JPH053119B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a zirconia heating structure that generates heat when energized and can be used up to high temperatures in an oxidizing atmosphere.
More specifically, there is a method for joining a zirconia heating element and a current-carrying lead member that has a sufficiently low electrical resistance even at room temperature for energizing the same, a heat-generating structure comprising a zirconia heating element and a current-carrying lead member, and a method for manufacturing the same. Regarding.

[Prior art] Zirconia heating elements are known as heating elements that can be used up _to high temperatures in an oxidizing atmosphere. Obtainable. Since the melting point of zirconium oxide is 2690°C, zirconia heating elements can achieve high temperatures of up to approximately 2000°C.

However, conventional zirconia heating elements are often damaged by localized current flow, and because of their low thermal conductivity and large expansion coefficient, they are susceptible to thermal shock, and there is a risk of damage due to the impact.

In order to overcome these drawbacks, the present applicant has previously applied for a zirconia refractory heating element containing zirconia fibers that generates heat when energized (Japanese Patent Application No. 63-26329).

Conventionally, in order to form a zirconia heat generating structure from these zirconia heat generating elements, a small hole was made in the body of the heat generating element, and a platinum wire was passed through the hole as a lead member for conducting electricity, and the platinum wire was twisted and fixed, or platinum paste was applied. However, a method has been adopted in which the diffusion area is as wide as possible to connect it to the current-carrying lead member.

[Problems to be Solved by the Invention] However, in the former method, there is a problem of loosening during use, and in the latter method, there are significant restrictions on the design of the furnace. Furthermore, damage may occur due to the local current flowing through the contact portion between the energizing lead member and the heating element body.

Another possibility is to use a castable to fix the heating element main body and the current-carrying lead member, but even if you use a conventional castable to fix both, it will not be able to follow the thermal expansion and contraction caused by electricity, and cracks will occur. In many cases, the current-carrying lead member could not be used as a heating element because it would be damaged by overheating due to an increase in contact resistance.

The present invention has been made in view of the above circumstances, and its purpose is to electrically and mechanically connect a zirconia heating element and a current-carrying lead member that has sufficient current-carrying properties even at room temperature. To provide a practical zirconia heating structure in which a heating element main body and a current-carrying lead member are joined using a composition that exhibits conductivity at high temperatures and can be firmly joined to each other, and a method for manufacturing the same.

[Means for Solving the Problem] In order to achieve this objective, the present inventors investigated the electrical resistance at high temperatures using a test piece made by molding a zirconia hardened composition into a rod shape and firing it.
Focusing on the fact that it has sufficient conductivity of about 3 to 50 Ωcm at 1700℃, we discovered that it can be applied to bonding lead members (wire rods, bars, plates) for conducting electricity to zirconia heating elements, and we have developed the present invention. I was able to complete it.

That is, the present invention provides a zirconia heating structure that generates heat when energized, which is composed of a first zirconia heating element and a current-carrying lead member, wherein the joint portion of the zirconia heating element and the current-carrying lead member and its surroundings are , from a zirconia hardening composition that exhibits self-hardening at room temperature by using zirconia fibers, zirconia powder, and a water-soluble zirconium salt whose water solubility is acidic as a binder, and using yttria or a water-insoluble yttrium compound as a hardening agent. The present invention relates to a zirconia heat generating structure characterized in that it is coated and bonded with the obtained cured product having good conductivity.

Second, the present invention provides a zirconia heat generating structure that generates heat when energized and includes a zirconia heat generating element and a current conducting lead member, wherein the joint portion of the zirconia heat generating element and the current conducting lead member and its surroundings are made of zirconia fibers. and a zirconia hardening composition that exhibits self-hardening properties at room temperature by using a water-soluble zirconium salt in which the zirconia powder and aqueous solution are acidic as a binder and using yttria or a water-insoluble yttrium compound as a hardening agent. The present invention relates to a zirconia heat generating structure, which is characterized in that the zirconia heat generating structure is coated and bonded with a cured body having a conductive property, and is impregnated with a zirconia sol and/or a zirconium compound solution after firing treatment.

Thirdly, the present invention provides a method for manufacturing a zirconia heat generating structure that generates heat when energized by joining a zirconia heat generating element and a lead member for conducting current, and the joint portion of the zirconia heat generating element and the lead member for conducting current and the surrounding area thereof. is self-hardening at room temperature by using zirconia fibers and zirconia powder, a water-soluble zirconium salt whose aqueous solution becomes acidic and which exhibits good conductivity during firing, as a binder, and yttria or a water-insoluble yttrium compound as a hardening agent. The present invention relates to a method for manufacturing a zirconia heat generating structure, which comprises coating and bonding using a zirconia cured composition exhibiting the following properties.

Fourthly, the present invention provides a method for manufacturing a zirconia heating structure that generates heat when energized by joining a zirconia heating element and an energizing lead member, and the joint portion of the zirconia heating element and the energizing lead member and its surroundings. is self-hardening at room temperature by using zirconia fibers, zirconia powder, and a water-soluble zirconium salt whose aqueous solution exhibits acidity, which exhibits good conductivity after firing, as a binder, and by using yttria or a water-insoluble yttrium compound as a hardening agent. The present invention relates to a method for manufacturing a zirconia heat-generating structure, which comprises coating and bonding using a zirconia cured composition having the following properties, and impregnating it with a zirconia sol and/or a zirconia compound solution after firing.

[Function] The zirconia heating element used in the zirconia heating structure of the present invention contains zirconia powder, additives,
After hot pressing or cold pressing of materials mixed with stabilizers, zirconia fibers, etc.,
A fired molded product, a molded product made by slip casting molding of a similar material, or a molded product made by molding zirconia fiber alone or a composite of zirconia fiber and zirconia powder using the papermaking method or casting method. can be used. However, among these zirconia heating elements, it is more desirable for practical use to include zirconia fibers. Further, the zirconia fiber may contain an oxide such as MgO, CaO, Y ₂ O ₃ or Gd ₂ O ₃ that acts as a stabilizer for zirconia.

The zirconia curing composition used in the present invention for fixing the zirconia heating element main body and the current-carrying lead member uses zirconia fibers, zirconia powder, and a water-soluble zirconium salt whose aqueous solution is acidic as a binder. Further, there may be mentioned a zirconia-based hardening composition that exhibits self-hardening properties at room temperature by using yttrium or a water-insoluble yttrium compound as a hardening agent.

The zirconia fiber used in the zirconia cured composition has excellent mechanical strength and thermal shock resistance, so it acts as a reinforcing material for the zirconia powder and absorbs stress due to the difference in thermal expansion with the current-carrying lead material. The conductivity is improved.

Also, due to the water-soluble zirconium salt as the binder and the water-insoluble yttrium compound as the hardening agent, it exhibits self-hardening properties at room temperature, and firmly joins the zirconia heating element and the current-carrying lead member.

The zirconia fiber used in the present invention consists essentially of zirconium oxide represented by the chemical formula ZrO ₂ , and if necessary, zirconium compounds such as zirconium carbonate and zirconium hydroxide, and Y ₂ O ₃ , MgO,
It contains a stabilizer such as CaO and consists of at least one of these. Examples of zirconia fibers that can be used in the present invention include pure zirconia fibers, lime-stabilized zirconia fibers, magnesia-doped zirconia fibers, ittria-doped zirconia fibers, ceria-stabilized zirconia fibers, gadoria-stabilized zirconia fibers, and mixtures thereof. has ittria-doped zirconia fiber.

The fiber length and fiber diameter of the zirconia fiber used in the present invention are, for example, from 0.1 to
50 mm, and 0.1 to 20 μm.

The zirconia powder used in the zirconia-based hardening composition used in the present invention consists essentially of zirconium oxide, and may also contain zirconium compounds such as zirconium carbonate and zirconium hydroxide, or Y ₂ O in addition to these, depending on the purpose. ₃ , MgO,
It contains a stabilizer such as CaO and consists of at least one of these. The particle size of this zirconia powder is not particularly limited in the present invention, and can be appropriately selected depending on the use, shape, etc. of the zirconia heating element.
m, preferably 0.5 to 500 μm.

When combining zirconia fiber and zirconia powder, the mixing ratio is 20 to 95% of the zirconia powder.
parts by weight, 5 to 80 parts by weight of zirconia fiber, preferably 15 to 70 parts by weight of zirconia fiber, and 30 to 85 parts by weight of zirconia powder. This is because the amount of zirconia fiber added is less than this lower limit, the effect of adding the fiber is small.

The water-soluble zirconium salt with acidic water solubility used in this cured zirconia composition is as follows:
Examples include zirconyl acetate, zirconyl acid chloride, zirconyl nitrate, zirconyl sulfate, etc., but zirconyl acetate is used in consideration of the fact that toxic gas is generated due to decomposition of the binder component when firing the molded product obtained by curing at room temperature. It is preferable to do so.

The concentration of the aqueous solution needs to be 5% or more; if the concentration is less than 5%, the strength after curing will be insufficient and the cured product will be difficult to handle.

Another essential component of the zirconium-based hardening composition is yttrium or a water-insoluble yttrium compound. Ittria needs to have a purity of 90% or more. Note that it is desirable that the particle size of ittria is 1 mm or less. If the purity of ittria is less than 90% or if the particle size exceeds 1 mm, it is not preferable because it becomes difficult for ittria to function as a hardening agent.

Examples of water-insoluble yttrium compounds include yttrium carbonate and yttrium hydroxide.
Typically, these water-insoluble yttrium compounds are
It is manufactured and sold in the form of a fine powder of 0.1 mm or less.
There is no need to particularly consider the particle size, but it is necessary that the purity of the ittria formed by heating is 90% or more.

The ratio of addition of yttria or a water-insoluble yttrium compound to the water-soluble zirconium salt is 1 part by weight of zirconium formed from the water-soluble zirconium salt, and 1 part by weight of yttria (formed by heating when using a water-insoluble yttrium compound). The range of 0.5 to 5 is preferable, and by adjusting the ratio within this range,
Curing time can be adjusted from 10 minutes to 10 hours. If the amount of ittria added is less than 0.5, the curing time will be too long, which is not practical.If the amount added is more than 5, the curing time will be too fast, and it may harden during kneading. Undesirable because of that.

The amount of the aqueous zirconia salt solution added to the zirconia huff eye bars and the zirconia powder can be adjusted as appropriate in the range of 10 to 60 parts by weight depending on the desired softness of the cup clay.

Furthermore, if viscosity adjustment is required when using this zirconia cured composition, a conventional water-soluble organic sizing agent such as polyvinyl alcohol, methylcellulose, galboxymethylcellulose, polyethylene oxide, etc. can be added.

Current-carrying lead members must have sufficient conductivity at room temperature, do not change in quality even at a certain high temperature, and do not have extremely low conductivity. Generally, such current-carrying lead members are made of platinum, dichloromethane, etc. Molybdenum silicide, silicon carbide, lanthanum chromite, and the like are known, and these can be used. For example, when platinum wire is used as a current-carrying lead member, the material is suitable as a current-carrying lead member for a zirconia heating element, as long as it is not exposed to temperatures above 1770° C., which is the melting point of platinum.

In the zirconia heating structure of the present invention, the zirconia heating element and the current-carrying lead member may be in direct surface contact, or they may be electrically connected via the above-mentioned zirconia curing composition. You may do so.
Also, before using the zirconia cured composition,
The energizing lead member and the zirconia heating element may be physically preset (for example, threaded, engaged with a groove, or wrapped). Furthermore,
Even if they are not preset, after the zirconia cured composition is cured, the cured body of the zirconia cured composition and the lead member, and the cured body of the zirconia cured composition and the zirconia heating element are physically set. It is also possible to use a method in which an uneven surface, such as a groove cut, is provided on the energizing lead member or the zirconia heat generating element so that the current-conducting lead member or the zirconia heating element is provided with grooves or the like.

The zirconia heat-generating structure of the present invention may be unfired, but it may also be fired, or it may be fired and then impregnated with a zirconia sol or zirconium compound solution that changes into zirconia upon firing. It fills the pores of the cured composition, makes the structure more dense, increases strength, and reduces electrical resistance to improve electrical conductivity.

The firing treatment is preferably performed at a temperature of 1200 to 1750°C, which is higher than the decomposition temperature of the binder component of the zirconia cured composition and lower than the heat resistance temperature of the current-carrying lead member.

Examples of the impregnating liquid include zirconia sol and/or a zirconium compound aqueous solution, which becomes zirconia upon firing. In a preferred embodiment of the present invention, the zirconia sol has a particle size of, for example, 70 mmμ.
It is a milky white colloidal liquid in which front and back zirconia are suspended in water. In addition, as the zirconium compound aqueous solution, for example, a zirconium salt aqueous solution, specifically zirconyl acetate, zirconyl nitrate, zirconyl acid chloride, zirconyl sulfate, zirconylammonium carbonate, etc. can be used, and zirconium salts such as tetrapropyl zirconate and tetrabutyl zirconate can be used. Hydrolyzed solutions of alkoxides can also be used. All of these are converted into zirconia by firing. This impregnating liquid can be sprayed onto the surface of the fired body or the fired body can be impregnated with the impregnating liquid.

Other impregnating liquid adjuvants can also be added in the present invention. For example, chlorides, sulfates, nitrates, etc. of magnesium, yttrium, calcium, samarium, cadmium, lanthanum, neodymium, etc. can be added as crystal stabilizers. The amount added is 0.5 to 30 parts by weight based on 100 parts by weight of zirconia in terms of ZrO ₂ of the impregnating liquid.

[Examples] The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 A zirconia heating element 1 containing 75% by weight of zirconia fibers and a rod made of molybdenum disilicide, which is a current-carrying lead member 3, were prepared using a zirconia curing composition 2 whose composition is described below in FIG. 1a. It was fixed as shown in FIG. Composition (parts by weight) Zirconia fiber 50 Zirconia powder 50 Zirconyl acetate aqueous solution (ZrO ₂ yield 20%) 55 Y ₂ O ₃ powder 4 The zirconia hardening composition was left for 4 hours until it self-hardened, and then heated at 110°C. After drying for 24 hours, it was calcined at 1400°C to develop strength to obtain a zirconia heat generating structure of the present invention.

Next, the obtained heat generating structure was set in an electric furnace, and one end of the molybdenum disilicide rod was led out of the furnace.
After preheating the conductor to 1500°C by clamping it, electricity was applied and used as a heating element. This heating element can generate heat up to 2,000 to 2,300°C when energized, and the bonding with the lead member is good, and the bond does not break when energized.

In addition, a heat generating structure equipped with a molybdenum disilicide conduction lead member that was dried at 110°C for 24 hours was heated to 800°C.
After calcination, it was set in a furnace and slowly preheated to 1500°C, then electricity was started and slowly heated to 2000°C.

According to this method, no SiO ₂ film is formed on the molybdenum disilicide bar in the part exposed outside the furnace during calcination.
Eliminates the need to remove the SiO ₂ film before clamping. In addition, FIGS. 1a and 1b showed almost the same bonding performance.

The zirconia cured composition used in this example was molded into a rod shape of 10 mm x 10 mm x 80 mm.
The electrical resistance at high temperature was investigated using a test piece fired at 1700℃ for 3 hours, and the result was 7.7Ω・cm at 1700℃.
It had a conductivity of .

Example 2 Grooves were cut on both ends 1 of a zirconia fiber heating element made by the paper-forming method, and a platinum wire 3 of 0.5 mmφ was wound around it as shown in Figure 2. A zirconia hardened composition 2 having the same composition as that used in Example 1 except that it contained 70 parts by weight of powder was applied to fill the grooves provided in the heating element, and the composition was heated at 1500°C for 2 hours. After baking for an hour, a zirconium acetate solution (ZrO ₂ yield 15%) was sprayed and left for 4 hours. Next, after drying at 110° C. for 24 hours, it was calcined at 1200° C., and one end of the platinum wire was attached to the outside of the furnace, and the platinum wire and the conducting wire were connected. After preheating to 1500°C, electricity was carefully started and gradually heated to 2000°C.

The zirconia cured composition used in this example was molded into a rod shape of 10 mm x 10 mm x 80 mm.
The electrical resistance at high temperature was investigated using a test piece fired at 1700℃ for 3 hours, and it was 6.2Ω・cm at 1700℃.
It had a conductivity of .

In addition, in this example, the heating element was heated to a temperature higher than the melting point of platinum, which is the lead member, but by increasing the area of the terminal part of the heating element, the temperature of the terminal part can be lowered. Therefore, it is possible to prevent the lead member from melting.

Example 3 A groove is cut on both ends 1 of a zirconia fiber heating element made by the paper-forming method, and after wrapping a platinum wire 3 around it as shown in Fig. 3, a sleeve 4 made of the same material as the main body of the heating element is covered. , zirconia fiber
A zirconia hardening composition 2 having the same composition as that used in Example 1 except that it contained 70 parts by weight and 30 parts by weight of zirconia powder was used to fill the space between the heating element body and the sleeve. The zirconium acetate aqueous solution (ZrO ₂
(yield: 7%) to obtain a zirconia heat generating structure of the present invention.

The zirconia cured composition used in this example was molded into a rod shape of 10 mm x 10 mm x 80 mm.
When we investigated the electrical resistance at high temperature using a test piece fired at 1700℃ for 3 hours, it was 8.0Ω・cm at 1700℃.
It had a conductivity of .

Example 4 Grooves and holes were machined in both ends 1 of a heating element made of a composite of zirconia fibers and zirconia powder containing 30 parts by weight of zirconia fibers, as shown in FIG. The same zirconia hardening composition 2 as used in Example 1 was used in the grooves and holes, except that the zirconia hardening composition 2 contained 85 parts by weight of zirconia powder and had a ZrO ₂ yield of 15% as an aqueous zirconium acetate solution. The composition was poured while being vibrated, and then the silicon carbide rod 3 that had been processed in advance was immediately inserted, and a portion of the surplus composition was used for coating the surface of the silicon carbide rod as shown in Figure 4c. , and allowed to stand for 4 hours. Thereafter, it was dried at 110°C for 24 hours and calcined at 800°C to obtain the zirconia heat generating structure of the present invention.

The zirconia cured composition used in this example was molded into a rod shape of 10 mm x 10 mm x 80 mm.
When we investigated the electrical resistance at high temperature using a test piece fired at 1700℃ for 3 hours, it was 5.5Ω・cm at 1700℃.
It had a conductivity of .

Example 5 In Example 2, the zirconia hardening composition described below was used to bond the platinum wire to the heating element body, and after construction, after drying at 40°C for 4 hours,
The mixture was further dried at 1500°C for 24 hours and calcined at 1500°C to obtain a zirconia heating element structure of the present invention. Composition (parts by weight) Zirconia fiber 30 Zirconia powder 70 Zirconyl acetate aqueous solution (ZrO ₂ yield 15%) 55 Y ₂ O ₃ powder 7 The zirconia cured composition used in this example was prepared into a 10 mm x 10 mm x 100 mm rod. Form into a shape,
When the electrical resistance at high temperature was investigated using a test piece fired at 1500°C for 2 hours, it was found to have a conductivity of 6Ω·cm at 1700°C.

Comparative Example 1 Composition (parts by weight) Zirconia powder 100 Zirconyl acid chloride aqueous solution (zirconia yield 20%)
50 Y ₂ O ₃ Powder 7 A zirconia heating element having the shape shown in FIGS. 1a and 1b and a lead member made of molybdenum disilicide were joined using the zirconia cured composition having the above-mentioned composition.

However, some cracks were observed in the cured product of the zirconia cured composition after drying, and
When it was calcined at ℃, cracks developed and the heating element body and molybdenum disilicide were separated on one side, making it impossible to use it as a heating structure.

Comparative Example 2 For joining the heating element shaped as in Example 3 and the platinum wire, 5 parts by weight of polyvinyl alcohol was further added to the zirconia curing composition used in Comparative Example 1 to strengthen adhesive strength and dry strength. A heat generating structure was formed using the cured composition.

After calcination, this heat-generating structure was used as a heat-generating element, but when it was kept at 2000°C for 1 hour three times, contact resistance occurred due to cracks in the cured product of the zirconia-based cured composition. The lead member made of the metal wire generated abnormal heat and the platinum wire was fused.

[Effects of the Invention] The following effects can be obtained by the present invention. That is, a substantial heating element containing zirconia fibers can be joined to a lead member using a zirconia cured composition containing zirconia fibers according to the method of the present invention, and furthermore, the cured product of the composition is conductive. Because of this, the area of contact between the heating element body and the current-carrying lead member can be expanded, and damage to the heating element body caused by local current flowing through the contact area can be prevented. This makes it possible to provide a heat generating structure for high temperatures that is even more practical.

Furthermore, if the pores of the cured composition are impregnated with a zirconia sol and/or an aqueous solution of a zirconium compound after the calcination treatment of the cured composition, the bond between the zirconia fibers or between the zirconia powder and the zirconia fibers becomes strong, and the electrical conductivity is improved. It can be further improved.

Furthermore, in the above embodiments, the heating element body of the zirconia heat generating structure of the present invention was explained as containing zirconia fibers.
The heating element main body used in the present invention is not limited to these, and conventionally used zirconia heating elements can also be used.

[Brief explanation of the drawing]

FIGS. 1a and b are diagrams for explaining the joint portion between the zirconia heating element and the lead member described in Example 1, and FIG. 2 is a diagram illustrating the joining portion between the zirconia heating element and the lead member described in Example 2. FIG. 3 is a diagram illustrating a joining portion between a zirconia heating element and a lead member described in Example 2, and FIGS. FIG. 3 is a diagram illustrating a joint portion between a quality heating element and a lead member. In the figure, 1... end of zirconia heating element, 2...
Zirconia hardened composition, 3...Lead member.

Claims (1)

[Scope of Claims] 1. A zirconia heating structure that generates heat when energized, which is composed of a zirconia heating element and a current-carrying lead member, wherein the joint portion of the zirconia heating element and the current-carrying lead member and its surroundings are: It is obtained from a zirconia hardening composition that exhibits self-hardening at room temperature by using zirconia fibers, zirconia powder, and a water-soluble zirconium salt in which the aqueous solution is acidic as a binder, and by using yttria or a water-insoluble yttrium compound as a hardening agent. A zirconia heat generating structure characterized in that it is coated and bonded with a cured material having good conductivity. 2. A zirconia heating structure that generates heat when energized, which is composed of a zirconia heating element and a current-carrying lead member, in which the joint portion of the zirconia heating element and the current-carrying lead member and its surroundings are made of zirconia fibers, zirconia powder, and an aqueous solution. It has good electrical conductivity obtained from a zirconia-based hardening composition that exhibits self-hardening properties at room temperature by using a water-soluble zirconium salt that is acidic as a binder and yttria or a water-insoluble yttrium compound as a hardening agent. A zirconia heat-generating structure, characterized in that the zirconia heat-generating structure is coated and bonded with a hardened body and is impregnated with a zirconia sol and/or a zirconium compound solution after firing treatment. 3. In a method for manufacturing a zirconia heating structure that generates heat when energized by joining a zirconia heating element and a current-carrying lead member, the joint portion of the zirconia heating element and the current-carrying lead member and its surroundings,
Shows good conductivity after firing with zirconia fibers and zirconia powder. Exhibits self-hardening at room temperature by using a water-soluble zirconium salt whose aqueous solution becomes acidic as a binder and using yttria or a water-insoluble yttrium compound as a hardening agent. A method for manufacturing a zirconia heat generating structure, which comprises coating and bonding using a zirconia cured composition. 4. In a method for manufacturing a zirconia heating structure that generates heat when energized by joining a zirconia heating element and a current-carrying lead member, the joint portion of the zirconia heating element and the current-carrying lead member and its surroundings,
Shows good conductivity after firing with zirconia fibers and zirconia powder. Exhibits self-hardening at room temperature by using a water-soluble zirconium salt whose aqueous solution becomes acidic as a binder and using yttria or a water-insoluble yttrium compound as a hardening agent. 1. A method for producing a zirconia heat-generating structure, which comprises coating and bonding using a zirconia cured composition, and impregnating it with a zirconia sol and/or a zirconia compound solution after firing.