JPS6143286B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a colloidal sol of crystalline zirconia, characterized in that most of the zirconium contained is monoclinic zirconia with crystallites of 30 to 100 Å, and the average size of secondary agglomerated particles does not exceed 500 Å, and a method for producing the same. Zirconia here refers to not only pure ZrO ₂ but also HfO ₂ of less than 10%, which is generally called zirconia industrially, and up to several % of HfO 2 .
It refers to zirconia in a broad sense, including Y ₂ O ₃ and those containing other stabilizers and impurities. Conventionally, a zirconium salt aqueous solution is heated under hydrothermal pressure.
A method for obtaining a zirconia hydrosol by heat treatment at 120 to 300°C is known (US Pat. No. 2,984,628), and it is also known that a zirconia fine particle suspension can be obtained by boiling an aqueous zirconium salt solution for a long time. There is [A. Clear Field; Inorganic Chemistry Volume 3
146 pages 1964, (A. Clearfield; Inorg. Chem. 3146
(1964)]. However, the former requires a considerable amount of time under high pressure and high temperature, and the latter requires an even longer heat treatment time, which is not only inefficient and unsuitable for industrial mass production, but also produces particles. The characteristics of the former are not satisfactory, and the size of the secondary agglomerated particles usually exceeds 1000 Å, and especially in the former, the size of the secondary particles is non-uniform, so that it has hardly been applied industrially. Through basic research, the present inventor established for the first time a method for quantitatively determining the degree of progress of the zirconia fine particle production reaction, and as a result of repeating a large number of experiments using this method under various conditions, We have finally discovered the reaction acceleration effect and ultrafine particle formation effect of hydrogen peroxide. A zirconium salt, for example, a 0.2 mol/aqueous solution of zirconyl chloride, is added in a flask equipped with a reflux condenser.
After boiling for about 100 hours, the zirconium in the solution almost completely turns into monoclinic zirconia crystals.
After separation and drying, there is almost no change even after heat treatment at 400°C in vacuum, and X-rays show only a monoclinic shape. In addition, aqueous ammonia is added to an aqueous zirconium salt solution, and the resulting hydroxide precipitate is dehydrated under reduced pressure.
The material heat-treated at 400°C has crystallized into square-shaped zirconia according to X-rays. Therefore, if ammonia is added to a suspension in the reaction process that has been heat-treated for a certain period of time, the resulting precipitate is carefully dried under reduced pressure, and heat-treated at 400°C in vacuum, a mixture of monoclinic zirconia and square zirconia can be obtained. and its quantitative ratio is
It can be easily determined by line diffraction, and is an accurate measure of the progress of the zirconia production reaction in solution. Comparison of experimental results using this method yields results that are significantly different from simply comparing the degree of cloudiness. for example
When 300 c.c. of a 0.2 mol/concentration zirconyl chloride aqueous solution is boiled for about 20 hours in a flask equipped with a reflux condenser, the solution becomes completely cloudy, but the amount of zirconia fine particles produced is about 10% of the total zirconia. On the other hand, using the method of the present invention, a zirconyl chloride aqueous solution of the same 0.2 mol/concentration was preliminarily changed from Cl ^- to OH ^- to 2.0 using an anion exchange resin, and then hydrogen peroxide was added. Water (30
%) When a solution made to 300 c.c. by adding 10 c.c. was boiled for 20 hours in the same flask, the solution became a thin emulsified sol, but the amount of zirconia fine particles produced was 100%. indicates that the production reaction has already been completed. This shows that the method of the present invention significantly accelerates the reaction for producing crystalline zirconia by hydrolysis, and that the product zirconia is extremely fine ultrafine particles. As described above, the present invention has extremely high economic value due to the advantages in industrial production due to promotion of the zirconia production reaction and high efficiency, and the advantages in characteristics based on the ultrafine particle nature of the monoclinic zirconia produced. However, this is all due to the addition of hydrogen peroxide to the starting aqueous zirconium salt solution during production. That is, in the present invention, most of the zirconium contained is monoclinic zirconia with crystallites of 30 to 100 Å,
This invention relates to a colloidal sol of crystalline zirconia, characterized in that the average diameter of secondary agglomerated particles does not exceed 500 Å. Furthermore, as for its production method, the concentration
Hydrogen peroxide or a compound that generates hydrogen peroxide is added to a 0.05 to 2.0 mole/aqueous solution of zirconium salt, and the solution is heated to 80 to 300°C to crystallize zirconia in a monoclinic form in the aqueous solution. In addition, an aqueous zirconium salt solution with a concentration of 0.05 to 2.0 mol/mole is prepared to a pH of 1 to 3, hydrogen peroxide or a compound that generates hydrogen peroxide is added, and this solution is heated to 80 to 300°C. It is characterized by crystallizing zirconia in a monoclinic form in an aqueous solution. In the method of the present invention, if the concentration of the zirconium salt solution is less than 0.05 mol/L, the efficiency is too low, and if it is 2.0 mol/L or more, the operation becomes extremely difficult.
The practical concentration range is within 2.0 mol/, and 0.2~
A more preferred concentration range is 1.0 mol/. By preparing the zirconium salt aqueous solution to a pH of 1 to 3, there is an effect that the hydrolysis reaction is further accelerated compared to when the pH is not adjusted, as will be described below. The detailed progress of crystalline zirconia formation by hydrolysis was compared under various conditions.
As shown in the figure. Figure 1 shows the change over time when 300 c.c. of a zirconyl chloride aqueous solution with a concentration of 0.2 mol/cm is continuously boiled in a flask equipped with a reflux condenser. This is the molar ratio of the amount of produced monoclinic zirconia fine particles to the amount of zirconium. This analysis method was performed as described above. In addition, the numbers attached to each curve in the figure indicate the conditions of the solution at the time of starting (before boiling), the PH value of the solution prepared with anion exchange resin and the amount of hydrogen peroxide (31%) added (cc ). As is clear from the figure, when simply heating a zirconyl chloride aqueous solution using the conventional method (black circles in the figure), continuous boiling for as long as 60 hours is required to complete the zirconia fine particle production reaction. However, the addition of hydrogen peroxide (0.2M, H ₂ O ₂ -10), which is the method of the present invention (white circle in the figure), has a remarkable effect of accelerating the reaction, and furthermore, the pH can be adjusted to 2.0 using an anion exchange resin. , and by adding hydrogen peroxide (0.2M, PH2, H ₂ O ₂ -10), it can be seen that the time to complete the production reaction is shortened to about 1/3. The following table compares the amount of hydrogen peroxide added and the amount of monoclinic zirconia fine particles produced after 20 hours of boiling in an experiment similar to that shown in Figure 1, and shows that even with the addition of a small amount of hydrogen peroxide, a clear reaction was already observed. A promoting effect is observed, but the maximum promoting effect appears when hydrogen peroxide is added in an equimolar ratio (1:1) to the molar ratio of zirconia in the solution, and a molar ratio of about 1/2 or more is practical. Show that something is true. Also, sodium peroxide, magnesium peroxide, etc., which generate hydrogen peroxide in solution, have a similar promoting effect.

[Table] Furthermore, Fig. 2 shows the effect of the present invention when the concentration of zirconyl chloride is high, and is an example in which aqueous ammonia is added to adjust the pH of the solution. Similar to Figure 1, the diagram shows ammonia water (28
%) solution (cc). The effect of the present invention becomes even more remarkable as the concentration of zirconyl chloride in the aqueous solution increases.If the solution is simply boiled at 0.5 mol/ml, a small amount of zirconia begins to be produced after 40 hours or more; However, by adding hydrogen peroxide and ammonia, ultrafine particles of monoclinic crystal zirconia are produced in a relatively short time even from a highly concentrated solution. The figure shows the molar ratio of the amount of zirconium contained in the solution to the amount of zirconia that is formed and crystallized, so it can be seen how the higher the concentration, the higher the efficiency. The heat treatment in the method of the present invention does not necessarily require boiling. The present invention is effective even at temperatures below 100°C, and exhibits similar effects even during high-temperature treatment in a pressurized atmosphere. The practical temperature range for this treatment is 80 to 300°C, depending on the production rate and equipment. Figure 3 shows the effect of the present invention at temperatures above 100°C, with 0.2 mol/
This is the result of maintaining a zirconyl chloride solution at 130°C under steam pressure. In this case as well, a transparent liquid that has been boiled for 1 hour after adding hydrogen peroxide in advance exhibits a production rate that is more than twice as high as that of a solution without the addition of hydrogen peroxide. The monoclinic crystalline zirconia ultrafine particles produced by the present invention all have crystallite diameters of 30 to 100 Å determined from the half width of powder X-ray diffraction peaks, which are almost the same as those obtained by simply boiling the solution or hydrothermally treating the solution at low temperatures. However, according to electron microscopic observation, there is a significant difference in the size of the secondary agglomerated particles. That is, normally, when the zirconia production reaction is completed, the diameter of the secondary agglomerated particles is 1000 Å or more, which forms a strong bond that cannot be easily split.
The size of the secondary agglomerated particles is less than 500 Å even at the completion of the reaction. Although the nature of the action of hydrogen peroxide in the present invention is not necessarily clear, it is essential for the miniaturization of the secondary agglomerated particles of zirconia that is produced, and therefore hydrogen peroxide has an effect on crystal nucleation rather than crystal growth. It is believed that there is. Furthermore, since ammonia or PH adjustment does not directly contribute to the miniaturization of secondary agglomerated particles, it is thought that they are effective in promoting crystal growth rather than nucleation. In any case, the method of the present invention improves the efficiency of producing monoclinic zirconia fine particles and makes the product ultrafine. That is, it enables industrial mass production of monoclinic crystalline zirconia ultrafine particles and improves the quality of applied products by making the ultrafine particles. The sol made of ultrafine crystalline zirconia particles obtained by the present invention has extremely fine secondary agglomerated particles, so it has high stability and high quality, and can be applied as a matting agent for synthetic fibers, a heat-resistant coating agent, etc. In this case, it can exhibit several times the coating properties at the same zirconia concentration compared to conventional products. Furthermore, if a base such as ammonia is added to this sol to cause the suspended particles to coagulate and settle, and the water is replaced with a polar solvent such as alcohol or acetone and dried, a fine powder consisting of isolated ultrafine particles of crystalline zirconia can be obtained. This is unique in that it is easier to sinter than any conventionally obtained zirconia powder. For example, this powder compact provides a high-purity zirconia sintered body consisting only of monoclinic crystals with almost theoretical density at a low temperature of 1100°C. This has conventionally been obtained only by hot pressing or a special method under hydrothermal heat. In addition, the sol of the present invention and the powder obtained from the sol have extremely fine secondary agglomerated particles, so they have excellent miscibility with other powders, and when used as raw materials for solid reactions such as the production of lead zirconate, the contact area As a result of this increase, it has extremely high reactivity and low-temperature sintering properties, and has the highest dispersibility among other ceramic additives, making it possible to uniformly add small amounts. Figures 1, 2, 3 and the table are examples showing that the method of the present invention is extremely superior in the production rate and efficiency of crystalline zirconia fine particles compared to the conventional method. Specific examples of the crystalline zirconia colloidal sol of the present invention and the fine powder obtained therefrom will be shown below. Example 1 Special grade reagent zirconyl chloride (ZrOCl ₂ 8H ₂ O) approx. 20
Dissolve g in about 300 c.c. of distilled water to make a solution of about 0.2 mol/g, and add anion exchange resin (Amberlite IR
-45) to adjust the pH of the solution to 2.0, add 10 c.c. of hydrogen peroxide (31%), and boil this solution for 20 hours in a flask with a reflux condenser to form a translucent emulsion. Obtained a sol. According to powder X-ray diffraction, the suspended particles had crystallites of about 50 Å, and according to electron microscope observation, the suspended particles were secondary particles of agglomerated crystallites and had an average size of 300 Å. Example 2 Special grade reagent zirconyl chloride (ZrOCl ₂ 8H ₂ O) 97g
Dissolve it in about 300 c.c. of distilled water to make a solution of about 1.0 mol/c., add 90 c.c. of hydrogen peroxide (31%) and stir, and then add 30 c.c. of aqueous ammonia (28%). was gradually added, and this solution was boiled for 50 hours in a flask equipped with a reflux condenser to obtain a translucent emulsion sol. When aqueous ammonia was added to this sol, the suspended particles coagulated and settled, so the sol was decanted, the water replaced with acetone, filtered, and dried. According to observation using an optical microscope and an electron microscope, the relatively large aggregated particles of this powder are easily broken due to physical adhesion, and the size of the strong secondary aggregated particles is 500 mm.
It is observed that the particle size is less than Å and the particle size is almost uniform. This powder was dried and molded into a 16 mm diameter disc in a mold at a molding pressure of 2 t/cm ² , and then fired in air at 1100°C for 1 hour.
A highly pure, dense polycrystalline body consisting only of monoclinic crystals with a bulk density of 96% was obtained.

[Brief explanation of the drawing]

FIG. 1 shows changes in boiling time and production rate of monoclinic ZrO ₂ in the method of the present invention and the conventional method. FIG. 2 shows the changes in boiling time and production rate of monoclinic ZrO ₂ in the method of the present invention and the conventional method when the zirconium salt concentration is changed. FIG. 3 shows changes in boiling time and production rate of monoclinic ZrO ₂ in the method of the present invention and the conventional method under hydrothermal conditions. In each case, white circles indicate the method of the present invention, and black circles indicate the conventional method.

Claims (1)

[Claims] 1 Most of the zirconium contained is crystallite 30
A colloidal sol of crystalline zirconia, which is monoclinic zirconia with a diameter of ~100 Å, and the average diameter of its secondary agglomerated particles does not exceed 500 Å. 2 Add hydrogen peroxide or a compound that generates hydrogen peroxide to a zirconium salt aqueous solution with a concentration of 0.05 to 2.0 mol/h, heat the solution to 80 to 300°C, and crystallize zirconia in a monoclinic form in the aqueous solution. A method for producing a colloidal sol of crystalline zirconia, the method comprising: 3 Prepare a zirconium salt aqueous solution with a concentration of 0.05 to 2.0 mol/pH to 1 to 3, add hydrogen peroxide or a compound that generates hydrogen peroxide, and heat the solution to 80 to 300°C to form zirconia in the aqueous solution. A method for producing a colloidal sol of crystalline zirconia, characterized by crystallizing it into a monoclinic form.