JPH058143B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention discloses a method for solving the problem of the formation of unsaturated oxides and maintaining oxygen in zirconia at its stoichiometric ratio (high oxidation degree). The present invention relates to a method for producing a zirconia-containing electrocast refractory in which most of the zirconia source is composed of extremely fine primary particles or aggregates thereof and has an extremely large specific surface area. [Prior art] Zirconia-containing electrocast refractories are broadly classified into so-called AZS containing 33 to 41% zirconia (ZrO ₂ ).
There are two types: refractories and ZrO ₂ refractories containing around 95% ZrO ₂ . The raw material for ZrO ₂ used in these refractories is
Generally, particles with a size of 100 μm or more are used. That is, natural minerals such as zircon sand and patudereout, and artificial minerals such as fused zirconia correspond to this. These raw materials have large particle sizes and all have extremely dense crystal grains. In rare cases, a fine powder zirconia source produced by adding an alkali or alkaline earth metal oxide to zircon sand, thermally decomposing it, and then chemically treating it with acid and neutralization is used as a raw material for AZS refractories. However, the effect of the present invention was not expected, and furthermore, it did not belong to the structure of the present invention. In the production of AZS refractories, the oxidizing atmosphere melting method, represented by the long arc method disclosed in Japanese Patent Publication No. 36-5375, has become commonplace today, resulting in a high degree of oxidation.
AZS refractories are manufactured. In addition, when the oxidizing template disclosed in JP-A-58-179536 is used in combination, a high degree of oxidation can be reliably maintained. (Reduction after casting can be prevented.) On the other hand, ZrO ₂ refractories cannot maintain a sufficiently high degree of oxidation even with the oxidizing atmosphere melting method mentioned above, and furthermore, because they are cast into graphite molds, they undergo reduction and become gray-black products. . Generally, ZrO ₂ is considered to be an extremely stable oxide even at high temperatures, but when it comes into contact with carbon or carbon monoxide at high temperatures close to its melting point, it tends to lose some of its oxygen and become an unsaturated oxide. The aforementioned oxidizing atmosphere melting method is one way to prevent this, but the degree of oxidation differs slightly each time it is melted, and product variations are likely to occur. Also,
In the case of ZrO ₂ refractories, they contain too much ZrO ₂ and cannot maintain a sufficient oxidation state using the oxidizing atmosphere melting method. In this way, the black-colored refractory in the reduced state is
When used in glass melting kilns, when it comes into contact with molten glass, it reduces the glass and releases bubbles into the glass. Once a black-colored refractory in a reduced state is heat-treated in an oxidizing atmosphere (for example, at 1,450°C), it usually turns light brown or yellow, and does not generate bubbles when it comes into contact with molten glass. The AZS refractory manufactured by the above-mentioned oxidizing atmosphere melting-oxidizing mold has properties equivalent to the above-mentioned heat-treated products. [Problems to be Solved by the Invention] The present invention solves the above-mentioned problem of reduction, that is, the formation of unsaturated oxides, and provides a method for maintaining oxygen in zirconia at its stoichiometric ratio (high degree of oxidation). It is something. [Means for Solving the Problems] The present invention provides a method for producing zirconia-containing electrocast refractories by melt casting containing zirconia raw material particles, and in which fine particles having an average primary particle size of 1 μm or less or granules in which these are aggregated are used. Using 90% or more of the total zirconia raw material, zirconia raw material particles having a specific surface area of 1 square meter/gram or more are used to adsorb oxidizing gas on the surface of the zirconia raw material particles to form an oxidizing atmosphere during melting. The gist of this paper is a method for producing zirconia-containing electrocast refractories, which is characterized by making the electrocast refractories white, yellow, or brown with a high degree of oxidation. [Function] In the present invention, most of the zirconia source is made up of extremely fine individual primary particles and has a large specific surface area. The surface of such fine particles adsorbs oxygen in the air or oxidizing gas such as nitric acid generated by decomposition of nitrate, which is an auxiliary raw material added as an oxidizing agent, and forms an oxidizing atmosphere during melting. Since these fine particles have excellent heat insulating properties, there is little chance of releasing the adsorbed gas through preheating prior to melting, allowing the adsorbed gas to act effectively. The diameter of the zirconia source fine particles used in the present invention is
It is approximately 1 μm or less. Preferably, these are aggregated in granular form. If only fine particles are used, they will be scattered by the impact of the arc, reducing the yield of raw materials and deteriorating the working environment. The specific surface area of this raw material should be at least 1 square meter/gram. Preferably, a stable oxidation state can be obtained at 5 square meters/gram or more. These zirconia sources can be made of zirconia alone,
A combination or mixture of silica or alumina may also be used. The fine particles may be formed by a chemical treatment such as using chemicals or by a mechanical method such as a ball mill, but the former method is preferred.
Preferably, all the zirconia sources should be used as raw materials for the above-mentioned fine particles (in order to obtain a large specific surface area), but if mechanical grinding is used or for economic reasons, coarser particles of about 10% should be used. The incorporation of particles or particles of smaller specific surface area is also possible. When this exceeds 10%, a gray zirconia refractory is produced after undergoing reduction. [Example] An example of the present invention will be described. Examples Raw materials having the following particle diameters and specific surface areas were used. Γ fine-grained zirconia A: Z-999 manufactured by Nippon Metal Chemical Co., Ltd. Secondary particle size: 2 μm Primary particle size: 0.1 μm Relative area: 15 m ² /g B: South African batdayite ore, published in 1983
- Finely ground after chlorination purification according to No. 32385 Particle size: 1 μm Specific surface area: 1.7 m ² /g Γ Zircon Sand (produced in Australia) Particle size: 100 μm or more Specific surface area: 0.01 m ² /g or less Γ Alumina C; Sumitomo Chemical Co., Ltd. A-21 Secondary particle size: 40 μm Primary particle size: 3 μm Specific surface area: 0.6 m ² /g D; Sumitomo Chemical Co., Ltd. A-HPS30 Primary particle size: 0.3 μm Center particle size: 0.4 μm Ratio Surface area: 6 m ² /g The raw materials shown in Table 1 were blended, melted in a 300 KVA arc furnace, and cast into a graphite mold. The mold was released 30 minutes after casting and slowly cooled in alumina powder. Two days later, the cast body was taken out and cut to obtain a sample. Zirconia refractories with a high degree of oxidation were obtained when the fine powder zirconia source accounted for 90% or more of the total zirconia source (Examples 1 to 3). The color tone of the sample remained unchanged by heat treatment. On the other hand, when a zirconia source with coarse grains of 10% or more and a small specific surface area was used (reference example), it turned gray and only changed to its original pure white color after heat treatment.

【table】

〔Effect of the invention〕

According to the method of the present invention, a zirconia-containing electrocast refractory with a high degree of oxidation (containing oxygen in a stoichiometric proportion of ZrO ₂ ) can be obtained. The oxide (state) can be easily determined by the color of the sample. The total amount of oxides of impurities such as Fe, Ti, Cu, Cr, Mn, etc. is 0.05% or less, and if the degree of oxidation is high, the color is pure white, and if it is reduced, it becomes gray. When a gray sample is heat-treated and oxidized in air, it turns pure white. Reduced ZrO ₂ containing more of the aforementioned impurities
Refractories appear gray, while those in an oxidized state become bright yellow to brown. Refractories with a high degree of oxidation do not undergo significant changes in color tone through oxidation heat treatment. Gray or black refractories have the disadvantage that when they come into contact with molten glass, they reduce the glass and cause bubbles to form in the glass, but this disadvantage has been overcome by the present invention.

Claims (1)

[Claims] 1. In the method of manufacturing zirconia-containing electrocast refractories by melting and casting raw materials containing zirconia raw material particles, fine particles with an average primary particle size of 1 μm or less or granular aggregates of these particles, whose specific surface area Using 90% or more of all zirconia raw materials, zirconia raw material particles having a diameter of 1 parallel meter/gram or more, adsorbing an oxidizing gas on the surface of the zirconia raw material particles, and forming an oxidizing atmosphere during melting,
A method for producing a zirconia-containing electrocast refractory, which is characterized by making the electrocast refractory white, yellow, or brown with a high degree of oxidation.