JPH03197357A - Zirconia/hafnia refractories - Google Patents

Abstract

PURPOSE:To improve resistance to fire, resistance to corrosion and resistance to spalling by subjecting a partially or completely stabilized ZrO2 layer containing a specific stabilizer and HfO2 layer to bonding in a solid solution state at the boundary part. CONSTITUTION:Partially or completely stabilized ZrO2 powder containing one or more species selected from CaO: 6-25mol%, MgO: 6-25mol%, Y2O3: 3-15mol% and CeO: 10-30mol% and HfO2 powder are charged to a mold so as to have a fixed layer thickness and press-molded under a cold hydrostatic pressure, then sintered above 1500 deg.C in an oxidative atmosphere to subject a boundary part between ZrO2 layer and HfO2 layer to bonding in a solid solution state.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a zirconia/hafnia-based composite refractory material that has excellent fire resistance, corrosion resistance, and spalling resistance against severe high-temperature conditions in all atmospheric systems. relating to things.

[Prior art] Refractories that can be used in high-temperature ranges exceeding 1800°C include single-phase materials such as alumina (IgOs), magnesia (MgO), and zirconia (ZrOi), as well as two-component materials. As magnesia/alumina (MgO
/Alt03 spinel), alumina/chromia (Al□
0. /C "Y0." etc. have been developed, but they have advantages and disadvantages in terms of fire resistance, stability in oxidizing/reducing high temperature atmospheres, and corrosion resistance when used in various industrial furnaces.

Among these materials, zirconia has a very high melting point of 2700°C and is excellent in stability at high temperatures (low vapor pressure, corrosion resistance, etc.), so it is used in a wide range of fields as an ultra-high temperature refractory. There is.

However, pure zirconia (ZrOx) has three different crystal structures depending on the temperature stage, and as this crystal system undergoes a large volume change when it undergoes a reversible transition, thermal spalling failure is difficult to achieve. It has the disadvantage of being easy to receive. As a measure to improve this, one or more oxides 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 to stabilize part or all of the crystal structure into a cubic crystal structure. There are known methods to do this, and various proposals have been made in the past.

For example, Japanese Patent Publication No. 56-4507 discloses calcium oxide (Cab) or magnesium oxide (MgO), and JP-A No. 61-155257 discloses yttrium (ygo).
i) and JP-A-59-152266 disclose a zirconia refractory whose spalling resistance is improved by adding cerium oxide (CeOz), and a method for producing the same.

However, these refractories have the problem of not being fully satisfactory in terms of spalling resistance due to the high thermal expansion and low thermal conductivity of zirconia, which is the main component. Moreover, zirconia can be used for nitrogen (N2) and -carbon oxide (
Since nitriding and carbonizing reactions are likely to occur in an atmosphere containing a large amount of
The temperature must be lowered to about 0° C., which has the disadvantage that it cannot be applied to a high-temperature furnace with a reducing atmosphere, such as a carbon black generating furnace.

In this regard, hafnia ()lfO□), which is a rare earth oxide, has a higher melting point than Zirphere, and has relatively stable material properties even in a neutral or reducing atmosphere. However, since hafnia is extremely expensive as a material, it cannot be used as a single refractory in various industrial furnaces.

(Problems to be Solved by the Invention) In view of the above-mentioned circumstances, the inventors have conducted intensive research and found that when both materials, stabilized zirconia and stabilized hafair, are laminated and integrated to form a two-layer structure, it is possible to solve the problem in an oxidizing atmosphere. As a matter of course, we confirmed that it exhibits excellent fire resistance performance in neutral and reducing atmosphere systems.

Regarding this type of composite refractory, there is an evaporation crucible in which the housing part of a crucible base material made of zirconia sintered body is thermally spray coated with ittria (Japanese Patent Application Laid-Open No. 166401/1983), or a silicon carbide refractory material and a different type of refractory material. A silicon carbide composite brick that is bonded to a material (for example, silicon carbide clay) through a serrated boundary (Japanese Utility Model Publication No. 55-75687)
There are several proposals, but all of them have the disadvantage that peeling between the eyebrows cannot be avoided under high temperatures.

By combining zirconia and hafnia, the present invention provides zirconia that has excellent fire resistance, corrosion resistance, and spalling resistance in a temperature range of around 2000°C in any atmospheric system, and does not cause peeling between the eyebrows. /Aims to provide hafnia-based refractories at low cost.

[Means to solve the problem]

Zirconia/according to the present invention to achieve the above object
Hafnia-based refractories include a partially or completely stabilized zirconia (ZrOr)'I layer containing one or more stabilizers selected from oxides of calcium, magnesium, yttrium, and cerium, and hafnia ( The structure is characterized by a laminated two-layer structure in which HfO2) layers are solid-solution bonded at the boundary.

The zirconia (ZrO
Y! 03), ceria (CeO□), etc., stabilized to at least 70% by one or more stabilizers selected from the group consisting of ceria (CeO□) and the like (the former is cubic, the latter is orthorhombic). These have low activity and are sized to be as close packed as possible. The reason for this particle size adjustment is that by using stabilized zirconia and hafnia particles with low activity as a skeleton, drying and firing shrinkage is reduced, preventing cracking during the manufacturing process, and forming a dense structure. This is to increase resistance to physical and chemical corrosion.

The boundary between the zirconia layer and the hafnia layer has a two-layer structure in which the zirconia component and the hafnia component form a solid solution with each other and are strongly bonded to each other. will not occur.

The zirconia/hafnia-based large-sized material of the present invention having the above-mentioned structure is produced by calcining a raw material whose particle size has been adjusted by pulverizing a partially or completely stabilized zirconia and hafnia ingot or by granulating fine powder. However, it can be manufactured by adding a molding binder to this, laminating the zirconia layer and hafnia layer to form two layers, and then sintering at a temperature of 1500° C. or higher.

The amount of stabilizer added varies depending on the type of stabilizer used, but it is generally calcia (Cab) 6 to 25 mol χ,
Magnesia (HgO) 5-25 mol χ, Ittria (Y
zOs) 3-15 mol χ, ceria (CeO) 10-3
It is preferable to set the amount in the range of 0 mol χ, and if the amount is below the above range, the degree of stabilization will be low and the effect of improving fire resistance, corrosion resistance and spalling resistance will not be exhibited, and if the amount exceeds the above range Addition no longer shows any improvement in effectiveness.

In laminated molding, powder particles of one of the components are placed in a non-adsorption forming mold such as a metal mold, and after being vibrated or tamped, the upper layer is filled with powder particles of the other component, and then uniaxial pressing or cold isostatic pressure is applied. This is done by molding with a press (CIP), or by pouring one component powder in a slurry state into a water-absorbing mold such as plaster, and after semi-drying, pouring another component powder and drying completely. be able to.

At this time, by changing the shape of the mold used and the filling amount of each composition, it is molded into a predetermined layer thickness and shape.

The molded body is sintered in an oxidizing atmosphere at a temperature of 1500°C or higher, preferably in the range of 1600 to 1800°C.

[For production]

The zirconia/hafnia-based refractory according to the present invention has a two-layer structure in which a partially stabilized or fully stabilized zirconia layer and a hafnia layer, which are excellent in fire resistance and corrosion resistance, are laminated and integrated. A comparison of the melting points, thermal expansion coefficients, and thermal conductivities of zirconia (ZrO2) and hafnia (HfO2) constituting both layers is as shown in the table below.

Therefore, when constructing a high-temperature furnace, by arranging a hafnia layer with a low coefficient of thermal expansion on the inner surface of the furnace, which is exposed to harsh conditions, fluctuations in thermal expansion caused by temperature differences between the inside and outside can be effectively suppressed. This improves spalling resistance and extends the service life even in all kinds of furnace atmospheres, such as acidic, neutral, and reducing.

Furthermore, since the ionic radii of zirconium and hafnium, which are the main components of each layer, are very close to each other (Zr: 0.80, Hf: 0°78), they have the property of being easy to interdiffuse.

This approximation property serves to strengthen the bond by forming a solid solution with each other at the boundary during laminated sintering.

These effects work together to provide high fire resistance that exhibits excellent fire resistance, corrosion resistance, and spalling resistance under severe usage conditions. Moreover, since there are few constituent parts of the expensive hafnia layer, the product can be supplied at a relatively low cost.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example 1 12 mol% of ittria (YzOs) was added as a stabilizer to commercially available hafnia (HfOg) powder and wet-mixed.
Dry. In the process of pulverizing the dried mixture, it was classified into coarse particles (particle size 1-2 g+plow), medium particles (particle size 250 μm-1 m5), and fine particles (particle size 250 μm or less). Then, the classified particles were calcined in air at a temperature of 1700°C and simultaneously stabilized (stabilization rate 95%), coarse particles, medium particles, and fine particles were blended in a weight ratio of sex: 4, and polyvinyl 40 d17 kg of 5% alcohol aqueous solution was added as a la binder and thoroughly kneaded.

On the other hand, 8 mol% of ittria was added as a stabilizer to commercially available zirconia (ZrOi) powder, and after calcination and stabilization at 1700°C (stabilization rate 100%), particle size classification and compounding were performed in the same manner as above. And the binder was mixed.

Kneaded hafnia and zirconia powder were sequentially filled into a mold to a predetermined layer thickness of 200 kgf/cm.
It was uniaxially press-molded at a pressure of 200° C. and dried at a temperature of 60° C. for 48 hours. Then, the obtained molded body was transferred to an electric furnace,
Sintering was carried out in the air at a temperature of 1800° C. for 1 hour.

In this way, the length is 230 mm, the width is 114 mm, and the thickness is 6.
0■-, hafnia layer is 20-1, zirconia layer is 4
An hour-shaped brick with an integral two-layer structure having a 0- shape was manufactured.

The characteristics of the obtained brick were a porosity of 20%, a three-point bending strength of 220 kg/cm'', and the layer boundaries were completely bonded by solid solution.

The above-mentioned drum-shaped brick was placed in a small high-temperature gas furnace using liquefied propane gas (LPG) and oxygen as fuel sources, with the hafnia layer facing toward the high temperature side of the furnace.
When kept at 00°C for 24 hours, no defects such as melting damage or cracks were observed in the structure.

Next, we carried out a fire resistance test by keeping the temperature at 2000°C for 24 hours while supplying nitrogen gas into the furnace. As a result, a slight amount of hafnium nitride (HfN) was found on the brick surface (hafnia surface).
However, there was no structural damage such as cracks, and sufficient fire resistance performance was observed.

Note that the raw material cost of the zirconia/hafnia-based refractory brick according to this example was about 176 yen compared to the same-shaped brick made entirely of hafnia (Comparative Example 1).

Comparative Example 1 Under the same conditions as in Example, a homogeneous regular brick made entirely of hafnia and partially stabilized with ittria was produced. The characteristics of this brick include a porosity of 22% and a three-point bending strength of 200 kg/
cm”.

The obtained bricks were subjected to a fire resistance test in the air and in a nitrogen gas atmosphere under the same conditions as in the examples. As a result, no signs of melting were observed on the exposed surface in the atmospheric environment, but small cracks were observed due to lack of spalling resistance due to the low thermal conductivity of this material. In addition, in the nitrogen atmosphere system, a small amount of hafnium nitride was formed on the surface and many microcracks were observed.

Comparative Example 2 Under the same conditions as in Example, a homogeneous and regular brick made entirely of zirconia and completely stabilized with ittria was produced. This brick has a porosity of 21% and a 3-point bending strength of 220kg.
/cm''.

The obtained bricks were subjected to a fire resistance test in the air and in a nitrogen gas atmosphere under the same conditions as in the examples. As a result, in the atmospheric environment, there was no erosion phenomenon in the structure and no deterioration in the strength of the material, but in the nitrogen atmosphere, a layer of zirconium nitride (ZrN) was formed on the surface and material damage was observed.

〔Effect of the invention〕

As described above, according to the present invention, the stabilized zirconia layer and the stabilized hafnia layer are laminated and integrated to form a two-layer structure, which provides sufficient fire resistance against severe high temperature conditions in all atmospheric systems. , a zirconia/hafnia-based composite refractory having corrosion resistance and spalling resistance can be supplied at a relatively low price.

Therefore, it is expected to be versatile as a lining material for various high-temperature heating furnaces and melting furnaces, and is also extremely useful as a lining material for carbon black generating furnaces, which requires durability in oxidizing and reducing atmosphere systems.

Claims (1)

[Claims] 1. A partially stabilized or fully stabilized zirconia (ZrO_2) layer and hafnia (HfO_2) containing one or more stabilizers selected from oxides of calcium, magnesium, yttrium and cerium.
A zirconia/hafnia-based refractory with a laminated two-layer structure in which the layers are solid-solution bonded at the boundary.