JPH0657842B2 - Powder sintering method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to powders of ceramic materials such as metals or metal oxides, carbides, nitrides, borides, etc., or among them, depending on the application. The present invention relates to a powder sintering method for sintering a mixed composition for sintering formed by adding and mixing a binder to two or more kinds of powders arbitrarily selected, and particularly as a pretreatment before the final sintering. , A method for removing the binder from the mixed composition for sintering.

[Conventional technology and problems to be solved]

Sintering of the above-mentioned conventional metal or ceramics material or a mixed composition thereof is performed by kneading and homogenizing the required powders of the composition components into a mold, pressurizing, and heating by Joule heat by energization. Then, it was sintering. As another method, a method of heating a mixed powder composition molded in a mold without applying electricity and heating it in a furnace to sinter it was used.

When sintering by these methods, it is necessary to select and use a chemical substance that does not remain in the molded body after sintering or does not harm the binder depending on the application. In some cases, it may be necessary to use suitable auxiliaries or solvents. For example, when molding and sintering a mixed composition powder of metal and ceramic, synthetic resin that is often used as an ordinary binder must be heated to vaporize and remove it before sintering, otherwise the decomposed carbon is unstable. There is a drawback that it remains in the sintered body uncertainly. To eliminate this drawback, use the mixed composition powder in the mold.
Sintering must be performed after heating the substrate to 300 to 600 ° C. to decompose it and discharging the generated substrate. However, this pretreatment requires a considerable amount of time to remove the binder.
Further, particularly in the case of ceramics production using a liquid such as water as a binder, the conventional natural drying in the air or heat drying in a high temperature air stream or a furnace requires removal of the binder and drying. It took time.

In view of such problems, an object of the present invention is to make it possible to efficiently perform a pretreatment for removing the binder from the mixed composition for sintering in a short time.

[Means for solving problems]

In order to achieve this object, the powder sintering method of the present invention, as a pretreatment before performing the final sintering, by adding microwaves to the mixed composition for sintering and further applying an electrostatic field for heating. It is characterized in that a treatment for removing the binder is performed.

[Action]

By irradiating the microwave with the electrostatic field applied, the heating is promoted and the binder removal treatment can be performed in a shorter time than in the case where the microwave is simply applied.

The reason why heating is promoted by applying an electrostatic field is considered as follows.

That is, in order to absorb electromagnetic waves in the microwave region and generate a rotation spectrum, the molecule must have a dipole, and the magnitude of the dipole moment is related to the absorption of microwaves due to the transition of the rotational level. ing. Therefore, it is considered that the dipole moment of the molecule is formed or increased by the application of the electrostatic field, and as a result, the absorption of microwaves is promoted and the heating is performed in a short time.

〔Example〕

For example, the following composition is used as the mixed composition powder.
That is, kaolin 36%, feldspar 33%, silica sand 22%, balance limestone, water 23%, well kneaded and uniformly dispersed mixed composition is pressed in a predetermined molding die to form a mixture for sintering. Form a composition.

Embodiment 1 An embodiment of the present invention will be described with reference to FIG. The tip portion 8 of the plus electrode wire 4 supported in the insulating material 2 inserted into the processing container 1 whose atmospheric pressure or pressure is reduced, and the mixed composition 6 which is the sintered material inserted into the same processing container 1
And are opposed to each other to form an electrostatic field. The mixed composition 6
Is connected to the negative electrode wire 5 supported in the insulating material 3. The inside of the container 1 is provided with a vacuum pump 7 so as to maintain the atmospheric pressure or a reduced pressure to a required atmospheric pressure, and a magnetron 9 for adding a microwave.

2450 with magnetron 9 for the mixed composition 6 for sintering
MHz, add 0.008kW / Kg power density and heat. After heating for about 1 hour, the temperature of the composition 6 reached 110 ° C. The weight at that time was 80% of the original weight, and the mixture was a pretreated mixed composition. This is a result of the removal of the water used as a binder in the original mixture. If the power density is set to 0.1kW / Kg and this is intermittently added with a pause, and then dried (at this time, ON for 1 minute and OFF for 5 minutes),
It reached 78% of the initial weight in 48 minutes. In addition to this
When an electrostatic field of 1.5 KV / cm was applied, the initial weight was 80% in about 38 minutes. When an electrostatic field of 3.0 KV / cm was applied, the same dry state was reached in about 32 minutes. Thus, as a pretreatment method, the binder was dried and removed by heating for a relatively short time by applying a microwave and an electrostatic field. As a result of these series of tests, when the microwave was added and dried, it took less than about half the time compared with the conventional heat drying, and when the electrostatic field was added and dried. Within about 1/3 of the time, the water used as the binder could be removed to obtain the required dry state.

The dry composition thus obtained could be sintered to obtain a good sintered body with high density and no pores.

The test conducted in a vacuum or reduced pressure atmosphere will be described. When the inside of the container 1 was decompressed to 5 torr, and the glow discharge was caused to dry by microwave, 2745MHz, 0.008kW / Kg and electric field 1KV / cm, the same as in Example 1 was dried in about 19 minutes. did it.

In this way, when the inside of the container 1 was decompressed, and the glow discharge was generated by applying the microwave and the electrostatic field, the drying time could be further shortened as compared with the case where the pressure was not reduced.

〔effect〕

As described above, according to the present invention, as a pretreatment for sintering a mixed composition of a powder body and a binder, it is possible to easily bond in a short time by adding a microwave and further applying an electrostatic field. The agent can be removed to the required state and dried, and the drying time can be significantly reduced. Therefore, the sintering work can be facilitated, and the drying time and thus the working time can be significantly shortened. Then, it was confirmed that a high-density sintered body having no pores can be obtained by subjecting the binder, which has been scattered and removed, to main sintering.

[Brief description of drawings]

 FIG. 1 is an exemplary explanatory view for carrying out the present invention. DESCRIPTION OF SYMBOLS 1 ... Processing container, 7 ... Vacuum pump 2,3 ... Insulator, 8 ... Electrode end 4,5 ... Electrode wire, 9 ... Magnetron 6 ... Sintering material (mixture composition for sintering)

Claims (3)

[Claims] 1. A powder of a ceramic material such as a metal or a metal oxide, a carbide, a nitride or a boride, or a combination of two or more kinds of powder selected arbitrarily from these powders according to the application. For the mixed composition for sintering mixed with the agent, as a pretreatment before the final sintering, a treatment of removing the binder by applying microwave and further applying an electrostatic field and heating is performed. Characteristic powder sintering method. 2. The powder sintering method according to claim 1, wherein a liquid is used as the binder. 3. A process of removing the binder by applying microwaves and further applying an electrostatic field to heat the binder,
The powder sintering method according to claim 1, which is performed in a reduced pressure atmosphere.