JP2818113B2 - Firing jig - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a firing jig used for firing functional ceramics such as ceramic capacitors.

[0002]

2. Description of the Related Art Functional ceramics represented by ceramic capacitors and the like are manufactured by firing barium titanate-based, strontium titanate-based, lead zirconate-based, and ferrite-based ceramics at a high temperature. When firing at a high temperature, a dense or porous refractory such as alumina, mullite, zirconia, or magnesia is used as a firing jig. The material of these firing jigs is determined in consideration of the price, life, reactivity at high temperature with the functional ceramic to be processed, and the like. It is extremely important to select a material that does not react with the functional ceramic to be fired at a high temperature. That is, when the reactivity between the two is high, the properties of the functional ceramic product are significantly impaired and the commercial value is lost.

For this reason, there is a case where a zirconia firing jig must be selected from the above materials. But,
Zirconia-based firing jigs are (1) easily deformed when used at high temperatures, (2) have poor thermal distribution due to low thermal conductivity, and (3) have a large thermal expansion coefficient and are heat resistant. There are problems with durability and cost, such as (4) being expensive, because cracks are likely to occur due to poor impact resistance. In order to solve this problem, zirconia is provided as a coating layer on the surface of a firing jig of alumina or alumina-silica which is superior to zirconia in physical properties other than the reactivity with the material to be fired, Attempts have been made to provide a balance in terms of performance, durability and price.

[0004] When zirconia is provided as a coating layer on the surface of an alumina or alumina-silica firing jig, meta-stabilized zirconia or stabilized zirconia is used so that the coating layer is not cracked or peeled off. Is used. Magnesia, calcia and yttria are generally known as zirconia stabilizers. As a coating layer, magnesia-stabilized zirconia has poor thermal stability,
In addition, calcia-stabilized zirconia is highly reactive with the alumina or alumina-silica material used as the base material, and migrates into the base material during use, causing peeling, cracking, and the like, resulting in a very short life. Because of the problem of
Generally, yttria-stabilized zirconia is selected. However, depending on the type of the functional ceramics, there is a conflicting problem that it reacts very easily with yttria-stabilized zirconia but may not react with calcia-stabilized zirconia.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a calcining-stabilized zirconia-coated alumina-based and alumina-silica-based sintering jig. An object of the present invention is to provide a firing jig which is excellent and can be used for a long period of time and which does not react with a fired object.

[0006]

The object of the present invention is to provide a firing jig in which a calcia-stabilized zirconia-based coating layer is provided on the surface of an alumina-based substrate. % Or more by adding and containing magnesia.

What is important in the present invention is that MgO is added to calcia-stabilized zirconia as a coating layer to impart the characteristics of the firing jig.

The alumina content of the alumina base material of the present invention is preferably at least 75% by weight, more preferably at least 85% by weight, most preferably at least 95% by weight. The remaining component is preferably mainly composed of silica, but may contain components such as zirconia, calcia, and magnesia as long as the object of the present invention is not hindered. As is well known, silica is preferably contained as mullite because it has the effect of improving the thermal shock resistance of an alumina-based substrate, but silica is also preferred as crystalline or silica-like glass or silica-containing glass or particles. Can also be present.
If the content of alumina is too low, not only the strength and heat resistance of the base material are lowered, but also the reaction with the zirconia layer as the coating layer is not preferred because the durability of the coating layer is poor.

The alumina-based substrate of the present invention may be either a dense or porous refractory, but the porosity of the alumina-based substrate is 10 to 10 from the viewpoint of the durability of the substrate and the adhesion of the coating layer.
80% is preferable, and 40-80% is more preferable. Further, a porous body having continuous vent holes is desirable. If the porosity is too low, the thermal shock resistance of the base material is reduced and the life as a firing jig is shortened, and the adhesiveness between the base material and the coating layer is reduced and the substrate is easily peeled off. Life is shortened.
If the porosity is too high, the strength of the base material decreases, which is not preferable as a firing jig. In addition, when the porous body is a sealed porous material, the thermal conductivity is reduced, and the temperature tends to be non-uniform.

The calcia-stabilized zirconia used in the present invention must be inactive in order to ensure non-reactivity with the material to be fired. The so-called electrofused zirconia obtained by pulverizing the dried product is preferable. On the other hand, it is necessary that the zirconia particles have a certain degree of activity from the viewpoint of adhesion to the alumina base material, and the average particle size of the zirconia particles is 1 to 10
0 μm is preferable, and it is more preferable to use zirconia particles of 3 to 50 μm. If the average particle size is too small, the zirconia layer will undergo heat shrinkage in the later-described baking step, and cracks and peeling will easily occur. If the average particle size is too large, the zirconia layer does not sufficiently adhere to the alumina base material even after the baking step described later, and thus the zirconia layer is liable to peel off and fall off.

The calcia-stabilized zirconia used in the present invention preferably has a degree of stabilization of 15% or more.
Here, the degree of stabilization is obtained by analyzing zirconia by a powder X-ray diffraction method and calculating from the diffraction intensity obtained by integrating peaks of the diffraction pattern by the following equation.

(Equation 1) M (-111): Diffraction intensity of (-111) plane of monoclinic zirconia M (111): Diffraction intensity of (111) plane of monoclinic zirconia C (111): Diffraction intensity of (111) plane of cubic zirconia Diffraction intensity T (111): Diffraction intensity of (111) plane of tetragonal zirconia If the degree of stabilization is less than 15%, a phase generated at 900 to 1200 ° C. of monoclinic zirconia (unstabilized zirconia), as is well known. There is a problem that peeling and cracking occur in the coating layer due to thermal expansion and contraction accompanying the transformation.

The added amount of magnesia used in the present invention may be 0.5% by weight or more, and the upper limit of the added amount can be arbitrarily set depending on the type of the material to be fired. However, in the coating step described below, it is necessary to temporarily disperse a mixture of zirconia powder and magnesia powder in water. However, as is well known, magnesia causes a hydration reaction and significantly impairs the dispersibility in water. % By weight or less is preferred.

The source of magnesia used in the present invention is magnesium oxide alone or magnesium carbonate,
Compounds such as magnesium chloride, magnesium hydroxide, and magnesium fluoride, or mixtures thereof are used.

The total thickness of the coating layer in the present invention is 40 to 7
00 μm is preferable, and 100 to 400 μm is more preferable. If the thickness of the coating layer is too small, the effect of suppressing the reaction between the object to be fired and the alumina base material is small, while if the thickness of the coating layer is too thick, cracking or peeling occurs due to heating and cooling operations, and the firing jig is used. Life tends to be shorter.

An example of the method for manufacturing the firing jig of the present invention is as follows. Extrusion molding, injection molding, press molding, and casting molding are performed by blending a ceramic raw material mainly composed of alumina with an average particle diameter of 0.1 μm to 1 mm as required and adding a binder as necessary. And the like. In order to obtain a base material having a porosity of 30% or more, it is advisable to add an organic pore-forming material and shape it.

After shaping, if necessary, drying is performed, followed by firing at 1200 to 1700 ° C. using an electric furnace, a gas furnace or the like. When a pore-forming material is added, 2
It is desirable to perform so-called degreasing at 00 to 600 ° C.

The calcined stabilized zirconia and magnesia mixed powder is subsequently applied to the surface of the fired body. The calcia-stabilized zirconia powder and magnesia powder are sufficiently mixed with water in advance by a known method such as a stirrer or a ball mill,
Disperse to form a coating slurry. When using other than magnesia alone as a magnesia supply source, mix it in the same manner in advance before preparing the coating slurry.
After calcining at 00 to 1200 ° C. to remove the carbonic acid group, hydroxyl group, chlorine group and the like by thermal decomposition, it is preferable to redisperse in water to obtain a slurry for coating.

When preparing the slurry, a water-soluble binder such as polyvinyl alcohol, carboxymethylcellulose, polyethylene glycol and methylcellulose may be added as needed. As a method of applying the water-soluble slurry, a coating layer is obtained on the surface of the alumina base material by using a known method such as a spray method, a flow coater method, a brush coating method, and a dipping method.

The alumina substrate coated with the coating layer is then baked at 800 to 1500 ° C. using an electric furnace or a gas furnace to obtain a firing jig of the present invention. The above manufacturing method is an example, and any method may be used as long as the structure of the firing jig of the present invention and the characteristics of the material are satisfied.

[0020]

According to the firing jig of the present invention, although the calcia-stabilized zirconia is coated on the surface of the alumina base material, the coating layer contains at least 0.5% of magnesia. Therefore, even when used for a long time, the coating layer can be used stably without cracking or peeling. Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 Commercially Sinterable Alumina Powder (Average Particle Diameter 0.5 μm, Alumina Purity 99.9%) 5
Acrylic beads 50 with 0 parts by weight and an average particle diameter of 200 μm
10% by weight of a 5% aqueous solution of PVA was added as a binder to parts by weight of the mixture, and the mixture was granulated, dried and sized, and then formed into a plate by a press forming machine. Then use an electric furnace at 400 ° C
After degreasing for 5 hours, baking at 1550 ° C for 3 hours
A flat alumina base material of 00 × 100 × 5 mm was prepared. The porosity of the obtained alumina base material was 75%.

A slurry obtained by adding and mixing magnesium hydroxide to calcia-stabilized fused zirconia having a degree of stabilization of 85% and an average particle diameter of 15 μm so as to have each composition shown in Table 1 in magnesia conversion at 800 ° C. The powder obtained by calcining was again dispersed and mixed in water to prepare a coating slurry.
The obtained slurry was coated on the above-mentioned alumina substrate so as to have a thickness of 200 μm by a spray method. Next, baking was performed at 1400 ° C. for 5 hours using an electric furnace to prepare a firing jig.

The obtained firing jig was placed in an electric furnace at 300 ° C. /
The temperature is raised at hr and maintained at 1400 ° C for 6 hours, then 300 ° C /
A heating / cooling test was performed up to 10 times in which the operation of cooling at hr was performed as one cycle, and the presence or absence of abnormalities such as cracks or peeling in the zirconia coating layer was visually determined. As an evaluation criterion, those in which an abnormality occurred in 1 to 5 times were evaluated as × 10.
A sample which did not cause any abnormality at the time was marked as ○.

[Table 1] * 1: No. As for 4,5, the dispersibility of magnesia was remarkably impaired and coating by the spray method was difficult, so the brush coating method was used.

Claims (1)

(57) [Claims] 1. A firing jig in which a calcia-stabilized zirconia coating layer is provided on the surface of an alumina base material, wherein at least 0.5% by weight of magnesia is added to calcia-stabilized zirconia as a coating layer. A firing jig characterized in that: