JP3131071B2 - Ceramic heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element having an oxide ceramic as a resistor.

[0002]

2. Description of the Related Art Conventionally, as a ceramic heating element, platinum (P) has been used on the surface of an insulating ceramic such as alumina.
In general, a resistor such as t) is formed by attaching a resistor, or a resistor such as tungsten is built in the surface or inside of a ceramic insulator.

On the other hand, P represented by barium titanate and the like
A resistance element called a TC thermistor is known. This element has a characteristic that the electric resistance has a positive temperature coefficient and the electric resistance sharply increases at a certain temperature. Usually, barium titanate is mainly used, and Nb or Ta
A small amount of a donor component such as Mn, Cu, or the like, or an acceptor component such as Mn or Cu for forming a grain boundary potential barrier is added.

The former heating element is used in a relatively high temperature range up to about 700 ° C., and the latter is used at a low temperature up to 350 ° C. These heating elements have a small resistance at the beginning of energization, so that they have a small resistance. It has advantages such as quick response to a certain temperature in a short time and a self-temperature control function.

[0005]

However, in the above-mentioned oxide-based heating element, the heating element having a built-in resistor has a disadvantage that the voltage distribution with respect to the heating element is non-uniform, so that local heating occurs. is there. On the other hand,
A thermistor or the like can generate uniform heat, but has a problem that it cannot be used for heat generation at a high temperature because its use limit temperature is as low as about 350 ° C.

SUMMARY OF THE INVENTION An object of the present invention is to provide a self-heating type heating element having a higher limit temperature for use as compared with the above-mentioned conventional products, a self-heating type heating element having a wide heating area, and excellent thermal shock resistance. I do.

[0007]

The inventor of the present invention has conducted studies on a resistor material of an oxide ceramic having a heat generation property at a high temperature. As a result, a perovskite-type composite oxide containing at least La and Cr or Mn is obtained. The present inventors have found that the material has a suitable resistance as a heating element at a high temperature and is excellent in uniform heat generation and thermal shock resistance at a high temperature.

That is, the ceramic heating element of the present invention comprises:
The composition formula is

[0009]

Embedded image

Wherein A is at least one selected from the group consisting of Ca, Sr, and Ba, and B is Y, Yb, S
at least one selected from the group consisting of c, Er, Dy, and Nd
The species C is at least one selected from Mn, Co, Fe, and Ni, and 0.05 ≦ x ≦ 0.40, 0 ≦ y
≦ 0.30, 0.30 ≦ z ≦ 0.60 and 0.95 ≦
p ≦ 1.0 and the open porosity is 1-30.
%, And a ceramic having an average crystal grain size of 30 μm or less is provided as a resistor.

The ceramic constituting the resistor of the ceramic heating element according to the present invention is itself 0.005 to 1%.
It has an electrical resistance of 30 Ω-cm and has a perovskite-type crystal phase as a main phase. In the present invention, the composition of the ceramic is limited to the above range because x
When the value is smaller than 0.05, in the LaMnO ₃ system,
When the solid solution undergoes a phase transformation around 800 ° C. and the temperature of the heating element is repeatedly increased and decreased, there is a problem that the element itself is broken. On the other hand, when the value x is larger than 0.6, a compound containing an alkaline earth element is precipitated, the electric resistance increases, and the heating element cannot be used as a good resistor.

Similarly, when the y value exceeds 0.5, a compound containing a rare earth element precipitates and the electric resistance increases, so that the compound does not function as a heating element. On the other hand, if the z value is less than 0.10, the sintering of the material becomes extremely poor, and sintering can be performed only at a high temperature of 1600 ° C. or more, which is limited in terms of economy. Further, when the p-value is less than 0.90, a compound containing Cr or the like is formed to increase the electric resistance. Conversely, when the p-value exceeds 1.05, La ₂ O ₃ is precipitated and the material is decomposed in a short time.

[0013]

Further, since the heating element is maintained at a high temperature for a long time, deformation and dimensional change are apt to occur. Further, since the temperature is rapidly raised to a high temperature, the heat shock resistance of the heating element itself needs to be large.

In particular, deformation and dimensional change are greatly affected by metal impurities contained in the material as a requirement other than the inherent properties of the material. The amounts of the metal impurities include Al, S
i, Zr, and the like. When the total amount exceeds 5% by weight, creep resistance at a high temperature is deteriorated, and sintering occurs over a long period of use, so that a predetermined shape cannot be maintained. Was. For this reason, the amount of the metal impurities is desirably 5% by weight or less, particularly preferably 2% by weight or less.

The thermal shock resistance has a deep relationship with the thermal shock resistance of the average crystal grain size, and the open porosity is 45% or less, particularly 1%.
３０30%, average grain size is 50 μm or less, especially 30 μm
It is desirable to be the following, and if it deviates from the above range, the desired thermal shock resistance cannot be obtained.

As shown in FIG. 1, for example, a heating element having a resistor having the above composition according to the present invention comprises a cylindrical resistor 1 made of a sintered body having the above composition, and both ends of the resistor 1 covered at both ends. The electrodes 2 and 3 are formed by a pair of electrodes
By applying a voltage of 40 V or less to the substrate, heat can be generated to a temperature of about 500 to 1200 ° C. as shown in FIG.

[0018]

[Function] LaMnO ₃ and LaCr containing CaO as a solid solution
As a result of detailed examination of the lattice defect structure of O ₃ , it was found that in these solid solutions, holes were predominantly generated as charge carriers at high temperatures and in the atmosphere. For example, L of CaO
For aMnO ₃ solid solution, the reaction is

[0019]

Embedded image

## EQU1 ##

Further, a similar lattice defect structure is generated in the LaCrO ₃ solid solution. However, the hole concentration is extremely high in LaMnO ₃ solid solution, and LaCrO 3
Very low concentration reversed in ₃ solid solution. Therefore, it is determined that the LaMnO ₃ solid solution has too low electric resistance and the LaCrO ₃ solid solution has too high electric resistance in order to be used as a heating element. For this reason, L
aMnO ₃ and LaCrO ₃ solid solution mainly consisting of Cr and M
A desired electrical resistance can be obtained by controlling the ratio of n to a specific range.

However, since this material is used at a high temperature, it must have excellent creep resistance. In addition, sintering must not proceed during use to cause dimensional change as a heating element. Therefore, as a result of studying the additives of the above-mentioned materials, it was found that by replacing a part of La with a rare earth element having the same valence, the creep resistance was excellent and the dimensional change was small. This is because the lattice defect structure does not change due to solid solution of ions at the same valence, the lattice distortion increases due to the small ion radius, the activation energy of cation diffusion increases, and as a result, It is considered that the creep was improved due to the slow diffusion rate of, and the sinterability was suppressed at the same time.

On the other hand, with respect to metal impurities, if the amount is small, it forms a solid solution in the crystal and does not greatly affect creep and sinterability, but if the amount of impurities increases and this precipitates at the grain boundary, it becomes positive. It has the effect of increasing the diffusion speed of ions at the grain boundary and promoting sintering. In addition, creep causes grain boundary sliding of the particles and deteriorates creep resistance. In particular, Al, Si, Zr, etc. degrade the creep resistance and at the same time promote sintering and promote dimensional change as a heating element.

Further, as a result of examining the microstructure of the above-mentioned material, it was found that a porous body had better thermal shock resistance than a dense one. This is considered to be due to the fact that the thermal conductivity of the porous product is smaller than that of the dense product. Therefore, in the present invention, the open porosity is limited to the above range as a measure of the density. In addition, since the thermal shock resistance and the crystal grain size have a deep relationship, and as the crystal grain size increases, the high-temperature strength decreases, the average crystal grain size is limited to the above range in the present invention.

According to the present invention, the resistor has a self-heating property by being energized by itself, and is a uniform sintered body (monolithic body). There is of course no local fever. Moreover, heat generation at a high temperature of 500 to 1200 ° C. is possible by energization, and the heat generation temperature can be greatly improved as compared with a self-heating type heating element used hitherto, thereby expanding the field of application. be able to.

[0026]

EXAMPLES La ₂ O ₃ and Y ₂ O having a commercial purity of 99.9% were used.
₃ , SrCO ₃ , CaCO ₃ , Mn ₂ O ₃ , Cr ₂ O ₃
Was used as a starting material, mixed with the compositions shown in Tables 1 and 2, and mixed with a ZrO ₂ ball for 12 hours.
The solid phase reaction was performed by calcining at 200 ° C. for 3 hours. This was pulverized for 24 hours using a ZrO ₂ ball, formed into a column shape, and fired at 1450 to 1500 ° C. for 5 hours to obtain a sintered body having an outer diameter of 6 mm and a length of 100 mm.

This was placed in electricity so that the distance between fulcrums was 80 mm, annealed at 1000 ° C. for 200 hours, and the deformation rate and the shrinkage rate of the outer diameter were measured. At this time, the deformation rate is obtained by dividing the amount of deflection by the distance between fulcrums of 80 mm.

The size of the columnar sintered body is 3 × 3.
A sample of × 60 mm was prepared, and the electric resistance was measured at 1000 ° C. On the other hand, a voltage of 10 to 30 V was applied to a sample of the same size in the atmosphere to rapidly raise the temperature to 800 ° C. or more in the atmosphere, and after maintaining for 5 minutes, the cooling was rapidly performed. This temperature cycle was repeated 100 times. When the temperature was less than 100 times, breakage was evaluated as x, and when the temperature was not damaged even after the heat cycle test, it was evaluated as ○. In addition, the total amount of metal impurities in all the samples was 0.3% by weight or less according to the ICP analysis.

Further, the open porosity of each sample was measured by the Archimedes method, and the average crystal grain size was measured by an SEM photograph. The three-point bending strength of the sintered body was measured based on JISR1601. The results of each measurement are shown in Tables 1 and 2.

[0030]

[Table 1]

[0031]

[Table 2]

According to Tables 1 and 2, C with respect to La
When the substitution amount x of a was smaller than 0.05, the sample was broken by repeated thermal cycling. Even if the substitution ratio of Ca and Sr exceeds 0.6 and the substitution amount y of Y exceeds 0.5, the electric resistance is large and does not function as a heating element. Further, with respect to the indefinite ratio, if the p value is smaller than 0.90, the deformation ratio and the shrinkage ratio become large. When the p value exceeded 1.05, La ₂ O ₃ was precipitated and the material was weathered in a short time. M
When the ratio of n was less than 0.10, the sinterability was extremely poor, and a desired shape could not be produced.

Example 2 La ₂ O ₃ , Y ₂ O ₃ , and Yb _{2 having} a purity of 99.9% commercially available
O ₃ , Sc ₂ O ₃ , Er ₂ O ₃ , Dy ₂ O ₃ , Nd ₂ O
₃ , SrCO ₃ , CaCO ₃ , BaCO ₃ , Mn
_A sample was prepared in the same manner as in Example 1 except that ₂ O ₃ , Cr ₂ O ₃ , CoO, FeO, and NiO were used as starting materials and weighed and mixed at the ratios shown in Tables 3 and 4 to obtain a sample. On the other hand, characteristics were evaluated in the same manner as in Example 1. The measurement results are shown in Tables 3 and 4.

[0034]

[Table 3]

[0035]

[Table 4]

According to Tables 3 and 4, Ca, Sr, B
a is the substitution effect of La, Y, Yb, Sc, Er, D
The same effect as in Example 1 was obtained with respect to the effect of the substitution of y and Nd. Further, substitution of Cr by Ni, Co, and Fe also showed the same effect as Mn.

Example 3 In Example 1, CaCO ₃ , SrCO ₃ , Y
₂ O ₃ and Mn ₂ O ₃ were mixed at the ratio shown in Table 5. In addition, Al ₂ O ₃ , SiO ₂ ,
A sintered body was obtained in the same manner as in Example 1 by appropriately adding ZrO ₂ . The deformation ratio, shrinkage ratio, electrical resistance, and the number of times until the sintered body were broken were measured and evaluated in the same manner as in Example 1 for the sintered body. Table 5 shows the results.

[0038]

[Table 5]

As is apparent from Table 5, it was found that the deformation rate and the shrinkage rate were increased by increasing the amount of metal impurities. In particular, when the amount of metal impurities was 5% by weight or less, relatively stable behavior was exhibited.

Example 4 In the above example, the raw materials having the composition Nos.
Calcined at 00 to 1450 ° C and zirconia balls for 12 to
This is pulverized for 24 hours, baked at 1300 to 1550 ° C., and has different open porosity and average crystal grain size 4 × 3 × 40.
mm and a sample having a size of 3 × 3 × 60 mm were obtained. The electrical resistance, the three-point bending strength, and the state of breakage by the heat cycle test were examined for each sample in the same manner as in Example 1, and the results are shown in Table 6. In Table 6, in the heat cycle test, those that were damaged less than 300 times were evaluated as x, 300
A sample that was damaged more than 500 times but less than 500 times was rated as Δ, and a sample that was not damaged even after 500 times was rated as ○.

[0041]

[Table 6]

According to Table 6, when the open porosity is 45% or less, the thermal shock resistance is excellent, and when it exceeds 45%, the strength and the thermal shock resistance deteriorate. Further, even if the average crystal grain size exceeds 50 μm, the strength and the thermal shock resistance were reduced.

Example 5 A sintered body having a composition of 3 × 3 mm and a length of 60 mm having the composition of Sample Nos. 5, 30, 33 and 57 in the above example was prepared. The open porosity is 5 to 7% and the average crystal grain size is 3 to 6 μm.
Met. The amount of metal impurities in this sintered body was 0.3% by weight or less based on the result of ICP analysis. This sample has an interval of 50
mm, a platinum terminal was attached, and the applied voltage was changed to measure the sample temperature. The result is shown in FIG. All the samples could be heated at a low voltage to a temperature of 800 ° C. or higher. Further, the temperature was almost uniform in a region of 50 mm between the electrodes.

[0044]

As described above in detail, according to the present invention, by applying a low voltage, self-heating at a high temperature of 500 to 1200 ° C. is possible, and there is no deformation or shrinkage at the time of high-temperature heating. A heating element with excellent stability can be provided. Thereby, the field of application of the ceramic heating element can be expanded.

[Brief description of the drawings]

FIG. 1 is a schematic view of one embodiment of a ceramic heating element according to the present invention.

FIG. 2 is a diagram showing a relationship between an applied voltage and a heating temperature of a ceramic heating element according to the present invention.

[Explanation of Signs] 1 Resistor 2, 3 electrodes

Claims (2)

(57) [Claims] (1) The composition formula is (La _1−x−y A _x B _y ) _p (Cr
_1-z C _z ) O _{3 ± δ} , where A is Ca, Sr, B
at least one selected from the group of a, B is Y, Yb,
At least one selected from the group consisting of Sc, Er, Dy, and Nd, and C is at least one selected from Mn, Co, Fe, and Ni, and 0.05 ≦ x ≦ 0.40, 0 ≦
y ≦ 0.30, 0.30 ≦ z ≦ 0.60 and 0.95
≦ p ≦ 1.0, and the open porosity is 1-30.
%, And a ceramic heat-generating element comprising, as a resistor, a ceramic having an average crystal grain size of 30 μm or less. 2. The method according to claim 1, wherein the total amount of metal impurities in said ceramic is 5%.
The ceramic heating element according to claim 1, wherein the content is not more than weight%.