JPH04260654A - Method for coating sintering auxiliary on ceramic powder - Google Patents

Abstract

PURPOSE:To produce ceramic powder having an excellent sintering property by coating ceramic powder with a polymer film containing the compound of a metallic element constituting a sintering auxiliary. CONSTITUTION:A method for coating ceramic powder with a sintering auxiliary comprising the steps of coating ceramic powder with a hydrophilic polymer containing the metal alkoxide of a metallic element constituting a sintering auxiliary to form a hydrophilic polymer layer, hydrolyzing a metal alkoxide contained in the hydrophilic polymer layer therein, and drying the hydrophilic polymer layer containing the hydrolyzable metal compound to form composite ceramic powder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of coating ceramic powder with a sintering aid to produce a ceramic powder with high sinterability that can form a sintered body with good physical properties.

0002

2. Description of the Related Art Conventionally, when sintering a ceramic molded body, sintering aids such as silica, alumina, and yttria have been blended to improve sinterability. In order to mix this sintering aid into the ceramic powder, it is usually dispersed by wet mixing using a ball mill or the like. but,
Metal compounds that serve as sintering aids often have large particle sizes and are tightly aggregated, so it is necessary to thoroughly crush them. Moreover, the specific gravity of the main raw material ceramic powder and sintering aid is
Particle sizes etc. often differ, making it difficult to uniformly disperse the sintering aid into ceramics. In addition, reaggregation of the sintering aid may occur in the slurry or during drying after the mixed powder, resulting in uneven distribution of the sintering aid. When molded and sintered using such a mixed powder, unevenly distributed sintering aids melt during the sintering process, and pores are generated in the sintered body. As a result, there is a problem that the strength of the sintered body cannot be sufficiently developed.

By the way, in order to improve the physical properties of a ceramic sintered body, there is a method in which, before sintering, a metal alkoxide of a metal element constituting a sintering aid is dispersed in ceramic powder using a sol-gel method, and then molded and sintered. There is a disclosure (Unexamined Japanese Patent Publication No. 1986-
76976). In addition, for the purpose of forming a uniform ceramic powder, agar is added to a solution containing multiple predetermined metals to form a gel, and multiple metals are precipitated at once, thereby synthesizing a mixed powder of raw materials for oxide superconductors. There is a disclosure (
(Japanese Patent Application Laid-Open No. 1-275411).

0004

[Problems to be Solved by the Invention] In the method of dispersing the alkoxide of the metal element constituting the sintering aid into ceramic powder using the sol-gel method, the metal element of the sintering aid adheres to the surface of the ceramic powder. However, the adhering sintering aid is likely to fall off the ceramic surface due to physical contact between the powders during subsequent steps such as injection molding processing. Further, since the metal alkoxide powder is usually a fine powder, it tends to aggregate and become unevenly distributed, and the physical properties of the sintered body are not significantly improved.

[0005] Furthermore, in order to gel a solution in which a predetermined metal is dissolved and precipitate the dissolved material to obtain a uniform composition,
This method requires the metal component to be in solution and cannot be applied to all ceramics. The present invention has been made in view of the above circumstances, and provides a ceramic powder with excellent sinterability by coating the surface of ceramic powder with a polymer film containing a metal compound of a metal element constituting a sintering aid. With the goal.

[0006]

[Means for Solving the Problems] The method of coating ceramic powder with a sintering aid of the present invention is to coat the ceramic powder with a hydrophilic polymer containing a metal alkoxide of a metal element constituting the sintering aid to make it hydrophilic. a hydrophilic coating step for forming a hydrophilic polymer layer, a hydrolysis step for hydrolyzing a metal alkoxide contained in the hydrophilic polymer layer in the hydrophilic polymer layer, and a hydrophilic coating step for forming a hydrophilic polymer layer containing the hydrophilic metal compound. It consists of a drying step of drying the polymer layer to form a composite ceramic powder.

In this method, first, in a coating step, ceramic powder is coated with a hydrophilic polymer containing a metal alkoxide of a metal element constituting a sintering aid. In this case, the surface of the ceramic powder may first be coated with a hydrophilic polymer, and then the hydrophilic polymer may be impregnated with a metal alkoxide, or it may be directly coated with a hydrophilic polymer containing a metal alkoxide. In the hydrolysis step, the hydrophilic polymer is brought into contact with water, gelled, and heated to hydrolyze the metal alkoxide within the polymer layer to form a metal compound. Since the polymer coating the ceramic is hydrophilic, it contains sufficient water and hydrolysis progresses within the gel film. Since the hydrophilic polymer forms a gel film, the generated metal compound can be retained in the polymer layer while being surrounded by gel. Therefore, agglomeration of metal compounds can also be prevented. In the drying step, water is removed from the hydrophilic polymer gel layer to obtain ceramic powder coated with a polymer layer containing a metal compound as a film.

[0008] Since the obtained ceramic powder has a metal compound which acts as a sintering aid retained in the polymer film, it does not fall off from the surface even during molding or other treatments. Therefore, the sintering aid is uniformly distributed in the ceramic powder. This polymer film is then removed during degreasing or sintering. Therefore, the sintering aid is uniformly dispersed on the surface of the raw ceramic material, resulting in a molded body with excellent sinterability.

Furthermore, the obtained sintered body is free from defects such as pores and can exhibit original physical properties such as strength. Examples of the hydrophilic polymers that can be used include polysaccharides such as agar and konjac, proteins such as gelatin, natural polymers such as DNA, and synthetic polymers such as polyacrylamide and polyvinyl alcohol.

Examples of the metal alkoxide of the metal element constituting the sintering aid include ethyl silicate, aluminum methoxide, aluminum ethoxide, aluminum isopropoxide, yttrium methoxide, yttrium ethoxide, and yttrium isopropoxide. Can be mentioned.

[0011]

[Operation] According to the coating method of the present invention, a coating layer of a hydrophilic polymer containing a metal alkoxide constituting a sintering aid is formed on the surface of a ceramic powder, and the coating layer is gelled with water. Hydrolyze the metal alkoxide in the layer. The metal compound formed by this hydrolysis is retained in the gel-like polymer layer. Therefore, even if this polymer layer is dried, it remains as it is, so as long as the ceramic surface is coated with the polymer, the metal compound as a sintering aid will also be present and will not fall off during injection molding or the like. Furthermore, since it exists within the gel of the polymer membrane, it does not aggregate. Therefore, it is possible to maintain a uniformly dispersed state of the metal compound in the ceramic powder,
Problems caused by uneven distribution of the sintering aid during the sintering process can be prevented.

0012

[Examples] Hereinafter, the present invention will be explained in detail using examples. (Example 1) (Coating step) Agar was added to 80°C warm water to form an aqueous solution containing 3% by weight agar. Add silicon nitride powder to this aqueous solution and
They were mixed to a concentration of % by weight. Once the temperature is 50℃
(temperature before the agar gels) yttrium methoxide [Y(OCH3)3] and aluminum methoxide [Al(OCH3)3] are added at 5% by weight each.
It was added and uniformly dispersed in the agar by stirring and mixing.

Next, the above mixed aqueous solution was spray-dried using a spray dryer to form a powder having an agar film containing a metal alkoxide on the surface of silicon nitride. (Hydrolysis step) Warm water at 60° C. was gradually added to this powder to cause the agar to absorb water and form a gel, and this temperature was maintained to hydrolyze the metal alkoxides contained in the agar. (Drying Step) Next, the hydrolyzate was dried by heating at 30° C. under reduced pressure to obtain a composite ceramic powder coated with a metal compound for a sintering aid.

[0014] A schematic cross-sectional diagram of this composite ceramic powder (
A) and a flow explanatory diagram (b) of the process are shown in FIG. This powder has a ceramic surface coated with a polymer gel containing a metal compound. Using this powder, a test piece for a bending test was molded by die press molding. This molded body was heated to 500° C. in the air at a heating rate of 10° C./Hr to remove organic components in the molded body. Next, it was sintered at 1800° C. in nitrogen to form a sintered body.

[0015] This sintered body was subjected to a four-point bending strength test according to JIS-R1601. As a result, 1000MPa
The strength was improved by about 30% compared to the strength of 700 MPa when sintered with a sintering aid mixed in the conventional method. Further, the structure of the sintered body was observed using an optical microscope, and it was found to be in good condition with no pores larger than 10 μm. (Example 2) Cast molding was performed using a slip in which the composite ceramic powder obtained in Example 1 was dispersed in water, and a molded body was sintered. The obtained sintered body exhibited good physical properties as in Example 1. (Example 3) (Coating process) Silicon nitride powder was added to an aqueous solution containing 3% by weight agar at 80°C, mixed to a concentration of 20% by weight, and dried with a spray dryer to coat with a hydrophilic polymer. It was made into a coated ceramic powder.

The above ceramic powder was added to water to gel the hydrophilic polymer. An aqueous solution containing 9% by weight each of yttrium methoxide [Y(OCH3)3] and aluminum methoxide [Al(OCH3)3] was added to this gelled product, and the metal alkoxide was attached or permeated into the gel by stirring and mixing. . (Hydrolysis step) The ceramic coated with the polymer gel containing the metal alkoxide and water was heated to 60° C. to hydrolyze the metal alkoxide in the gel. (Drying process) Ceramics covered with the gel obtained in the hydrolysis process are heated to 30°C under reduced pressure to remove water in the gel layer and dried to form a composite coated with a metal compound for sintering aid. It was made into ceramic powder.

[0017] A schematic cross-sectional view of this composite ceramic powder (
A) and a flow explanatory diagram (b) of the process are shown in FIG. In this case, a gel layer is formed on the surface of the ceramic powder, and a gel layer containing a metal compound is formed on the surface of the gel layer. This powder was molded and sintered in the same manner as in Example 1. The obtained sintered body exhibited good physical properties as in Example 1.

[0018]

According to this coating method, the sintering aid can be uniformly coated on the ceramic powder, so that even if a small amount is added, the sintering property is good and the high-temperature strength is improved. Furthermore, since the sintering aid is uniformly retained in the gel of the polymer layer, it is possible to prevent the sintering aid from agglomerating due to drying.

Furthermore, since the ceramic powder is coated with a polymer film, agglomeration of the ceramic powders can be prevented due to steric hindrance. In addition, the powder has good fluidity and moldability is improved.

[Brief explanation of the drawing]

[Figure 1] Schematic cross-sectional diagram of the composite ceramic powder obtained in Example 1 (a) and flow explanatory diagram of its manufacturing method (b)
It is.

[Figure 2] Schematic cross-sectional diagram of the composite ceramic powder obtained in Example 2 (a) and flow explanatory diagram of its manufacturing method (b)
It is.

Claims (1)

[Claims] 1. A coating step of coating a ceramic powder with a hydrophilic polymer containing a metal alkoxide of a metal element constituting a sintering aid to form a hydrophilic polymer layer; a hydrolysis step of hydrolyzing a metal alkoxide contained in the hydrophilic polymer layer; and a drying step of drying the hydrophilic polymer layer containing the hydrolyzed metal compound to obtain a composite ceramic powder. Method of coating powder with sintering aid.