JP3145568B2 - Ceramic heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a ceramic heater element comprising a composite oxide-based ceramic of LaCrO ₃ system.

[0002]

2. Description of the Related Art As a ceramic heating element, a resistor such as platinum is coated on the surface of a conventional insulating ceramic such as alumina or a resistor such as tungsten is embedded in an insulating ceramic. It is used.
These heating elements are used in a relatively high temperature range up to about 700 ° C., but generate heat locally and the shape is limited to a cylindrical or flat plate.

On the other hand, as a heating element, a resistance element called a PTC thermistor represented by barium titanate is known. This element has an electric resistance having a positive temperature coefficient and when the electric resistance exceeds a certain temperature, the electric resistance becomes higher. It has the feature of increasing rapidly. For example, barium titanate-based P
The TC thermistor is an Nb, Ta donor for semiconductor conversion.
A trace amount of a component or an acceptor component for forming a grain boundary potential barrier of Mn or Cu is added. This heating element is used in a relatively low temperature range up to about 350 ° C., has a small electric resistance at the beginning of energization, has excellent responsiveness, and reaches a predetermined temperature in a very short time. In addition, since this element has a high electric resistance at a high temperature, it is also characterized by having a self-temperature control function.

[0004]

However, in the above-described element having a heating element on the surface or inside of the insulating ceramic, when a voltage is applied, the voltage distribution is not uniform, so that a local heat is generated. And the disadvantage that the shape of the heating element is limited. A PTC thermistor having a self-temperature control function has a drawback that its operating limit temperature is as low as 350 ° C., although its shape can be changed arbitrarily.

It is an object of the present invention to provide a self-heating type heating element having a higher usable temperature limit than the above-mentioned conventional products and having an arbitrary shape.

[0006]

Means for Solving the Problems The present inventors have paid particular attention to LaCrO ₃ as an oxide ceramic resistor,
As a result of repeated studies on the performance as a heating element, C
La which dissolves at least one of a, Sr, Ba and Mg
LaCrO ₃ -based ceramics containing a CrO ₃ solid solution as a main crystal phase and containing, as a second component, an oxide of at least one element selected from the group consisting of Y and rare earth elements such as Yb, Nd, and Er can be used at high temperatures. It has been found that a uniform heating element having a large heating area can be obtained.

Hereinafter, the present invention will be described in detail. The heating element of the present invention has a main crystal phase of a LaCrO ₃ perovskite solid solution containing at least one element of Ca, Ba, Sr and Mg. is there. Ca, Ba and Sr are La substitution elements for LaCrO ₃ and Mg is a substitution element for Cr, and these are La and Cr.
Substitution is contained at a ratio of 1 to 30 atomic% with respect to r.

A significant feature of the heat generating element of the present invention is that the structure is composed of a main crystal composed of the LaCrO ₃ -based perovskite solid solution and a second phase, and Y and La, Yb, Sc, Er as the second phase. , Nd, Gd, D
It is characterized by containing an oxide of a rare earth element such as y.

When Y or a rare earth element is contained in the second phase, it is desirable that the second phase contains 0.001 to 20% by weight, particularly 1 to 5% by weight in terms of oxide in the total amount. In the second phase, Y and rare earth oxides such as Yb, Nd, Er and the like exist alone or as a composite oxide with La ₂ O _3, and it is particularly desirable to exist as a crystalline phase. The addition ratio of Y and rare earth elements to the total amount is 0.
If the amount is less than 001% by weight, it is difficult to sinter the material, and if the ratio exceeds 20% by weight, the electrical resistance tends to increase, which makes the material less suitable as a heating element.

When the second phase contains an element of Group 5a of the periodic table such as Si, V, Nb, Ta, etc., 0.001 to 15% by weight, particularly 1 to 5% by weight of the total amount in terms of oxide. Is desirably contained at a ratio of This is because if the amount is less than 0.001% by weight, it is difficult to sinter the material, and if it exceeds 15% by weight, the electrical resistance tends to increase, which makes the material less suitable as a heating element. S added
It is desirable that i, V, Nb, and Ta precipitate as oxide crystals.

In the present invention, Ca, Sr and Mg, which are solid solution components of LaCrO ₃ , contain a small amount of CaO, Sr
O and MgO may be precipitated, but there is no particular problem.

Further, since the heating element may require a rapid temperature rise, it must be essentially resistant to thermal shock. Therefore, in the present invention, as a heating element, as a result of examining the relationship between the thermal shock resistance, electrical resistance, and open porosity of the material,
It has been found that when the open porosity is increased, the resistance to thermal shock is increased, but the electrical resistance is increased and the element tends not to function as a heating element. Then, when the optimal open porosity was examined, the open porosity was 30% or less, especially 2 to 1%.
It has been found that 0% or less is desirable.

Further, the crystal grain size of the heating element is also one of the factors affecting the thermal shock. If the crystal grain size is too large or too small, the thermal shock of the heating element tends to be weak. . Therefore, as a result of examining the crystal grain size, it was found that the average crystal grain size of the main crystal phase was good in the range of 0.5 to 30 μm, particularly 3 to 10 μm.

Next, a method of manufacturing the above ceramic heating element will be described. Specifically, L constituting the main crystal phase,
a, Cr metal oxides, Ca, Sr, Ba oxides and Y or rare earth element oxides forming the second phase;
Alternatively, using Si, an oxide powder of an element of Group 5a of the periodic table, or a metal compound such as a carbonate, a nitrate, or an acetate that forms an oxide by heat treatment, the composition may satisfy the above-described composition range. And then mixed by a well-known method such as a ball mill or a vibration mill, and then forming the mixed powder into a predetermined shape by a die press, an extrusion method, or a cold isostatic pressing method, and then, at 1200 to 1650 ° C. By baking in an oxidizing atmosphere for 2 to 10 hours, a heating element can be manufactured.

When the dimensional accuracy of the heating element is required, a LaCrO ₃ solid solution powder containing Ca, Sr, and Ba is prepared in advance, and then Y, a rare earth element oxide, Si, After adding and mixing the oxide of the element of Group 5a of the Table, molding is performed in the same manner as described above.
It is good to perform baking.

At the time of firing, a powder of Cr ₂ O ₃ is added to the above-mentioned mixed powder in an amount of 0.01 to 1 in addition to the above composition.
The addition by weight improves sinterability and can be reduced by about 50 ° C. as compared to the case where no sintering temperature is added.

According to the ceramic heating element of the present invention, the above-mentioned ceramic material is used as a resistor to energize itself, so that it has a self-heating property and can generate uniform heat because it is a uniform sintered body. In addition, since the operating temperature can be increased as compared with the conventional self-heating type heating element, the field of use as the element can be greatly expanded. The heating element according to the present invention includes, for example, a resistor 1 made of a cylindrical sintered body and electrodes 2 and 3 formed at both ends of the resistor as shown in FIG. This heating element can be operated at a temperature of about 400 to 1200 ° C. by applying a voltage of 50 V or less to the electrodes 2 and 3 as shown in FIG. The heating element of the present invention can be manufactured in any shape such as a cylindrical shape, a cylindrical spiral shape, a honeycomb structure, etc., in addition to a cylindrical shape.

[0018]

In general, lanthanum chromite represented by LaCrO ₃ is originally an insulator.

[0019]

Embedded image

A hole is generated as represented by Such a LaCrO ₃ solid solution has a low hole concentration and can be used as a heating element.

However, a major problem of the LaCrO ₃ solid solution is that it is extremely difficult to manufacture an element due to its difficulty in sintering. Generally, LaCrO ₃ solid solution is 2000 ° C in air.
Sintering cannot be performed unless the temperature is higher than 1900 ° C. in an inert gas such as Ar. LaCrO ₃ solid solution is expected to be used as a heating element, but has not been put to practical use.
As a result, the manufacturing cost becomes extremely high.

In the present invention, the LaCrO ₃ solid solution contains rare earth elements such as Y and Yb and Nd, or Si and Nd.
When an oxide of a Group 5a element of the periodic table such as b is added, L
It has been found that sintering of the aCrO ₃ solid solution is extremely accelerated and sintering is possible even at a temperature of 1650 ° C. or less.
According to the present invention, when an oxide such as Y, Yb, Si, or Nd is added, these elements displace solid solution with La of the LaCrO ₃ -based main crystal at a high temperature, and La oxide is generated on the surface of the main crystal. The La oxide and the Cr oxide vapor evaporated from LaCrO ₃ react to form a liquid phase containing La, which suppresses the evaporation of the Cr oxide and promotes the diffusion of La and Cr ions and the like in the liquid phase. As a result, it is presumed that sintering is promoted. Further, when the additive is La, the La oxide directly reacts with the evaporating component and promotes sintering by preventing condensation of the Cr component.

In addition, the heating element of the present invention can generate heat in a temperature range of 400 to 1200 ° C. by applying a low voltage, and since it is a self-heating type, the heating area is large and uniform. Also, an arbitrary shape can be selected as the element shape.

[0024]

【Example】

Example 1 La _0.9 Ca _0.1 CrO ₃ and La _0.9 Ba _0.1 Cr having a purity of 99.5% or more and an average crystal particle diameter of about 2 to 3 μm.
O ₃ , La _0.9 Sr _0.1 CrO ₃ , LaCr _0.9 Mg
_An oxide composed of Y and a rare earth element was added to the _0.1 CrO ₃ powder at a ratio shown in Table 1, and the mixture was subjected to ball milling.
After mixing for 3 hours at a temperature of 1500-1600 ° C.
By firing for a time, a sintered body having a size of 4 × 4 × 65 mm was prepared.

The open porosity of this sample was measured by Archimedes' method, and the average crystal grain size of the main crystal phase was measured by a scanning electron microscope. Further, a Pt electrode was adhered to the sintered body, and the electric resistance in the air at 1000 ° C. was measured. The results are shown in Table 1.

[0026]

[Table 1]

From this, the samples of Nos. 1 and 2 without additives did not sinter at this temperature at all. In contrast, the product of the present invention has an addition amount of an oxide such as Y of 0.001.
Samples Nos. 3 and 12, which were smaller than the weight percent, had insufficient material, the open porosity was greater than 30%, and the electrical resistance was large. In addition, sample N whose amount of addition exceeds 20% by weight
o. In Examples 12 and 25, the electric resistance increased. Among the samples of the present invention, the samples with an addition amount of 0.001 to 20% by weight all have an open porosity of about 1 to 15% and an electric resistance of 0.15 Ω-cm or less. Showed especially the characteristics optimal for the heating element.

Reference Example La _0.9 Ca _0.1 CrO ₃ , La _0.9 Sr _0.1 CrO ₃ , La with a purity of 99.3% or more and an average crystal particle diameter of about 2 to 3 μm
Example 1 The oxides of Si, Nb, V, and Ta were added at the ratios shown in Table 2 to Cr _0.9 Mg _0.1 CrO ₃ powder.
In the same manner as in the above, a sintered body having a size of 4 × 4 × 65 mm was produced. Using this sample, the open porosity, the crystal particle diameter, and the electrical resistance were measured in the same manner as in Example 1. The results are shown in Table 2.

[0029]

[Table 2]

From the above, if the addition amounts of Si, Nb, V and Ta are less than 0.001% by weight, the densification is not sufficient,
The open porosity was greater than 30% and the electrical resistance was increased.

When the amount exceeds 15% by weight, the electric resistance increases. On the other hand, when the amount added is 0.001 to 1
In the range of 5% by weight, all had an open porosity of about 1 to 15%, and exhibited an electrical resistance of 0.15 Ω-cm or less.

Example 2 Samples Nos. 5 and 22 of Example 1 and Sample N of Reference Example
o. 44, a Pt electrode was attached so that the distance between the electrodes was 50 mm, and the temperature of the sample was measured in the air while changing the applied voltage. The result is shown in FIG. As is clear from FIG.
The temperature reached within 0 seconds. The temperature distribution between the electrodes was smaller than ± 20 ° C. This indicates that the ceramic of the present invention can be used as a heating element for high-temperature operation.

[0033]

As described in detail above, the ceramic heating element of the present invention can generate heat in a temperature range of 400 to 1200 ° C. by applying a low voltage, and is a self-heating type, so that the heating area is large. Is wide and uniform, and an arbitrary shape can be selected as an element shape.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a structure of a ceramic heating element of the present invention.

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

[Explanation of symbols]

 1 resistor 2, 3 electrodes

Claims (1)

(57) [Claims] 1. A main crystal phase comprising a LaCrO ₃ -based solid solution containing at least one element of Ca, Sr, Ba and Mg, and a second crystal containing an oxide of at least one of Y and rare earth elements. And Y
And rare earth elements in the total amount of 0.001-2 in oxide equivalent
0% by weight and the main crystal phase has an average crystal grain size of 3
A ceramic heating element having a thickness of 10 to 10 μm.