JPS6183654A - Magnesia clinker and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnesia clinker which has excellent corrosion resistance and is suitable as a raw material for refractories for converters such as ¥5J steel furnace refractories, particularly magnesia carbon refractories. (especially seawater magnesia clinker) and its manufacturing method.

2. Description of the Related Art Recent developments in steelmaking technology have been remarkable, and there is a demand for steelmaking furnace refractories that can keep pace with this development. In other words, advances in steelmaking technology have led to demands for refractories used in steelmaking furnaces to withstand severe conditions. Therefore, expensive raw materials such as fused magnesia, which were rarely used in the past, have come to be used as raw materials for steelmaking furnace refractories. In particular, since fused magnesia is often used in magnesia carbon refractories used as refractories for converters, an inexpensive calcined magnesia (especially seawater magnesia clinker) to replace it is eagerly desired. The seawater referred to here refers to general seawater from the ocean, excluding bittern brine, etc.

It is said that magnesia clinker suitable as a raw material for magnesia carbon refractories is one with a large crystal size, a high bulk specific gravity, and one with high MIJO purity. A large magnesia clinker is desired, and therefore, as a magnesia source for magnesia carbon refractories, an average crystal size of 80
There have been attempts to use μ magnesia clinker alone or in combination with electrofused magnesia.

Problems to be Solved by the Invention The clinker as used in the present invention generally refers to a substance whose components have a low melting point melted by firing, and the whole solidifies into a lump. BACKGROUND ART Conventionally, so-called electrofused magnesia, which is produced by completely melting magnesia clinker or the like with electric heat and then solidifying it, is well known as magnesia having large crystals and high bulk specific gravity. However, as can be seen from the manufacturing process, fused magnesia is produced in small quantities and is expensive, so magnesia clinker with large crystals and high specific gravity is required as a substitute for fused magnesia. . However, unlike electrofused magnesia, clinker made by firing inevitably contains trace amounts of impurities and pores, and the presence of these impurities and pores has the disadvantage that crystal growth is difficult.

Generally, clinker is manufactured by molding magnesium hydroxide produced by the reaction of slaked lime with seawater or brine, or by calcining the magnesium hydroxide at a temperature of 600 to 1000°C, or by calcining natural magnesite. After shaping the powdery light-calcined magnesium obtained by firing, it is fired at a high temperature of 1900°C or higher.The magnesia clinker obtained by this firing has a crystal size of at most 20 to 40 μ There was.Fez○3 and 3
Some magnesia clinkers made from magnesite containing a large amount of i02 have crystal diameters of 60 microns or more. However, the purity of these magnesia clinkers was less than 97%.

As a method of increasing the MaO crystal diameter in magnesia clinker, there is a method of increasing the purity of MgO, and a method of increasing the purity of MgO,
As disclosed in No. 104054, there is a method using ZrO2 as an additive.

The method to increase MqO purity is to heat it once at 800°C to 1400°C.
By hydrating the calcined magnesia, removing calcium oxide, and calcining it again, the purity of M(to) was reduced to 99.5.
% or more, high specific gravity, and large crystal magnesia clinker by 1.7%, but even with this method, it is not possible to obtain magnesia clinker with a crystal diameter of 100μ or more, and the step of removing calcium oxide is required. It is complicated and the manufacturing cost increases significantly.

Regarding the method using additives, there is currently a patent application pending for magnesia clinker with an average crystal size of 60μ or more produced by adding ZrO2, but magnesia clinker with an average crystal size of 100μ or more can be produced by adding ZrO2 alone. It was difficult to remove 1 q of clinker.

That's where this invention comes from! The object of the present invention is to provide a magnesia clinker suitable as a raw material for refractories for steel furnaces, particularly magnesia carbon refractories with excellent corrosion resistance.

Means for Solving the Problems In view of the above objects, the present invention provides an excellent magnesia clinker.
The present invention was arrived at as a result of intensive research into the development of

That is, in the present invention, (a) the purity of MgO is 97 wt% or more, and (b)
The content of CaO is 20 wt% or less, and (C)B
203 content is 0.01 wt% or more, (d) Si02 content is 0.3 wt% or less, (e) MQ O, Ca ○, Bz Os
, the content of impurities other than Si02 is 2wt
% or less, and the bulk specific gravity and apparent porosity are each 3.35 ((1/
CG) or more and 3.0 (vo1%) or less, and (a) magnesia clinker-1, characterized in that the average crystal diameter of magnesia is 100μ or more, and magnesium hydroxide or lightly calcined magnesia A method for producing magnesia clinker, which comprises adding magnesia powder having a round shape and an average particle size of 15μ or more at 0.2 to 20.0 wt% in terms of Mgo, and then firing the mixture. Regarding.

In the present invention, in order to improve the durability of the refractory, M
The purity of gO needs to be 97 wt% or more. Roughly speaking, 98wt% or more is preferable, and CaO is particularly 1.0%.
~2. Owt% * Desirably, B203 is especially 0.0
3 to 0.1 wt% is desirable. Also, S i O2 ha 0
．． 1 to 0.2 wt% power W1. : Preferably, MCI O
, CaO, B203, impurities other than Si02 are 1.0
It is desirable that it is less than wt%.

The bulk specific gravity is 3.35 (g/cc) or more, preferably 3.45 (J/C (1) or more,
The average crystal diameter of magnesia is 100μ or more, especially 120μ
The number of crystal grains of 100 to 200 μ is preferably 50% or more, particularly 60% or more of the total number of crystal grains.

By the way, when the structure of magnesia clinker is observed under a microscope on its fractured surface, it consists of a collection of small magnesia crystals and a matrix interposed between these crystals.
When magnesia crystals are called crystal particles, in the case of conventional high-purity magnesia clinker, the average diameter is usually 20 to 4.
It is 0μ. However, the magnesia clinker of the present invention
has an average crystal diameter of 100μ or more, and 100~
The crystal grains of 200μ account for more than 50% of the total number of crystal grains, and their distribution is uniform and the bulk specific gravity is high. Therefore, the magnesia clinker of the present invention has improved corrosion resistance due to slabs.

This is presumed to be because magnesia clinker is often eroded by slag through the matrix made of CaO or 3i02 rather than the magnesia crystal particles, and as the magnesia crystal particles become larger, contact with the matrix is hindered. be done. Furthermore, it is presumed that corrosion resistance of the magnesia clinker caused by slag is greatly improved because the distribution of magnesia crystal particles is made uniform.

Further, in the present invention, the number of pores in the magnesia crystal is preferably 1000/1III12 or more. This is because when the bulk specific gravity is constant, each pore is fine, which prevents slag from entering the pores and prevents erosion of the slab.

Furthermore, it is well known that increasing the density of magnesia clinker greatly contributes to improving the durability of refractories, and in the present invention, bulk specific gravity j, 35 ((1/C
C) or more, the corrosion resistance is significantly improved, especially 3-45
(a/cc) or more, the corrosion resistance is significantly improved due to higher density.

Therefore, a magnesia clinker having large crystals that satisfies the conditions of the present invention exhibits superior corrosion resistance and increases durability, and is therefore suitable as a raw material for magnesia carbon refractories. In addition, raw materials for converter refractories such as magnesia dolomite refractories and magnesia chromium refractories,
Furthermore, it is suitable for wide use as a raw material for large-sized products for steelmaking furnaces.

The magnesia clinker of the present invention can be obtained, for example, as follows. That is, 6 magnesium hydroxide
Magnesia powder for blending, that is, a magnesia single crystal with a crystal diameter of 15μ or more or a crystal aggregate of 5 turns or less, is added to light calcined magnesia calcined at 00 to 1200°C.
20W [%] was uniformly blended, and this was pressure-molded into an almond shape at a pressure of 2t/cm2 or more, then put into a rotary kiln and fired at a maximum temperature of 1800-2000℃,
The magnesia clinker of the present invention can be obtained.

In the present invention, even if light calcined magnesia which is calcined at 600 to 1200°C after compounding magnesium hydroxide with magnesia single crystals or aggregates of 5 or less particles having an average particle size of 15 μ or more is used, the present invention can be achieved. Magnesia clinker could be obtained.

The average particle diameter of magnesia for compounding must be 15 microns, and preferably 30 to 100 microns.

In addition, the amount of magnesia compounded is 0.2 to 20.0w.
The t% is desirable, 1.0 to 5. Ow% is particularly desirable.

If the average particle diameter of the blended magnesia is less than 15 microns outside the scope of this invention, the effect of large crystallization of the crystal particles in the magnesia clinker will be reduced. In addition, the blending amount of magnesia with an average particle size of 15μ or more is 0.2wt%.
If it is less than 20 W (%), the effect of large crystallization of the magnesia clinker crystal particles will be reduced, and if it exceeds 20 W (%), the bulk specific gravity will suddenly decrease.

In other words, the relationship between the average particle diameter of the magnesia powder for compounding when 2 wt % of the above magnesia powder for compounding is blended with light calcined magnesia, and the bulk specific gravity and average crystal diameter of the magnesia clinker after baking is calculated as follows. Shown in the figure. As shown in this figure, the average particle diameter of magnesia powder for compounding is 1
It is necessary that it is 5μ or more; if it is smaller than that, it is impossible to obtain a magnesia clinker with an average crystal diameter of 100μ or more.

Furthermore, the average particle size of the magnesia powder is in the range of 30 to 100μ, and the average particle size of the magnesia clinker is 120μ.
This is a particularly desirable blending amount.

Then, after blending the magnesia powder with an average particle size of 45μ in the above compounding magnesia into the light burnt magnesia,
FIG. 8 shows the relationship between the blending ratio of magnesia powder for compounding during firing and the bulk specific gravity and average crystal diameter of the magnesia clinker after firing. As shown in this figure, when the blending ratio is o, 2 W t96 or more, the average crystal diameter is 1
It is possible to obtain magnesia clinker of 00μ or more,
Also 20. Bulk specific gravity 3.35 (g/CC) below OWE%
The above magnesia clinker can be obtained. Rough blend vj ratio is 1.0 to 5. Ovt% range, average crystal diameter 120μ or more and due north 13,45 ((1/c
c) The above magnesia clinker can be obtained.

Therefore, the blending ratio of magnesia powder is 0.2 to 20.09 t.
%, 1.0 to 5. A particularly desirable blending ratio is within the range of Owt%.

In this invention, the shape of the magnesia particles for compounding is preferably round, such as a sphere or ellipsoid, rather than flat, and particles with a large length-to-width ratio, such as needles, are preferable. Unsuitable for large crystallization.

In the present invention, crystal growth can be further promoted by further adding Zr 02. zr
The amount of ○2 added is 0.05 to 0.5 wt% relative to MgO.
is preferable, more preferably 0.1 to 0°2 wt%
It is.

In the case of alumina, the idea of adding alumina with an average grain size of 10μ to promote crystal growth is as follows: 1.
B, Cutler ([KINETTC8OF
HIGH TEMPERATURE JW, D.

KINGERY, MIT Publishing, 1959, p. 120). However, the shape of the magnesia added to promote crystal growth within the magnesia clinker must be carefully examined.
If the shape of the doped alumina used in the alumina crystal growth shown by Tler et al. is acicular or similar, for example as shown in FIG. 4, the effect of large crystal growth will not appear at all. That is, as shown in FIG. 3, by blending magnesia with a circular shape or a shape close to this, large crystallization and other effects expected in this invention can be obtained. be.

In addition, in this invention, the magnesia powder for compounding is 5
An aggregate of crystals consisting of less than one crystal is preferable, and a single crystal is more preferable because the effect is remarkable.

The magnesia powder for compounding in the present invention includes, for example, one that is fired at a high temperature and is taken out as a powder without being subjected to any special pulverization treatment.

The bulk specific gravity, crystal diameter, and average crystal diameter of the magnesia clinker obtained by the present invention are determined by the JSPS method 2 proposed by the 124th committee of the Japan Society for the Promotion of Science: The apparent ratio was measured according to ``Methods for measuring specific gravity and bulk specific gravity'' and Gakushin method 3: ``Measurement of size of periclase in magnesia clinker and its description method''.

In addition, chemical analysis of magnesium hydroxide, light calcined magnesia, and magnesia clinker was performed according to Jakushin Method 1: "Chemical analysis method of magnesia clinker."

That is, the bulk specific gravity and apparent porosity of magnesia clinker are measured as follows.

(1) Crush all grain size of magnesia clinker.3.
Select a particle size of 36-2.00 mm and accurately weigh out about 15 g. (W+: (1) (2) Place the magnesia clinker sample in a 1mm wire mesh basket, place the beaker containing the basket in a desiccator, keep the pressure under reduced pressure for about an hour, and then remove the white sample from the separating funnel. Pour kerosene into the beaker until it reaches the top.

After that, exhaust the air for about 20 minutes.

(3) Take out the beaker containing the evacuated sample from the desiccator, then take out the basket containing the sample from the beaker, and accurately measure its content (Wz: g) in oil.

4) Remove the sample from the basket, remove excess or insufficient oil from the surface, and quickly measure its weight (W3).
:Weigh g).

(day Calculated bulk specific gravity (a/cc) -W+ XρWl (
W2-W4) Apparent porosity-W3-W+ xloo (%)
However, W! ``h''rami''a3 Pond weight ρ: Specific gravity of white kerosene Also, the average crystal grain was measured as follows.

DJ Take at least three or more lumps of about 7.93 mrR, cut them into two equal parts, and fill the cut surfaces with resin.

)2) While observing the surface-polished sample with a reflection microscope, select three average parts and ask the observer to measure the length of the crystal in the vertical direction, especially the length of the crystal in the horizontal direction.

(3) This length is defined as the crystal diameter, and their average value is defined as the average crystal diameter.

Furthermore, the analytical methods for magnesium hydroxide, magnesium oxide, and magnesia clinker are described above in JSPS Method 1.
The method was based on "Chemical analysis method for magnesia clinker" with some improvements and additions.

Analysis of 8203 was carried out in the following manner based on ASTM C-574. (Mannit method) Sample 5g ↓ Using a filtration pH meter, adjust the pH to 6.9 while adding NaOH aqueous solution to this solution. Manninto (HOCH2(CH
Add 10g of (OH)4CH20H), (1+20>Na
Titrate with an OH aqueous solution and determine the content of 8203 from the titration amount.

The analysis method for Zr02 is as follows.

Add a few drops of indicator and heat the solution. While maintaining the temperature at 90℃, M/100 Titrate with EDTA solution.

Moreover, the average particle diameter of magnesia for compounding was measured as follows.

(1) Embed magnesia powder in epoxy resin and polish the surface.

(2) While observing the polished surface with a reflection microscope, measure the particle length in the vertical direction and the particle length in the horizontal direction.

B) This size is defined as the particle diameter, and their number average value is defined as the average particle diameter.

The number of pores in magnesia crystals was measured as follows.

In other words, while observing the surface of the polished clinker using a reflection microscope, photographs are taken from three fields of view. From one photo,
Ten 50μ square fields of view were selected, and the number of pores within each field of view was counted and converted to the number per 1111 squares.

For each photograph, the average value of the field of view at 10 locations is calculated and expressed as a number rounded to the nearest 10 digits. Furthermore, the average value of the values from the three photographs is determined.

This value is expressed as the number of pores within the crystal.

LL Example 1 Chemical composition is Mg067.0wt%, Ca in terms of oxide
01,12vt%, S i O20,14wt%, A
I 2030,04wt%, Fe 2030,04w
t%, BzO30,06wt%, ZrO20,
09wt% magnesium hydroxide in a box-type electric furnace.
Lightly calcined magnesia obtained by holding at a temperature of 50"C for 3 hours has an average particle size of 45μ and a rounded shape of 5" as shown in Figure 3.
A pellet (iommφ, 5111mj-1) made by homogeneously blending magnesia powder for compounding consisting of less than 100% crystals and molding it at a pressure of 2t/Cll12 at a maximum temperature of 2000℃ in an oxygen-propane furnace. Holds time.

The bulk specific gravity of the magnesia clinker produced in this way is
The apparent porosity, average crystal diameter and chemical composition are as shown in Table 1. In addition, the fractured surface of the clinker was polished and observed under a microscope, and its appearance is shown in FIG. Figure 5 shows the distribution of the crystal diameters of magnesia clinker, which was obtained by reading more than 150 pieces according to the Jakushin method. The number in parentheses represents the percentage of crystals within the corresponding crystal diameter range.

In addition, the relationship between the average particle diameter of the magnesia powder for blending and the bulk specific gravity and crystal diameter of the magnesia clinker after firing is as shown in the graph in Figure 7, and the ratio of the magnesia powder to be blended above The relationship between the bulk specific gravity J3 of the magnesia clinker after firing and the crystal diameter is as shown in the graph of FIG.

Example 2 Magnesium hydroxide used in Example 1 was fired at a maximum temperature of 900°C in a multi-stage firing furnace to produce light fired magnesia with a rounded shape as shown in Figure 3 with an average particle size of 63μ. Bulk specific gravity, apparent porosity and average crystal diameter of magnesia clinker made by blending 3 wt% of single crystal and molding the pellet into an almond shape under a pressure of 2 t/cm2 or more in a Tari kiln at a maximum temperature of 2000°C. , and chemical composition are shown in Table 1.

Also, looking at the distribution of magnesia crystal diameters, it is 100 to 20
The number of crystal grains with a diameter of 0 μ accounted for 60% of the total number of crystal grains.

Example 3 Chemical composition is oxide conversion, Ma 068.0wt%, Ca
Qo, 04%, S i O20, 19wt%, A I
2030,04wt%, F e 203o, o4wt
%, B2030.06 wt% magnesium hydroxide was kept at a temperature of 900°C for 3 hours in a box-type electric furnace, and a rounded magnesia single crystal with an average size of 50μ as shown in the m3 diagram was added to the light calcined magnesia. Uniformly blended at 2wt%, 2t/
A pellet formed into a cylindrical shape under a pressure of cm' (diameter 10 f)
fffflX height 5 mm) was maintained at a maximum temperature of 2000° C. for 1 hour in an oxygen-propane gas furnace. The bulk specific gravity of the magnesia clinker obtained in this way is 1q, the apparent porosity is
The average crystal size and chemical composition are shown in Table 1.

Furthermore, looking at the crystal diameter of magnesia, the number of crystal diameters of 100 to 200 μ accounted for 55% of the total number of crystal particles.

Example 4 Magnesium hydroxide used in Example 1 had an average particle size of 45
As shown in Figure 3, magnesia powder consisting of 5 or less rounded crystals was mixed with 2wt% of MGI○, and was kept at a temperature of 900℃ for 3 hours in a box electric furnace. I got burnt magnesia. This light burnt magnesia is molded into a cylindrical shape under a pressure of 2t/cm2 (diameter: 10ml, 1l,
The specimen was kept at a high temperature of 2000° C. for 1 hour in an oxygen-propane furnace. The bulk specific gravity, apparent porosity, average crystal diameter, and chemical composition of the magnesia clinker thus obtained are as shown in Table 1. Also, looking at the distribution of magnesia crystal diameters, the crystal diameter is 100 to 2.
The loss of 00 μm accounted for 58% of the total number of crystal grains.

Example 5 Chemical composition is Mg087.4wt%, Ca in terms of oxide
Qo, 95vt%, S i Oz 0.19wt%, A
I 20 s O, 04wt%, F e2 Q s
Lightly calcined magnesia obtained by firing magnesium hydroxide containing 0.04wt% B and 2030.06wt% B in a multi-stage furnace at a maximum temperature of 900°C has an average particle size of 48μ and a rounded shape as shown in Figure 3. A pellet containing 2wt% of magnesia powder consisting of crystals of less than 100% by MaO conversion and molded into an almond shape under a pressure of 2t/cm' or more is made into a pellet with a maximum of 202mm.
It was fired in a rotary kiln at 0°C. Table 1 shows the bulk specific gravity, apparent porosity, average crystal diameter, and chemical composition of this magnesia clinker. Further, when looking at the distribution of the crystal size of magnesia, the crystal size of 100 to 200 μm accounted for 52% of the total number of crystal particles.

Comparative Example 1 A pellet (diameter 10 mmφ, height 5
mm) to a maximum temperature of 2000℃ in an oxygen-propane furnace.
It was held for 1 hour. The bulk specific gravity, average crystal diameter and chemical composition of the magnesia clinker thus obtained are shown in Table 1. The broken surface of the clinker was polished and the VA was observed using a microscope, as shown in FIG. Further, as in Example 1, the distribution of magnesia crystal diameters is shown in FIG.

Comparative Example 2 Two magnesia powders having an acicular shape and an average particle size of 45μ as shown in Fig. 4 were added to the lightly calcined magnesia used in Example 1.
A pellet (diameter 10 mm, height 5 mm) formed into a cylindrical shape under a pressure of 2 t/cm2 and heated to a maximum temperature of 2
The temperature was maintained at 000°C for 1 hour. The bulk specific gravity, average crystal diameter, and chemical composition of the magnesia clinker thus obtained were as shown in Table 1.

[Table 1]] Next, Example ``+--5, Comparison example 1..., 2'r
I! 'J Rade Gunnesia Crine 7J--approximately 5 each
g (, - cut out a cubic sample piece, +57
Place it in an electric furnace at 0'''C, preheat it to the same temperature, and preheat it to 301℃.
Approximately 309 slag (chemical composition Ca 043.2wt%,
SiO? 23.9W1%, Fe 20332,
9W + %) (, 'Input・1.O:, 4 hours at the same temperature, A: 15, Take the sample from Ruth it Buy for a few minutes - U f'i
Sushi 2 f6 dropped 1; Goshita's t3 outside the furnace - (7. Cooled at room temperature 1. <5-q,
Determining pB, i4 fi'l of cylinder slug bending
't't (7) I was confused. The results are shown in Table 2.

As detailed in No. 1 above in Table 2, the magnesia clinker with large crystal powder of the present invention has a corrosion resistance of 1 (r = 21), magnesia clinker with large crystal powder of the present invention. 1. Suitable for large copper alloys!
Contains 17 gnesino'υ) with an average particle diameter of 5 μ or more! 1-A) is a simple and inexpensive method to obtain crystal diameter, bulk specific gravity, and more! , 11 of the high-height ratio Φ of 35 (g/cc) or more. ! ,! Qinzuru. .

[Brief explanation of drawings]

Figures 1 and 2 are reflection micrographs showing the crystal structure of the fractured surface of the magnesia alkaline linker, Figure 3 is a reflection microscope photograph of the crystals on the polished surface of the compounding magnesia ladle, and Figure 4 is: Reflection micrograph of the polished surface of oblique 7 gnesia powder. Figures 5 and 6 are graphs of the relationship between the crystal diameter and number percentage of magnesia clinker. Figure 7 is the crystal diameter of the 7 gnesia powder for blending and after firing. Figure 8 is a diagram showing the relationship between the magnesia crystal diameter and bulk specific gravity of the magnesia clinker. C゛ Yes. Patent applicant: Shinmezu Kagaku Choku Co., Ltd. Patent attorney: Mr. Komatsu Attorney: Patent attorney 4 1f! 1 11". ) Tsuchinoi (chamber i31 to J (→ )) to arc to N ~ (゛,te1 Fig. 4. ) Proceedings (Method) % Formula % Case Description Patent Application 1984-200430M Name of the Invention Magnesia Clinker and its Manufacturing Process Name Name Nippon Kagaku Kogyo Co., Ltd. 4, Agent Address: 107 (Telephone: 58G-8854)
Address: 4-13-5 Akasaka, Minato-ku, Tokyo Date of amendment order: January 9, 1985 (Shipping date: 1932)
(January 29, 0) Subject of amendment Contents of amendment in the brief explanation of drawings section in the specification (1) In the specification, page 29, line 4, "reflection microscope/photograph showing crystal structure" has been changed to "crystalline structure". "A photograph showing the structure of the (2) In line 6 of the same page, "reflection type mirror photograph" is corrected to "photograph showing structure." (3) In lines 7-8 of the same page, "reflection micrograph" is corrected to "photograph showing crystal structure."

Claims (7)

[Claims] (1) (a) The purity of MgO is 97 wt% or more, and (
b) The content of CaO is 20 wt% or less, and (C) B
The content of _2O_3 is 0.01wt% or more, (d) the content of SiO_2 is 0.3wt% or less, and (e) the content of impurities other than MgO, CaO, B_2O_3, and SiO_2 is 2wt% or less. (f) Bulk specific gravity and apparent porosity are each 3.35 (g/c
c) or more, and 3.0 (vol%) or less, and (g) the average crystal diameter of magnesia is 100 μ or more. Magnesia clinker is characterized by: (2) The number of pores in the magnesia crystal is 1000/m
The magnesia clinker according to claim (1), which has a m^2 or more. (3) The magnesia clinker according to claim (1), wherein crystal grains of magnesia crystals having a size of 100 to 200 microns account for 50% or more of the total number of crystal grains. (4) For magnesium hydroxide or light calcined magnesia, use magnesia powder with a round shape and an average particle size of 15 μ or more in an amount of 0.2 to 20.0 wt in terms of MgO.
1. A method for producing magnesia clinker, which is characterized in that magnesia clinker is blended with % and then fired. (5) The method for producing magnesia clinker according to claim 11, wherein the magnesia powder has an average particle diameter of 30 to 100 μm. (6) The method for producing magnesia clinker according to claim (4), wherein the magnesia powder is composed of a single crystal or five or less crystals. (7) The method for producing magnesia clinker according to claim (4), wherein the blended amount of magnesia powder is 1.0 to 5.0 wt%.