Refractory composition

Abstract

The present invention provides a highly stable refractory composition of a magnesium silicate binding type, which attains both reactivity and strength. This refractory composition includes, as a main material, a refractory raw-material mixture comprising 0.2-5 mass% of a magnesia raw material having a specific surface area of 1-25 m2 / g, 0.2-15 mass% of a silica raw material having a specific surface area of 5 m2 / g or larger, and other refractory raw materials as the remainder. The ratio of the surface area of the silica raw material in the refractory raw-material mixture to the surface area of the magnesia raw material in the refractory raw-material mixture is 1 or greater.

Description

fireproof composition

[0001] This invention relates to a refractory composition used in the manufacture of various refractory materials.

[0002] Traditionally, cement-based binders such as alumina cement and Portland cement have been commonly used as binders for refractories. However, these cements emit large amounts of carbon dioxide during manufacturing, so from an environmental perspective, there is a strong demand for the development of cement-free binders. To meet this demand, magnesium silicate-based refractories are attracting attention. However, conventional magnesium silicate-based refractories have had the following problems.

[0003] For example, Patent Document 1 discloses a technique for bonding activated magnesia and siliceous powder by reaction. However, when activated magnesia is used as a binder, magnesium hydroxide may be formed as a byproduct. This reaction causes the structure to expand, leading to problems such as crack formation and reduced strength, resulting in a decrease in quality.

[0004] Furthermore, Patent Document 2 discloses a refractory material using magnesia powder with a particle size of 75 μm or less and siliceous particles, and a method for its application. However, because the particle size of the magnesia powder is large and it has poor reactivity as a magnesium silicate bond, it was necessary to add hydraulic transition alumina to harden it and impart strength. In this case, hardening adjustment is difficult, the application methods are limited, and because alumina is included as a chemical component of the matrix, its use is restricted in some applications.

[0005] JP-A-5-229876 JP-A-10-291868

[0006] Thus, despite their potential environmental compatibility, conventional magnesium silicate-based refractories suffered from problems of insufficient reactivity and reduced strength. Specifically, magnesium silicate bonds are inherently unreactive due to the low solubility of the magnesia and silica that form the bond, and if low-activity raw materials are used, the curing reaction does not proceed sufficiently. To address this problem, raw materials with a large specific surface area and high activity are generally used. However, if the activity of the magnesia raw material used is excessively high, the hydration reaction proceeds excessively, and a large amount of magnesium hydroxide is produced as a byproduct.

[0007] The formation of magnesium hydroxide causes the following problems: (1) It takes a long time for it to redissolve during curing and form magnesium silicate bonds. (2) The large volume change causes cracking in the refractory material. (3) The strength of the refractory material decreases. (4) When used at high temperatures, magnesium hydroxide decomposes again, causing further strength loss. (5) There is a risk of rehydration after decomposition, which is problematic in actual use.

[0008] In view of the above, the problem that the present invention aims to solve is to provide a highly stable magnesium silicate-based refractory composition that achieves both reactivity and strength.

[0009] To solve the above problems, the inventors conducted extensive research and found that by optimizing the specific surface area of ​​the magnesia and silica raw materials and further controlling their surface area ratio, an excellent magnesium silicate-based refractory composition that balances reactivity and strength can be obtained.

[0010] In other words, according to one aspect of the present invention, the following fire-resistant composition is provided: having a specific surface area of ​​1 to 25 m². ２ Magnesia raw material with a density of 0.2 to 5% by mass, and a specific surface area of ​​5 m². ２ A refractory composition comprising a refractory raw material compound as the main material, containing 0.2 to 15% by mass of silica raw material in a quantity of 1 / g or more, with the remainder being other refractory raw materials, wherein the ratio of the surface area of ​​the silica raw material in the refractory raw material compound to the surface area of ​​the magnesia raw material in the refractory raw material compound is 1 or more.

[0011] According to the present invention, a highly stable magnesium silicate-bonded refractory composition that achieves both reactivity and strength can be obtained. That is, according to the present invention, by ensuring the reactivity of magnesia while minimizing the formation of the by-product magnesium hydroxide, a magnesium silicate-bonded refractory composition having appropriate reactivity and stable strength development can be provided. Since this refractory composition basically does not require the use of cement, it is an environmentally-friendly product that can contribute to the reduction of carbon dioxide emissions.

[0012] The refractory composition of the present invention is used for producing various refractory materials such as shaped refractories including refractory bricks and unshaped refractories including castables, and is mainly composed of a refractory raw material blend. In the refractory composition of the present invention, the refractory raw material blend has a specific surface area of 1 to 25 m ２ / g magnesia raw material (hereinafter referred to as "fine magnesia raw material") in an amount of 0.2 to 5% by mass, and the specific surface area is 5 m ２ / g or more silica raw material (hereinafter referred to as "fine silica raw material") in an amount of 0.2 to 15% by mass, with the remainder consisting of other refractory raw materials.

[0013] In the present invention, the fine magnesia raw material refers to highly reactive magnesia, also called light-burned magnesia, active magnesia or calcined magnesia, as well as finely pulverized refractory aggregate raw materials such as fused magnesia and sintered magnesia, having a specific surface area of 1 to 25 m ２ / g. Generally, active magnesia with a specific surface area exceeding 30 m ２ / g and high reactivity is used, but in the present invention, magnesia having a specific surface area of 1 to 25 m ２ / g, which exhibits appropriate reactivity for magnesium silicate bonding, is used. That is, when the specific surface area of the magnesia raw material is less than 1 m ２ / g, the formation of magnesium silicate bonds is insufficient, and sufficient strength cannot be obtained. On the other hand, when the specific surface area of the magnesia raw material exceeds 25 m ２ / g, the formation of magnesium hydroxide cannot be suppressed, resulting in the various problems mentioned above. The MgO content in the fine magnesia raw material is preferably 90% by mass or more, and impurities that are unavoidably mixed in during the production process of the fine magnesia raw material are permissible.

[0014] Furthermore, in this invention, the silica fine powder raw material refers to a fine material mainly composed of silica, such as silica flower, fused silica, or quartz that has been pulverized into an ultrafine powder, with a specific surface area of ​​5 m². ２ This refers to silica with a specific surface area of ​​5 m² or more. As such silica fine powder raw materials, very high-purity silica produced industrially for its own purpose as silica flower, so-called white carbon, anhydrous or hydrated amorphous silica, evaporated silica, and relatively low-purity volatile silica obtained as a by-product can be used, but among these, if the specific surface area is 5 m² or more ２ Use highly active silica of 5 m² / g or higher. Such silica fine powder raw materials are highly active and highly reactive with magnesia, allowing for efficient formation of magnesium silicate bonds and the creation of a strong structure. In other words, the specific surface area of ​​the silica raw material is 5 m². ２ Below 1 / g, magnesium silicate bonding is insufficient, and sufficient strength cannot be obtained. In this invention, the upper limit of the specific surface area of ​​the silica fine powder raw material is not limited from the viewpoint of obtaining the effects of the present invention, however, the upper limit of the specific surface area of ​​industrially available silica fine powder raw materials is 400 m². ２ It is approximately / g. SiO in silica fine powder raw material ２ The content of is preferably 90% by mass or more, and impurities that are unavoidable to be mixed in during the manufacturing process of the silicate fine powder raw material are acceptable. Here, the specific surface area of ​​the refractory raw material can be determined using gas adsorption measurement methods such as the general BET specific surface area.

[0015] In the refractory composition of the present invention, the content of magnesia fine powder raw material in the refractory raw material formulation is 0.2 to 5% by mass. If the content of magnesia fine powder raw material is less than 0.2% by mass, the formation of magnesium silicate bonds will be insufficient, and sufficient strength cannot be obtained. On the other hand, if the content of magnesia fine powder raw material exceeds 5% by mass, the formation of magnesium hydroxide cannot be suppressed, and the above-mentioned problems will occur.

[0016] Furthermore, in the refractory composition of the present invention, the content of silica fine powder raw material in the refractory raw material blend is 0.2 to 15% by mass. If the silica fine powder raw material content is less than 0.2% by mass, the formation of magnesium silicate bonds will be insufficient, and sufficient strength cannot be obtained. On the other hand, if the silica fine powder raw material content exceeds 15% by mass, the particle size composition will be excessively fine, resulting in reduced fluidity and moldability, and low density and low strength.

[0017] Furthermore, one of the technical features of the present invention is that the ratio of the surface areas calculated from the specific surface area and content of these magnesia fine powder raw materials and siliceous fine powder raw materials, that is, the ratio of the surface area of ​​the silica fine powder raw material in the refractory raw material mixture to the surface area of ​​the magnesia fine powder raw material in the refractory raw material mixture (hereinafter referred to as the "S / M surface area ratio") is 1 or more. This S / M surface area ratio is expressed by the following formula. By setting this S / M surface area ratio to 1 or higher, the formation of magnesium hydroxide, a by-product in magnesium silicate-bonded refractory compositions, can be suppressed to the greatest extent possible.

[0018] In the refractory composition of the present invention, as described above, the refractory raw material blend contains 0.2 to 5% by mass of magnesia fine powder raw material and 0.2 to 15% by mass of silica fine powder raw material, with the remainder consisting of other refractory raw materials. In the present invention, the type of other refractory raw materials is not particularly limited, and general refractory raw materials can be used. For example, refractory aggregate raw materials such as electrofused alumina, sintered alumina, electrofused magnesia, sintered magnesia, fused silica, zircon, spinel, chamotte, and pyrophyllite, as well as metal raw materials or alloy raw materials such as aluminum and silicon. Since the refractory composition of the present invention utilizes magnesium silicate bonding, cement-based binders such as alumina cement and Portland cement do not need to be used in principle, but they can be used as auxiliary materials. However, in this case, the total content should be 1% by mass or less in proportion to 100% by mass of the refractory raw material blend, preferably 0.2% by mass or less.

[0019] In the refractory composition of the present invention, one or more of the alkali metal salts or ammonium salts of polycarboxylic acid, polyacrylic acid, or phosphoric acid can be added to the above-mentioned refractory raw material mixture in a total addition rate of 0.01 to 1% by mass. That is, the inventors have found that adding an appropriate amount of the above-mentioned alkali metal salt or ammonium salt to the above-mentioned refractory raw material mixture has the effect of suppressing the formation of magnesium hydroxide in the process of forming magnesium silicate bonds. Furthermore, although magnesia fine powder raw material and silica fine powder raw material have the property of coagulating violently when kneaded with water, this can be significantly suppressed, resulting in a substantial reduction in moisture content, improved workability, and increased strength through densification.

[0020] Furthermore, in the refractory composition of the present invention, a sugar compound can also be added to the above-mentioned refractory raw material mixture at an addition rate of 0.01 to 1% by mass. By adding an appropriate amount of sugar compound, the formation of magnesium hydroxide is suppressed by the chelating effect of the sugar, and further, strength can be improved as it acts as a temporary binder after drying. Here, in the present invention, "sugar compound" refers to a compound having a polyhydric alcohol structure, including glucose, sucrose, fructose, sorbitol, molasses, etc. That is, it includes a wide range of compounds mainly composed of carbohydrates, such as reducing sugars or their derivatives, oligosaccharides, sugar alcohols, naturally derived molasses, and sugar processed products.

[0021] Furthermore, in the refractory composition of the present invention, in addition to the alkali metal salts or ammonium salts and sugar compounds mentioned above, various additives such as detonation inhibitors and dispersants may be added as appropriate. Specific examples of detonation inhibitors include organic fibers and organic blowing agents. Specific examples of organic fibers include high-molecular-weight organic fibers such as vinylon (containing polyvinyl alcohol), rayon, polyester, nylon, polypropylene, and polyethylene. Although the alkali metal salts or ammonium salts mentioned above also act as dispersants, other dispersants may be used in the present invention. These additives are added to the refractory raw material mixture in the same way as the alkali metal salts or ammonium salts and sugar compounds mentioned above. The addition rate may be the same as that of a general refractory composition. In addition to the above-mentioned refractory raw material mixture, as well as the alkali metal salts or ammonium salts, sugar compounds, and various additives mentioned above, coarse grains with a particle size of 8 mm or more may also be used in the refractory composition of the present invention. These coarse grains play a role in preventing the propagation of cracks that occur in the matrix of the refractory structure.

[0022] The method for producing refractories using the refractory composition of the present invention may be the same as in the conventional method. For example, by adding an appropriate amount of water to the above-mentioned refractory raw material mixture and kneading it, then shaping it by press molding or pouring it into a casting mold, curing it, and then drying or heat treating it, various types of refractories (refractory construction bodies), such as shaped refractories like refractory bricks and unshaped refractories like pourable materials, can be obtained.

[0023] The present invention will be described in more detail below using examples. These examples are not intended to limit the scope of the present invention.

[0024] <Examples of Shaped Refractories> Test specimens of refractories obtained by adding 2 to 5% by mass of water to the refractory compositions shown in Table 1, kneading and molding, and then heat-treating at 150°C for 20 hours were used for each evaluation test. As other refractory raw materials, sintered alumina with a particle size between 0.074 mm and less than 5 mm was used.

[0025] For the evaluation of reactivity, the magnesium hydroxide content was determined by powder X-ray diffraction (external standard method). A content of 0% by mass was evaluated as ◎ (excellent), a content greater than 0% by mass but less than 1% by mass was evaluated as ○ (good), and a content of 1% or more by mass was evaluated as × (poor). For the evaluation of strength, the bending strength measured in a three-point bending test at room temperature was evaluated as ◎ (excellent) if it was greater than 3 MPa, ○ (good) if it was greater than 1 MPa but 3 MPa or less, and × (poor) if it was 1 MPa or less. For the overall evaluation, if both the reactivity and strength evaluations were ◎, it was evaluated as ◎ (excellent), if at least one evaluation was ○ and there were no × evaluations, it was evaluated as ○ (good), and if at least one evaluation was ×, it was evaluated as × (poor). ◎ (excellent) or ○ (good) was considered a pass.

[0026]

[0027] Examples 1 to 3 show different content levels of magnesia fine powder raw material in the refractory raw material formulations, but all are within the scope of the present invention and all exhibit appropriate reactivity and strength. In contrast, Comparative Example 1 is an example where the content level of magnesia fine powder raw material in the refractory raw material formulation is below the lower limit of the present invention, resulting in insufficient formation of magnesium silicate bonds and a lack of strength. On the other hand, Comparative Example 2 is an example where the content level of magnesia fine powder raw material in the refractory raw material formulation exceeds the upper limit of the present invention, resulting in failure to suppress the formation of magnesium hydroxide and a decrease in strength.

[0028] Examples 4 to 6 show different content levels of silica fine powder raw material in the refractory raw material formulations, but all are within the scope of the present invention and all exhibit appropriate reactivity and strength. In contrast, Comparative Example 3 is an example where the content level of silica fine powder raw material in the refractory raw material formulation is below the lower limit of the present invention, resulting in insufficient formation of magnesium silicate bonds and a lack of strength, as well as failure to suppress the formation of magnesium hydroxide. On the other hand, Comparative Example 4 is an example where the content level of silica fine powder raw material in the refractory raw material formulation exceeds the upper limit of the present invention, resulting in an excess of fine powder in the particle size composition, leading to low density and low strength.

[0029] Examples 7 to 9 show different specific surface areas of the magnesia fine powder raw material, but all are within the scope of the present invention and all exhibit appropriate reactivity and strength. In contrast, Comparative Example 5 is an example where the specific surface area of ​​the magnesia raw material is below the lower limit of the present invention, resulting in insufficient formation of magnesium silicate bonds and failure to exhibit strength. On the other hand, Comparative Example 6 is an example where the specific surface area of ​​the magnesia raw material exceeds the upper limit of the present invention, resulting in failure to suppress the formation of magnesium hydroxide and a decrease in strength.

[0030] Examples 10 and 11 show different specific surface areas of silica fine powder raw materials, but both fall within the scope of the present invention and exhibit appropriate reactivity and strength. In contrast, Comparative Example 7 is an example where the specific surface area of ​​the silica raw material falls below the lower limit of the present invention, resulting in insufficient formation of magnesium silicate bonds and a lack of strength, as well as failure to suppress the formation of magnesium hydroxide. Comparative Example 8 has an S / M surface area ratio of less than 1, which failed to suppress the formation of magnesium hydroxide and resulted in reduced strength.

[0031] <Examples of Shaped Refractories> Test specimens of refractories obtained by adding 6 to 8% by mass of water to the refractory compositions shown in Tables 2 and 3, kneading, molding, and then curing thoroughly, followed by demolding and drying at 150°C for 20 hours, were used for each evaluation test. As other refractory raw materials, sintered alumina with a particle size between 0.074 mm and less than 5 mm was used. The test methods for each evaluation test are as described above.

[0032]

[0033]

[0034] In Table 2, Examples 12 to 18 are examples in which one or more substances selected from polycarboxylic acid, polyacrylic acid, or alkali metal salts or ammonium salts of phosphoric acid were added to the refractory composition at an addition rate of 0.01 to 1% by mass. Specifically, in Examples 12 to 14, sodium polyacrylate was added, and in Examples 15 to 18, potassium polyacrylate, ammonium polyacrylate, sodium polycarboxylate, and sodium hexametaphosphate were added, respectively. All of these received an overall evaluation of ◎, showing excellent reactivity and strength. Example 19 is an example in which no additives were added, Example 20 is an example in which sodium hexametaphosphate was added at an addition rate of 2% by mass, and Example 21 is an example in which polyacrylic acid was added at an addition rate of 0.1% by mass. All of these received an overall evaluation of ○, showing appropriate reactivity and strength. From a comparison of Examples 12-18 and Examples 19-21, it can be said that in order to achieve both excellent reactivity and strength, it is effective to add one or more selected from polycarboxylic acids, polyacrylic acid, or alkali metal salts or ammonium salts of phosphoric acid at an addition rate of 0.01 to 1% by mass.

[0035] In Table 3, Examples 22 to 27 are examples in which a sugar compound was added to the refractory composition at an addition rate of 0.01 to 1% by mass. All of them received an overall evaluation of ◎, showing excellent reactivity and strength. Example 28 is an example in which no sugar compound was added, and Example 29 is an example in which a sugar compound was added at an addition rate of 2% by mass. Both of these received an overall evaluation of ○, showing moderate reactivity and strength. From the comparison between Examples 22 to 27 and Examples 19 to 21, it can be said that adding a sugar compound at an addition rate of 0.01 to 1% by mass is effective in achieving both excellent reactivity and strength.

Claims

1. Specific surface area of ​​1 to 25 m² ２ Magnesia raw material with a density of 0.2 to 5% by mass, and a specific surface area of ​​5 m². ２ A refractory composition comprising a refractory raw material compound as the main material, containing 0.2 to 15% by mass of silica raw material in a quantity of 1 / g or more, with the remainder being other refractory raw materials, wherein the ratio of the surface area of ​​the silica raw material in the refractory raw material compound to the surface area of ​​the magnesia raw material in the refractory raw material compound is 1 or more.

2. The fire-resistant composition according to claim 1, wherein one or more selected from polycarboxylic acid, polyacrylic acid, or alkali metal salts or ammonium salts of phosphoric acid are added to the fire-resistant raw material mixture in a total addition rate of 0.01 to 1% by mass.

3. The fire-resistant composition according to claim 1 or 2, wherein sugar compounds are added to the fire-resistant raw material mixture at a total addition rate of 0.01 to 1% by mass.

Images