JPH0625037B2 - Manufacturing method of ceramic products - Google Patents

Description

Detailed Description of the Invention A. Object of the Invention (1) Field of Industrial Application The present invention relates to a method for producing a ceramic product using Si ₃ N ₄ or SiC powder.

(2) Conventional technology Conventionally, when manufacturing this kind of product, Y which exerts a sintering action on powder such as Si ₃ N ₄ at a sintering temperature of the powder.
_A compact is obtained by using a mixed powder in which a large amount of sintering aid powder such as ₂ O ₃ , Al ₂ O ₃ and MgO is dispersed, and then the compact is sintered under normal pressure or high pressure and fired. A method of obtaining a bonded body and then performing mechanical processing on the sintered body is adopted (NIKKEI NEW MATERIALS 19
See the February 24, 1986 issue).

(3) Problems to be solved by the invention However, since the sintered body obtained through the above steps has a large hardness, it is difficult to process with a tool other than the diamond tool, and the diamond tool is used. However, it takes a lot of processing time and the productivity of ceramic products is poor. Further, when a large amount of the sintering aid is used as described above, there is a problem that the high temperature strength of the ceramic product deteriorates because most of the sintering aid remains in the ceramic product.

In view of the above, the present invention obtains a pre-sintered body having a predetermined strength and improves the productivity of ceramic products by machining the pre-sintered body to improve the efficiency of the processing work. In addition, it is an object of the present invention to provide the above-mentioned manufacturing method capable of obtaining a ceramic product excellent in high temperature strength.

B. Structure of the Invention (1) Means for Solving the Problems The present invention provides a ceramic powder of Si ₃ N ₄ or SiC that is calcined at a temperature lower than the sintering temperature of the ceramic powder. A molded body is obtained by using a mixture in which one or more sintering aids containing both an alkali metal oxide and SiO ₂ which exert a binding action are dispersed, and then the molded body is subjected to the temperature lower than the sintering temperature. To obtain a temporary sintered body by temporary sintering; a step of machining the temporary sintered body to obtain a primary intermediate product; eluting the alkali metal oxide with an acid from the primary intermediate product To obtain a secondary intermediate product, and sintering the secondary intermediate product at the sintering temperature and converting the SiO ₂ into Si ₃ N ₄ or Si.
And a step of changing to C.

In addition, the present invention provides a ceramic powder of Si ₃ N ₄ or SiC containing alkali metal oxides and SiO ₂ which exert a pre-sintering action on the ceramic powder at a temperature lower than the sintering temperature of the ceramic powder. A step of obtaining a compact using a mixture in which one or more sintering aids containing both are dispersed, and then presintering the compact at the temperature lower than the sintering temperature to obtain a temporary sintered body Machining the temporary sintered body to obtain a primary intermediate product; sintering the primary intermediate product at the sintering temperature and converting the SiO ₂ into Si ₃ N
₄ or SiC to obtain a secondary intermediate product; and a step of eluting the alkali metal oxide with an acid from the secondary intermediate product.

(2) Operation To obtain a pre-sintered body having a strength that can withstand machining and a hardness that can be machined by ordinary cemented carbide tools by the pre-sintering action of the specific sintering aid. You can

Therefore, it is possible to efficiently machine the temporary sintered body, improve the productivity of the ceramic product, and improve the dimensional accuracy.

In the sintering aid, most of the alkali metal oxides are removed by the elution treatment with acid, and most of the SiO
_{Since 2} can be changed to Si ₃ N ₄ or SiC, that is, the same kind of material as the ceramic powder, the sintering aid, which causes high temperature strength deterioration, hardly remains in the ceramic product.

This makes it possible to obtain a ceramic product having high strength at high temperature.

(3) Example A ceramic powder made of Si ₃ N ₄ or SiC is a main component of a ceramic product, and has a diameter of 0.1 to 1 μm.

A sintering aid that exerts a pre-sintering effect on the ceramic powder at a temperature lower than the sintering temperature, that is, a compound containing both an alkali metal oxide and SiO ₂ is xNa ₂ O.ySiO. ₂ , xK ₂ O · ySiO ₂ ,
xLiO ₂ · ySiO ₂ (where x = 1 and 2, y = 1
To 3) are applicable, and one or more compounds selected from these are used.

These compounds produce a vitreous substance at a temperature lower than the sintering temperature and exert a pre-sintering action. For the purpose of facilitating the production of the vitreous substance, a small amount of B is added to the compound. ₂ O ₃ , MgO, etc. may be blended.

The sintering aid is used in the state of a dispersion liquid using a dispersion medium of 30 to 40% by weight. Water is suitable as the dispersion medium. When the sintering aid is used in the form of dispersoid as described above, the sintering aid is miniaturized and its reactivity is improved.

In the above compound, an alkali metal oxide, B ₂ O ₃ , M
gO and the like are eluted with nitric acid as an acid, a single acid such as hydrochloric acid, or a mixed acid thereof, and SiO ₂ undergoes N in the sintering process.
_It can be changed to Si ₃ N ₄ in a _two- gas atmosphere, and to SiC in a reducing atmosphere containing C powder.

Further, an organic lubricant such as ammonium stearate is used if necessary for the purpose of improving moldability.

The blending amounts of the ceramic powder, the sintering aid and the organic lubricant are as follows: ceramic powder 92 to 99.9% by weight sintering aid 0.1 to 3% by weight organic lubricant 0 to 5% by weight.

The reason for limiting the blending amount of each component as described above is as follows.

In the case of the sintering aid, if the blending amount is less than 0.1% by weight, the pre-sintering effect of the sintering aid cannot be sufficiently obtained, so that the strength of the pre-sintered body becomes low and the mechanical strength of the machine is reduced. The temporary sintered body may collapse during processing. On the other hand, if it exceeds 3% by weight, the sintering aid becomes excessive, resulting in a decrease in strength of the pre-sintered body and residual in the ceramic product, resulting in a decrease in high temperature strength thereof.

In the case of an organic lubricant, even if its content exceeds 5% by weight, the effect of improving the formability hardly changes, and rather its removal lowers the production efficiency.

When a molded product is obtained by using a mixture in which a sintering aid and an organic lubricant are dispersed in the ceramic powder, various molding methods such as a slip casting method, a pressure molding method, and an injection molding method can be used. Used. Molding pressure is 25-15
0 MPa is suitable.

In addition, the temporary sintering conditions for obtaining a temporary sintered body from the above-mentioned molded body are 1200 to 1500 ° C. and 0.5 to 5 hours. By this temporary sintering treatment, the molded body exhibits a linear shrinkage rate of 0.1 to 5%. This linear shrinkage rate changes mainly due to the blending amount of the sintering aid. Bending strength of temporary sintered body is 70 ~ 350MP
a, Vickers hardness Hmv is 200 to 600, relative density is 65 to 77%, and porosity is 23 to 35%.

Thus, the pre-sintered body is a porous body, and the growth of crystal grains such as ceramic powder is in the very initial stage of sintering.
Since it has a relatively low hardness and has a predetermined strength, it has good machinability such as lace processing and drilling.
A cutting speed of 10 mm / min can be obtained and it does not collapse during processing. In order to optimize this machinability, the Vickers hardness Hmv of the pre-sintered body is 300-50.
Set it to 0.

As the sintering method, an atmospheric pressure sintering method, a hot pressing method, a HIP treatment (hot isostatic pressing treatment) by a capsule method, or the like is adopted.

Sintering conditions vary depending on the ceramic powder, and Si ₃ N ₄
In the case of, the temperature is 1500 to 1750 ° C. for 30 minutes or more, and in the case of SiC, the temperature is 1600 to 2200 ° C. for 30 minutes or more.

[Example I]

Ceramic powder Si ₃ N ₄ 96.7-99.9% by weight Firing aid Na ₂ O · SiO ₂ 0.1-3.0% by weight Organic lubricant ammonium stearate 0.3% by weight In the above range, Si ₃ N ₄ and Na ₂ O.SiO
The raw material powders of various mixing ratios are prepared by changing the mixing amount of ₂ ,
After mixing each raw material powder in a ball mill for 24 hours, a pressure molding method is applied to each raw material powder to obtain a molding pressure of 100 MPa.
Then, the cylindrical molded body 1 shown in FIG. 1 (a) is obtained. In each molded body 1, a = 35 mm and b = 120 mm.

Each of the dried compacts 1 was placed in a vacuum furnace, and N ₂ gas was circulated in the furnace under the condition of 30 ml / min, and the furnace pressure was 0.8 Torr.
r, the temperature in the furnace is 1200 ° C., and the calcination process is performed for 2 hours to obtain a calcination body. During the process of raising the temperature in the furnace, the temperature is maintained at 650 ° C. for 1 hour to remove ammonium stearate.

Figure 2 shows the relationship between the bending strength of the _Na 2 O · SiO ₂ amount and the temporary sintered body in presintered body, for example, _Na 2 O ·
It is possible to obtain a pre-sintered body having a bending strength of about 340 MPa when the content of SiO ₂ is 1% by weight.

Figure 3 shows the relationship between the Vickers hardness of _{Na 2} O · SiO 2 amount and calcined body of presintered body, _Na 2 O ·
SiO ₂ amount 0.5 to 3.0% by weight is a good range of machinability.

FIG. 4 shows the relationship between the blended amount of Na ₂ O / SiO _{2 in the} temporary sintered body and the relative density of the temporary sintered body. Each temporary sintered body is a porous body having a relative density of about 67% or more. I understand.

Each temporary sintered body is cut using a normal cemented carbide bite, and as shown in FIG. 1 (b), a large diameter portion 2 and a medium diameter portion 3
And a primary intermediate product 7 comprising a small diameter portion 4 and a large diameter portion 2 having a blind hole 5 and a small diameter portion 4 having a male screw 6 is obtained. The size of each part of the primary intermediate product 7 is a ₁ = 30 mm, a
₂ = 16 mm, a ₃ = 20 mm, a ₄ = 18 mm, b ₁ = 25
mm, b ₂ = 15 mm, b ₃ = 30 mm, b ₄ = 3 mm, b ₅ =
It is 40 mm.

The cutting speed was 3 to 10 mm / min, and no chipping was observed in the tool.

HIP treatment by the capsule method was performed on each of the primary intermediate products 7 as a sintering treatment in an atmosphere of N ₂ gas at 1000 atm.
It is applied under the condition of 50 ° C. for 2 hours to obtain a secondary intermediate product.

FIG. 5 shows the relationship between the content of Na ₂ O · SiO _{2 in the} secondary intermediate product and the relative density of the secondary intermediate product. Each secondary intermediate product has a relative density of about 85% or more. It is significantly improved compared to that.

By the sintering process, of the sintering aid included in the first intermediate product, SiO ₂ most are changed to Si 3 _{N 4,} thus the ceramic powder and the same type material.

Each secondary intermediate product is immersed in 30% nitric acid, and Na ₂ O of the sintering aid is eluted to obtain a ceramic product. It has been confirmed that 80 to 90% of Na ₂ O is removed by this elution treatment, and the rest is hardly observed by EPMA (X-ray microanalyzer).

FIG. 6 shows the relationship between the bending strength and the temperature of the ceramic product. The line (v) corresponds to the ceramic product obtained by the present invention and the line (w) corresponds to the conventional product. In the conventional type, 90 wt% of Si ₃ N ₄ was mixed with 6 wt% of Y ₂ O ₃ and 4 wt% of Al ₂ O ₃ as a sintering aid that exerts a sintering action at a sintering temperature. 1750 ° C, 2
It was obtained by sintering under the condition of time. Line (x) corresponds to the secondary intermediate product of the present invention, that is, before the elution treatment with acid.

As is clear from FIG. 6 line (v), the ceramic product obtained according to the present invention has superior strength in the high temperature range of 700 ° C. or higher as compared with the conventional product (w). . Further, this high temperature strength is significantly improved by the elution treatment with an acid, as is clear from the comparison between the line (v) and the line (x).

Example II

Ceramic powder Si ₃ N ₄ 99.0% by weight Sintering aid Na ₂ O / SiO ₂ 0.5% by weight B ₂ O ₃ 0.2% by weight MgO 0.3% by weight Raw material powder prepared by blending Is mixed in a ball mill for 24 hours, and then the slip casting method is applied to the raw material powder to obtain a prismatic shaped body having a length of 40 mm, a width of 80 mm and a length of 100 mm.

The dried molded body is placed in a vacuum furnace and subjected to a sintering treatment under the same temporary sintering conditions as in Example I to obtain a temporary sintered body.

In this temporary sintered body, Na ₂ O, B ₂
O ₃ and MgO are Na ₃ B ₄ O ₇ , NaMgB ₄ O ₇
It produces a glassy compound that is soluble in acid.

Mechanical processing such as grinding and drilling is applied to the temporary sintered body 1
Next get intermediate products.

The first intermediate product was immersed in 25% nitric acid heated to 50 ° C. to elute most of the Na ₃ B ₄ O ₇ , NaMgB ₄ O ₇ , and thus Na ₂ O, B ₂ O ₃ and MgO components. To obtain a secondary intermediate product.

Si ₃ N ₄ powder and C powder together with the secondary intermediate product were encapsulated under vacuum, and 1000 atm as a sintering process,
HIP treatment is performed at 1750 ° C. for 2 hours to obtain a ceramic product.

In this sintering process, among the sintering aids, SiO ₂ is Si
It is reduced like O ₂ + 2C → SiC + 2CO and converted into SiC, which is the same substance as the ceramic powder. In this case, CO is generated, but the amount thereof is small and therefore does not hinder the densification of the ceramic product. The reason for encapsulating the Si ₃ N ₄ powder in the capsule is to prevent the oxidation of the secondary intermediate product.

FIG. 7 shows the relationship between the fracture probability distribution and the fracture stress of a ceramic product in a Weibull distribution. The line (y) is the ceramic product obtained by the present invention, and the line (z) is the conventional one. Corresponding to each. In the conventional one, 86 wt% of Si ₃ N ₄ was mixed with 7 wt% of MgO and 7 wt% of Y ₂ O ₃ as a sintering aid which exerts a sintering action at its sintering temperature. , 1750 ° C., and sintered for 2 hours.

As is clear from FIG. 7 line (y), the ceramic product obtained according to the present invention has a fracture probability distribution within a practicable range of a fracture stress of about 550 MPa to about 750 MPa as compared with the conventional product shown by the line (z). Is low, and therefore the reliability of the strength is extremely high.

C. EFFECTS OF THE INVENTION As described above, according to the present invention, a primary intermediate product is obtained by machining the temporary sintered body obtained by the temporary sintering action using the specific sintering aid, and Since the ceramic product is obtained through the sintering process based on the next intermediate product, the productivity of the ceramic product can be improved and the dimensional accuracy thereof can be improved.

Further, most of the above-mentioned sintering aids are eluted with an acid, and most of SiO ₂ is changed into a substance similar to the ceramic powder such as Si ₃ N ₄ or SiC, so that the ceramic product is deteriorated in high temperature strength. The sintering aid, which is a factor of, hardly remains. This makes it possible to provide a ceramic product having high strength at high temperature.

[Brief description of drawings]

Fig. 1 (a) is a perspective view of the molded body, Fig. 1 (b) is a vertical sectional front view of the primary intermediate product, and Fig. 2 is the blending amount of Na ₂ O / SiO ₂ and the bending strength of the temporary sintered body. Is a graph showing the relationship between
A graph showing the relationship between the amount of ₂ O / SiO ₂ compounded and the Vickers hardness of the pre-sintered body, and FIG. 4 is a graph showing the relationship between the amount of Na ₂ O / SiO ₂ compounded and the relative density of the temporary sintered body, Fig. 5 is a graph showing the relationship between the amount of Na ₂ O / SiO ₂ compounded and the relative density of the secondary intermediate product after the sintering step, and Fig. 6 is a graph showing the relationship between the bending strength of the ceramic product and the temperature. FIG. 7 is a graph showing the relationship between the fracture probability distribution and the fracture stress of ceramic products. 1 …… Molded body, 7 …… Primary intermediate product

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C04B 35/58 X

Claims (2)

[Claims] 1. A ceramic powder made of Si ₃ N ₄ or SiC, which exhibits a pre-sintering action on the ceramic powder at a temperature lower than the sintering temperature of the ceramic powder, and an alkali metal oxide and SiO _2. A mixture is obtained by dispersing one or more sintering aids containing both of the above, and a molded body is obtained, and then the molded body is presintered at a temperature lower than the sintering temperature to obtain a temporary sintered body. A step of machining the temporary sintered body to obtain a primary intermediate product; a step of eluting the alkali metal oxide with an acid from the primary intermediate product to obtain a secondary intermediate product; and the secondary The intermediate product is sintered at the sintering temperature and the SiO ₂ is mixed with Si ₃ N ₄ or S.
a step of converting to iC; 2. A ceramic powder made of Si ₃ N ₄ or SiC, which exhibits a pre-sintering action on the ceramic powder at a temperature lower than the sintering temperature of the ceramic powder, and an alkali metal oxide and SiO _2. A mixture is obtained by dispersing one or more sintering aids containing both of the above, and a molded body is obtained, and then the molded body is presintered at a temperature lower than the sintering temperature to obtain a temporary sintered body. Step: Machining the pre-sintered body to obtain a primary intermediate product; Sintering the primary intermediate product at the sintering temperature and converting the SiO ₂ into Si ₃ N
₄ or SiC to obtain a secondary intermediate product; and a step of eluting the alkali metal oxide from the secondary intermediate product with an acid;