JP3100549B2 - Porous ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous ceramic obtained by using a slurry for producing a porous ceramic containing a zirconia sol as an essential component, and more specifically to a highly active metal such as titanium or a titanium alloy. The present invention relates to a porous ceramic for forming a mold useful for precision casting.

[0002]

2. Description of the Related Art Conventionally, as a method of producing a zirconia sol from an aqueous solution of a zirconium salt, a method in which a precipitate obtained by reacting an aqueous solution of a zirconium salt with a basic substance is peptized with an acid or an aqueous solution of a basic zirconium salt is used. It is known to form a sol by injecting and mixing a substance at a pH that does not cause precipitation. 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 the solution is also known. The sol obtained by these methods is then freed of ions.

[0003] The zirconia sol thus obtained is coated on the surface of a base material such as metal, glass, plastic, etc., and is coated on the base material with heat resistance, abrasion resistance, chemical resistance, insulation, antireflection, ultraviolet light. In addition to being used as a coating agent to impart or improve performance such as absorption and hardness, as an inorganic binder, a molding binder used by impregnating a porous refractory material and a mold binder such as a titanium metal casting. Used as Further, they are used as piezoelectric materials, conductive pastes, electronic members such as humidity sensors and temperature sensors, catalysts, and other composite materials.

However, the zirconia sol produced by the above-mentioned conventional method has a low concentration or is poor in transparency due to a large particle diameter of the sol particles. However, satisfactory performance has not yet been obtained in fields requiring thick film coating and adhesive strength as a binder.

When the zirconia sol is used as a coating agent or a binder, particularly in a high temperature range, an element such as calcium, magnesium, yttrium or the like is added as a stabilizer in order to prevent a volume change due to a phase transformation of zirconia. However, the zirconia sol to which these other elements are added has a drawback that the viscosity is increased, or the stability over time such as gelation or aggregation occurs. To prevent such an increase in viscosity, it is conceivable to adjust the pH of the sol, but the effect is not sufficient.

[0006] Generally, porous molds used in the precision mold method include wax, naphthalene, low melting point alloy, urea,
A cast model made into a desired shape with a material that can be removed by heat such as styrofoam or a chemical such as water and solvent, that is, a material that can be removed thermally or chemically (referred to as a “cast model” in the present invention). A slurry in which refractory fine particles and a binder are mixed (hereinafter, also referred to as “molding agent”) and refractory particles the same as or different from the refractory fine particles are alternately applied and dried to form a mold (the present invention). Is referred to as a “raw mold”), the internal mold model is removed by thermal or chemical treatment or the like, and the resulting green mold is fired.

For the slurry as the template, various ceramic template such as silica, magnesia, zirconia, and calcia have been developed. However, when casting a highly active metal such as titanium or a titanium alloy, when using a mold made of a silica-based mold agent that is generally widely used for refractory metal casting, the metal-mold reaction is remarkable, and a good Castings cannot be obtained. For this reason, the use of magnesia, zirconia, and calcia based mold agents, which have low reactivity with these highly active metals and have the effect of suppressing oxidation, is being studied. Besides, the strength of the raw mold,
It is not satisfactory in terms of heat shrinkage and the like, and various improvements are required.

[0008] In addition to zirconia sol, zirconium salts such as zirconium acetate and zirconium nitrate, and zirconium alkoxides such as zirconium butoxide in addition to zirconia sol as a binder for producing a mold used in a precision mold such as titanium or a titanium alloy. It is known that such is used. As is clear from the method of manufacturing the porous ceramic mold used for the precision mold described above,
The binder plays a large role in the strength of the green mold and the mold, and a conventionally well-known zirconia-based binder could not provide a satisfactory result. For this reason, for the purpose of improving the dispersibility, flowability or stability of the mold material, and improving the strength of the green mold and the mold, a combination with various organic binders and surfactants has been studied, and some improvement has been made. However, it is still not sufficiently satisfactory, and the development of an even better binder, particularly a zirconia sol, has been desired.

[0009]

Accordingly, an object of the present invention is to provide a porous ceramic having excellent mechanical strength and the like.

It is still another object of the present invention to provide a porous ceramic which is useful as a mold for precision casting of titanium or a titanium alloy.

[0011]

The objects of the present invention are to provide a transparent zirconia sol obtained by heating an aqueous zirconium salt solution in the presence of urea and the refractory fine particles according to the present invention. This is achieved by ceramics characterized by firing a slurry that is contained as an essential component.

Further, these objects are the present invention according to claim 2, wherein the refractory fine particles are calcia-stabilized zirconia treated with an acid in the present invention according to claim 1. This can also be achieved by using ceramics.

[0013] Further, these objects are the present invention according to claim 3, wherein the transparent zirconia sol is compounded with a chelating agent and a compound of a metal other than zirconium in the transparent zirconia sol. The present invention is also achieved by a ceramic characterized by the following.

Further objects of the present invention are to heat an aqueous zirconium salt solution in the presence of urea on the surface of a casting model made of a thermally or chemically removable material according to the present invention. The slurry containing the transparent zirconia sol and the refractory fine particles obtained as essential components is applied to form a slurry layer, the refractory particles are supported on the slurry layer, and the operation of drying is performed a plurality of times. To form a multi-layer coating layer, and then thermally or chemically remove the casting model to produce a green mold comprising the multi-layer coating layer, and finally firing the green mold to obtain a green mold The present invention is also achieved by a porous ceramic characterized by being a casting mold that can be used.

Further, these objects are attained by claim 5
The present invention according to claim 4, which is the present invention described above, is also achieved by a porous ceramic, wherein the mold is a titanium or titanium alloy casting mold.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a zirconia sol which is a component of the slurry used in the present invention is prepared by heating a transparent zirconia sol obtained by heating an aqueous solution of a zirconium salt in the presence of urea. It is a high-concentration zirconia sol obtained by heating and concentrating at a temperature of not more than ° C, and this high-concentration zirconia sol is transparent.

The zirconia sol is produced by adding urea to an aqueous solution of a zirconium salt selected from water-soluble zirconium salts such as zirconium oxychloride, zirconium nitrate, zirconium sulfate and zirconium acetate, and heating the mixture. This reaction is characterized in that the concentration of ammonia produced by the hydrolysis of urea according to the following formula is extremely uniform in an aqueous solution, and the particle size of the zirconia sol produced from this ammonia and zirconium salt is extremely small. .

(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂ The heating temperature at this time is 60 to 300 ° C. The amount of urea is 0.2 to 4 mol, preferably 0.5 to 2 mol, per 1 mol of the zirconium salt. The reaction is stopped while the sol thus obtained maintains transparency. After cooling the sol, it is concentrated using an ultrafiltration membrane. The ions in the sol are discharged out of the system together with the water. If the concentration of ions in the sol after concentration is high, the step of adding pure water to the sol and concentrating is repeated, or the ions are removed using an ion exchange resin. Next, the sol after concentration is further concentrated by heating the sol. This concentration is performed 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 can have a concentration of up to 50% by weight as ZrO ₂ and is stable for a long time.

This transparent zirconia sol is acidic, its pH is 0.1 to 6, and its viscosity is 5 to 3,000 cp depending 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 of the zirconia sol is adjusted with water or a hydrophilic organic solvent as necessary. It can be performed.

Further, a high-performance zirconia sol can be obtained by mixing a chelating agent and a metal compound other than zirconium (hereinafter referred to as other metal compounds) with the transparent high-concentration zirconia sol obtained by the above method.

The chelating agents usable in the present invention include oxyphenols such as catechol and pyrogallol, amino alcohols such as diethanolamine and triethanolamine, oxyacids such as glycolic acid, lactic acid and hydroxyacrylic acid, and methyls thereof. ,
Ethyls, esters such as hydroxyethyl, oxyaldehydes such as glycolaldehyde, glycine, amino acids such as alanine, acetylacetone, benzoylacetone, stearoylacetone, stearoylbenzoylmethane, β-diketones such as dibenzoylmethane, acetoacetic acid, Β-ketone acids such as propionyl acetic acid, benzoyl acetic acid and their methyl, ethyl, n
And esters such as -propyl, i-propyl, n-butyl and t-butyl. Among these, β-diketones, and β-dicarbonyl compounds such as β-ketone acids and esters thereof are preferably used.

The addition amount of the chelating agent may be relatively small, and the effect is sufficiently exhibited in the range of 0.02 to 1 mol times with respect to zirconia in the sol, preferably 0.05 to 0.8.
It is mole% times. In addition, even if it is added more than 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 compounds such as aluminum, yttrium, calcium, magnesium, titanium, tin, indium, cerium, and silicon. These metal element compounds can be used alone or in combination of two or more depending on the purpose of use of the sol. Among these metal element compounds, a compound of yttrium, calcium or magnesium is important for the purpose of using the sol of the present invention, and is usually 0.5 to 20 mol%, preferably 1 to 18 mol% as an oxide with respect to zirconia. %.

The timing and method of adding the above-mentioned chelating agent and metal element compound are not particularly limited, and they can be added at any time before the formation of the transparent zirconia sol and after the formation. For example, (1) after heating a zirconium salt aqueous solution and urea to form a transparent zirconia sol,
After (2) the transparent zirconia sol is concentrated by the ultrafiltration membrane, (3) the zirconia sol may be concentrated by the ultrafiltration membrane and added after heating. Also, (4) the zirconium salt aqueous solution and urea may be added to a mixed solution. As in (4) above, even when the sol-forming reaction is carried out after the addition of the chelating agent and the concentration is carried out using an ultrafiltration membrane, the chelating agent does not flow out of the system. In addition, since each component can be uniformly mixed before the sol generation reaction, it is possible to obtain a high-performance zirconia-based sol having higher homogeneity, and further, from particles in which zirconia and other components are combined. It is possible to produce sols of different types. 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 corresponding to the required stabilization time is added, and A metal element compound may be added and blended immediately before use.

This high-performance zirconia-based sol is stable at room temperature for at least 6 months even at a high concentration.

The slurry for ceramics production (hereinafter simply referred to as "slurry") used in the present invention contains the above-mentioned transparent or high-concentration zirconia sol and refractory fine particles as necessary components.

As the refractory fine particles, any fine particles generally used in the production of ceramics as a refractory substance can be used, but it is considered that they are used in the production of a mold for casting titanium or a titanium alloy. if you did this,
In particular, zirconia; zirconium completely or partially stabilized with CaO, Y ₂ O _3, or MgO; Wo ₃ ; Y ₂ O ₃ ; T because of its low reactivity with molten titanium.
hO ₂ ; MgO; and CaC which becomes CaO when calcined
such as o ₃ are preferably used. Among these, Ca
Zirconia completely or partially stabilized with O (referred to as "calcia-stabilized zirconia" in the present invention)
Is preferred, and particularly, electrofused calcia-stabilized zirconia widely used as a refractory material is economically preferable. This fused calcia stabilized zirconia contains CaO
It is contained at a ratio of 6% by weight, and is used as a powder by pulverizing an ingot.

When a slurry is prepared by using the above-mentioned electrofused calcia-stabilized zirconia fine particles as the refractory fine particles, the pH of the obtained slurry changes with time, and further, the viscosity of the slurry increases in a short time. It may gel and become unusable as a slurry. As a result of examining the cause, part of CaO added as a stabilizer for zirconia did not form a solid solution with zirconia,
Eluted by an acid such as nitric acid or hydrochloric acid, and the eluted C
It has been found that aO causes viscosity increase and gelation of the slurry.

To cope with this, free CaO which is not dissolved in the fused calcia-stabilized zirconia may be removed in advance by an acid treatment using nitric acid, hydrochloric acid or the like.
Specifically, for example, after treating the electro-dissolved calcia-stabilized zirconia fine particles with an acid such as nitric acid, thoroughly washing the filtrate until no nitrate groups are observed, drying, and freeing the thus obtained free Calcia-stabilized zirconia fine particles substantially free of CaO may be added to the transparent zirconia sol. By doing so, impurities such as iron mixed in when crushing the ingot can be removed, and a slurry can be prepared with good reproducibility.

When the amount of free CaO contained is relatively small, an acid is appropriately added so as to keep the pH of the slurry constant so as to stabilize the slurry over time or to make the slurry transparent when preparing the slurry. An acid corresponding to the amount of CaO eluted into the zirconia sol may be added in advance.

The particle size of the refractory fine particles is not particularly limited, and can be appropriately determined in consideration of the type and use of the target ceramic molded body, the stability of the slurry, and the like.

The ratio of the transparent zirconia sol and the refractory fine particles in this slurry is not particularly limited.
It can be appropriately determined in consideration of the stability of the slurry and the like.
It is used in a ratio of up to 5 times by weight, preferably 2 to 4 times by weight.

To this slurry, additives generally used for this kind of slurry, such as a surfactant and a dispersant, can be added.

When this slurry is used in a method such as coating, it is important to adjust the viscosity and stability over time. In such a case, the viscosity of the slurry is adjusted by adjusting the amount of water or acetic 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 nitric acid and hydrochloric acid. Further, the slurry can be stably maintained in this viscosity state for one month or more.

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

First, zirconia, WO ₃ , Y ₂ O ₃ , T ₂ completely or partially stabilized with zirconia, CaO, Y ₂ O _3, MgO or the like is added to a transparent zirconia sol.
At least one type of refractory fine particles selected from hO ₂ , MgO, CaCO ₃ ,
The slurry is added 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 the surface condition of the casting to be produced and the like, which constitutes the casting model, for example, the permeation state of the wax at the time of melting. 200 to 400 mesh, preferably 300 to 380 mesh is used.

The slurry includes a surfactant for improving the wettability between the casting model and the slurry, a dispersant for improving the dispersibility of the refractory particles, an antifoaming agent for promoting defoaming of the slurry, Additives generally used in the field of ceramics production, such as an organic binder for improving the strength of the green mold, can be appropriately added as needed. When these additives are added, the viscosity of the slurry may increase, or the slurry may be solidified,
Great care must be taken in its implementation.

The slurry 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 mold made of porous ceramics of the present invention is applied to a casting model separately molded with wax or the like, and the slurry is coated on the casting model, or the casting model is immersed in the slurry. To form a slurry layer, and before the slurry layer is dried, the operation of supporting the refractory particles, for example, by sprinkling the slurry layer on the slurry layer, is usually repeated three or more times to form a multilayer coating layer. After formation, a green mold from which the casting mold is removed is manufactured.

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

The green mold obtained by the above method uses zirconia sol as a binder and further uses zirconia or the like as refractory particles, and thus may have a drawback of being heavy or expensive. . In this case, the coating layer is formed by the above-described method from the initial layer which comes into contact with the molten metal during casting to a few layers, and the subsequent layers are widely used for casting iron-based castings and the like. It is desirable to apply a mold manufacturing method using silica gel as a binder. This method is a method using silica colloid sol, ethyl silicate and the like as a binder, and a method using zircon sand, alumina, fused silica and the like as refractory particles,
When this method is used as a method for complementing the raw template according to the present invention, it is desirable to use a silica-based sol, adjust a basic slurry, and use it. 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 according to the present invention can be obtained.

For example, when the casting model is made of wax, the casting mold can be easily removed by a usual dewaxing method. For example, it is preferable to use a steam at about 150 ° C. in an autoclave and to remove the wax in a short time so that the multilayer coating layer does not crack due to expansion.

Lastly, after removing the remaining wax and the like from the obtained green mold by heat treatment or the like as necessary,
It is fired in a temperature range of 0 to 1600 ° C. to produce a target mold.

The ceramics of the present invention can be used not only as a mold material as described above but also for various ceramic molded bodies such as crucibles and setters. Further, it can be used, for example, as a coating agent or an impregnating agent for imparting heat resistance.

[0047]

The present invention will now be described more specifically with reference to examples. Hereinafter, first, a method for producing a zirconia sol used for producing the ceramic of the present invention will be described as a reference example, and then, examples of the present invention will be described.

Reference Example 1 (Production of zirconia sol 1 used in the present invention) 18% by weight aqueous solution of zirconium nitrate 3 as ZrO ₂
0 kg and 3 kg of urea were added to 200 liters of pure water. Next, the aqueous solution was heated to a temperature of 120 ° C. to obtain a transparent zirconia sol. After cooling the sol, lead to sol to ultrafiltration device, and concentrated as ZrO ₂ up to 10 wt%. Then, the sol was heated and concentrated to a temperature of 35 ° C. while maintaining the temperature at 50 ° C. or less under vacuum to obtain a transparent zirconia sol at 25% by weight for a long time.

Reference Example 2 (Production 2 of zirconia sol used in the present invention) 18% by weight aqueous solution of zirconium nitrate 3 as ZrO ₂
An aqueous solution obtained by adding 0 kg and 3 kg of urea to 180 liters of pure water was heated in a jacketed stirring tank under reflux at normal pressure for about 8 hours to obtain a transparent zirconia sol.

After cooling the transparent zirconia sol,
The mixture was placed in an ultrafiltration apparatus, and water and unwanted ions were discharged out of the system and concentrated to about 10% by weight as ZrO ₂ . Then, the sol was heated and concentrated in a concentrating vessel equipped with a stirrer while maintaining the sol at 40 ° C. or less under vacuum to obtain 27% by weight as ZrO ₂
A transparent zirconia sol was obtained. This sol was stable for a long time despite its high concentration.

To 1 kg of the transparent zirconia sol thus obtained was added 20 ml of acetylacetone.
Then, yttrium hydroxide was added to zirconia so as to contain 3 mol% as yttria, and the mixture was sufficiently stirred to obtain a transparent high-concentration zirconia sol containing 3 mol% of yttria. This sol was stable for more than 6 months.

Reference Example 3 (Production 3 of zirconia sol used in the present invention) Transparent high-concentration zirconia sol 1 obtained in Reference Example 2
30 ml of acetylacetone was added to kg, and then 26.1 g of diethoxycalcium was added and sufficiently stirred to obtain a transparent zirconia-based sol containing 4% by weight as calcia based on the zirconia sol. This sol was stable for more than 6 months.

Example 1 (1) Production of Transparent Zirconia Sol 18% by weight zirconium nitrate aqueous solution 3 as ZrO ₂ 3
0 kg and 3 kg of urea were added to 200 liters of pure water. Next, this aqueous solution was heated to a temperature of 101 ° C. to obtain a transparent zirconia sol. After cooling the sol, it was led to an ultrafiltration device and concentrated to 10% by weight as ZrO ₂ . Further, this sol was heated and concentrated under a vacuum at 50 ° C. or lower to obtain a transparent zirconia sol having a concentration of 25% by weight.
This zirconia sol has a pH of 1.5 and a viscosity of 200 cp.
And was stable for a long time.

(2) Adjustment of Slurry The viscosity of the zirconia sol was adjusted to 50 cp by adding nitric acid to the zirconia sol obtained in the above (1) to adjust the pH to 0.7. To 1 part by weight of this zirconia sol, 3 parts by weight of calcia-stabilized zirconia fine powder passed through a 325 mesh screen was added with stirring to prepare a slurry. A surfactant (trade name: DISCOL AN706, manufactured by Daiichi Kogyo Chemical Co., Ltd.) was added to the slurry.

The viscosity of the obtained slurry was determined according to Zahn Cup No. 4 was 75 seconds and the pH was 1.8. This slurry was stable for one month or more.

(3) Production of green mold using ceramics according to the present invention 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. The plate was immersed in the slurry obtained in the above (2), sprinkled with 60-120 mesh calcia-stabilized zirconia particles, and then dried at room temperature to form a three-layer coating layer. . Subsequently, two more coating layers were formed in the same manner as described above except that the calcia-stabilized zirconia particles of 24 to 70 mesh were used, to form a total of five coating layers.

Next, one end of the brass plate was heated and the brass plate was pulled out of the coating layer while melting the wax. The wax remaining in the obtained green mold was washed away with kerosene.

(4) Production of Mold The green mold obtained in the above (3) was fired at the temperature shown in Table 1 to produce a mold.

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

Test piece dimensions: width 12 mm, length 40 mm, thickness 6 mm Measurement conditions: span 30 mm measurement temperature room temperature bending speed 0.5 mm / min Each test was performed 10 times, and the average value is shown in Table 1.

[0061]

[Table 1]

Example 2 The viscosity of the zirconia sol was adjusted to 50 cp by adding nitric acid to the transparent zirconia sol having a concentration of 25% by weight and adjusting the pH to 0.7. To 1 part by weight of the zirconia sol, 3 parts by weight of electrofused calcia-stabilized zirconia fine powder (available from Daiichi Rare Element Co., Ltd.) passed through a 325 mesh screen was added with stirring to prepare a slurry. When the stirring of the slurry was continued at room temperature,
It gelled in time and became unusable as a slurry.

The above electrofused calcia-stabilized zirconia fine powder was added to a 10% aqueous nitric acid solution and subjected to an acid treatment with stirring for 20 hours. After the acid treatment, the zirconia fine powder was separated by filtration, washed until no nitrate was found in the filtrate with pure water, and then dried. A slurry was prepared in the same manner as described above using the thus obtained acid-treated electrofused calcia-stabilized zirconia fine powder. This slurry did not show a tendency to increase in viscosity over time and was stable for one month or more. The calcia (CaO) content in the electrofused calcia-stabilized zirconia fine powder before and after the acid treatment was measured by fluorescent X-ray analysis, and the results were as follows. 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 acid treatment.

[0064]

According to the present invention described above, the high-performance zirconia sol used is transparent and has a concentration of ZrO.
₂ , it is possible to increase to about 50% by weight,
Moreover, even at such a high concentration, the stability is excellent, and the viscosity does not increase, and no gelation or aggregation occurs. Further, even when used as a coating agent or a binder particularly in a high temperature region, a volume change caused by a phase change of zirconia is prevented, and various properties such as excellent heat resistance and adhesive strength can be exhibited. The slurry containing the zirconia sol as one of its components is stable without thickening or gelling for a long period of time. In particular, when calcia-stabilized zirconia fine particles subjected to acid treatment are used as the refractory fine particles, a stable slurry can be obtained for a long period of time.

By using the slurry of the ceramics of the present invention, a mold suitable for precision casting of highly active metals such as titanium, zirconium, magnesium or alloys thereof can be manufactured. When this mold is used, a reaction between these metals and the mold can be effectively prevented, so that a casting having excellent skin can be manufactured. Further, the present invention can manufacture a mold capable of casting a complicated and large structure.
Further, according to the present invention, a porous ceramic molded body having excellent mechanical strength and the like can be obtained by molding and baking the slurry into a desired shape. Furthermore, the slurry used in the present invention can be used as a coating agent, for example, to cover the surface for imparting heat resistance or the like with ceramics.

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 1-209598 (32) Priority date August 15, 1999 (August 15, 1989) (33) Priority claim country Japan (JP) (56) References JP-A-4-240166 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 38/00-38/10

Claims (5)

(57) [Claims] 1. A ceramic obtained by firing a slurry containing, as essential components, a transparent zirconia sol and refractory fine particles obtained by heating an aqueous solution of a zirconium salt in the presence of urea. 2. The ceramic according to claim 1, wherein the refractory fine particles are calcia-stabilized zirconia treated with an acid. 3. The ceramic according to claim 1, wherein the transparent zirconia sol is mixed with a chelating agent and a compound of a metal other than zirconium. 4. A transparent zirconia sol and refractory fine particles obtained by heating an aqueous solution of a zirconium salt in the presence of urea are essential components on the surface of a casting model made of a thermally or chemically removable material. A slurry layer is formed by coating a slurry layer, the refractory particles are supported on the slurry layer, and a drying operation is performed a plurality of times to form a multilayer coating layer, and then the casting model , Which is a casting mold obtained by thermally or chemically removing a green mold made of the above-mentioned multiple coating layers and finally firing the green mold. 5. The porous ceramic according to claim 4, wherein the mold is a titanium or titanium alloy casting mold.