Manufacturing method of silica stone brick

Abstract

To provide a manufacturing method of silica stone brick having low thermal expansion coefficient capable of accelerating transformation to tridymite even when using a silica stone raw material that hardly transforms to tridymite.SOLUTION: In a manufacturing method of silica stone brick by mixing a refractory raw material compound containing a silica stone raw material having a percentage content of Fe2O3 of 0.1 mass % or under, followed by molding and firing, one or more kinds of quick lime, hydrated lime, calcium chloride, and calcium carbonate in CaO conversion of 2-4 mass%, feldspar of 0.2-1 mass%, and iron oxide in Fe2O3 conversion of 0.5-1.5 mass% are added to 100 mass% of the silica stone raw material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing silica bricks suitably used in coke ovens and hot blast stoves.

Background Art

[0002] Silica bricks are produced by kneading a refractory raw material composition mainly composed of a naturally occurring silica raw material and adding a transfer accelerator such as CaO thereto, and firing at around 1450 ° C after molding. The mineral composition of the silica bricks thus produced has a composition mainly composed of cristobalite and tridymite in which the crystal structure in the silica raw material has been transferred from quartz during firing.

[0003] On the other hand, silica bricks used in coke ovens are required to have a small thermal expansion rate. However, since silica bricks containing a large amount of cristobalite have a large thermal expansion rate, those with a high content of tridymite having a smaller thermal expansion rate are required.

[0004] The ease of transfer of quartz in the silica raw material to tridymite during firing is easily affected by the crystal grain size of quartz and the impurity components in the silica raw material, and the crystal grain size and the amount of impurities in the raw material vary depending on the origin of the silica raw material. Therefore, silica bricks manufactured using a silica raw material that is difficult to transfer to tridymite have a problem that the thermal expansion rate becomes large due to insufficient transfer to tridymite and are not suitable for use in coke ovens.

[0005] As a manufacturing method for promoting this transfer to tridymite, Patent Document 1 discloses adding 0.05 to 0.25% by weight of a soda lime silicate-based melt and 0.1 to 1.0% by weight of iron oxide in terms of Fe2O3 to the silica raw material. However, the silica bricks obtained by this manufacturing method still have a problem that the thermal expansion rate is too large for use in coke ovens.

[0006] In Patent Document 2, for the purpose of suppressing frost formation on the brick surface of the upper structure of the glass melting tank, silica bricks for glass kiln tanks containing CaO: 0 to 1.5%, K2O: 0.3 to 1.5% (however, CaO + K2O ≤ 1.5%, CaO / K2O ≤ 3) are disclosed. Patent Document 2 also discloses that K2SO4 or potassium water glass is used as the K2O-containing raw material. However, even with this manufacturing method, there is a problem that the thermal expansion coefficient becomes large when using a silica raw material with few impurities.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] The problem to be solved by the present invention is to provide a method for manufacturing silica bricks with a small thermal expansion coefficient by promoting the transition to tridymite even when using a silica raw material that is difficult to transition to tridymite.

Means for Solving the Problems

[0009] The present inventors have found that even when adding lime components such as quicklime and slaked lime and iron oxide as conventional general transition promoters to a silica raw material with an Fe2O3 content of 0.1% by mass or less, the transition to tridymite is insufficient. Based on this finding, various studies were conducted on the transition promoter. As a result, it was found that by adding feldspar to the conventional general transition promoters, lime components and iron oxide, the transition to tridymite is promoted, and as a result, it is possible to manufacture silica bricks with a small thermal expansion coefficient, leading to the completion of the present invention.

[0010] That is, according to one aspect of the present invention, the following method for manufacturing silica bricks is provided. In a method for producing silica bricks, a refractory raw material composition containing a silica raw material with an Fe₂O₃ content of 0.1 mass% or less is kneaded, molded, and then fired. Based on 100 mass% of the silica raw material, one or more of quicklime, slaked lime, calcium chloride, and calcium carbonate are added in terms of CaO at 2 to 4 mass%, feldspar is added at 0.2 to 1 mass%, and iron oxide is added in terms of Fe₂O₃ at 0.5 to 1.5 mass%.

Advantages of the Invention

[0011] According to the present invention, even when using a silica raw material that is difficult to transfer to tridymite, the transfer to tridymite can be promoted, and silica bricks with a small coefficient of thermal expansion can be produced.

Embodiments for Carrying Out the Invention

[0012] The types and contents of impurities in silica raw materials vary depending on the production area, which affects the ease of transfer to tridymite during the production of silica bricks. Among these impurities, Fe₂O₃ has a significant impact on the ease of this transfer. That is, silica raw materials with an Fe₂O₃ content exceeding 0.1 mass% could obtain a coefficient of thermal expansion suitable for use in coke ovens by the conventional production method using lime and iron oxide as transfer promoters. However, for silica raw materials with an Fe₂O₃ content of 0.1 mass% or less, the transfer to tridymite is insufficient, resulting in a large coefficient of thermal expansion. Therefore, the method for producing silica bricks of the present invention is particularly effective when using a silica raw material with an Fe₂O₃ content of 0.1 mass% or less. The chemical composition of the silica raw material is measured in accordance with JIS R2212-1:2006 Chemical Analysis Methods for Refractory Products.

[0013] In the present invention, one or more of quicklime (CaO), slaked lime (Ca(OH)₂), calcium chloride (CaCl₂), and calcium carbonate (CaCO₃) are added at an addition rate of 2 to 4% by mass in terms of CaO based on 100% by mass of the silica raw material. If the addition rate in terms of CaO (hereinafter referred to as "CaO addition rate") is less than 2% by mass, the conversion to tridymite is insufficient and the thermal expansion rate increases. Even if it exceeds 4% by mass, the conversion rate to tridymite does not increase, and instead, there is a concern that white spots may occur on the brick surface after firing and the yield may decrease. Note that even if the CaO addition rate exceeds 4% by mass, there is almost no adverse effect on the creep resistance.

[0014] Among quicklime, slaked lime, calcium chloride, and calcium carbonate, slaked lime can be used as a so-called lime milk dispersed in water, and there is an advantage that a kneaded material suitable for molding can be obtained by wetting the raw materials during kneading. Also, when the amount of CaO is insufficient with only lime milk, one or more of quicklime, slaked lime, calcium chloride, and calcium carbonate can be added as a powder raw material with a particle size of 0.1 mm or less.

[0015] Feldspar is added at an addition rate of 0.2 to 1% by mass based on 100% by mass of the silica raw material. If the addition rate of feldspar is less than 0.2% by mass, the conversion to tridymite is insufficient and the thermal expansion rate increases. If it exceeds 1% by mass, the creep resistance decreases. As the feldspar, one or more of potassium feldspar (KAlSi₃O₈), alkali feldspar ((Na,K)AlSi₃O₈), and albite (NaAlSi₃O₈) can be used. Among these, potassium feldspar (KAlSi₃O₈) is easy to use because of its higher effect of promoting the conversion to cristobalite. The feldspar can be added as a powder with a particle size of 0.1 mm or less. These feldspars can be those generally commercially available as ceramic raw materials.

[0016] Iron oxide is added at an addition rate of 0.5 to 1.5% by mass in terms of Fe2O3 based on 100% by mass of the silica raw material. If the addition rate in terms of Fe2O3 (hereinafter referred to as "Fe2O3 addition rate") is less than 0.5% by mass, the transfer to tridymite is insufficient and the thermal expansion rate increases. If it exceeds 1.5% by mass, the creep resistance decreases. As the iron oxide, one or more of iron(II) oxide: FeO, iron(III) oxide: Fe2O3, and iron(II,III) oxide: Fe3O4 can be used as powders with a particle size of 0.1 mm or less.

[0017] In addition, clay can be added according to the shape and size of the bricks to be manufactured. By adding clay, the plasticity of the brick earth is easily obtained and a molded body with high strength can be obtained. The clay to be used can be used without problems as long as it is a commonly used clay such as in ordinary alumina-silica fired bricks, for example, bentonite.

[0018] In the method for manufacturing silica bricks of the present invention, silica bricks can be obtained by adding water or lime milk to a refractory raw material mixture containing a silica raw material and the above-mentioned transfer promoter, kneading, molding, and firing. The kneading conditions and molding conditions may be the same as those in the prior art. The firing conditions may also be the same as those in the prior art and can be set around 1450°C.

Examples

[0019] Table 1 shows the compositions of the refractory raw material mixtures in the examples and comparative examples of the present invention and the evaluation results of the obtained bricks.

[0020]

Table 1

[0021] First, the refractory raw materials shown in Table 1 will be described. As the silica raw material, natural silica raw material was used, and its chemical composition was 99.8 mass% of SiO2, 0.05 mass% of Fe2O3, 0.1 mass% of Al2O3, and 0.02 mass% of CaO. As the clay, bentonite with an Al2O3 content of 40 mass% and an SiO2 content of 45 mass% was used. As the iron oxide, iron(III) oxide with a purity of 99 mass% and a particle size of 0.1 mm or less was used. As the quicklime, the one with a purity of 99 mass% and a particle size of 0.1 mm or less was used. As the lime milk, a suspension in which slaked lime (Ca(OH)2 of 99 mass% or more) was dispersed in water to a concentration of 20 mass% was used. As the feldspar, potassium feldspar (KAlSi3O8), alkali feldspar ((Na,K)AlSi3O8), and albite (NaAlSi3O8) were used. In Table 1, the addition rate of iron oxide is shown as a Fe2O3 conversion value, and the addition rates of quicklime and lime milk are shown as CaO conversion values, respectively. These conversion values are calculated values calculated from the purity, concentration, blending amount, etc. of each raw material.

[0022] The refractory raw material mixture in Table 1 was kneaded, formed into the shape of parallel bricks, and after drying, the bricks obtained by firing at 1450 °C in a single kiln were evaluated for the thermal expansion rate and creep resistance at 1000 °C. The thermal expansion rate was evaluated by the method described in JIS R 2207. The thermal expansion rate at 1000 °C was marked as 〇 (qualified) when it was 1.24% or less, △ (qualified) when it exceeded 1.24% and was 1.27% or less, and × (unqualified) when it exceeded 1.27%. The creep resistance was evaluated by a creep test. The creep test was carried out at 1550 °C for 50 hours with a load of 0.2 MPa using a sample with a size of 50 mm in diameter × 50 mm in height. The deformation rate at 1550 °C was marked as 〇 (qualified) when it was -0.5% or more and 0 or less, △ (qualified) when it was -1.0% or more and less than -0.5%, and × (unqualified) when it was less than -1.0%.

[0023] Examples 1 to 7 are examples with different addition rates and types of feldspar, but they are within the scope of the present invention. The thermal expansion rate is sufficiently small, and the deformation in the creep test is also small, resulting in good results. In contrast, Comparative Example 1 is an example without adding feldspar, and the thermal expansion rate has increased. In Comparative Example 2, the addition rate of feldspar exceeds the upper limit of the present invention, and the deformation in the creep test has increased.

[0024] Examples 8 to 10 are examples with different CaO addition rates, but they are within the scope of the present invention and have good results. In contrast, in Comparative Example 3, the CaO addition rate is below the lower limit of the present invention, and the thermal expansion rate has increased. Comparative Example 4 is an example where the CaO addition rate exceeds the upper limit of the present invention. Although the thermal expansion rate and creep resistance are good, white spots have occurred on the surface of the bricks.

[0025] Examples 11 to 13 are examples with different Fe2O3 addition rates, but they are within the scope of the present invention and have good results. In contrast, in Comparative Example 5, the Fe2O3 addition rate is below the lower limit of the present invention, and the thermal expansion rate has increased. In Comparative Example 6, the Fe2O3 addition rate exceeds the upper limit of the present invention, and the creep resistance has decreased.

[0026] Examples 14 and 15 are examples with different addition rates of the transfer promoter, that is, different CaO addition rates and Fe2O3 addition rates, but they are within the scope of the present invention and have good results.

Claims

1. Fe ２ O ３ In a method for producing silica bricks, a refractory raw material composition containing a silica raw material with a content of Based on 100% by mass of the silica raw material, 2 to 4% by mass of one or more of quicklime, slaked lime, calcium chloride, and calcium carbonate in terms of CaO, 0.2 to 1% by mass of feldspar, and 0.5 to 1.5% by mass of iron oxide in terms of Fe ２ O ３ are added respectively, and a method for manufacturing silica bricks.

2. The method for manufacturing silica bricks according to claim 1, wherein the feldspar is potassium feldspar.

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