JP2604047B2 - Porous high zirconia cast refractory and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a porous high zirconia cast refractory and a method for producing the same.

(Related Art) Zirconia-based refractories containing a large amount of zirconia having excellent corrosion resistance to molten glass have been frequently used for bricks of a glass melting furnace. Such zirconia-based refractories include, for example, Al having a ZrO ₂ content of 30 to 50% by weight.
₂ O ₃ —ZrO ₂ —SiO ₂ -based cast refractories (AZS refractories) are known. Also, recently, when the content of ZrO ₂ is 80% by weight or more,
The use of highly zirconia-based cast refractories, which are structurally dense and have excellent corrosion resistance, is also increasing.

The conventional zirconia-based refractory described above is a refractory which is sufficiently satisfied by its excellent corrosion resistance when used in a place where it comes into direct contact with molten glass. However, it is not suitable for a place not in direct contact with the molten glass, for example, a superstructure of a glass melting furnace, or cannot take advantage of its excellent features.

Specifically, in the AZS refractory, there is a problem that a so-called sweating phenomenon occurs in which a glass-like component flows down from the surface of a brick during use, and this sweat mixes with molten glass to generate a cord. .

In addition, the high zirconia cast refractory has poor resistance to thermal shock (spalling resistance) required in the upper structure of the glass melting furnace due to its dense structure. Moreover, since the refractory having the above composition originally has a high density of ZrO ₂ and further has a small shrinkage rate during cooling from a molten state to room temperature, it is extremely heavy compared to other refractories having the same volume. Had the property of Such a high bulk density of the refractory is advantageous from the viewpoint of corrosion resistance, but is disadvantageous in terms of cost in applications that do not necessarily require high corrosion resistance because expensive zirconia is frequently used.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and has a sufficient corrosion resistance to alkali vapor, is lightweight, has excellent spalling resistance, and furthermore has a sweating phenomenon. It is an object of the present invention to provide a porous high zirconia cast refractory which does not show the above problem and a method for producing such a refractory in a simple process.

[Structure of the Invention] (Means for Solving the Problems) The porous high zirconia cast refractory of the present invention has a structure of 80 to 98.
15% to 40% of pores containing ZrO ₂ by weight and uniformly dispersed therein, and having a diameter of
70% of all pores in the range of 0.2-2mm
It is characterized by occupying the above.

The reason for limiting the porosity is that if it is less than 15%, it is not possible to obtain a lightweight, high zirconia cast refractory having excellent spalling resistance, while if it exceeds 40%, corrosion resistance to alkali vapor and suspended raw materials will not be obtained. This is because the refractory is deteriorated and a refractory having sufficient strength cannot be obtained. More preferred porosity is in the range of 15-25%.

The reason that the ratio of the pores having a diameter in the range of 0.2 to 2 mm is limited to the above range is that if the ratio of the pores is set to less than 70%, it is possible to obtain a lightweight, porous, high zirconia cast refractory having excellent spalling resistance. Because you can't.

The composition of the porous high zirconia cast refractory according to the present invention improves the corrosion resistance and, from the viewpoint of preventing the sweating phenomenon,
80-98% of ZrO ₂ , 2-15% of SiO ₂ , Al ₂ O ₃
But from 0.5 to 11% B ₂ O ₃ is 0.1% to 1.0%, it is preferable that alkali metal oxides is in the range of 0.1% to 1.0%.

In addition, the method for producing a porous high zirconia cast refractory of the present invention comprises, in a high zirconia raw material, at least one or more selected from Zr, Si and Al as a foaming agent in a metal, carbide or nitride state. It is characterized by containing 5% by weight, melting and then casting and gradually cooling.

The high zirconia-based raw material should have a composition that falls within the composition range of the refractory, assuming that the entire amount of the blowing agent is converted into an oxide after blending, melting, and casting the blowing agent. Is desirable.

Zr, SiC, AlC, Zr ₃ N ₄ , Si ₃ N ₄ , AlN and the like can be given as examples of the above-mentioned foaming agents as carbides or nitrides of Zr, Si and Al. It is desirable that the metal of Zr, Si, and Al or a compound of any of these be mixed in the form of fine powder in the raw material.

The reason for limiting the amount of the foaming agent is that if the amount is less than 1% by weight, a refractory having the above porosity cannot be produced. On the other hand, if the compounding amount exceeds 5% by weight, the amount of gas generated during melting becomes too large and the temperature of the melt does not rise. As a result, the flowability at the time of pouring the melt into the mold deteriorates and the moldability increases. Not only is reduced, but also pores having a uniform diameter cannot be uniformly dispersed.

The foaming agent may be used by mixing it with the refractory raw material from the beginning, or may be mixed with some raw materials at a high concentration and used in the final stage of melting, or may be previously set in a mold. Then, a foaming agent may be contained at the time of casting. However, in general, it is preferable to use the raw material in which the foaming agent is mixed in its entirety because fine and uniform pores can be formed in the refractory.

For the melting, for example, a method using a carbon electrode in an arc-type arc light furnace can be adopted. This melting temperature is 2400-2600
It is desirable to be in the range of ° C.

(Action) According to the present invention, pores containing 80 to 98% by weight of ZrO ₂ and uniformly dispersed therein are formed at a predetermined ratio, and the pores have a diameter of 0.5 to 2 mm. By having a structure in which the ratio of fine pores accounts for 70% or more of the total pores, it has sufficient corrosion resistance to alkali vapor, is lightweight, has excellent spalling resistance, and has no perspiration. High quality zirconia cast refractories can be obtained.

Further, according to the method of the present invention, the high zirconia-based raw material contains at least one or more selected from Zr, Si and Al as a foaming agent in a metal, carbide or nitride state in an amount of 1 to 5% by weight, and after melting. Casting and slow cooling A porous high zirconia cast refractory having fine pores and excellent characteristics as described above can be manufactured by a simple process.

That is, conventionally, as a method for forming bubbles in the melt, various carbonates, nitrates, sulfates, and the like are added to the raw material, and these are heated and decomposed to form carbon dioxide, nitrogen gas, and sulfurous gas in the melt. Methods for generating bubbles are known.
For example, the various salts are widely used as fining agents for molten glass in the glass industry. However, all the bubbles generated by these additives escape from the molten glass at a high temperature. The fining action utilizes such a property, and it is difficult to leave a large amount of bubbles in the melt.

It is also known that peroxides and hydroxides also generate air bubbles, but the air bubbles generated are relatively large and it is difficult to leave 5% or more of the porosity in the refractory. is there.

For this reason, in the present invention, at least one selected from Zr, Si and Al as a foaming agent is added to the high zirconia-based raw material.
By incorporating a predetermined amount or more in the form of a metal, carbide or nitride in a state of metal and carbide and melting, a large amount of bubbles can be generated in the high zirconia melt, and bubbles can be hardly removed even at high temperature. The foam has a small diameter (0.2-2mm)
, Are uniformly dispersed in the structure, and are also excellent in reproducibility of foaming, so that the above-mentioned porous high zirconia-based cast refractory having fine and numerous pores can be obtained.

Specifically, foam is generated as the raw material containing the foaming agent starts to melt. This foam tends to escape from the melt little by little during the melting process, but largely remains. This is considered to be due to the fact that the generated bubbles are extremely fine and a gas component for generating the bubbles.
The foaming mechanism of such a foaming agent has many unclear points. But,
According to the study of the present inventors, it is highly possible that the foam component generated in the melt in a large amount is oxygen, and that the foaming phenomenon is observed for a composition having a high zirconia content,
It was observed that the color of the melt was light gray indicating a slightly reduced state. Extrapolating such facts, the added blowing agent is decomposed at high temperature, to generate oxygen while reducing the ZrO ₂ act on ZrO ₂ generates a large amount and fine bubbles described above, the blowing agent itself It is believed that the oxidized state also finally joins the components of the refractory in an oxidized state.

(Example) Hereinafter, an example of the present invention will be described in detail.

Examples 1 to 10 and Comparative Examples 1 to 6 High-purity zirconia as a ZrO ₂ raw material, flattery sand as a SiO ₂ raw material, Bayer method alumina as an Al ₂ O ₃ raw material, and other raw materials such as a foaming agent as reagents Each of them was blended so as to have a composition shown in Table 1 below so as to have a weight of 100 kg, and these were sufficiently mixed with a mixer to prepare 16 kinds of raw material compositions.

Next, after melting each raw material at 2500 ° C. using a carbon electrode in a 300 kVA arc furnace, the molten material was cast into a carbon mold, and gradually cooled to produce 16 types of zirconia cast refractories. did.

For each of the cast refractories of Examples 1 to 10 and Comparative Examples 1 to 6, porosity, pore distribution, spalling resistance,
The perspiration and corrosion resistance were examined. The results are shown in Table 1 below. Comparative Example 5 in Table 1 is a known AZS-based cast refractory, and Comparative Example 6 is a known high zirconia-based cast refractory. In addition, various physical properties were measured by the following methods. In addition, some of the cast refractories of the comparative examples have a composition with a burrow, but the physical properties test was performed on a portion other than the burrow.

. Porosity From 10 or more parts representing each cast refractory, one test piece of 30 × 30 × 60 mm was cut out, and apparent porosity was calculated according to JIS R 2205, and calculated from the average value. .

. Pore distribution From 10 or more parts representing each cast refractory, cut out a dice-shaped test piece of 10 × 10 × 10 mm in size, and polished any one surface with diamond,
Using a mirror with a scale, the pore distribution at every 0.1 mm is counted for 10 visual fields. The ratio of the pore distribution was calculated from the average value of ten test pieces.

. Spalling resistance A test piece of 30 × 30 × 60 mm was cut out from each cast refractory, and the test piece was put in a furnace at 1200 ° C., kept for 15 minutes, taken out of the furnace, and rapidly cooled in water for 30 minutes. The spalling resistance was evaluated with the number of cycles until peeling occurred as the number of cycles.

. Sweating property A core with a diameter of 20 mm and a length of 80 mm is extracted from each cast refractory with a diamond drill, and this core is removed.
After heating in a furnace at 1600 ° C. for 4 hours, the core was taken out, and the surface of the core was visually inspected to evaluate the sweating ability based on whether or not the glass phase had leached.

. Corrosion resistance A test piece with a size of 10 x 80 x 80 mm is cut out from each cast refractory, and this test piece is placed in a Toshiba Monoflux crucible with an inner diameter of 50 mm and a depth of 50 mm in a soda lime glass: soda ratio of 1: 1. After storing together with the mixed alkali source and covering with a lid, it is kept in a furnace at 1500 ° C. for 72 hours. In addition, the said alkali source is replenished in principle every 12 hours. After heating in the furnace, the test piece was cut in half and the amount of erosion (depth) was measured with a caliper to evaluate the corrosion resistance.

As is clear from Table 1 above, all of the cast refractories of Examples 1 to 10 have a composition having a ZrO ₂ content of 80% by weight or more and a porosity of 5 to 40%. Distribution is uniform, and pores with a diameter of 0.2 to 2 mm
70% or more, withstands spalling resistance of 10 times or more, has a good corrosion resistance to alkali vapor of about 0.5 mm, and has no perspiration.

On the other hand, the cast refractories of Comparative Examples 1 and 3 had a high ZrO ₂ content of 80% by weight or more, and the blowing agent used was the same as that of the present example, but the amount exceeded 5% by weight. Satisfies pore condition and spalling resistance, but corrosion resistance
It does not have a value of 1 mm or more, which is a satisfactory value.

The cast refractory of Comparative Example 2 had a very low porosity of 5.2% and a low spalling resistance because the type of the foaming agent was different from that of this example.

The cast refractories of Comparative Examples 4 and 6 had a ZrO ₂ content of 80% by weight.
Although the above was high, the foaming agent was not blended in the raw material at all, or less than 1% was blended, so that the spalling resistance was unsatisfactory.

Since the cast refractory of Comparative Example 5 had a low ZrO ₂ content of 34% by weight, it had low spalling resistance and also had problems in sweating.

[Effects of the Invention] As described in detail above, according to the present invention, since a large amount of fine pores are uniformly distributed inside, lightness and smoothness are maintained without impairing sweating properties and corrosion resistance to alkali vapor. Poring resistance is remarkably increased, and a porous high zirconia cast refractory suitable for the upper structure of a glass melting furnace, an inner lining material of an ultra-high temperature furnace, and the like, and a method for manufacturing such a refractory in a simple process at a low cost. Can be provided.

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Claims (2)

(57) [Claims] 1. A ratio of pores containing 80 to 98% by weight of ZrO ₂ and having uniformly distributed therein 15 to 40% of pores and having a diameter of 0.2 to 2 mm among these pores. Is a porous high zirconia cast refractory characterized by having at least 70% of all pores. 2. A high zirconia-based raw material, Zr as a foaming agent,
A porous high zirconia cast refractory characterized in that at least one selected from Si and Al is contained in a metal, carbide or nitride state in an amount of 1 to 5% by weight, melted, cast and gradually cooled. Manufacturing method.