JPH03177357A - Burning of barium titanate-based semiconductor porcelain - Google Patents

Abstract

PURPOSE:To prevent scattering of the characteristics by accommodating a BaTiO3-based molding in a burning sheath composed of an SiC layer and Al2O3 layers so that the molding is located on the Al2O3 layer side, placing the sheath in a furnace and carrying out burning. CONSTITUTION:A prescribed ratio of respective components are weighed so as to have a composition of BaTiO3 semiconductor porcelain and the weighed components are mixed, ground and dried. A suitable amount of a binder is added to the resultant dried powder of the raw materials and the obtained mixture is granulated and subsequently press-formed so as to obtain a molding 6. On the Al2O3 layer 1 side in a burning sheath composed of an SiC layer 2 sandwiched between Al2O3 layers 1, powdery ZrO2 7 is then laid over and the molding 6 is accommodated thereon. The burning sheath is subsequently placed in a furnace, burnt by raising the temperature to a prescribed temperature at a prescribed rate and then cooled, thus obtaining the objective BaTiO3- based semiconductor porcelain.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a barium titanate semiconductor porcelain whose resistance value changes depending on the ambient temperature, which is used for temperature compensation and as a temperature sensor for controlling current. The present invention relates to a method for firing semiconductor porcelain.

Conventional technology A barium titanate-based positive temperature coefficient thermistor uses barium titanate as its main component and is made into a semiconductor.

It contains trace amounts of one or more oxides such as La, Ce, Nb, Bi, Sb, and W. It becomes a semiconductor when fired at a suitable temperature, and is a positive oxide whose resistance increases significantly at a certain temperature (Curie point). It has the characteristic of showing resistance temperature change.

The Curie point of barium titanate is 120.
It is around ℃. This Curie point is barium titanate (
It can be changed by partially substituting Ba and Ti in BaTiO3). For example, in order to move the Curie point to a higher temperature, some of the Ba must be replaced with lead (
Pb). In addition, in order to move the Curie point to a lower temperature, it is necessary to replace part of Ba with strontium (Sr) or replace part of Tf with tin (Sr).
It is known that it can be obtained by substituting with n).

By the way, in order to manufacture barium titanate-based semiconductor ceramics, it is usually necessary to fire at a high temperature of 1200°C to 1400°C. However, the barium titanate-based semiconductor porcelain used for temperature compensation is a B al-xS rxT i 03 system or BaTi1-xSrx○3 system, which has a Curie point on the low temperature side. In terms of characteristics, current control is performed using the part where the resistance value increases linearly at temperatures above the Curie point. For this reason, the characteristics required for a temperature compensation element are the resistance value R25 and 80°C at room temperature (25°C).
There is a standard value of the ratio of resistance values Rao at °C, ie, R80/R25. It is generally known that in firing, the faster the cooling rate from the maximum temperature, the smaller the value of R80/R25. When firing such barium titanate-based semiconductor porcelain, alumina (A!
! Zirconium oxide (Zr02
) powder is laid down, the molded bodies are arranged on top of it, and fired in a single furnace or tunnel furnace where the temperature can be set.

Problems to be Solved by the Invention However, in the conventional configuration described above, the faster the cooling rate from the maximum temperature during firing, the faster the firing rate of alumina becomes, even though the temperature in the firing furnace is at the set value. Since the heat capacity of the pod is large, the pod cannot keep up with the temperature in the furnace, and the sintered body in contact with the pod is affected by this, resulting in variations in properties.

The present invention solves the above-mentioned conventional problems, and provides a sintered body that suppresses variations in the properties of the sintered body due to the cooling process even when the cooling rate from the maximum temperature is increased during firing. The object of the present invention is to provide a method for firing barium titanate-based semiconductor porcelain that can be obtained.

Means for Solving the Problem In order to achieve this problem, the method for firing barium titanate-based semiconductor porcelain of the present invention is such that the firing sheath containing the barium titanate-based molded body is composed of a SiC layer and an At2203 layer. It is characterized in that it is fired using a material having Here, the side where the molded body is stored is A220.
When there are three layers and the molded body is housed on the SiC layer, the baricum titanate molded body is highly reactive with SiC and cannot be used.

Effect This configuration allows AQ 203 (molecular heat cp-12
4,7J-ma l-'d e g-') and a smaller specific heat of S i C (Cp=48.6J-
By creating a structure with layers of ma 1−'deg=),
The heat dissipation of the fired pod is better than that of only Al2O3, and the heat capacity of the fired pod can be reduced, making it easier for the fired pod to keep up with the set temperature in the firing furnace. It is possible to obtain barium titanate-based semiconductor porcelain with suppressed variations in properties.

Moreover, in the present invention, the SiC layer is At! The reason for using the fired sheath in combination with the Ae 203 layer is that SiC has high thermal conductivity and excellent fire resistance.
This is because the coefficients of thermal expansion are almost the same. In particular, A
If the fired pod is constructed using a material with a coefficient of thermal expansion different from e203, the fired pod will warp during firing, which is not preferable.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross section of the fired pod used in this example. FIG. 1(a) shows a sandwich-like fired pod consisting of an A0203 layer 1 and a SiC layer 2.

In addition, FIG. 1(b) shows Ae 203 similarly to FIG. 1(a).
Although the fired sheath is composed of layer 1 and SiC layer 2, it shows a fired sheath composed of two layers.

Next, thermocouples were attached to the upper surfaces of the fired pods made of Ae 203 layer and the above two types of fired pods, respectively, to measure the temperature. At this time, the temperature setting in the firing furnace is
The cooling was performed from 1400°C at a cooling rate of 400°C per hour.

The results are shown in FIG. The actual IA in Figure 2 is the temperature inside the furnace at this time, the actual MB is the result of measuring the fired pods in Figures 1 (a) and (b), and the solid line C is the temperature of the conventional Ae.
These are the results when a fired pod consisting of 203 layers was measured. As can be seen from this result, by using a fired pod consisting of an i203 layer and a SiC layer, the temperature of the fired pod during the cooling process during firing is almost the same as the set value in the furnace, rather than a fired pod made of only Ae2ChM. It is shown that the temperature is about

Next, a specific example in which a molded body is housed in a firing sheath shown in FIGS. 1(a) and 1(b) and fired will be described.

Here, the molded body was prepared as follows. First, the composition is B a T io, e+ S no, +s○3+0
．． 014Nb20s+0.024S io2 +0.0
IAf! Commercially available high-purity raw materials were weighed to give a weight of 2.0 mm, put into a rubber-lined pot mill together with agate cobbles, mixed, crushed, and dried. After adding 10% by weight of polyvinyl alcohol (P, V, A) as a binder to this dried raw material and granulating it, using a hydraulic press, a pressure of 80
It was molded into a disk shape of 10 mm in diameter and 1.2 mm in thickness at 0 kg/cJ to obtain a molded body.

Next, as shown in FIG. 3, the above molded body 6 was housed in the entire firing sheath. At this time, powder 7 made of zirconium oxide (ZrO2) was spread inside the fired sheath.

Moreover, as shown in FIG.
The experiment was carried out using a sandwich-shaped fired pod provided with a C layer 2.

Here, the size of the fired pod used in this example was 280 rrm in length and width, and 10 mm in thickness (Al2
O3 layer; 3mmX2. SiC layer; 4 m). Then, the fired pod containing the molded body was placed in a firing furnace where the temperature could be set, and the temperature was raised to 1380°C at a heating rate of 200°C per hour. After firing at 1380°C for 1 hour, the temperature was lowered by changing the cooling rate. , barium titanate-based porcelain samples were obtained.

Next, the characteristics of the sample obtained in this way were compared with conventional Ae
This was also investigated using a fired pod consisting of only 203 layers. That is, 50 sintered bodies in each pod were randomly sampled, aluminum sprayed electrodes were attached to both sides of the sample, and the average and standard deviation (Sn-+) of the room temperature resistance value (R25) were calculated. did. Also, the ratio of the resistance value at room temperature to the resistance value at 80°C (Rao) (R80/R25
) was measured and the average value was calculated. The results are shown in the first section below.
Shown in Table and Table 2. Table 1 shows the results when using the fired pod of the present invention consisting of a SiC layer and an Al2O3 layer, and Table 2 shows the results of the conventional At! These are the results when using No. 203 fired pods.

Table 1 Table 1 The above results show that when the fired pod of the present invention is used, the heat dissipation of the fired pod is At! Barium titanate is better than 203 alone, and the heat capacity of the fired pod can be reduced, allowing it to keep up with the set temperature during the cooling process in the firing furnace, suppressing variations in the properties of the sintered body. This shows that it is possible to obtain semiconducting porcelain.

Effects of the Invention As described above, the present invention provides barium titanate-based semiconductor porcelain that suppresses variations in the characteristics of the sintered body due to the cooling process during firing by using a fired sheath composed of a SiC layer and an Ae 203 layer. It is something that can be obtained.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views of fired pods according to embodiments of the present invention, Figure 2 is a graph showing temperature changes of fired pods in embodiments of the present invention and conventional examples, and Figure 3.
The figure is a sectional view showing the process of firing barium titanate semiconductor ceramics in an embodiment of the present invention. 1...Al1203 layer, 2...SiC
layer.

Claims (1)

[Claims] A barium titanate-based molded body is combined with a SiC layer and Al_2
The titanium titanium oxide is characterized in that the molded body is placed on the side of the Al_2O_3 layer in a fired sheath consisting of O_3 layers, the fired sheath is placed in a firing furnace, and the barium titanate-based molded body is fired. A method for firing barium acid semiconductor porcelain.