primary particles of zirconium oxide in which calcium oxide is not dissolved, the better. In the case where there are primary particles of zirconium oxide in which calcium oxide is not dissolved, there is solid solubility of magnesium oxide during sintering. Tends to be reduced, and is easily affected by temperature variations during sintering, which may cause a solid solution state in each crystal of the obtained sintered body and, consequently, the performance of the sintered body to vary.

  The zirconium oxide mixed powder of the present invention has a monoclinic crystal ratio in the range of 70 to 99 mol%, more preferably in the range of 75 to 90%. The monoclinic crystal ratio is obtained by the following formula for the mixed diffraction intensity and the monoclinic diffraction intensity of tetragonal and cubic crystals for the peak obtained by the powder X-ray diffraction method. However, the value after correction by the Lorentz factor is used for the diffraction intensity.

If the monoclinic crystal ratio is less than 70%, the sintering temperature becomes unstable, resulting in a sintered body having a monoclinic crystal ratio of 60% or less, and the thermal shock resistance deteriorates. End up. On the other hand, if it exceeds 99%, solid solution hardly occurs at the time of sintering, and since the sintering temperature becomes unstable, the monoclinic crystal ratio of the sintered body exceeds 80% and the stability of the electromotive force is deteriorated. .

  The zirconium oxide mixed powder of the present invention contains 6 to 12 mol% magnesium oxide and 0.1 to 2 mol% calcium oxide. If the content of magnesium oxide is less than 6 mol%, stabilization after sintering does not occur sufficiently, and oxygen ion conductivity is hindered, so the response speed in electromotive force measurement is slow, and the electromotive force value is not good. Tend to be stable. On the other hand, if it exceeds 12 mol%, the magnesium oxide layer is deposited alone after sintering, and the thermal shock resistance tends to be inferior. More preferably, it is 7-9 mol%. In addition, when the content of calcium oxide is less than 0.1 mol, the amount of solid solution of calcium oxide in zirconium oxide in the obtained sintered body decreases, and thermal shock resistance and electromotive force stability due to variations in sintering temperature. When the content exceeds 2 mol%, the thermal shock resistance is reduced due to the presence of a large amount of calcium oxide at the grain boundary after sintering. More preferably, it is 0.5-1.5 mol%. In addition, all of the magnesium oxide contained in the zirconium oxide mixed powder may be dissolved in zirconium oxide, or a part thereof may be dissolved. Further, all of the calcium oxide contained in the zirconium oxide powder may be dissolved in zirconium oxide, or a part thereof may be dissolved.

  The content of magnesium oxide or calcium oxide contained in the zirconium oxide powder can be obtained by ICP emission analysis.

  Moreover, it is preferable that the average secondary aggregation diameter of the particle | grains when the zirconium oxide mixed powder of this invention is made into a slurry form by water dispersion is 0.3-2 micrometers. More preferably, it is 0.3-1 micrometer, More preferably, it is 0.5-0.8 micrometer. The average secondary agglomerated diameter of the particles in the form of the slurry reflects the ease of sintering of the powder, and is sufficiently dispersed over 5 minutes or more with an ultrasonic disperser with a zirconium oxide mixed powder output of 100 W or more. It is obtained in a slurry state. Here, the average secondary agglomerated diameter refers to a median diameter in a volume conversion particle size distribution measured by a laser diffraction method. If the average secondary agglomerated diameter of the particles in the slurry is less than 0.3 μm, the agglomeration force of the powder after drying is strong, and therefore, density unevenness is likely to occur during molding, and cracking during sintering tends to occur due to thermal expansion distortion In addition, if it exceeds 2 μm, the density of the sintered body tends to decrease, so that the oxygen ion conductivity is deteriorated, and the electromotive force characteristics may be affected.

The zirconium oxide mixed powder of the present invention preferably has a BET specific surface area of 5 to 16 m ² / g. More preferably, it is 7-15 m < ² > / g, More preferably, it is 8-12 m < ² > / g. When the BET specific surface area is less than 5 m ² / g, tend to electromotive force characteristic reduces the ionic conductivity for density decreases of the resulting sintered body is poor, exceeds 16m ² / g, the cohesive force of the powder Therefore, density unevenness occurs in the obtained sintered body, and the sintered body tends to break due to distortion of thermal expansion during sintering. In the present specification, the BET specific surface area is measured using nitrogen as an adsorbed molecule.

  The zirconium oxide mixed powder of the present invention may contain a silicate compound such as aluminum silicate and magnesium silicate in an amount of about 0.1 to 0.5% by weight in addition to the raw materials. By adding a silicate compound such as aluminum silicate or magnesium silicate, a glass layer can be deposited at the crystal grain boundaries, and the thermal shock resistance at high temperatures can be improved. Here, if the amount converted to silicon oxide is less than 0.1% by weight, the growth of the glass layer at the time of sintering becomes insufficient and the impact resistance improving effect may not be sufficient. On the other hand, if it exceeds 0.5% by weight, the glass layer becomes too thick, the oxygen ion conductivity at the grain boundary deteriorates, and the electromotive force varies when used as an oxygen sensor for molten steel.

  Further, by adding 0.5 to 2 mol% of aluminum oxide with respect to 100 mol% of zirconium oxide, the strength of the sintered body can be further increased, and damage due to thermal shock in a high temperature region can be prevented. Here, if the aluminum oxide is less than 0.5 mol%, the effect of improving the strength of the sintered body is not sufficient, and if it exceeds 2 mol%, the alumina crystal generated in the sintered body becomes too large. When the difference in coefficient of thermal expansion increases, this may become a starting point for fracture, and the thermal shock resistance may deteriorate.

  Next, a method for producing the zirconium oxide mixed powder of the present invention will be described. The production method is not particularly limited as long as the composition ratio and the monoclinic crystal ratio are as described above, and a hydrate gel is precipitated using a neutralizing agent in an acidic aqueous solution generally used as a production method of fine ceramic powder. A neutralization coprecipitation method or a hydrolysis method in which hydroxyl ions are activated to obtain a hydrate sol and thermally decompose it can also be applied. However, the neutralization coprecipitation method and the hydrolysis method are different in the neutralization point and reaction rate from zirconium salt, magnesium salt and calcium salt to hydrate, and the hydrate composition is not uniform. It is often difficult to obtain powders of different composition.

  Therefore, in order to obtain the powder of the present invention, a method of mixing oxides is preferable. In particular, in order to balance the solid solution of calcium oxide and magnesium oxide with respect to zirconium oxide, it is preferable to use a zirconium oxide powder in which only calcium oxide is dissolved in advance.

  Specifically, it is preferable to use a zirconium oxide powder in which 0.04 to 2 mol% of calcium oxide is dissolved as a raw material for obtaining the zirconium oxide mixed powder of the present invention. More preferably, a zirconium oxide powder in which 0.05 to 0.5 mol% of calcium oxide is dissolved is used. When the solid solution amount of calcium oxide is less than 0.04 mol%, the amount of calcium oxide solid solution in the primary particles of the obtained zirconium oxide mixed powder tends to be insufficient. On the other hand, when a powder in which calcium oxide exceeds 2 mol% is used as a solid solution, the thermal shock resistance of the sintered body deteriorates as described above. As the zirconium oxide powder used as a raw material, for example, a solution in which a required amount of calcium oxide is dissolved in a synthesis stage by a neutralization coprecipitation method or the like can be used.

The zirconium oxide powder used in the production method of the present invention preferably has a BET specific surface area of 5 m ² / g or more. More preferably, the BET specific surface area is preferably 5 to 30 m ² / g, and more preferably 8 to 15 m ² / g. If the BET specific surface area of zirconium oxide is less than 5 m ² / g, the primary particles of zirconium oxide are large, so the uniformity after mixing with magnesium oxide deteriorates. There is a risk of breaking.

Next, each oxide raw material powder is weighed so that magnesium oxide is preferably 6 to 12 mol% and calcium oxide is preferably 0.1 to 2 mol% in the zirconium oxide powder in which calcium oxide is dissolved. , Mix. The mixing amount of magnesium oxide is more preferably 7 to 10 mol%, and the mixing amount of calcium oxide is more preferably 0.5 to 1.5 mol%. The amount of calcium oxide mixed here is an amount including calcium oxide solid-dissolved in zirconium oxide. The magnesium oxide powder to be added preferably has a BET specific surface area of 14 m ² / g or more, and more preferably 20 m ² / g or more. When the BET specific surface area of the magnesium oxide powder is less than 14 m ² / g, the uniformity with the zirconium oxide is deteriorated, so that solid solution unevenness is likely to occur, and each primary particle contained in the zirconium oxide mixed powder is oxidized. The solid solution state of magnesium may be non-uniform.

  The magnesium oxide used in the production method of the present invention is preferably a single crystal powder. By using a single crystal, a zirconium oxide mixed powder having high purity and excellent dispersibility of magnesium oxide can be obtained.

  The calcium oxide used in the production method of the present invention preferably has a particle size of 100 μm or less after passing through a mesh. More preferably, it is 50 micrometers or less, More preferably, it is 10 micrometers or less. When the particle size exceeds 100 μm, mixing with zirconium oxide becomes non-uniform and may exist as foreign matter in the sintered body. The smaller the particle size, the better. However, if it is about 1 μm, it is often sufficient for the purpose of the present invention.

  Calcium oxide preferably has a purity of 99% or higher, more preferably 99.99% or higher. If the purity is less than 99%, the impurities may adversely affect the sintered body.

After the zirconium oxide powder, magnesium oxide powder, and calcium oxide powder are mixed, heat treatment is performed at 900 ° C. to 1100 ° C. in the atmosphere. The mixing may be performed by a general method such as dry mixing or wet media mixing, but it is preferable that the mixing is sufficiently performed so as to achieve mixing up to the level of secondary aggregated particles. In addition, it can be controlled so that magnesium oxide is partly dissolved in zirconium oxide by heat treatment at 900 to 1100 ° C. in the atmosphere and the monoclinic crystal ratio is 70% to 99%. When the maximum temperature exceeds 1100 ° C., the resulting zirconium oxide mixed powder has a BET specific surface area of less than 5 m ² / g and a monoclinic crystal ratio of less than 70%. I can't. On the other hand, when the temperature is lower than 900 ° C., primary particles in which magnesium oxide is not dissolved are generated, which adversely affects the properties of the sintered body. As a method for controlling the crystal structure, there is preferably a method in which the cooling rate from the maximum temperature to 500 ° C. is set to 1 to 3 hours. This has the effect of reducing the retransformation of the zirconia crystals that have been changed to tetragonal crystals by such rapid cooling into monoclinic crystals, and it is possible to leave some tetragonal crystals.

The heat-treated powder obtained as described above is appropriately pulverized and dried to obtain a zirconium oxide mixed powder. As the pulverization, wet pulverization is preferably used, and the secondary agglomerated particle size is preferably 0.3 to 2 μm, more preferably 0.3 to 1 μm, and further preferably 0.3 to 0.8 μm by pulverization. Adjust to. In addition, it is preferable that a predetermined amount of silicic acid compound and aluminum oxide is weighed and added and mixed during the pulverization. The silicic acid compound used has a purity of 99.9% or more and a BET specific surface area of 10 m ² / g or more, more preferably Aerosil having a BET of 50 m ² / g or more. The aluminum oxide to be used preferably has a purity of 99.9% or more and a BET specific surface area of 10 m2 / g or more. In order to further improve the moldability, an appropriate amount of an organic binder such as PVA or an acrylic compound may be added to the slurry before drying.

  The zirconium oxide mixed powder of the present invention is preferably used as a raw material for various sintered bodies in order to enable the production of sintered bodies with little variation in characteristics. That is, the sintered body obtained by sintering the zirconium oxide mixed powder of the present invention at 1700 ° C. or higher, more preferably 1720 to 1770 ° C. has excellent thermal shock resistance and electromotive force stability. It is suitably used for a solid electrolyte element for sensors, a nozzle of a molten steel outlet, and the like.

  When this sintered body is used as an oxygen sensor for molten steel, a Tammann tube shape in which a cylinder is sealed once is preferable. This is because a reference material that keeps the oxygen concentration constant is placed inside. The molded body thus formed and processed is sintered at a temperature of 1700 ° C. or higher, and a solid electrolyte element for an oxygen sensor having excellent thermal shock resistance and electromotive force stability is obtained.

Hereinafter, the present invention will be described specifically by way of examples. The physical property measurement and evaluation of the examples were performed as follows.
(1) AEM analysis method The powder to be measured was a 0.1 wt% dilute aqueous solution, dried on a sample stage, and primary particles were observed at a magnification of 100,000 by FESTEM. Ten primary particles were randomly selected and subjected to EDX element point analysis, and all primary particles containing both Mg and Ca were detected as ◯, and either or both of Mg and Ca were not detected. When there was even one particle, it was set as x.
(2) Presence / absence of cracks in sintered body The sintered body was immersed in a color check solution (penetration liquid FAW-3 manufactured by NOF Corporation) for several minutes, and the presence or absence of cracks in the sintered body was visually determined after washing with water.
(3) Monoclinic rate of sintered body The surface of the sintered body was polished by several mm by # 100 honing, and further subjected to lapping mirror surface treatment using an abrasive. The surface was subjected to X-ray diffraction measurement using CuKα rays with an X-ray diffraction measurement device, and the monoclinic crystal ratio was determined by the following formula. However, the value after correction by the Lorentz factor was used for the diffraction intensity.

Thus, it measured about 10 sintered compacts and calculated | required the average value. As the X-ray diffractometer, CN4037A1, RAD-C system manufactured by Rigaku Denki Co., Ltd. was used.

(4) Thermal shock resistance A solid electrolyte element composed of a sintered body was quickly immersed in molten steel, held for 15 seconds, quickly pulled up, and allowed to cool at room temperature. The temperature of the molten steel was 1500 ° C. in the case of a sample not containing silicon oxide and aluminum oxide, and 1700 ° C. in the case of a sample containing silicon oxide and aluminum oxide. About the element after cooling, the erosion state of iron was confirmed as it was, and then it was immersed in the above-mentioned color check solution and washed with water. Since the color check solution penetrates into the cracked portion, it was visually inspected. Evaluations were made with a sample having three or more microcracks, a sample having up to two sites, and a sample having none at all. In addition, the case where even one crack was so large that iron erosion occurred was marked as x. If 10 are evaluated for each type and there is x even if there is one, the overall evaluation is x. If there is no x, even if there is △, there is a comprehensive evaluation △. .
(5) Stabilization of electromotive force As shown in FIG. 1, a mixture of chromium oxide powder and metal chromium powder, which is a standard substance of oxygen concentration, is used as a reference electrode inside solid electrolyte elements 1 and 2 composed of sintered bodies. The molybdenum metal rod 8 was inserted, and the release port was completely sealed with alumina cement so that air could not enter inside. Further, as a measuring electrode, an Fe bar 5 was penetrated into the molten steel. Two pieces (1, 2) of each electrode connected to the potentiometer 3 and the recorder chart 4 are prepared, and simultaneously immersed in a molten steel 6 at 1500 ° C. adjusted to an oxygen concentration of several to several tens of ppm. The value was measured. This was evaluated 10 times for each type, 20 in total. The electromotive force value changes as the temperature of the solid electrolyte element rises, and becomes stable when the temperature is stabilized. When the difference between the two electromotive forces is 10 mV or less at the time of entering the stable region, the stability of the electromotive force is evaluated as ◯.

  Next, the present invention will be specifically described based on an actual prototype method and the result. However, the present invention is not limited to these examples.

(Example 1)
Zirconium oxide powder having a BET specific surface area of 10 m ² / g in which 0.05 mol% of calcium oxide is dissolved is oxidized with magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 15 m ² / g. Put in a wet media agitation mixer (attritor) so as to be 8.0 mol% magnesium and 1.0 mol% calcium oxide, put water to a concentration of 30 wt%, and mix well to form a slurry. From this slurry, a dry powder was obtained with a disk-type spray dryer. The dried powder was fired at 1000 ° C. to obtain a calcined powder. In addition, cooling from 1000 degreeC to 500 degreeC was performed in 2 hours. To the obtained calcined powder, 0.3% by weight of silicon oxide powder and 1% by mole of aluminum oxide powder were added, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When this sintered compact property was measured, as shown in Table 2, it showed excellent electromotive force stability and thermal shock resistance.

(Example 2)
Zirconium oxide powder having a BET specific surface area of 7 m ² / g in which 1.5 mol% of calcium oxide is solid-solved is oxidized with magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 20 m ² / g. A dry powder was obtained by thoroughly mixing in the same manner as in Example 1 so that the content of magnesium was 7.2 mol%. This dry powder was fired at 1100 ° C. to obtain a calcined powder. The cooling from 1100 ° C. to 500 ° C. was performed in 2 hours. To this calcined powder, 0.2% by weight of silicon oxide powder and 1% by mole of aluminum oxide powder were added, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape to obtain a Tamman tube sintered body similar to Example 1. When this sintered compact property was measured, as shown in Table 2, it showed excellent electromotive force stability and thermal shock resistance.

(Example 3)
Oxidized magnesium oxide powder and calcium oxide powder (purity 99.99%) with a BET specific surface area of 5 m ² / g and zirconium oxide powder with a BET specific surface area of 15 m ² / g in which 0.1 mol% of calcium oxide was dissolved. A dry powder was obtained by thoroughly mixing in the same manner as in Example 1 so that the magnesium content was 9.5 mol% and the calcium oxide content was 0.3 mol%. This dry powder was fired at 950 ° C. to obtain a calcined powder. The cooling from 950 ° C. to 500 ° C. was performed in 2 hours. The calcined powder was wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape to obtain a Tamman tube sintered body similar to Example 1. When this sintered compact property was measured, as shown in Table 2, it showed excellent electromotive force stability and thermal shock resistance.

Example 4
Zirconium oxide powder having a BET specific surface area of 10 m ² / g in which 0.5 mol% of calcium oxide is solid-solved is oxidized with magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 15 m ² / g, respectively. A dry powder was obtained by sufficiently mixing in the same manner as in Example 1 so that the magnesium content was 9.5 mol% and the calcium oxide content was 1.0 mol%. The dried powder was fired at 1050 ° C. to obtain a calcined powder. The cooling from 1050 ° C. to 500 ° C. was performed in 3 hours. The calcined powder was wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape to obtain a Tamman tube sintered body similar to Example 1. When this sintered compact property was measured, as shown in Table 2, it showed excellent electromotive force stability and thermal shock resistance.

(Comparative Example 1)
A zirconium oxide powder having a purity of 99.99% and a BET specific surface area of 9 m ² / g was mixed with magnesium oxide powder and a calcium oxide powder (purity 99.99%) having a BET specific surface area of 15 m ² / g of 9.0 mol of magnesium oxide. %, Put in a wet media agitator (attritor) so that the concentration of calcium oxide is 1.0 mol%, add water to a concentration of 30% by weight, 0.2% by weight of silicon oxide powder, aluminum oxide The powder was added to 1 mol%, wet-mixed and spray-dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, Ca and Mg were not detected. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When this sintered body characteristic was measured, as shown in Table 3, the thermal shock resistance was excellent, but the electromotive force stability varied depending on the sintering temperature.

(Comparative Example 2)
Zirconium oxide powder having a BET specific surface area of 99.99% purity is 20 m ² / g, a magnesium oxide powder having a BET specific surface area of 20 m ² / g magnesium oxide 8.2 mol%, and so as to wet media-agitation type mixer (Attritor), water was added to a concentration of 30% by weight, and mixed well to form a slurry. The slurry was dried with a disk-type spray dryer. The dried powder was fired at 750 ° C. to obtain a calcined powder. The cooling from 750 ° C. to 500 ° C. was performed in 2 hours. To this calcined powder, 0.3% by weight of silicon oxide powder and 1% by mole of aluminum oxide powder were added, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, primary particles in which Ca was not confirmed were present. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When the characteristics of the sintered body were measured, as shown in Table 3, the thermal shock resistance varied depending on the sintering temperature, and the electromotive force stability was poor.

(Comparative Example 3)
Zirconium oxide powder having a BET specific surface area of 4 m ² / g in which 1.0 mol% of calcium oxide is solid-dissolved is oxidized to magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 15 m ² / g, respectively. Put in a wet media agitation mixer (attritor) so that the magnesium content is 8.5 mol%, add water to a concentration of 30% by weight, mix thoroughly to form a slurry, and use this slurry as a disk spray dryer. A dry powder was obtained. The dried powder was fired at 1300 ° C. to obtain a calcined powder. In addition, cooling from 1300 degreeC to 500 degreeC was performed in 4 hours. To this calcined powder, 0.4% by weight of silicon oxide powder and 1% by mole of aluminum oxide powder were added, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When the characteristics of the sintered body were measured, as shown in Table 3, the electromotive force stability and the thermal shock resistance varied depending on the difference in sintering temperature.

(Comparative Example 4)
Zirconium oxide powder having a BET specific surface area of 10 m ² / g in which 0.05 mol% of calcium oxide is dissolved is oxidized with magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 15 m ² / g. Put in a wet media agitation mixer (attritor) so that the concentration of magnesium is 4.0 mol% and calcium oxide is 1.5 mol%, add water to a concentration of 30 wt%, and mix well to form a slurry. From this slurry, a dry powder was obtained with a disk-type spray dryer. The dried powder was fired at 1000 ° C. to obtain a calcined powder. In addition, cooling from 1000 degreeC to 500 degreeC was performed in 2 hours. To this calcined powder, 1% by weight of silicon oxide powder and 3% by mole of aluminum oxide powder were added, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, both Ca and Mg were confirmed. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When the characteristics of the sintered body were measured, as shown in Table 3, the electromotive force stability and the thermal shock resistance were inferior.

(Comparative Example 5)
Zirconium oxide powder having a BET specific surface area of 10 m ² / g in which 0.05 mol% of calcium oxide is dissolved is oxidized with magnesium oxide powder and calcium oxide powder (purity 99.99%) having a BET specific surface area of 5 m ² / g. Put in a wet media stirrer mixer (attritor) so that it will be 13.1 mol% magnesium and 1.0 mol% calcium oxide, put water to a concentration of 30 wt%, mix well to make a slurry, From this slurry, a dry powder was obtained with a disk-type spray dryer. This dry powder was fired at 1100 ° C. to obtain a calcined powder. The cooling from 1100 ° C. to 500 ° C. was performed in 3 hours. To this calcined powder, silicon oxide powder was added to 0.3% by weight, wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, some primary particles in which Mg was not confirmed were present. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When the characteristics of the sintered body were measured, as shown in Table 3, the thermal shock resistance varied depending on the sintering temperature, and the thermal shock resistance was inferior.

(Comparative Example 6)
A zirconium oxide powder having a purity of 99.99% and a BET specific surface area of 15 m ² / g is mixed with magnesium oxide powder and a calcium oxide powder (purity 99.99%) having a BET specific surface area of 10 m ² / g of 8.0 mol of magnesium oxide. %, Calcium oxide 3.0 mol% in a wet media stirring type mixer (attritor), water is added to a concentration of 30% by weight, mixed well to make a slurry, this slurry is a disk type Dry powder was obtained with a spray dryer. The dried powder was fired at 1000 ° C. to obtain a calcined powder. In addition, cooling from 1000 degreeC to 500 degreeC was performed in 2 hours. The calcined powder was wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, primary particles in which Ca was not confirmed were present. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When the characteristics of the sintered body were measured, as shown in Table 3, the thermal shock resistance varied depending on the sintering temperature, and the thermal shock resistance was inferior.

(Comparative Example 7)
A zirconium oxide powder having a BET specific surface area of 10 m ² / g in which magnesium oxide was dissolved by a coprecipitation method was prepared. Calcium oxide powder (purity 99.99%) was added to this powder so that it might become 1.0 mol% with respect to a zirconium oxide, and it wet-mixed to make a slurry, and this slurry was dried powder with a disk type spray dryer. Got. The dried powder was fired at 900 ° C. to obtain a calcined powder. The cooling from 900 ° C. to 500 ° C. was performed in 2 hours. The calcined powder was wet pulverized and dried to obtain a powder. Table 1 shows the physical properties of the obtained powder. When this powder was subjected to EDX element point analysis using FESTEM, primary particles in which Ca was not confirmed were present. This powder was formed into a Tamman tube shape and sintered at 1740 ° C., 1750 ° C., and 1760 ° C. in a small electric furnace (Kantal super furnace) to obtain a Tamman tube sintered body having a thickness of 0.8 mm. . When this sintered compact characteristic was measured, as shown in Table 3, the electromotive force stability and the thermal shock resistance were inferior.

It is an electric circuit schematic diagram for electromotive force stability measurement.

Explanation of symbols

1: Solid electrolyte 1
2: Solid electrolyte 2
3: Potential meter 4: Recorder chart 5: Measuring electrode (Fe bar)
6: Molten steel 7: Reference material 8: Molybdenum metal rod

Claims (6)

  6-12 mol% magnesium oxide, 0.1-2 mol% calcium oxide, a part of the magnesium oxide and a part of the calcium oxide are in solid solution, and the monoclinic crystal ratio is 70-99%. A certain zirconium oxide mixed powder.   2. The zirconium oxide mixed powder according to claim 1, wherein the particles have an average secondary aggregation diameter of 0.3 to 2 μm when formed into a slurry by water dispersion. The zirconium oxide mixed powder according to claim 1 or 2, wherein the BET specific surface area is 5 to 16 m ² / g.   A method for producing a zirconium oxide mixed powder in which a zirconium oxide powder, a magnesium oxide powder and a calcium oxide powder in which 0.04 to 2 mol% of calcium oxide is dissolved are mixed and heat-treated at 900 to 1100 ° C. in the atmosphere.   Zirconium oxide powder, magnesium oxide powder and calcium oxide powder in which 0.04 to 2 mol% of calcium oxide is solid-dissolved are mixed so that calcium oxide is 0.1 to 2 mol% and magnesium oxide is 6 to 12 mol%. The method for producing a zirconium oxide mixed powder according to claim 4. The BET specific surface area of the zirconium oxide powder in which 0.04 to 2 mol% of calcium oxide is solid-dissolved is 5 m ² / g or more, and the BET specific surface area of the magnesium oxide powder is 14 m ² / g or more. Method for producing a zirconium oxide mixed powder.

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