JPH0355414B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a highly pure zirconia sol and a method for producing zirconia fine powder with excellent dispersibility using the same. Zirconia has three types of crystal structures: monoclinic, tetragonal, and cubic, and has properties not found in other materials, such as corrosion resistance, toughness, and oxygen ion conductivity. It is predicted that it will become increasingly important as a material in the future, with applications in a variety of applications such as sensors, electronic components, various structural materials, and biomaterials. And as the present invention provides,
High-purity zirconia sol and fine powder with excellent dispersibility can be used for the following purposes. That is, the sol or fine powder provided by the present invention is dispersed in ceramics or metals and used for reinforced ceramics or dispersion-strengthened alloys, and furthermore, the sol or fine powder provided by the present invention is dispersed in base materials such as glass, plastic molded products, sheets, films, etc. Alternatively, a coating film containing a sol or fine powder as provided by the present invention is formed on the above substrate, and the substrate has properties such as heat resistance, reaction prevention, conductivity, ultraviolet absorption, hardness, and chemical resistance.
Used to add or improve functions such as durability. In particular, when these colloidal sols and fine powders are applied to transparent substrates, there is an advantage that the above functions can be improved without impairing the transparency of the substrate. [Prior Art] As a method for producing zirconia sol from an aqueous zirconium salt solution, a precipitate produced by a reaction between an aqueous zirconium salt solution and a basic substance is peptized with an acid, or an aqueous zirconium salt solution is injected with a base. A known method is to generate a sol by injecting and mixing a chemical substance to a pH level that does not cause precipitation. Furthermore, a method is known in which a zirconia-based colloidal sol is obtained by heating and hydrolyzing an aqueous solution containing a zirconium salt under normal pressure or increased pressure. [Problems to be solved by the invention] However, when using the sol or colloidal sol produced by the above method, it is necessary to remove anions and unreacted metal ions from the sol solution obtained after the reaction. becomes. Known methods for cleaning this sol include diffusion dialysis or electrodialysis using a semipermeable membrane, and methods using ion exchange resins, but these methods require a long time for cleaning or require a long cleaning operation. The disadvantage is that it is complicated. Recent advances in ultrafiltration technology have made it possible to wash sol more easily and efficiently than the above methods. However, when the zirconia sol was cleaned using pure water in this method, a phenomenon was observed in which the cleaning effect decreased as the sol was cleaned. This seems to be because some kind of affinity exists between the sol particles and the ions, and the ions that should be washed away remain strongly attached to the sol particles. Thus, in the present invention, when cleaning zirconia sol using an ultrafiltration membrane, by adding a basic substance to prevent sol aggregation, the above-mentioned affinity is destroyed, the cleaning efficiency is increased, and the ion concentration in the sol is extremely increased. In this way, the aim is to produce a zirconia sol with high purity and high storage stability. [Means] A zirconia sol is prepared from an aqueous solution of a zirconium salt selected from water-soluble zirconium salts such as zirconyl chloride, zirconyl nitrate, zirconyl sulfate, or zirconyl organic acids such as zirconyl acetate. Conventionally known methods are used to produce this sol, and the above-mentioned acid peptization method, base addition method, and thermal hydrolysis method are appropriately used. Thereafter, this sol solution is introduced into an ultrafiltration device and washed. It is preferable to use a circulation type filtration device because it reduces membrane clogging, and the solvent containing anions and metal ions is discharged from the system, and the concentrated colloidal sol solution is continuously washed by adding the solvent. Do this.
At this time, washing is performed by adding a basic substance that does not cause aggregation of sol particles to the sol solution. Preferably, a method is adopted in which the sol is first washed to some extent with pure water only, then the basic substance is added, and washing is continued. The amount of the basic substance added is determined by the pH of the sol solution.
It is sufficient that the amount is from neutral to slightly alkaline, that is, in the range of 5.0 to 9.0. Further, in order to further ensure the effect of the addition of the basic substance, washing may be carried out while adding the basic substance together with water continuously or twice or more. After washing, concentrate to the required sol concentration to obtain high purity zirconia sol. The sol obtained as a result of such washing is stable over a wide pH range and at high purity for a long period of time, and can be used as a zirconia sol. Among these sols, those treated with basic organic salts are particularly excellent in these properties. From the sol solution, ordinary heating drying, dielectric heating method,
A highly dispersible fine powder that can easily loosen a solvent can be easily obtained by a coupled drying method, a spray drying method, or the like. Furthermore, the powder obtained by adding a separately prepared sol of at least one of itria, calcia, magnesia, and ceria before drying can be made into a densified powder by shaping and firing. In addition, when pure water is used as a solvent for washing the sol, after concentrating the washed sol, it is added to various alcohols including polyhydric alcohols and dehydrated by heated distillation, or other organic solvent-based dehydrating agents are used to remove water. By removing it, a highly pure sol dispersed in an organic solvent can be prepared. Further, the powder obtained by drying the organic solvent sol can be dispersed in water or a suitable organic solvent to form a colloidal solution again. In addition, the fired dry powder is easily loosened, and can be particularly dispersed in a highly monodisperse state in a solvent, and has high dispersibility. [Effect] Cleaning of zirconia sol using an ultravortex membrane is as follows:
Although it is an efficient cleaning method, the cleaning efficiency tends to decrease as cleaning progresses.
It is practically difficult to reduce unnecessary ions below a certain level. This is thought to be because some kind of affinity exists between the sol particles and unnecessary ions, which prevents the unnecessary ions from passing through. The present invention improves the cleaning efficiency of the sol by adding a small amount of a basic substance to the sol during cleaning to break off this affinity. However, the basic substance added here needs to be one that does not cause aggregation of the sol, and specific examples include the following. Strong basic substances such as sodium hydroxide and potassium hydroxide, or salts of strong bases and weak acids such as sodium carbonate and potassium carbonate, or alkali metal salts of carboxylic acids such as formic acid, acetic acid, and tartaric acid, acetylacetone, 2,4- Basic organic salts such as alkali metal salts of β-diketones such as hexadione meet this requirement. Further, the salts used here can be easily removed by a washing operation, so that almost no salts remain in the sol after washing with the membrane. The highly cleaned sol thus obtained is stable at high concentrations and over a wide pH range. In particular, when the above-mentioned organic salts are used as basic substances, the dispersibility of the obtained sol in organic solvents is improved, and the high-purity zirconia sol obtained by the present invention can be used in combination with other materials. It has the advantage that the conditions for its use can be greatly expanded. Comparative Example Six aqueous zirconyl nitrate solutions (concentration: 0.2 mol/min) were prepared and hydrolyzed by boiling under reflux for 100 hours to produce a milky white colloidal sol. The pH of this colloidal sol after hydrolysis was 0.7.
Then, the average passage hole is about 100 Å with a total passing area of 8000 cm ²
The colloidal sol is pumped into a filtration device equipped with a filtration membrane, and the liquid that has passed through the membrane is discharged, and the liquid containing colloid particles that is not filtrated is returned to its original state for continuous filtration and concentration. Ta. When the colloidal sol reached about 2, pure water was added to bring the total to 15. This was again concentrated and concentrated to about 2. This process was repeated until the NO ^- ₃ ion in the colloidal zoal was reduced to 10 ppm or less, and finally the colloidal solution was concentrated to 2. Table 1 shows the change in nitrate ion (NO ^- ₃ ) concentration in the sol due to washing. Although it is recognized that the cleaning effect of the membrane is large, NO ^- ₃ in the sol
As the ion concentration decreases, the cleaning efficiency decreases,
In order to reduce the NO ^- ₃ ion concentration in the sol to 10 ppm or less, the amount of pure water used increases and a long cleaning time is also required. Example 1 Six zirconyl nitrate aqueous solutions (concentration: 0.2 mol/min) were prepared and hydrolyzed by boiling under reflux for 100 hours to produce a milky white colloidal sol. The pH of this colloidal sol after hydrolysis was 0.7.
Then, the average passage hole is about 100 Å with a total passing area of 8000 cm ²
The colloidal sol is pumped into a filtration device equipped with a filtration membrane, and the sol is filtered.The liquid that has passed through the membrane is discharged, and the liquid containing colloid particles that is not filtrated is returned to its original state for continuous filtration and concentration. Summer. When the colloidal sol reached about 2, pure water was added to bring the total to 15. This was again concentrated and concentrated to about 2. Repeat this process until the NO ^- ₃ ions in the colloidal sol are below 100ppm.
After dissolving acetylacetone in a 10% aqueous sodium carbonate solution, the cooled solution was added to the colloidal sol to adjust the pH to 7.5. Then NO ^- ₃ in the sol
Washing was repeated until the ions were below 1 ppm. Table 2 shows the change in NO ^- ₃ ion concentration in the sol due to washing. When a basic substance is added, the concentration of NO ^- ₃ ions in the sol rapidly decreases, and NO ^- ₃ is effectively reduced.
It was possible to transition to an ion-free state in a relatively short time and economically. After washing, the colloid solution was filtered and concentrated to 1.5. A part of the thus obtained colloidal sol was freeze-dried to obtain zirconia fine powder.
The specific surface area of the obtained fine powder was 140 m ² /g,
Further, as a result of differential thermal analysis, no heat generation was observed at around 450°C, indicating that the fine powder was a crystalline fine powder. In addition, ethylene glycol was added to the remaining colloidal sol and heated to distill off water, resulting in a zirconia colloidal sol dispersed in ethylene glycol. Next, the colloidal sol was heated under reduced pressure to remove ethylene glycol and obtain a fine powder. The thus obtained fine powder was easily redispersed in water or alcohol by adding it to water or alcohol and stirring gently.

【table】

[Table] Example 2 Zirconyl oxychloride aqueous solution (concentration 0.2 mol/
) was prepared and hydrolyzed by boiling under reflux for 100 hours to produce a milky white colloidal sol. The pH of this colloidal sol after hydrolysis was 0.7. Then, a membrane with a total filtration area of 8000 cm ² and an average passage hole of about 100 Å is set, and the colloidal sol is pumped into the filtration device to conduct filtration. was returned to its original state and continuously over-condensed. When the colloidal sol reached about 2, pure water was added to bring the total to 15. Furthermore, this was again subjected to over-concentration to a concentration of about 2. This process is repeated until the chloride ions (Cl ^- ) in the colloidal sol
When the pH was below 100 ppm, a 1% aqueous sodium hydroxide solution was added to adjust the pH to 6.8. Thereafter, washing was repeated until the chlorine ion (Cl ^- ) in the sol was 1 ppm or less. Finally, the colloidal sol was concentrated to 2. The amount of sodium ions (Na ⁺ ) remaining in the sol was 0.6 ppm. Example 3 Zirconyl oxychloride aqueous solution (concentration 0.25 mol/
) to which 30.05g of urea and 2.4g of acetic acid were prepared.
Added ml. This solution was boiled for 5 hours to hydrolyze and produce a light purple transparent sol. The pH of the sol after this reaction was 4.1. Then add this sol to 15
After diluting ^the sol to The liquid containing sol particles was returned to its original state and continuously over-concentrated.
When the sol is about 2, add pure water and reduce the total to 15
And so. Furthermore, this was again subjected to over-concentration to a concentration of about 2. This process was repeated until the chlorine ion (Cl ^- ) in the sol was 100 ppm or less, and a 1% aqueous sodium hydroxide solution was added to adjust the pH to 6.0. Thereafter, washing was repeated until the chlorine ions in the sol were reduced to 1 ppm or less. Finally, the sol was concentrated to 2. The sodium ion (Na ⁺ ) remaining in the sol is
It was 0.3ppm.

Claims (1)

[Claims] 1. When a zirconia sol is generated using an aqueous zirconium salt solution and then the sol is washed using an ultrafiltration membrane, the sol is first washed with pure water only, and then a basic substance is added to the sol for washing. A method for producing a high-purity zirconia sol.