JPH01103936A - High density magnesia/chromium-base clinker and production thereof - Google Patents

Abstract

PURPOSE:To contrive enhancement of bulk specific gravity by constituting the title clinker of specified composition in which purity of MgO is high and the constitution of impurities is controlled. CONSTITUTION:Magnesia/chromium-base clinker consists of composition of by weight >=98.0% MgO, 0.02-1.50% CaO, 0.10-0.50% SiO2, <=0.20% Fe2O3, <=0.20% Al2O3, <=0.30% B2O3 and 0.05-0.40% Cr2O3 and has >=3.42 bulk specific gravity and >=35mu mean crystal diameter. In the case of producing this clinker, for example, chromium compd. is added to slurry or hydrated cake of magnesium hydroxide in a range within 0.05-0.40% expressed in terms of oxide and uniformly dispersed. In the case of slurry, cake is obtained by dehydrating it and made to activated light burnt magnesia by lightly burning at at 600-1,100 deg.C and this is molded at >=2T/cm<2> pressure. This molded material is fed to a rotary kiln and calcined at maximum temp. of 1,800-2,000 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a magne-shea film with improved characteristics, which is mainly composed of MgO and contains an appropriate amount of impurities such as Cab1SiO2.
Regarding chromium-based clinker and its manufacturing method, it is heavily used as a raw material for basic refractories such as steel-making furnaces.

[Prior Art] Recent advances in steel manufacturing technology have been remarkable, and the conditions for lining refractories are becoming increasingly severe. As various steelmaking furnaces are operated at high temperatures, there is a demand for refractories that have high strength and corrosion resistance at high temperatures and have excellent durability.

Therefore, it was necessary to use a high-density but expensive electric fusion product, which has rarely been used as a refractory raw material for steelmaking furnaces. Along with this, there has been a demand for an inexpensive, high-density fired crystal magnesia-chromium-based clinker to replace magnesia-chromium-based refractories, which are one of the steelmaking furnace refractories.

Magnesia-chromium clinker suitable for magnesia-chromium refractories is said to have a high bulk specific gravity, high MgO purity, and a composition of impurities such as CaO1Si02. Among these conditions, it is especially necessary to have a high bulk specific gravity, so when manufacturing refractories, high-density raw materials such as magnesia chromium-based electric products are partially blended.
Designed to increase durability.

[Problems to be Solved by the Invention] Clinker as used in the present invention generally refers to a material in which fine crystal grains and low melting point impurities coexist due to firing at high temperatures, resulting in a dense microstructure. .

Magnesia-chromium clinker used as a raw material for magnesia-chromium refractories must have a high bulk specific gravity. However, in clinker produced by firing, the presence of impurities and pores is unavoidable, inhibiting densification and making it difficult to significantly increase the bulk specific gravity.

In general, magnesia clinker is manufactured using magnesium hydroxide produced by reacting a slurry made by slaked seawater or acupuncture water with quicklime or calcined dolomite, or naturally occurring magnesite, either as is, or by lightly calcined or molded. It is fired at a high temperature of 1700° C. or higher by appropriately combining the following steps.

The magnesia clinkers thus obtained range in bulk specific gravity from high to low, and from high to low MgO purity.

The bulk specific gravity of magnesia clinker, which is commercially available as a raw material for magnesia-chromium refractories, is at most 3.38-3.
A clinker with an increased MgO purity of 40 has an even lower bulk specific gravity.

Methods for increasing bulk specific gravity include methods of ultrafinely pulverizing raw materials such as magnesium hydroxide and methods of using various additives. The method of ultrafine pulverization has the disadvantage that the pulverization efficiency is poor and the manufacturing cost increases significantly, and the material in the pulverizer is worn out and contamination due to contamination is also significant.

In the method using additives, various additives have been tried, but some have been found to have compositions with low MgO purity and are added in large amounts, or have been found to improve the bulk specific gravity but have a significantly high bulk specific gravity. (For example, Japanese Patent Publication No. 53-5323, U.S. Patent No. 2.48)
7.290).

Therefore, the object of the present invention is to provide a magnesia-chromium-based clinker that is suitable as a raw material for magnesia-based chromium-based refractories and has a high MgO purity and a significantly increased bulk specific gravity by controlling the composition of impurity components. .

[Means for Solving the Problems] In order to achieve the above object, Magnesium L was developed.

In other words, the present invention has a chemical composition (expressed in weight%) of Mg
O98.0% or more Ca O0.20-1.50% Si O20,10-0.50% Fe 20 s 0.20% or less AI 20
3 0.20% or less 8203 0.30% or less Cr 203 0.05 to 0.40%, 3.
A high-density magnesia-chromium clinker with a bulk specific gravity of 42 or more and a crystal diameter of 35 μm or more, and a raw material prepared by mixing a chromium compound with magnesium hydroxide, are lightly calcined, pressure-formed, and then fired. Density magnesia
This article relates to a method for producing chromium-based clinker.

In the present invention, in order to further improve the properties of magnesia-chromium-based refractories, it is necessary to form direct bonds densely by high-temperature firing. ) or more are required.

If the purity of MgO is low, a large amount of impurities will be present in the densification process during sintering, which will be an inhibiting factor, and the bulk specific gravity will not be significantly high.

CaO is preferably 0.20 to 1.50%, and 0.20 to 1.50%. aO~
1.20% is most preferred. 5i02 is 0.1θ~0.
50% is preferred, and 0.20-0.40% is most preferred.

In order to obtain a significantly high bulk specific gravity, the composition of these two impurity components is important, and the weight ratio of CaO/5iOz must be adjusted to 2 to 5.
5% to 0.40% is preferred, 0.1-0 to 0.30%
is most preferred. This is the component that contributes the most to improving the bulk specific gravity in the coexistence of CaO and 5iOz,
In order to generate spinel (MgCICrzO3), the formation of direct bonds is promoted in magnesia-chromium refractories. If CrzOs is less than 0.05%, the improvement in bulk specific gravity is small, and if it exceeds 0.40%, it leads to an increase in the amount of impurities, which becomes a factor that inhibits high density. Also, Fe2O3 and Al2O3 are preferably 0.20% or less, and 0.10%
The following are most preferred.

B2O3 is preferably 0.30% or less, more preferably 0.20% or less, and most preferably 0.10% or less.

In particular, 8203 significantly lowers the hot bending strength, which is an important property of the clinker obtained, and a portion of it gasifies and evaporates during firing, thus hindering high density.

FIG. 1 shows experimental results proving the relationship between the composition of these impurity components and the bulk specific gravity. This experiment used magnesium hydroxide as a raw material shown in Table 1 below, and CaO/5
iOz and B2O3 components were adjusted to obtain magnesium hydroxide of A-H, and chromium oxide with an average particle size of 0.58 μm was added to each as shown in FIG. Light firing was carried out in an electric furnace maintained at 900℃, and a 2T/
It was molded at a pressure of cs+2. The molded body was fired at 1800° C. for 1 hour in an LPG-oxygen furnace.

To explain the relationship between the composition of impurity components and bulk specific gravity in Table 1 A to H, A and CSE have CaO/5LO2 between 2 and 5, and the amount of CaO increases in order. In particular, since E contains a small amount of B2O3, when chromium oxide is added, the bulk specific gravity of magnesia clinker becomes the highest.

On the other hand, B and D have CaO/5i02 outside the range of 2 to 5, and B has a high content of B2O3, so even if chromium oxide is added, the bulk specific gravity remains low.

This result clearly shows that there is a deep relationship between the composition of impurity components of CaO1SiOz and B2O3 and chromium oxide.

The bulk specific gravity is preferably 3.42 or more, more preferably 3.45 or more, and most preferably 3.48 or more.

In general, it is known that when the density of magnesia-chromium clinker increases, the direct bond of magnesia-chromium refractories becomes stronger and contributes greatly to improving performance, and therefore corrosion resistance. The improvement in resistance is significant.

Crystal size is an important property that indicates the degree of sintering of clinker. If sintering is insufficient, the reaction of impurities existing at grain boundaries will not proceed, and the crystal size will be small, making it difficult to produce refractories. This results in the disadvantage of large shrinkage.

Therefore, the average crystal diameter is preferably 35 μm or more, and 40 μm or more.
■The above is most desirable.

The magnesia clinker of the present invention can be produced, for example, as follows.

A chromium compound is added to a slurry of magnesium hydroxide or a water-containing cake in a range of 0.05 to 0.40% in terms of oxide and uniformly dispersed. In the case of a slurry, it is dehydrated to obtain a cake, which is lightly calcined at a temperature of 600 DEG C. to 1100 DEG C. to form active, lightly calcined magnesia, which is then molded at a pressure of 2 T/am' or more. The magnesia clinker of the present invention can be obtained by feeding this molded product into a rotary kiln and firing it at a maximum temperature of 1800°C to 2000°C.

The magnesium hydroxide used in the present invention may be naturally produced or artificially produced using natural magnesia raw materials, but considering the purity and sintering properties of magnesium hydroxide, seawater magnesia Most preferably, magnesium hydroxide obtained from the manufacturing process is used.

As the chromium compound, any of oxides, salts, chromic acid, its salts, and dichromates may be used, but oxides in the form of powder are preferred from the viewpoint of convenience in handling and ease of uniform dispersion. Chromium oxide (Cr203) convenient for mixing
) have different particle sizes, and the use of powder with a smaller average particle size will result in a magnesia clinker with a higher bulk specific gravity.

When comparing chromium oxide with an average particle size of 3.6μI and 0.58μI, it was found that the bulk specific gravity of clinker was 0, and O1~0.
．． A difference of 0.03 was observed. To achieve the most desirable bulk specific gravity of 3.48 or more, chromium oxide having an average particle diameter of 1 μm is preferred.

In the present invention, the chromium compound is added to the magnesium hydroxide slurry or water-containing cake because this method is simple and allows for the most uniform dispersion. This is an indispensable method for increasing bulk specific gravity.

When mixing into a water-containing cake, there is a limit to the moisture content, and 3
When the moisture content is less than 0%, uniform dispersion becomes impossible, and of course, this is impossible even in a dry state.

In the present invention, since a magnesia-chromium clinker with a high bulk specific gravity must be used, it is necessary to lightly sinter magnesium hydroxide in which a chromium compound is uniformly dispersed. The light firing temperature is preferably 800°C to 1100°C, and the light firing temperature is 750°C to 1100°C, where light firing magnesia has high activity and has the best sinterability.
Particularly preferred is 1050°C.

The light burnt magnesia is then pressure molded. The higher the density of the molded product, the higher the bulk specific gravity of the clinker, so 2 T/c
■Requires pressure of 2 or more.・A briquette machine that can obtain high pressure or a hydraulic press is used for molding, but a briquette machine is effective in terms of clinker particle size structure and molding efficiency.

The molded product is fed into a rotary kiln and fired. The higher the temperature, the higher the bulk specific gravity, the more the reaction between impurity components progresses, and the more uniformly the chromium oxide is diffused into the periclase, so firing must be carried out at a maximum temperature of 1800°C to 2000°C.

The chemical composition of the raw materials used for the present invention and the obtained clinker was determined by dissolving the sample in hydrochloric acid and preparing I CAP-5751 (
Measured using Nippon Jarrell Atsushi). In addition, the bulk specific gravity, apparent specific gravity, and apparent porosity of the obtained clinker were calculated using the JSPS method 2 proposed by the 124th Committee of the Japan Society for the Promotion of Science, and the apparent porosity, apparent specific gravity, and bulk of magnesia clinker. It was measured according to the method for measuring specific gravity, and the crystal diameter was also measured according to the same proposed Gakushin method 3, the method for measuring the size of periclase in magnesia clinker and its description.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Using magnesium hydroxide as a raw material shown in Table 1, adding water glass to adjust the amount of 5i02 (SO2/MgO-0,
25%). Chromium oxide powder with an average particle diameter of 0.58 μs was added to give a Cr 203 /M g O ratio of 0.15%, and mixed at a slurry concentration of 200 g M g O/cross. The slurry was filtered into a cake and lightly calcined in a rotary kiln at a maximum temperature of 900°C. 2 Team by supplying lightly burnt magnesia to the briquette machine
It was molded at a pressure of 2. This molded product was fed into a rotary kiln and fired at a maximum temperature of 2000°C. The chemical composition, physical properties, and crystal diameter of the obtained magnesia clinker were
It was as shown in the table.

Example 2 Adding slaked lime slurry, water glass, and boric acid purified using magnesium hydroxide as the raw material shown in Table 1 to produce Cab,
SiO2, B2O3 amount: A (CaO/MgO-0
, 95%, 5iOz/M g O-0, 25%, B 2
03/MgO-0.08%).

Hereinafter, magnesia clinker was prepared in the same manner as in Example 1.
I got it. The chemical composition, physical properties, and crystal diameter are as shown in Table 2.

Example 3 A slurry of magnesium hydroxide (Mg0270g/l) obtained in the seawater magnesia manufacturing process was filtered to form a water-containing cake with a water content of 45%. This cake was fed to a clay kneader and kneaded while adding chromium oxide so that the ratio of Cr 203 /MgO was 0.296.

This mixed material was lightly burned in a multi-stage furnace at a maximum temperature of 880'C,
The obtained light burnt magnesia was heated in a briquette machine for 2 T.
It was molded at a pressure higher than eam'.

The molded product is fed into a rotary kiln and the maximum temperature is 1980℃.
It was fired in The chemical composition, physical properties, and crystal diameter of this magnesia clinker were as shown in Table 2.

Example 4 Magnesium hydroxide slurry (Mg0247g/l) obtained in the seawater magnesia production process was filtered to remove water content of 4
It was made into a 7% water content cake.

To this cake, boric acid was added at 0.25% in 8203/MgO, and chromium oxide with an average particle size of 0.58 μm was added in Cr2O5/MgO.
The mixture was fed to a clay kneader and kneaded while adding O to give a concentration of 0.2%. This mixture was lightly calcined in a multi-stage furnace at a maximum temperature of 820° C., and the resulting lightly calcined magnesia was molded in a briquette machine at a pressure of 2 T/cm 2 or more.

The molded product is fed into a rotary kiln and the maximum temperature is 1930℃.
It was fired in

The chemical composition, physical properties, and crystal diameter of this magnesia clinker were as shown in Table 2.

Comparative Example 1 A cake was obtained by filtering the magnesium hydroxide slurry obtained in the seawater magnesia manufacturing process. This cake was lightly calcined in a multi-stage furnace at a maximum temperature of 850''C, and the resulting lightly calcined magnesia was molded in a briquette machine at a pressure of 2 Tlcl'' or higher.

The molded product is fed into a rotary kiln and the maximum temperature is 1950℃.
It was fired in The chemical composition, physical properties, and crystal diameter of this magnesia clinker were as shown in Table 2.

Comparative Example 2 This is a commercially available example of magnesia clinker used as a raw material for magnesia-chromium refractories. Its chemical composition, physical properties, and crystal diameter are shown in Table 2.

Using the magnesia clinkers obtained in Examples 1 to 4 and Comparative Example 1.2, 35% of Turkish chromium ore was added to each of the magnesia clinkers to prepare magnesia-chrome bricks.

The bricks were prepared as follows.

Particle size composition (%) Magnesia Chromite 3.36-2.001m 15 -2.
00~1.00 10 -1.00~0
．． 25 10 50.25 or less
30 fine powder 30- Molding Binder = 28° Addition of 5% Be'MgSO4 aqueous solution Molding pressure 2Ton/cm2 Firing Drying: Hold at 120℃ for 16 hours Calcination 7Hold at 1800℃ for 2 hours The obtained fired brick was placed in a horizontal rotary furnace A test for slag erosion was conducted on the inside.

The conditions for the erosion test were as follows.

Chemical composition of slag (%) CaO40 SiOz 30 Fezes 30 Four cycles of reaction for 2 hours were performed at the erosion temperature and the amount of slag from 1650 to 1700°C. Slag was discharged every cycle, and 1 kg/cycle of slag was added to cause an erosion reaction.

After cooling, the bricks from the rotary furnace were dismantled, and the difference in dimensional reduction before and after erosion was determined and converted into an index. The results are shown in Table 3 regarding the corrosion resistance of magnesia chrome bricks.

Table 2 Table 3 [Effects of the Invention] As described above, the magnesia-chromium clinker of the present invention having a bulk specific gravity of 3.42 or more exhibits excellent erosion resistance, and the magnesia-chromium refractory of the present invention Ideal as a raw material. Furthermore, this invention has the remarkable effect of producing magnesia clinker having a bulk specific gravity of 3.42 or more using a simple method of adjusting the amount of impurity components in magnesium hydroxide and mixing a chromium compound.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between Cr203Iik and bulk specific gravity of a magnesia clinker prepared by mixing chromium oxide with magnesium hydroxide having a different composition of impurity components and firing it. Patent applicant Shin Nippon Chemical Industry Co., Ltd. Agent Patent attorney Hide Komatsu Agent Patent attorney Hiroshi Asahi

Claims (5)

[Claims] (1) Chemical composition (in weight percent): MgO 98.0% or more CaO 0.20-1.50% SiO_2 0.10-0.50% Fe_2O_3 0.20% or less Al_2O_3 0.20% or less B_2O_3 0. A high-density magnesia-chromium clinker having a bulk specific gravity of 3.42 or more and an average crystal diameter of 35 μm or more. (2) The high-density magnesia-chromium clinker according to claim (1), which has crystals with a bulk specific gravity of 3.45 or more and an average crystal diameter of 40 μm or more. (3) A method for producing a high-density magnesia-chromium clinker, which is characterized in that a raw material of magnesium hydroxide mixed with a chromium compound is lightly calcined, pressure-molded, and then fired. (4) High-density magnesia according to claim (3), wherein the magnesium hydroxide is a slurry or a water-containing cake.
Production method of chromium-based clinker. (5) A method for producing a high-density magnesia-chromium clinker according to claim (3) or (4), wherein the light firing temperature is 600 to 1100°C.