JPH06229842A - Molding for detecting heat history - Google Patents

Abstract

PURPOSE:To improve the indicated-temperature detecting accuracy of a molding for detecting heat history so as to strictly manage a baking process and, at the same time, to manage baking in a high-temperature region in an inert gas atmosphere by using an unbaked ceramic molding containing Si3N4 and/or SiC and a sintering assistant in a specific composition as the molding. CONSTITUTION:The fluctuation of the burning shrinkage factor of the title molding is reduced and the indicated-temperature detecting accuracy is improved to + or -5 deg.C by setting the mixing ratio of Si3N4 in the molding at >=60mol%. In addition, the molding is made to detect heat history within a temperature of 1,500-2,000 deg.C by setting the mixing ratio of a sintering assistant at <=40mol%. In addition, when the mixing ratio of the sintering assistant of boron, carbon, etc., is set at <=30mol%, the molding can be used in a vacuum or inert gas atmosphere. Then an unbaked molding is formed of a raw material having such a composition by forming chord sections 12 and 22 in complete roundness sections 11 and 11 by pressing and chamfering 14 corner sections, and then, printing a mark 13 indicating the surface side while the particle size, green density, etc., of the raw material are strictly managed. When the molding is formed in such a shape, no warping occurs and the dimensions of the molding can be accurately measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for detecting a thermal history in a firing process of ceramics or the like, and particularly in firing in a nitrogen atmosphere, a vacuum or an inert atmosphere when firing silicon nitride or silicon carbide. Of 1500-2000
The present invention relates to a molded article for detecting heat history in the temperature range of ° C.

[0002]

2. Description of the Related Art In the firing process of ceramics, the thermal history of the body to be fired changes depending on the temperature profile, the type of firing furnace, the settings in the furnace, and the like. That is, even if the firing temperature is the same, the thermal history will be different if other conditions are different, and it is necessary to correctly detect this thermal history.

For example, the thermal history of a body to be fired has been detected by using a Zegel cone as disclosed in Japanese Utility Model Publication No. 56-29441. Zegel cones are provided with a plurality of triangular pyramids having different melting temperatures on a support, and after firing this Zegel cone together with the body to be fired, the thermal history of the triangular pyramids falls, It was supposed to detect. However, since it cannot detect accurately, it is now less used.

Therefore, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 1-184388, an unsintered compact of ceramics is used, and this compact is fired together with the body to be sintered, and then the dimensional change due to shrinkage is measured. By doing so, the thermal history was detected. For example, a ring-shaped molded body 20 as shown in FIG. 2 or a sheet-shaped molded body 30 as shown in FIG. 3 was used.

When measuring such a dimensional change due to firing shrinkage, the dimensional change is conveniently converted into a temperature, but this temperature does not represent an actual temperature but represents a thermal history. Therefore, in the present invention, it is referred to as an instruction temperature.

[0006]

SUMMARY OF THE INVENTION However, the above-mentioned ceramic molded body for thermal history detection has a problem of Al ₂ O ₃ or Si.
Since it was composed of a natural raw material containing O ₂ as a main component and containing a large amount of impurities, there were variations in the firing shrinkage, and the accuracy of the detected indicated temperature was poor.

Further, the ring-shaped one shown in FIG. 2 has a large volume, and thus requires a large space in the firing furnace.
The sheet-like material shown in FIG. 3 has a problem that warpage occurs and the dimension cannot be measured correctly.

On the other hand, the applicant of the present invention has filed Japanese Patent Application Laid-Open No. 4-653.
As disclosed in Japanese Patent Publication No. 69, 99.7% by weight or more of Al ₂
It was proposed that a ceramic green body containing O _{3 be used} as a thermal history detection body, but it could only be used in an oxidizing atmosphere. In other words, the molded body containing Al ₂ O ₃ as a main component is decomposed in an atmosphere such as nitrogen, vacuum, or inert gas, and the firing shrinkage greatly varies, so that the detected indicated temperature is inaccurate. It was

[0009]

Therefore, the present invention is based on Si ₃
A ceramic unfired compact having a composition of N ₄ and / or SiC of 60 mol% or more and a sintering aid of 40 mol% or less is used as a thermal history detecting compact.

Specifically, Si ₃ N _{4 is} 60 mol% or more,
A ceramic unfired molded body having a composition of 40 mol% or less of a sintering aid such as a rare earth oxide can be used as a thermal history detection molded body and can be used particularly in a nitrogen atmosphere.

Here, the reason why Si ₃ N _{4 is set} to 60 mol% or more is to reduce the variation in the firing shrinkage and to make the detected indicated temperature accuracy ± 5 ° C. The reason why the amount of the sintering aid is 40 mol% or less is that the amount of the sintering aid is 40 mol%.
This is because if the amount is more than 1,700 ° C. or less, it will be completely sintered and densified, and the thermal history cannot be detected, and preferably 20 mol% or less. Furthermore, although MgO, Al ₂ O ₃ or the like may be used as a sintering aid, it is preferable to use a rare earth oxide such as Y ₂ O ₃ in order to reduce the variation in shrinkage. It is desirable that the content of the product be 0.5 mol% or more.

Another composition is 70 mol% of SiC.
As described above, a ceramic unfired molded body having a composition of 30 mol% or less of a sintering aid such as boron or carbon can be used as a thermal history detection molded body, and can be used particularly in a vacuum or an inert atmosphere.

Here, the reason why the SiC content is 70 mol% or more is to reduce the variation in the firing shrinkage and to set the accuracy of the detected indicated temperature to ± 5 ° C. The reason why the amount of the sintering aid is 30 mol% or less is that if the amount of the sintering aid is more than 30 mol%, it will be completely sintered and densified at a temperature of 1750 ° C. or less, and the thermal history can be detected. This is because it disappears, and it is preferably 15 mol% or less. Further, although Al ₂ O ₃ or the like may be used as a sintering aid, it is preferable to use boron, a boron compound, or carbon in order to reduce the variation in shrinkage, and the boron content is 0.1 mol% or more. , Carbon is desirably contained in an amount of 2 mol% or more.

Further, as another composition, Si ₃ N ₄ and SiC are contained in a total amount of 60 mol% or more, and Y ₂ O ₃ and Al ₂ O _{3 are} contained.
It is also possible to use a ceramics unfired molded body having a composition of a sintering aid such as 40 mol% or less as a thermal history detector.

Although the above-mentioned sintering aid is a component that promotes the sintering of ceramics, in the present invention, all components other than Si ₃ N ₄ and / or SiC, which are the main components, are burnt. Use as a co-agent.

[0016]

EXAMPLES Examples of the present invention will be described below.

As shown in FIGS. 1 (a) and 1 (b), the heat history detecting molded body 10 of the present invention has a chord portion 12 parallel to the disc body.
12 is formed, and the remaining circular arc portions serve as measurement surfaces 11 having excellent roundness. Further, a recess 13 is formed on one side by marking such as dots or alphabets for distinguishing the front side and the back side, and chamfers 14 are provided on the upper and lower corners.

Further, the compact 10 has a composition of 60 mol% or more of Si ₃ N ₄ and / or SiC and 40 mol% or less of a sintering aid, and the particle size of the raw material powder, the green density of the compact, etc. It is an unsintered compact obtained by press-molding under extremely strict control. Then, as will be described later, the firing temperature is changed under a certain condition, the dimension after firing of the molded body 10 is measured, and the relationship between the dimension and the firing temperature is prepared as a conversion table. After that, when firing is performed under different conditions, the molded body 10 is fired together with the body to be fired, and the dimensional change after firing is measured, so that the indicated temperature can be obtained from the conversion table.

As described above, the indicated temperature is not an actual temperature but a thermal history for convenience. That is, by using the heat history detecting molded body of the present invention, it is possible to manage the heat history itself by obtaining the indicated temperature even when the firing conditions are different.

The molded body 10 of the present invention is made of Si ₃ N ₄
And / or SiC as the main component, so nitrogen,
The indicated temperature can be detected with high accuracy in a non-oxidizing atmosphere such as vacuum or inert atmosphere.

Further, the molded body 10 of the present invention has the chord portion 1
Since it has 2 and 12, it has a smaller area than the conventional example shown in FIG. 3 and does not require a large space in the firing furnace. The string portions 12 and 12 do not have to be parallel to each other and may be formed only at one place. Furthermore, since the molded product 10 of the present invention is a press-molded product having a wall thickness of about 3 to 10 mm, warpage does not occur,
Further, at the time of dimension measurement, as shown in FIG. 1A, a constant pressure micrometer may be used to measure between the arcuate measurement surfaces 11 and 11, and the same diameter D can be accurately measured even if the measurement position is deviated.

The shape of the molded body 10 of the present invention is not limited to the shape shown in FIG. 1, and various shapes can be used as long as the shape has a uniform density.

Example 1 A sintering aid containing yttrium oxide (Y ₂ O ₃ ) was added to purified silicon nitride (Si ₃ N ₄ ) raw material, wet-milled with silicon nitride balls, and laser-scattering method was used. Particle size analysis is performed to obtain an average particle size of 0.6 ± 0.05 μm. 1 wt% of a wax-based binder was added to and mixed with the raw material powder, and spray-dried to obtain granules having good fluidity. The granules were placed in an air-conditioned molding chamber as shown in FIG.
Press molding into the shapes shown in (a) and (b).
The green density of the molded body was set within the range of 1.950 ± 0.005 g / cm ³ to obtain the molded body for thermal history detection of the present invention.

When firing was performed while changing the amount of the sintering aid in the above raw materials, as shown in the results in Table 1, the amount of the sintering aid was 4%.
If the content is more than 0 mol%, it will be densified at 1700 ° C. and will not shrink at higher temperatures, so
It could not be used above ℃. In the case of a normal silicon nitride firing furnace, since it is necessary to measure at least 1750 ° C., the amount of the sintering aid must be 40 mol% or less. It was also found that when the amount of the sintering aid was 20 mol% or less, it was used in the temperature range up to 1900 ° C.

[0025]

[Table 1]

Then, in exactly the same manner as above, the amount of the sintering aid containing Y ₂ O ₃ was 10 mol%, and the diameter D was 22.300 m.
A heat history detection molded body 10 of m was prepared. This molded body 1
0 was degreased at 350 ° C. for 1 hour, and using a firing furnace that was rigorously controlled and calibrated, in a nitrogen atmosphere, the heating rate was 200 ° C. /
Sometimes, the maximum firing temperature was maintained for 2 hours, and the firing rate was set to 300 ° C./hour for firing. The dimension of the molded body 10 after firing is 20 ° C.
Was measured with a constant pressure micrometer.

The firing temperature (instructed temperature) was variously changed, and the firing of 20 compacts 10 was repeated three times. The results are shown in Table 2 and FIG.

Further, from the dimensional variation (3σ) at each temperature and the dimensional change amount (tangent slope) per 1 ° C. at that temperature, the detection accuracy of the indicated temperature = ± dimensional variation / per 1 ° C. The detection accuracy (3σ) of the indicated temperature was calculated from the dimensional change amount. As a result, as shown in Table 2, within the range of 1450 to 1900 ° C, the detection accuracy of the indicated temperature could be within ± 5 ° C.

Further, although Table 2 shows the dimensions of the molded body for each indicated temperature of 50 ° C., a conversion table for the dimensions of the molded body and the indicated temperature can be obtained by measuring the dimensions for each of the finer indicated temperatures. Can be

[0030]

[Table 2]

Further, in the above embodiment, in order to obtain the heat history detecting molded body 10, the grain size of the raw material is 0.6 ± 0.05 μm.
m, green density of molded body 1.950 ± 0.005 g / cm ³
However, neither is limited to this value,
It can be changed in various ways. Normally, the particle size is controlled at ± 0.1 μm, and the raw density is ± 0.0
If the variation was suppressed within the range of 1 g / cm ³ , the indicated temperature detection accuracy could be ± 5 ° C.

Example 2 Boron carbide (B ₄ C) was added as a sintering aid to a purified β-silicon carbide raw material containing 500 ppm or less of metal impurities, wet-milled with silicon carbide balls, and subjected to a laser light scattering method. Particle size analysis is performed to obtain an average particle size of 0.5 ± 0.05
The range is μm. To this raw material powder, a water-soluble phenolic resin is added and mixed so that the carbon after pyrolysis becomes a predetermined amount,
Granules with good fluidity are obtained by spray drying, and these granules are press-molded in an air-conditioned molding chamber into the shape shown in FIGS. 1 (a) and 1 (b). Within the range of 2.100 ± 0.005 g / cm ³ ,
A heat history detection molded body having a diameter D of 2.300 mm was obtained.

The molded body 10 was degreased in vacuum at 800 ° C. for 1 hour to completely pyrolyze the phenol resin, and then the temperature was raised to 500 in vacuum by using a firing furnace calibrated strictly. C./hour, the maximum baking temperature was maintained for 1 hour, and the temperature was lowered at 800.degree. C./hour for baking. The dimension of the molded body 10 after firing was measured at 20 ° C. with a constant pressure micrometer.

The firing temperature (instructed temperature) was variously changed, and the firing of 20 compacts 10 was repeated three times. The results are shown in Table 3 and FIG.

From the dimensional variation (3σ) at each temperature and the dimensional change amount (tangent slope) per 1 ° C. at that temperature, the detection accuracy of the indicated temperature = ± dimensional variation / per 1 ° C. The detection accuracy (3σ) of the indicated temperature was calculated from the dimensional change amount. As a result, as shown in Table 3, within the range of 1600 to 2000 ° C, the detection accuracy of the indicated temperature could be within ± 5 ° C.

Further, although Table 3 shows the dimensions of the molded body for each indicated temperature of 50 ° C., a conversion table for the dimensions of the molded body and the indicated temperature can be obtained by measuring the dimensions for each of the finer indicated temperatures. Can be

[0037]

[Table 3]

Further, in the above embodiment, in order to obtain the heat history detecting molded body 10, the particle diameter of the raw material is 0.5 ± 0.05 μm.
m, green density of molded body 2.100 ± 0.005 g / cm ³
However, neither is limited to this value,
It can be changed in various ways. Normally, the particle size is controlled at ± 0.1 μm, and the raw density is ± 0.0
If the variation was suppressed within the range of 1 g / cm ³ , the indicated temperature detection accuracy could be ± 5 ° C.

[0039]

As described above, according to the present invention, Si ₃ N _{4 is used.}
And / or by using a ceramic unfired molded body having a composition of 60 mol% or more of SiC and 40 mol% or less of a sintering aid as a molded body for thermal history detection, the detection accuracy of the indicated temperature is within ± 5 ° C. Since it can be made highly accurate, the firing process can be strictly controlled even if the firing conditions are changed, and an excellent sintered body can be obtained. In addition, it is possible to control firing in a temperature range of 1500 to 2000 ° C., particularly in nitrogen, vacuum, and an inert atmosphere.

[0040]

[Brief description of drawings]

FIG. 1A is a plan view showing a heat history detection molded body according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along line XX in FIG. 1A.

FIG. 2 is a perspective view showing a conventional molded body for heat history detection.

FIG. 3 is a perspective view showing a conventional molded body for heat history detection.

FIG. 4 is a graph showing the relationship between firing shrinkage and indicated temperature in the heat history detection molded body of the present invention.

FIG. 5 is a graph showing the relationship between the firing shrinkage ratio and the indicated temperature in the heat history detection molded body of the present invention.

[Explanation of symbols]

 10 ... Mold for heat history detection 11 ... Measurement surface 12 ... Chord portion 13 ... Recessed portion 14 ... Chamfer

Claims (1)

[Claims] 1. A molded article for thermal history detection, comprising a ceramic unfired molded article having a composition of 60 mol% or more of Si ₃ N ₄ and / or SiC and 40 mol% or less of a sintering aid.