JPH0497937A - Production of ceramic sintered body - Google Patents

Abstract

PURPOSE:To obtain a ceramic sintered body having high strength at high temp. by casting slip prepd. by adding a specified peptizer to ceramic powder dispersed in a petroleum hydrocarbon solvent as a dispersion medium and sintering the cast slip. CONSTITUTION:Intermolecular oligo-ester of the dimer or higher oligomer of 12-hydroxystearic acid as a peptizer is added to ceramic powder dispersed in a petroleum hydrocarbon solvent as a dispersive medium to prepare a slip. This slip is cast and sintered to obtain a desired ceramic sintered body. By this method, even when fine ceramic powder is used, satisfactory dispersibility and flowability are ensured and characteristics and viscosity necessary for slip for casting can be obtd. Since the viscosity of the slip used is sufficiently low, not only pressure casting but also vibration casting or sludge discharging casting can be adopted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a ceramic sintered body, and more specifically, the present invention relates to a method for manufacturing a ceramic sintered body, and more specifically, a method for slipping particularly fine ceramic powder using a petroleum-based hydrocarbon solvent as a dispersion medium. The present invention relates to a method of manufacturing a ceramic sintered body having high high temperature strength by casting and firing.

[Conventional technology]

The slip casting method involves dispersing and peptizing the cotton in a solvent to create a slurry, pouring it into a water-absorbing plaster mold, and leaving the slurry in the mold until it reaches the desired thickness. This is a method to make green molded bodies by solidifying it.
In recent years, fine ceramics have come to be widely used, especially when manufacturing large products, products with complex shapes, or manufacturing small quantities as prototypes.

Silicon nitride sintered bodies, which have recently been actively developed as structural ceramics for automobile engine parts, are molded using a cast molding method, in which silicon nitride powder and sintering aids are dispersed using water as a dispersion medium. A slip is used. As a peptizing agent for promoting the dispersion of these solid powders, especially silicon nitride powder, water glass, aqueous ammonia, diethylamine, sodium alginate, ammonium polyacrylate (molecules 13,000 to 12,000: for example, Toagosei A6114), etc. is known and used.

However, in mass production, it is difficult to sufficiently eliminate the water vapor generated in the furnace, so during firing, part of the silicon nitride reacts with residual moisture to generate ammonia gas, and at the same time, silica is generated. The presence of silica in the silicon nitride sintered body reduces high temperature strength. In particular, when high-purity silicon nitride is used, if it is cast in a slip using water as a dispersion medium and fired, the high-temperature strength of the sintered body at 800° C. or higher is significantly reduced. In addition, water-based slips tend to leave air bubbles, making it difficult to obtain high-strength products, have a slow drying speed, and have a high boiling point, which takes a long time to dry. There are problems such as the tendency for cracks to occur in the molded product because the gas exhibits a large volume change.

Therefore, in order to solve these problems, the present applicant used an organic solvent as a dispersion medium for the silicon nitride slip in the production of silicon nitride sintered bodies using the casting method. He also disclosed a method using a slip containing lecithin or polyoxyethylene laurylamine as a deflocculant (JP-A-62-292676 and JP-A No. 62-292-67).
No. 297268).

[Problem to be solved by the invention]

However, as the particle size of the silicon nitride powder used for the slip becomes finer than before, the slip viscosity increases, and as a result, the concentration of the dispersion medium must be increased, the density of the molded product decreases, and the strength of the cast molded product increases. A problem arose in that the temperature decreased (casting became difficult). This is thought to be because the powders cohere more strongly and the peptizing force becomes relatively smaller.

Therefore, an object of the present invention is to ensure good dispersibility and fluidity even when such fine ceramic powder is used, and to obtain properties and viscosity necessary for a slip for casting.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention uses an intermolecular oligoester of dimer or more of 12-hydroxystearic acid as a deflocculant to produce a ceramic powder slip using a petroleum-based hydrocarbon solvent as a dispersion medium. The present invention provides a method for producing a ceramic sintered body, which is characterized in that the resulting slip is cast and fired.

The reason why petroleum-based hydrocarbon solvents are used as dispersion media is that they do not contain water and their vapor pressure can be selected depending on the application.0 Petroleum-based hydrocarbon solvents include isoparaffins, naphthenes, aromatic hydrocarbons, and mixtures. Yes, distillation range is 8
0 to 300″C is preferred.

Ceramic powder is effective not only for silicon nitride but also for alumina, etc., and is not particularly limited. The size of the ceramic powder is also not limited, but the present invention uses finer particles than conventional ones, typically about 1Pm in average particle size. It is particularly effective for the following powders: Examples of sintering aids include yttria, ytterbium oxide, scandium oxide, alumina, magnesia, spinel, and aluminum nitride. The amount of sintering aid is generally 1 to 1 of the solid content (silicon nitride and sintering aid).
20% by weight, usually 3 to 12% by weight.

The intermolecular oligoester of 12-hydroxystearic acid dimer or more as a deflocculant is adsorbed on the surface of the powder particles and has the effect of reducing the viscosity of the slip due to its steric repulsive force. The monomer is solid at room temperature, has a weak function as a surfactant, and cannot be expected to be very effective as a dispersant. On the other hand, as the polymerization progresses and the amount exceeds 1O, the cohesive force between the molecules of the adsorbed intermolecular oligoester of 12-hydroxystearic acid becomes stronger, so that the viscosity decrease becomes less noticeable. The amount of the intermolecular oligoester of 12-hydroxystearic acid to be added is not particularly limited and may be selected depending on the embodiment of casting. Deflocculating agent is 1
If it exceeds 0% by weight, degreasing is required, which is a problem, but if degreasing is carried out, the amount of deflocculant is not limited to 10% by weight or less. However, - for boat fishing, the solid content is 0.7
~10% by weight is preferred. A particularly optimum slip viscosity for casting is achieved with an amount of peptizer within this range.

The ratio of solids to solvent is generally 40 = 60 ~ in volume ratio
The ratio is in the range of 65:35, depending on the ease of filling of the powder used, but preferably 45:55 to 60:4.
It is in the range of 0.

The amount added is preferably 1 to 8 wt%.

According to the method of the present invention, the viscosity of the slip is sufficiently low, so that not only the pressure casting method but also the vibration casting method, the sludge casting method, etc. can be applied to casting. The casting itself can be carried out in a conventional manner, and the subsequent firing can also be carried out in accordance with a conventional method. Incidentally, the viscosities of slips suitable for various casting methods are generally as follows.

Pressure casting 5.0OOcρ or less Vibration casting 3.000cp or less Sludge casting 1,000cρ or less According to the present invention, a slip of 5.000cρ or less can be obtained.

Si3N4 powder (average particle size 0.2 amount 1m) as the main raw material
96-t%, Yt03 powder (average particle size 0-6i10-6
Amount 1% and MgA I! t04 (average particle size 0.4)
20 parts by weight of an isoparaffinic solvent (distillation range 156-175°C) is added to 100 parts by weight of a mixed powder consisting of 2-1% powder, and 12-hydroxystearic acid hexamer oligomer is added as a deflocculant to this. Ester was added in the amount shown in Table 1 and mixed to prepare a slip.

The viscosity of each slip was measured using a Brookfield viscometer at a rotational speed of 1100 rpm using a conventional method, and the results are also shown in Table 2.

For comparison, Table 1 also shows the cases where lecithin and polyoxyethylene laurylamine were used instead of benzene as the solvent and the hexameric oligoester of 12-hydroxystearic acid as the peptizer in the above.

Furthermore, a molded body with a diameter of 50 mm, a thickness of 10-1, and a length of 50 m was molded using the slip under condition 111a4 of the example, and was dried at 50°C for 24 hours in nitrogen gas, resulting in a bulk density of 51% TD ( A molded article with a good theoretical density) could be obtained. When this was sintered in N2 gas at 1700-1800°C, a good sintered body was obtained.

On the other hand, when similar molding was performed using the condition Na3 of the comparative example, cracks were found after drying at 50° C. for 24 hours in nitrogen gas. The bulk density of the fragments was measured and was found to be 40% TD.

〔Effect of the invention〕

According to the present invention, the viscosity can be reduced while maintaining the peptizing property of a slip for casting molding using fine ceramic powder,
Since there is no need to reduce the density of the cast body, it is possible to obtain a ceramic fired body with high strength.

Claims (1)

[Claims] 1. In order to produce a ceramic powder slip using a petroleum-based hydrocarbon solvent as a dispersion medium, an intermolecular oligoester of 12-hydroxystearic acid dimer or more is added as a deflocculant, and the resulting slip is cast and formed. A method for manufacturing a ceramic sintered body, which comprises firing the ceramic sintered body.