JPH0615422B2 - Degreasing method for ceramic molded body - Google Patents

Description

Detailed Description of the Invention A. Object of the Invention (1) Field of Industrial Application The present invention relates to a degreasing method for a ceramic molded body, which comprises removing an organic binder from a ceramic molded body formed by adding an organic binder to ceramic powder.

(2) Conventional technology The organic binder plays a useful role such as imparting moldability to the ceramic powder in the molding process and improving the strength of the ceramic molded body, but it is accompanied by decomposition in the sintering process. Since the gas is generated and causes deformation and destruction of the ceramic molded body, it is necessary to degrease the ceramic molded body and remove the organic binder before the sintering process.

Conventionally, as this kind of degreasing method, there is known a method in which a ceramic molded body is heated in a furnace in a non-oxidizing atmosphere, and then in an oxidizing atmosphere to thermally decompose an organic binder (special feature: (See Kai 61-77672).

(3) Problems to be Solved by the Invention However, in the above method, since the heating process is divided into two stages with the atmosphere completely reversed, the atmosphere control in the furnace is troublesome and the work is complicated. There is a problem that becomes.

Also, general organic binders tend to decompose rapidly at a predetermined temperature and generate a large amount of gas at a time, and also have a coefficient of thermal expansion far from that of ceramic powder and expand during the temperature rising process. And the contraction are repeated, cracks are generated in the ceramic molded body due to the high gas pressure accompanying the generation of the large amount of gas, the difference in the coefficient of thermal expansion, and repeated expansion and contraction, and in extreme cases, the ceramic molded body may May be destroyed.

Therefore, in the above-mentioned conventional method, the heating rate in each heating process of the ceramic molded body is divided into a plurality of stages, and the heating rate of each stage is set extremely slowly, and between the upper stage and the next stage. A constant temperature heating region must be provided, and it takes 200 to 240 hours for degreasing treatment, and there is a problem that work efficiency is extremely poor.

In view of the above, it is an object of the present invention to provide the above-mentioned degreasing method in which the atmosphere in the furnace can be easily controlled and the production efficiency can be improved.

B. Configuration of the Invention (1) Means for Solving Problems The first aspect of the invention is that the organic binder has a coefficient of thermal expansion substantially equal to that of the ceramic powder, and the decomposition progresses substantially in proportion to the temperature rise. It is characterized in that the organic binder is decomposed by heating the ceramic molded body under reduced pressure while circulating an inert gas.

A second aspect of the present invention uses, as the organic binder, one having a coefficient of thermal expansion substantially equal to that of the ceramic powder and physical properties in which decomposition progresses in a substantially proportional manner with respect to temperature rise. To the agent, a halide that lowers the decomposition start temperature of the agent and moderates the progress of the decomposition is added, and the organic binder is decomposed by heating the ceramic molded body under reduced pressure in an inert gas flow. It is characterized by

(2) Operation In the first aspect of the invention, the atmosphere in the furnace is a simple depressurization while the inert gas is flowing, so that control is easy.

Also, since the heating is performed under reduced pressure, the boiling point, decomposition temperature and vapor pressure of the organic binder are lower than those under atmospheric pressure, and the decomposition of the organic binder is approximately proportional to the temperature increase in a relatively low temperature range. To progress. As a result, the thermal decomposition of the organic binder can be carried out gradually and at a constant rate, and the thermal expansion coefficient of the organic binder is almost the same as that of the ceramic powder. Can be efficiently performed by avoiding generation of cracks therein.

Furthermore, since the organic binder is thermally decomposed during the flow of the inert gas, the generated gas in the furnace is smoothly discharged to the outside by the inert gas, and the gas in the ceramic molded body is exhausted and the organic binder is melted. The clogging of the ceramic molded body due to the above can be prevented by the inert gas that has entered the ceramic molded body, whereby the residue of the organic binder can be prevented from staying in the ceramic molded body.

The residue is mainly carbon, which hinders the improvement of the density of the ceramic product that has undergone the sintering process.
The absence of residue in the ceramic molded body is extremely beneficial for obtaining a dense ceramic product.

In the second invention, the organic binder is added with a halide which lowers the decomposition initiation temperature and slows down the progress of decomposition, so that the organic binder is decomposed at a lower temperature than in the first invention. It is possible to alleviate the increase in the amount of gas generated by the start of the organic binder, and thereby more reliably avoid the occurrence of cracks in the ceramic molded body.

(3) Example Ceramic molded body, ceramic powder, an organic binder,
The ceramic molded body is molded by using a raw material mixed with a sintering aid and the like, and the ceramic molded body is subjected to a degreasing treatment to remove the organic binder.

As the ceramic powder, Si ₃ having a diameter of 0.1 to 1 μm is used.
This applies to simple powders of N ₄ , SiC, ZrO ₂ , TiC, TiN, etc., and mixed powders of those selected from these powders.

As the organic binder, polyvinyl alcohol binder, polyvinyl alcohol emulsion, stearic acid emulsion, ammonium alginate binder,
Paraffin-based and silicone-based waxes, cellulose-based binders, alkylbenzene-based binders, acrylic resin-based emulsions, polyvinyl butyral-based binders, methacrylic resin-based binders, etc. are applicable.

FIG. 1 shows the progress of decomposition of various organic binders in the degreasing treatment of a ceramic compact made of Si ₃ N ₄ in relation to the furnace temperature and the weight reduction rate of the organic binder. . Each organic binder is used alone, and N ₂ gas as an inert gas is passed through the furnace at a flow rate of 70 ml / min for degreasing treatment, and the temperature rising rate in the furnace is 5 ° C./min.
Done in.

The line I corresponds to an acrylic resin emulsion, the line II to a polyvinyl alcohol-based binder, the line III to a polyvinyl alcohol-based emulsion, the line IV to an ammonium alginate-based binder, and the line V to a paraffin wax.

As is clear from FIG. 1, each organic binder tends to rapidly decompose at a predetermined temperature and generate a large amount of gas at one time.

When an organic binder showing such a tendency is used alone,
Due to the high gas pressure caused by the generation of a large amount of gas, a crack may be generated in the ceramic molded body, which may be broken.

FIG. 2 shows the relationship between the coefficient of thermal expansion of the organic binder in the ceramic compact and the temperature in the furnace. The measurement of the coefficient of thermal expansion is
N ₂ gas is circulated in the furnace at a flow rate of 70 ml / min, and the temperature is raised in the furnace at a rate of 5 ° C./min. Line VI
Corresponds to the ammonium alginate-based binder, and line VII corresponds to the polyvinyl alcohol-based binder. Line VIII shows the coefficient of thermal expansion of Si ₃ N ₄ .

As is clear from FIG. 2, the ammonium alginate-based binder of line VI and the polyvinyl alcohol-based binder of line VII have a coefficient of thermal expansion far from that of Si ₃ N _{4 of} line VIII, and are Repeat expansion and contraction.

When an organic binder that exhibits such thermal behavior is used, cracks occur in the ceramic molded body.

In the present invention, a new mixed type is prepared by mixing several kinds of the organic binders, having a thermal expansion coefficient substantially equal to that of the ceramic powder, and having a physical property that decomposition proceeds substantially proportionally with temperature rise. An organic binder is prepared, and the mixed organic binder is added to ceramic powder to form a ceramic compact.

In the degreasing treatment, the ceramic molded body was placed in a vacuum furnace, and the molded body was washed with an inert gas such as N ₂ gas at a flow rate of 0.1.
It is performed by heating to about 650 ° C. under reduced pressure of about 10 Torr to decompose the mixed organic binder.

In the degreasing treatment, if the atmosphere in the furnace is reduced to a simple one in which the pressure is reduced while the inert gas is flowing, the control becomes easy.

Since the heating is performed under reduced pressure, the boiling point, decomposition temperature and vapor pressure of the mixed organic binder are lower than those under atmospheric pressure, and the mixed organic binder is used in a relatively low temperature range of about 100 to about 650 ° C. Decomposition of the system binder proceeds almost proportionally with increasing temperature. As a result, the thermal decomposition of the mixed organic binder can be carried out gradually and at a constant rate, and the thermal expansion coefficient of the mixed organic binder is almost the same as that of the ceramic powder. The degreasing treatment of the body can be efficiently performed while avoiding the occurrence of cracks.

Furthermore, since the organic binder is thermally decomposed during the flow of the inert gas, the gas generated in the furnace is smoothly discharged to the outside by the inert gas, and the gas discharged in the ceramic molded body and the mixed organic binder It is possible to prevent clogging of the ceramic molded body due to the molten content by means of the inert gas that has entered the ceramic molded body, thereby preventing the residue of the mixed organic binder from remaining in the ceramic molded body. You can

The residue is mainly carbon, which hinders the improvement of the density of the ceramic product that has undergone the sintering process.
The absence of residue in the ceramic molded body is extremely beneficial for obtaining a dense ceramic product.

When the furnace pressure is lower than 0.1 Torr, the significance of circulating N ₂ gas is lost, and when it exceeds 10 Torr, the depressurizing effect cannot be obtained.

Further, in the present invention, a mixed organic binder is added with a halide that lowers the decomposition start temperature and moderates the progress of decomposition, and the decomposition of the mixed organic binder is performed without adding a halide. Starting at a lower temperature than in the case, it is possible to alleviate an increase in the amount of gas generated by the mixed organic binder, thereby more reliably avoiding the occurrence of cracks in the ceramic molded body.

Examples of the halide include benzoyl chloride, dichlorodiphenylsilane, alkylchlorosilane, and other alkyl chlorides.

The sintering aid exhibits a sintering action at the sintering temperature of the ceramic powder, and this kind of sintering aid has a diameter of 0.1 to 1
A single powder of μm of Al ₂ O ₃ , Y ₂ O ₃ , MgO, SiO ₂ or the like and a mixed powder of those selected from these powders are applicable.

[Example I]

<Ceramic powder> 90 parts by weight of Si ₃ N ₄ <Sintering aid powder> 6 parts by weight of Y ₂ O ₃ 100 parts by weight of a mixed powder of 4 parts by weight of Al ₂ O ₃ and the following mixed organic bonding A raw material powder is obtained by adding an agent and a halide.

<Mixed type organic binder> Polyvinyl alcohol binder 2 parts by weight Stearic acid emulsion 2 parts by weight Ammonium alginate binder 5 parts by weight Paraffin wax 12 parts by weight Cellulose binder 0.5 parts by weight Alkylbenzene binder 1 part by weight Acrylic resin emulsion 3 parts by weight <halide> Benzoyl chloride 0.002 parts by weight A pressure molding method is applied to the raw material powder to obtain a molding pressure of 100M.
As shown in Fig. 3 (a) at Pa, a = 45 mm, b = 45 m
A prismatic ceramic molded body 1 with m and c = 120 mm is molded. In this case, the added amount of the mixed organic binder is about 22% of the total amount, and belongs to the category where the added amount is large under the application of the pressure molding method. By increasing the ratio, it is possible to prevent lamination during molding and increase the density of the ceramic molded body 1 to about 55% of the theoretical density.

Place the ceramic molded body 1 in a drying furnace at 110 ° C for 12
Dry for ~ 24 hours.

The dried ceramic molded body 1 is placed in a vacuum furnace, N ₂ gas is circulated at a furnace internal pressure of 0.8 Torr at a flow rate of 30 ml / min, and the thermal treatment described below is performed under the conditions of FIG.

That is, the temperature rising rate of 15 ° C / min is followed by 650 ° C.
Degreasing process for 45 minutes at constant temperature (Fig. 4, line IX)
a, IXb), the temperature rising rate is 20 ° C / min, and then 1
Pre-sintering process (4th step of maintaining constant temperature at 200 ° C for 2 hours)
(Figures IXc and IXd), and a cooling process of cooling the furnace at a constant temperature of 800 ° C for 10 minutes to prevent abrupt shrinkage of the temporary sintered body, and then to cool the furnace after cooling at a cooling rate of 30 ° C / min. (FIG. 4, lines IXe, IXf, IXg).

The line X in FIG. 5 shows the change in the furnace pressure in the degreasing step. The decrease in the furnace pressure after the increase is due to the amount of gas generated by the decomposition of the mixed organic binder. The mixed organic binder starts to decompose at about 100 ° C. The pressure inside the furnace gradually rises because it decomposes almost proportionally and gradually. At the furnace temperature of about 650 ° C., the mixed organic binder is completely decomposed, so that the furnace pressure reaches a peak, and then the furnace pressure is rapidly decreased to 0. Maintained at 8 Torr.

Fig. 6 shows the degreasing process during N ₂ gas flow with a heating rate of 5 ° C / mi
The relationship between the temperature in the furnace and the weight reduction rate of the organic binder in the case of the condition of n is shown, and the line XI corresponds to the mixed organic binder.

As can be seen from the line XI, the mixed organic binder has about 1
Decomposition starts at 15 ° C., and thereafter, the decomposition proceeds almost proportionally to the temperature increase, and complete decomposition occurs at about 650 ° C.

Line XII corresponds to the other mixed organic binder used in the present invention, and is the same as the above except that its compounding component does not contain benzoyl chloride and thus halide.

As is clear from the comparison between the lines XI and XII, when the halide is added, the decomposition start temperature of the mixed organic binder is lowered, and the progress of the decomposition is moderated, so that the increase in the amount of generated gas is moderated. .

In FIG. 2, the line XIII shows the coefficient of thermal expansion of the halide-containing mixed organic binder, and as is clear from the line XIII, the mixed organic binder has a thermal expansion coefficient substantially equal to that of Si ₃ N ₄ of the line VIII. Have a rate.

As described above, using a specific mixed organic binder,
When the degreasing step is performed under the above-mentioned conditions, cracks do not occur and it is possible to obtain a temporary sintered body that is substantially the same as the ceramic molded body.

In FIG. 6, as a comparative example, line XIV shows the relationship between the furnace temperature and the weight reduction rate of the binder in the mixed organic binder in which paraffin wax, ammonium alginate binder and acrylic resin emulsion are mixed. Indicates. As is clear from the line XIV, in the case of the comparative example, the degree of progress of the decomposition varies depending on the temperature, and particularly about 350 to about 40.
The decomposition progresses rapidly at 0 ° C., and as a result, cracks are observed in the pre-sintered body.

FIG. 3 (b) is an intermediate product 2 obtained by milling and lacing the pre-sintered body obtained by the above treatment.
And the dimensions of each part are a ₁ = 40 mm, b ₁ = 40 mm,
c ₁ = 30 mm, c ₂ = 20 mm, c ₃ = 60 mm, d ₁ = 2
5 mm and d ₂ = 10 mm.

When the ceramic molded body is pre-sintered as described above, since the pre-sintered body has an appropriate hardness, it becomes possible to perform machining such as milling, lace processing, and drilling.

When the surface properties of the intermediate product after the lace processing were examined, it was confirmed that there was no residue such as carbon.

The intermediate product was subjected to HIP treatment (hot isostatic pressing treatment) to which the capsule method was applied, with a pressure of 1000 atm and a temperature of 17
Si ₃ N ₄ was applied under the conditions of 00 ° C. and a treatment time of 2 hours.
Is sintered to obtain a ceramic product.

Example II

<Ceramic powder> 90 parts by weight of Si ₃ N ₄ <Sintering aid powder> 6 parts by weight of Y ₂ O ₃ 100 parts by weight of a mixed powder of 4 parts by weight of Al ₂ O ₃ and the following mixed organic bonding A raw material powder is obtained by adding an agent and a halide.

<Mixed type organic binder> Paraffin wax 25 parts by weight Stearic acid emulsion 5 parts by weight Polyvinyl butyral binder 5 parts by weight Cellulose binder 1 part by weight Methacrylic resin binder 3 parts by weight <Halide> Benzoyl chloride 0.1 parts by weight In this case, the amount of the mixed organic binder added is about 37% of the total amount.
%.

An injection molding method is applied to the raw material powder to obtain a ceramic compact similar to that in Example I, and then dried in the same manner as in Example I,
Thermal treatment, lacing and HIP treatment are carried out to obtain a ceramic product similar to that of Example I.

In FIG. 5, the line XV shows the change in the furnace pressure in the degreasing step in the thermal treatment, and it is clear that it has a tendency almost equal to the line X in Example I.

When a sample was cut out from the ceramic product, the surface of the sample was polished and subjected to an optical microscope inspection, and a fractured surface was subjected to a scanning electron microscope inspection, it was confirmed to be normal.

C. EFFECTS OF THE INVENTION According to the present invention, by using the organic binder and the heating atmosphere specified as described above, the atmosphere control is facilitated, the organic binder is decomposed and removed, and the ceramic molded body is cracked. It can be performed efficiently and surely without performing.

Further, by adding the halide specified as described above to the organic binder, it is possible to more reliably avoid the occurrence of cracks in the ceramic molded body.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the weight reduction rate of various organic binders and the temperature in the furnace during degreasing, and FIG. 2 is a graph showing the relationship between the coefficient of thermal expansion of various organic binders and the temperature in the furnace. FIG. 3 (a) is a perspective view of the ceramic molded body, FIG. 3 (b) is a perspective view of the intermediate product, and FIG. 4 is a graph showing the relationship between the temperature in the furnace and the time in the thermal treatment of the ceramic molded body. FIG. 5 is a graph showing the relationship between the furnace pressure and the furnace temperature during degreasing, and FIG. 6 is a graph showing the relationship between the weight reduction rate of various mixed organic binders and the furnace temperature during degreasing. is there.

Claims (2)

[Claims] 1. A degreasing method for a ceramic molded body, wherein the organic binder is removed from a ceramic molded body formed by adding an organic binder to the ceramic powder, and the ceramic powder is used as the organic binder. An organic material having substantially the same coefficient of thermal expansion and physical properties in which decomposition progresses in a substantially proportional manner with respect to a temperature increase is used, and the ceramic molded body is heated under reduced pressure in an inert gas flow to produce the organic compound. A method for degreasing a ceramic molded body, which comprises decomposing a system binder. 2. A degreasing method for a ceramic molded body, comprising removing the organic binder from a ceramic molded body formed by adding an organic binder to the ceramic powder, wherein the ceramic powder is used as the organic binder. An organic binder having substantially the same coefficient of thermal expansion and physical properties in which decomposition proceeds in a substantially proportional manner with respect to temperature rise is used.
It is characterized in that the organic binder is decomposed by lowering the decomposition start temperature thereof and adding a halide that moderates the progress of decomposition, and heating the ceramic molded body under reduced pressure in an inert gas flow. And a method for degreasing a ceramic molded body.