JPH0329287A - Zirconia heating structure - Google Patents

Abstract

PURPOSE:To use a lead member which has electric conductivity at the ordinary temperature by winding a fireproofing sheet made up of flexible specific material around an end portion and touchingly junctioning a lead member to the surface of the sheet. CONSTITUTION:A fireproofing sheet 5 which is flexible at an ordinary temperature and formed by addingly mixing flexible binder at 20-50 parts by weight to aggregates at 100 parts by weight made up of zirconia fiber at 5-80 parts by weight and zirconia powder at 20-95 parts by weight to which zirconia stabilizer is added is wound around the end portion of a zirconia heating element 1. When a lead member for current flow is touchingly junctioned to the surface of a sheet 5, the member 6 is never overheated, free from occurrence of a crack, etc., and damage caused by an arc due to a local current flow so that a conventional lead member through which a current flows at an ordinary temperature can be used.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a zirconia heating structure that can be used up to high temperatures in an oxidizing atmosphere and generates heat when energized. The present invention relates to a zirconia heat generating structure that is well bonded to a current-carrying lead member that has sufficiently low electrical resistance even near room temperature.

[Conventional technology]

Zirconia heating elements are known as heating elements that can be used up to high temperatures in oxidizing atmospheres, such as zirconium oxide (
Zirconia heating elements, which can be obtained by adding small amounts of other oxides to Zr 0 2 ) and sintering at high temperatures, can be heated to high temperatures up to approximately 2000°C because the melting point of zirconium oxide is 2690°C. can be obtained.

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 eliminate these drawbacks, the applicant has previously applied for a zirconia fire-resistant heating element that contains zirconia fibers and generates heat when energized (Japanese Patent Application No. 63-26329).
issue).

Conventionally, in order to form a zirconia heating structure consisting of a heating element main body and an energizing lead member from these zirconia heating elements, a pore is made in the heating element main body, and a platinum metal is injected into the zirconia heating element as an energizing lead member. The methods used were to thread wires through, entangle and fix them, or to apply platinum paste and to connect them to current-carrying lead members over as wide a diffusion area as possible.

[Problem to be solved by the invention]

However, with these methods, the former has the problem of loosening during use, and the latter has major restrictions on the design of the furnace. Furthermore, damage may occur due to so-called arcing phenomenon in which current locally flows through the contact portion between the current-carrying lead member and the heating element body.

Another option is to use caster pulls to fix the heating element body and the energizing lead member, but even if you use conventional castables to fix both, it will still be able to follow the thermal expansion and contraction caused by energizing, which may cause cracks to occur. In many cases, the current-carrying lead member could not be used as a heat generating 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-mentioned circumstances, and its purpose is to provide a zirconia heating element and a current-carrying lead member that has sufficient current-carrying property even at room temperature to conduct electricity to the zirconia heating element to prevent the above-mentioned arc generation phenomenon. An object of the present invention is to provide a practical zirconia heat generating structure that is well bonded to solve the problem.

[Means to solve the problem]

Thus, the present invention provides for 100 parts by weight of aggregate obtained from 5 to 80 parts by weight of zirconia fibers and 20 to 95 parts by weight of zirconia powder to which a zirconia stabilizer has been added to the end of a zirconia heating element. Flexible binder 20-50
A zirconia heat generating structure is provided by wrapping a fireproof sheet which is flexible at room temperature and formed by adding and blending parts by weight, and contacting and bonding a conductive lead member to the surface of this sheet.

The present invention also provides a zirconia heat generating structure in which the surface of the lead member is further covered with a fireproof sheet to further enhance the thermal protection of the lead member.

The present invention will be explained in detail below.

First, regarding the zirconia heating element used in the zirconia heating structure of the present invention, this heating element is made by hot-pressing or cold-pressing a material containing an appropriate mixture of zirconia powder, additives, stabilizers, zirconia fibers, etc. After pressing, a fired molded body or a molded body made by slip-casting a similar material and fired, or a molded body made of zirconia fiber alone or a composite of zirconia fiber and zirconia powder, and molded by paper making, casting, or extrusion. It is possible to use a molded body that has been burnt. However, among these zirconia heating elements, it is more desirable for practical use to include zirconia fibers. In addition, the zirconia fiber contains M g O SC a O − which acts as a zirconia stabilizer.
It may also contain oxides such as Y203 and Gd203.

Next, the fireproof sheet used in the present invention is made of aggregate 1 made from 5 to 80 parts by weight of zirconia fibers and 20 to 95 parts by weight of zirconia powder to which a zirconia stabilizer has been added.
It has a formulation in which 20 to 50 parts by weight of a flexible binder is added to 00 parts by weight.

The zirconia fiber consists essentially of zirconium oxide represented by the chemical formula ZrO2, and may also contain zirconium compounds such as zirconium carbonate and zirconium hydroxide, or Y203, M
It contains a stabilizer such as gO and CaO, and consists of at least one of these. Zirconia fibers that can be used in the present invention include, for example, pure zirconia fibers, lime-stabilized zirconia fibers, magnesia-doped zirconia fibers, yttria-stabilized zirconia fibers, ceria-stabilized zirconia fibers, gadoria-stabilized zirconia fibers, and mixtures thereof. Preferred is yttria stabilized zirconia phino.

This zirconia fiber can be manufactured by various methods. For example, by using an aqueous solution of a dicornium compound as a starting material (spinning solution) and turning it into a fiber to form a fiber precursor (bricursor), the fiber precursor is It can be manufactured by firing, and can be appropriately selected depending on the use, shape, etc. of the zirconia refractory.

The fiber length and fiber diameter of the zirconia fiber used in this invention are, for example, 0, 1 to 50, respectively.
Open and 0. It is 1 to 20 μm.

The amount of zirconia fiber added is 5 to 80 parts by weight based on 20 to 95 parts by weight of zirconia powder, and 10 to 80 parts by weight.
-50 parts by weight is more preferred. If the amount of this fiber is less than 5 parts by weight, the reinforcing effect will be small, and if it exceeds 80 parts by weight, it will be difficult to form into a fireproof sheet.

Zirconia powder consists essentially of zirconium oxide, and may also contain zirconium carbonate or zirconium carbonate depending on the purpose.
It consists of a zirconium compound such as zirconium hydroxide or a stabilizer such as Y 2 0 3, MgO, CaO, etc., and is made of at least one of these.

This powder can be obtained, for example, by a method for producing fine powder by spray drying. The particle size of this zirconia powder is not particularly limited in the present invention, and can be appropriately selected depending on the shape and size of the heating element according to the present invention.
For example, the particle size is 0.1 to 1000 μm, preferably 0.
．． It can be set to 5 to 500 μm.

The zirconia stabilizer is a crystal stabilizer for zirconia or a precursor that is converted into the crystal stabilizer by heating. That is, the crystal stabilizer is a metal oxide that exhibits a crystal stabilizing effect on zirconia and/or a metal salt that forms a metal oxide upon heating. Examples of such stabilizers include oxides, carbonates, basic carbonates, acetates, oxalates, nitrates, chlorides of magnesium, yttrium, calcium, gadolinium, cerium, samarium, cadmium, lanthanum, neodymium, etc. , sulfates, etc., and powders of oxides, chlorides, carbonates, and basic carbonates of magnesium, calcium, and yttrium are preferable from an economic standpoint.

The particle size of the metal oxide and metal salt stabilizers is 0.
0 1 it m~1 mm, preferably 0.1 μm~
It is 0.31III1. If it is less than 0.01 μm, migration phenomenon may occur during drying, and 1
This is because if it exceeds +w, the function as a stabilizer will decrease and the strength will deteriorate.

The amount of the crystal stabilizer added is 0.5 to 70 parts by weight, preferably 1 to 30 parts by weight, in terms of oxide, per 100 parts by weight of zirconia. If the amount is less than 0.5 parts by weight, the crystallization and stabilizing effect of the zirconia molded body will be small, and the strength will not be developed.On the other hand, if it exceeds 70 parts by weight, no further effect will be obtained, and the steam If the pressure is high, the atmosphere of the electric furnace may be contaminated with lri, which impairs the properties of the zirconia refractory heating element.

The flexible binder is composed of an emulsion of a suitable synthetic resin such as vinyl acetate resin or acrylic acid ester, and one or more types of plasticizers such as ethylene glycol, glycerin, and dibutylucrein.

The amount of plasticizer added is preferably 5 to 25 parts by weight per 100 parts by weight of the synthetic resin emulsion.

The blending amount of such a flexible binder is 100% of the aggregate
It is preferably 20 to 50 parts by weight. If this amount is less than 20 parts by weight, the fireproof sheet will not have sufficient flexibility, and cracks will easily occur when the fireproof sheet is laminated. Moreover, if it exceeds 50 parts by weight, there is a drawback that the structure of the refractory heating element becomes brittle after the flexible binder disappears by heating.

A reinforcing binder can be added to the fireproof sheet if necessary. The reinforcing binder is preferably a sol or an aqueous solution that becomes zirconia or a similar compound thereof upon firing. Examples of reinforcing binders include aqueous solutions of water-soluble salts such as zirconyl acetate, zirconium acetate, yttrium acetate, zirconium chloride, yttrium chloride;
Examples include zirconia sol, which is used in a blending range of about 0 to 30 parts by weight.

By using this reinforcing binder, the fireproof sheet becomes self-hardening and has high strength, so that the fireproof sheet can be easily handled during drying and baking.

A fireproof sheet having flexibility at room temperature can be obtained by forming a raw material for a fireproof sheet having the above-mentioned composition into a sheet by rolling it with a roll or extruding it by extrusion molding. The thickness of this fireproof sheet is 0. 1~lm
It is preferable to have a diameter of about m.

In the present invention, the fireproof sheet is fixed to the heating element by pressing it down and fixing it to the lower layer, or by using mortar as described below.
It may also be fixed by applying a zirconia hardening composition.

The zirconia hardening composition is a zirconia hardening composition that exhibits self-hardening properties at room temperature by using a water-soluble zirconium salt whose aqueous solution is acidic as a binder and using yttria or a water-insoluble yttrium compound as a hardening agent. Can be mentioned.

Examples of water-soluble zirconium salts whose aqueous solutions are acidic to be used in this zirconia-based hardening composition include zirconium acetate, zirconyl acetate, zirconium acid chloride, zirconium nitrate, and zirconium sulfate. Considering the fact that toxic gas is generated due to decomposition of the binder component during firing, it is preferable to use zirconium acetate or zirconyl acetate.

Note that the concentration of the aqueous solution must 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 zirconia cured composition is yttria or a water-insoluble yttrium compound. Yttria needs to have a purity of 90% by weight or more. Note that the particle size of yttria is preferably IIIlm or less. If the purity of yttria is less than 90% by weight or if the particle size exceeds lnuw, it is not preferable because yttria becomes difficult to exert its effect as a hardening agent.

Examples of water-insoluble yttrium compounds include yttrium carbonate and yttrium hydroxide.

Usually, these water-insoluble yttrium compounds are 0.1 m
It is produced and sold in the form of a fine powder of n+ or less, so there is no need to particularly consider the particle size, but it is necessary that the purity of the yttria formed by heating is 90% by weight or more.

The ratio of addition of yttria or a water-insoluble yttria compound to the water-soluble zirconium salt is to as yttria formed) 0.5
A range of 5 to 5 is preferable, and by adjusting the ratio within this range, the curing time can be adjusted to a range of 10 minutes to 10 hours. If the amount of yttria added is less than 0.5, the curing time will be too long, which is not practical, and if the amount added is more than 5, the curing time will be too fast, resulting in hardening during kneading. This is not desirable because it may occur.

The zirconia cured composition used in the present invention can be prepared by appropriately adding and mixing refractory raw material powder, organic substances, fiber raw materials, etc. to the composition consisting of the above-mentioned components.

In addition to applying the cured composition to the wrapped end of the heating element as described above, it may also be applied to the entire surface of the fireproof sheet and then bonded to the heating element.

Thereafter, a conductive lead member is wrapped around the surface of the fireproof sheet, or mortar is further applied to the surface of the lead member, and a fireproof sheet is further wound around the surface of the lead member to obtain a bonded body.

A zirconia refractory heating element according to the present invention can be obtained by drying and then firing the joined body constructed in this manner. The firing temperature can be, for example, 800°C or higher, preferably 1400°C or higher, and more preferably 1500°C or higher.
The temperature is 2400°C.

Below this lower temperature limit, the sintering strength is weak. Further, the firing can also be performed by induction heating or electrically heating the bonded body after the drying process.

Next, the structure of the present invention will be explained in more detail with reference to FIGS. 1 to 4.

In FIG. 1, an end portion 2 of a round rod-shaped heating element 1 having a constant length has a larger diameter than a central portion 3, and a slope portion 4 is formed between the end portion 2 and the central portion 3.
is formed. A fireproof sheet 5 according to the present invention is wrapped around the end portion 2, and a lead wire 6 is also wound around the surrounding surface.

In FIG. 2, a fireproof sheet 5 is further wrapped around the lead wire 6.

In FIG. 3, a round heating element 7 with a uniform diameter up to the end is further provided with a separate small heating element 8 of the same length around the end.
A fireproof sheet 5 is wound around the end of the separate heating element 8, and a lead wire 6 is wound around the outside thereof. This heating element 7
A through hole 9 is provided in the center. Figure 4 has a slope part 4 similar to Figure 12, but also has a through hole 10 in the center as in Figure 3, and a fireproof sheet 5 is wrapped around the end to lead. A wire 6 is wound around it.

〔Example〕

Example 1 50 parts by weight of yttria-stabilized zirconia fiber (Y7Z Fihar manufactured by Shirorenga Co., Ltd.), yttria-stabilized zirconia powder (Y203 7%, Z r 0 2 9
2%) 50 parts by weight of polyvinyl acetate emulsion as a flexible binder and a plasticizer (dibutylphthalein).
33 parts by weight were added and kneaded thoroughly, transferred onto a flat plate and rolled using a roller to give a thickness of 0.5 mm.
J flexible fireproof sheet was produced.

This fireproof sheet was wrapped around a heating element previously fired at 1800°C and pressed and crimped, and then a platinum wire serving as a reed member was wrapped around it and dried in this state at 100°C for 10 hours. Thereafter, it was fired at 1500°C to obtain a heat generating structure.

Next, the obtained heat generating structure was set in an electric furnace, one end of the molybdenum disilicide strip was led out of the furnace, the conducting wire was clamped, and after preheating to 1500°C, electricity was applied to use it as a heat generating element. This heating element can generate heat up to 2,000 to 2,300° C. when energized, and it is well bonded to the lead member, and does not break when energized.

Example 2 28 parts by weight of polyvinyl acetate emulsion was prepared by blending 20 parts by weight of yttria-stabilized zirconia fiber, 65 parts by weight of yttria-stabilized zirconia powder, and 15 parts by weight of ceria powder, and adding 18% of a plasticizer (ethylene glycol) thereto. and zirconyl acetate water'l'ii lf
8 parts by weight of k (20% concentration as Z r 0 2) were added and kneaded to produce a flexible fireproof sheet with a thickness of 1 mm. This sheet is attached to a zirconia heating element fired at 1700°C using a self-hardening composition containing zirconia fibers, that is, the above-mentioned zirconia hardening composition, and a platinum wire serving as a lead member is wound on top of it. I attached the sheet. After drying this joined body 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 the temperature was gradually heated to 2000°C. The lead part has a good connection and there was no melting trouble after 50 repeated tests.

Comparative Example 4 See the sweetfish bodies of 1st to 4U!・I tried to preheat the platinum wire to 1500°C in the afternoon and then heat it to 2000°C without using it, but all the lead wires melted just before reaching 2000°C.

〔effect〕

Thus, according to the present invention, by joining the zirconia pongee main body and the current-carrying lead member using a fireproof sheet, the so-called reduction in arc generation, which conventionally occurs during use, does not occur and the contact area due to this is reduced. It is possible to obtain a zirconia heating element that can be used satisfactorily without causing damage.

[Brief explanation of drawings]

Figures 1 to 4 are explanatory diagrams of each embodiment of the zirconia heating structure according to the present invention. 1... Zirconia heating element, 5... Fireproof sheet, 6
...Lead member for energizing.

Claims (1)

[Claims] 1. In a zirconia heating structure that generates heat when energized and includes a zirconia heating element and a lead member for conducting current, a zirconia fiber 5 is attached to the end of the zirconia heating element.
-80 parts by weight and 20 to 50 parts by weight of a flexible binder to 100 parts by weight of aggregate consisting of 20 to 95 parts by weight of zirconia powder to which a zirconia stabilizer has been added. 1. A zirconia heat-generating structure comprising a flexible fireproof sheet wrapped around the sheet and the current-carrying lead member contact-bonded to the surface of the sheet. 2. A zirconia heat generating structure characterized in that the surface of the lead member is further covered with a fireproof sheet.