JPS6311314B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for sintering ceramic powder sintered bodies, which produces high quality materials that cannot be obtained by conventional vacuum sintering methods or gas atmosphere sintering methods. This invention relates to a new sintering method that enables the production of ceramic sintered bodies.

(Conventional technology) Conventional ceramic powder sintered bodies were produced using vacuum sintering and reduced pressure.
Reduction was performed using H ₂ atmosphere sintering and reduced pressure CO atmosphere sintering.

(Problems to be Solved by the Invention) However, since the reduction could not be carried out completely, a large amount of harmful oxygen remained in the ceramic sintered body, impeding sinterability. Ceramic sintered bodies containing nitrogen have been sintered in a reduced pressure or pressurized _N2 atmosphere to prevent the decomposition of nitrogen in the sintered body, but even if denitrification can be prevented, a large amount of nitrogen in the ceramic sintered body remains. This had the disadvantage that a dense ceramic sintered body could not be obtained due to the formation of cavities.

The object of the present invention is to provide an innovative sintering method to improve the above-mentioned drawbacks of the sintering method. The present invention will be explained in detail below.

(Means for Solving the Problems) The sintering method of the present invention, when sintering ceramic powder, performs part or all of the sintering process using plasma supplied from a microwave power source provided separately from the furnace body. This method is characterized by being carried out in a gas atmosphere.

The above-mentioned ceramics include, for example, those listed below.

_Al2O3 as _the main component, _Al2O3 with 10-40wt% TiC added, _Al2O3 with 10-40wt _{% ZrO2} , _Al2O3 with _{10wt %} A combination of ~40 wt% SiC whiskers, a combination of ~, a main component of Si ₃ N ₄ , a main component of SiC, and a main component of AlN.

(Function) As described later, the present invention
This is a sintering method characterized by generating a gas plasma atmosphere using a microwave power source using an atmosphere of H ₂ , N ₂ , CO, He, and Ar gases alone or in a mixed state.

Plasmas are classified into two types: thermal plasma, which is in an equilibrium state in which electrons and ions have approximately the same energy, and low-temperature plasma, which is in a non-equilibrium state, where electron energy is larger than the energy of ions and gas molecules.

The present invention is a sintering method using the latter low-temperature plasma. In the case of low-temperature plasma, ions and gas molecules are excited to temperatures of several hundred to 1,000 degrees, and electron temperatures reach tens of thousands of degrees. These high-energy electrons and gas molecules collide inelastically, dissociating the gas molecules into highly reactive atoms called radicals, which has the effect of promoting gas reactions.

For example, by turning a reducing gas such as H ₂ or CO into plasma, it may be possible to reduce materials that are difficult to reduce based on so-called thermodynamics based on chemical equilibrium theory.

First, plasma sintering using H ₂ (hereinafter referred to as H ₂ plasma sintering) has the following advantages and effects compared to conventional vacuum sintering or gas atmosphere sintering.

The primary purpose of H ₂ plasma sintering is to reduce the ceramic sintered body. Compared to conventional sintering in a reduced-pressure H ₂ atmosphere, H ₂ plasma sintering requires a lower concentration (smaller gas flow rate), making it more resource-saving and economical. Furthermore, in conventional reduced-pressure H ₂ atmosphere sintering, the H ₂ atmosphere is set at several tens to hundreds of Torr to enhance the reducing effect, but harmful oxygen in the ceramic sintered body cannot be completely removed. First, due to this pressure, unnecessary gases such as H ₂ O contained in the ceramic sintered body cannot be sufficiently degassed, which impedes sinterability. In the case of H ₂ plasma sintering, complete reduction is performed in an H ₂ atmosphere plasma of several hundred Torr, and furthermore, unnecessary gases can be sufficiently degassed due to the high vacuum. From the above, H ₂ plasma sintering can produce a ceramic sintered body with extremely low amounts of harmful oxygen and voids.

Next, we will discuss the effects of _N2 plasma sintering.
When sintering N ₂ -containing ceramic sintered bodies, conventional vacuum sintering causes significant denitrification of the ceramic sintered bodies; for example, in the case of Si ₃ N ₄ ceramics, denitrification occurs in the surface layer.
There was a problem in that a separate layer of Si ₃ N ₄ and sintering aid was formed, resulting in a decrease in surface hardness. _N2
In the case of atmosphere sintering, it is necessary to introduce a high concentration of _N2 gas to prevent denitrification, which does not sufficiently degas the inside of the ceramic sintered body, causing the generation of nitrogen. . _N2 for these sintering methods
In the plasma sintering method, although the N ₂ flow rate is small, radical N ₂ activated by the plasma is generated.
Not only is it possible to effectively prevent denitrification and control _N2 , but the high vacuum also allows unnecessary gases generated inside the ceramic sintered body to be easily exhausted, preventing the formation of cavities. Has characteristics.

Next, we will discuss the results of CO plasma sintering.
CO plasma sintering has a significant reducing effect. This is similar to the case of H ₂ or N ₂ plasma sintering described above, but compared to conventional CO atmosphere sintering, it is effective at a lower concentration and can sufficiently degas. moreover
In H ₂ , N ₂ , CO, He, and Ar plasma sintering, the surface of the sintered body is plasma-etched by the activated gas, thereby cleaning the surface of the ceramic sintered body and improving the properties of the sintered body.

Additionally, if sintering is performed in an atmosphere in which plasma is generated by mixing these H ₂ , N ₂ , CO, and Ar gases, a combined effect of denitrification prevention and reduction can be imparted to the sintered body. . This is a property that cannot be obtained by conventional vacuum sintering and atmosphere sintering.

The above is remarkable for ceramics whose main component is silicon nitride.

Furthermore, ceramics containing alumina as a main component are extremely difficult to sinter because the surface of the alumina particles is inert, and it is necessary to perform pressure sintering using a hot press method.

However, pressure sintering is significantly lacking in productivity, so in order to perform pressureless sintering with excellent productivity, approximately 2wt% of sintering aids such as magnesium oxide are added.
Pressureless sintering is generally performed by generating and activating a glass phase on the surface of alumina particles.

However, since such a glass phase has a low melting point, adding a large amount impairs the heat resistance of the ceramic.

Therefore, by activating the surface of alumina particles using the plasma sintering method of the present invention and keeping the amount of sintering aid added low, ceramics with excellent heat resistance can be produced by pressureless sintering. make it possible.

The apparatus and sintering furnace used in the plasma sintering method of the present invention will first be described with reference to the drawings.

FIG. 1 shows an embodiment of the apparatus and sintering furnace used for sintering according to the present invention. Inside the stainless steel furnace body 1, a graphite heater 2, a heat insulating material 3 such as carbon wool, and a graphite reaction tube 4 for storing a workpiece 5 are arranged, and a rotary pump connected to the furnace body through a valve 6 is arranged. 7 to maintain a vacuum.
The reaction tube 4 is connected to a quartz introduction tube 8. On the other hand, H ₂ , N ₂ , CO, Ar, and He gases are in cylinder 23~
27, enters the other end of the introduction pipe 8 via flowmeters 18 to 22 and valves 13 to 17, and enters the microwave oscillator 1.
2. The microwave from the tuner 11 passes through the waveguide 10
is introduced into the reaction tube as plasma gas 9.

Figures 2 and 3 are used for the sintering of the present invention separately from those shown in Figure 1, chronologically staggered (Fig. 2), or used in combination with those shown in Figure 1. Another embodiment of the apparatus and the sintering furnace is shown in FIG. This is an example in which plasma gas 9 is generated. FIG. 3 shows an example in which a microwave oscillator 12 and a high frequency oscillator 28 are combined to generate a gas with high plasma density.

(Examples) Examples will be further described below to help understand the present invention.

Example 1 Commercially available Si ₃ N ₄ powder with an average particle size of 1μ, Al ₂ O ₃ powder and Y ₂ O ₃ powder with approximately the same particle size were mixed with 93% by weight of Si ₃ N ₄ ,
Containing 3% by weight of Y ₂ O ₃ and 5% by weight of Al ₂ O ₃ , using a silicon nitride ball and a nylon-lined pot.
Ball milling was carried out for 120 hours.

After adding an adhesive to this powder, embossing was performed at a pressure of 2 t/cm ² . After removing the adhesive at 400°C in the air, it is heated from room temperature to 1200°C using the equipment shown in Figure 1.
2.45GHz microwave oscillation power 1KW and 0.5Torr
The temperature is increased while generating H ₂ plasma, and then
Sintering was performed at 1650°C for 1 hour using N ₂ plasma with a microwave oscillation power of 5KW and 30Torr.

The density of the ceramic produced by the microwave plasma sintering method of the present invention is 99.9% or more of the theoretical density, and there are no cavities, and the amount of nitrogen contained in the ceramic sintered body is less than the theoretical value. 99.4% remained.

For comparison, the same stamped body was sintered using conventional sintering techniques in N ₂ at 100 Torr from room temperature to 1200°C, and then sintered at 1800°C in a N ₂ stream at 9.5 atm for 2 hours. The obtained comparison product has a density of the theoretical density.
Only 98.5%, and the nitrogen content is 89.5 of the theoretical value
Only % remained.

Example 2 68.5% by weight of commercially available Al ₂ O ₃ powder with a particle size of about 1 μ, TiC
Powder 30.0% by weight, Y ₂ O ₃ 1.0% by weight, NiO 0.5% by weight
Mixed, stamped, and 2.45G using the equipment shown in Figure 1.
When sintered at 1550°C for 1 hour in H ₂ plasma at 5 Torr with a microwave oscillation power of 1 KW at Hz, a ceramic sintered body with a theoretical density of 99.5% was obtained.

It has been known that ceramics with this composition cannot be densified unless hot-pressed.

(Effects of the Invention) As described above, according to the present invention, a ceramic sintered body without voids and with little denitrification can be easily obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram illustrating the schematic configuration of the apparatus and sintering furnace used in the present invention, and Figures 2 and 3 are used in conjunction with the one in Figure 1 in the present invention over time. Figures illustrating the schematic configuration of an apparatus and a sintering furnace are shown, respectively. 1...Furnace body, 2...Heater, 3...Insulating material, 4
... Reaction tube, 5 ... Processing object, 6, 13, 14,
15, 16, 17...Valve, 7...Rotary pump, 8...Introduction pipe, 9...Plasma, 10...
... Waveguide, 11 ... Tuner, 12 ... Microwave oscillator, 18, 19, 20, 21, 22 ... Flow meter, 23 ... H ₂ cylinder, 24 ... N ₂ cylinder,
25...CO cylinder, 26...Ar cylinder, 27...
...He cylinder, 28...High frequency oscillator, 29...
Matching box, 30...copper coil.

Claims (1)

[Claims] 1. A sintering process characterized in that when sintering ceramic powder, part or all of the sintering process is performed in a plasma gas atmosphere supplied from a microwave power source provided separately from the furnace body. Conclusion. 2 In claim 1, H ₂ , N ₂ ,
A sintering method performed in a plasma gas atmosphere containing CO, He, and Ar gases alone or in a mixed state.