JPH06101371B2 - ZrO (bottom 2) method and electrode bonding method for heating element - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode joining method and an electrode joining structure of a zirconia heating element used when it is necessary to heat to an ultrahigh temperature of 1800 ° C. or higher in the air or an oxidizing atmosphere. It is a thing.

[Conventional technology]

Conventional non-metallic heating elements, such as zirconia heating elements, are usually made as follows.

That is, as shown in FIG. 5, a round bar 1 made of zirconia (ZrO ₂ ) having a constant length and diameter is first formed by pressure molding or extrusion molding and then dried and fired. Subsequently, the heating element 1a in the central portion is processed by a lathe and polished to be a heating element. Furthermore, the zirconia fiber sheet 2 having flexibility at room temperature is wound around the outer periphery of the end portion at least twice and the end portion of the platinum lead wire 3 is inserted between them, or the end portion of the lead wire 3 is previously attached to the attachment portion of the sheet 2. It was made by inserting, crimping it, and winding it.

[Problems to be solved by the invention] However, in the zirconia heating element produced in this way, the zirconia sheet used expands or contracts at a high temperature during use, cracks, or shifts, and current cannot be applied. . Moreover, since the heating element reaches an extremely high temperature of around 1800 ° C., the platinum lead wire melts and evaporates and becomes thin, resulting in a problem of disconnection. Further, expansion or shrinkage of the zirconia molded body of the electrode causes a gap between the zirconia molded body and a crack or an electrode surface to separate the electrode portion,
Since it easily breaks and has a short life, its solution has been a problem in practical use.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an electrode joining method and a joining structure capable of extending the life of the electrode even at an extremely high temperature.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the resistance temperature characteristic at a lower temperature is superior to that of the ZrO ₂ heating element, and it is close to the coefficient of thermal expansion of ZrO ₂ , and in order to prevent the oxidation of molybdenum like the heating element made of molybdenum disilicide SiO ₂ It is used as a lanthanum chromite extension terminal material that does not form a SiO ₂ insulating film on the joint surface with a ZrO ₂ heating element by forming a system oxide film.

Lanthanum chromite is an equimolar mixture of Cr ₂ O ₃ and La ₂ O _3.
The specific resistance can be made smaller than that of zirconia by setting the X of the solid solution La _1-X Ca _X CrO ₃ in which a part of La is replaced by Ca to 0.2 or less. The conductivity is strongly influenced by the atmosphere and exhibits conductivity at an oxygen partial pressure of 10% or more. Even when heating in a vacuum or an inert gas, the conductivity can be obtained by treating in an oxygen atmosphere in advance.

The lanthanum chromite, which is a zirconia heating element terminal and an extension terminal, uses the slight difference in thermal expansion between the zirconia heating element and the lanthanum chromite.Since the zirconia heating element has a slightly higher coefficient of thermal expansion, The lanthanum chromite side is a convex type and the concave type is joined.

In Fig. 1, a vertical cross-sectional view of Fig. 1 (a) and Fig. 1 (b).
As can be seen from the cross-sectional view of FIG. 3, a large-diameter ZrO ₂ terminal 10 is formed at the end of the cylindrical ZrO ₂ heating element 11, and a conical convex portion 12 whose diameter decreases toward the tip is formed at the tip. To form. The cylindrical ZrO ₂ heating element 11 and the ZrO ₂ terminal 10 are provided, for example, with ZrO _{2 as a} core material.
It is formed by winding a sheet and firing it. On the other hand, a cylindrical lanthanum chromite extension terminal 20 in which a conical recess 21 is formed so that the shape of the protrusion 12 is the same as the ZrO ₂ terminal 10 is formed.
Then, the contact surfaces of the ZrO ₂ terminal 10 and the extension terminal 20 are bonded with the mortar 30. In the figure, the tip of the ZrO ₂ heating element 11 is projected from the convex portion 12, but the ZrO ₂ heating element 11
The tip of the terminal may be flush with the tip of the convex portion 12, in which case the extension terminal does not have to have a hollow structure.

In FIG. 2, the protrusion 13 at the tip of the ZrO ₂ terminal is not conical, but as shown in the sectional view of FIG. It is formed by tapering so that the width becomes narrower, and the recess is formed in the extension terminal 20 so that the shape thereof corresponds to the shape. The joining method is the same as in the case of FIG.

In FIG. 3, the convex portion 14 at the tip of the ZrO ₂ terminal forms an inverse tapered convex portion as compared with the case of FIG. 2, and the concave portion is formed in the extension terminal 20 so that the shape corresponds to this. It is a thing. In this example, since it is slid from the lateral direction to be fitted, the tip of the ZrO ₂ heating element 11 is made flush with the tip of the convex portion 12, or the depth of the recess of the extension terminal is set to the tip of the heating element 11. It needs to be deep enough to escape from.

The conditions that the joining mortar used at this time should have are as follows.

The electrical resistance of mortar is low. The adhesive strength is high. There is no change in the mortar structure. The above conditions are ZrO ₂ quality 0-100 wt%, lanthanum chromite 100-0 wt% mortar, or ZrO ₂ quality 0-100. It is possible to fill it with a mortar by weight%, CeO ₂ 0-50% by weight.

As shown in FIG. 4, a preheating chamber 41 formed in the outer furnace 40
The inner furnace (ZrO ₂ furnace 40 is placed in the preheating chamber 41 is heated to about 1000 ° C. by the heater 43. ZrO ₂ is an insulator,
When it is heated to about 1000 ° C, it exhibits conductivity, and when it is energized by the power source E in this state, it functions as a heating element.

As a result of various experiments, the following characteristics were found, and it became possible to extend the service life by using a usage type suitable for the usage conditions.

That is, as CrO ₂ O ₃ was added to ZrO ₂ , the adhesive strength decreased, but the electrical resistance decreased, and the high temperature range (2000
There is no microstructural change at (° C), but the thermal expansion is large and the shrinkage rate is small.

As lanthanum chromite is added to ZrO ₂ , the adhesive strength increases and the electrical resistance decreases, but at high temperature (2000
At ℃), microstructural changes occur due to evaporation of CrO ₂ O ₃ components in the mortar.

Therefore, a material obtained by adding CeO ₂ to ZrO _2, bonding positions in common also that the addition of lanthanum chromite to ZrO _2, the fourth
As shown in the figure, it is located outside the ZrO ₂ furnace and is located at least 10 m / m or more from the surfaces S1 and S2 of the ceiling / bottom plate.
Further, the mortar joining can further improve the durability by using it under the following operating conditions.

That is, in order to increase the rate of temperature rise (starting energization from 1500 ° C. and reaching 2000 ° C.), it is desirable to use a mortar with low electrical resistance, such as ZrO ₂ lanthanum chromite mortar, or ZrO ₂ ˜CeO. Either ₂ type mortar may be used, but since the thermal expansion of mortar is large, the joining position is the ceiling,
It should be located at a position 20m / m or more from the bottom plate surface, and since the adhesive strength will be reduced, the size of the heating element will be made slightly smaller. In this case, the maximum operating temperature is 2000 ° C to 2100 ° C, which enables high temperature heat generation.

Since the extension terminal is interposed, it can be joined to the lead wire at a room temperature or low temperature part (room temperature to about 400 ° C) away from the end of the heating element. It is possible to eliminate such troubles.

〔Example〕

As shown in Fig. 1, the outer diameter of the terminal of the ZrO ₂ heating element is φ18 to φ20 m / m.
A convex taper with a height of 5 to 20 m / m and a diameter of 16 to 14 m / m to 12 to 10 m / m. Φ17m / m to φ15m / m to φ18m outside diameter of lanthanum chromite heating element φ18m / m to φ20m / m
A concave taper with a height of 5 to 20 m / m and a height of 13 m / m to 11 m / m will be provided, and the joint allowance will be 1 m / m.

(A) As a joint material, Y ₂ O ₃ 7 wt% stabilized ZrO ₂ grains (0.1 m / m
20% by weight of powdered lanthanum chromite particles (0.1m / m diameter or less) added to 30% by weight, and 1% by weight of methylcellulose as a binder (zrO ₂ = 15%). % Was added and bonded using a kneaded mortar. When energization of the ZrO ₂ heating element was started from 1500 ° C, it took 30 minutes to raise and lower the temperature to 2000 ° C in the conventional case (platinum type), whereas in the case of this example Can be shortened to 20 minutes, and
The number of repetitions of 1500 ° C. to 2000 ° C. was limited to 50 times in the conventional one due to the detachment of the electrode part, but in the present embodiment, it was 10 times.
It became possible 0 times. In addition, it was possible to extend it to 1000 hrs, while it was 500 hrs continuously at 2000 ° C in the past.
It has become possible to increase the size of the O ₂ heating element from 300 m / m to 400 m / m.

(B) Y ₂ O ₃ 7% by weight stabilized ZrO ₂ grains as joint fillers (0.1 m / m
Diameter of less than 85% by weight and CeO ₂ particles (0.1 m / m diameter or less) at 15% by weight.
Wt% zirconium acetate aqueous solution (ZrO ₂ = 15%) 20 wt%
Was added and the mixture was bonded using a kneaded mortar. The size of the ZrO ₂ heating element is 300m / m, which is the same as the conventional one, but by setting the bonding position to be 40m / m from the ceiling, the ZrO ₂
The heating element started to be energized, and it was possible to raise the temperature to a high temperature of 2100 ° C. in 30 minutes in the present example, while the conventional one was up to 2000 ° C. In addition, 1500 ℃ ⇔2100 ℃ can be repeated up to 100 times, resulting in a high durability of 2100 ℃ continuously for 1000 hours.

(C) As a joint material, 7 wt% Y ₂ O ₃ stabilized ZrO ₂ grains (0.1 m / m
100% by weight or less), 20% by weight of methylcellulose 1% by weight zirconium acetate aqueous solution (ZrO ₂ = 15%) was added as a binder, and the mixture was bonded using a kneaded mortar. Zr
The size of the O ₂ heating element is 300m / m, but the maximum operating temperature is up to 2050 ° C, and the rate of temperature increase / decrease is the same as before.
Repeated 1500 ℃ ⇔2050 ℃ 100 times, 2050 ℃ continuous 1000
hr and high durability were obtained.

The above is the structure of FIG. 1, but when the above mortar is used in the joint structure of the mold shown in FIGS. 2 and 3,
The same durability result as in FIG. 1 was obtained.

〔The invention's effect〕

According to the present invention as described above, both ends of the ZrO ₂ heating elements, ZrO ₂ quality 0 lanthanum chromite made extension terminals to form an electrode
-100% by weight, lanthanum chromite 100-0% by weight mortar, or ZrO ₂ 0-100% by weight, CeO ₂₀ 0-50% by weight
By bonding with mortar, it is possible to lower the electric resistance and increase the bonding strength. Also
The connection between the ZrO ₂ heating element and the extension terminal of the lanthanum chromite is
Using the difference in thermal expansion between ZrO ₂ and lanthanum chromite, a taper type connection method can be used to bond to the lead wire at room temperature or low temperature (room temperature to 400 ° C) away from the end of the heating element, resulting in heat generation. Problems such as breakage of the platinum wire in the body terminal and damage to the electrode were eliminated, and the number of cycles of the heating element could be dramatically increased.

[Brief description of drawings]

1, 2 and 3 are views for explaining an electrode connection structure of the present invention, FIG. 4 is a view for explaining a method of energizing a heating element, and FIG. 5 is a conventional electrode connection. It is a figure for demonstrating a structure. 10 ... ZrO ₂ terminal, 11 ... ZrO ₂ heating element, 12 to 14 ... convex part, 20 ... lanthanum chromite extension terminal, 21 to 23 ... recessed part.

Claims (2)

[Claims] 1. A lanthanum chromite extension terminal for forming electrodes on both ends of a ZrO ₂ heating element, containing 0 to 100% by weight of ZrO ₂ and 100 to 0% by weight of lanthanum chromite, or ZrO.
_A method for joining electrodes of a ZrO ₂ heating element, characterized in that _two substances are bonded by 0-100 wt% and CeO ₂ 0-50 wt% by mortar. 2. An electrode joining structure joined by the method according to claim 1, wherein a tapered convex portion formed on both terminal portions of the heating element and an end surface of a lanthanum chromite extension terminal forming an electrode. Zr characterized in that the concave part formed in is fitted and the contact surface of the heating element and the extension terminal is bonded with mortar.
O ₂ heating element electrode bonding structure.