Siliceous castable refractory

Abstract

To provide a siliceous castable refractory which has high strength after curing and after drying, and which is excellent in terms of volume stability at high temperatures.SOLUTION: A siliceous castable refractory according to the present invention contains 1-15 mass% of silica flour, 0.1-5 mass% of magnesia that has an average particle diameter of 100 μm or less, and 0.1-5 mass% of borosilicate glass that has an average particle diameter of 500 μm or less, with the balance being mainly made up of a siliceous starting material that does not contain silica flour.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a siliceous castable refractory that is suitable for use in the construction of furnaces such as coke ovens, hot stoves, and CDQs. [Background technology]

[0002] Generally, when constructing a kiln using shaped bricks, a large number of bricks must be laid, which takes time and requires a large number of manpower. Therefore, in recent years, construction has become more common using precast blocks (hereinafter simply referred to as "blocks") made of castable refractories, which are easier to make larger than shaped bricks.

[0003] Here, the operating temperatures of furnaces such as coke ovens, hot stoves, and CDQs are high and subject to large temperature changes, so materials with low thermal expansion and contraction are required. Materials with large thermal expansion and contraction can cause cracks due to thermal stress, reducing the block's strength and causing problems such as gas leaks through the cracks and damage to the furnace walls. For this reason, blocks are required to have excellent volume stability in the high-temperature range of around 1200°C, i.e., at high temperatures. Furthermore, when handling blocks during construction on-site, they are lifted by a crane, but this makes them unstable, and if the block is not strong enough, there is a risk of it coming into contact with other blocks and being damaged. If a block is damaged, there are safety issues such as it falling, and the damaged area requires a lot of time and effort to repair, and if the damage is severe, the block must be discarded. Furthermore, careful work is required to prevent impacts to the block, which can reduce work efficiency. For these reasons, blocks are required to be strong.

[0004] In response to such demands, Patent Document 1 discloses that a block containing 96% by mass of fused silica, phosphate, and / or calcium oxide has a cold compressive strength of 30 MPa or more. However, the block disclosed in Patent Document 1 does not have sufficient strength after curing, which causes problems such as breakage during production, particularly when the block is removed from the frame. Furthermore, when producing large blocks, a firing step is required to develop strength, which increases production costs.

[0005] Furthermore, in the examples of blocks in Patent Document 2, fused silica raw material and silica fume are used as the refractory raw materials, and magnesia fine powder with a particle size of 75 μm or less is added as the hardener, condensed phosphate as the dispersant, and phosphate (phosphate glass) as the sintering aid in amounts of 0.4 mass %, 0.2 mass %, and 1 mass %, respectively, based on 100 mass % of the refractory raw material mixture. However, even with the blocks in Patent Document 2, the strength after curing was not necessarily sufficient.

[0006] Furthermore, Patent Document 3 discloses that a block made of a silica castable refractory material in which 3.0 to 9.3 mass% of colloidal silica calculated as solid SiO2 and 0.04 to 0.30 mass% of sodium silicate calculated as solid Na2O are added to 100 mass% of a silica refractory raw material blend consisting of fused quartz and fired silica, has a compressive strength of approximately 30 MPa. However, the block in Patent Document 2 suffers from problems such as shrinkage cracks during production due to the aggregation and shrinkage of the colloidal silica, sintering shrinkage during hot working, and shrinkage under load due to the formation of a liquid phase by the Na2O component, i.e., poor volume stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-137447 [Patent Document 2] International Publication No. 20 / 213629 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-189322 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a siliceous castable refractory which has high strength after curing and drying and which also has excellent volume stability in the hot state. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted extensive testing and research into the composition (raw material composition) of siliceous castable refractories, and have discovered that by combining silica flour, magnesia fine powder, and borosilicate glass powder, it is possible to obtain a castable refractory that has high strength after curing and drying and also has excellent volume stability when hot.

[0010] That is, according to one aspect of the present invention, there is provided the following siliceous castable refractory. A siliceous castable refractory containing 1 to 15 mass% of silica flour, 0.1 to 5 mass% of magnesia having an average particle size of 100 μm or less, and 0.1 to 5 mass% of borosilicate glass having an average particle size of 500 μm or less, with the remainder consisting mainly of siliceous raw materials not containing silica flour. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a siliceous castable refractory which has high strength after curing and drying and is excellent in volume stability in the hot state. DETAILED DESCRIPTION OF THE INVENTION

[0012] The siliceous castable refractory according to the present invention contains 1 to 15 mass% silica flour, 0.1 to 5 mass% magnesia having an average particle size of 100 μm or less, and 0.1 to 5 mass% borosilicate glass having an average particle size of 500 μm or less, with the remainder consisting mainly of siliceous raw materials not containing silica flour. That is, as described above, the present invention is technically characterized by the combination and blending of silica flour, magnesia fine powder (referring to "magnesia having an average particle size of 100 μm or less," the same applies hereinafter), and borosilicate glass powder (referring to "borosilicate glass having an average particle size of 500 μm or less," the same applies hereinafter), thereby enabling the production of a castable refractory that has high strength after curing and drying and excellent volume stability in hot conditions.

[0013] Specifically, silica flour and magnesia powder form a gel-like magnesium silicate hydrate in the presence of water, which acts as a binder. Then, at high temperatures, a dehydration reaction forms an amorphous magnesium silicate bond. The borosilicate glass powder then forms a bond with the magnesium silicate. This combined bond formation improves the bond strength after curing and drying.

[0014] In the present invention, the content of silica flour is 1 to 15% by mass. If the content of silica flour is less than 1% by mass, the bonding strength is insufficient, and if it exceeds 15% by mass, the thermal shrinkage becomes excessive. Here, in the present invention, silica flour means silica having an average particle diameter of 20 μm or less and a BET specific surface area of ​​10 m 2 / g or more. Such silica flour includes very high purity silica industrially produced for its own purpose, so-called white carbon, anhydrous or hydrous amorphous silicic acid, evaporative silica, and by-product volatile silica of relatively low purity. Volatile silica is generated as a by-product when zirconia is produced from zircon by arc melting, or when silicon or ferrosilicon is produced. In the present invention, one or more of these silica flours are used, and volatile silica is inexpensive and industrially effective. As mentioned above, silica flour has an average particle size of 20 μm or less and a BET specific surface area of ​​10 m2 / g or more, and is very active and highly reactive with magnesia, so that a strong bond can be formed. The silica flour content is preferably 7 to 13 mass %.

[0015] In the present invention, the content of the magnesia fine powder is 0.1 to 5% by mass. If the content of the magnesia fine powder is less than 0.1% by mass, the bonding strength is insufficient, while if it exceeds 5% by mass, the effect of shrinkage during heating becomes significant, resulting in defects such as cracking. In the present invention, fine powders such as electrofused magnesia, sintered magnesia, and lightly burned magnesia can be used as the magnesia fine powder. Furthermore, to form a stronger bond, magnesia having an average particle size of 10 μm or less can be used at a content of 0.3 to 3% by mass. As magnesia having an average particle size of 10 μm or less, lightly burned magnesia can be used, for example. Lightly burned magnesia is obtained by firing magnesite, magnesium hydroxide, or the like at a relatively low temperature, for example, 1400°C or less, usually 1000 to 1400°C. Lightly burned magnesia is generally called activated magnesia or calcined magnesia. Its average particle size is 1 μm or less, and it is particularly effective when rapid strength development is desired for construction purposes. In the present invention, the average particle size refers to the volume average particle size corresponding to the median cumulative value (D50) of the cumulative curve measured with a laser diffraction / scattering particle size distribution analyzer.

[0016] In the present invention, borosilicate glass powder is used at a content of 0.1 to 5 mass% to not only contribute to improving the strength of the silica castable refractory after curing and drying, but also to exhibit the effect of improving volume stability during hot working. If the content of borosilicate glass powder is less than 0.1 mass%, the effect of suppressing shrinkage during hot working becomes insufficient, while if it exceeds 5 mass%, the liquid phase ratio becomes excessive, resulting in large hot shrinkage. As the borosilicate glass powder used in the present invention, any commercially available borosilicate glass powder such as frit can be used without any particular problems. The content of borosilicate glass powder is preferably 0.3 to 5 mass%.

[0017] In the present invention, the remainder other than the silica flour, magnesia fine powder, and borosilicate glass powder described above is mainly composed of a siliceous raw material that does not contain silica flour. Examples of such a siliceous raw material include fused silica, silica stone, silica brick chips, and pyrotechnic stone. In the present invention, the siliceous raw material refers to a refractory raw material containing more than 50% by mass of SiO2.

[0018] In the present invention, the balance may contain, in addition to the siliceous raw material, other refractory raw materials such as chamotte, zircon, and zirconia, as needed. The balance may also contain dispersants, organic fibers, and the like used in ordinary castable refractories, in addition to the refractory raw materials. Specific examples of dispersants include polycarboxylic acid polymers, sodium polyacrylate, and condensed phosphates. Furthermore, cement may be used as a binder in the balance. However, since the use of a large amount of cement tends to reduce volume stability at high temperatures, the cement content is preferably 6% by mass or less, and more preferably 0% by mass, i.e., no cement is used. In this invention, cement refers to Portland cement, whose main minerals are tricalcium silicate (3CaO·SiO2), dicalcium silicate (2CaO·SiO2), tricalcium aluminate (3CaO·Al2O3), and calcium aluminum ferrite (4CaO·Al2O3·Fe2O3), as well as alumina cement, whose main mineral is calcium aluminate (CaO·Al2O3).

[0019] As described above, in the present invention, the balance may include various refractory raw materials, dispersants, etc. in addition to the siliceous raw materials, but the balance in the present invention is composed primarily of the siliceous raw materials. Specifically, when the balance is taken as 100% by mass, the siliceous raw materials account for a total amount of more than 50% by mass.

[0020] The castable refractory according to the present invention can be applied to the manufacture of precast blocks, as well as to the lining of kilns. When applied to the manufacture of precast blocks, an appropriate amount of water is added to the raw material mixture of the castable refractory, and the mixture is kneaded, poured into a casting flask, cured, removed from the flask, and dried to obtain a siliceous precast block. When applied to the lining of kilns, the process is basically the same, with the steps of kneading, pouring, curing, removing from the flask, and drying being carried out. In either case, the drying temperature can be about 100 to 400°C. [Example]

[0021] To the castable refractory material with the composition shown in Table 1, 6.4 mass% of construction water was added, and the material was mixed, poured, cured, removed from the mold, and then dried at 150°C for 20 hours to obtain a silica precast block specimen, which was then used for various evaluation tests.

[0022] [Table 1]

[0023] In Table 1, the fused silica used was a mixture of particles with a particle size of 1 mm or more but less than 5 mm and particles with a particle size less than 1 mm in a mass ratio of 6:4. The chemical composition of the fused silica was 99.7 mass% SiO2. The silica flour used had an average particle size of 0.5 μm. The chemical components of the silica flour were 96% by mass of SiO2 and 0.2% by mass of Na2O. The magnesia fine powder used was light-burned magnesia with an average particle size of 0.1 μm, whose chemical composition was 98 mass % MgO. The borosilicate glass powder used had an average particle size of 30 μm. The chemical components of the borosilicate glass powder were 25 mass % B2O3 and 25 mass % Na2O. The dispersant used was a polycarboxylic acid polymer.

[0024] For evaluation, the residual linear change rate after heating to 1200°C was measured after holding at 1200°C for 3 hours using the dimensions after curing as the standard, in accordance with JIS R 2554. This residual linear change rate is an index of volume stability at high temperatures, and a residual linear change rate of -0.4% or more was evaluated as ◎ (excellent), -0.5% or more but less than -0.4% was evaluated as ○ (good), and less than -0.5% was evaluated as × (poor). The bending strength after curing and after drying was measured in accordance with JIS R 2553. The bending strength after curing was evaluated as ⊚ (excellent) when it was 3 MPa or more, ○ (good) when it was 2 MPa or more and less than 3 MPa, and × (poor) when it was less than 2 MPa. The bending strength after drying was evaluated as ⊚ (excellent) when it was 5 MPa or more, ○ (good) when it was 3 MPa or more and less than 5 MPa, and × (poor) when it was less than 3 MPa. An overall evaluation was made based on the above evaluation results. The overall evaluation was as follows: if all the evaluation results were ⊚, it was evaluated as ⊚ (excellent); if at least one evaluation result was ◯ and there were no × evaluation results, it was evaluated as ○ (good); if at least one evaluation result was ×, it was evaluated as × (bad).

[0025] In Table 1, Examples 1 to 4 are examples with different silica flour contents, but all were within the range of the present invention and showed good results. In contrast, Comparative Example 1 is an example in which the silica flour content is below the lower limit of the present invention, resulting in low strength. On the other hand, Comparative Example 2 is an example in which the silica flour content is above the upper limit of the present invention, resulting in an increase in the residual linear change rate in the negative direction, i.e., the material shrinks, resulting in poor volume stability.

[0026] Although Examples 5 to 8 have different borosilicate glass powder contents, all of them were within the range of the present invention and achieved good results. In contrast, Comparative Example 3 is an example in which the borosilicate glass powder content is below the lower limit of the present invention, resulting in low strength. On the other hand, Comparative Example 4 is an example in which the borosilicate glass powder content is above the upper limit of the present invention, resulting in an increase in the residual linear change rate in the negative direction, i.e., the material shrinks, resulting in poor volume stability.

[0027] Examples 9 to 12 are examples in which the content of magnesia fine powder is different, but all are within the range of the present invention and showed good results. In contrast, Comparative Example 5 is an example in which the content of magnesia fine powder is below the lower limit of the present invention, resulting in low strength. On the other hand, Comparative Example 6 is an example in which the content of magnesia fine powder is above the upper limit of the present invention, resulting in an increase in the residual linear change rate in the negative direction, i.e., the material shrinks, resulting in poor volume stability.

[0028] Examples 13 to 15 are examples containing cement in the range of 2 to 6 mass %, and were evaluated as passing the test.

Claims

1. The siliceous castable refractory contains 1 to 15 mass% of silica flour, 0.1 to 5 mass% of magnesia having an average particle size of 100 μm or less, and 0.1 to 5 mass% of borosilicate glass having an average particle size of 500 μm or less, with the remainder consisting mainly of siliceous raw materials not containing silica flour.

2. 2. The siliceous castable refractory according to claim 1, wherein the magnesia raw material has an average particle size of 10 μm or less and a content of the magnesia raw material of 0.3 to 3 mass %.

3. 3. The siliceous castable refractory according to claim 1, wherein the cement content is 6 mass % or less (including 0).

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