JP2844100B2 - Zirconia refractory and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zirconia refractory having excellent fire resistance, corrosion resistance and spalling resistance under severe use conditions, and a method for producing the same.

[Conventional technology]

Alumina (Al ₂ O ₃ ), magnesia (MgO), zirconia (ZrO ₂ ), etc. are generally known as refractories that can be used in a high temperature range exceeding 1800 ° C. Among them, zirconia has a temperature of 2700 ° C. It has a very high melting point and excellent stability at high temperatures (low vapor pressure, corrosion resistance, etc.), so it is widely used as an ultra-high temperature refractory.

By the way, pure zirconia (ZrO ₂ ) has three kinds of different crystal structures depending on the temperature stage, and when this crystal system undergoes a reversible transition, it undergoes a large volume change. There is a disadvantage that it is easily affected. As a measure to improve these, one or more kinds of alkaline earth metals such as calcium and magnesium, rare earth elements such as lanthanum and cerium or yttrium are added in the form of oxides, and part or all of the crystal structure is stabilized to cubic. Various methods have been known, and various proposals have conventionally been made.

For example, Japanese Patent Publication No. 56-4507 discloses calcium oxide (CaO) or magnesium oxide (MgO).
Japanese Patent No. 5257 discloses yttria (Y ₂ O ₃ ) and JP-A-59-15.
No. 2266 discloses a zirconia refractory having improved spalling resistance by adding cesium oxide (CeO ₂ ), respectively, or a method for producing the same.

[Problems to be solved by the invention]

Among the above-mentioned various stabilizers, calcium oxide, magnesium oxide, etc. have the advantage that the material price is inexpensive, but the solid solution easily occurs due to the influence of unavoidable impurities such as silica and alumina or the sintering aid, and thus it is sufficient. The effect of improving spalling resistance cannot be expected. On the other hand, the addition of yttria has a significant effect on the stabilization of zirconia and has the property of greatly contributing to the improvement of fire resistance, corrosion resistance and spalling resistance.However, since the material price is extremely high, it is widely used in various industrial furnaces. There is a problem that cannot be done.

The present invention has been made to solve the above problems, the purpose is to achieve high fire resistance by laminating and integrating a zirconia composition containing yttria and a zirconia composition containing calcium oxide as a stabilizer, It is an object of the present invention to provide an inexpensive general-purpose zirconia refractory having corrosion resistance and spalling resistance and a method for producing the same.

[Means for solving the problem]

The zirconia refractory according to the present invention for achieving the above object comprises a partially stabilized or fully stabilized zirconia (ZrO ₂ ) material layer containing yttria (Y ₂ O ₃ ) or less, referred to as “YZ layer”.
That. ) And calcium oxide (CaO) and partially or fully stabilized zirconia layer (hereinafter referred to as “CZ layer”)
That. ) Has a two-layer structure in which the layers are integrated.

The partial stabilization of the YZ layer and the CZ layer refers to a crystal composition in which cubic zirconia is at least 70% or more, and the complete stabilization refers to zirconia having a 100% cubic structure. Therefore, in the present invention, it is necessary to obtain a composition having a stabilization ratio of 70% or more, and if the stabilization ratio is less than 70%, a high spalling resistance cannot be secured.

The laminating interface between the YZ layer and the CZ layer constituting the two-layer structure has a structure in which the layers are firmly bonded and integrated.

The method for producing the above zirconia refractory according to the present invention is a partially stabilized or fully stabilized zirconia (ZrO ₂ ) composition containing yttria (Y ₂ O ₃ ) (hereinafter referred to as “YZ composition”). ) And calcium oxide (CaO)
Zirconia (ZrO ₂ ) -based composition (hereinafter, referred to as “CZ composition”), which is partially or completely stabilized, is integrally molded so as to be laminated in a predetermined layer thickness and shape.
It comprises a process characterized by sintering at a temperature of 00 ° C. or higher.

The addition amount of yttria in the YZ composition is 4 to 10 mol%
When the amount is less than 4 mol%, the stabilization degree is low and the effect of improving the fire resistance, corrosion resistance and spalling resistance is not exhibited, and the addition exceeding 10 mol% is no longer effective. Improvement is not observed. It is desirable that the added amount of calcium oxide in the CZ composition be in the range of 5 to 15 mol%. If the content is less than 5 mol%, zirconia will not be sufficiently stabilized, and the addition exceeding 15 mol% is unnecessary.

For lamination molding of the YZ composition and the CZ composition, for example, one of the composition particles is placed in a non-adsorptive mold such as a mold, and after vibrating or tapping, the other layer is filled with the other composition particles. Then, one of the compositions is poured into a water absorbing mold such as gypsum in a slurry state by a uniaxial press or a cold isostatic press (CIP), and then another composition slurry is poured after semi-drying. This can be done by a completely drying method. At this time, by changing the shape of the mold used and the filling amount of each composition, it is formed into a predetermined layer thickness and shape.

The integrally molded body is heated to 1500 ° C or higher by a conventional method, preferably 16 ° C.
The zirconia refractory of the present invention is obtained by sintering in the temperature range of 00 to 1800 ° C.

(Operation)

The zirconia refractory according to the present invention has a two-layer structure in which a YZ layer stabilized with an yttria component and a CZ layer stabilized with a calcium oxide component are laminated and integrated, which is excellent in fire resistance, corrosion resistance and spalling resistance. Therefore, the zirconia inherently improves refractory properties and has a laminated structure with an inexpensive CZ layer, so that a refractory having the same performance as that of the YZ plain type can be provided at low cost. Therefore, for example, when constructing a high-temperature furnace, by arranging the YZ layer so as to be located in the furnace surface exposed to severe conditions, a very durable furnace wall is formed at a relatively low cost. .

Further, according to the method for producing a zirconia refractory according to the present invention, since the main components of the YZ composition and the CZ composition are both zirconia, they are interdispersed at the lamination interface, and a strong sintered state is always obtained. . Therefore, phenomena such as exfoliation and stress destruction which are observed in a laminate of different substances in a practical process do not occur at all, and a stable use state for a long period of time is realized.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

(1) Production of refractories A zirconia (ZrO ₂ ) clinker (YZ composition) having a composition containing 5.1 mol% of yttria (Y ₂ O ₃ ) and a stabilization rate of 90%
A zirconia (ZrO ₂ ) clinker (CZ composition) containing 8.3 mol% of calcium oxide (CaO) and a stability of 84% was used as a raw material. Each of the YZ composition and the CZ composition was coarse (grain size 1-2 mm) and medium (grain size 250 μm-1 m).
m), as fine particles (particle size 250 μm or less) at a weight ratio of 5: 1: 4, and a 40% aqueous solution of polyvinyl alcohol 5% / kg
Was added as a binder and kneaded well.

The kneaded YZ composition and CZ composition were sequentially filled into a mold so as to have a predetermined layer thickness, uniaxially pressed at a pressure of 200 kgf / cm ² , and dried at a temperature of 60 ° C. for 48 hours. Then
The obtained compact was transferred to an electric furnace and sintered at a temperature of 1700 ° C. for 1 hour.

In this way, the YZ layer is 230 mm long, 114 mm wide and 65 mm thick.
An integrated two-layer brick with 5 mm and 60 mm CZ was fabricated.

For comparison, only the YZ composition (Comparative Example 1) and the CZ composition (Comparative Example 2) used as the raw materials in the examples were used to produce regular bricks in the same manner as in the examples.

(2) Performance Evaluation Each of the normal bricks obtained above was set in a small high-temperature gas furnace using liquid propane gas (LPG) and oxygen as fuel sources. At this time, the regular bricks of the examples were mounted such that the YZ layer was on the high temperature side in the furnace.

The furnace is fired and heated in an oxidizing atmosphere with a burn rate of 110% for 200%.
Fire extinguishing after heating to 0 ° C (heating rate 800 ° C / hr), approx. 30
A heat cycle test was performed under the condition that the furnace was cooled for 1 minute and the temperature was raised again at 1200 ° C.

Among the properties, the porosity is measured by the Archimedes method (medium: distilled water), and the corrosion test is performed by injecting an aqueous sodium carbonate solution into a furnace at 1800 ° C and bringing it into contact with the brick surface (YZ layer in the example). The state of the erosion was determined by X-ray diffraction and appearance (no reaction: good, reaction: no). Table 1 compares these results.

From the results shown in Table 1, the bricks of the Examples were excellent in that no defective portions such as erosion and cracks were observed after 10 heat cycles as in Comparative Example 1 even though the yttria-containing layer was 5 mm. It was found to have fire resistance, corrosion resistance and spalling resistance. On the other hand, in Comparative Example 2, 2
Many cracks occur on the surface at the time of the heat cycle,
In one part, a defective part was observed.

〔The invention's effect〕

As described above, according to the present invention, by forming a two-layer structure by laminating and integrating a yttria-containing zirconia layer and a calcium oxide-containing zirconia layer, a zirconia refractory which is inexpensive and has excellent fire resistance, corrosion resistance and spalling resistance is obtained. Things can be provided and manufactured.

Therefore, versatility is expected as a lining material for various high-temperature heating furnaces and melting furnaces.

Claims (2)

(57) [Claims] 1. A yttria (Y ₂ O ₃₎ partially or fully stabilized zirconia (ZrO ₂₎ including the quality layer part containing calcium oxide (CaO) or fully stabilized zirconia (ZrO ₂₎ Zirconia refractory consisting of a two-layer structure in which porous layers are laminated and integrated. 2. A yttria (Y ₂ O ₃₎ parts including or fully stabilized zirconia (ZrO ₂₎ Quality composition and moieties containing calcium oxide (CaO) or fully stabilized zirconia (ZrO ₂ ) The quality composition to a predetermined layer thickness,
A method for producing a zirconia refractory, comprising: integrally molding so as to be laminated in a shape; and sintering at a temperature of 1500 ° C. or higher.