JP2783969B2 - Zirconia refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia refractory, for example, a partially stabilized stabilizing member suitable for a heat storage member which is required to be stable in volume and shape of a high-temperature heat exchanger which repeats heating and cooling. It relates to zirconia refractories.

[0002]

2. Description of the Related Art It is known that zirconia alone undergoes irregular thermal expansion and contraction at around 1100 ° C. due to phase transformation from monoclinic to tetragonal. In the production of refractories, etc.,
When it is intended to obtain a compact that requires a firing step using such zirconia alone as a raw material, during the firing step, a large volume expansion accompanying transformation from a tetragonal system to a monoclinic system particularly during cooling is performed. To cause tissue destruction,
It is difficult to obtain a molded body. And using stabilized or partially stabilized zirconia as a raw material, or further using CaO, Mg
By adding oxides such as O and Y ₂ O ₃ together as a stabilizer, these oxides are dissolved at a high temperature to form a partially or fully stabilized zirconia having a partially or entirely cubic crystal structure. It is common to obtain a compact.

[0003] Further, thermal shock resistance is required under use conditions where heating and cooling are repeated. Zirconia, particularly stabilized tetragonal zirconia, has a large thermal expansion coefficient and low thermal shock resistance. On the other hand, there is a method of improving the thermal shock resistance by increasing the porosity to some extent, but even in such a case, when subjected to a heat treatment at a high temperature of 1800 ° C. or more, except for a very dense material structure, the sintering is performed. Causes volume contraction.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a zirconia refractory having excellent volume stability and thermal shock resistance even under repeated use conditions of heating and cooling to a high temperature.

[0005]

The zirconia refractory of the present invention is zirconia stabilized or partially stabilized by yttria (hereinafter also referred to as stabilized zirconia).
And a non-stabilized zirconia, wherein the composition ratio of the non-stabilized zirconia is from 7% by weight to 20% by weight and a fired body at a temperature of 1800 ° C. or more. .

The zirconia refractory of the present invention is a composition of zirconia stabilized or partially stabilized by yttria and unstabilized zirconia, wherein the composition ratio of the unstabilized zirconia is 7% by weight. % To 20% by weight, and is a fired body at a temperature of 1800 ° C. or higher and has an apparent porosity of 20% to 27%.

The stabilized zirconia has a yttria stabilization ratio of 80% to 100%, preferably 90% to 100%.
%belongs to. If the stabilization ratio is lower than 80%, the structure is destroyed during the heating / cooling operation, which is not preferable. Such a stabilized zirconia may be formed using particles having a particle size of 5 mm or less, preferably 3 mm or less when it is made a refractory. If the particle size exceeds 5 mm, sintering hardly proceeds even at 1800 ° C., and a stable material structure for achieving the object of the present invention cannot be obtained.

[0008] Unstabilized zirconia (stabilization rate 0%) is
It has an optimum composition ratio of 7% by weight to 20% by weight in the whole zirconia, preferably the particle size of the unstabilized zirconia used. If the composition ratio of the unstabilized zirconia is less than 7% by weight, since the sintering shrinkage of the entire structure is larger than the expansion of the unstabilized zirconia, the volume of the refractory shrinks each time heating and cooling are repeated, and the unstabilized. When the composition ratio of the zirconia fluoride is more than 20% by weight, the volume of the refractory expands each time heating and cooling are repeated because the expansion exceeds the shrinkage, so that the volume stability cannot be obtained.

[0009] When the unstabilized zirconia is used as a refractory, it is preferable to use a non-stabilized zirconia having a particle diameter of 0.0001 mm to 0.5 mm, preferably 0.001 mm to 0.3 mm. When the particle size is smaller than 0.0001 mm, unstabilized zirconia, when subjected to a firing step or heat treatment, undesirably pulls out the stabilizer yttria from the stabilized zirconia and stabilizes itself. On the other hand, if it exceeds 0.5 mm, the expansion during cooling becomes too large, and the material structure is greatly destroyed.

[0010] Further, in making a refractory, a refractory material composed of unstabilized zirconia and stabilized zirconia is used as a binder, for example, one of carboxymethylcellulose, methylcellulose, polyethylene oxide, polyvinyl alcohol and the like, or a binder thereof. A mixture of water and water, or an aqueous solution is added. The proportion of the binder in the mixture or the aqueous solution is 2% by weight to 10% by weight.
And a mixture thereof or an aqueous solution is added in an amount of 2 parts by weight to 6 parts by weight, preferably 3 parts by weight to 5 parts by weight, based on 100 parts by weight of the refractory material. Is kneaded in a kneader generally used for kneading.

Then, the molding pressure is 200 kg by a uniaxial press.
/ Cm ^{2 to} 500 kg / cm ² ,
C. and dried at 1800.degree. C. or more to obtain the desired zirconia refractory. The firing temperature is set to 1800 ° C. or higher in order to achieve a stable material structure in order to achieve the object of the present invention.

The apparent porosity of the refractory obtained by such a molding method is measured by an Archimedes method or the like, and can be controlled by adjusting the molding pressure.
In the present invention, the molding pressure is set to 200 kg / cm ² -5
By not making it as high as 00 kg / cm ² , the apparent porosity can be made relatively high as 20% to 27%, which effectively works to increase the thermal shock resistance. The fact that the volume before and after heating and cooling at 1800 ° C. or higher is stable means that the physical material structure does not change before and after that. This is presumed to be achieved by the following mechanism occurring inside the material structure of the zirconia refractory. That is, the volume shrinks due to sintering in the temperature raising / high temperature holding process and 1100 in the cooling process.
At about ９００900 ° C., the unstabilized zirconia undergoes a phase transformation from tetragonal to monoclinic, causing an expansion in volume. Since the contraction and expansion occur continuously, the volume of the molded body does not increase or decrease before and after heating and cooling, and the stability of the volume can be obtained.

[0013]

The zirconia refractory of the present invention has a temperature range from room temperature to 18 ° C.
In contrast to heating and cooling treatment up to a temperature of 00 ° C. or higher, by comprising both components showing shrinkage due to sintering and expansion due to phase transformation, it is possible to sequentially generate their actions each time the heating and cooling treatment is performed. A zirconia refractory having excellent volume stability before and after heating and cooling can be obtained.

Further, by making the apparent porosity of the zirconia refractory of the present invention relatively high at 20% to 27%, a zirconia refractory having excellent volume stability and high thermal shock resistance can be obtained.

[0015]

Example 1 A zirconia-based refractory was prepared at a ratio shown in Table 1 using a mixture of unstabilized zirconia having a stabilization rate of 0% and yttria-stabilized zirconia having a stabilization rate of 98% as a raw material. did.

The particle size of the raw material is composed of coarse, fine and fine particles in the same manner as ordinary refractories.
１1 mm, about 1 mm or less for fine-grained parts, and about 0.1 mm for fine-grained parts.
It has a particle size distribution of 3 mm or less. As shown in Table 1, the coarse particle size and the fine particle portion are yttria-stabilized zirconia, and a part or all of the yttria-stabilized zirconia in the fine particle region between them has a particle size distribution of 10 μm to 300 μm.
The sample was replaced with unstabilized zirconia of μm.

[0017]

[Table 1]

To the raw material composition thus obtained, a mixture of commercially available carboxymethylcellulose powder and water in a weight ratio of 1:20 was added as a binder at a ratio of 3% by weight, and the mixture was kneaded. Molding pressure about 30
It was molded at 0 kg / cm ² .

The molded body is fired at 1850 ° C. for 5 hours,
A zirconia refractory was obtained. The dimensions of the refractory were measured and heat treated again at 1850 ° C. for 5 hours. Further, the same operation was performed, and heat treatment was performed under the same conditions.

As a method of evaluating the stability of the volume due to the heat treatment, the dimensional change (linear change rate) before and after the heat treatment was measured. That is, it was evaluated that the closer the absolute value of the linear change rate before and after the heat treatment was to zero, the smaller the change in dimension and the more stable the volume. Table 2 shows the test results.

From Table 2, it can be seen that the blending amount whose absolute value of the linear change rate is close to 0 is from about 10% by weight to the upper limit in the present invention, ie, 20% by weight. It can be seen that the rate increases, ie expands.

[0022]

[Table 2]

[0023]

Example 2 As shown in Table 3, similar to Example 1,
In a normal refractory composition consisting of three parts of coarse, fine, and fine parts, part or all of the stabilized zirconia in the fine particle size range is replaced with unstabilized zirconia having a particle size distribution of 0.5 μm to 80 μm. Then, a zirconia refractory was manufactured and tested in the same manner as in Example 1. Table 4 shows the test results.

From Table 4, it can be seen that the blending amount whose absolute value of the linear change rate is close to 0 is around 7% by weight. In addition, in the case of this example in which the particle size distribution of the unstabilized zirconia is smaller than that of the example 1, it can be seen that the blending amount of the unstabilized zirconia for achieving the object of the present invention approaches the lower limit of 7%. Further, it can be seen that the linear change rate decreases or shrinks each time the heat treatment is repeated with a lower blending amount, and increases or expands each time the heat treatment is repeated with a higher blending amount.

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

Example 3 The zirconia-based refractory obtained in the same manner as in Example 1 with the raw material composition shown in Table 5 was measured for molding dimensions, and then heat-treated at 1700 ° C. for 5 hours was repeated twice. 1 Tested similarly. Table 6 shows the results of the test.

From Table 6, it can be seen that the line change shows expansion at any compounding amount due to the heat treatment. For example, even if the linear change rate is small, if the directionality is positive, under the condition of using a plurality of molded bodies such as refractories for a heat exchanger in combination, the tensile stresses act on each other. Therefore, it cannot be said that it is appropriate as a usable material.

[0029]

[Table 5]

[0030]

[Table 6]

[0031]

Fourth Embodiment From the results of the first embodiment, 1850 was obtained for Test Nos. 1-4 having a negative linear change rate and the smallest absolute value.
The linear change rate and the bending strength were measured before and after the heat treatment at 5 ° C., which was repeated 5 times for 5 hours. In addition, as a comparison, the same measurement was performed for the heat treatment repeated five times at 1500 ° C. for 5 hours. Table 7 shows the results. From these results, the strength was 1800
It can be seen that there is not much difference between the heat treatment at 1500C and the heat treatment at 1500C, but the dimensional stability is effective when subjected to the heat treatment at 1800C or more.

[0032]

[Table 7]

[0033]

According to the present invention, the zirconia refractory is 180
By combining the shrinkage of the stabilized zirconia by sintering at a high temperature of 0 ° C. or more and the expansion of the unstabilized zirconia at the time of cooling, the size or volume for heating and cooling from room temperature to a high temperature of 1800 ° C. or more is obtained. Is used at 1800 ° C. or higher,
Further, it is suitable as a regenerator for a high-temperature heat exchanger in which a structure is formed by combining a plurality of refractories or a refractory for structural materials such as a high-temperature industrial furnace.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of unstabilized zirconia and the linear change rate (total) in Examples 1 and 2.

[Explanation of symbols]

Open circles show the results of Example 1 and black circles show the results of Example 2.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshikazu Yamamura 2-3-1, Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside Kobe Steel, Ltd. Takasago Works (72) Inventor Shuhei Naya 2-chome, Araimachi, Takasago City, Hyogo Prefecture No. 1 Inside Kobe Steel, Ltd. Takasago Works (56) References JP-A-6-56537 (JP, A) JP-A-57-7367 (JP, A) (58) Fields investigated (Int. Cl. ⁶⁾ , DB name) C04B 35/48

Claims (2)

(57) [Claims] 1. A composition of zirconia stabilized or partially stabilized with yttria and unstabilized zirconia, wherein the composition ratio of the unstabilized zirconia is 7% by weight or more.
A zirconia refractory which is a fired body at a rate of 20% by weight and at a temperature of 1800 ° C. or more. 2. A composition of zirconia stabilized or partially stabilized by yttria and unstabilized zirconia, wherein the composition ratio of the unstabilized zirconia is 7% by weight or more.
A zirconia-based refractory having a ratio of 20% by weight, a fired body at a temperature of 1800 ° C. or higher, and an apparent porosity of 20% to 27%.