JP2013053052A - Castable refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a castable refractory by specifying physical properties of silica fine powder raw material with high slaking inhibiting effect of a magnesia raw material while having excellent slaking resistance.SOLUTION: The castable refractory contains the magnesia raw material, the silica fine powder raw material, and a binder and additive water. The silica fine powder raw material has a specific surface area of ≥15 (m/g) and ≤50 (m/g), and has dispersibility in which the viscosity of a kneaded product by kneading the silica fine powder, the binder, and the additive water by the mass ratio of 1:1:3 reaches ≤1.2 (Pa s).

Description

  The present invention mainly relates to a castable refractory for constructing a side wall of a molten steel pan.

  In recent years, the amount of castable refractories used for the side walls of molten steel pans has been increasing year by year because of the simplification and labor saving of refractory construction.

  In order to improve the steel quality, the operation during the use of the ladle is becoming severe. For this reason, castable refractories are required to satisfy the needs for durability (melting resistance, thermal shock resistance). Furthermore, castable refractories are also required to meet the needs of reducing furnace material costs and improving productivity. In order to meet these needs, castable refractories have improved durability.

  At present, castable refractories using alumina-magnesia are widely used as castable refractories for molten steel ladle side walls.

However, castable refractories using alumina-magnesia may cause pulverization and destruction of the structure during the drying process. As a mechanism by which the construction body breaks, it is generally known that the vapor pressure inside the construction body becomes high during drying, and digestion of magnesia accompanied by the volume expansion of the formula (1) proceeds.
MgO + H ₂ O → Mg (OH) ₂ (1)

  Regarding the digestion suppression of magnesia, it is considered as an important issue when using castable refractories using alumina-magnesia, and various studies have been conducted. For example, Non-Patent Document 1 discloses that the addition of a siliceous fine powder raw material has an effect of inhibiting magnesia digestion. Specifically, it is disclosed that a hydrous silicate is produced on the surface of magnesia, thereby having an effect of inhibiting digestion of magnesia.

Samukawa et al., "Digestion Phenomena of Magnesia-Containing Castables" Refractory, 40 [5] 1988 p300-302.

  As described above, it is known that the addition of a siliceous fine powder material has an effect of inhibiting digestion of the magnesia material. For this reason, it is important to obtain knowledge about how the physical properties of the siliceous fine powder material affect the digestion inhibitory effect of the magnesia raw material in order to realize a castable refractory with excellent digestion resistance.

  However, the above-mentioned document does not describe how the physical properties of the siliceous fine powder material affect the digestion inhibitory effect of the magnesia material.

  The subject of this invention is specifying the physical property of the siliceous fine powder raw material with the high digestive suppression effect of a magnesia raw material, and realizing a castable refractory excellent in digestion resistance.

The castable refractory of the present invention is a castable refractory containing a magnesia raw material, a siliceous fine powder raw material, a binder and added water, and the siliceous fine powder raw material is 15 (m ² / g) or more and 50 (m ² / G) The viscosity of a kneaded material having a specific surface area of not more than 1 and kneading the siliceous fine powder raw material, the binder and the added water at a mass ratio of 1: 1: 3 is 1.2 (Pa · s) or less. It has the dispersibility which becomes.

  According to the present invention, by specifying the physical properties of the siliceous fine powder raw material having a high digestive suppression effect of the magnesia raw material, specifically, the specific surface area and dispersibility (viscosity value), the castable refractory excellent in digestion resistance Can be realized.

It is a figure which shows the result of X-ray diffraction. It is a figure which shows the result of TG measurement. It is a figure which shows the relationship between the CaO density | concentration (mass%) in a silica, and a viscosity value.

  The castable refractory of the present invention is a general cement castable or low cement castable in which alumina cement is mainly used as a magnesia raw material, a siliceous fine powder raw material, and a binder.

  As the magnesia material, known magnesia materials such as electrofused magnesia clinker, sintered magnesia clinker, natural magnesia clinker can be used alone or synthesized with these materials, or magnesia / alumina spinel, etc., preferably A magnesia material can be used alone.

  As the siliceous fine powder raw material, amorphous silica can be used.

  As the binder, alumina cement is mainly used, and hydraulic alumina or the like may be used in combination with the alumina cement.

  The castable refractory of the present invention can contain a calcia raw material, a zirconia raw material, and an explosion prevention agent in addition to the above-described magnesia raw material, siliceous fine powder raw material and binder. Moreover, it is also possible to use a digestion inhibitor together.

  The added water is added in an amount of about 3 to 20% by mass with respect to the total amount of 100% by mass of the mixture.

  In the castable refractory of the present invention, the specific surface area and dispersibility (viscosity value) are selected as the physical properties of the siliceous fine powder raw material having a high digestive suppression effect of the magnesia raw material in order to further enhance the digestive inhibitory effect of the magnesia raw material Identify. Details will be described later.

  Hereinafter, specific embodiments will be described.

  Table 1 is a table showing the chemical composition and physical properties of silica as a siliceous fine powder material added to the castable refractory. Physical property values indicate specific surface area and dispersibility (viscosity value). The specific surface area and the viscosity value will be described later. A to J indicate silicas having different chemical compositions (brands).

  Table 2 is a table showing the evaluation results of castable refractories to which silicas A to J shown in Table 1 are added.

  The alphabet letters “A” to “J” of the castable refractories 1A to 1J are associated with the codes “A” to “J” of the added silica. For example, the castable refractory to which silica A is added is 1A. The castable refractory 1K indicates a castable refractory without addition of silica.

  The castable refractories 1A to 1J include 40% by mass of the total amount of sintered alumina and alumina cement as a binder, 60% by mass of magnesia as a magnesia material, and the total amount of sintered alumina, alumina cement, and magnesia is 100. It is a composition in which 6% by mass of silica is added as an outer shell with respect to mass%. The castable refractory 1K is a composition containing 40% by mass of the total amount of sintered alumina and alumina cement and 60% by mass of magnesia. Magnesia having a purity of 95% or more and an average particle size of about 10 μm was used.

  Next, the evaluation result will be described.

  The evaluation shown in Table 2 was performed on the castable refractories 1A to 1K subjected to autoclave treatment.

  In the autoclave treatment, water is added to the above-mentioned composition (after adding 17% by mass of water as an outer shell to 100% by mass of the combined amount of sintered alumina, alumina cement and magnesia), the mixture is kneaded, and then the frame is added. And cured at 20 ° C. for 24 hours, and by applying a temperature (152 ° C.) and a pressure (0.5 MPa) for 3 hours in an autograve.

  The linear change rate was evaluated in order to measure the volume expansion amount by digestion reaction of magnesia. Specifically, the linear change rate evaluated the linear change rate of the castable refractories 1A to 1K before and after the autoclave treatment.

  For the cracks, the appearance of the castable refractories 1A to 1K after the auto-graving treatment was visually observed, and the relative evaluation was performed in three stages: no crack, fine crack, and large crack.

  As shown in Table 2, when the linear change rate was + 2.0% or less, there was no significant change in appearance and no cracks were confirmed. For this reason, it can be said that the linear change rate of the castable refractory is preferably + 2.0% or less.

Powder X-ray diffraction evaluated the peak size of Mg (OH) ₂ (hereinafter referred to as brucite). The magnitude of the peak was evaluated relative to four levels: none, small, medium and large.

  FIG. 1 is a diagram showing an example of a result of powder X-ray diffraction of a castable refractory after autoclaving. B peak indicates brucite produced by magnesia digestion reaction.

  The castable refractory with silica added (1A, 1C, 1F, 1G, 1H) has a smaller peak of brucite than the castable refractory without silica addition 1K. That is, if silica was added, it was confirmed that the magnesia digestion inhibitory effect worked. In addition, it was confirmed that the castable refractories 1A, 1C, 1F, 1G, and 1H to which silica was added tended to have a higher linear change rate and larger cracks as the peak of brucite increased.

  However, the amount of brucite produced cannot be clearly evaluated by powder X-ray diffraction. For this reason, the castable refractory after the autoclave treatment was subjected to TG measurement (thermogravimetric measurement), and the amount of brucite produced was evaluated. And based on the result of TG measurement, the relationship between the amount of brucite generation, the line change rate, and cracks was evaluated.

  The larger the peak of brucite obtained by TG measurement, the larger the amount of brucite produced. The magnitude of the peak was evaluated relative to four levels: none, small, medium and large.

  FIG. 2 is a diagram showing an example of a result of TG measurement of the castable refractory after the autoclave treatment.

  In FIG. 2, the weight loss peak around 400 ° C. is due to dehydration (evaporation of water) of brucite. As shown in FIG. 2, the results were obtained in the order of 1K> 1H> 1G> 1F> 1C> 1A in the amount of brucite produced.

From this result, it was confirmed that the greater the amount of brucite produced, the higher the line change rate and the larger the cracks. In FIG. 2, AH ₃ represents Al ₂ O ₃ .3H ₂ O, and C ₃ AH ₆ represents 3CaO.Al ₂ O ₃ .6H ₂ O.

  From the results of the above-mentioned powder X-ray diffraction and TG measurement, it was confirmed that when silica is added to the castable refractory, the expansion of the castable refractory is suppressed and the formation of brucite is also suppressed. In addition, it was confirmed that as the amount of brucite generated increased, the expansion of the castable refractory, that is, the linear change rate increased, and the cracks also increased. If this result is due to the reaction between magnesia and silica, it is considered that the reactivity of silica greatly affects the digestion inhibiting effect of magnesia. In order to confirm the reactivity of silica, the specific surface areas of silica A to J were measured.

  The specific surface area was measured by a nitrogen adsorption method. Since the technique for measuring the specific surface area by the nitrogen adsorption method is a known technique, the description thereof is omitted here.

  In Table 1, the measurement result of the specific surface area of silica AJ is shown.

When the specific surface area of silica is less than 15 (m ² / g) based on the evaluation results of specific surface area, linear change rate, and crack, the linear change of castable refractories to which silica is added (for example, castable refractories 1G, 1H) The rate exceeded + 2.0%, and cracks (microcracks or large cracks) were confirmed. Moreover, about the castable refractories 1A-C using silica A-C, when the specific surface area of the used silica became large, it was confirmed that the value of a linear change rate becomes small. This is because, as the specific surface area of silica increases, the reactivity between silica and magnesia increases, so the proportion of magnesia that reacts with water decreases, the digestion suppression effect of magnesia increases, and the expansion reaction of magnesia decreases. It is considered a thing.

  However, although the silica F has a larger specific surface area than the silicas B and C, the value of the linear change rate of the castable refractories F is larger than that of the castable refractories B and C, and microcracks were also confirmed. This is considered to be because even if the specific surface area is large, if the silica is present in an aggregated state without being dispersed, the reactivity of the silica may be apparently lowered.

  Therefore, the dispersibility of silica was measured. The dispersibility of silica is measured by generating a slurry-like kneaded material kneaded at a ratio of silica: binder: water = 1: 1: 3, and measuring the viscosity of the kneaded material with a B-type viscometer. It was. As the binder, alumina cement was applied.

  In the viscosity measurement, for example, when the silica is dispersed in the kneaded product, the viscosity of the kneaded product is low, and thus the viscosity value is low. On the other hand, when the silica is not dispersed in the kneaded product, the viscosity of the kneaded product is high, and thus the viscosity value is high.

  In Table 1, the measurement result of the viscosity of silica AJ is shown.

  In each case where alumina cement or hydraulic alumina is used as the binder, the kneaded material containing silica F has a viscosity value (1.30 Pa · s) higher than the viscosity value of the kneaded material containing silica B or silica C. Indicated. That is, in the kneaded material containing silica F, the silica was present in an agglomerated state without being dispersed in the kneaded material, compared to the kneaded material containing silica B or silica C. This result shows that silica F cannot react efficiently with magnesia, and the digestion inhibitory effect of magnesia did not work efficiently. For this reason, it is considered that the linear change rate of the castable refractory 1F is higher than that of the castable refractory 1B or 1C (+ 2.1%), and a micro crack is generated.

  Also, from the viscosity value of the kneaded product, the linear change rate of the castable refractory, and the evaluation results of the crack, when the viscosity value of the kneaded product is 1.2 (Pa · s) or less, the linear change rate of the castable refractory is +2. It was 0% or less, and no crack was observed.

Here, silica J has a specific surface area of 60 (m ² / g), and from this point, an improvement in reactivity is expected, but the kneaded product has a high viscosity value of 2.10 Pa · s and is castable. The line change rate of J was as high as + 5.5%, and a large crack was generated. This is probably because the specific surface area was too large and the dispersibility was lowered. As described above, when the specific surface area is increased, the dispersibility of the silica is lowered. However, as can be seen from the result of the silica E, a predetermined dispersibility can be ensured until the specific surface area is 50 (m ² / g).

From the above evaluation results of specific surface area and dispersibility (viscosity value), the specific surface area of silica is 15 (m ² / g) or more and 50 (m ² / g) or less, and the viscosity value of the kneaded product is 1. 2 (Pa · s) or less is required.

  FIG. 3 shows the relationship between the CaO concentration (mass%) in silica and the viscosity value. “A” to “F” in FIG. 3 correspond to silica “A” to “F” in Table 1, respectively.

The concentration of CaO was 0.27% by mass or less for silicas A to E, and 0.28% by mass for silica F. Silicas A to E are 15 (m ² / g) or more and 50 (m ² / g) or less, and the viscosity value of each kneaded product of silicas A to E is 1.2 (Pa · s) or less. Since the castables 1A to 1E do not cause cracks, the CaO concentration in silica is preferably 0.27% by mass or less. Further, when the CaO concentration is 0.28% by mass or more, the viscosity value exceeds 1.2 (Pa · s) because the cohesiveness of silica increases due to the action of Ca ²⁺ (calcium ions), and the dispersion of silica This is thought to be due to a decrease in sex.

  In the above-described embodiment, a composition in which 6% by mass of silica is added as an outer shell to a total amount of 100% by mass of sintered alumina, alumina cement, and magnesia, that is, the addition amount of silica is used as the addition amount of magnesia. In contrast, although the mass ratio is 0.1, the present invention is not limited to this. For example, the addition amount of silica may be added so that the mass ratio is 0.01 or more and 1.0 or less with respect to the addition amount of magnesia. If it is the addition amount of the silica of this range, the magnesia digestion inhibitory effect can be acquired. As the amount of magnesia added to the castable refractory increases, the influence of digestion of magnesia on the castable refractory increases. Therefore, the amount of silica added is preferably determined according to the amount of magnesia added. Further, when the addition amount of silica with respect to the addition amount of magnesia is 0.03 or more in mass ratio, a higher digestion suppression effect of magnesia is obtained, so the addition amount of silica is 0 by mass ratio with respect to the addition amount of magnesia. More preferably, it is 0.03 or more and 1.0 or less.

Claims (3)

A castable refractory containing a magnesia raw material, a siliceous fine powder raw material, a binder and added water,
The siliceous fine powder raw material has a specific surface area of 15 (m ² / g) or more and 50 (m ² / g) or less, and the siliceous fine powder raw material, the binder and the added water are 1: 1: 3. A castable refractory having dispersibility in which the viscosity of the kneaded material kneaded at a mass ratio is 1.2 (Pa · s) or less. The siliceous fine powder raw material is
The castable refractory according to claim 1, wherein the CaO content is 0.27% by mass or less.   The castable refractory according to claim 1 or 2, wherein a linear change rate before and after the autoclave treatment is + 2.0% or less.

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