JPS62123073A - Method of burning ceramic material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for firing a ceramic material mainly composed of lead-containing barium titanate.

Conventional technology Traditionally, ceramic materials mainly made of barium titanate can be made into semiconductors by doping with a pentavalent element close to the atomic radius of titanium or a trivalent element close to the atomic radius of barium. It is known as a positive temperature coefficient therminuta semiconductor in which the resistance value abnormally increases near the Curie point. This positive temperature coefficient thermistor has been applied as a heating element by utilizing its characteristic of generating heat at a constant temperature due to its self-temperature control function. In recent years, demand for high-temperature heating elements as heating element materials has increased.

On the other hand, in order to operate a positive temperature coefficient thermistor at a high temperature, the Curie point must be moved to the high temperature side, and in order to do so, it is necessary to replace some of the barium atoms in barium titanate with lead.

Hitherto, firing of lead-containing materials of this type has been carried out in pod methods using vertical and side-by-side arrangements as shown in FIGS. 2 and 3, respectively. That is, in FIGS. 2 and 3, fi+ is a molded body of ceramic material,
(2) is a magnesia pod, and (3) is a magnesia pod lid. By the above-mentioned pod packing method, 12
Ceramic materials were fired at temperatures ranging from 00°C to 1400°C.

Problems to be Solved by the Invention However, the peak point of lead oxide is 4.5 x 1O-1Pa at 880°C1, and the vapor pressure is 100OK.
When fired using the method described above, lead tends to scatter. Further, due to the air convection caused by the high temperature around the element, lead easily evaporates, resulting in a ceramic sintered body having a component pattern as shown in FIG. That is, in FIG. 4, lead evaporates in the device peripheral area (5) and becomes an insulator. On the other hand, the central part of the element (6) is bluish and semiconducting.
This results in a non-uniform ceramic sintered body. This phenomenon causes variations in the specific resistance of the positive temperature coefficient thermistor, resulting in problems such as poor yield, lowering the element withstand voltage, and deteriorating the durability of the product.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a method for firing a ceramic material that can suppress lead evaporation.

Means for Solving the Problems In order to achieve this object, the present invention provides a molded product having a diameter of about 3 mm or more larger than that of the molded product at the upper and lower ends of a row of molded products stacked in an array. Place a pair of molded bodies,
This method of firing a ceramic material is characterized in that the vertical rows of the molded bodies are fired in a magnesia pod sandwiching them from above and below. However, the diameter of the molded body to be fired is approximately 2071 tJl or less.

Effect: When firing is performed with this configuration, lead evaporates from the large shaped bodies located at the top and bottom ends of the stacked rows, resulting in a solid lead atmosphere around the outside of the shaped bodies to be fired. Evaporation of lead from the molded body to be fired is suppressed.

In addition, the large-shaped upper and lower molded bodies prevent air convection,
The upward scattering of lead vapor due to air convection within the pod is suppressed. Therefore, extreme lead scattering from the molded body is suppressed.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the state inside the pod of a ceramic firing method according to an embodiment of the present invention. In Figure 1, (1) is a ceramic molded body with a diameter of 11117 m, (2) is a magnesia pod, (3) is a magnesia pod lid, and (4) is a protective mold made of a similar ceramic material with a diameter of 20212j11. It is the body.

Here, the molded body (1) is (Ba□, 6B pbo, 3
2) T'io3+o,.

The raw material weighed to have a composition of 01Y203+0.001Mn02 was ball milled, then calcined at 127g/nil, then calcined at 1100'C, and after ball milling, the diameter was 17 mm and the thickness was 3 mm. It is shaped like a circular disk. Next, in a magnesia sheath (3) shown in Fig. 1, a molded body 3 with a diameter of about 20M and a thickness made in the same manner as the molded body (1) is placed.
, OrIljl is placed, a large number of molded bodies (1) are stacked on top of this, and a second protective molded body (4) is placed on top of it. In this state, the pods are placed in an electric furnace and fired at 1250°C to 1300°C. The sintered body fi+ thus produced was provided with an ohmic silver electrode and its electrical properties were measured.

In order to confirm the effects of the present invention, the weight difference between the molded body and the sintered body is examined as a direct indicator of the state of lead scattering in addition to the electrical property values. The table below shows a comparison of the positive temperature coefficient thermistor characteristics and ceramic replacement characteristics of the ceramic element according to this example thus obtained and the element according to the conventional method.

Further, when the diameter of the upper and lower molded bodies was 197IIJ11 or less, lead scattering similar to that in the conventional method occurred.

As described above, according to this embodiment, it is possible to suppress lead evaporation, and it is possible to obtain a ceramic element which is considerably denser and more homogeneous than the conventional method. This solves the problem mentioned earlier, and reduces the variation in resistivity.
The applied voltage and the electrical characteristics of the positive temperature coefficient thermistor have been improved.

Effects of the Invention As described above, the present invention makes it possible to suppress lead evaporation during firing, yield a denser and more homogeneous ceramic sintered body than conventional methods, and improve the electrical characteristics of positive temperature coefficient thermistors. .

[Brief explanation of drawings]

Fig. 1 is a sectional view inside the pod showing the state of the ceramic firing method according to an embodiment of the present invention, Figs. 2 and 3 are sectional views inside the pod showing the state of the conventional firing method, and Fig. 4 is the conventional method. FIG. 3 is a diagram showing a ceramic element obtained in FIG. (1)・φ... Ceramic molded body (diameter 17U) (2
)...Magnesia pod (3)...Magnesia pod lid (4)...Ceramic molded body (diameter 20vIjl)
) Patent applicant: Matsushita Electric Industrial Co., Ltd. Agent: Kenbe Niimi (1 other person) figure

Claims (1)

[Claims] When firing a disc-shaped compact with a diameter of about 20 mm or less, which is mainly made of lead-containing barium titanate, in a magnesia pod, a large number of these compacts are fired.
It is characterized by stacking in rows and heating and firing with a pair of disc-shaped molded bodies made of the same material having a diameter of about 3 mm or more larger than these molded bodies arranged so as to overlap the upper and lower end surfaces of the stacked rows. A method for firing ceramic materials.