JPH11339935A - Ceramic heater and evaluating method for re powder used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent discoloration and defective insulation by forming a heating resistor with Re powder having a large crystal piece, and setting the diffusion distance of Re into a ceramic body within a specific range. SOLUTION: The diffusion length of Re is set to 0.2 mm or below, the Re powder having the grain size of 0.5-3 μm, preferably 0.8-2.0 μm, and a half-power bandwidth of a main peak by an X-ray analysis at 2θ=0.6 deg. or below is used for a heating resistor, then the crystal piece of the Re powder is increased, the crystallinity of the Re crystal is improved, the humidity resistance of the Re powder is improved, and the powder having a good sintering property is obtained. When the weight increase of the Re powder when it is left at the temperature of 40 deg. and the humidity of 90% for 24 hrs is set to 1% or below, the diffusion of Re can be prevented, and discoloration and the deterioration of an insulation property can be prevented. For the evaluation of acid resistance, the Re powder is left in the constant-temperature and constant-humidity atmosphere for a fixed period, and the weight increase during the period is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater for heating a sensor used for detecting the oxygen concentration of exhaust gas from an automobile and a ceramic heater used for a soldering iron, a petroleum vaporizer and the like.

[0002]

2. Description of the Related Art Conventionally, as a ceramic heater for heating a sensor used for detecting the oxygen concentration of automobile exhaust gas,
It is general that a heating resistor made of W powder is built in alumina ceramic.

On the other hand, in order to improve the durability, the composition of the heat generating resistor is, for example, a W-Re alloy (Japanese Patent Laid-Open No.
0-19069, JP-A-5-315055, JP-A-8-108
No. 273813.) or a W-Mo alloy is used. When the composition of the heat generating resistor is alloyed, the temperature coefficient of resistance of the heat generating element is reduced, and the inrush current at the time of temperature rise can be reduced. Therefore, the power generation capacity of the power supply and the current capacity of the wiring portion can be reduced, and the cost can be reduced. Although various combinations are possible as the high melting point metal that can be used for the heating element, the combination of W and Re is most advantageous from the viewpoint of high-temperature durability.

However, since the cost of the powder is too high to use the alloy powder from the beginning, generally, for example, a method of mixing W powder and Re powder and alloying them at the time of firing is adopted. I was

[0005]

In the above-described ceramic heater manufacturing process, when the W powder and the Re powder are mixed and alloyed at the time of firing, when the Re powder is pulverized to improve the reactivity with W, There is a drawback that the hygroscopicity of the Re powder increases and the powder is oxidized, and at the time of firing, Re diffuses into the ceramic and discolors black.

Further, when the diffusion of Re becomes severe, there is a problem that the insulation between the electrode patterns deteriorates and the durability of the heater deteriorates. It is very difficult to manage this point, especially in a humid season such as during the rainy season, and this has been a problem in using Re powder.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, in order to prevent the electric insulation of the ceramic heater from being lowered, the diffusion distance of Re into the ceramic body is determined by the heating resistor forming portion. It was found that it was necessary to reduce it to 0.2 mm or less.

Further, the inventors of the present invention have studied a method for reducing the diffusion distance of Re to 0.2 mm or less. As a result, it has been found that the method can be realized by the following adjustment.

First, as the Re powder used for the heating resistor, a powder having a particle size of 0.5 to 3 μm and a half width of the main peak by X-ray diffraction of 2θ = 0.6 ° or less should be used. Was found.

Alternatively, as Re powder, 40 ° C. × 90%
It has been found that it is only necessary to use a material having a weight increase of 1% or less when left for 24 hours under humidity.

By these operations, the diffusion distance of Re during firing can be reduced to 0.2 mm or less, and even if a W-Re-based heating resistor is used, it does not discolor and has good insulation and durability. Can be obtained stably.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1A is a developed view showing the structure of a general ceramic heater. In this ceramic heater, first, a through hole 121 is formed in a first ceramic green sheet 12, filled with W ink by a printing method, and a pattern of a heating resistor 14 made of a mixture of W-Re is formed on one surface. The terminal 123 is formed on the tape surface on the back side by a printing method.
The second green sheet 13 is adhered to the surface on which the heating resistor 14 is formed, and the adhered green sheet 13 is further adhered to the ceramic rod 11.
Baking in a reducing atmosphere at 00 ° C.

Thereafter, as shown in FIG. 1 (b), the terminal portion 123 is plated with Ni (not shown), and furthermore, a lead wire lead-out terminal wire 15 is brazed with a brazing material (not shown) to form a ceramic. Make a heater. Thus, a ceramic heater in which the heating resistor 14 is built in the ceramic body 16 can be obtained.

The heating resistor 14 is composed of a mixture of 10 to 50% by weight of Re and 90 to 50% by weight of W. The diffusion distance of Re into the ceramic body 14 after firing is 0.2%.
mm or less. In addition, the diffusion distance of Re means that the heating resistor 14 is exposed by planar polishing of a ceramic heater, a 100 times SEM photograph of the vicinity of the heating resistor 14 is taken, and the concentration distribution of Re by EPMA is analyzed by line analysis or surface analysis. The distance between the end of the heating resistor 14 and the point at which the Re concentration in the ceramic body 16 is reduced to 1/20 with respect to the Re concentration of the heating resistor 14 as measured by analysis.

As described above, by reducing the diffusion of Re, it is possible to prevent the ceramic body 16 from discoloring and lowering the insulating property, and to obtain a ceramic heater having excellent durability.

In order to reduce the diffusion of Re, a Re powder having a particle size of 0.5 to 3 μm and a half width of a main peak by X-ray diffraction of 2θ = 0.6 ° or less is used. May be used to form the heating resistor 14.

Here, the reason why the half width of the main peak of the Re powder by X-ray diffraction is set to 0.6 ° or less is that the crystallite of the Re powder is increased and the crystallinity of the Re crystal is improved. This is because the moisture resistance of the powder is improved. Normal,
Chloride powders such as salt and rock salt, which are said to have strong hygroscopicity and deliquescent, can improve hygroscopicity and deliquescence by improving the crystallinity of the powder in this way. I have. The present invention applies this concept to Re powder.

The size of the Re powder is usually 0.1 to 5 μm.
However, the crystallites are in the range of 0.005 to 0.5.
It is as small as about 05 μm. Each powder is made up of tens to thousands of crystallites. Since the crystallite is very small, it is very difficult to measure this size directly, but the diffraction angle (2
A method of indirectly measuring the crystallite size by measuring θ) has been established. That is, the peak waveform of the crystal with respect to the diffraction angle (2θ) of the X-ray is measured by X-ray diffraction, and the width of 2θ at half the peak height of the peak waveform is defined as the half width. . The half width has a correlation with the size of crystallites constituting the powder, and the smaller the crystallite, the larger the half width.

Conventionally, as the Re powder, a fine powder has been used in order to improve the reactivity with W. Therefore, the half width of the main peak of the conventional Re powder by X-ray diffraction is 1
It was a large value over degrees. The present inventor has proposed that the conventional R
It was presumed that the poor moisture resistance of the e powder was due to the low crystallinity of the Re powder. Therefore, in order to improve the moisture resistance of the Re powder, the crystal size of the Re powder was increased, that is, the half width of the X-ray diffraction peak was reduced.

As a method of reducing the half width of the Re powder, it is effective to increase the heat treatment temperature during the production of the Re powder or to extend the maximum temperature holding time.

However, when such a treatment is performed, the particle size of the Re powder increases, the reactivity with the W powder deteriorates, and the resistance temperature coefficient of the heating element cannot be adjusted to a target level, and the firing of the heating element does not occur. There is a problem in that the bondability decreases and the durability deteriorates. In this regard, the present inventors have studied,
The average particle size of the powder is 0.5 to 3.0 μm, preferably
It was found that a powder having a good sinterability was obtained when the thickness was 0.8 to 2.0 μm.

As described above, regarding the adjustment of the half width of the main peak of the Re raw material by X-ray diffraction, the half width was 0.6 °.
Exceeding the range is not preferable because the hygroscopicity of the Re raw material increases and the diffusion distance of Re into the ceramic body 16 during firing becomes 0.2 mm or more. Further, when the heat treatment temperature of the Re raw material is increased, the half width is reduced. However, when the heat treatment temperature is excessively increased, the particle size becomes too large, and when the average particle size exceeds 3 μm, the reactivity with the W powder is reduced. However, the effect of reducing the target temperature coefficient of resistance of the heating element cannot be obtained. Further, when the half width of the Re powder exceeds 0.6 °,
Although the particle size of the powder becomes smaller, the reactivity with W is improved and the temperature coefficient of resistance is reduced, the hygroscopicity of Re is large, and the ceramic body 16 discolors during firing.

It has been found that in order to reduce the diffusion of Re, it is sufficient to use a Re powder having a weight increase rate of 1% or less when treated in an atmosphere at a temperature of 40 ° C. and a humidity of 90% for 24 hours. Was.

The evaluation method based on the weight increase rate is as follows.
It is as follows.

First, Re powder was placed on a glass preparation, anhydrous isopropyl alcohol (IPA) was dropped on the powder, dried in a dryer at 80 ° C., and the powder was fixed on the preparation. Subtract the tare weight and weigh the powder.

Next, the prepared slide on which the Re powder was
The powder may be left in a thermo-hygrostat at 0 ° C. × 90% humidity for 24 hours, and the change rate of the powder weight before and after the standing may be measured.

If the Re powder whose weight increase exceeds 1% is used, the ceramic body 16 near the heating resistor 14 turns black during firing, resulting in a decrease in insulation. On the other hand, when the Re powder having the weight change rate of 1% or less is used, the diffusion of Re can be prevented, and the diffusion distance is set to 0.2 mm or less to prevent discoloration and decrease in insulation. can do.

The method of measuring the weight increase before and after standing in a thermo-hygrostat as described above is also useful as a method for evaluating the oxidation resistance of the Re raw material.

Here, the condition of the thermo-hygrostat is 40 ° C.
Although the humidity was fixed at 90% humidity, any condition can be set for this. In order to measure the Re powder weight, anhydrous IPA was used as a solvent for fixing the powder, but other solvents may be used as long as they do not contain water. Furthermore, the temperature of the dryer for measuring the dry weight of the powder was 80 ° C. in this case, but other temperatures can be used if the conditions are always kept constant. As the carrier on which the powder is placed, a glass preparation was used this time. However, as long as the substrate itself has no hygroscopicity and has strength enough to withstand handling, a substrate such as an alumina substrate may be used.

[0031]

Embodiments of the present invention will be described below.

The Re compound powder (for example, rhenium oxalate) is dry-pulverized to an average particle diameter of 1 μm or less, and further heat-treated at 300 ° C. for 2 hours in a reducing atmosphere to reduce the half width of the main peak of the powder by X-ray diffraction to 0%. About 5 °. This powder is further pulverized with a ball mill to an average particle size of 1 μm. 25% by weight of the Re powder thus obtained, average particle size 1 μm
Then, 75% by weight of W powder and 3% by weight of a cellulosic binder and an appropriate solvent are added, and the mixture is mill-mixed for 24 hours, and further kneaded with three rolls to prepare a paste forming the heat generating resistor 14.

This paste is printed on a green sheet of alumina having a purity of 92% to form a heating portion and a lead portion. Further, after the lead take-out part, through-hole processing, and through-hole embedding processing, the green sheet is adhered to the alumina rod. Thereafter, firing is performed at 1600 ° C. in a reducing atmosphere to obtain a ceramic heater.

If necessary, Ni plating is applied to the external electrodes, and the Ni leads are brazed with Au-Cu brazing or Ag-Cu brazing. When power is supplied to the heater, power is supplied through this Ni wire.

In a humidification test in which the above-mentioned Re powder was left at 40 ° C. × 90% humidity for 24 hours, the weight increase of the Re powder was within 1%, and the discoloration of the ceramic body 16 of the obtained ceramic heater was reduced. Almost never occurred. The diffusion distance of Re into the ceramic body 16 was within 0.2 mm from the end of the heating resistor 14.

The diffusion distance is measured by exposing the heating resistor 14 by polishing the heater to a flat surface,
Was confirmed. That is, a 100-fold SEM photograph of the vicinity of the heating resistor 14 was taken, and the Re
Is measured by line analysis or surface analysis, and the distance between the point in the ceramic body 16 where the Re concentration decreases to 1/20 and the end of the heating resistor 14 with respect to the Re concentration of the heating resistor 14 is determined. The diffusion distance of Re was used.

For example, as shown in FIG. 3, in the conventional ceramic heater, Re diffuses to the outside with respect to the width (dotted line) of the heating resistor 14, and the diffusion distance r exceeds 0.2 mm. In contrast, as shown in FIG.
In the ceramic heater of the present invention, the diffusion distance of Re is set to 0.1.
It turns out that it can be set to 2 mm or less.

Here, in the case where Re powder having a large weight increase by a humidification test left in a constant temperature and constant temperature chamber is used, the discoloration range (diffusion distance) of the ceramic body 16 due to the diffusion of Re is 0.5 to 1.0 mm. There are also things that extend. This discoloration due to the diffusion of Re is not preferable because not only is the commercial value inferior in appearance but also the durability of the ceramic heater is deteriorated.

The method of measuring the half-value width of the Re powder by X-ray diffraction is as follows, although the apparatus manufactured by Lint was used this time, but is not limited thereto. The conditions were as follows: acceleration voltage 200 kV × current 5 mA, scan speed 2
Measured in ° / min. Regarding the measurement of the half-value width, the width at a position half the height of the main peak on the chart was evaluated by a width of 2θ, and a method generally used was used. These days,
A method has been provided for automatically measuring the half width by computer processing of the X-ray diffraction chart data, but this method may be used.

Next, as shown in Table 1, the particle size of the Re powder,
Ceramic heaters were manufactured using different half-value widths, and the heat resistance was evaluated and the temperature coefficient of resistance was measured. In the durability evaluation, the applied voltage was adjusted so that the highest temperature portion of the heat generating portion was 1200 ° C., and the durability time was measured. The endurance time is
The resistance value was evaluated by the time at which the resistance value was increased by 10% with respect to the initial resistance, or the time at which the wire was disconnected, and the average time of ten pieces was measured.

[0041] With respect to the resistance temperature coefficient of the heating resistor, and the measured resistance value R ₂₀ of the room temperature (20 ° C.), the resistance value R ₁₀₀₀ upon heating the heating element 1000 ° C., resistance by substituting the number 1 The temperature coefficient was calculated.

[0042]

(Equation 1)

As shown in Tables 1 and 2, the half width of the Re powder was set to 0.6 ° or less, and the average particle size was 0.5 to 0.5.
In the case of 3.0 μm (Re-3 to 9), the weight increase after the humidification test left in a thermo-hygrostat was 1% or less, and R
The diffusion distance of e (discoloration area width after firing) was reduced to 0.2 mm or more, and the durability was improved.

When an experiment was conducted by changing the content of Re within the range of 10 to 50% by weight, the same result as described above was obtained.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

As described above, according to the present invention, W-Re
In a ceramic heater using a series heating resistor, discoloration and insulation failure of the ceramic body can be prevented, and a ceramic heater having good durability can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of a ceramic heater according to the present invention, in which (a) is an exploded perspective view and (b) is a perspective view after being combined.

FIG. 2 is EPMA line analysis data showing Re diffusion of the ceramic heater of the present invention.

FIG. 3 shows E showing the Re diffusion of a conventional ceramic heater.
It is PMA line analysis data.

[Explanation of symbols]

 11: Ceramic rod 12: First ceramic green sheet 121: Through hole 122: Terminal connection part 123: Terminal part 13: Second ceramic green sheet 14: Heating resistor 16: Ceramic body

Claims (4)

[Claims] 1. A ceramic heater in which a heating resistor made of a mixture of Re and W is incorporated in a ceramic body, wherein the heating resistor is formed using Re powder having a large crystallite. A ceramic heater, characterized in that the diffusion distance of contained Re into the ceramic body is 0.2 mm or less. 2. The particle size of the Re powder is 0.5 to 3 μm, and the half width of the main peak by X-ray diffraction is 2θ = 0.
The ceramic heater according to claim 1, wherein the angle is 6 ° or less. 3. The ceramic heater according to claim 1, wherein the weight increase of said Re powder when left at 40 ° C. × 90% humidity for 24 hours is 1% or less. 4. A method for evaluating Re powder, which comprises leaving Re powder in a constant-temperature and constant-humidity atmosphere for a certain period of time, measuring the weight increase before and after standing, and evaluating the oxidation resistance of Re powder.