JPH1164118A - Thermal hysteresis sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure an indicated temperature in a wide range of high temperature area under non-oxidizing atmosphere by manufacturing a non-baked body in which a specified wt.% by inner ratio of Y2 O3 is added to AlN as base material by CIP(cold isostatic pressurization) molding, and setting its density within a specified range. SOLUTION: In this thermal hysteresis sensor, a non-baked compact in which about 4-5 wt.% by inner ratio of Y2 O3 is added to AlN as base material is manufactured by CIP molding. Further, the density is preferably set within the range of about 1.9-2.3 g/cm<3> . The sintering characteristic of the manufactured compact is significantly influenced by the uniformity of the mixing state of AlN powder with Y2 O3 and the constancy of form, surface activity and grain size distribution of each powder. Therefore, for a mixed powder obtained by pulverizing mixing treatment such as ball mill treatment, it is important to perform the form observation, specific surface area measurement, and grain size distribution measurement of the powder in the same manner as the starting material powdery to confirm whether the results satisfy prescribed conditions or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat history sensor for detecting a heat history in a high-temperature firing step of a ceramic product or the like, and more particularly, to a temperature control of 1450.degree. The present invention relates to a heat history sensor capable of measuring a heat history of a body to be fired in a high temperature range of ℃ with high accuracy.

[0002]

2. Description of the Related Art A firing process in a ceramic product manufacturing process is an important process that determines the quality of a product in a series of manufacturing processes. However, the temperature distribution of the firing furnace varies depending on the shape of the furnace, the heating method, and the characteristics of the thermocouple for sensing the temperature, and the temperature distribution tends to be non-uniform especially in a large firing furnace. Under such circumstances, if the product is fired with a heat history not reaching the predetermined temperature or conversely, a heat history higher than the predetermined temperature, a decrease in the mechanical strength of the product due to excessive or insufficient sintering, Alternatively, various functional characteristics are reduced, and the manufacturing yield is reduced.

In order to avoid such a situation, when a large number of products are fired in a large-scale firing furnace, the arrangement of the products and the shape of the jig are taken into consideration so that the temperature distribution in the firing furnace becomes uniform. Usually, the firing conditions are set so that if the firing is performed in a certain temperature range, the quality of the product is kept substantially equal. Also, when transferring a product that has been prototyped using a small firing furnace to production using a large firing furnace, temperature calibration of the firing furnace is an indispensable operation.

A method using a Zegel cone or a thermal chip has been generally adopted as a method of measuring the temperature of each part in a firing furnace or calibrating a temperature of a thermocouple or the like. Seegel cones are set up with triangular pyramids with different melting temperatures on a support base with an inclination, and fixed with mortar, etc.
After firing together with the object to be fired, the thermal history is detected from the manner in which the triangular pyramid falls down. However, in this method, since the measurement error reaches several tens of degrees, the use thereof has been decreasing in recent years.

Further, the thermal chip is an unsintered molded body having a ring shape or a substantially rectangular flat plate shape with one side of an arc, which is fired at the same time as an object to be fired, and detects a thermal history from a firing shrinkage rate. Things. However, since this molded body is manufactured using a large amount of natural raw materials containing many impurities, the firing shrinkage varies, and a measurement error of about ± 10 ° C. is inevitable. In particular, the temperature program during firing is complicated. In such a case, the measurement error tends to increase.

Further, since the thermal chip is for firing an unsintered molded body, it is needless to say that the shrinkage rate varies not only with temperature but also with time, but the maximum temperature holding time in the baking program remains unchanged. It is not always the actual holding time. Therefore, the temperature obtained from the firing shrinkage dimension of the thermal chip is not a measured actual temperature but a thermal history, and the temperature measured in this manner is generally called an indicated temperature. Then, even if the firing furnaces are different, it is possible to minimize the difference in the thermal history of the product by keeping the indicated temperature constant.

[0007]

In order to reduce the measurement error of the above-mentioned conventional thermal history sensor, an unsintered molded body called "Referthermo" has recently been sold by the Fine Ceramics Center. I have. Refathermo reduces firing shrinkage errors in conventional thermal chips by strictly controlling the composition of the raw material, particle size distribution, molding density, etc., and mainly uses Al ₂ O ₃ as a base material, under air atmosphere, 1000 ° C ~ 17
It is suitably used for calibration of the firing temperature of 00 ° C.

Japanese Patent Application Laid-Open No. 5-302857 discloses a heat history detecting molded article composed of an unsintered molded article using AlN as a base material and controlling the content of impurities and the content of oxygen. It is described that it is suitably used for firing non-oxide ceramics at a temperature of from 1C to 1950C.

[0009] Although an improved unsintered green body has been developed as described above, the maximum operating temperature of the reference thermostat is 170.
Since it is 0 ° C., it cannot be applied to firing non-oxide ceramics which require firing at a higher temperature and in a non-oxidizing atmosphere. Further, Japanese Patent Laid-Open No. 5-30
If the applicable temperature range of the heat history detecting molded body described in Japanese Patent No. 2857 can be expanded and a good calibration curve showing the relationship between firing shrinkage and the indicated temperature can be obtained, the applicable range of use can be further expanded. There is.

[0010] Japanese Unexamined Patent Publication (Kokai) No. Hei 5-302857 discloses that in a molded article for thermal history detection using AlN as a base material, if the metal component other than AlN is not less than 0.3% by weight, Is densified below 1650 ° C.
Although it is described that the molded body is liable to change and the thermal history cannot be measured accurately, the inventors of the present invention have studied a thermal history sensor using AlN as a base material.
Contrary to the description in JP-A-57-57, it has been clarified that by mixing an appropriate amount of an appropriate additive, a thermal history sensor usable in a temperature range of 1450 ° C. to 2000 ° C. can be produced.

[0011]

That is, according to the present invention, AlN is used as a base material, and Y ₂ O ₃ is contained in an internal ratio of 4 to 5% by weight.
There is provided a thermal history sensor comprising a green compact to which addition has been made. Further, in the thermal history sensor of the present invention, it is preferable that the unsintered molded body is manufactured by the CIP molding method, and the density of the molded body is in the range of 1.9 to 2.3 g / cm ^3. Is preferred.

[0012]

According to the thermal history sensor of the present invention, the applicable temperature range is as wide as 1450 ° C. to 2000 ° C., and the relationship between the firing shrinkage and the indicated temperature in this temperature range changes smoothly. Therefore, accurate measurement of the heat history becomes possible. This makes it possible to accurately calibrate the radiation pyrometer and the like used in the actual operation of the firing furnace and to accurately reduce the variation in the temperature distribution in the firing furnace. Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

The unsintered molded body as the thermal history sensor of the present invention has a composition in which AlN is used as a base material and Y ₂ O ₃ which is an additive for controlling sintering is added thereto. Powder is suitably used as a raw material in the production of the green compact, and various commercially available powders can be used. However, with respect to purity, powder having a purity of 99% or more is preferably used. It is preferable to obtain an accurate indicated temperature.

It is preferable to use mass-produced powders for each raw material as long as the production method is constant. This is because many of such powders generally have constant powder characteristics, and the production cost can be reduced. However, in actual use, it is preferable to measure and confirm the powder characteristics for each lot from the standpoint of keeping the characteristics of the molded body constant.

The basic powder characteristics to be confirmed here include the morphology, surface activity, and particle size distribution of the powder, but the surface activity can be examined by substituting the specific surface area of the powder. . The evaluation of these properties was performed by SEM
It can be easily performed by observation, measurement of specific surface area by BET method, measurement of particle size distribution by laser diffraction method, and the like.

In preparing the mixed powder by mixing the powders selected in this way, various known pulverizing and mixing methods can be used, and a wet ball mill is inexpensive in terms of equipment and has good mixing. It is preferable as a method for obtaining a powder. In the case of using a ball mill, for example, if nylon balls containing iron balls are used, only the mixing process can be mainly performed without pulverizing the raw material powder. It is possible to simultaneously grind and mix the body.

When a ball mill is used, it is preferable to use a volatile organic solvent such as alcohol as a solvent and not use water. When water is used, the surface of the raw material powder is oxidized, and the purity of the raw material may be reduced.

Here, the mixing state of the AlN powder and the Y ₂ O ₃ powder is uniform, the form of each powder is constant, and the surface activity of each powder is constant. Since the fact that the particle size distribution of each powder is constant greatly affects the sintering characteristics of the compact to be produced, the mixed powder obtained after the pulverization and mixing treatment such as a ball mill treatment is the raw material powder. It is important to confirm the morphology of the powder, measure the specific surface area, and measure the particle size distribution in the same manner as described above, and confirm that these results satisfy predetermined conditions.

In this way, a binder, a plasticizer and the like are added to the slurry obtained by performing the mixing process so as to satisfy the predetermined conditions or the mixed powder obtained by drying the slurry, and a granulating process is performed. A flowable granule suitable for molding is produced.

In molding the obtained granulated powder, there are few parameters to be controlled in the production conditions of the molded body, and the constant density of the molded body is necessary in order to keep the shrinkage characteristics of the molded body constant. preferable. Therefore, in the present invention,
The press molding method is preferably used, but the uniaxial pressing method is not preferable because anisotropy occurs in the applied pressure and thus anisotropy occurs in the firing shrinkage ratio. CIP (cold isostatic pressing)
A molding method is adopted. According to the CIP molding method, since the molded body is pressed isotropically, no shrinkage anisotropy occurs during firing, and deformation such as warping due to firing hardly occurs.

Next, the produced CIP molded body is green-processed (white-processed) into a predetermined shape. At this time, when processed into a rectangular parallelepiped shape having a certain thickness, warpage and deformation during firing can be prevented as compared with the case of forming a thin plate, and sample damage during raw processing is reduced, which facilitates production. . In addition, the molding density of the produced molded body must be within a certain range. This is because a variation in the molding density leads to a variation in the sintering state, leading to a problem that the shrinkage rate is not constant or cracks or the like occur during firing.

The produced compact is taken out immediately or from a state where it is stored under a certain condition under which the compact is not deteriorated, and calcined at various temperatures in a non-oxidizing atmosphere (set temperature of a calciner). The indicated temperature is determined from the obtained firing shrinkage.

In this way, based on the prepared calibration curve or conversion table between the firing shrinkage ratio and the indicated temperature, a different firing furnace is used, and when firing is performed under different firing conditions, this molding is performed together with the object to be fired. By sintering the body and measuring the shrinkage after sintering, the support temperature can be obtained from the above-mentioned calibration curve or conversion table, and the operating state of the sintering furnace is controlled so that the indicated temperature is constant. Thus, it is possible to manufacture a product of a constant quality.

The embodiment of the present invention described above is large, and all of the production of the molded body as the heat history sensor, the production of the calibration curve, and the subsequent measurement of the indicated temperature are performed at a predetermined place or the like where these operations are required. A mode in which the result is defined as a standard condition such as a place where the work is performed, and a heat history sensor and a calibration curve which are manufactured under specific conditions and determine the indicated temperature are distributed and used as products. In the hands of the
And the embodiment used by the user.

In the latter case of these embodiments, it takes a certain period of time for the product to reach the user's hand and be actually used, and the product is stored for a certain period of time. Needless to say, it is required that the shrinkage characteristics do not change. Also in the former embodiment, it is preferable that the characteristics of the molded body do not change with time. Therefore, it is preferable that the molded body is stored under certain conditions under which certain deterioration does not occur.

Here, in the green compact, since the surface activity of the powder is maintained in a high state, moisture in the air is easily adsorbed on the surface of the powder, and the binder may be deteriorated with time. You. Therefore, it is preferable to preserve the molded body by degreasing and calcining it so as to maintain a certain strength and to have almost no hygroscopicity. By processing like this,
It becomes possible to maintain stable firing shrinkage characteristics over a long period of time.

[0027]

Hereinafter, the present invention will be described in more detail with reference to examples. Using Tokuyama Soda Ltd. H-grade (99.9% purity) powder as a starting material of the AlN powder, which on the inner ratio 3-6% by weight equivalent of Shin-Etsu Chemical Co., Ltd. Y ₂ O ₃ powder (purity: 99.9%) The mixture was added, and a ball mill treatment was performed for 20 hours using IPA as a solvent to perform a mixing treatment. An acrylic resin was added as a binder to the obtained slurry at an external ratio of 4% by weight and spray-dried to prepare a granulated powder.

[0028] The prepared granulated powder is prepared with a bottom shape of 50 mm x
Using a mold with a size of 50 mm or more, 200 kg / cm
After the primary molding at a pressure of ² , the resultant was packed in an ice bag and subjected to a CIP treatment at a pressure of 5 t / cm ² for 10 seconds to perform a secondary molding. As for the molding of the granulated powder, the granulated powder may be filled in a rubber mold and directly subjected to the CIP treatment.

Next, the produced CIP compact was
It was green-processed into a shape of × 10 mm × 20 mm, and it was confirmed that the dimensional accuracy was within a range of ± 0.25% of a predetermined value. The molded body was stored in a dryer at 40 ° C. to 50 ° C. or a desiccator with nitrogen purge, and the quality was constantly controlled.

The formed compact is fired at various temperatures in an atmosphere heating furnace equipped with a radiation pyrometer that uses the temperature of 1200 ° C. or more, and further, the firing shrinkage obtained by repeating the operation more than ten times From the relationship between the rate and the firing temperature,
FIG. 1 shows the result of preparing the calibration curve. At this point, the firing temperature becomes the specified temperature.

From FIG. 1, when the amount of Y ₂ O ₃ added is 3 wt%, the starting temperature of firing shrinkage becomes high, and it is difficult to measure the indicated temperature at a temperature of 1650 ° C. or less. On the other hand, Y
_{When the} added amount of ₂ O ₃ is 6 wt%, the temperature at which the firing shrinkage starts becomes low, and as a result, it becomes almost dense at 1680 ° C.
It turns out that it is impossible to measure the indicated temperature at a higher temperature.

On the other hand, when the added amount of Y ₂ O ₃ is 4 to 5 wt.
In the case of%, a calibration curve that smoothly changes at 1450 ° C. to 2000 ° C. was obtained, and it was clear that excellent characteristics were exhibited as the thermal history sensor. The measurement error is
± 0.40% in the measurement temperature range, for example, 1500
At ℃, it was in the range of 1500 ℃ ± 6 ℃.

It should be noted that, among the compacts fired to prepare the calibration curve shown in FIG. 1, several samples whose firing shrinkage deviated significantly from other samples or which caused fire cracking were confirmed. These results were found to be related to the compact density at the time of producing the compact, and it was clear that the proper compact density suitable for the calibration curve was in the range of 1.9 to 2.3 g / cm ^3. became. In other words, if the density of the molded body is smaller than this range, the shrinkage ratio varies, while if it is larger than this range, unreasonable stress remains in the molded body and cracks occur during firing. it was thought.

[0034]

As described above, according to the thermal history sensor of the present invention, an accurate measurement of the indicated temperature can be performed in a wide temperature range of 1450 ° C. to 2000 ° C. in a non-oxidizing atmosphere. It has a remarkable effect that the calibration of the thermocouple or the radiation pyrometer of the furnace or the optimization of the firing conditions can be easily performed. As a result, there is an advantage that the quality of the product to be fired can be kept constant.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between firing shrinkage and firing temperature of a thermal history sensor of the present invention.

Claims (3)

[Claims] 1. An AlN substrate having a Y ₂ O ₃ content of 4 to 4
A thermal history sensor comprising an unfired molded body to which 5% by weight is added. 2. The thermal history sensor according to claim 1, wherein the unfired molded body is manufactured by a CIP molding method. 3. The green compact having a density of 1.9 to 2.
The thermal history sensor according to claim 1, wherein the thermal history sensor is in a range of ³ g / cm ³ .