JP2985106B2 - Reduction resistant magnesia clinker and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory magnesia clinker suitable for a refractory for a steelmaking furnace, particularly a magnesia carbon brick, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in the field of steelmaking, there has been an increasing tendency to rationalize operations such as upgrading and continuous casting of steel, increasing the temperature of converters and ladles, increasing the time of molten steel processing, or increasing the ladles. With the introduction of scouring methods, the refractories used in these are exposed to extremely severe conditions. Magnesia carbon bricks are widely used as refractories for steelmaking furnaces because they have excellent spalling resistance and slag erosion resistance and therefore have high durability in actual furnaces. However, as steelmaking conditions have become more stringent, magnesia carbon bricks of a quality that can withstand more severe conditions have been desired.

In general, when placed at high temperature together with magnesia carbon, the following reactions occur (s; solid, g; gas). MgO (s) + C (s) → Mg (g) ↑ + CO (g) ↑ Conventionally, it was thought that the wear of magnesia carbon bricks was mainly caused by erosion by molten slag. However, severer steelmaking conditions, especially operation The above reaction became not negligible with increasing temperature. In other words, it is pointed out that if these reactions proceed in magnesia carbon brick, the structure of magnesia, which is an aggregate, is deteriorated, and voids in the brick due to evaporation of magnesia are further promoted by slag erosion. . These reactions also cause a decrease in brick strength.

In order to suppress this reaction, magnesia
Various attempts have been made regarding the improvement of carbon bricks.
You. For example, in Japanese Patent Application Laid-Open No. 58-120567,
Gnesia Clinker Al_TwoO_ThreeCoated with fine powder
Forming spinel on the particle surface
Prevents evaporation of magnesia. Al_TwoO_Three
Attempts to add magnesia clinker to sinter
The purpose is to improve the digestibility and digestion resistance
You. For example, in Japanese Patent Application Laid-Open No. 3-177355,
_TwoO_ThreeTo the magnesia grain boundary by adding 1.5 to 15%
The clinker having formed a flannel is disclosed in
No. 1 discloses Al_TwoO _ThreeFrom 0.5 to 10%, and C
A clinker containing 0.5 to 5% of aO has been reported.
I have.

[0005]

However, in the method disclosed in Japanese Patent Application Laid-Open No. 58-120567, although the evaporation of MgO is suppressed, the basic property of magnesia, which is inherent in spinel, is a neutral refractory. Therefore, it is expected that the slag erosion resistance is significantly deteriorated. Also, JP-A-3-177355 and JP-A-Hei-3
No. 193,661 discloses a method using spinel or Al _2.
Forming an O ₃ —CaO-based compound at the magnesia grain boundary,
It improves slag erosion resistance and digestion resistance,
Considering the purpose and function of the invention, it has nothing to do with the invention. Further, the clinker specified in these patents cannot be expected to have the reduction resistance as an effect of the present invention. As described above, no attempt has been made to make the magnesia clinker itself less likely to react with carbon, and no example has been reported in which a remarkable effect has been recognized.

An object of the present invention is to provide a magnesia clinker which does not easily react with carbon at high temperatures without impairing the basic properties and high slag resistance inherent to magnesia, and a method for producing the same. .

[0007]

Means for Solving the Problems As a result of research on improvement of magnesia crystal itself, the present inventors have found that a certain amount of Al ₂ O ₃ is dissolved in the lattice of magnesia crystal to form a carbon solution at a high temperature. It has been found that the reaction with is significantly reduced. This method is completely different from the conventional method in that no other compound is interposed in the magnesia crystal and in the grain boundary. That is, reduction resistance was successfully imparted while maintaining the excellent properties inherent to magnesia. Furthermore, these manufacturing methods were established and the invention was completed.

That is, according to the present invention, (A) the composition comprises MgO
94% by weight or more, 0.2 to 5% by weight of Al ₂ O ₃ and 1.0% by weight or less of other components, (B) bulk density of 3.3 g / cm ³ or more, and apparent porosity of 3 % (C) at a temperature of 1600 ° C.
The reduction-resistant magnesia clinker is characterized in that at least 30% by weight of l ₂ O ₃ is dissolved in the magnesia crystal lattice.

Hereinafter, the present invention will be described in detail. Al ₂ O ₃ in the present invention should be in the range of 0.2 to 5 wt%. If the content of Al ₂ O ₃ is lower than 0.2% by weight, the amount of solid solution in magnesia becomes insufficient, and the reaction with carbon cannot be suppressed. If the content of Al ₂ O ₃ is more than 5% by weight, Al ₂ O ₃ mainly exists as spinel at the periclase grain boundary, and the slag resistance is significantly deteriorated. Furthermore, the present inventors have found for the first time that the grain boundaries of spinel and magnesia are vulnerable to reduction by carbon. Therefore, for the purpose of the present invention,
It is not preferable to contain a large amount of Al ₂ O ₃ . From the above, the content of Al ₂ O ₃ is 0.2 to 5% by weight, preferably 1.5 to 3.5% by weight.

In the present invention, other components must be not more than 1.0% by weight. Other components include CaO, SiO ₂ , Fe ₂ O ₃ , B ₂ O _{3 and the} like. In particular, one of the other components, CaO is Al ₂
It is known to react with O ₃ to form low melting compounds. By forming these compounds, the solid solution of Al ₂ O ₃ in magnesia crystals, which is a feature of the present invention, is inhibited. Furthermore, the present inventors have found that CaO promotes the reaction of magnesia carbon. Therefore C
The aO content is preferably 0.5% by weight or less, preferably 0.4% by weight or less, and more preferably 0.3% by weight or less. Since SiO ₂ also forms a low melting point compound like CaO, it is preferably 0.3% by weight or less, more preferably 0.2% by weight or less, in order to enhance slag erosion resistance. Fe ₂ O ₃ and B ₂ O ₃ are also preferably 0.1% by weight or less for the same reason as SiO ₂ .

However, the chemical composition is not limited to the range defined in the present invention.
Even if_TwoO_ThreeCaO and its
If the other impurity components are relatively large, Al_TwoO_Three
Forms compounds with these impurity components,
Sufficient amount of Al to shear crystal _TwoO_ThreeDoes not achieve solid solution
No. Further Al_TwoO_ThreeAre unevenly distributed in the clinker
The same applies to the case where Therefore, at a temperature of 1600 ° C
And the total Al contained in the clinker_TwoO_Three30 of them
% Or more must be dissolved in the magnesia crystal lattice
Is required, preferably at least 50% by weight, more preferably
Or more than 70% by weight. Al_TwoO_ThreeThe amount of solid solution
If less, spinel or Al_TwoO_ThreeAncestry
Reaction with carbon is promoted by interposing a compound
Is advanced. Thus, Al_TwoO_ThreeIn the magnesia crystal
Dissolution suppresses the reaction with carbon.
The reason is not yet clear, but the lattice constant of the magnesia crystal is
The decrease is related to the shorter interatomic distance
It is estimated that there is.

The bulk density of the magnesia clinker of the present invention is 3.3 g / cm ³ or more and apparent porosity is 3
% Or less. If the bulk density is lower than this or the apparent porosity is higher than this, the reaction with carbon proceeds and the evaporation of magnesia is accelerated. When the bulk density is further increased, the reaction with carbon is further suppressed. Therefore, the bulk density is preferably 3.35 g / cm ³ or more, and the apparent porosity is 2.5% or less, more preferably the bulk density is 2.5% or less. 3.4 g / cm ³ or more, and apparent porosity is 2% or less.

The average crystal diameter of the magnesia clinker of the present invention is preferably at least 40 μm. If it is 40 μm or less, the reduction resistance slightly decreases. However, when the average particle diameter is in the range of 40 μm or more, there is no significant correlation between the reduction resistance and the crystal particle diameter, and an unnecessarily large crystal diameter is meaningless from the viewpoint of reduction resistance. Unnecessarily large crystallization due to a high firing temperature or the like is not preferable because it causes an increase in cost. Another feature of the magnesia clinker of the present invention is that it is composed of uniform magnesia crystals having a uniform particle size.

The reduction-resistant magnesia clinker according to the invention
-The composition based on burning is 98.9% by weight or more of MgO,
And CaO 0.5% by weight or less, SiO_Two 0.3 weight
% Or less, other impurity components including 1.1% by weight or less,
Magnesium hydroxide or lightly burned magne
Al with an average particle size of 20 μm or less with respect to shear_TwoO _ThreeAh
Or Al_TwoO_ThreeAluminum compound
Is added and mixed, and then fired. What
In addition, the burning of the burning standard refers to a temperature of 1400 ° C. or more.

Here, magnesium hydroxide can be produced by reacting an aqueous solution containing magnesium such as seawater, bitter water, or brine with an alkali source such as lime milk. Light burned magnesia can be obtained by calcining magnesium hydroxide and has a specific surface area of 10 to 30 m ² / g.
Is preferable for improving sinterability. These specific surface areas can be easily achieved by calcining in a temperature range of 800 to 1000 ° C. As the aluminum compound, aluminum hydroxide, aluminum oxide, aluminum lactate, alumina sol and the like are used. Here, the average particle size of these aluminum compounds needs to be 20 μm or less, preferably 10 μm or less, and more preferably 5 μm or less. If the average particle size of the aluminum compound is larger than 20 μm, the structure becomes uneven and a sufficient amount of solid solution cannot be achieved. The addition and mixing of these aluminum compounds with magnesium hydroxide or lightly burned magnesia is preferably performed to be sufficiently uniform. Either dry mixing or wet mixing may be performed, but more uniform mixing with the magnesium hydroxide slurry is achieved. The powder obtained by adding and mixing these aluminum compounds is formed into a compact. As a molding machine, a briquette machine or the like can be used, and molding is performed at a molding pressure of 1 ton / cm ² or more, preferably 2 ton / cm ² or more. Here, a mixture of magnesium hydroxide and an aluminum compound is preferably calcined once before molding to obtain a high-density clinker. The calcination temperature at this time is 800 to 10 as in the above.
00 ° C. is preferable, and the specific surface area of the obtained powder is 10 to 3
It is preferably 0 m ² / g. The obtained molded body is
It is fired at a temperature of 1700 ° C. or more, preferably 1800 ° C. or more by a firing furnace such as a rotary kiln.

Various measuring methods in the present invention are as follows. (1) Chemical composition After finely pulverizing the sample to about 10 μm or less using a disk mill, 0.5 g is accurately measured. These are dissolved by heating with hydrochloric acid and diluted to 250 ml. If insolubles are generated during the dissolution of hydrochloric acid, a sample and a flux (a mixture of 4 g of anhydrous sodium carbonate and 2 g of anhydrous sodium tetraborate) are separately mixed and then placed in a platinum crucible and alkali-melted at 1000 ° C. After cooling, the mixture is dissolved by heating with hydrochloric acid and diluted to 250 ml to prepare a sample for analysis. These sample solutions were subjected to CaO, SiO ₂ , F
Each component of e ₂ O ₃ , Al ₂ O ₃ and B ₂ O ₃ is analyzed.
However, in the analysis of B ₂ O ₃ , only hydrochloric acid dissolution is used, and if insolubles are generated, the analysis is performed after filtration. Note that the MgO component was calculated by subtracting the sum of the oxide equivalent values of the respective components measured above from 100%. (2) Bulk density Gakushin method 2 proposed by the 124th Committee of the Japan Society for the Promotion of Science
The measurement was carried out according to “Method for measuring apparent porosity, apparent specific gravity and bulk density of magnesia clinker”. This will be described in detail below.

The sample clinker was crushed and 3.36
Choose a particle size of ~ 2.00 mm and accurately weigh about 15 g. (W ₁ g) The above sample was put in a basket made of wire mesh having an opening of 1 mm, a beaker containing the basket was placed in a desiccator, and then kept under reduced pressure for about 1 hour. Inject until until. After evacuation for another 20 minutes, the beaker is taken out of the desiccator and the basket containing the sample is weighed in white kerosene. (W ₂ g) Remove the sample from the basket, remove excess white kerosene adhering to the surface without excess and deficiency, and weigh it quickly. (W ₃ g) Calculated by the following equation.

[0018]

(Equation 1)

(3) Average crystal size The Gakushin method 3 proposed by the 124th Committee of the Japan Society for the Promotion of Science
The measurement was carried out according to "Measurement of size of periclase in magnesia clinker and description method thereof". That is, the sample is crushed and five particles having a size of about 7 mm are taken and embedded in resin. Next, these are polished and observed with a reflection microscope. At this time, three average portions are selected, and the length of the crystal in the up-down direction and the length in the left-right direction are measured for the observer for 50 or more crystals per one place. The average value was defined as the average crystal diameter. (4) Lattice constant at 1600 ° C. A sample clinker was pulverized to collect a portion of 3.36 to 2.00 mm. These were put in a platinum crucible and heated at 1600 ° C. for 1 hour in an electric furnace. At the same time as the completion of the heating, they were put into water and rapidly cooled, and then dried to obtain a sample for measuring lattice constant. After these were pulverized, the peak positions were precisely measured by powder X-ray diffraction. The peaks used for X-ray diffraction were (220), (311), and (40) of MgO.
0) and (420). A lattice constant was calculated from the obtained four plane intervals (d) using the least squares method.
Note that the apparatus was corrected using silicon powder having a purity of 99.999% as an internal standard. (5) Solid solution amount of Al ₂ O ₃ in magnesia at 1600 Calculated from the lattice constant of magnesia clinker. This will be described in detail below. A predetermined amount of commercially available aluminum oxide (alumina) powder having a purity of 99.99% is added to commercially available magnesium oxide powder having a purity of 99.9%, and the mixture is wet-mixed with ethanol in a ball mill as a solvent, filtered, dried and molded. And 1 hour at 1800 ° C. using an LPG-O ₂ furnace. The fired product was put into water at the same time as the firing, and then dried to obtain a sample for preparing a calibration curve. Finely crush these,
The lattice constant was measured by powder X-ray diffraction. The method of measuring the lattice constant here is the same as in (4). FIG. 1 shows the relationship between the obtained lattice constant and the weight percentage of Al ₂ O ₃ . In these samples, powder X-ray diffraction confirmed that all the Al ₂ O ₃ was in solid solution. Using FIG. 1 as a calibration curve, the amount of solid solution of Al ₂ O ₃ was calculated from the value of the lattice constant of the sample magnesia clinker. (6) Weight loss rate in the presence of carbon at 1600 ° C. As a measure of reduction resistance, the weight loss of magnesia clinker in the presence of carbon at 1600 ° C. was measured. Crush the magnesia clinker to 3.36 to 2.00 mm
Was collected in an amount of about 10 g. After precisely weighing these, commercially available high-purity graphite powder (purity 99.6%) 5
g, mixed in a carbon crucible and placed in an electric furnace
Heat treatment was performed at 1600 ° C. for 3 hours in an (argon) atmosphere. The heating and cooling rates were 5 ° C./min, and the Ar flow rate was 1
00 ml / min. After the heat treatment, the sample was separated from graphite by a sieve and weighed, and the weight loss rate was calculated by the following equation.

Weight reduction rate (%) = (W ₀ −W ₁ ) / W ₀ × 100 W ₀ : Weight of original sample W ₁ : Weight after heat treatment at 1600 ° C. in the presence of carbon

[0021]

The present invention will be specifically described below with reference to examples and comparative examples of the present invention.

[0022]

Examples 1-4, Comparative Examples 1 and 2 Seawater and calcium hydroxide slurry were reacted to obtain magnesium hydroxide powder having the chemical composition shown in Table 1 on a burning basis. The magnesium hydroxide of A in Table 1 was calcined in an electric furnace at 870 ° C. for 3 hours to obtain a magnesium oxide powder. At this time, the specific surface area measured by the BET method was 11.0 m ² / g. A predetermined amount of commercially available fine alumina having a purity of 99.6% by weight and an average particle diameter of 1 μm was added thereto, and then sufficiently mixed. After mixing, these powders were formed into a cylinder having a diameter of 30 mm and a height of 20 mm under a pressure of 2 ton / cm ² . The obtained molded body was fired in an LPG-O ₂ furnace at 180 ° C for 1 hour. Tables 2 and 3 show the chemical composition and physical properties of the sintered body obtained by cooling. FIG. 2 shows a powder X-ray diffraction pattern of the sample for lattice constant measurement (heat-treated) used in Example 3. From the powder X-ray diffraction pattern of FIG. 2, the constituent mineral is only magnesia, and no secondary mineral such as spinel is recognized. Therefore, at a temperature of 1600 ° C., Al ₂ O
It is clear that the solid solution of ₃ is sufficiently occurring.

[0023]

Examples 5 to 7 The same procedures as in Examples 1 to 4 were carried out except that the magnesium hydroxide of Table 1B was used, the calcination temperature was 900 ° C., and the amount of commercially available fine alumina was changed. Was. At this time, the specific surface area of the light-burned magnesia was 15.0 m ^2.
/ G. Table 2 shows the chemical composition and physical properties of the sintered body obtained by cooling.

[0024]

Comparative Example 3 Firing was performed under the conditions of Examples 5 to 7 without adding alumina powder. Table 3 shows the chemical composition and physical properties of the sintered body obtained by cooling.

[0025]

Comparative Example 4 The same procedure as in Example 3 was carried out except that the calcination temperature was 950 ° C. using the magnesium hydroxide of Table C. At this time, the specific surface area of lightly burned magnesia was 14.2.
m ² / g. Table 3 shows the chemical composition and physical properties of the sintered body obtained by cooling.

[0026]

Comparative Example 5 Purity 99.6% by weight, average particle diameter 50 μm
Example 1 except that 3% by weight of commercially available alumina was added and mixed.
4 was performed under the same conditions. Table 4 shows the chemical composition and physical properties of the sintered body obtained by cooling.

[0027]

Example 8 The same procedure as in Comparative Example 5 was carried out except that the commercially available alumina having a purity of 99.6% by weight and an average particle diameter of 50 μm used in Comparative Example 5 was pulverized using a ball mill and then added and mixed. The average particle size of the alumina added at this time was 12 μm.
m. Table 4 shows the chemical composition and physical properties of the sintered body obtained by cooling.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

The reduction-resistant magnesia clinker of the present invention has such a characteristic that it does not easily react with carbon at high temperatures, which has never been seen before. This improves properties that have been considered inevitable in magnesia, and is expected to be applied in various fields. In particular, magnesia carbon bricks using the magnesia clinker of the present invention can reduce the reaction between magnesia and carbon in bricks, which has been regarded as a problem in the past, contribute to improvement in durability and use at higher temperatures. It is possible. Furthermore, the reduction-resistant magnesia clinker of the present invention is manufactured by a relatively simple method of dissolving alumina in a solid solution, and is not industrially excellent because it does not involve a significant increase in cost.

[Brief description of the drawings]

FIG. 1 shows the amount of solid solution of Al ₂ O ₃ of the present invention and magnesia 1
5 is a graph showing lattice constants at 600 ° C., which is used when calculating the amount of Al ₂ O ₃ dissolved in a sample clinker.

FIG. 2 is a powder X-ray diffraction pattern of a sample for lattice constant measurement of Example 3 of the present invention.

[Explanation of symbols]

1 diffraction peak of MgO (111) 2 diffraction peak of MgO (200) Kβ ₁ 3 diffraction peak of MgO (200) 4 diffraction peak of MgO (220) Kβ ₁ 5 diffraction peak of MgO (220) 6 diffraction peak of MgO (311) Diffraction peak 7 Diffraction peak of MgO (222)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-103936 (JP, A) JP-A-3-193661 (JP, A) JP-A-58-120568 (JP, A) JP-A-61-1986 261243 (JP, A) JP-A-60-96570 (JP, A) JP-A-2-180746 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/04 C01F 5 / 02

Claims (2)

(57) [Claims] 1. The composition (A) has a composition of 94% by weight or more of MgO and 0.2 to 5% by weight of Al ₂ O ₃ and 1.0% by weight or less, and (B) a bulk density of 3. 3 g / cm ³ or more, apparent porosity of 3% or less; (C) At a temperature of 1600 ° C., the above component Al ₂ O
_3. A reduction-resistant magnesia clinker, characterized in that at least 30% by weight of ₃ is dissolved in a lattice of magnesia crystals. 2. An average particle size of 20 μm or less with respect to magnesium hydroxide or lightly burned magnesia having a composition based on a burning standard of 98.9% by weight or more of MgO and 1.1% by weight or less of other impurity components. A method for producing a reduction-resistant magnesia clinker, which comprises adding and mixing Al ₂ O ₃ or an aluminum compound which is thermally decomposed into Al ₂ O ₃ , followed by firing.