JP2547477B2 - Zirconia sol and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zirconia sol and a method for producing the same. More specifically, a transparency that is useful as a coating agent that imparts various properties such as heat resistance and abrasion resistance to a substrate or an inorganic binder that provides high adhesive strength, or for the production of zirconia-based composite fine powder and zirconia-based fibers. It relates to a zirconia sol and a method for producing the same.
In particular, a slurry for producing a porous ceramics containing the zirconia sol as an essential component and a porous ceramics obtained by using the slurry, more specifically, a porous material useful for precision casting of highly active metal such as titanium or titanium alloy. TECHNICAL FIELD The present invention relates to a transparent zirconia sol suitable for manufacturing a mold made of porous ceramics and a manufacturing method thereof.

BACKGROUND ART Conventionally, as a method for producing a zirconia sol from an aqueous zirconium salt solution, a method in which a precipitate obtained by reacting an aqueous zirconium salt solution with a basic substance is peptized with an acid or a basic substance is precipitated in an aqueous zirconium salt solution. A method is known in which a sol is produced by injecting and mixing at a pH that does not cause sol. Furthermore, a method of obtaining a zirconia colloid sol by heating an aqueous solution containing a zirconium salt under normal pressure or under pressure to hydrolyze is also known. Ions are then removed from the sol obtained by these methods.

The zirconia sol thus obtained is coated on the surface of a base material such as metal, glass or plastic, and the base material has heat resistance, abrasion resistance, chemical resistance, insulation, antireflection, ultraviolet absorption, hardness. In addition to being used as a coating agent to impart or improve such properties, it is also used as an inorganic binder such as a molding binder used by impregnating a porous refractory material or a binder for molds such as metal titanium castings. It Further, it is also used as a piezoelectric material, a conductive paste, an electronic member such as a humidity sensor and a temperature sensor, a catalyst, and a raw material for other composite materials.

However, the zirconia sol produced by the above-mentioned conventional method has a low concentration or is inferior in transparency due to the large particle size of the sol particles, and therefore, when used as a coating agent or an inorganic binder, has a certain level of performance. Although it can be demonstrated, it has not yet obtained sufficiently satisfactory performance in the fields where thick film coating and adhesive strength as a binder are required.

Further, when the zirconia sol is used as a coating agent or a binder particularly in a high temperature range, it is desirable to add an element such as calcium, magnesium or yttrium as a stabilizer in order to prevent a volume change due to the phase transformation of zirconia. However, the zirconia sol to which these other elements are added has the drawback of being inferior in stability over time, such as an increase in viscosity, gelation or aggregation. In order to prevent such an increase in viscosity, it is possible to adjust the pH of the sol, but the effect is not sufficient.

Further, in general, the porous mold used in the precision mold method is
A cast model made of a material that can be removed by heat or water and chemicals such as solvent such as wax, naphthalene, low melting point alloy, urea, Styrofoam, etc. In the invention, a slurry obtained by mixing refractory fine particles and a binder (referred to as a "casting model") (hereinafter sometimes referred to as "template") and refractory particles that are the same as or different from the refractory fine particles are alternated. By coating and drying on a mold to form a mold (in the present invention, "green mold"), the internal mold model is removed by thermal or chemical treatment, and the resulting raw mold is baked. Being manufactured.

For the slurry as the templating agent, various ceramic templating agents such as silica type, magnesia type, zirconia type and calcia type have been developed. However, when casting a metal having a high activity such as titanium or a titanium alloy, when a mold made of a silica-based templating agent which is widely used for casting high melting point metal is used, a metal-template reaction is remarkably excellent. No cast can be obtained. For this reason, the application of magnesia-based, zirconia-based, and calcia-based templating agents, which have low reactivity with these highly active metals and have an effect of suppressing oxidation, is being investigated. In addition to the above, the raw mold strength and heat shrinkage are not satisfactory, and various improvements are required.

In addition to zirconia sol, zirconium salts such as zirconium acetate and zirconium nitrate, and zirconium alkoxides such as zirconium butoxide are used as binders for producing molds used in precision molds such as titanium or titanium alloys. It is known that this is done. As is clear from the manufacturing method of the porous ceramics mold used for the precision mold described above, the binder plays a large role in the strength of the raw mold and the mold, and the conventionally known zirconia-based binder is sufficiently satisfactory. I couldn't get any good results. Therefore, for the purpose of improving the dispersibility, fluidity or stability of the template material, and improving the strength of the raw template and the template, use in combination with various organic binders and surfactants has been studied, and some improvements have been made. However, it is still not sufficiently satisfactory, and there has been a demand for the development of an even better binder, especially zirconia sol.

Therefore, an object of the present invention is to provide a transparent zirconia sol, particularly a high-performance zirconia sol which is transparent at a high concentration and a method for producing the same.

Another object of the present invention is to provide a high-performance zirconia sol which is stable for a long period of time without causing an increase in viscosity or gelation, and which is thermally and chemically stable as a coating agent, an inorganic binder, etc. and a method for producing the same. Is to provide.

Still another object of the present invention is to provide a high-performance zirconia sol useful as a coating agent that imparts various properties such as heat resistance and abrasion resistance to a substrate or an inorganic binder that can obtain high adhesive strength, and a method for producing the same. That is.

DISCLOSURE OF THE INVENTION These various objects include heating a zirconium salt aqueous solution in the presence of urea to obtain a transparent zirconia sol, and adding a chelating agent and a compound of a metal other than zirconium to the transparent zirconia sol. It is achieved by a method for producing a high-concentration zirconia sol, which comprises concentrating with an ultrafiltration membrane and then concentrating with heating at a temperature of 80 ° C. or lower.

Further, these various purposes include heating a zirconium salt aqueous solution in the presence of urea to obtain a transparent zirconia sol, concentrating the zirconia sol with an ultrafiltration membrane, and forming a chelating agent and a compound of a metal other than zirconium. Is also added, and then the mixture is heated and concentrated at a temperature of 80 ° C. or lower, which is also achieved by a method for producing a high-concentration zirconia sol.

Further, these various purposes, to obtain a transparent zirconia sol by heating the zirconium salt aqueous solution in the presence of urea, to concentrate the zirconia sol with an ultrafiltration membrane, then heat concentration at a temperature of 80 ℃ or less. It is also achieved by a method for producing a high-concentration zirconia sol, characterized in that a high-concentration zirconia sol is obtained by adding a chelating agent and a compound of a metal other than zirconium to the high-concentration zirconia sol.

Further, these various purposes include mixing a chelating agent and a compound of a metal other than zirconium in an aqueous zirconium salt solution, and heating the mixture in the presence of urea to obtain a transparent zirconia sol. It can also be achieved by a method for producing a high-concentration zirconia sol, which comprises concentrating with a filtration membrane and then concentrating with heating at a temperature of 80 ° C. or lower.

Further, these various purposes include heating a zirconium salt aqueous solution in the presence of urea to obtain a transparent zirconia sol, concentrating the zirconia sol with an ultrafiltration membrane, and then 80 ° C.
A high-concentration zirconia sol obtained by heating and concentrating at the following temperature, which is also achieved by a high-concentration zirconia sol characterized in that a chelating agent and a compound of a metal other than zirconium are added to the zirconia sol. To be done.

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a transparent zirconia sol obtained by heating an aqueous zirconium salt solution in the presence of urea is concentrated by an ultrafiltration membrane, and further concentrated by heating at 80 ° C. or lower. Gives a high-concentration zirconia sol. This high-concentration zirconia sol is transparent. A high-performance zirconia sol is obtained by blending the transparent high-concentration zirconia sol with a chelating agent and a compound of a metal other than zirconium.

Hereinafter, the present invention will be described in detail. First, urea is added to a zirconium salt aqueous solution selected from water-soluble zirconium salts such as zirconium oxychloride, zirconium nitrate, zirconium sulfate and zirconium acetate, and heated to produce a zirconia sol. This reaction is characterized by the extremely small particle size of the zirconia sol produced from the ammonia and the zirconium salt, because the concentration of ammonia produced by the hydrolysis of urea according to the following equation is extremely uniform in the aqueous solution. .

The heating temperature of _{(NH 2) 2 CO + H} 2 O → 2NH 3 + CO 2 at this time is 60 to 300 ° C.. The amount of urea is 0.2 to 4 mol, preferably 0.5 to 2 mol, based on 1 mol of the zirconium salt. The reaction is stopped while the sol thus obtained remains transparent. After cooling the sol, it is concentrated using an ultrafiltration membrane. Ions in the sol are discharged out of the system together with water. When the concentration of ions in the sol after concentration is high, the process of adding pure water to the sol and concentrating it is repeated, or the ions are removed using an ion exchange resin. Next, the concentrated sol is further concentrated by heating the sol. This concentration is carried out at a sol temperature of 80 ° C or lower, preferably 5 to 60 ° C, more preferably 10 to 40 ° C.

The transparent zirconia sol thus obtained has a concentration of ZrO ₂
It can be up to 50% by weight and is stable for a long time. Also, this transparent zirconia sol is acidic and its pH is
The viscosity is 0.1 to 6, and the viscosity is 5 to 3,000 cp although it depends on the concentration or pH.

Since this transparent zirconia sol is mixed with water or a hydrophilic organic solvent at an arbitrary ratio, when used as a binder, the concentration should be adjusted with water or a hydrophilic organic solvent, if necessary. You can

Furthermore, a high-performance zirconia sol can be obtained by blending a chelating agent and a metal compound other than silconium (hereinafter referred to as another metal compound) with the transparent high-concentration zirconia sol obtained by the above method.

As the chelating agent that can be used in the present invention, catechol, oxyphenols such as pyrogallol, amino alcohols such as diethanolamine and triethanolamine, glycols, lactic acid, oxyacids such as hydroxyacrylic acid and their methyl, ethyl, Esters such as hydroxyethyl, oxyaldehydes such as glycolaldehyde, amino acids such as glycine and alanine, acetylacetone, benzoylacetone, stearoylacetone, stearoylbenzoylmethane, β-diketones such as dibenzoylmethane, acetoacetic acid, propionylacetic acid Β-, such as benzoyl acetic acid
Ketone acids and their esters such as methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl and the like can be mentioned. Of these, β-diketones, and β-dicarbonyl compounds such as β-ketone acids and their esters are preferably used.

The chelating agent may be added in a relatively small amount, and the effect is sufficiently exhibited in the range of 0.02 to 1 mol times with respect to the zirconia in the sol, preferably 0.05 to 0.8 mol%. In addition,
Even if added in excess of 1 mol times, the quantitative effect is small and it is not economical.

Other metal compounds that can be used in the present invention include
Examples thereof include compounds such as aluminum, yttrium, calcium, magnesium, titanium, tin, indium, cerium, and silicon. These metal element compounds may be used alone or in combination of two or more, depending on the purpose of use of the sol. Among these metal element compounds, yttrium, calcium or magnesium compounds are important for the purpose of use of the sol of the present invention, and usually 0 as an oxide with respect to zirconia.
It is added in the range of 5 to 20 mol%, preferably 1 to 18 mol%.

There are no particular restrictions on the timing and method for adding the chelating agent and the metal element compound, and the chelating agent and the metal element compound can be added at any time before the transparent zirconia sol is formed and after the transparent zirconia sol is formed. For example, (1) after heating the zirconium salt aqueous solution and urea to form a transparent zirconia sol, (2) after concentrating the transparent zirconia sol with an ultrafiltration membrane,
(3) It may be added after being concentrated by an ultrafiltration membrane and further heated. Further, (4) it may be added to a mixed solution of an aqueous zirconium salt solution and urea. As shown in (4), even if the sol-forming reaction is performed after adding the chelating agent, and further the concentration is performed using the ultrafiltration membrane, the chelating agent is not observed to flow out of the system. Further, since each component can be uniformly mixed before the sol-forming reaction, it is possible to obtain a high-performance zirconia-based sol with higher homogeneity, and further, from particles in which zirconia and other components are combined. It is possible to produce Further, (5) depending on the application, it may be necessary that the content of the chelating agent is small, but in this case, only the chelating agent which is commensurate with the required stabilization time is added, You may add and mix a metal element compound just before using a sol.

The high-performance zirconia-based sol of the present invention is usually stable at room temperature for 6 months or longer even at high concentration.

The ceramics-producing slurry (hereinafter simply referred to as "slurry") obtained by using the transparent or high-concentration zirconia sol according to the present invention contains the transparent or high-concentration zirconia sol and refractory fine particles as necessary components. To do.

As the refractory fine particles, any of those generally used in the production of ceramics as a refractory substance can be used, but when considered to be used in the production of a mold for titanium or titanium alloy casting, when melted, Due to its low reactivity with titanium, especially zirconia; zirconia fully or partially stabilized with CaO, Y ₂ O ₃ or MgO; Wo ₃ ; Y ₂ O ₃ ; ThO ₂ ; MgO; and calcined Then Ca becomes CaO
Co ₃ or the like is preferably used. Among these, zirconia completely or partially stabilized with CaO (referred to as "calcia-stabilized zirconia" in the present invention) is preferable, and particularly, electrofused calcia stabilization that has been widely used as a refractory material from the past. Zirconia is economically preferable.
This electrofused calcia-stabilized zirconia contains CaO in a proportion of 2 to 6% by weight, and is used as a powder by crushing an ingot.

When a slurry is prepared by using the above fused fused calcia-stabilized zirconia fine particles as refractory fine particles, the pH of the resulting slurry changes with time, or the slurry thickens in a short time and gels. In some cases, it cannot be used as a slurry. As a result of investigating the cause of this, a part of CaO added as a stabilizer for zirconia does not form a solid solution with zirconia and is eluted by acids such as nitric acid and hydrochloric acid. It was found to cause stickiness and gelation.

In order to deal with this, free CaO which is not solid-soluted in the fused zirconia fused with calcia may be removed in advance by acid treatment using nitric acid, hydrochloric acid or the like. Specifically, for example, after treating the electrodissolved calcia-stabilized zirconia fine particles with an acid such as nitric acid, sufficient washing is performed until nitrate roots are no longer observed in the filtrate, followed by drying, and the free thus obtained Calcia-stabilized zirconia fine particles that do not substantially contain CaO may be added to the transparent zirconia sol. By doing this, impurities such as iron mixed in when the ingot is crushed can be removed, and the slurry can be prepared with good reproducibility.

Further, when the free CaO contained is relatively small, an acid is appropriately added so that the pH of the slurry becomes constant,
The slurry may be stabilized with time, or an acid corresponding to the amount of CaO eluted in the transparent zirconia sol may be added in advance when the slurry is prepared.

There is no particular limitation on the particle size of the refractory fine particles,
It can be appropriately determined in consideration of the type and intended use of the intended ceramic molded body, and the stability of the slurry.

The ratio of the transparent zirconia sol and the refractory fine particles in the slurry utilizing the present invention is not particularly limited, and can be appropriately determined in consideration of the stability of the slurry, etc. The sol is used in an amount of 1 to 5 times by weight, preferably 2 to 4 times by weight.

Additives generally used in this type of slurry, such as a surfactant and a dispersant, can be added to the slurry.

When using this slurry in a method such as coating, adjustment of its viscosity and stability over time are important, but regarding slurry viscosity in such a case, adjustment of water content or acetic acid, nitric acid, The optimum viscosity can be easily realized by adjusting the pH to 3 or less, preferably 2 or less by adding acids such as hydrochloric acid. Further, the slurry can be stably maintained in this viscosity state for one month or more.

Porous ceramics are obtained by firing this slurry utilizing the present invention at a high temperature. Therefore, if the above-mentioned slurry is molded into a desired shape in advance and fired, a porous ceramic molded body having a desired shape can be manufactured. More specifically, as the slurry, as a casting material containing the transparent zirconia sol as a binder, particularly effective in producing a casting mold used for precision casting of highly active metal such as titanium or titanium alloy. Can be used.
There is no particular limitation on the method of manufacturing the casting made of this porous ceramics, and for example, it can be manufactured by the following method.

First, zirconia, CaO, Y ₂ O is added to the transparent zirconia sol.
_A transparent zirconia sol containing at least one kind of refractory fine particles selected from zirconia, WO ₃ , Y ₂ O ₃ , ThO ₂ , MgO, CaCO ₃ , etc., which are completely or partially stabilized with ₃ or MgO. ~ 5 times by weight, preferably 1.5 to 3.5 times by weight, and stirred at a relatively low speed to prepare a slurry.

The particle size of the refractory fine particles is appropriately determined in consideration of not only the surface state of the casting to be produced, but also the casting model, for example, the permeation state of the wax when melted,
Usually, 200 to 400 mesh, preferably 300 to 380 mesh is used.

The slurry, a surfactant for improving the wettability between the casting model and the slurry, a dispersant for improving the dispersibility of refractory fine particles, a defoaming agent for promoting defoaming of the slurry, a raw mold Additives generally used in the field of ceramics production, such as an organic binder for improving strength, can be appropriately added as needed. Addition of these additives may increase the viscosity of the slurry or may cause the slurry to solidify.

The slurry utilizing the present invention has a feature that a sufficient mold strength and mold strength can be obtained without using an organic binder, so that a mold having a complicated shape can be easily manufactured.

Next, the slurry is applied to a casting model separately molded with wax or the like, for example, the casting model is coated with the slurry, or the casting model is immersed in the slurry to form a slurry layer. After the refractory particles are dried, for example, the operation of sprinkling and supporting the slurry layer on the slurry layer is usually repeated three or more times to form a multi-layer coating layer, and then the casting mold is removed to produce a raw mold. To do.

The refractory particles used to form the multilayer coating may be of the same type as the refractory particles used to prepare the slurry, but may be selected from those having low reactivity with the molten titanium. The particle size of the refractory particles is not particularly limited, but is usually coarser than the refractory particles used for preparing the slurry, and 20 to 200 mesh is used.

The green mold obtained by the above method uses zirconia sol as a binder and further uses zirconia or the like as refractory particles, so that it may be disadvantageous in that it is heavy and expensive. In this case, a coating layer is formed by the above method from the first layer that comes into contact with the molten metal during casting to the second to third layers, and the subsequent layers are widely used for casting iron-based castings. It is desirable to apply the mold manufacturing method using silica gel as a binder. This method is a method using silica colloid sol, ethyl silicate, etc. as a binder, and zircon sand, alumina, fused silica, etc. as refractory particles. When used as, it is desirable to use a silica sol and prepare a basic slurry for use. By using this basic slurry, the effect of improving the strength and water resistance of the coating layer from the first layer to the second to third layers can be obtained.

The removal of the casting mold can be easily performed by a normal dewaxing method when the casting model is made of wax, for example. For example, it is advisable to use steam at about 150 ° C. in an autoclave and dewax in a short time so that expansion does not cause cracks in the multi-layer coating layer.

Finally, after removing the remaining wax and the like from the obtained raw mold by heat treatment or the like, the raw mold is fired in a temperature range of 800 to 1600 ° C. to produce a target mold.

The slurry using the present invention can be used for producing various ceramic molded bodies such as crucibles and setters, in addition to the above-mentioned mold material. Furthermore, it can be used as a coating agent or an impregnating agent for imparting heat resistance, for example.

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 As a ZrO ₂ , 30 kg of an 18 wt% zirconium nitrate aqueous solution and 3 kg of urea were added to 200 pure water. Then the aqueous solution at 120 ° C
The transparent zirconia sol was obtained by heating to the temperature of. After cooling the sol, the sol was introduced into an ultrafiltration device and concentrated to 10% by weight as ZrO ₂ . Next, the sol was heated and concentrated to a temperature of 35 ° C. while maintaining the temperature at 50 ° C. or lower under vacuum to obtain a transparent zirconia sol which was stable at 25 wt% for a long period of time.

Example 2 30 kg of a zirconium nitrate aqueous solution of 18% by weight as ZrO ₂ and 3 kg of urea were added to pure water 180, and the resulting aqueous solution was heated in a jacketed stirring tank under normal pressure reflux for about 8 hours to obtain a transparent zirconia sol. It was

After cooling this transparent zirconia sol, put it in an ultrafiltration device to discharge water and unnecessary ions out of the system to produce ZrO ₂
Was concentrated to about 10% by weight. Next, this sol was heated and concentrated in a concentrator equipped with a stirrer while maintaining it at 40 ° C. or lower under vacuum to obtain 27 wt% of transparent zirconia sol as ZrO ₂ . This sol was stable for a long time despite its high concentration.

Transparent high-concentration zirconia sol obtained in this way
20 ml of acetylacetone was added to 1 kg. Next, yttrium hydroxide was added to zirconia so that the yttria content was 3 mol%, and the mixture was sufficiently stirred to obtain a transparent high-concentration zirconia sol containing 3 mol% yttria. This sol was stable for more than 6 months.

Example 3 1 kg of transparent high-concentration zirconia sol obtained in Example 2
Acetylacetone (30 ml) was added thereto, and then diethoxycalcium (26.1 g) was added thereto and sufficiently stirred to obtain a transparent high-concentration zirconia-based sol containing 4% by weight of calcia relative to the zirconia sol. This sol was stable for more than 6 months.

Example 4 (1) Production of transparent zirconia sol 30 kg of an 18 wt% zirconium nitrate aqueous solution as ZrO ₂ and 3 kg of urea were added to pure water 200. Then, this aqueous solution
A transparent zirconia sol was obtained by heating to a temperature of 101 ° C.
After cooling this sol, it was introduced into an ultrafiltration device and concentrated to 10% by weight as ZrO ₂ . Furthermore, this sol is placed under vacuum 50
The mixture was heated and concentrated while keeping the temperature below ℃ to obtain a transparent zirconia sol having a concentration of 25% by weight. The pH of this zirconia sol is 1.
5. The viscosity was 200 cp and it was stable for a long time.

(2) Preparation of slurry By adding nitric acid to the zirconia sol obtained in the above (1) to adjust the pH to 0.7, the viscosity of the zirconia sol is adjusted to 5
Adjusted to 0 cp. To 1 part by weight of this zirconia sol, 3 parts by weight of calcia-stabilized zirconia fine powder passing through a 325 mesh screen was added with stirring to prepare a slurry.
Surfactant (trade name: Discol AN70 in this slurry)
6, manufactured by Daiichi Kogyo Yakuhin Co., Ltd.) was added.

The viscosity of the obtained slurry was 75 seconds in Zahn cup No. 4, and the pH was 1.8. The slurry was stable for more than 1 month.

(3) Production of green mold Wax was thinly applied to a brass plate having a width of 50 mm, a length of 170 mm and a thickness of 3 mm. This plate was immersed in the slurry obtained in the above (2), and 60 to 120 mesh calcia-stabilized zirconia particles were sprinkled on the plate, followed by drying at room temperature to form three coating layers. . Subsequently, two coating layers were further formed in the same manner as described above except that 24-70 mesh calcia-stabilized zirconia particles were used to form a total of five coating layers. Next, one end of the brass plate was heated to melt the wax, and the brass plate was removed from the coating layer. The wax remaining in the obtained green mold was washed off with kerosene.

(4) Manufacture of mold A mold was manufactured by firing the raw mold obtained in (3) above at the temperature shown in Table 1.

(5) Measurement of mold strength The mold obtained in (4) above was cut out with a diamond cutter to prepare a test piece, and its strength was measured by a three-point bending strength test method.

Test piece dimensions: width 12 mm, length 40 mm, thickness 6 mm Measuring conditions: span 30 mm Measuring temperature room temperature Bending speed 0.5 mm / min Tests were performed 10 times each, and the average values are shown in Table 1.

Table 1 Firing temperature (° C) Bending strength (kg / cm ² ) 150 32 1100 38 1200 61 1300 85 1400 118 1500 129 1600 155 Example 5 25% by weight concentration of transparent zirconia sol prepared in Example 4 and nitric acid Was added to adjust the pH to 0.7 and the viscosity of the zirconia sol was adjusted to 50 cp. 1 part by weight of this zirconia sol is a fine powder of fused zirconia stabilized with fused calcia that passes through a 325 mesh screen (sold by Daiichi Rare Elements Co., Ltd.) 3
Parts by weight were added with stirring to prepare a slurry. When the stirring of this slurry was continued at room temperature, it gelled in 1 hour and became unusable as a slurry.

The above-mentioned fine powder of fused zirconia stabilized with fused calcia was added to a 10% aqueous nitric acid solution, and an acid treatment was carried out for 20 hours with stirring. After the acid treatment, the zirconia fine powder was filtered off, washed with pure water until no nitrate was found in the filtrate, and then dried.
The acid-treated electrofused calcia-stabilized zirconia fine powder thus obtained was used to prepare a slurry in the same manner as above. This slurry was stable for one month or more without showing a tendency of thickening over time. The calcia (CaO) content in the fine powder of fused zirconia stabilized by fused silica before and after the acid treatment was measured by a fluorescent X-ray analysis method.

Before acid treatment 3.91% by weight After acid treatment 3.35% by weight From the above results, it is understood that free CaO is removed by the acid treatment.

INDUSTRIAL APPLICABILITY The high-performance zirconia-based sol of the present invention is transparent, and its concentration as ZrO ₂ can be increased up to about 50% by weight, and the stability is excellent even at such a high concentration. The viscosity does not increase, and gelation or aggregation does not occur.

Further, even when it is used as a coating agent or a binder particularly in a high temperature range, the volume change due to the phase change of zirconia is prevented, and various properties such as excellent heat resistance and adhesive strength can be exhibited.

Furthermore, the slurry using the zirconia sol of the present invention is stable without thickening or gelling for a long period of time. In particular, when the acid-treated calcia-stabilized zirconia fine particles are used as the refractory fine particles, a stable slurry can be obtained for a long period of time.

Further, by using the slurry using the zirconia sol of the present invention, it is possible to manufacture a mold suitable for precision casting of highly active metals such as titanium, zirconium, magnesium or alloys thereof. When this mold is used, the reaction between these metals and the mold can be effectively prevented, so that a casting having excellent skin can be produced. Further, by using the slurry of the present invention, a mold capable of casting a complex and large structure can be manufactured. Further, when the slurry of the present invention is molded into a desired shape and fired, a porous ceramics molded body having excellent mechanical strength and the like can be obtained.

The slurry can also be used as a coating agent for imparting heat resistance and the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C04B 38/00 303 C04B 35/48 AZ (31) Priority claim number Japanese Patent Application No. 1-209598 ( 32) Priority Day 1 (1989) August 15 (33) Priority claiming country Japan (JP) (56) Reference JP 62-52131 (JP, A) JP 62-270419 (JP, A) ) JP-A-62-226815 (JP, A) JP-A-63-2809 (JP, A)

Claims (7)

(57) [Claims] 1. A zirconium salt aqueous solution is heated in the presence of urea to obtain a transparent zirconia sol, and the transparent zirconia sol is blended with a chelating agent and a compound of a metal other than zirconium. Concentrated by
A method for producing a high-concentration zirconia sol, which comprises heating and concentrating at a temperature of 80 ° C or lower. 2. A transparent zirconia sol is obtained by heating an aqueous zirconium salt solution in the presence of urea, the zirconia sol is concentrated by an ultrafiltration membrane, and a chelating agent and a metal compound other than zirconium are blended. Then, the method for producing a high-concentration zirconia sol, which comprises heating and concentrating at a temperature of 80 ° C. or lower. 3. A high concentration is obtained by heating an aqueous zirconium salt solution in the presence of urea to obtain a transparent zirconia sol, concentrating the zirconia sol with an ultrafiltration membrane, and then concentrating it by heating at a temperature of 80 ° C. or lower. A method for producing a high-concentration zirconia sol, which comprises obtaining a zirconia sol and adding a chelating agent and a compound of a metal other than zirconium to the high-concentration zirconia sol. 4. A chelating agent and a compound of a metal other than zirconium are mixed with an aqueous zirconium salt solution and heated in the presence of urea to obtain a transparent zirconia sol. The zirconia sol is passed through an ultrafiltration membrane. Concentrate and then 80 ° C
A method for producing a high-concentration zirconia sol, which comprises heating and concentrating at the following temperature. 5. The chelating agent is an oxyphenol,
Amino alcohols, oxyacids and their esters, oxyaldehydes, amino acids, β-diketones, and at least one selected from the group consisting of β-ketone acids and their esters The method according to at least one of claims 1 to 4. 6. Obtained by heating an aqueous zirconium salt solution in the presence of urea to obtain a transparent zirconia sol, concentrating the zirconia sol by an ultrafiltration membrane, and then concentrating by heating at a temperature of 80 ° C. or lower. A high-concentration zirconia sol, characterized in that a chelating agent and a compound of a metal other than zirconium are mixed in the zirconia sol. 7. A group in which the chelating agent comprises oxyphenols, aminoalcohols, oxyacids and their esters, oxyaldehydes, amino acids, β-diketones, and β-ketone acids and their esters. 7. The zirconia sol according to claim 6, which is at least one selected from the group consisting of: