JP4320852B2 - Hydrated zirconia dry powder, production method thereof and use thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrated zirconia dry powder. By calcining this dry powder, functional ceramics such as solid electrolytes for fuel cells, oxygen sensors, NOx sensors, thermal barrier coating materials, and structural ceramics such as pulverizer members, precision machine parts, optical connector parts, etc. A fine zirconia powder having excellent moldability and excellent sinterability can be produced.
[0002]
Here, in the present specification, “hydrated zirconia” refers to what is called zirconium hydroxide, crystalline hydrated zirconia, amorphous hydrated zirconia, or the like.
[0003]
[Prior art]
Conventionally, as a method for producing fine zirconia powder, an aqueous solution of zirconium salt or an aqueous solution in which a stabilizer is dissolved in a zirconium salt aqueous solution is heated and hydrolyzed, and the resulting hydrated zirconia sol is dried and calcined. Methods for obtaining fine powder are widely known.
[0004]
Also known is a method of obtaining a zirconia powder by washing and concentrating a zirconia sol obtained by heat hydrolysis with an ultrafiltration membrane and then drying and calcining the concentrated sol of hydrated zirconia obtained.
[0005]
[Problems to be solved by the invention]
However, with a zirconia powder obtained by merely hydrolyzing an aqueous solution of a zirconium salt, when a sintered body is formed by molding and sintering, a sufficient sintered body density cannot be obtained. The mechanical strength was also significantly reduced, and it was not a satisfactory powder for use in the aforementioned ceramic applications.
[0006]
On the other hand, a zirconia powder obtained by using a zirconia sol washed and concentrated by an ultrafiltration membrane is a powder that is relatively excellent in sinterability, but has a low light bulk density. When producing a sintered body by molding, a large mold is required, the molding pressure must be increased, and the shrinkage rate during sintering also increases, so cracking during sintering, etc. There is a problem that it is easy to occur. In addition, when used for injection molding by kneading with an organic binder, the fluidity of the kneaded product with this binder is poor, the releasability from the mold is also poor, and there is a problem that injection molding cannot be performed well. . Thus, in the conventional method, a powder that is sufficiently satisfactory in terms of both formability and sinterability applied to the above-described ceramics application has not been obtained.
[0007]
Then, the objective of this invention is providing the hydrated zirconia dry powder which can manufacture the zirconia powder which can be satisfied in both moldability and sinterability, and its manufacturing method.
[0008]
[Means for solving the problems]
As a result of intensive investigations, the present inventors have focused on the relationship between the moldability and sinterability of dry powder of hydrated zirconia and the zirconia fine powder obtained by calcining the zirconia powder. It has been found that the above problem can be solved by setting the true bulk density of the dried zirconia powder to 1.00 to 1.40 g / cm ³ , and the present invention has been achieved. Here, the true bulk density of the dry powder is defined as A × {when the dry weight density of the dry powder is Ag / cm ³ , and the volatile content when the dry powder is calcined at 1000 ° C. is B wt%. 1- (B / 100)} refers to the bulk density.
[0009]
Hereinafter, the present invention will be described in detail.
[0010]
In the present invention, in the hydrous zirconia dry powder, 1.00～1.40G the true bulk density of the dry powder / cm ^3, and more preferably, unless the 1.10~1.30g / cm ³ Don't be. This is because when the true bulk density of the dry powder is lower than this range, the bulk density of the zirconia powder obtained by firing the dry powder becomes small, and when producing ceramics by casting molding and press molding. This is because a large mold is required, the molding pressure must be increased, and the shrinkage rate during sintering increases, so that there is a problem that cracks are likely to occur during sintering. In addition, in the case of injection molding, the fluidity of the kneaded material with the binder is remarkably lowered, and injection molding cannot be performed well.
[0011]
On the other hand, if the true bulk density is higher than the above range, the bulk density of the zirconia powder obtained therefrom will be high, but when this is molded and sintered, a sufficient sintered body density cannot be obtained. In addition, the mechanical strength of the sintered body is also lowered.
[0012]
In the present invention, what is particularly important is not only defined for the light bulk density of the dried powder of hydrated zirconia but also for the true bulk density considering the amount of volatile matter. It is. The relationship between the true bulk density of hydrated zirconia dry powder and the moldability and sinterability of zirconia powder is not clear. It is considered that the true bulk density obtained by subtracting the effect of adhesion represents the substantial structure between the particles of the hydrated zirconia dry powder, and as a result, the true bulk density contributes to formability and sinterability. It is presumed to have a large influence.
[0013]
Here, the method for producing the hydrated zirconia dry powder of the present invention will be described in detail.
[0014]
First, a hydrated zirconia sol is obtained by heat hydrolysis of an aqueous zirconium salt solution. At this time, the method of heat hydrolysis is not limited, but the following methods are preferable from the viewpoint of productivity and operability. That is, a part of the solution containing the zirconia sol obtained by hydrolysis of the zirconium salt aqueous solution is continuously and / or intermittently discharged from the reaction tank, and the volume of the solution containing the zirconia sol is kept constant. As described above, it is a method of obtaining a zirconia sol by continuously and / or intermittently supplying an aqueous zirconium salt solution in the same amount as the amount discharged. Here, “continuous” means that the zirconia sol is withdrawn from the reaction vessel at a constant discharge rate, and at the same time, an aqueous zirconium salt solution adjusted to a predetermined concentration at the same supply rate as the discharge rate is supplied into the reaction vessel. , "Intermittent" means that a certain amount of zirconia sol (hereinafter referred to as "supply ratio (vol.%)") Is expressed as a ratio between the amount of liquid supplied and the amount of liquid in the reaction vessel. Immediately after extraction from the tank, the same amount of zirconium salt aqueous solution as the amount discharged is added to the reaction tank and hydrolyzed for a predetermined time (hereinafter referred to as “intermittent time”), and this series of operations is repeated.
[0015]
In this way, by carrying out heat hydrolysis, a hydrated zirconia sol having excellent productivity and high conversion can be easily obtained. Examples of the zirconium salt used in the production of the zirconia sol used in the present invention include zirconium oxychloride, zirconium nitrate, zirconium chloride, and zirconium sulfate. In addition to this, a mixture of zirconium hydroxide and acid can be used. It may be used.
[0016]
In the present invention, the zirconia sol obtained by the above method is subjected to filtration washing and concentration by ultrafiltration. The ultrafiltration membrane preferably has a fractional molecular weight of 500 to 3,000,000. When the molecular weight cut off is less than 500, the filtration rate is remarkably lowered and the filtration efficiency is lowered. On the other hand, if the molecular weight cut off exceeds 3,000,000, the sol particles are poorly captured and the yield is lowered, and the strength as an ultrafiltration membrane is also lowered. As the type of the ultrafiltration membrane module to be used, any of a planar membrane module, a tubular membrane module, a spiral module, and a capillary membrane module can be used, but the filtration area is wide and the filtration efficiency is good. Therefore, a capillary membrane module is desirable.
[0017]
As the ultrafiltration method, a circulation method in which zirconia sol is filtered by circulating it through a membrane module by a pump and the filtrate is discharged is preferable. At this time, impurities in the zirconia sol can be efficiently removed by adding pure water. Also, a basic solution such as sodium hydroxide or ammonia can be added during filtration and washing. By performing only filtration without adding pure water, it can be concentrated to a desired concentration. By carrying out washing in this manner, the dispersibility of the concentrated liquid is improved. As a final concentrated liquid, a zirconia concentrated sol having a high zirconia concentration of 20 to 50% by weight and a high purity and a high dispersibility is obtained. Obtainable.
Since it can be concentrated to a high concentration in this way, a significant improvement in productivity can be expected in the subsequent drying step.
[0018]
In the present invention, it is particularly important to add a zirconium salt aqueous solution to the zirconia concentrated sol thus obtained in order to control the bulk density of the dry powder. Examples of the zirconium salt used here include zirconium oxychloride, zirconium nitrate, zirconium chloride, and zirconium sulfate, but are not particularly limited. Further, the zirconium salt aqueous solution is preferably added in an amount of 3 to 25% by weight in terms of zirconia with respect to the zirconia component in the concentrated sol. When the addition amount is less than this range, the bulk density is not sufficiently increased, and the effect on moldability is small. Further, if the amount added is more than this range, the aggregated particles increase and the sinterability decreases.
[0019]
Next, for example, a salt such as Y, Ca, Mg, or Ce, a hydroxide, or an oxide as a stabilizer is added to the zirconia concentrated sol in a solid, aqueous solution, or slurry state, and the mixture is stirred and mixed.
[0020]
The drying method of the zirconia concentrated sol thus obtained is not limited, and examples thereof include spray drying, a method of adding an organic solvent and drying, and spray drying is preferable from the viewpoint of productivity. The shape of the dry powder obtained by spray drying is preferably spherical. This is because the true light bulk density of the dry powder becomes 1.00 or more by making it spherical. In order to obtain a spherical dry powder, it is important to adjust the pH to 2.0 or less after mixing the stabilizer and the zirconium salt. When pH becomes higher than 2.0, the shape of the obtained dry powder becomes a depressed sphere, and the true bulk density becomes lower than 1.00. Thus, in order to make pH into 2.0 or less, if acids, such as hydrochloric acid, a sulfuric acid, and nitric acid, are added, it can adjust easily.
[0021]
By the method described above, a dried powder of hydrated zirconia having a true bulk density in the range of 1.00 to 1.40 g / cm ³ can be obtained.
[0022]
Hereinafter, a method of obtaining zirconia fine powder using this hydrated zirconia dry powder will be described in detail.
[0023]
In the present invention, the dried hydrated zirconia powder is calcined. The calcining temperature at this time is preferably in the range of 300 to 1300 ° C. When the calcining temperature is lower than 300 ° C., it becomes difficult to obtain a zirconia powder sufficiently dissolved in the stabilizer. On the other hand, when the temperature is higher than 1300 ° C., the particles are dispersed due to strong aggregation due to sintering between particles. It becomes difficult to obtain a good zirconia powder. More preferably, it is 400-1200 degreeC. The holding time for calcination is preferably 0.5 to 10 hours, and the heating rate is preferably 0.5 to 10 ° C./min. If the holding time at the time of calcination is less than 0.5 hours, it is difficult to uniformly calcinate, and if it is longer than 10 hours, the productivity is lowered, which is not preferable. In addition, when the rate of temperature rise is less than 0.5 ° C / min, the time until the set temperature is reached becomes longer, and when it is greater than 10 ° C / min, the powder scatters vigorously during calcination, resulting in poor operability. Productivity decreases. Since the calcined powder obtained as described above hardly causes strong aggregation between particles, it becomes a finely dispersible zirconia powder simply by grinding. Moreover, you may add an alumina etc. as a sintering auxiliary agent as needed at the time of a grinding | pulverization. In the zirconia fine powder thus obtained, the sintering aid is uniformly dispersed, and a zirconia sintered body in which the sintering aid is uniformly solidified during sintering can be easily obtained.
[0024]
【The invention's effect】
As described above, by using the hydrated zirconia dry powder of the present invention, it becomes possible to produce a zirconia fine powder excellent in both formability and sinterability suitable for ceramics applications.
[0025]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
[0026]
Example 1
An aqueous solution having a ZrOCl ₂ concentration of 0.3 mol / liter was boiled under reflux and hydrolyzed for 200 hours to prepare a zirconia sol. This solution was used as a starting solution, boiled under reflux, and an intermittent operation type hydrolysis reaction was performed. The intermittent condition was set such that the supply ratio was 5% and the intermittent time was 0.5 hour. 100 liters of zirconia sol extracted from the reaction vessel was recovered after 100 hours had elapsed from the start. Subsequently, concentration was performed with a filtration apparatus in which an ultrafiltration ultrafiltration membrane module (fractionated molecular weight 6,000, total filtration area 0.1 m ² , capillary membrane module) was set. In the filtration method, first, zirconia sol was filtered by circulating it through a membrane module with a pump, and concentrated to 20 liters. Next, 5 mol% of a 2.5 mol / liter zirconium oxychloride aqueous solution was added to the concentrated zirconia sol in terms of zirconia, and 3 mol% of yttrium chloride in terms of Y ₂ O _{3 was} further added. The pH of the solution at this time was 0.50. The mixed solution was spray dried at an inlet temperature of 170 ° C. and an outlet temperature of 90 ° C. to obtain a dry powder. When this dry powder was observed by SEM, there was no depressed sphere and it was a completely spherical dry powder. At this time, the light weight bulk density was 1.50 g / cm ³ , the volatile content when calcined at 1000 ° C. was 23.6% by weight, and the true light weight bulk density was 1.14 g / cm ³ . The dried powder was calcined at 1050 ° C. for 2 hours, washed with water and pulverized.
[0027]
The obtained zirconia fine powder was molded by a mold press at a molding pressure of 700 kgf / cm ² , and the compact density was 2.60 g / cm ³ . Further, when the obtained molded body was sintered at 1500 ° C. for 2 hours, the sintered body density was 6.06 g / cm ³ and the bending strength was 135 kgf / mm ² .
[0028]
Further, after kneading 1500 g of this zirconia powder and 300 g of an acrylic binder with a kneader at 140 ° C. for 1 hour, the fluidity of this kneaded product was evaluated by the melt index method, and the result was 175 g / 10 min.
[0029]
The above results are shown in Table 1.
[0030]
The MI value in Table 1 indicates an evaluation value by the melt index method.
[0031]
When this kneaded product was actually used in an injection mold, it was possible to mold without problems with regard to fluidity, and there was no problem with respect to release from the mold.
[0032]
Examples 2-4
The same procedure as in Example 1 was performed except that the amount of zirconium oxychloride added as a zirconium salt aqueous solution was 8, 10, and 20% by weight in terms of zirconia was added to the concentrated sol. The obtained results are shown in Table 1.
[0033]
Comparative Example 1
The same procedure as in Example 1 was performed except that only yttria was added to the concentrated sol.
[0034]
The results are shown in Table 1. Further, when the kneaded material prepared with the acrylic binder was used and actually used in an injection mold, the fluidity of the kneaded material was poor and injection molding could not be performed.
[0035]
Comparative Example 2
This was performed in the same manner as in Example 1 except that the zirconium oxychloride was added in an amount of 30% by weight in terms of zirconia as an aqueous zirconium salt solution to the concentrated sol. The results are shown in Table 1.
[0036]
Comparative Example 3
An aqueous solution having a ZrOCl ₂ concentration of 0.4 mol / liter was hydrolyzed for 100 hours at the boiling temperature under reflux. Yttrium chloride was added to this zirconia sol (in terms of Y ₂ O ₃ , 3 mol%) and spray-dried to obtain a dry powder. The dried powder was calcined at 1050 ° C. for 2 hours, washed with water and pulverized. Molding the resultant fine zirconia powder in Example under the same conditions, was then sintered, the molded body density was 2.55 g / cm ^3, the sintered density of 5.95 g / cm ^3, flexural strength 77kgf / Mm ² . The results are shown in Table 1.
[0037]
[Table 1]

Claims (4)

When the dry bulk density of the hydrated zirconia powder is Ag / cm ³ and the volatile content when the dry powder is calcined at 1000 ° C. is B wt%, it is expressed as A × {1- (B / 100)}. Ri true range near the bulk density 1.00~1.40g / cm ³ that is, to include the Y, Ca, an oxide of at least one element selected from the group consisting of Mg and Ce as a stabilizer Hydrated zirconia dry powder characterized by. After washing and concentrating the hydrous zirconia sol obtained by thermal hydrolysis of a zirconium salt aqueous solution by ultrafiltration, adding a zirconium salt aqueous solution to the hydrated zirconia sol, subsequently, as a stabilizer, Y, 2. The method according to claim 1, wherein a salt, hydroxide or oxide of at least one element selected from the group consisting of Ca, Mg and Ce is added in the form of a solid, an aqueous solution or a slurry and then dried. The manufacturing method of hydrated zirconia dry powder as described in any one of. The method of manufacturing a hydrated zirconia dry powder according to paragraph 2 claims, the production of a hydrated zirconia dry powder aqueous solution of zirconium added to the hydrated zirconia A sol, characterized in that an aqueous solution of zirconium oxychloride Method. A zirconia fine powder is produced by calcining a hydrated zirconia dry powder containing an oxide of at least one element selected from the group consisting of Y, Ca, Mg and Ce as a stabilizer according to claim 1 how to.