JPH0948672A - Preparation of ceramic slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain ceramic slurry capable of blocking a metal ion eluted into water and keeping good slurry properties over a long period by adding a specific substance thereto in preparing aqueous slurry of ceramics containing an alkaline earth metal. SOLUTION: In preparing an aqueous slurry of ceramics containing an alkaline earth metal, e.g. magnesia, calcia, alumina-magnesiaspinel, cordierite, frostbite, or talc, a cheating agent is used. Ethylenediamine tetraacetate, triethylene tetramine, etc., are exemplified as the chelavting agent and citric acid is most preferably used as the cheleting agent. The chelating agent is used in an amount of preferably 0.1-20 pts.wt., further preferably 1-5 pts.wt. based on 100 pts.wt. ceramic powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for preparing an aqueous ceramic slurry.

[0002]

2. Description of the Related Art Generally, when a ceramic powder is dispersed in water, the surface charge of the ceramic powder is adjusted, and a dispersant is added to prevent the powder particles from electrically repulsing and agglomerating to form a ceramic slurry. I am preparing. As the dispersant, acrylic acid-based polymers are mainly used, and polyacrylic acid, polyacrylic acid ammonium salt, polyacrylic acid metal salt, acrylic acid-acrylic acid ester copolymer, methyl acrylate-acrylic acid copolymer is used. Polymeric organometallic and ammonium salts have been used.

However, the above dispersant exhibits little effect on ceramics containing an alkaline earth metal such as magnesia, calcia, alumina-magnesia spinel, cordierite, forsterite and talc. This is a ceramic containing alkaline earth metal,
It is presumed that this is because the solubility in water is higher than that of other oxide ceramics, so that metal ions are eluted in water and inhibit the above-mentioned dispersant which is usually used.

[0004]

The present inventors have completed the present invention as a result of continuing diligent research in order to solve the above-mentioned existing problems, and the purpose thereof is alkaline earth. A method for preparing an aqueous slurry of ceramics containing a group metal.

[0005]

The above-mentioned object can be achieved by a method for preparing a ceramic slurry, which comprises adding a chelating agent when preparing an aqueous slurry of a ceramic containing an alkaline earth metal. Further, the effect becomes more remarkable by using citric acid as the chelating agent.

An important point in the present invention is that when the ceramic containing an alkaline earth metal is dispersed in water, the added chelating agent blocks the divalent ions eluted in the water in preference to the dispersant. It is in.

In the present invention, the chelating agent is presumed to adjust the pH of the slurry and the zeta potential of the dispersed particles by blocking the ionized alkaline earth metal ions eluted in water. As a result, good slurry properties can be realized. In particular, ceramics containing an alkaline earth metal have a higher solubility in water than other ceramics, and therefore the addition of a chelating agent is more effective.

As the chelating agent, acetylacetone,
Adenine, 2-aminoethanol, 2-aminoethanethiol, imidazole, ethylamine, ethylenediamine, ethylenediaminetetraacetate, catechol,
Citric acid, glycylglycine, glycine, L-glutamic acid, acetic acid, 2.4 diaminobutyric acid, diethylenetriamine, L-cysteine, oxalic acid, triethylenetetramine, picolinic acid, histidine, 2.2'bipyridyl, pyridine, 1/10 Phenanthroline, L-phenylalanine, phenol, malonic acid and the like can be mentioned.

Of these chelating agents, the citric acid described in claim 2 of the present invention is most preferable. In the present invention, citric acid refers to citric acid, citric acid salts, and citric acid derivatives. Citric acid can block divalent ions released in water for the longest time, does not emit an odor, and is harmless to the human body.

According to the slurry preparation method of the present invention, stable slurry properties are exhibited for several hours to several days, but thereafter the chelating effect gradually decreases and the viscosity of the slurry increases. However, by further adding the chelating agent in sequence, the effect is restored, and as a result, the slurry can be stored for a long period of time.

The amount of the chelating agent added is preferably 0.1 to 20 parts by weight, more preferably 1 to 5 parts by weight, based on 100 parts by weight of the ceramic powder. If the addition amount is less than 0.1 part by weight, the released metal cannot be effectively blocked, which is not preferable. On the other hand, when the amount exceeds 20 parts by weight, the chelating effect remains unchanged, but most of the chelating agents do not participate in the block of the free metal. Also, excessive addition can leave problems during subsequent degreasing.

Ceramics applicable to the method for preparing a ceramic slurry of the present invention include oxides containing alkaline earth metals such as magnesia, calcia, barrier, cordierite, talc, forsterite, magnesium carbonate, calcium carbonate and barium carbonate. Carbonate and
The raw material which mixed these is mentioned. Further, it has a relatively high solubility in water like alkaline earth metals and is effective for zinc oxide, lead oxide and the like, which are easily eluted in the form of divalent ions.

As the other additives that can be used in the present invention, it is preferable to use an additive that is dispersed in water. Examples of dispersion-type additives include binders of wax-based emulsions and epoxy-based emulsions. Water-soluble additives such as commonly used polymer dispersants and alcohol binders may impede the effect of blocking free ions of the chelating agent, and therefore their use is preferably avoided.

With respect to the ceramic slurry of the present invention, it is possible to use ordinary ceramics manufacturing techniques such as cast molding, tape molding, spray film formation, spray drying and press molding after slurry preparation. Then, it can be used as various ceramic products through drying, degreasing and firing steps. In this degreasing process, organic substances such as chelating agents are incinerated and removed.

[0015]

【Example】

Example 1 3 parts by weight of various chelating agents shown in Table 1 and 25 parts by weight of ion-exchanged water were weighed with respect to 100 parts by weight of magnesia powder,
The mixture was stirred with a homodisper for 1 minute to prepare a slurry. The change with time in the properties of the prepared slurry was measured with a B-type viscometer.

[Table 1] * Is a comparative example Unit is centipoise Here, EDTA-2NH4 is ammonium salt of ethylenediaminetetraacetate, EDTA-2Na is sodium salt of ethylenediaminetetraacetate, TETA is triethylenetetramine simple substance, citric acid is citric acid simple substance, Polyacrylic acid NH4 represents an ammonium salt of polyacrylic acid. N
In the case of o.5, the viscosity became too high after 6 hours or more and could not be measured. After the lapse of 72 hours, 3 parts by weight of various chelating agents were further added, and all the slurries No. 1 to No. 4 were restored to their initial properties.

Example 2 100 parts by weight of magnesia powder and 25 parts by weight of ion-exchanged water were weighed out by weight of citric acid shown in Table 2 to prepare a slurry in the same manner as in Example 1, and the properties after 1 hour were measured. Was evaluated.

[Table 2]

Example 3 For various ceramic powders shown in Table 3, N of Example 1
A slurry was prepared in the same manner as in o.4, and the properties after 1 hour were evaluated.

[Table 3]

Example 4 100 parts by weight of magnesia, 25 parts by weight of water, 3 parts by weight of citric acid, and 1 part by weight of a binder of a wax-based emulsion were mixed for 3 hours with a ball mill, and the slurry properties were observed. It was a slurry. After that, it was cast-molded, and then dried, degreased and fired, and a magnesia sintered body could be produced.

[0019]

As described above, according to the method for preparing a ceramic slurry of the present invention, metal ions eluted in water are blocked in an aqueous slurry of a ceramic containing an alkaline earth metal to obtain good slurry properties. Can be maintained for a long time.

Claims (2)

[Claims] 1. A method for preparing a ceramic slurry, which comprises adding a chelating agent when preparing an aqueous slurry of a ceramic containing an alkaline earth metal. 2. The method for preparing a ceramic slurry according to claim 1, wherein citric acid is used as the chelating agent.