JP3266352B2 - Molded body for thermal history detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In the process of firing ceramics, the thermal history of the object 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, if other conditions are different, the thermal history will be different, and it is necessary to correctly detect the thermal history.

For example, the thermal history of a body to be fired has been detected using a Zegel cone disclosed in Japanese Utility Model Application Laid-Open No. 56-29441. A Zegel cone is one in which a plurality of triangular pyramids having different melting temperatures are provided on a support base.After firing this Zegel cone together with the object to be fired, the thermal history is determined by the manner in which each triangular pyramid falls. Was to be detected. However, since accurate detection is not possible with this, it is rarely used at present.

Accordingly, as shown in, for example, Japanese Patent Application Laid-Open No. 1-184388, after a ceramic green compact is fired together with a body to be fired, the dimensional change due to shrinkage is measured. By doing so, the thermal history has been 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 has been used.

When such a dimensional change due to firing shrinkage is measured, the dimensional change is conveniently converted to a temperature. However, this temperature is not a measurement of the actual temperature, but a thermal history. Therefore, in the present invention, it is referred to as an indicated temperature.

[0006]

However, the ceramic molded body for detecting thermal history described above is made of Al ₂ O ₃ or Si.
Since it was made of a natural raw material containing O ₂ as a main component and containing a large amount of impurities, the firing shrinkage ratio varied, and the accuracy of the detected indicated temperature was poor.

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

On the other hand, the present applicant has disclosed in Japanese Patent Laid-Open No.
No. 69, 99.7% by weight or more of Al ₂
It was proposed to use a ceramic green compact containing O ₃ as a thermal history detecting compact, but this could only be used in an oxidizing atmosphere. In other words, a molded body containing Al ₂ O ₃ as a main component is decomposed in an atmosphere of nitrogen, vacuum, inert gas, or the like, and has a large variation in firing shrinkage. Was.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an Si ₃
An unfired ceramic molded body having a composition of not less than 60 mol% of N ₄ and / or SiC and not more than 40 mol% of a sintering aid is used as a heat history detecting molded body.

More specifically, at least 60 mol% of Si ₃ N ₄ ;
A ceramic unsintered compact 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 detecting compact, and can be used particularly in a nitrogen atmosphere.

Here, the reason why the content of Si ₃ N _{4 is set} to 60 mol% or more is to reduce the variation in the firing shrinkage and to make the accuracy of the detected indicated temperature ± 5 ° C. The reason why the sintering aid is set to 40 mol% or less is that the sintering aid is 40 mol% or less.
If the amount is larger than 1,700 ° C. or less, it is completely sintered and densified, and the thermal history cannot be detected. Preferably, the content is 20 mol% or less. Further, MgO, Al ₂ O ₃ or the like may be used as a sintering aid, but it is preferable to use a rare earth oxide such as Y ₂ O ₃ in order to reduce variation in shrinkage. Is desirably contained in an amount of 0.5 mol% or more.

In another composition, 70 mol% of SiC is used.
As described above, a ceramic green compact having a composition of 30 mol% or less of a sintering aid such as boron or carbon is used as a thermal history detecting compact, and can be used particularly in a vacuum or inert atmosphere.

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

Further, as another composition, the total content of Si ₃ N ₄ and SiC is 60 mol% or more, and Y ₂ O ₃ and Al ₂ O ₃
A ceramic unsintered compact having a composition of 40 mol% or less of a sintering aid such as the above can be used as the thermal history detector.

The sintering aid is a component that promotes sintering of ceramics. In the present invention, all components other than the main components Si ₃ N ₄ and / or SiC are sintered. A binder.

[0016]

Embodiments of the present invention will be described below.

As shown in FIGS. 1 (a) and 1 (b), a heat history detecting molded body 10 of the present invention comprises a chord portion 12 parallel to a disc body,
12 are formed, and the remaining arc portions are measurement surfaces 11 and 11 having excellent roundness. In addition, a concave portion 13 is formed on one side by engraving such as a dot or an alphabet for distinguishing the front and back sides, and a chamfer 14 is formed on the corners of the upper and lower surfaces.

Further, the compact 10 has a composition of not less than 60 mol% of Si ₃ N ₄ and / or SiC and not more than 40 mol% of a sintering aid. Is a green compact formed by press molding with strict control of As will be described later, the firing temperature is changed under certain conditions to measure the dimensions of the molded body 10 after firing, and the relationship between the dimensions and the firing temperature is prepared as a conversion table. Thereafter, when firing is performed under different conditions, the molded body 10 is fired together with the fired object, and the indicated temperature can be obtained from the above conversion table by measuring the dimensional change after firing.

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

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

Further, the molded body 10 of the present invention is characterized in that the chord 1
Since it has 2, 12, the area is smaller than that of the conventional example shown in FIG. 3, and a large space is not required in the firing furnace. Note that the chords 12 and 12 need not be parallel to each other, and may be formed only at one location. Furthermore, since the molded body 10 of the present invention is a press-molded article having a thickness of about 3 to 10 mm, no warpage or the like occurs,
Further, at the time of dimension measurement, as shown in FIG. 1 (a), the measurement between the arc-shaped measurement surfaces 11, 11 may be performed by a constant-pressure micrometer, and the same diameter D can be accurately measured even if the measurement position is shifted.

The shape of the molded body 10 of the present invention is not limited to the shape shown in FIG. 1, but may be various as long as it is a simple shape having a uniform density.

Example 1 To a purified silicon nitride (Si ₃ N ₄ ) raw material, a sintering aid containing yttrium oxide (Y ₂ O ₃ ) was added, wet pulverized with a silicon nitride ball, and subjected to laser light scattering. Particle size analysis is performed to make the average particle size 0.6 ± 0.05 μm. A 6% by weight wax-based binder was added to the raw material powder, mixed and spray-dried to obtain granules having good fluidity. The granules were placed in an air-conditioned molding room as shown in FIG.
(A) Press molding into the shape shown in (b).
By setting the green density of the molded body within a range of 1.950 ± 0.005 g / cm ^3, a molded body for heat history detection of the present invention was obtained.

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

[0025]

[Table 1]

Next, in the same manner as described above, the amount of the sintering aid containing Y ₂ O ₃ was 10 mol%, and the diameter D was 22.300 m.
m of the heat history detecting molded body 10 was prepared. This molded body 1
Degreased at 350 ° C. for 1 hour, and in a sintering furnace strictly controlled and calibrated, in a nitrogen atmosphere, at a temperature rising rate of 200 ° C. /
At this time, the sintering was carried out at a maximum sintering temperature for 2 hours and at a temperature lowering rate of 300 ° C./hour. The size of the molded body 10 after firing is set to 20 ° C.
Was measured with a constant pressure micrometer.

The firing temperature (indicated temperature) was changed variously, and firing of 20 molded bodies 10 was repeated three times. The results are as shown in Table 2 and FIG.

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

Further, Table 2 shows the dimensions of the compact at each indicated temperature of 50 ° C. By measuring the dimensions more precisely at each designated temperature, a conversion table of the dimensions of the compact and the designated temperature is obtained. It can be.

[0030]

[Table 2]

In the above embodiment, in order to obtain the heat history detecting molded body 10, the raw material has a particle diameter of 0.6 ± 0.05 μm.
m, green density of molded article 1.950 ± 0.005 g / cm ³
However, neither is limited to this value.
Various changes can be made. Usually, the particle size is controlled at ± 0.1 μm, and the green density is controlled at ± 0.0
If the variation was suppressed within the range of 1 g / cm ³ , the detection accuracy of the indicated temperature could be made ± 5 ° C.

Example 2 Boron carbide (B ₄ C) was added as a sintering aid to a purified β-silicon carbide raw material having a metal impurity content of 500 ppm or less, wet-pulverized with a silicon carbide ball, and subjected to laser light scattering. Perform a particle size analysis to find an average particle size of 0.5 ± 0.05.
μm range. A water-soluble phenol resin is added and mixed with the raw material powder so that the carbon after pyrolysis becomes a predetermined amount,
By spray drying, granules having good fluidity are obtained, and the granules are press-molded in an air-conditioned molding chamber into the shapes shown in FIGS. 1 (a) and 1 (b). Within the range of 2.100 ± 0.005 g / cm ³ ,
A heat history detecting molded body having a diameter D of 2.300 mm was obtained.

The molded body 10 is degreased in vacuum at 800 ° C. for 1 hour to completely thermally decompose the phenol resin, and then heated in a sintering furnace strictly controlled and calibrated in a vacuum at a heating rate of 500 ° C. The sintering was carried out at a maximum sintering temperature of 1 hour at a rate of 800 ° C./hour and at a temperature lowering rate of 800 ° C./hour. The dimensions of the molded body 10 after firing were measured at 20 ° C. with a constant pressure micrometer.

By varying the firing temperature (instruction temperature) in various ways, firing of each of the 20 compacts 10 was repeated three times. The results are as shown in Table 3 and FIG.

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

Further, Table 3 shows the dimensions of the compact at each indicated temperature of 50 ° C. By measuring the dimensions at each indicated temperature more precisely, a conversion table of the dimensions of the compact and the designated temperature is obtained. It can be.

[0037]

[Table 3]

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

[0039]

As described above, according to the present invention, Si ₃ N ₄
And / or by using a ceramic green body having a composition of not less than 60 mol% of SiC and not more than 40 mol% of a sintering aid as a molded body for detecting thermal history, the detection accuracy of the indicated temperature is extremely within ± 5 ° C. Because of high precision, the firing process can be strictly controlled even when 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. in a nitrogen, vacuum, or inert atmosphere.

[0040]

[Brief description of the drawings]

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

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Heat history detection molded body 11 ... Measurement surface 12 ... String part 13 ... Concave part 14 ... Chamfer

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01K 11/00 G01K 5/50 G01K 11/06 C04B 35/565 C04B 35/584

Claims (1)

(57) [Claims] 1. A molded article for detecting thermal history, comprising a ceramic unsintered molded article having a composition of not less than 60 mol% of Si ₃ N ₄ and / or SiC and not more than 40 mol% of a sintering aid.