JP3012260B2 - High purity, coarse crystal sintered magnesia clinker and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-purity, coarse-crystal sintered magnesia clinker and a method for producing the same. More specifically, the present invention relates to a sintered magnesia clinker suitable for a refractory raw material for steel making, such as a magnesia-carbon refractory and a magnesia-chromium refractory, and a method for producing the same.

(Prior Art) With the remarkable progress of steelmaking technology, refractories are required to be used under increasingly severe conditions. Magnesia refractories, which are typical basic refractories, have the advantage of high slag erosion resistance and high hot strength due to the high melting point of periclase, but also have high spalling resistance due to their large coefficient of thermal expansion. It has a drawback that it is inferior in properties.

Therefore, in order to improve the spall resistance, use in combination with graphite and chromium ore, ie, magnesia-carbon (MgO-C) refractories and magnesia-
Chromium is used as (MgO-Cr ₂ O ₃₎ refractory.

In MgO-C refractories, slag is believed to preferentially erode not from the graphite part but from the magnesia clinker part, especially from the aggregated periclase grain boundaries of the flux and pores within the clinker. Therefore Mg
As a magnesia raw material for an OC refractory, a clinker having a low impurity, a high grade, a high bulk density and a large periclase crystal is required. This is why MgO-C refractories using electrofused magnesia are often used in furnaces or parts with severe operation. Also in MgO-Cr ₂ O ₃ refractory, with the severe reduction of operation of various steelmaking furnaces, are required to be large in strength and erosion resistance at high temperatures, the use ratio of the fused products is increasing. However fused magnesia is expensive, therefore as magnesia raw material currently _{MgO-C, MgO-Cr 2} O 3 refractory, and economic consideration in view by the combination of sintered magnesia clinker and electro-fused magnesia is made I have.

(Problems to be Solved by the Invention) Magnesia clinker used as a raw material for MgO-C refractories is required to have a high bulk density and a large periclase crystal grain size. Also of high quality is required as MgO-Cr ₂ O ₃ refractory. However, in the conventional sintered magnesia clinker, the presence of impurities and pores is not performed, the growth of periclase crystals is inhibited, and it is difficult to significantly increase the bulk density.

Also, conventionally, various mineralizers have been added to improve sinterability, but when these are added to low-grade magnesium hydroxide to produce a sintered magnesia clinker, an improvement in bulk density is observed. However, the mineralizer reacts with the impurities to form a flux, which intervenes at the periclase crystal grain boundaries, and thus does not contribute to increasing the size of the periclase crystal. In addition, when a mineralizer is added to high-grade magnesium hydroxide, this addition cannot be said to be effective, but rather decreases the erosion resistance due to aggregation of the flux component due to the increase in the flux amount due to the additive. There is concern.

However, when high-purity Cr ₂ O ₃ is added as a mineralizer to high-grade magnesium hydroxide, the amount of flux generated is small because both materials use less impurities, and the Cr ₂ O 3
_The authors and others have found that the solid solution ₃ in periclase crystals promotes direct bonding of periclase crystals and increases periclase crystals.

Therefore, the present invention provides high-grade magnesium hydroxide and magnesium hydroxide having excellent slag wettability by adding Cr ₂ O ₃ as a raw material of MgO—C and MgO—Cr ₂ O ₃ refractories, and having few impurities. By adding Cr, the amount of reaction with impurities of Cr ₂ O ₃ is kept low, most of the Cr ₂ O ₃ is dissolved in periclase crystals, and the bulk density is increased without increasing the amount of flux. To provide a coarse, high-grade magnesia clinker.

(Means for Solving the Problems) The present invention has been researched and developed in view of the above problems.

That is, the present invention relates to
Containing ₂ O ₃ , the content of Cr ₂ O ₃ is 0.4-6.5% by weight and MgO
And the content of components other than Cr ₂ O ₃ is 1.0% by weight or less, the average grain size of periclase is 60 μm or more, and the number of periclase crystals having a particle size of 150 μm or more is the total number of particles of the crystal. Is a sintered magnesia clinker characterized by at least 10%.

Sintered magnesia clinker of the present invention, expressed in terms of weight percent on the _{oxide, Cr 2 O 3 0.40~6.5% MgO} , Cr 2 O 3 other components 1.0% of the chemical composition, and more preferably, MgO 93.0% or more , CaO 0.50% or less, B ₂ O ₃ 0.10% or less, Cr ₂ O ₃ 0.40 to 6.5% chemical composition, more preferably MgO 93.1% or more, CaO 0.30% or less, B ₂ O ₃ 0.05% or less, Cr ₂ O _3. Has a chemical composition of 0.40-6.5%.

The sintered magnesia clinker of the preferred chemical composition usually has a bulk density of at least 3.40 g / cm ³ and a particle size of 150 μm.
The number of particles of the above periclase crystal accounts for at least 12% of all the particles of the crystal. The more preferred sintered magnesia clinker usually has a bulk density of at least 3.45 g / cm ³ and an average crystal grain size of periclase of 80 μm or more, and the number of particles of periclase crystals having a particle size of 150 μm or more is the crystal. Account for at least 20% of the total particles.

Particularly preferred sintered magnesia clinker of the present invention is at least have a bulk density of 3.48 g / cm ³ and an average grain diameter of periclase 100μm or more, and a particle size 1
The number of particles of periclase crystals of 50 μm or more accounts for at least 27% of the total particles of the crystals.

Regarding the form of existence of Cr ₂ O ₃ , the contained Cr ₂ O ₃ is almost completely dissolved in periclase crystals.

According to the present invention, the above-mentioned sintered magnesia clinker according to the present invention is a magnesium hydroxide or magnesium oxide having the following composition: 99.0% or more of MgO, 0.50% or less of CaO, 0.15% or less of B ₂ O ₃ , based on a standard value of ignition. And a chromium compound, and the resulting mixture is subjected to pressure molding, followed by firing.

The above-mentioned magnesium hydroxide or magnesium oxide preferably has the following composition: 99.4% or more of MgO, 0.30% or less of CaO, and 0.05% or less of B ₂ O _{3 on} a burning reference value. As the magnesium hydroxide and magnesium oxide, magnesium hydroxide obtained by adding an alkaline material such as lime milk to seawater containing magnesium and a calcined product thereof are preferably used.

Further, as the chromium compound as a Cr ₂ O ₃ raw material, chromium oxide powder, potassium dichromate, or the like is suitably used. These are used as a powder or, in the case of a water-soluble substance such as potassium dichromate, as an aqueous solution.
As the Cr ₂ O ₃ raw material, it is desirable to use a raw material with less undesired substances. When a powdery raw material such as chromium oxide is used, one having an average particle size of several μm or less is preferably used so that a sufficiently uniform mixing with the magnesia raw material can be achieved.

The mixing of the Cr ₂ O ₃ raw material and magnesium hydroxide or the like is preferably performed by using magnesium hydroxide as a slurry so as to achieve uniform mixing with the Cr ₂ O ₃ raw material.

Further, the mixing of the Cr ₂ O ₃ raw material and the magnesium oxide is preferably performed by using both as a powder.

The amount of chromium material used depends on the clinker's Cr ₂ O ₃ content.
It should be in the range of 0.4-6.5% by weight. When the Cr ₂ O ₃ content is 0.4% by weight or less, the effect of the added chromium compound is small. When the Cr ₂ O ₃ content is 6.5% by weight or more, MgCr ₂ O ₃ is used in addition to Cr ₂ O ₃ which is dissolved in periclase crystals. Partially precipitates as ₃ (picrochromite), and the amount of flux increases against the object of the present invention. The resulting mixture is then pressed and, if necessary, dried or calcined.

Drying is at a temperature of 80 to 300 ° C, and calcining is at a temperature of 800 to 1200 ° C
It is preferable to carry out in.

Press molding, these mixtures, dried or calcined,
For example, it is molded at a molding pressure of 1 t / cm ² or more, preferably 2 t / cm ² or more.

Furthermore, firing is performed, for example, by a rotary kiln at a temperature.
It is carried out at 1800 ° C. or higher, preferably at 1900 ° C. or higher.

Thus, according to the present invention, a sintered magnesia clinker as described above is manufactured by the above manufacturing method. That is, in the magnesia clinker thus obtained, most of the added Cr ₂ O ₃ component is solid-dissolved in the periclase crystal without aggregating at the periclase crystal grain boundary part (matrix part). In the periclase crystal, direct bonding between crystals is promoted, and the crystal is coarsened.
The bulk density has also improved.

Periclase average crystal grain size of the entire clinker is 60μ
m or more, preferably 80 μm or more, more preferably
Have at least 100 μm. Furthermore, the ratio of periclase crystals having a size of 150 μm or more in the entire clinker crystals is
10% or more, preferably 12% or more, more preferably
It accounts for at least 20%, particularly preferably at least 27%.

The bulk density of the clinker is preferably 3.40 g / cm ³ or more, more preferably 3.45 g / cm ³ or more, particularly preferably
3.48 g / cm ³ or more.

When the clinker of the present invention is used for producing magnesia-carbon refractories or magnesia-chromium refractories,
It is expected that a refractory exhibiting very high slag erosion resistance will be obtained by its direct connection of bulk density and periclase crystals. Therefore, the clinker of the present invention is expected to replace expensive electrofused products.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by the examples.

(Chemical composition) The measurement was carried out in accordance with the “JSPS Method for Chemical Analysis of Magnesia Clinker” (Refer to the Refractory Handbook, 1981) determined by the Society for the Promotion of Science, 124th Committee, Test Methods Subcommittee.

(Bulk density (bulk specific gravity)) “A method for measuring apparent porosity, apparent specific gravity and bulk specific gravity of magnesia clinker” determined by the Society for the Promotion of Science, 124th Committee, Test Methods Subcommittee (1981 edition)
It was determined from the following formula according to the refractory notebook).

W ₁ : Dry weight of clinker (g) W ₂ : Weight of white kerosene-saturated sample in white kerosene (g) W ₃ : Weight of white kerosene-saturated sample (g) S: White kerosene at measurement temperature Specific gravity (g / cm ³ ) (Periclase average crystal grain size) According to the Fullman method (Journal of Metals, 447, 1953),
The grain size of each crystal on the photograph of the polished surface was all read (50 or more), and the average value was multiplied by 1.57 to obtain the average value of the periclase crystal grain size. Further, in order to show the distribution of the crystal grain size, the ratio of the particles occupying 150 μm or more and the ratio of the particles occupying 200 μm or more were determined as the ratio of the crystals.

MgO 99.5 wt% in Example -1 burning reference value, CaO 0.20 wt%, B ₂ O ₃
To a magnesium hydroxide slurry having 0.02% by weight, C
Using chromium oxide having an average particle size of 3.5 μm and a purity of 98.9% by weight of Cr ₂ O ₃ as a source of r ₂ O _{3, the} content of Cr ₂ O ₃ was 1.5 as a standard value for burning.
% By weight, and sufficiently mixed and stirred.
After dewatering and drying this mixed slurry, the temperature is set to 1000 in an electric furnace.
C. for 1 hour and calcined. This calcined product is subjected to a molding pressure of 2t.
/ After forming a cylindrical pellet with cm ^2, crushed, particle size 1
A 2 mm molded crushed product was obtained. Further, it was formed into a cylindrical pellet of φ20 × H20 mm at a molding pressure of 6 t / cm ² . This molded product was sintered at a temperature of 200 ° C. for 30 minutes using an oxygen-propane furnace.

Table 1 shows the chemical composition, apparent porosity and bulk density of the obtained sintered body, and the distribution of the average crystal grain size and the crystal grain size of periclase. FIG. 1 shows the X-ray powder diffraction pattern of the sintered body, FIG. 2 shows a reflection micrograph of the sintered body, and FIG. 3 shows an EPMA photograph.

MgO 99.5 wt% in Example -2 burning reference value, CaO 0.20 wt%, B ₂ O ₃
To a magnesium hydroxide slurry having 0.02% by weight, C
Using chromium oxide having an average particle size of 3.5 μm and a purity of 98.9% by weight of Cr ₂ O ₃ as a source of r ₂ O _{3, the} content of Cr ₂ O ₃ was 1.5 as a standard value for burning.
% By weight, and sufficiently mixed and stirred.
After dewatering this mixed slurry, it was calcined at a temperature of 1000 ° C. for 1 hour. This calcined product was formed into almond-like pellets at a molding pressure of 2 t / cm ² . This molded product is heated in a rotary kiln
Sintered at 2000 ° C.

Table 2 shows the chemical composition, apparent porosity and bulk density of the obtained sintered body, as well as the distribution of the average crystal grain size and the crystal grain size of periclase.

[Brief description of the drawings]

FIG. 1 is an X-ray powder diffraction diagram for one example of the magnesia clinker of the present invention. FIG. 2 is a reflection micrograph showing the crystal grain structure of one example of the magnesia clinker of the present invention. FIG. 3 is an X-ray (EPMA photograph) of one example of the magnesia clinker of the present invention. FIG. 3 (A) is a secondary electrophotograph, FIG. 3 (B) is an Mg Kα-X-ray image, and FIG.
(A) is a Si Kα-X-ray image and (E) is a Cr Kα-X-ray image.

Continuation of the front page (56) References JP-A-61-201657 (JP, A) JP-A-60-96571 (JP, A) JP-A-61-83654 (JP, A) JP-A-62-91460 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/00-35/22

Claims (9)

(57) [Claims] [Claim 1] and Cr ₂ O ₃ content was dissolved in periclase crystal, Cr ₂ O content of ₃ 0.4 to 6.5% by weight and MgO and Cr ₂ O ₃
The content of other components is 1.0% by weight or less, the average crystal grain size of periclase is 60 μm or more, and the grain size is
A sintered magnesia clinker, wherein the number of particles of a periclase crystal having a size of 150 μm or more accounts for at least 10% of all particles of the crystal. Wherein represents the sintering magnesia linker in terms of weight percent on the oxide, MgO 93.0% or more, CaO 0.50% or less, B ₂ O ₃ 0.10% or less, the chemical composition of the Cr ₂ O ₃ 0.40 to 6.5% 2. A sintered magnesia clinker according to claim 1, having a bulk density of at least 3.40 g / cm < ³ >. 3. The sintered magnesia clinker according to claim 1, wherein the number of particles of periclase crystals having a particle size of 150 μm or more accounts for at least 12% of all the particles of the crystals. . 4. expressed in terms of weight percent of the sintered magnesia clinker oxide, MgO 93.1% or more, CaO 0.30% or less, B ₂ O ₃ 0.05% or less, the chemical composition of the Cr ₂ O ₃ from .40 to 6.5% Has a bulk density of at least 3.45 g / cm ³ and an average grain size of periclase of 80 μm or more, and a particle size of 150 μm.
The sintered magnesia clinker according to any one of claims 1 to 3, wherein the number of particles of the periclase crystal of m or more accounts for at least 20% of the total particles of the crystal. 5. The method of claim 1, wherein the periclase has a bulk density of at least 3.48 g / cm ³ and the average grain size of the periclase is at least 100 μm, and the number of periclase crystals having a particle size of at least 150 μm is at least 5. A sintered magnesia clinker according to any one of claims 1 to 4 occupying at least 27%. 6. The sintered magnesia clinker according to claim 1, wherein most of the Cr ₂ O ₃ contained therein is dissolved in periclase crystals. 7. A mixture obtained by mixing a chromium compound with magnesium hydroxide or magnesium oxide having the following composition in terms of the standard value of burning: 99.0% or more of MgO, 0.50% or less of CaO, and 0.15% or less of B ₂ O ₃ . 7. A method for producing a sintered magnesia clinker according to any one of claims 1 to 6, wherein the material is pressed and then fired. 8. The method according to claim 7, wherein the magnesium hydroxide or magnesium oxide has the following composition in terms of a burning reference value: 99.4% or more of MgO, 0.30% or less of CaO, and 0.05% or less of B ₂ O ₃ . Method. 9. The method according to claim 7, wherein magnesium oxide obtained by adding an alkaline raw material such as lime milk to seawater is used.
The method described in the section.